Description:
FORM – 2

THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003

COMPLETE SPECIFICATION
(SEE SECTION 10, RULE 13)

“DUAL-BAND FEED SYSTEM FOR SATELLITE COMMUNICATIONS (SATCOM)”
BY
BHARAT ELECTRONICS LIMITED
WITH ADDRESS: OUTER RING ROAD, NAGAVARA, BANGALORE 560045, KARNATAKA, INDIA

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED. 

TECHNICAL FIELD OF THE INVENTION
[0001] The present disclosure generally relates to communications and more particularly relates to a dual-band feed system for receive only satellite communication (SATCOM) frequencies.
BACKGROUND OF THE INVENTION
[0002] Deep space exploration satellite systems require high power, high gain antenna systems for transmitting data from the satellite back to a ground station located on the Earth. The satellite systems are typically equipped with antenna systems including antenna feeds for transmitting and/or receiving linearly/ circularly polarized uplink and/or downlink signals. Further, the rapid deployment of satellites of new frequency bands in the earth’s orbit and increasing demand for warfare measures requires the use of the same antennas operating simultaneously in two or more frequency bands.
[0003] The earth station antennas are typically reflector type antennas and are located at the earth end of satellite links. High directional gain is needed to receive the weak signals from the satellite or transmit the strong signal to the satellite. To that effect, large size reflector is used. However, the reflector antenna being frequency independent, the feed horn used with these reflector antenna limits the operational bandwidth/ frequency bands. Therefore, to use the same reflector antenna at two or more frequency bands, a multiband feed horn is required. Further, the radiation efficiency and side lobe levels of the reflector antenna generally depend on the illumination taper by the feed at the reflector. Hence, it is also required that the multiband feed horn be configured with substantially the same feed taper at different frequency bands. The dual-band functionality with appropriate illumination taper may be achieved by numerous methods. One of the methods is by frequency selective surface (Frequency Selective Surface, FSS). However, it requires two (the low-frequency and high-frequency) feeds which are located at the virtual focus and real focus of the FSS hyperbola.
[0004] Further, other traditional dual-band antenna solutions were implemented in the multi-band horn antenna which introduced high-order modes with a fundamental mode. Although the feed horn works in two frequency bands at the same time, the propagation of the high-order modes with the fundamental mode reduces the efficiency of the feed horn. In order to overcome the aforesaid problem, the existing dual-band feed horn may use a coaxial choke horn which may have complex turnstyle junctions. However, the use of coaxial choke horns involves fabrication complexities and makes the feed horn cumbersome. Furthermore, the existing dual-band feed systems have poor cross polar-performance and narrow bandwidth operation.
[0005] Therefore, there is a need for a dual-band feed system with improved performance for receive only satellite communication (SATCOM) frequencies, in addition to providing other technical advantages.
OBJECTIVE OF THE INVENTION
[0006] The main objective of the present invention is to provide a compact dual-band feed system with improved performance, wide-band operation, symmetric radiation patterns, high efficiency required for receive only applications in the earth station antenna (ESA) segment.
SUMMARY OF THE INVENTION
[0007] An aspect of the present invention is to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below.
[0008] Accordingly, in one aspect of the present disclosure, a feed system for satellite communication is disclosed. The feed system includes a feed horn. The feed horn includes a waveguide section and a first set of traverse slots for propagation of first frequency signals. The feed horn corresponds to an outer conductor of the feed system. The feed system includes a dielectric loaded waveguide feed positioned coaxially with the waveguide section of the feed horn. The dielectric loaded waveguide feed is configured to facilitate propagation of second frequency signals. The dielectric loaded waveguide feed corresponds to an inner conductor of the feed system. Further, the feed system includes a polarisation diplexer of coaxial structure configured to receive a portion of the dielectric loaded waveguide feed and a portion of the waveguide section extending from the feed horn, thereby operatively coupling the feed horn with the polarisation diplexer. The polarisation diplexer includes a first port associated with a first polarisation, and a second port associated with a second polarisation for the first frequency signals. The feed system further includes a stepped polarisation diplexer. The stepped polarisation diplexer includes a third port and a fourth port. The stepped polarisation diplexer is configured to receive a remaining portion of the waveguide section extending from the polarisation diplexer. The third port is associated with the first polarisation and the fourth port is associated with the second polarisation for the second frequency signals. The second polarisation corresponds to an orthogonal polarisation. Further, the first set of traverse slots of the feed horn is configured to prevent interference between the first frequency signals and the second frequency signals while propagating in the waveguide section of the feed horn and the dielectric loaded waveguide feed, respectively.
[0009] Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
[0010] The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference features and modules.
[0011] FIG. 1 illustrates a schematic representation of a four-port dual-band feed system for satellite communications, in accordance with an embodiment of the present disclosure;
[0012] FIGS. 2 and 3 represent a cross-sectional view of the four-port dual-band feed system of FIG. 1, in accordance with an embodiment of the present disclosure;
[0013] FIG. 4 depicts a plot of electric fields of different modes propagating inside coaxial circular waveguide geometry, in accordance with an embodiment of the present disclosure;
[0014] FIG. 5 is a schematic view of axially displaced cassegrain (ADC) reflector antenna, in accordance with an embodiment of the present disclosure;
[0015] FIG. 6 depicts a plot of return loss and isolation of both vertically and horizontal polarised signals of first and second ports at C-band frequencies, in accordance with an embodiment of the present disclosure;
[0016] FIG. 7 depicts a plot of feed elevation and azimuth plane co-polarized and cross-polarized radiation patterns at C-band mid-frequency 3.8 GHz for first polarisation (of a first port), in accordance with an embodiment of the present disclosure;
[0017] FIG. 8 depicts a plot of feed elevation and azimuth plane co-polarized and cross-polarized radiation patterns at C-band mid-frequency 3.8 GHz for second polarisation (of a second port), in accordance with an embodiment of the present disclosure;
[0018] FIG. 9 depicts a plot of return loss and isolation of both vertically and horizontal polarised signals of third and fourth ports at Ku-band frequencies, in accordance with an embodiment of the present disclosure;
[0019] FIG. 10 depicts a plot of feed elevation and azimuth plane co-polarized and cross-polarized radiation patterns at C-band mid frequency 11.725 GHz for first polarisation (of the third port), in accordance with an embodiment of the present disclosure;
[0020] FIG. 11 depicts a plot of feed elevation and azimuth plane co-polarized and cross-polarized radiation patterns at C-band mid frequency 11.725 GHz for second polarisation (of the fourth port), in accordance with an embodiment of the present disclosure;
[0021] FIG. 12 depicts a plot of cross-frequency band isolation of the third port/the first port and the fourth port/the first port in the frequency range 10.7-12.75 GHz, in accordance with an embodiment of the present disclosure;
[0022] FIG. 13 depicts a plot of cross-frequency band isolation of the third port/the second port and the fourth port/the second port in the frequency range 10.7-12.75 GHz, in accordance with an embodiment of the present disclosure;
[0023] FIG. 14 depicts a plot of ADC reflector elevation and azimuth plane radiation patterns at C-band mid-frequency 3.8 GHz for first polarisation (of the first port), in accordance with an embodiment of the present disclosure;
[0024] FIG. 15 depicts a plot of ADC reflector elevation and azimuth plane radiation patterns at C-band mid-frequency 3.8 GHz for second polarisation (of the second port), in accordance with an embodiment of the present disclosure;
[0025] FIG. 16 depicts a plot of ADC reflector elevation and azimuth plane radiation patterns at C-band mid-frequency 11.725 GHz for first polarisation (of the third port), in accordance with an embodiment of the present disclosure; and
[0026] FIG. 17 depicts a plot of ADC reflector elevation and azimuth plane radiation patterns at C-band mid-frequency 11.725 GHz for second polarisation (of the fourth port), in accordance with an embodiment of the present disclosure.
[0027] It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative methods embodying the principles of the present disclosure. Similarly, it will be appreciated that any flow charts, flow diagrams, and the like represent various processes which may be substantially represented in computer readable medium and so executed by a computer or processor, whether or not such computer or processor is explicitly shown.
DETAILED DESCRIPTION OF THE INVENTION
[0028] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.
[0029] The terms and words used in the following description and claims are not limited to the bibliographical meanings but are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purposes only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
[0030] It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces. References in the specification to “one embodiment” or “an embodiment” mean that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.
[0031] By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations, and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.
[0032] The figures discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way that would limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged communications system. The terms used to describe various embodiments are exemplary. It should be understood that these are provided to merely aid the understanding of the description and that their use and definitions in no way limit the scope of the invention. Terms first, second, and the like are used to differentiate between objects having the same terminology and are in no way intended to represent a chronological order, unless where explicitly stated otherwise. A set is defined as a non-empty set including at least one element.
[0033] In the following description, for purpose of explanation, specific details are set forth in order to provide an understanding of the present disclosure. It will be apparent, however, to one skilled in the art that the present disclosure may be practiced without these details. One skilled in the art will recognize that embodiments of the present disclosure, some of which are described below, may be incorporated into a number of systems. However, the systems and methods are not limited to the specific embodiments described herein. Further, structures and devices shown in the figures are illustrative of exemplary embodiments of the present disclosure and are meant to avoid obscuring the present disclosure.
[0034] Various embodiments of the present disclosure are further described with reference to FIG. 1 to FIG. 17.
[0035] FIG. 1 illustrates a simplified block diagram representation of a dual-band feed system (100), in which at least some embodiments of the present disclosure can be implemented. Although the dual-band feed system (100) is depicted to include one or a few components arranged in a particular arrangement in the present disclosure, it should not be taken to limit the scope of the present disclosure. The dual-band feed system (100) is hereinafter interchangeably referred to as “the feed system (100)”.
[0036] The feed system (100) includes a feed horn (110) with a polarisation diplexer (120) and a stepped polarisation diplexer (130). As shown, the polarisation diplexer (120) includes a first port (121) and a second port (122). The first port (121) is associated with a first polarisation and the second port (122) is associated with a second polarisation for the first frequency signals. Further, the stepped polarisation diplexer (130) includes a third port (131) and a fourth port (132). The third port (131) is associated with the first polarisation and the fourth port (132) is associated with the second polarisation for the second frequency signals. Furthermore, the second polarisation corresponds to an orthogonal polarisation. It is evident that the feed system (100) corresponds to a 4-port dual-band feed system.
[0037] In an embodiment, the first frequency signals may be C-band signals and the second frequency signals may be Ku-band signals. Alternatively, the first and second frequency signals may include any other satellite communications (SATCOM) frequencies. It is to be noted that, each of the first port (121), the second port (122), the third port (131) and the fourth port (132) may include waveguide flange interfaces for connecting C-band & Ku-band receivers which will be explained further in detail.
[0038] Referring to FIGS. 2 and 3 in conjunction with FIG. 1, the feed system (100) includes an outer conductive structure and an inner conductive structure. The outer conductive structure includes the feed horn (110) and the inner conductive structure includes a dielectric loaded waveguide feed (140). In one embodiment, the feed horn (110) and the dielectric waveguide feed (140) are of coaxial configuration or coaxial structure. In other words, the feed horn (110) and the dielectric loaded waveguide feed (140) may be a cylindrical structure, where the feed horn (110) is arranged coaxially to the dielectric loaded waveguide feed (140).
[0039] More specifically, the feed horn (110) includes a waveguide section (1101), a first set of traverse slots (1102), and two or more pairs of waveguide chokes (1103). The first set of traverse slots (1102) (e.g., two slots) are appropriately inserted in a traverse slot section configured in the waveguide section (1101). The waveguide section (1101) is operatively coupled to the waveguide chokes (1103) through the first set of traverse slots (1102). In an embodiment, the depth of the first set of traverse slots (1102) may be of about one-sixth to one-eighth of the operating wavelength of the first frequency signals. Further, the first set of traverse slots (1102) of the feed horn (110) is configured to prevent interference between the first frequency signals and the second frequency signals while propagating in the waveguide section (1101) and the dielectric loaded waveguide feed (140).
[0040] Furthermore, the length of the waveguide chokes (1103) may be of about one-fourth to one-eighth of the operating wavelength of the first frequency signals. Starting with the first choke of one-fourth. The waveguide chokes (1103) are configured to provide at least substantially symmetric E-plane and H-plane radiation patterns of the first frequency signals by adjusting the phase of E-field, and substantially unequal E-plane and H-plane radiation patterns of the first frequency signals. Specifically, a first waveguide choke of the two or more pairs of waveguide chokes (1103) may be of about one-fourth of the operating wavelength and a third waveguide choke may be of about one-eighth of the operating wavelength. The feed horn (110) has substantially unequal E & H-plane radiation patterns. The length of a fourth waveguide choke and last waveguide choke may be of about one-fourth of the operating wavelength to make symmetric E & H-plane radiation patterns by adjusting the phase of the E-field. Further, the spacing between each of the waveguide chokes may be of about one-fifth of the C-band operating wavelength.
[0041] The C-band (or the first frequency signals) in the feed horn (110) is in a coaxial configuration and includes a first fundamental mode (301) and a second fundamental mode (302) (as shown in FIG. 4). The first fundamental mode (301) may be TEM mode (301) and the second fundamental mode (302) may be TE11 mode (302). The second fundamental mode (302) is a higher mode compared to the first fundamental mode (301). The first fundamental mode (301) may produce null at bore-sight while the second fundamental mode (302) produces a peak at the beam bore-sight. The feed horn (110) is configured for feeding to a reflector surface of a reflector antenna by exciting the second fundamental mode (302) along with suppressing the first fundamental mode (301).
[0042] The dielectric loaded waveguide feed (140) is loaded with a pair of waveguide rings (1401,1402) and a dielectric rod (1404). The height of the waveguide rings (1401,1402) may be kept between a range of 1/8 to 1/12 of the operating wavelength of the first frequency signals (or the C-band frequency) for excitation of the higher TE11 mode (or the second fundamental mode). The pair of waveguide rings (1401) and (1402) are separated by a distance corresponding to of one-fourth of operating wavelength of the first frequency signals for at least providing excitation to a second fundamental mode and broadband impedance matching. In one implementation, the waveguide rings (1401) and (1402) may be separated by a distance of one-fourth of the operating wavelength of the C-band frequency for broadband impedance matching.
[0043] The second frequency signals (or the Ku-band signals) are received through the dielectric loaded waveguide feed (140). In an embodiment, the material of the dielectric rod (1404) may be of low loss rexolite with a dielectric constant of 2.53. The radius of the waveguide rings may be selected to pass the second frequency signals (i.e., the Ku-band (10.7-12.75 GHz) signal) with least attenuation. Further, the dielectric rod (1404) is configured with a plurality of segments. In one configuration, the dielectric rod (1404) may include five segments in which a first segment is a conical tapered section that is inserted in the waveguide section (1401). This section provides impedance matching for the Ku-band signals. A second segment is a cylindrical section with the same radius of the waveguide section (1401). A third segment is a cylindrical section with a radius less than the second segment. The third segment acts as a mode converter from the second fundamental mode (302) of the waveguide section (1401) to a hybrid second fundamental mode. This results in the radiation pattern being rotationally symmetric. A fourth segment is a cylindrical section with a radius less than the third segment. The fourth segment has length 2 times of the Ku-band operating wavelength. The fourth segment provides the gain and feed taper required for proper illumination of the reflector. A fifth segment is a conical tapered section that provides impedance matching with the air. Further, an overall length of the dielectric rod (1404) may be four times of the Ku-band operating wavelength excluding the length of the first segment which is fully inserted in the waveguide section (1401).
[0044] The feed system (100) further includes a dielectric flange (14021) positioned on the dielectric rod (1404). The dielectric flange (14021) is configured to adjust the position of the dielectric loaded waveguide feed such that a phase center of the radiation pattern for both the first frequency signals and the second frequency signals coincides and high secondary efficiency is achieved.
[0045] Further, the feed horn (110) is directly connected to the polarisation diplexer (120) with the waveguide section (1101) of the feed horn (110) extending to the polarisation diplexer (120). Moreover, the waveguide rings (1401,1402) (or the Ku band waveguide) also extend through the polarisation diplexer (120). In other words, the polarisation diplexer (120) of coaxial structure is configured to receive a portion of the dielectric loaded waveguide feed (140) and a portion of the waveguide section (1101) extending from the feed horn (110). This configuration results in operatively coupling the feed horn (110) with the polarisation diplexer (120). In this configuration, the polarisation diplexer (120) has the TEM mode as the first fundamental mode (301) and the TE11 mode as the second fundamental mode (302) (or the next higher waveguide mode). It is to be noted that one end of the polarisation diplexer (120) is connected to the feed horn (110) and another end is shorted using a circular flange (1201).
[0046] The polarisation diplexer (120) further includes a first stepped discontinuous structure (1203) for providing a wide bandwidth operation in the first frequency signals. The first stepped discontinuous structure (1203) is configured in conformity with an aperture of the first port (121) and a first traverse groove (1202) of the polarisation diplexer (120) being connected to the first port (121) through the first stepped discontinuous structure (1203). More specifically, the first traverse groove (1202) is cut into the outer waveguide section (1101) at a distance of about one-fourth of the guided wavelength of the C-band frequency (or the first frequency signals) from the shorted waveguide flange (1201). The first traverse groove (1202) cut in the outer waveguide section (1101) excites the second fundamental mode 302. Further, the first traverse groove (1202) is connected to first port (121) through the first stepped discontinuous structure (1203) in height and width. The first stepped discontinuous structure (1203) may be configured to match an opening of the first port (121) with that of the first traverse groove (1202) to improve an impedance matching level of the second fundamental mode (302) with the waveguide section (1101). Further, the first traverse groove (1202) radially cut into outer the waveguide section (1101) provides a narrow frequency band of operation. Further, the polarisation diplexer (120) includes a first fin (1204) of a blade-shaped structure for providing a wide bandwidth operation in the first frequency signals. In particular, the blade shaped first fin (1204) is included on the dielectric loaded waveguide feed (140) which provide wideband matching of second fundamental mode (302) to the waveguide section 1101. The first fin (1204) is orthogonal to the first traverse groove (1202) and is narrow enough to pass the first polarisation signal fields to the first port (121).
[0047] The polarisation diplexer (120) further includes a second stepped discontinuous structure (1206) for providing wide bandwidth operation in the first frequency signals. The second stepped discontinuous structure (1206) is configured in conformity with an aperture of the second port (122) and a second traverse groove (1205) of the polarisation diplexer (120) being connected to the second port (122) through the second stepped discontinuous structure (1206). More specifically, the second traverse groove (1205) is cut into the outer waveguide section (1101) which is orthogonally oriented to the first traverse groove (1202) at a distance of about half of the guided wavelength of the C-band frequency (or the first frequency signals) from the first traverse groove (1202). Further, the second traverse groove (1205) is connected to the second port (122) through the second stepped discontinuous structure (1206) in height and width. The second stepped discontinuous structure (1206) may be configured to match an opening of the second port 122 with that of the second traverse groove (1205) to improve the matching level of the second fundamental mode (302) with the waveguide section (1101). Further, the second traverse groove (1205) radially cut into outer the waveguide section (1101) provides a narrow frequency band of operation. Further, the polarisation diplexer (120) includes a second fin (1207) of a blade-shaped structure for providing a wide bandwidth operation in the first frequency signals. The second fin (1207) is orthogonal to the second traverse groove (1205) and is narrow enough to pass the second polarisation signal fields. Further, maintaining the distance of about half of the guided wavelength of C-band frequency provides high isolation between the first and second polarisations.
[0048] Further, the stepped polarisation diplexer (130) is used for the realization of the first port (121) and the second port (122) of the Ku-band signals. The waveguide section (1401) extends through the coaxial polarisation diplexer (120) to the outside of the circular flange (1201) and is connected to the stepped polarisation diplexer (130). In other words, the stepped polarisation diplexer (130) is configured to receive a remaining portion of the waveguide section (1401) extending from the polarisation diplexer (120). The aperture of the stepped polarisation diplexer (130) connected to the waveguide section (1401) is square matching the diameter of the waveguide section (1401). This square aperture is tapered down to a rectangular opening which is the third port (131) for the first polarisation of the second frequency signals (or the Ku-band signal). The tapering is carried on one surface (1301) of the stepped polarisation diplexer (130) with a stepped taper while the other is a flat surface (1302). For achieving orthogonal second polarisation of the Ku-band, the stepped polarisation diplexer (130) includes a second set of traverse slots (such as a slot (1303)) cut on the flat surface. The second set of slots (1303) is connected to the fourth port (132) through the multi-steps. These multi-steps are used to match the opening of the fourth port (132) with that of the slot (1303) to improve the matching level of the first fundamental mode (301). Further, the feed system (100) may be fabricated separated, and joined together with waveguide flanges (1208, 1304) to achieve the finished product.
[0049] The feed system (100) is used with an axially displaced cassegrain (ADC) reflector (200) (as shown in FIG. 5). Hence, not only individual Radio Frequency (RF) performance of the feed system at C-band Ku band frequencies was analysed but also the performance with the reflector (200) is performed. As a necessary condition for a feed being used for two or more different frequency bands, the phase center of the radiation from the feed at both frequency bands should coincide to achieve high secondary efficiency as explained above. The performance results of the feed system (100) for the first and second frequency signals are listed below in the table 1 and table 2.

Table 1 (C-Band parameters)

Table 2 (Ku-Band parameters)

[0050] Referring to FIG. 6, a plot (400) depicting a return loss and isolation at C-band frequencies 3.4-4.2 GHz of the feed system (100). The return loss of the first port (121) and the second port (122) is depicted as (401, 402), respectively, and isolation between the first and second ports (121, 122) is depicted as (403). In the C-band frequencies 3.4-4.2 GHz, a least value of the return loss (401, 402) is -13.28 dB while the isolation (403) is -51.14 dB. Thus, the operating bandwidth at C-band frequencies (3.4-4.2GHz) is 21%.
[0051] Referring to FIG. 7, a plot (500) depicts azimuth and elevation radiation pattern at C-band mid-frequency 3.8 GHz of the first port (121). Further, co-polarised and cross-polarised radiation patterns at an angle, phi=0° cut patterns (501 and 503) respectively. Furthermore, co-polarised and cross-polarised radiation patterns at an angle, phi=90° cut patterns (502 and 504), respectively. The feed taper at a 30-degree angle may be 9.1 dB to 11.6 dB while the cross-polarization of -34.70 dB may be achieved.
[0052] Referring to FIG. 8, a plot (600) of the feed system (100) depicts azimuth and elevation radiation pattern at C-band mid-frequency 3.8 GHz of the second port (122). Further, co-polarised and cross-polarised radiation patterns at an angle phi=0° cut the patterns (601 and 603) respectively. Furthermore, co-polarised and cross-polarised radiation patterns at an angle phi=90° cut patterns (602 and 604) respectively. It is evident that the radiation patterns (501, 502, and 601, 602) are substantially symmetric, a quality parameter of feed horn radiation. The feed taper at 30 degrees may be 9.1 dB to 11.6 dB while cross-polarization of-37.1 dB may be achieved.
[0053] Referring to FIG. 9, a plot (700) of the feed system (100) depicts return loss and isolation at Ku-band frequencies 10.7-12.75 GHz. The return loss of the third port (131) is depicted as (701) and the return loss of the fourth port (132) is depicted as (702). Isolation is depicted as (703) between the third and fourth ports (131, 132). For example, in the Ku-band frequencies 10.7-12.75 GHz, the least value of the return loss (701, 702) may be -10.9 dB while isolation (703) may be -53.7 dB. Thus, the operating bandwidth at C-band frequencies (3.4-4.2GHz) may be 17.48%.
[0054] Referring to FIG. 10, a plot (800) of the feed system (100) depicts azimuth and elevation radiation pattern at Ku-band mid-frequency 11.725 GHz of the third port (131). Further, co-polarised and cross-polarised radiation patterns at an angle phi=0° cut patterns (801 and 803) respectively. Furthermore, co-polarised and cross-polarised radiation patterns at an angle phi=90° cut patterns (802 and 804) respectively. The feed taper at 30 degrees angle may be -12.7dB to -16.9dB while cross-polarization of -37.50 dB may be achieved.
[0055] Referring to FIG. 11, a plot (900) of the feed system (100) depicts azimuth and elevation radiation patterns at C-band mid-frequency 11.725 GHz of the fourth port (132). Co-polarised and cross-polarised radiation patterns at an angle phi=0° cut patterns (901 and 903) respectively. Further, co-polarised and cross-polarised radiation patterns at an angle phi=90° cut patterns (902 and 904) respectively. It is evident that the radiation patterns (801, 802 and 901, 902) exhibit symmetry which is a quality parameter of the feed horn radiation. The feed taper at 30 degrees may be -13.7dB to -16.7dB while cross-polarization of -32.00 dB may be achieved.
[0056] Referring to FIG. 12, a plot (1000) depicts the isolation of the third port (131)/the first port (121), and the fourth port (132)/the first port (121). The isolation of the third port (131)/the first port (121), and the fourth port (132)/the first port (121) are depicted as (1001) and (1002) in the plot (1000), respectively. Further, the achieved cross frequency isolation for the third port (131) to the first port (121) is improved compared to -42 dB.
[0057] Referring to FIG. 13, a plot (1100) depicts isolation of the third port (131)/the second port (122) and the fourth port (132)/the second port (122). The isolation of the third port (131)/the second port (122) and the fourth port (132)/the second port (122) are depicted as (1101) and (1102) in the plot (1100), respectively. Further, the achieved cross frequency isolation for the third port (131) to the fourth port (132) is improved compared to -40 dB.
[0058] Referring to FIG. 14, a plot (1200) of ADC reflector depicts elevation and azimuth plane radiation patterns at C-band mid-frequency 3.8 GHz for the first polarisation of the first port (121). Co-polarised radiation patterns cut at an angle phi=0° (as shown in pattern (1201) of FIG. 12) and at an angle phi=90° (as shown in pattern (1202 of FIG. 12)) are symmetric.
[0059] Referring to FIG. 15, a plot (1300) of the ADC reflector depicts elevation and azimuth plane radiation patterns at C-band mid-frequency 3.8 GHz for the second polarisation of the second port (122). Co-polarised radiation patterns cut at an angle phi=0° (as shown in pattern (1305) of FIG. 13) and at an angle phi=90° (as shown in pattern (1306)) are symmetric. The achieved secondary gain at the first port (121) may be 49.10 dBi and the second port (122) may be 48.98 dBi, which corresponds to high secondary efficiency of 62% at 3.8 GHz and for 9M antenna size.
[0060] Referring to FIG. 16, a plot (1400) of the ADC reflector depicts elevation and azimuth plane radiation patterns at Ku-band mid-frequency 11.725 GHz for the first polarisation of the third port (131). Co-polarised radiation patterns cut at an angle phi=0° (as shown in pattern (1405)) and at an angle phi=90° (as shown in pattern (1406)) are symmetric.
[0061] Referring to FIG. 17, a plot (1500) of ADC reflector depicts elevation and azimuth plane radiation patterns at Ku-band mid-frequency 11.725 GHz for the second polarisation of the fourth port 132. Co-polarised radiation patterns cut at an angle phi=0° (as shown in pattern (1501)) and an angle at an angle phi=90° (as shown in pattern (1502)) are symmetric. The achieved secondary gain at the first port (131) may be 59.10 dBi and the second port (132) may be 58.96 dBi which corresponds to high secondary efficiency greater than 65% at 11.725 GHz and for 9 M antenna size. As described above, the novel 4-port dual polarised dual frequency band feed system (100) has very wide operating bandwidth of 21% at C-band frequencies (3.4-4.2GHz) and 17.48% at Ku-band frequencies (10.7- 12.75GHz) and low cross polarisation better than -32 dB at all the four ports (121, 122, 131 and 132) and high secondary efficiency of 62% & 65% at C and Ku-band frequencies. The feed system (100) has very high cross frequency band isolation of better than -40 dB (as shown in patterns (901,902, 1001, and 1002)). The feed system (100) is 4-port to cater to polarisation diversity and is very compact in size (length may be less than 435mm, the diameter may be less than 220mm) i.e. it has at least one-fourth of length and half of aperture diameter compared to currently available feed horns at similar frequency band.
ADVANTAGES
[0062] In an advantageous aspect of the present disclosure, a compact high performance twin band feed system is disclosed. The feed system has wider bandwidth, symmetric radiation pattern parameters, very low cross-polarisation, high efficiency, and very high cross-frequency band isolation at both of the frequency bands.
[0001] In another advantageous aspect of the present disclosure, the feed system has polarisation diversity i.e. dual polarisation (2-ports for each band) in both the frequency bands, thus resulting in an improvement in the quality of the received signal.
[0002] In another advantageous aspect of the present disclosure, the feed horn is designed to be used in dual reflector antenna systems operating simultaneously at C-Band and Ku band receive only Satellite Communication (SATCOM) frequencies.
[0003] The various embodiments described above are specific examples of a single broader invention. Any modifications, alterations or the equivalents of the above-mentioned embodiments are pertaining to the same invention as long as they are not falling beyond the scope of the invention as defined by the appended claims. It will be apparent to a person skilled in the art that the system and method for autonomous recovery of space based or terrestrial objects may be provided using some or many of the above-mentioned features or components without departing from the scope of the invention. It will be also apparent to a skilled person that the embodiments described above are specific examples of a single broader invention which may have greater scope than any of the singular descriptions taught. There may be many alterations made in the invention without departing from the spirit and scope of the invention.
[0063] In the foregoing detailed description of embodiments of the invention, various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the invention require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the detailed description of embodiments of the invention, with each claim standing on its own as a separate embodiment.
[0064] It is understood that the above description is intended to be illustrative, and not restrictive. It is intended to cover all alternatives, modifications and equivalents as may be included within the scope of the invention as defined in the appended claims. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein,” respectively.
, Claims:
1. A feed system (100) for satellite communication, comprising:
a feed horn (110) comprising a waveguide section (1101) and a first set of traverse slots (1102) for propagation of first frequency signals, wherein the feed horn corresponds to an outer conductor of the feed system;
a dielectric loaded waveguide feed (140) positioned coaxially with the waveguide section of the feed horn, the dielectric loaded waveguide feed configured to facilitate propagation of second frequency signals, wherein the dielectric loaded waveguide feed corresponds to an inner conductor of the feed system;
a polarisation diplexer (120) of coaxial structure configured to receive a portion of the dielectric loaded waveguide feed and a portion of the waveguide section extending from the feed horn, thereby operatively coupling the feed horn with the polarisation diplexer, wherein the polarisation diplexer comprises a first port (121) associated with a first polarisation, and a second port (122) associated with a second polarisation for the first frequency signals; and
a stepped polarisation diplexer (130) comprising a third port (131) and a fourth port (132), the stepped polarisation diplexer configured to receive a remaining portion of the waveguide section extending from the polarisation diplexer, wherein the third port is associated with the first polarisation and the fourth port is associated with the second polarisation for the second frequency signals, wherein the second polarisation corresponds to an orthogonal polarisation, and
wherein the first set of traverse slots of the feed horn is configured to prevent interference between the first frequency signals and the second frequency signals while propagating in the waveguide section of the feed horn and the dielectric loaded waveguide feed, respectively.

2. The feed system (100) as claimed in claim 1, wherein the feed horn further comprises two or more pairs of waveguide chokes (1103) operatively coupled to the waveguide section through the first set of traverse slots, the two or more pairs of waveguide chokes providing at least substantially symmetric E-plane and H-plane radiation patterns of the first frequency signals by adjusting a phase of E-field, and substantially unequal E-plane and H-plane radiation patterns of the first frequency signals.

3. The feed system (100) as claimed in claim 1, wherein the feed horn and the polarisation diplexer are associated with a first fundamental mode (301) and a second fundamental mode (302), and wherein the feed horn is configured for feeding to a reflector surface of a reflector antenna by exciting the second fundamental mode along with suppressing the first fundamental mode.

4. The feed system (100) as claimed in claim 1, wherein the dielectric loaded waveguide feed comprises a pair of waveguide rings (1401,1402) and a dielectric rod (1404) configured with a plurality of segments, and wherein the pair of waveguide rings are separated by a distance corresponding to of one-fourth operating wavelength of the first frequency signals for at least providing excitation to a second fundamental mode and broadband impedance matching.

5. The feed system (100) as claimed in claim 1, wherein the feed system further comprises a dielectric flange (14021) positioned on a dielectric rod, the dielectric flange configured to adjust a position of the dielectric loaded waveguide feed such that a phase center of the radiation pattern for both the first frequency signals and the second frequency signals coincides and high secondary efficiency is achieved.

6. The feed system (100) as claimed in claim 1, wherein the polarisation diplexer is configured with a first stepped discontinuous structure (1203) and a second stepped discontinuous structure (1206) for providing wide bandwidth operation in the first frequency signals.

7. The feed system (100) as claimed in claim 6, wherein,
the first stepped discontinuous structure is configured in conformity with an aperture of the first port and a first traverse groove (1202) of the polarisation diplexer being connected to the first port through the first stepped discontinuous structure, and
the second stepped discontinuous structure is configured in conformity with an aperture of the second port and a second traverse groove (1205) of the polarisation diplexer being connected to the second port through the second stepped discontinuous structure.

8. The feed system (100) as claimed in claim 6, wherein the polarisation diplexer comprises a first fin (1204) and a second fin (1207) of a blade-shaped structure for providing wide bandwidth operation in the first frequency signals.

9. The feed system (100) as claimed in claim 1, wherein the second traverse groove (1205) is orthogonally oriented to the first traverse groove at half of a guided wavelength of the first frequency signals from the first traverse groove for providing isolation between the first polarisation and the second polarisation.

10. The feed system (100) as claimed in claim 1, wherein the first frequency signals and the second frequency signals correspond to C-band signals and Ku-band signals, respectively.