Apparatus and method for calibrating a broadband radio frequency receiver chain

The present invention relates to a device and a calibration method of measuring the power of signals with a wideband radio frequency receiver chain.

The invention finds particular application in the field of broadband amplitude finding for the location of emission sources in radio frequency bands.

A radio frequency receiver chain is connected at the outlet to a receiving antenna and comprises an input block and a set of hardware modules and digital computing means, for example a computing processor.

In the field of finding, several reception antennas and multiple receive chains are used to allow measurement of the direction of arrival of the signal from a transmission source. In this area, several techniques exist. Among them, one is commonly used for its implementation simplicity, this is the amplitude finding. This is based on the use of the power of the signals delivered by the antenna array direction, of which the score is generally equally distributed over the angular range of interest, very generally 360 ° in the horizontal plane to measure the deposit. For this finding, it is necessary to have a good measurement accuracy of the power of the radiofrequency signal received by each receiving antenna. However, each receive chain induces measurement inaccuracies its own. In order to get a good measurement accuracy, it is necessary to calibrate each RF receiver chain.

A broadband receiver chain is composed of a set of several processing modules, interconnected by cables which may have a length of several meters.

It is known to use an injection system and measurement of a calibration signal, which requires a broadband radio frequency signal generator injected at the input of the reception chain and a device for measuring the power of said radio frequency signal input and output of the reception chain. Such a system is complex and cumbersome.

U.S. Patent 6,700,537 B1 discloses a radio frequency receiver calibration system broadband a locating system having at least two processing channels. This patent proposes using a single noise source for calibration, noise is distributed on processing channels. This calibration system requires a sound distribution system to the various ways and allows only a relative calibration between the various channels used.

The invention aims to remedy the above drawbacks by proposing a method and a calibration device for broadband radio frequency receiving chain, which is less complex and which exhibits improved calibration accuracy than known systems.

To this end, the invention relates to a power calibration method of a radio frequency receiver chain broadband capable of receiving an input radio frequency signal from a receive antenna, in a frequency band, set implemented in a calibration device comprising said broadband radio frequency receiver chain and means adapted to perform spectrum analysis, said receiving channel having an input connected to input block of a set of radio frequency treatment, the method being characterized in that it comprises:

- a first calibration phase of the input block, comprising, for at least one temperature value of said input block and a frequency, generating a spectral density given noise power by means of a source selectable and controllable noise of the input block, and then computing and storing at least one spectral density equivalent noise power reduced at the input of said input block,

- a second calibration phase of the power gain of the reception chain comprising: generating a given spectral density noise power; measuring a spectral density of the noise power at the output of the reception chain; calculating the power gain of the reception chain according to the spectral density of noise power at the output of the reception chain and the spectral density equivalent noise power reduced at the input corresponding to the spectral density noise power given.

Advantageously, the use of a noise source in the input block of a receiver chain enables a calibration of the most accurate power reception system while minimizing the hardware complexity induced.

The method according to the invention may also have one or more of the features below:

- in the first phase of calibration of the input block, the calculating includes: obtaining a power gain of the input block for said temperature value and said frequency; generating a noise having a given spectral density noise power and the measurement of a spectral density of noise power at the output of the input block; calculating a spectral density equivalent noise power reduced at the input of said input block based on the power gain of the input block and the power spectral density of noise at the output of the input block.

- the first calibration phase of the input block is repeated for a plurality of frequencies in the band of the reception channel frequency and / or a plurality of temperature values ​​of the input block.

- means adapted to perform a spectral analysis being a radio frequency processing assembly processing module, the measurement of the spectral density of noise power at the output of the reception chain is obtained at the output of said processing module.

- means adapted to perform a spectral analysis being a calibrated auxiliary receiver comprising a spectrum analyzer and the receive chain having an outlet block connected to the output of the radio frequency processing assembly, adapted to tilt between a first position routing the radio frequency signal to a primary output of the reception chain and a second feeding position of the radio frequency signal to an auxiliary output of the reception chain, to which is connected, during calibration, the calibrated auxiliary receiver, the method further comprises, a first calibration phase of the output block of calculating a difference in gain between said main outlet and said auxiliary outlet, for at least the frequency and the input block temperature value considered in first calibration step of the input block, and in the second phase, the step of calculating the gain pui t on of the receiver chain also taking into account said deviation gain introduced by the output block.

The invention also relates to a calibration device in power of a radio frequency receiver chain broadband comprising a broadband radio frequency receiving chain adapted to receive an input RF signal to a receiving antenna in a frequency band, the receive chain comprising an input block, a set of radio frequency treatment, and means adapted to perform a spectrum analysis, wherein the input block comprises a noise source connected to input a tilting member adapted to connect the input noise source of a block of circuits downstream of the input block, the output of said downstream circuit block being connected in input of the RF treatment, the device for implementing a calibration method according to the above method. The device according to the invention may also have one or more of the features below:

- said receiving channel having a clean background noise, the noise power introduced by said noise source is greater than the power of said self-noise of the reception chain.

- the tilting member is capable of tilting between a first injecting position switch in block downstream circuits of the input block from the input radio frequency signal, and a second injection position, in block downstream circuits of the input block, the noise generated by the noise source.

- said noise source is a noise diode.

- means adapted to perform a spectrum analysis is a processing module which is provided with the set of radio frequency treatment, measurement of the spectral density of noise power at the output of the reception chain is obtained at the output of said processing module .

- the device further includes an output block, connected to the output of the entire radio frequency treatment, comprising an own tilting member to tilt between a first position routing the radio frequency signal to a primary output of the reception chain, and a second feeding position of the radio frequency signal to an auxiliary output of the reception chain (60), the means adapted to perform a spectral analysis being a calibrated auxiliary receiver comprising a spectrum analyzer and connected, during calibration, to the auxiliary output.

The invention also relates to a direction finding device comprising a plurality of receiving channels broadband radio frequency, each connected to a reception antenna, and a calculation unit adapted to calculate an angle of incidence of a radio frequency signal received by said receiving antennas, characterized in that it comprises, for each of said receiving channels, a power calibration device according to the preceding device.

Other features and advantages of the invention emerge from the description which is given below, with illustrative and non limitative, with reference to the appended figures, in which:

1 shows diagrammatically calibration device in power of a wideband receiver system according to a first embodiment;

Figures 2 and 3 show the main modules of an input block of a wideband receiver system according to a first embodiment;

Figure 4 is a flowchart of the main steps of a method of calibrating a broadband reception chain according to one embodiment;

- Figure 5 schematically shows the calibration device of a broadband reception chain according to a second embodiment;

Figures 6 and 7, the main modules of an output block of the calibration device of Figure 5;

8 schematically represents the calibration device of a broadband receiver system of Figure 5 in the calibration mode;

- Figure 9 shows schematically a radio direction finder according to an embodiment.

FIG 1 schematically illustrates a device for calibrating a broadband radio frequency receiver chain 2. In this example, this is a superheterodyne receiver followed by a spectral analysis.

The reception chain 2 is connected at the outlet of an antenna 4, and comprises a number of connected modules, including an input unit 6, usually connected closer to the antenna.

In one embodiment, the input unit 6 is connected to the output of the antenna 4 by a cable 5, whose length is of the order of 0-20 centimeters.

The output of the input unit 6 is connected to a radio frequency processing unit 8, comprising hardware modules and of digital calculation means.

The entire radio frequency treatment 8 comprises, in this example, a frequency-changing module (transposition) 10, adapted to convert a radio frequency signal RF from first given frequency in a second frequency signal FI, called intermediate frequency, usually less than the first frequency.

The output of the frequency changing unit 10 is connected an analog-digital converter 12, the output of which is connected a signal processing module 14, adapted to perform a spectral analysis treatment. In one embodiment, the signal processing module 14 is a FPGA on the same circuit board as the analog-digital converter 12.

The various modules constituting the reception system 2 are connected via cables 16, 18, whose total length may exceed ten meters. These cables induce loss of power of the radiofrequency signal.

RF is the radiofrequency signal at the input of receiver 2, and RF S the radio frequency signal output from the receiver 2.

The radio frequency receiver chain 2 is able to operate in a frequency band [F 1; F 2 ], for example from 2 to 18GHz.

The signal strength is measured at the end of reception chain, causing the knowledge of the power gain of the receive chain can be deduced the power of the input signal of said channel.

The invention allows precisely calculate the power gain of a receiver chain for a variety of frequency and temperature values ​​of the input block 6, as explained in detail below.

This gain in power is the ratio of the output power P s to the power of input Ρ ,. It can be expressed in decibels (dB) as follows:

G,B = 101og 101og(Ps ) - 101og(i> )

Where log () function is the logarithm base 10.

In other words, the power gain of the reception chain is the difference between the power of the output signal and the power of the input signal, both expressed in logarithmic units.

The power of the output signal is calculated on the basis of the spectral analysis. This is the square of the complex signal of the module, in the mathematical sense, corresponding to a pitch frequency or Fourier transform box.

The power gain of a reception system 2 as schematically shown in Figure 1 depends, inter alia, installed cables 16, 18 and the temperature of the various electronic units 6, 10, 12. The calibration can conveniently be remade with each significant change in temperature indicated by a sensor integrated in one of the blocks. It may otherwise be made only system initialization assuming that the differential gain of differences related to changes in temperature are low.

The reception chain has a background noise of its own, depending on the various components of the receiver chain. This clean sound of the reception system is not precisely known, however it is possible to determine its own maximum noise level of the receiver.

In one embodiment of the calibration device of the invention, illustrated in Figures 2 and 3, the input unit 6 of a reception chain broadband radiofrequency 2 comprises a block 22 of upstream circuit and a block 24 conventional downstream circuits. For example, the block 22 comprises a frequency band limitation filter and vis-à-vis protection circuits strong signals and block 24 includes amplifiers and variable attenuators. It is preferable to introduce the most upstream possible noise, thus limiting the block 22 to a minimum of functions.

The input unit 6 further comprises a noise source 26 and a tilting member 28. These members 26 and 28 are added for carrying out the calibration function.

The tilting member 28 is for example a switch, which, when in a position POS 2, switches the circuit so as to inject the noise provided by the noise source 26 at the input of the downstream circuits of block 24 .

Thus, the tilting member 28 allows to choose between the calibration mode of the reception chain 2 (POS 2 ), wherein noise is injected into the receiver 2 (shown in Figure 3) and the operating mode nominal (shown in Figure 2), wherein the switch is in a position POSi.

Alternatively, the tilting member 28 is a coupler.

The noise source 26 provides a given noise spectral density calibration mode, the spectral density is a frequency bandwidth by power (expressed for example in dBm / MHz). The spectral density is normalized.

The noise source 26 is an added component in the input block 6 having characteristics determined to obtain a good calibration accuracy.

In particular, the noise source 26 is selected to provide a noise power larger than that of the noise of the reception chain.

For example, to obtain an accuracy of 0.5 dB, the noise power of the noise source 26 should be greater than 10 dB in the power of self-noise of the reception chain fed back to the input.

In one embodiment, is used to realize the noise source 26, a diode-type component broadband noise having a REC ( "excess noise ratio") of 30dB.

Advantageously, such a component is very small.

Alternatively, an amplifier is used as a noise source 26, its input being connected to a matched load and its output delivering the desired noise.

Thus, the addition of such a component 26 and a switch 28 in an input block of a broadband radio frequency receiver chain is very compact.

In addition, when the tilting member 28 is in the POSi position illustrated in Figure 2, the receiver is operating in nominal reception mode without disturbance.

In calibration mode, the noise source 26 is energized, the tilt member 28 is in position POS 2 , and the noise is fed as input to the downstream block 24.

Figure 4 is a flowchart of the main steps of a calibration method of the broadband reception chain according to one embodiment of the invention.

The method comprises two phases, a first phase 40 input block calibration 6 vis-à-vis the noise source and a second phase 42 of calibrating the complete reception chain.

During a first step 44 of the first phase 40, a calibration table of the input block, which provides the power gain input-output of this block, as a function of the frequency F, the RF signal, input and the temperature T k of the input unit 6 is obtained.

There is thus a first input block calibration table including gain values Gi of the power input unit (F T ,, k ).

This first table is established in factory, upon successive injections of radio frequency signals, and power measurements at the input and output of the input block.

Preferably, a set of temperature values T k ranging from -40 ° C to + 85 ° C are considered, and a set of frequency values F, included in the frequency band of the reception system, with no predetermined frequency, for example of the order of 10MHz.

Alternatively, a single temperature T value corresponding to an intended use of the receiver is considered.

Then, during a step 46 for determining noise spectral density, the tilting member 28 is tilted in calibration mode (POS 2 ) and the noise source 26 is powered.

The noise spectral density
is measured at the output of the input block, for each frequency F, and each temperature T k of the first calibration table of the input block.

In this step, a measuring instrument, for example a spectrum analyzer is connected to the output of the input block.

At a step 48 of calculating equivalent spectral density is calculated for each spectral density noise
output measured the equivalent spectral density reduced input of the input block, denoted N e (F, T k ): N e (F i , t k ) = N s (F i , t k ) - G l (F i , t k ), provided that these expressions are expressed in consistent logarithmic unit therebetween. Equivalent spectral density reduced input of the input block is obtained by a mathematical calculation.

These calculated values ​​are stored in a second calibration table of the input block.

The gain of the tilting member 28 is assumed to be identical in both positions POSi and POS 2 .

In phase 42 of calibrating the reception chain, in a step 50, the tilting member 28 is in position POS 2 to be in calibration mode,

noise from the noise source 26 is injected in the input of block 24. It measures the spectral density output noise spectral analysis N m (Fj) at each frequency F ,.

Knowing the temperature T k of the input block, and the equivalent spectral density at the input, the power gain of the reception chain is calculated in a calculation step 52 as follows:

G r (F i , t k ) = N m (F i ) - N e (F i , t k ), provided that these expressions are expressed in consistent logarithmic unit therebetween.

The gain values ​​of the power reception channel is stored in a calibration table of the reception chain.

In the nominal operating mode of the receiver, the gain values in the power stored reception channel are used to determine the power P, a radio frequency RF signal at the antenna output from the power P s measured the output of the reception chain, depending on the frequency f of the RF signal and the temperature T measured or estimated input block:

P t = P s - G r (f, T), provided that these expressions are expressed in consistent logarithmic unit therebetween.

5 shows a calibration device with a receiving channel 60 which does not include a spectral analysis.

The reception chain 60 has an input block 62, which receives an RF signal from an antenna 4, and a radio frequency processing assembly 64, which may include active and passive elements including cables.

The input block 62 is similar to the input block 6 described above.

In this embodiment, the input block 60 comprises a block 66 of upstream circuit and a downstream circuit block 68, similar to the blocks 22 and 24 previously described.

II further comprises a noise source 70 and a first tilting member

72.

The calibration device of Figure 5 further comprises an output block 74 which is added to allow calibration.

This output device 74 includes a second tilting member 76, adapted to tilt between a first position POS is of the radiofrequency signal routing to a downstream circuit module 78, the output S r provides the output RF signal of the receiver. This position POS has corresponds to a nominal operating mode.

The second tilting member 76 comprises a second POS position b , which routes the RF signal to an auxiliary output S iN x, on which is plugged, in calibration mode, a calibrated auxiliary receiver comprising a spectrum analyzer.

To perform the calibration, a first calibration phase of the input blocks 62 and outlet 74 is implemented.

The calibration of the input block 62 is similar to the calibration of the input block 6 described previously, it is not recalled here.

For calibration of the output block 74, analogously to what was described for the calibration of the input block 6 is first brought the second tilting member 76 in position POS has and measuring the power gain G 2 (Figure 6) between the input E 2 and the output S r , depending on the frequency and the temperature of the input block 62, in dB.

Then, the tilting member 76 is in position POS b , and measuring the power gain G 3 between the input E 2 and the auxiliary output S to a function of the frequency and the temperature of the input block 62 in dB.

The difference gain G 4 in dB, between the main output and the auxiliary output for frequencies and temperatures in the input block considered, is calculated and stored in a calibration table of the output block, is therefore:

G 4 (F I , t K ) = G 2 (F I , t K ) - G 3 (F I , t K ).

Then, in a second phase, the entire reception chain is calibrated.

The input blocks 62 and outlet 74 are placed in calibration mode via the respective switching elements 72 and 76, as shown in Figure 8.

In this step, a calibrated measuring instrument, for example a spectrum analyzer is connected to the auxiliary output of the output block 74.

Input is injected noise, via the noise source 70, to noise spectral density N e (F i , t k ) = N s (F i , t k ) - G l (F i , t k ).

As output, the spectral density is measured output noise N my (Fi).

G is then calculated m (F t T k ) = N ^ F - N ^ F ^).

In this embodiment, the power gain of the reception system is given by:

G -r (F I , t K ) = the GF I , t K ) + G 4 (F I , t K ).

The gain values of the power reception chain, for the frequency values F, and temperature T k data are stored in a calibration table of the reception chain.

In the nominal operating mode of the receiver 60, the values of power gain of receive chain stored are used to determine the power P e of a radiofrequency signal RF at the antenna output from the power P r measured output of the reception chain, depending on the frequency f of the RF signal and the measured temperature T or estimated input block:

P e = P r - G r (f, T).

The invention finds particular application in the field of finding amplitude, for determining the arrival angle Θ of a radiofrequency signal in a given reference, e.g., reference to a carrier, such as an aircraft or a ship, on which the direction finder is embedded.

A finder uses directional antennas n, n being greater than or equal to 2.

For example, a direction finder 100 to four antennas and four receiving channels is illustrated schematically in Figure 9.

Each of the receiving antennas A1 to A4 is oriented at a predetermined reception angle in a repository, for example, 45 degrees, 135 degrees 225 degrees and 315 degrees.

A radio frequency RF signal incident is received by the four antennas A1 to A4, their differences in orientation are they issue different powers.

A respective receiving system 1 10, 120, 130 and 140 is connected the output of each antenna, and the power of received signals respectively used to calculate the angle of arrival of the radiofrequency signal RF Θ incident. The calculation is performed by a module 150.

The calculation is performed by any method known amplitude finding.

The accuracy of the calculated angle depends on the quality of the measurement of the power of each reception chain.

Advantageously, each chain RECEPTION 1 10, 120, 130 and 140 is calibrated by applying one of the embodiments described above.

Thus, is calculated for each chain receiving power gain calibration tables G r i , with i ranging from 1 to 4 in the previous example (four antennas), as a function of various values of frequency and temperature.

The gain values G r i calculated is stored and supplied to the module 150 which carries out the calculations.

Advantageously, the direction finding accuracy is increased.

The invention applies in particular to the calibration gain broadband reception channels comprising distributed modules on one or several tens of meters, especially for the case where such receivers are already embedded on a carrier. Indeed, in this case access to certain modules of the receive chain is difficult. Advantageously, the invention allows calibration of the power gain of the entire reception chain without precise knowledge of the modules that compose it with the exception of input blocks 6 or 62 and the output blocks 74.

CLAIMS

1. - A method of calibrating power of a broadband radio frequency receiving chain adapted to receive an input RF signal with a receiving antenna (4) in a frequency band, used in a device calibration comprising said broadband radio frequency receiver chain and means adapted to perform spectrum analysis, said receiving channel having an input unit (6) connected in input a set of radio frequency processing (8), the method being characterized in that it comprises:

- a first phase (40) calibration of the input block (6), comprising, for at least one temperature value of said input block and a frequency, a generation of a given spectral density noise power, by means of a noise source (26) selectable and controllable of the input block, and then the steps of calculating and storing at least one spectral density equivalent noise power reduced at the input of said input block,

- a second phase (42) of the calibration power gain of the reception chain comprising the steps of:

- generation (50) of a given spectral density noise power,

- measuring (50) a spectral density of the noise power at the output of the reception chain,

- calculation (52) of the power gain of the channel reception based on the spectral density of noise power at the output of the reception chain and the spectral density equivalent noise power reduced at the input corresponding to the spectral density of given noise power generated in the generating step (50).

2. - Method according to claim 1, characterized in that in the first calibration phase of the input block, the calculation includes the steps of:

- obtaining (44) a power gain of the input block (6) for said temperature value and said frequency,

- generating a noise having a spectral density data noise power and the measuring (46) a spectral density of the noise power at the output of the input block,

- calculating (48) a spectral density equivalent noise power reduced at the input of said input block based on the power gain of the input block and the spectral density of noise power at the output of the input block .

3. - Method according to claim 1 or claim 2, characterized in that the first calibration phase of the input block (6) is repeated for a plurality of frequencies in the reception channel frequency band and / or a plurality of temperature values ​​of the input block.

4. - Process according to any one of claims 1 to 3, characterized in that the means adapted to perform a spectrum analysis is a processing module (14) of the set of radio frequency processing (8), measuring of the power spectral density of noise at the output of the reception chain is obtained at the output of said processing module.

5. - Method according to any one of claims 1 to 3, characterized in that the means capable of performing a spectral analysis being a calibrated auxiliary receiver comprising a spectrum analyzer and the receive chain comprising an output block ( 74) connected to the output of the entire radio frequency processing (64) adapted to switch between a first position routing the radio frequency signal to a primary output of the reception chain and a second feeding position of the radio frequency signal to a auxiliary output of the reception chain, to which is connected, during calibration, the calibrated auxiliary receiver, the method further comprises, a first calibration phase of the output block of calculating a gain difference between said main outlet and said auxiliary outlet, for at least the frequency and the temperature value of the input block (62) considered in the first gr e calibration step of the input block, and in the second phase, the step of calculating the power gain of the receiver chain also taking into account said deviation gain introduced by the output block.

6. - A calibrating power of a broadband radio frequency reception system, comprising a broad band radiofrequency receiving chain adapted to receive an input RF signal with a receiving antenna (4), in a strip frequency, the receive chain (2, 60) having an input block (6, 62), a radio frequency processing unit (8, 64), and means adapted to perform a spectrum analysis,

characterized in that the input unit (6, 62) comprises a noise source (26, 70) connected in input of a tilting member (28, 72) adapted to connect the sound source (26, 70) entry in a block (24, 68) downstream circuits of the input block, the output of said block (24, 68) downstream circuits being connected in input of the radio frequency processing (8, 64), the device adapted to implement a calibration method according to any one of claims 1 to 5.

7. - Device according to claim 6, characterized in that said receiving channel (2, 60) having a clean background noise, the noise power introduced by said noise source (26, 70) is greater than the power said self-noise of the reception chain.

8. - Device according to claim 6 or claim 7, characterized in that the tilting member is a switch adapted to switch between a first position

(POSi) injection, in the block (24, 68) downstream circuits of the input block from the input radio frequency signal, and a second position (POS 2 ) for injecting, in the block (24, 68 ) downstream circuits of the input block, the noise generated by the noise source (26, 70).

9. A device according to any one of claims 6 to 8, characterized in that said noise source (26, 70) is a noise diode.

10. - Device according to any one of claims 6 to 9, characterized in that the means adapted to perform a spectrum analysis is a processing module (14) which is provided with the entire radio frequency processing (8), the measuring the spectral density of noise power at the output of the reception chain (2) being obtained at the output of said processing module.

January 1. - Device according to any one of claims 6 to 9, characterized in that it further includes an output block (74), connected to the output of the entire radio frequency processing (64), comprising a rocking member ( 76) adapted to switch between a first position routing the radio frequency signal to a primary output of the reception chain (60) and a second feeding position of the radio frequency signal to an auxiliary output of the reception chain (60), the means adapted to perform a spectral analysis being a calibrated auxiliary receiver comprising a spectrum analyzer and connected, during calibration, to the auxiliary output.

12. - Device DF comprising a plurality of radio frequency reception channels (1 10, 120, 130, 140) broadband, each connected to a receiving antenna (A 1; A 2 , A 3 , A 4 ), and a calculation unit (150) adapted to calculate an incidence of a radio frequency signal received by said receiving antennas angle,

characterized in that it comprises, for each said receiving channel (1 10, 120, 130, 140), a power calibration device according to any one of claims 6 to 1 of 1.