CALIBRATION AND TESTING DEVICE FOR AN ACTIVE ANTENNA,
PARTICULARLY A NOSE-CONE ANTENNA OF AN AIRBORNE RADAR.
The invention relates to the general field of the testing of proper
5 operation and the calibration of active antennas. It deals more particularly
with the actions for testing proper operation and calibration which -are
executed outside of the manufacturing process. These actions can be carried
out after mounting the antenna on the equipment which uses this antenna, or
else in an on-site verification process after repair of the antenna, in particular
10 in the case of exchange of one or more of the active elements (or sub-arrays)
of which it consists.
In the process for manufacturing an active antenna, the testing of
proper operation of the antenna as well as its calibration generally represent
15 final actions. These are relatively complex actions which sometimes require
the implementation of significant means on account of the size of the
manufactured antenna and the density of the active elements on the surface
of the antenna.
In a known manner, use is generally made of means forming a
20 measurements base, which means make it possible to carry out either nearfield
tests, having regard to the distance at which the measurement is
performed, or far-field tests at a distance from the antenna such that the
radiation pattern of the antenna is formed.
The test and calibration actions carried out in the near field, that is to
25 say in a zone where the antenna pattern is not yet formed, generally require
the installation of the antenna in an enclosure, an anechoic chamber, in such
a way that the test signals received by the antenna are not impaired by
spurious signals originating notably from the reflection of the signals emitted
by the test system on structures surrounding the antenna under test.
30 The means used to carry out the tests of proper operation and the
calibration of an antenna in the production phase generally comprise, in
addition to the anechoic enclosure mentioned above, means for generating
and radiating particular test signals making it possible to test the unitary or
group operation of the various active elements constituting the antenna, as
35 well as the overall operation of the antenna in the various envisaged modes
of operation. They furthermore comprise measurement means which make it
possible to compare the characteristics of the signal actually received by the
antenna with those expected. These are therefore means which are
consequent, efficacious and necessarily centralized in a given place.
Accordingly when repairing a fault with an antenna on a utilization site,
5 such equipment is rarely employed, so that the testing of proper operation
and the calibration of an antenna after a maintenance action are generally
more cursory than those carried out in the factory, short of being able to
deploy in each maintenance workshop the appropriate means.
To alleviate this relative lack of means it is possible to implement
I o various known solutions.
A first solution consists, after repair, in having the test and the
calibration of the antenna be performed by a centralized structure having the
appropriate means, the production factory for example. However, such a
procedure gives rise to non-negligible transport costs, especially for antennas
15 of large size, and increases the equipment immobilization time. This is why
the adoption of such a procedure is generally accompanied by a temporal
spacing of the maintenance actions, the antennas considered being, for
example, designed to operate in a degraded state for which certain active
elements are faulty.
20 Another solution consists, after executing maintenance actions, in
carrying out only simple tests and extrapolating the operating state and the
calibration of the antenna on the basis of the results of these tests. However,
such a procedure does not always make it possible, in a case where failure is
noted with a test, to distinguish the precise cause of the malfunction recorded
25 (i.e. the failed element at the origin of an erroneous test) so that it is
sometimes necessary, when in doubt, to replace several elements of the
antenna so as to be certain of remedying the problem at the origin of the
unsuccessful test.
30 An aim of the invention is to propose a test system making it possible
to carry out on site the tests of proper operation and the actions for
calibrating an active antenna, in particular an active antenna of the type of
those fitted to nose-cone radars, mounted on aircraft.
Another aim of the invention is to propose a solution making it possible
35 to use the means of the radar on which the antenna is mounted as means for
generating a test signal and to carry out the appropriate measurements, or
else the antenna itself, if it has signal generation and reception functions as
well as functions for measuring the amplitude and phase of the signal
received.
5
For this purpose the subject of the invention is a test and calibration
device for active antenna, comprising a plurality of active emission-reception
elements arranged so as to form a radiating surface. Said device comprises:
- a measurement enclosure configured to be mounted in front of the
10 radiating surface of the antenna on the structure supporting the antenna and
in which is positioned a test probe able to collect and to radiate microwavefrequency
electromagnetic signals,
- means for generating a microwave-frequency radioelectric test signal
as well as means for performing the reception of a microwave-frequency
15 radioelectric signal and for performing a vector measurement of the signal
received.
The device according to the invention is characterized in that the
measurement enclosure itself comprises:
- a wall forming a cavity provided with an aperture, the aperture being
20 configured in such a way that the cavity is closed by the radiating surface of
the antenna when the enclosure is mounted on the structure supporting the
antenna;
- means making it possible to position the test probe inside the cavity
in a given position;
25 - fixing means making it possible to carry out the mounting of the
measurement enclosure on the structure supporting the antenna, these
means being configured so as to ensure, after mounting, a known axial
positioning of the measurement enclosure with respect to the radiating
surface of the antenna.
30 According to the invention, the wall forming the cavity is covered on its
internal face with elements absorbing radioelectric waves. Its external face is
furthermore configured to form an electrical shielding.
According to a particular embodiment of the device according to the
35 invention, suited to the testing of a radar active antenna mounted in the nose
of an aircraft and placed under the hood forming the nose cone of said
aircraft, the measurement enclosure fixing means are identical to the means
making it possible to fix the hood on the front structure of the aircraft which
supports the antenna.
5
According to a particular embodiment of the device according to the
invention, the depth of the cavity defined by the measurement enclosure is
determined so as to allow an intermediate-field or far-field measurement of
the signal received by the test probe when one or more active elements of
lo the antenna are emitting, having regard to the position of the test probe in the
cavity.
According to a particular mode of the previous embodiment, the
dimensions of the measurement enclosure are determined in such a way
15 that, having regard to the position of the probe in the cavity, the distance of
the probe from each of the active elements constituting the antenna is
greater than d2/2.h, d representing the size of the equivalent radiating
aperture of an active element of the antenna or of a sub-array consisting of
active elements.
20
According to a particular embodiment of the device according to the
invention, the measurement enclosure is configured so as to define a cavity
whose dimensions make it possible to position the test probe at a fixed
position for which it covers the entirety of the active surface of the antenna
25 and for which it is illuminated by the main lobe of the radiation pattern of each
of the active elements constituting the antenna.
According to a particular embodiment of the device according to the
invention, having regard to the depth D2 of the cavity defined by the
30 measurement enclosure and to the dimensions of the pattern of the test
probe used, the measurement enclosure comprises a plurality of test probes.
Each probe is mounted on a means making it possible to position it inside the
cavity in a known position. The number of test probes and the position of
each of these probes are defined in such a way that the union of their
35 radiation patterns covers the entirety of the active surface of the antenna and
that each of the probes is illuminated by the main lobe of the radiation pattern
of one or more active elements, or active sub-arrays, constituting the
antenna.
5 According to a particular embodiment of the device according to the
invention, having regard to the depth D2 of the cavity defined by the
measurement enclosure and to the dimensions of the pattern of the test
probe used, the test probe is mounted on positioning means configured so as
to allow the positioning of the test probe at various positions inside the cavity.
10 These positions are determined in such a way that, for each position, the test
probe is illuminated by the main lobe of the radiation pattern of one or more
active elements, or active sub-arrays, constituting the antenna and that the
set of positions allows the probe to cover the set of active elements, or active
sub-arrays, constituting the antenna.
15
According to a particular mode of the previous embodiment, the
means making it possible to position the test probe inside the cavity are
configured in such a way that when the measurement enclosure is fixed on
the structure supporting the antenna the distance separating a test probe
20 from each of the elements of the antenna that it covers differs, from a given
theoretical value, by a discrepancy that is less than the discrepancy AL
defined by:
AL = ( A.~ h) /360
25
where Aq represents the systematic phase error expressed in degrees.
In a particular embodiment, the means for generating a microwavefrequency
radioelectric test signal and the means for performing the
30 reception of a microwave-frequency radioelectric signal and for performing a
vector measurement of the signal received consist of the radar equipment
associated with the tested antenna.
As the device does not make it necessary to dismantle the antenna of
35 the radar, neither therefore is it necessary to use external
generationlreception means since those of the radar can be used and are
naturally present. This saves time and space. Moreover, the measurements
being made with the means of the radar, the calibration carried out also
integrates the defects of the radar chain (necessarily present) thereby
5 making it possible to improve the performance of the overall system.
The subject of the invention is also a test system comprising a radar
equipped with an active antenna and a test and calibration device as claimed
in any one of the preceding claims.
In a particular embodiment, the enclosure consists of a peripheral wall,
10 defining a cavity, the enclosure comprising an aperture exhibiting sufficient
dimensions such that the active face of the antenna can be placed at the
entrance of the cavity without any hardware obstacle being placed between
active face of the antenna and the interior of the cavity and in which the
enclosure is arranged so as to be able to encompass the entirety of the
15 antenna in such a way that the antenna (19) closes the aperture.
The subject of the invention is also a method for carrying out the
testing of an active antenna in emission or in reception by means of the
20 device according to the invention, in which the means for generating a
microwave-frequency radioelectric test signal and the means for performing
the reception of a microwave-frequency radioelectric signal and for
performing a vector measurement of the signal received being constituted by
the radar equipment associated with the tested antenna, in which:
25 - a microwave-frequency test signal is produced, which is radiated
inside the measurement enclosure by means of the emission chain of the
radar or of the antenna under-test
- the reception and the demodulation of the signal picked up by
reception means is performed by means of the radar reception chain,
30 - the signal picked up by the antenna under-test is digitized by means
of the radar signal processing means or of the antenna under-test.
The subject of the invention is also a first method for carrying out the
35 testing of an active antenna in emission by means of the device according to
the invention, the means necessary for generating a microwave-frequency
radioelectric test signal and the means necessary for performing the
reception of a microwave-frequency radioelectric signal and for performing a
vector measurement of the signal received being provided by the radar
5 equipment associated with the tested antenna. According to this method:
- a microwave-frequency test signal and a reference signal are
produced by means of the radar emission chain. The test signal is thereafter
radiated inside the measurement enclosure, via the antenna under test;
- the reception and the demodulation of the signal picked up by the
10 test probe on the one hand and of the reference signal on the other hand are
performed separately, by means of the radar reception chain;
- the relative amplitude and the relative phase of the signal picked up
by the antenna under test are measured with respect to the amplitude and to
the phase of the reference signal. This relative amplitude and phase are
15 determined, after digitization of the two signals, by the radar signal
processing means and compared with theoretical reference values.
The subject of the invention is also a method for carrying out the
testing of an active antenna in reception by means of the device according to
20 the invention, the means for generating a microwave-frequency radioelectric
test signal and the means for performing the reception of a microwavefrequency
radioelectric signal and for performing a vector measurement of
the signal received being constituted by the radar equipment associated with
the tested antenna.
25 According to this method:
- a microwave-frequency test signal is produced by means of the radar
emission chain. The test signal is thereafter radiated inside the measurement
enclosure, via the test probe;
- the reception and the demodulation of the signal picked up by the
30 antenna under test on the one hand and of the signal picked up by an
auxiliary antenna secured to the antenna under test, the latter signal being
considered to be reference signal, are performed separately, by means of the
radar reception chain;
- the relative amplitude and the relative phase of the signal picked up
35 by the antenna under test are measured with respect to the amplitude and to
the phase of the reference signal. This relative amplitude and phase are
determined, after digitization of the two signals, by the radar signal
processing means and compared with theoretical reference values.
5 The subject of the invention is also a second method for carrying out
the of an active antenna in emission by means of the device according to the
invention, the means for generating a microwave-frequency radioelectric test
signal and the means for performing the reception of a microwave-frequency
radioelectric signal and for performing a vector measurement of the signal
10 received being constituted by the radar equipment associated with the tested
antenna. According to this method:
- a microwave-frequency test signal and a reference signal are
produced by means of the radar emission chain. The test signal is radiated
inside the measurement enclosure, via the antenna under test. The radiated
15 test signal is obtained by transposing a test signal into intermediate
frequency whose frequency is deduced, by frequency multiplication, from a
reference clock which also serves as reference for the radar signal
processing means;
- the reception and the demodulation of the signal picked up by the
20 test probe are performed by means of the radar reception chain;
- the amplitude discrepancy and phase discrepancy of the signal
picked up by the antenna under test are measured with respect to the
reference clock, the amplitude and the phase of the picked-up signal being
determined, after digitization, by the radar signal processing means and
25 compared with theoretical reference values.
The subject of the invention is further a method for carrying out the
testing of an active antenna in reception by means of the device according to
the invention, the means for generating a microwave-frequency radioelectric
30 test signal and the means for performing the reception of a microwavefrequency
radioelectric signal and for performing a vector measurement of
the signal received being constituted by the radar equipment associated with
the tested antenna. According to this method:
- a microwave-frequency test signal and a reference signal are
35 produced by means of the radar emission chain. The test signal is radiated
inside the measurement enclosure, via the test probe. The radiated test
signal is obtained by transposing a test signal into intermediate frequency
whose frequency is deduced, by frequency multiplication, from a reference
clock which also serves as reference for the radar signal processing means;
5 - the reception and the demodulation of the signal picked up by the
antenna under test are performed by means of the radar reception chain;
- the amplitude discrepancy and phase discrepancy of the signal
picked up by the antenna under test are measured with respect to the
reference clock. The amplitude and the phase of the measured signal are
10 determined, after digitization, by the radar signal processing means and
compared with theoretical reference values.
The characteristics and advantages of the invention will be better
appreciated by virtue of the description which follows, which description relies
15 on the appended figures which represent:
- Figure 1, a schematic illustration representing the structure and the
composition of the enclosure of the device according to the invention;
- Figure 2, a schematic illustration of a first implementation variant of
20 the invention;
- Figure 3, a schematic illustration exhibiting a first embodiment of the
means making it possible to radiate a test signal and to collect the signals
emitted by the various elements of the antenna;
- Figure 4, a schematic illustration exhibiting a second embodiment of
25 the means making it possible to radiate a test signal and to collect the signals
emitted by the various elements of the antenna;
- Figures 5 and 6, schematic illustrations exhibiting a third embodiment
of the means making it possible to radiate a test signal and to collect the
signals emitted by the various elements of the antenna;
30 - Figure 7, a schematic diagram describing the means associated with
the measurement enclosure for carrying out the tests of proper operation and
for calibrating the antenna in emission or in reception;
- Figure 8, a schematic diagram of a measurement in emission with
respect to a reference path;
35 - Figure 9, a schematic diagram of a measurement in reception with
respect to a reference path which may be either the auxiliary path of the
antenna or a coupling of the test signal;
- Figure 10, a schematic diagram of a measurement in emission using
the doppler signal, synchronous with the measurement period, so as to
5 circumvent a reference path;
- Figure 11, a schematic diagram of a measurement in reception using
the doppler signal, synchronous with the measurement period, so as to
circumvent a reference path.
10 The system according to the invention is described hereinafter in the
document through its application to the testing and to the calibration of
electronic-scanning active antennas for aircraft nose cone radar, for which it
is particularly adapted. However this particular application is presented here
by way of nonlimiting exemplary embodiment of the scope of the invention.
15
Generally, an electronic-scanning active antenna is an array antenna
which comprises electronic devices allowing changes in the shape and the
direction of the beam emitted (and of the beam received). Depending on their
nature, these electronic devices (phase shifters, switches, filters) which are
20 connected to the radiating elements, act on the shape, the direction, the
frequency or the polarization of the radiated electromagnetic wave. Such
antennas which can exhibit varied structures, are however classed, in a
known manner, into two large families: so-called passive antennas and socalled
active antennas.
25 An electronic-scanning active antenna is an antenna whose structure
includes, in a known manner, devices for amplifying the signals emitted or
received. Such an antenna forms an array of active elementary emission and
reception paths, which can be combined in various ways. Subsidiarily its
structure can also integrate electronic devices carrying out conventional
30 functions such as frequency transposition or digital coding of the signals.
The adjustment and verification of the proper operation of active
antennas generally include a so-called calibration phase.
Calibration consists firstly in measuring on the assembled antenna the
35 amplitude and phase dispersions in emission or reception recorded on the
various elementary paths of the antenna, these dispersions being due
notably to the dispersions of the components forming these elementary
active paths as well as to the dispersions of assembly. It thereafter consists
in determining the appropriate amplitude and phase corrections to be applied
5 to the various elementary active paths to compensate for these dispersions.
To carry out the action of calibrating an active antenna the test system
according to the invention comprises, as illustrated by Figure 1, a test
enclosure 11 which depending on the cases of use may be associated with
10 various types of complementary means. The function of these
complementary means is to generate a test signal. This test signal is emitted,
according to case, either by a radiating element placed in the enclosure in
proximity to the antenna and independent of the antenna, the latter then
being tested in reception, or by the antenna itself, the latter then being tested
i s in emission. The function of these complementary means is also to carry out
the reception and the processing of the signals received, either by an
antenna-independent sensor placed in the enclosure in proximity to the
antenna and independent of the antenna, the latter then being tested in
emission or by the antenna itself, the latter then being tested in reception.
20 For this purpose, the enclosure 11 consists of a peripheral wall 12,
defining a cavity 13. According to the invention, the enclosure 11 comprises
an aperture of sufficient dimensions such that the active face 14 of the
antenna can be placed at the entrance of the cavity without any hardware
obstacle being placed between active face of the antenna and the interior of
25 the cavity 13. Advantageously, the enclosure is arranged so as to be able to
encompass the entirety of the antenna 19 the antenna 19 in such a way that
closes the aperture 19 as is represented in Figure 1. This makes it possible
to avoid radiation losses during the test as well as exterior disturbances. This
also protects the operators from exterior leakages.
30 As illustrated by Figure 1, the internal face of the wall 12 of the
enclosure 11 is covered with a structure 15 absorbing the electromagnetic
radiations which strike it. In this way, advantageously, only the direct
radiations are considered.
The enclosure 11 also comprises a radiating element 16 mounted in
35 the cavity 13 by way of a support 17. This radiating element 16 constitutes a
test probe making it possible either to emit a signal toward the antenna 19, or
to receive the signal emitted from the antenna 19. This radiating element can
for example consist of a horn or of any other reciprocal radiating device.
5 According to a preferred embodiment of the invention, the enclosure
11 is configured so as to be able to be positioned in an automatic manner in
a known, fixed relative position with respect to the antenna. In this way,
insofar as the position of the probe in the enclosure 11 is known, the known
fixed positioning of the enclosure with respect to the antenna makes it
10 possible to ascertain at any instant the position of the probe 16 with respect
to the plane of the antenna 14 facing the cavity 13. For this purpose the
enclosure 11 comprises means making it possible to carry out its mounting in
a precise position on the structure which supports the antenna during the
trials undertaken.
15 The illustrations 2-a and 2-b of Figure 2 present schematic views
(views from above) of a particular embodiment of the enclosure according to
the invention, suited to the testing of an antenna 19 fitted to a nose cone
radar 11 1 of an aircraft 21. The enclosure 11 is here preferably equipped with
fixing means identical to those 23 making it possible to fix the hood 22, the
20 radome, constituting the nose of the aircraft 21 on the structure supporting
the radar and the antenna at the level of the aircraft. In this way, the means
serving for the support of the radar and of the antenna during the workshop
maintenance actions generally being provided with these same fixing means
so as to be able to carry out trials of the radar integrating the hood, the
25 enclosure according to the invention advantageously makes it possible to
carry out tests on the antenna equally well when it is mounted on a workshop
maintenance support as when it is still (or again) mounted on an airplane.
Alternatively, in the absence of the fixing means described above, the
enclosure can be associated with any means making it possible to position
30 the enclosure, and consequently the probe 16, opposite the antenna 19, in a
position position and an orientation known with respect to the plane of the
antenna.
According to the invention, the probe 16 is positioned in the cavity 13
35 in such a way as to occupy a known position with respect to the plane of the
antenna 19 when the enclosure 11 is correctly positioned. The positioning of
the probe is ensured by means suitable for guaranteeing the positioning
precision required to allow the implementation of the tests of proper operation
of the elements of the antenna as well as the angular calibration of the latter.
5 It is recalled at this juncture that the precision of amplitude and phase
calibration of an antenna consisting of radiating elements is directly related to
the prior knowledge of the transfer function between various radiating
elements, taken separately or constituted into sub-arrays and the probe, this
transfer function being able to be determined in a theoretical manner, through
10 electromagnetic simulations, or else experimentally. It is also dependent on
the precision of the amplitude and phase measurements carried out during
calibration.
Now, the control of these transfer functions for a given position of the
probe 16 with respect to the antenna plane 14, imposes certain constraints.
15 It is thus preferable to position the probe 16 in the intermediate-field or
far-field zone remote from the radiating elements or sub-arrays grouping
these elements together. Such remoteness does indeed make it possible to
avoid the effects of overly fast variations of the radiated field as a function of
position, effects that are encountered in the case of near-zone
20 measurements. In this way, the effect of a slight error in positioning of the
probe with respect to the envisaged position is advantageously less
noticeable.
Thus according to the invention, the distance d between each element
(or sub-array) and the probe is, typically, chosen greater than D*/(~.AD). here
25 represents the value of the radiating aperture equivalent to the element (or to
the sub-array) considered and A the mean operating wavelength of the
antenna.
As illustrated by Figure 3, it is likewise preferable, in order to obtain a
sufficient and predictable level of transfer function, to position the probe 16 in
30 such a way that its radiation pattern 31 intercepts the main lobe 32 radiated
by each element (or sub-array).
Likewise also, it is preferable to use a probe, the radiation pattern of
whose main lobe 31 intercepts the whole of the antenna for the distance Dl
considered.
Alternatively, notably in the case where the antenna to be tested is of
large size, or else in the case where the depth of the enclosure is more
restricted or else in the case where the radiation pattern of the probe 16 used
is more restricted, it is possible, as illustrated by Figure 4, to implement
5 several probes positioned in various locations, each probe being used to test
a given portion of the antenna, that is to say some of the active elements
constituting the antenna. In this case the various probes are disposed,
preferably, in a plane a distance D2 away from the plane of the antenna, in
such a way that each subset of active elements forming a given portion of the
10 antenna is covered (i.e. illuminated) by the main lobe 41 of the radiation
pattern of at least one of the probes and can, hence, be tested by means of
this probe.
Moreover, insofar as the calculated transfer function corresponds to a
given position of the probe considered with respect to the antenna plane, the
15 obtaining of precise calibration measurements requires precise positioning of
the probe 16 at the location for which the transfer function considered has
been determined. Typically, positioning precision compatible with the
precision of the amplitude-phase measurements which is sought for the
calibration is notably obtained if the difference ad, between the actual
20 distance between the probe and the antenna element (or the sub-array)
considered and the distance considered to determine the transfer function, is
less than the product (Aqmax A)/360, where Aqmax represents the permitted
maximum error in the phase measurement expressed in degrees.
Concerning the precision of the calibration measurements, it is also
25 recalled that the precision of amplitude and phase calibration of an antenna
consisting of radiating elements also determines the control of the direction of
pointing of the antenna, the antenna - probe axis having to be controlled with
a better precision than the precision of angular harmonization sought for the
antenna. It is recalled here that the angular harmonization precision
30 corresponds to the precision with which the radioelectric axis of the antenna
coincides with its mechanical axis.
According to the embodiment considered various positioning means
are implemented.
35
According to a first embodiment illustrated by Figure 3, a probe 31
exhibiting a sufficiently wide radiation pattern 32, non-directional, so that,
having regard to the distance Dl separating the probe from the plane of the
antenna, the whole of the radiating surface of the antenna 19 is covered is
5 implemented for example by this pattern (i.e. illuminated) and that the probe
31 is illuminated by the main lobe of the pattern of each sub-array or of each
radiating element to be tested.
In this first mode the probe 31 is placed in a fixed position inside the
cavity 13. Accordingly it is fixed to the wall 12 of the enclosure by way of a
10 rigid support 17. The dimensions of the enclosure 12, the depth Dl in
particular, are moreover defined in such a way that the main lobe of the
radiation pattern 33 of each of the radiating elements constituting the
antenna encompasses the position of the probe. The radiation pattern of the
probe 31 is for its part defined in such a way that the latter can illuminate the
I 5 whole set of active elements constituting the antenna.
In this embodiment, the precise positioning of the probe 31 with
respect to the plane of the antenna 19 under test is thus advantageously
ensured on the one hand by the fixed tie linking the probe 31 to the enclosure
12 and on the other hand by the precise positioning and orientation of the
20 enclosure with respect to this same antenna plane, which positioning and
orientation are guaranteed by the use of the fixing means described above.
In this particular embodiment the positioning of the probe is furthermore
fixed.
25 This first embodiment, although advantageous, makes it necessary,
however, to employ a probe positioned in such way that, having regard to its
radiation pattern, it is capable of covering, on its own, the radiating surface of
the antenna 19 and of being illuminated by the main lobe of the pattern of
each sub-array or of each radiating element to be tested. Furthermore, this
30 condition makes it necessary to employ an enclosure of a sufficient depth D.
Now, this set of conditions is not necessarily simple to fulfill, so that, in order
to alleviate the problems of illumination and of depth of the device, one is
sometimes required to envisage alternative embodiments, such as those
described hereinafter in the text.
35
According to a second embodiment, illustrated by Figure 4, a plurality
of probes (two probes 41 and 42 in the illustration of Figure 4) is for example
implemented. The number and the positions of the probes implemented are
determined in such a way that each portion of the surface of the antenna 19
5 is covered by the radiation pattern of at least one probe and that the main
lobe of the pattern of each sub-array or of each radiating element to be
tested illuminates at least one of the probes.
In this second embodiment each of the probes 41, 42 is placed in a
fixed position inside the cavity 13, at a distance D2 from the radiating surface
10 of the antenna. Accordingly it is fixed to the wall 12 of the enclosure by way
of a rigid support 43, of the same type as the support 17 mentioned above.
According to a third embodiment, a single probe 51 is for example
implemented, as illustrated by Figure 5, mounted on means making it
15 possible to make it move inside the cavity, in a plane parallel to the plane of
the antenna, or along a given direction in this plane for example.
The amplitude of movement is defined in such a way that, having
regard to the dimensions of the radiation pattern of the probe 51, the
positions that it can occupy allow it to cover each portion of the surface of the
20 antenna 19 and to be illuminated by the main lobe of the radiation pattern of
each of the sub-arrays or radiating elements to be tested.
The means of movement are configured in such a way that the precise
position of the probe with respect to a given reference point 0 is always
known, the position of the reference point 0 being known precisely itself.
25 Figure 6 illustrates in a schematic manner an exemplary embodiment of such
means, in which the probe 51 is mounted on a carriage 61, mobile in
translation along a guide rod 62, itself guided in translation by two slideways
63 and 64 in a direction perpendicular to its axis. The various translation
motions are impressed by motor means, not represented in the figure,
30 configured to ensure precise control of the movement of the carriage and of
the positioning in x and in y of the carriage 62, and therefore of the probe 51,
with respect to the reference point 0.
According to the invention, the test enclosure described in the
35 foregoing text is associated, as illustrated by the diagram of Figure 7, with
stimulation means 71 and measurement means 72. The object of the
stimulation means 71 is to generate a test signal intended to be emitted
either by the test probe 31 (or 51), or the test probes 41 and 42, placed in the
enclosure 11, so as to carry out the test of the reception function of the
5 antenna 19, or by the antenna 19 itself, so as to test the emission function of
the antenna. The object of the measurement means 72 is, for their part,
either to carry out the reception and the measurement of the signal received
by the test probe 31 (or 51), or the test probes 41 and 42, placed in the
enclosure 11 when carrying out the test of the emission function of the
10 antenna, or to carry out the reception and the measurement of the signals
received by the active elements constituting the antenna when carrying out
the test of the reception function of the latter.
According to the invention, the nature and the shape of the signals
constituting the stimuli, and also the processing applied to the signals
15 received, depend mainly on the test carried out: test of proper operation of an
active element or of a group of active elements of the antenna or calibration
test, in emission or in reception.
Moreover, the stimulation means 71 and the measurement means 72
can consist of apparatuses specifically designed to carry out these tests,
20 including off-the-shelf means configured in an appropriate manner. They are
then hooked up to the antenna under test and to the test probe 31 (51), or to
the test probes 41 and 42, with the aid of switching means 73 and
orchestrated by appropriate synchronization and control means 74. The
device according to the invention then integrates these stimulation and
25 measurement means.
Alternatively, when the radar equipment associated with the tested
antenna 19 comprises a test path, the stimulation and measurement
functions can be carried out by using the radar itself.
30
Alternatively again if the antenna considered comprises signal
generation and reception means as well as means for measuring the
amplitude and phase of the signal received, the stimulation and
measurement functions can be carried out using the antenna itself.
In a particular embodiment, the means for generating a microwavefrequency
radioelectric test signal and the means for performing the
reception of a microwave-frequency radioelectric signal and for performing a
vector measurement of the signal received consist of the radar equipment
5 associated with the tested antenna.
The subject of the invention is also a test system comprising a radar
11 1 equipped with an active antenna 19 and a test and calibration device for
said antenna such as described above.
Hereinafter in the text are described two schemes, two methods,
10 making it possible to carry out calibration and test measurements by means
of the measurement enclosure 11 according to the invention and by
implementing the technical means of the radar to carry out the stimulation
and measurement functions. The radar is assumed here to be a coherent
Doppler radar making it possible to carry out amplitude and phase
15 measurements of the signal received.
In the two methods described, the wave emitted is generated by a
frequency synthesizer at medium frequency and then transposed to
microwave-frequency. Moreover the wave received is baseband
demodulated by the local transposition oscillators arising from the
20 synthesizer. The measurements are performed in emission and in reception
since the transfer function is different.
The first method is illustrated by Figures 8 and 9. It consists, in a
conventional manner, in comparing the signals to be measured with a known
25 reference signal.
Figure 8 presents the hardware configuration corresponding to the use
of the technical means of the radar within the framework of the first method,
for the emission test of one or more active elements of the antenna, this test
30 obviously being equally able to cover the testing of a single element 81 or
that of the complete antenna 19.
In accordance with this first method, the signal arising from the
synthesizer integrated into the radar IF generation and reception means 83 is
transposed to microwave-frequency and emitted by the various radiating
35 elements 81 under test. The radiated signal is for its part tapped off by the
test probe 82 of the measurement enclosure 11 according to the invention
and transmitted to the receiver 85 of the radar, via a first reception path 84 or
measurement path, while ensuring control of the possible decouplings and
leakages. The measurement path is either the main reception processing
5 path of the radar or a deviometry measurement path or another auxiliary
path.
Furthermore, in order to have a permanent phase reference for all the
paths, a part of the emission signal is steered toward the receiver 85 by a
10 second reception path 86 or reference path, which is one of the radar
reception paths (deviometry path or auxiliary path).
In order to be able to adopt such a measurement configuration, the
measurement enclosure according to the invention is associated with
appropriate switching means 88 such as those illustrated in Figure 8. These
15 means consist for example of a power coupler 881 (3dB coupler), of a switch
882, and of an isolating and steering element 883, of circulator type for
example, these elements being themselves previously calibrated so as to
ascertain the phase shift and the attenuation that they introduce into the
measurement chain.
20 Accordingly, after baseband demodulation, the radar processing
means 87 carry out a spectral decomposition of the signals transmitted by
the reception paths 84 and 86, by Fast Fourier Transform [FFT] of the 2
signals for example, and measure their vector difference.
It should be noted that in this embodiment, the baseband wave is
25 shifted in frequency at the level of the emitted wave by a value of the order of
a few Kilohertz with respect to the reception which is the basebandprocessed
frequency.
Figure 9 presents the hardware configuration corresponding to the use
30 of the technical means of the radar within the framework of the first method,
for the test in reception of one or more active elements 81 of the antenna,
this test obviously being equally able to cover the test of a single element 81
or that of the complete antenna 19.
In accordance with this first method, the signal arising from the
35 synthesizer integrated into the radar IF generation and reception means 83 is
transposed to microwave-frequency and emitted by the test probe 82 of the
measurement enclosure 1 1.
The signal radiated by the test probe 82 is received by each radiating
element 81 or group of radiating elements and transmitted to the receiver 85
5 on the one hand by the main reception path 91 (measurement path) and on
the other hand by an auxiliary reception path 92 (reference path) associated
with an auxiliary antenna 93 which can consist of a particular active element
of the antenna. The auxiliary reception path 92 here constitutes the phase
reference required for the measurements.
10 Accordingly, after baseband demodulation, the radar processing
means 87 carry out a spectral decomposition of the signals transmitted by
the reception paths 91 and 92, by Fast Fourier Transform [FFT] of the 2
signals for example, and measures their vector difference. The vector
measurement of amplitude and phase between the various radiating
15 elements or groups of radiating elements is thus carried out as for the tests in
emission, by comparison of the signals received with the reference path 92.
The second method presented is illustrated by Figures 10 and 11. The
advantageous character of this second method consists in that, in
20 contradistinction to the method described above, it does not require the use
of a reference path to carry out measurements in emission or in reception.
The innovation here consists in rendering the measured signal
synchronous with the temporal reference which regulates the spectral
analysis, carried out by FFT. The measured signal is here the microwave-
25 frequency signal transmitted to the receiver of the radar and transposed to
baseband and then digitized, this signal being either the signal picked up by
the measurement probe 82 (test of the antenna in emission), or the signal
received by one or more active elements 81 of the antenna (test of the
antenna in reception). Accordingly, the period of the temporal reference
30 being equal to T, the synthesizer of the radar IF generation and reception
means 83 is configured so as to synthesize a test wave of period equal to N x
1/T. Thus, over time, the baseband wave generated by the synthesizer can
be considered to be a phase reference for the signals obtained after spectral
decomposition.
35
Figure 10 presents the hardware configuration corresponding to the
use of the technical means of the radar within the framework of the second
method, for the emission test of one or more active elements of the antenna,
this test obviously being equally able to cover the test of a single element 81
5 or that of the complete antenna 19.
The signal arising from the synthesizer integrated into the radar IF
generation and reception means 83 is emitted by the various radiating
elements 81. This signal is tapped off by the test probe 82 of the
measurement enclosure 11 and transmitted via a reception path 104, or
10 measurement path, to the receiver 85 of the radar.
Accordingly, after baseband demodulation, the radar processing
means 87 carry out a spectral decomposition of the signal transmitted by the
reception path 104, by Fast Fourier Transform [FFT] for example, and directly
measures the absolute vector value.
15 Advantageously, as illustrated by Figure 10, in order to be able to
adopt such a measurement configuration, it is not necessary to associate
particular switching means which are complementary with the measurement
enclosure 11 according to the invention.
20 Figure 11 presents the hardware configuration corresponding to the
use of the technical means of the radar within the framework of the second
method, for the test in reception of one or more active elements 81 of the
antenna, this test obviously being equally able to cover the test of a single
element 81 or that of the complete antenna 19.
25 In accordance with this second method, the signal arising from the
synthesizer of the radar IF generation and reception means 83 is transposed
to microwave-frequency and emitted by the test probe 82 of the
measurement enclosure 1 1.
The signal radiated by the test probe 82 is received by each radiating
30 element 81 or group of radiating elements and transmitted to the receiver 85
on the one hand by the single main reception path 11 1, or measurement
path. The auxiliary antenna 93 is not used here, insofar as no external phase
reference is required.
Accordingly, after baseband demodulation, the radar processing
35 means 87 carry out a spectral decomposition of the signal transmitted by the
reception path 11 1 (measurement path), by Fast Fourier Transform [FFT] for
example. The vector measurement of amplitude and phase is thus carried
out in a direct manner just as for the emission tests.
5 It should be noted that these two methods of measurement can of
course be implemented equally well using a measurement enclosure
comprising a single probe, such as that illustrated by Figures 3 and 5, as a
measurement enclosure comprising several probes, such as that illustrated
by Figure 4.
10

1. A test system intended to carry out actions for testing and
calibrating an active antenna (19) in a zone where the antenna
pattern is not yet formed comprising a radar equipped with an active
antenna (19), the test system comprising said active antenna (19),
said antenna consisting of a plurality of active emission-reception
elements arranged so as to form a radiating surface (14), said device
comprising:
- a measurement enclosure (1 1) configured to be mounted in
front of the radiating surface (14) of the antenna on the structure
(1 11) supporting the antenna and in which is positioned at least one
test probe (16) able to collect and to radiate microwave-frequency
electromagnetic signals,
- means (71) for generating a microwave-frequency
radioelectric test signal as well as means (72) for performing the
reception of a microwave-frequency radioelectric signal and for
performing a vector measurement of the signal received;
characterized in that the measurement enclosure (1 1) comprises:
- a wall (12) forming a cavity (1 3) provided with an aperture, the
aperture being configured in such a way that the cavity is closed by
the radiating surface (14) of the antenna when the enclosure (1 1) is
mounted on the structure (1 11) supporting the antenna;
- means making it possible to position the test probe inside the
cavity in a given position;
- fixing means (23) making it possible to carry out the mounting of
the measurement enclosure (1 1) on the structure (1 11) supporting
the antenna, these means being configured so as to ensure, after
mounting, a known axial positioning of the measurement
enclosure (11) with respect to the radiating surface (14) of the
antenna; The wall (12) forming the cavity (13) being covered on its
internal face with elements (15) absorbing the radioelectric waves,
its external face being configured to form an electrical shielding;
the device comprising a plurality of probes and being furthermore
characterized in that, having regard to the depth 02 of the cavity
24
(13) defined by the
dimensions of the pattern of the test probe used, the measurement
enclosure comprises a plurality of test probes (41, 42), each probe
being mounted on a means (43) making it possible to position it
inside the cavity (13) in a known position, the number of test
probes and the position of each of these probes being defined in
such a way that the union of their radiation patterns covers the
entirety of the active surface (14) of the antenna (19) and that
each of the probes (41, 42) is illuminated by the main lobe of the
radiation pattern of one or more active elements, or active subarrays,
constituting the antenna (19),
or, the device comprising a single probe, and being characterized
in that, having regard to the depth D2 of the cavity (13) defined by
the measurement enclosure (11) and of the dimensions of the
pattern of the test probe used (51), said test probe is mounted on
positioning means (61-64) configured so as to allow the
positioning of the test probe (51) at a plurality of positions inside
the cavity (13), these positions being determined in such a way
that, for each position, the test probe (51) is illuminated by the
main lobe of the radiation pattern of one or more active elements,
or active sub-arrays, constituting the antenna (19) and that the
whole set of positions allows the probe (51) to cover the set of
active elements, or active sub-arrays, constituting the antenna
(1 9);
the dimensions of the measurement enclosure (11) being
determined in such a way that, having regard to the at least one
position of each probe (16) in the cavity (1 I), the distance of the
probe from each of the active elements or sub-array of active
elements constituting the antenna is greater than d2/2.~,d
representing the size of the equivalent radiating aperture of an
active element of the antenna (19) or of a sub-array consisting of
active elements.
2. The test system as claimed in claim 1, characterized in that the
active antenna to be tested being a radar antenna mounted in the
nose of an aircraft and placed under the hood (22) forming the nose
cone of said aircraft, the measurement enclosure fixing means (23)
are identical to the means making it possible to fix the hood on the
front structure of the aircraft which supports the antenna.
3. The test system as claimed in one of claims 1 or 2, characterized
in that the depth of the cavity (13) defined by the measurement
enclosure (1 1) is determined so as to allow an intermediate-field or
far-field measurement of the signal received by the test probe (16)
when one or more active elements of the antenna (19) are in
emission, having regard to the position of the test probe (16) in the
cavity (1 3).
4. The test system as claimed in any one of claims 1 to 3,
characterized in that the means (61-64) making it possible to
position the test probe (51) inside the cavity (13) are configured in
such a way that when the measurement enclosure (11) is fixed on
the structure (1 11) supporting the antenna the distance separating
a test probe (51) from each of the elements of the antenna (19) that
it covers differs, from a given theoretical value, by a discrepancy
that is less than the discrepancy AL defined by:
Acp representing the systematic phase error expressed in degrees.
5. The test system as claimed in any one of claims 1 to 4, in which
the means for generating a microwave-frequency radioelectric test
signal and the means for performing the reception of a microwavefrequency
radioelectric signal and for performing a vector
measurement of the signal received consist of the radar equipment
associated with the tested antenna.
6. The test system as claimed in any one of the preceding claims,
in which the enclosure (11) consists of a peripheral wall (IZ),
defining a cavity (13), the enclosure (11) comprising an aperture
exhibiting sufficient dimensions so that the active face (14) of the
antenna can be placed at the entrance of the cavity without any
hardware obstacle being placed between active face of the antenna
and the interior of the cavity (13) and in which the enclosure is
arranged so as to be able to encompass the entirety of the antenna
(19) in such a way that the antenna (19) closes the aperture.
7. A method for carrying out the testing of an active antenna (81)
in emission or in reception, of a test system as claimed in any one
of the preceding claims, by means of the test and calibration device,
in which the means (83-89) for generating a microwave-frequency
radioelectric test signal and the means (83-85) for performing the
reception of a microwave-frequency radioelectric signal and for
performing a vector measurement of the signal received consisting
of the radar equipment (1 11) associated with the tested antenna
(19) in which:
- a microwave-frequency test signal is produced, which is
radiated inside the measurement enclosure (1 1) by means of the
radar emission chain,
- the reception and the demodulation of the signal (84) picked
up by reception means are performed by means of the radar
reception chain,
- the signal picked up by the antenna under-test is digitized
by means of the radar signal processing means.
8. The method for carrying out the testing of an active antenna
(81) in emission as claimed in the preceding claim,
in which, a microwave-frequency test signal and a reference signal
are produced by means of the radar emission chain, the test signal
being radiated inside the measurement enclosure ( I I ) , via the
antenna under test (81);
- the reception and the demodulation of the signal (84) picked
up by the test probe (82) on the one hand and of the reference
signal (86) on the other hand are performed separately by means of
the radar reception chain;
- the relative amplitude and the relative phase of the signal
(84) picked up by the antenna under test (19) are measured with
respect to the amplitude and to the phase of the reference signal
(86), this relative amplitude and phase being determined, after
digitization of the two signals, by the radar signal processing means
(87) and compared with theoretical reference values.
9. The method for carrying out the testing of an active antenna (81)
in reception as claimed in claim 7 in which:
- a microwave-frequency test signal is produced by means of
the radar emission chain, the test signal being radiated inside the
measurement enclosure (1 I), via the test probe (82);
- the reception and the demodulation of the signal (91) picked
up by the antenna under test (81) on the one hand and of the signal
(92) picked up by an auxiliary antenna (93) secured to the antenna
under test (81), the latter signal (92) being considered to be
reference signal, are performed separately by means of the radar
reception chain
- the relative amplitude and the relative phase of the signal
(91) picked up by the antenna under test are measured with respect
to the amplitude and to the phase of the reference signal (92), this
relative amplitude and phase being determined, after digitization of
the two signals, by the radar signal processing means (87) and
compared with theoretical reference values.
10. The method for carrying out the testing of an active antenna (81)
in emission as claimed in claim 7, in which
- a microwave-frequency test signal and a reference signal
are produced by means of the radar emission chain, the test signal
being radiated inside the measurement enclosure ( I I ) , via the
antenna under test (81), the test signal being obtained by
transposing a test signal to intermediate frequency whose
frequency is deduced, by frequency multiplication, from a reference
clock which also serves as reference for the signal processing
means (87) of the radar (1 11);
- the reception and the demodulation of the signal (101)
picked up by the test probe (82) are performed by means of the
radar reception chain;
- the amplitude and phase discrepancy of the signal (101)
picked up by the antenna under test (81) are measured with respect
to the reference clock, the amplitude and the phase of the pickedup
signal (191) being determined, after digitization, by the signal
processing means (87) of the radar (111) and compared with
theoretical reference values.
11. The method for carrying out the testing of an active antenna
(81) in reception as claimed in claim 7, in which:
- a microwave-frequency test signal and a reference signal
are produced by means of the radar emission chain, the test signal
being radiated inside the measurement enclosure (1 I), via the test
probe (82), the test signal being obtained by transposing a test
signal to intermediate frequency whose frequency is deduced, by
frequency multiplication, from a reference clock which also serves
as reference for the signal processing means (87) of the radar
(111);
- the reception and the demodulation of the signal (1101)
picked up by the antenna under test (81) are performed by means
of the radar reception chain;
- the amplitude and phase discrepancy of the signal (1 101)
- picked up by the antenna under test (81) are measured with respect
30 to the reference clock, the amplitude and the phase of the
measured signal being determined, after digitization, by the signal
processing means (87) of the radar and compared with theoretical
reference values. -
-- -------- - . --- -
Dated this 22.01.2014
[S WATI PAHUJA]
OF REMFRY & SAGAR
ATTORNEY FOR THE APPLICANT[S]