Claims:1. A truncated offset Gregorian reflector antenna device (100), the device comprising:
a main reflector (102) having a reflective surface with a focal point, the main reflector is configured with a first rim (108), said main reflector is truncated by removing at least a portion of the first rim;
a sub-reflector (104) coupled to the main reflector (102), the sub-reflector (104) is configured with a second rim (110), said sub-reflector (104) is truncated by removing at least a portion of the second rim; and
a feed assembly (106) coupled to the main reflector via the sub-reflector (104),
wherein the sub-reflector is oriented such that a first foci of the sub-reflector is coincident with the focal point of the main reflector and second foci of the sub-reflector is coincident with the phase center of the feed assembly, and
wherein the first rim (108) of the main reflector and the second rim (110) of the sub-reflector are truncated to effect better sidelobe levels of a radio frequency (RF) signal transmitted from the antenna device to meet the required satellite communication regulations.
2. The truncated offset Gregorian reflector antenna device as claimed in claim 1, wherein the feed assembly (106) and the sub-reflector (104) are mounted inside the perimeter of the antenna device without blocking the beam path.
3. The truncated offset Gregorian reflector antenna device as claimed in claim 1, wherein the feed assembly (106) comprises a high efficiency horn (112), a coupling waveguide (114) and an orthomode transducer (OMT) (116) for polarisation discrimination.
4. The truncated offset Gregorian reflector antenna device as claimed in claim 3, wherein the high efficiency horn (112) is a scalar profiled corrugated horn (SPCH).
5. The truncated offset Gregorian reflector antenna device as claimed in claim 4, wherein the radiation pattern of the feed horn is achieved such that efficiency of antenna device is enhanced.
6. The truncated offset Gregorian reflector antenna device as claimed in claim 1, wherein the main reflector (102) is a combination of parabolic shape.
7. The truncated offset Gregorian reflector antenna device as claimed in claim 1, wherein the sub-reflector (104) is a combination of elliptical shape.
8. The truncated offset Gregorian reflector antenna device as claimed in claim 1, wherein the antenna device has a cross-polar compensated geometry.
9. The truncated offset Gregorian reflector antenna device as claimed in claim 1, wherein the truncated shape of first rim (108) and the second rim (110) are configured such that the sidelobes of the RF signal transmitted from the antenna device are reduced below the prescribed satellite communication regulations.
, Description:TECHNICAL FIELD
[001] The present disclosure relates, in general, to an antenna system and more specifically, relates to a truncated antenna providing high efficiency and better sidelobe levels to meet the required satellite communication regulations.

BACKGROUND
[002] Reflector antennas are extensively used in satellite and wireless communication systems because of their high directional properties, structural simplicity and lightweight (in the case of glass fibre/carbon fibre reflectors). The most popular reflector is the parabolic one and the first type, in this case, is the axis-symmetric reflector antenna. This type of antenna provides excellent radiation properties but suffers from feed or sub-reflector aperture blockage.
[003] Offset reflector antennas including dual offset reflector antennas are in widespread use, because of their low aperture blockage and simplicity. These reflector antennas reduce aperture-blocking effects, which represents a very significant advantage for the offset configuration over comparable axis-symmetric counterparts. Aperture blocking leads to scattered radiation, which results in a loss of system and a general degradation in the suppression of sidelobe. The offset reflector antennas provide excellent isolation between the reflector and primary-feed/sub-reflector with the primary-feed voltage standing wave ratio (VSWR) can be made to be essentially independent of the reflector. However, single offset reflector antennas suffer from poor cross-polarisation.
[004] Dual offset reflector antennas are used for improved cross polarisation and higher efficiency but these systems have significantly large overall antenna system size. The problem of reducing the size of a dual offset Gregorian reflector type antenna with a circular aperture without adversely affecting performance has been explored by several authors. The antenna systems used for satellite communication (SATCOM) are required to comply with the International Telecommunication Union (ITU) regulations (ITU-R S.580-6). The transmitting antenna pattern should not cause interference to other adjacent satellites. To avoid this interference, the sidelobe levels of the antenna are required to be reduced to acceptable limits. Satellite communications are currently used at different frequency bands such as C band, Extended C Band, Ku band and the like.
[005] Existing technology in the field of antenna system provides antenna solution in C band with reduced antenna/radome size but compromised system radio frequency (RF) performance such as lower efficiency and higher sidelobe levels. In the known art, the antenna system has been disclosed as a part of an effective marine stabilized antenna system. In the antenna of the system, the sidelobe level to meet the ITU-R S.580-6 regulation skirting for off-axis angle = 26.5° has not been disclosed while its clearly evident cutting the ITU skirting and for ±180° off-axis angles, regulations ITU-R S.580-6and ITU-R S.465 (for off-axis angle = 26.5°) the achieved regulation cutting is 20.5%. This does not comply with the regulations ITU-R S.580-6 and ITU-R S.465 and hence may not be suitable for use in SATCOM. Further, the reported efficiency of the antenna is 41% with a diameter 2.2m, gain of 39.55 dBi, and frequency 6.425 GHz.
[006] Therefore, there is a need in the art for an efficient antenna system to complying with International Telecommunication Union (ITU) regulatory requirements for antenna sidelobe levels (SLL).

OBJECTS OF THE PRESENT DISCLOSURE
[007] An object of the present disclosure relates, in general, to an antenna system, and more specifically, relates to a truncated antenna providing high efficiency and better sidelobe levels to meet the required satellite communication regulations.
[008] Another object of the present disclosure is to provide an antenna device that enables high efficiency and better sidelobe levels to meet the required satellite communication regulations.
[009] Another object of the present disclosure is to provide an antenna device with a feed horn that reduces the size required for the antenna, compared to a dual offset reflector antenna with conventional feed.
[0010] Another object of the present disclosure uses a truncated 2.2m diameter antenna and achieves a typical gain of 40.7 dBi (at 6.1375 GHz) with 58 % efficiency and ITU-R S.580-6 regulation skirting cutting of less than 4.6 % (cut =0°) thus completely complying ITU-R S.580-6 regulation skirting at all cuts (cut=0°, 90°, 45°) at 6.1375 GHz.
[0011] Another object of the present disclosure is to provide a compact antenna device with higher efficiency, higher data rates, and lower operating costs, while complying with the international SATCOM regulations at all cut angles.
[0012] Another object of the present disclosure is to provide efficient and reduced size antenna device while meeting required regulations results in overall cost savings and satisfaction to the customer.
[0013] Yet another object of the present disclosure provides the operation of the present antenna that has been verified at C-Band linear frequencies for transmission at 5.85-6.725 GHz and receiving at 3.4-4.2 GHz.

SUMMARY
[0014] The present disclosure relates, in general, to an antenna system and more specifically, relates to a truncated antenna providing high efficiency and better sidelobe levels to meet the required satellite communication regulations. The present disclosure relates to the realization of a truncated dual offset reflector antenna. The antenna system consists of a main truncated parabolic reflector, a special shape truncated sub-reflector and a highly efficient feed horn to reduce overall antenna size. The antenna system geometry is designed to work at C Band SATCOM frequencies.
[0015] In an aspect, the present disclosure provides a truncated offset Gregorian reflector antenna device, the device includes a main reflector having a reflective surface with a focal point, the main reflector is configured with a first rim, the main reflector can be truncated by removing at least a portion of the first rim, a sub-reflector coupled to the main reflector, the sub-reflector is configured with a second rim, the sub-reflector is truncated by removing at least a portion of the second rim and a feed assembly coupled to the main reflector via the sub-reflector, wherein the sub-reflector is oriented such that a first foci of the sub-reflector is coincident with the focal point of the main reflector and second foci of the sub-reflector is coincident with the phase center of the feed assembly, and wherein the first rim of the main reflector and the second rim of the sub-reflector are truncated to effect better sidelobe levels of a radio frequency (RF) signal transmitted from the antenna device to meet the required satellite communication regulations.
[0016] In an embodiment, the feed assembly and the sub-reflector can be mounted inside the perimeter of the antenna device without blocking the beam path.
[0017] In another embodiment, the feed assembly may include a high efficiency horn, a coupling waveguide and an orthomode transducer (OMT) for polarisation discrimination.
[0018] In another embodiment, the high efficiency horn is a scalar profiled corrugated horn (SPCH).
[0019] In another embodiment, the radiation pattern of the feed horn is achieved such that efficiency of antenna device is enhanced.
[0020] In another embodiment, the main reflector is a combination of parabolic shape.
[0021] In another embodiment, the sub-reflector is a combination of elliptical shape.
[0022] In another embodiment, the antenna device has a cross-polar compensated geometry.
[0023] In another embodiment, the truncated shape of first rim and the second rim are configured such that the sidelobes of the RF signal transmitted from the antenna device are reduced below the prescribed satellite communication regulations.
[0024] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The following drawings form part of the present specification and are included to further illustrate aspects of the present disclosure. The disclosure may be better understood by reference to the drawings in combination with the detailed description of the specific embodiments presented herein.
[0026] FIG. 1A illustrates an exemplary representation of truncated offset Gregorian antenna (TOGRA) device, in accordance with an embodiment of the present disclosure.
[0027] FIG. 1B illustrates an exemplary view of the rims of the truncated Gregorian offset reflector antenna, in accordance with an embodiment of the present disclosure.
[0028] FIG. 1C illustrates an exemplary view of RF feed assembly, in accordance with an embodiment of the present disclosure.
[0029] FIG. 2 illustrates ITU standards for sidelobe level compliance for satellite communication antenna, in accordance with an embodiment of the present disclosure.
[0030] FIG. 3 is a ray diagram of conventional offset Gregorian reflector antennas (OGRA).
[0031] FIG. 4 illustrates an exemplary ray diagram of the proposed antenna device, in accordance with an embodiment of the present disclosure.
[0032] FIG. 5A illustrates an exemplary view of antenna radiation pattern at cut=0°, in accordance with an embodiment of the present disclosure.
[0033] FIG. 5B illustrates an exemplary view of antenna radiation pattern at cut=90°, in accordance with an embodiment of the present disclosure.
[0034] FIG. 6 illustrates an exemplary view of the antenna pattern showing the compliance to ITU-R S580.6 which includes antenna elevation and azimuth plane radiation patterns, in accordance with an embodiment of the present disclosure.
[0035] FIG. 7A illustrates an exemplary view of antenna pattern of typical ITU skirting at cut=0° degrees, in accordance with an embodiment of the present disclosure.
[0036] FIG. 7B illustrates an exemplary view of the antenna pattern operating at 45degrees, in accordance with an embodiment of the present disclosure.
[0037] FIG. 7C illustrates an exemplary view of the antenna pattern operating at 90 degrees, in accordance with an embodiment of the present disclosure.
[0038] FIG. 8 illustrates an exemplary graphical view of antenna co-polarisation and cross-polarisation radiation patterns, in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION
[0039] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. If the specification states a component or feature “may”, “can”, “could”, or “might” be included or have a characteristic, that particular component or feature is not required to be included or have the characteristic.
[0040] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0041] The present disclosure relates, in general, to an antenna system, and more specifically, relates to a truncated antenna providing high efficiency and better sidelobe levels to meet the required satellite communication regulations.
[0042] The present disclosure aims at the realization of a truncated dual offset reflector antenna. The antenna system may include a main truncated parabolic reflector, a special shape truncated sub-reflector and a highly efficient feed horn to reduce overall antenna size. The antenna system geometry is designed to work at C Band satellite communication (SATCOM) frequencies. The feed horn is configured with scalar profiled corrugations (SPC). The truncated shape of rims of TOGRA is such that sidelobes of a radio frequency (RF) signal transmitted from the TOGRA are reduced below the prescribed SATCOM regulations. The present disclosure can be described in enabling detail in the following examples, which may represent more than one embodiment of the present disclosure.
[0043] FIG. 1A illustrates an exemplary representation of truncated offset Gregorian reflector antenna (TOGRA) device, in accordance with an embodiment of the present disclosure.
[0044] Referring to FIG. 1A, a truncated offset Gregorian reflector antenna (TOGRA) device (also referred to as device 100, herein) of antenna system may be configured to comply with International Telecommunication Union (ITU) regulatory requirements for antenna sidelobe levels (SLL). The device 100 may include a main reflector 102, a sub-reflector 104, and a microwave feed assembly 106.The geometry of the antenna system may be designed to work at C-band SATCOM frequencies. The term antenna system generally refers to the truncated parabolic reflector including but not limited to truncated sub-reflector, the feed horn, and other radio frequency (RF) sub-systems. The whole antenna system has higher efficiency and better sidelobe levels compared to currently available similar systems while meeting worldwide SATCOM regulations.
[0045] In an exemplary embodiment, device 100 as presented in the example may contain around 2.2m diameter main reflector 102 of a combination of paraboloidal shape, and the sub-reflector 104 of a combination of elliptical shape. As can be appreciated, the present disclosure may not be limited to this configuration but may be extended to other configurations. In an embodiment, the main reflector 102 having a reflective surface with a focal point. The sub-reflector 104 coupled to the main reflector 102 and the feed assembly 106 coupled to the main reflector 104 via the sub-reflector 104.The operation of the present antenna has been verified at C-Band linear frequencies for transmission at 5.85-6.725 GHz and receiving at 3.4-4.2 GHz. The implemented system complies with worldwide SATCOM regulations including ITU-RS580.6 and ITU-R S.465.
[0046] FIG. 1B illustrates an exemplary view of the rims of the truncated Gregorian offset reflector antenna, in accordance with an embodiment of the present disclosure. As shown in FIG. 1B, a rim108 (also referred to as a first rim 108) of the main reflector 102 and a rim 110 (also referred to as second rim 110) of the sub-reflector 104 are truncated to achieve superior performance such as high efficiency and better sidelobe levels compared to currently available similar antennas. The truncated shape of the rims (108, 110) of the main reflector 102, and sub-reflector 106 are such that sidelobes of a RF signal transmitted from the device 100 are reduced below the prescribed SATCOM regulations. The antenna device 100 has higher efficiency and better sidelobe levels compared to currently available similar systems while meeting worldwide SATCOM regulations.
[0047] The truncated sub-reflector 104 may be oriented such that first foci of the truncated sub-reflector 104 can be coincident with the focal point of the main reflector 102 and second foci of the sub-reflector 104 with the phase center of the feed horn 106. In an exemplary embodiment, the present disclosure uses the truncated 2.2m diameter antenna and achieves a typical gain of 40.7 dBi at 6.1375 GHz with 58 % efficiency and ITU-R S.580-6 regulation skirting cutting of less than 4.6 % (cut =0°) thus completely complying ITU-RS.580-6 regulation skirting at all cuts (cut=0°, 90°, 45°) at 6.1375 GHz.
[0048] The main reflector 102 may be truncated by removing at least a portion of the first rim 108 and the sub-reflector 104 may be truncated by removing at least a portion of the second rim 110, where the truncated shape of the first rim 108 and the second rim 110 may be configured such that the sidelobes of the RF signal transmitted from the antenna device 100 may be reduced below the prescribed satellite communication regulations.
[0049] For example, in the transmitting mode, the feed assembly 106 may receive the microwave signals and launches those signals onto the truncated sub-reflector 104; the truncated sub-reflector 104 may reflect the signals onto the truncated main reflector 102, which in turn reflects the radiation across the face of the paraboloid. In the receiving mode, the truncated main reflector 102 is illuminated by an incoming signal and reflects this energy to illuminate the truncated sub-reflector 104, where the truncated sub-reflector may reflect this incoming energy into the feed assembly 106 for transmission to the receiving equipment.
[0050] FIG. 1C illustrates an exemplary view of RF feed assembly, in accordance with an embodiment of the present disclosure. As shown in FIG. 1C, the feed assembly 106 may include a high-efficiency horn 112, a coupling waveguide 114 and an orthomode transducer (OMT) 116 for polarisation discrimination. In an exemplary embodiment, to achieve the improved performance, a high-efficiency feed has been used which employs a scalar profiled corrugated horn (SPCH) 112 that may provide a wideband of around 3.4-6.725 GHz symmetric radiation pattern, which increases the overall antenna efficiency.
[0051] In an embodiment, the antenna device 100 may have cross-polar compensated geometry, where the geometry of the antenna device 100 departs from the traditional approach in a number of respects, particularly in a configuration including feed assembly 106 and sub-reflector 104 that are mounted inside the perimeter of the antenna device 100 without blocking the beam path. As a result, the overall size of the antenna device 100 may be reduced, which may provide cost benefits in satellite communication.
[0052] The embodiments of the present disclosure described above provide several advantages. One or more of the embodiments provide the antenna device 100 that enables high-efficiency and better sidelobe levels to meet the required satellite communication regulations. TOGRA with the proposed feed horn 106 may reduce the size required for the antenna, compared to a conventional dual offset feed, while providing higher efficiency and better sidelobes compared to presently available similar antenna systems. Compact antenna with higher efficiency provides, reduced antenna size, higher data rates, and lower operating costs while complying with the international SATCOM regulations (ITU-R S580.6 and ITU-R S.465) at all cut angles (cuts=0°,90°, 45°). The present disclosure relates to efficient and reduced size antenna device 100 while meeting required regulations results in overall cost savings and satisfaction to the customer.
[0053] FIG. 2 illustrates ITU standards for sidelobe level compliance for satellite communication antenna, in accordance with an embodiment of the present disclosure.
[0054] Referring to FIG. 2, the ITU regulation is referred as a skirting, where the skirting and the antenna radiation pattern are represented on the same diagram and are compared to each other to determine, how well sidelobes levels meets the regulation.
[0055] FIG. 3 is a ray diagram of conventional offset Gregorian reflector antennas (OGRA).
[0056] Referring to FIG. 3, the offset Gregorian reflector antenna (OGRA) 300 is a dual offset reflector antenna that consists of a main parabolic dish, an elliptical sub-reflector and a feed horn in which both sub-reflector and feed horn are out of the main beam path, hence it provides low sidelobes, however, this results in increased antenna size, as the feed is mounted outside the perimeter of the antenna. A further attempt has been made to mount sub-reflector and feed horn inside perimeter of the antenna, as a result, it provides the reduced size of the antenna, however, these configurations suffer from beam blockage 302 by feed and support structures, resulting in undesired high sidelobes and hence does not comply to worldwide SATCOM regulations.
[0057] FIG. 4 illustrates an exemplary ray diagram of the proposed antenna device, in accordance with an embodiment of the present disclosure.
[0058] Referring to FIG. 4, a ray diagram 400 of the antenna device 100, which consist of a truncated offset Gregorian reflector antenna. In this antenna device 100, the sub-reflector 104 and the feed assembly 106 can be oriented such that the sub-reflector 104, the feed assembly 106 and other supporting struts do not block the beam path which shows significant inventiveness in achieving ray optics 402 with the configuration of the antenna device 100. As result, this configuration provides very low levels of sidelobes, thus complying with the international SATCOM regulations. TOGRA may include a 2.2mdiameter of the main truncated reflector 102 of paraboloidal shape, the truncated sub-reflector 104 of elliptical shape, and the feed assembly 106. The truncated sub-reflector 104 may be oriented such that it’s one foci can be coincident with the focal point of the main reflector 102 and other foci with the phase center of the feed assembly 106.
[0059] An exemplary view of antenna radiation patterns 500 is illustrated, in accordance with an embodiment of the present disclosure. FIG. 5A depicts the antenna showing radiation pattern 502 at cut=0° angle.
[0060] FIG. 5B illustrates an exemplary view of antenna radiation pattern at cut=90°, in accordance with an embodiment of the present disclosure. FIG. 5B depicts the antenna showing radiation pattern 504 at cut=90° angle.
[0061] FIG. 6 illustrates an exemplary view of the antenna pattern 600 showing the compliance to ITU-R S580.6which includes antenna elevation and azimuth plane radiation patterns, in accordance with an embodiment of the present disclosure. As shown in FIG 6, the plot of an antenna pattern (cut=0°) 602 and (cut= 90°) 604 of the TOGRA within± 20°, an ITU-R S580.6 skirting 606 as shown in FIG. 6. The radiation patterns 602 and 604 within ± 20°of the antenna, fully complies with the ITU regulations represented by typical skirting 606; no sidelobe is exceeding the skirting (regulation), whereas maximum cutting allowed as per ITU specification is 10%.
[0062] FIG. 7A illustrates an exemplary view of antenna pattern of typical ITU skirting at cut=0° degrees, in accordance with an embodiment of the present disclosure. As shown in FIG. 7A, a plot of an antenna pattern 702, at cut=0° degrees, a typical ITU skirting 700 is shown. Operation at about 0° fully complies with the ITU regulations (Regulation% = 4.5 shown as 702, which is within the specification of 10%, as described above). The plots as shown in FIG. 7A to 7C of an antenna pattern showing the compliance to ITU-R S580.6 and ITU-R S.465 which includes cut=0°, cut=45° and cut=90° radiation patterns respectively.
[0063] FIG. 7B illustrates an exemplary view of antenna pattern operating at 45 degrees, in accordance with an embodiment of the present disclosure. The antenna pattern 704 operating at 45 degrees are shown with a typical ITU skirting 700.
[0064] FIG. 7C illustrates an exemplary view of antenna pattern operating at 90 degrees, in accordance with an embodiment of the present disclosure. The antenna pattern 706 operating at 90 degrees are shown with a typical ITU skirting 700. These results show full compliance to SATCOM regulations ITU-R S580.6 and ITU-R S.465 as no sidelobe is cutting the combined ITU (ITU-R S580.6 and ITU-R S.465) skirting 700.
[0065] FIG. 8 illustrates an exemplary graphical view 800 of antenna co-polarisation and cross-polarisation radiation patterns, in accordance with an embodiment of the present disclosure. Referring to the FIG. 8, a plot of antenna co-polarisation 802, cross-polarisation at cut=0° 804, cross-polarisation at cut=90° 806. Referring to FIG. 8; the disclosed antenna device 100 provides very low cross-polarisation levels.
[0066] It will be apparent to those skilled in the art that the antenna device 100 of the disclosure may be provided using some or all of the mentioned features and components without departing from the scope of the present disclosure. While various embodiments of the present disclosure have been illustrated and described herein, it will be clear that the disclosure is not limited to these embodiments only. Numerous modifications, changes, variations, substitutions, and equivalents will be apparent to those skilled in the art, without departing from the scope of the disclosure, as described in the claims.

ADVANTAGES OF THE PRESENT DISCLOSURE
[0067] The present disclosure provides an antenna device that enables high efficiency and better sidelobe levels to meet the required satellite communication regulations.
[0068] The present disclosure provides an antenna device with a feed horn that reduces the size required for the antenna, compared to a dual offset reflector antenna with conventional feed.
[0069] The present disclosure uses a truncated 2.2m diameter antenna and achieves a typical gain of 40.7 dBi (at 6.1375 GHz) with 58 % efficiency and ITU-R S.580-6 regulation skirting cutting of less than 4.6 % (cut =0°) thus completely complying ITU-R S.580-6 regulation skirting at all cuts (cut=0°, 90°, 45°) at 6.1375 GHz.
[0070] The present disclosure provides a compact antenna device with higher efficiency, higher data rates, and lower operating costs, while complying with the international SATCOM regulations at all cut angles.
[0071] The present disclosure is to provide efficient and reduced size antenna device while meeting required regulations results in overall cost savings and satisfaction to the customer.
[0072] The present disclosure provides the operation of the present antenna that has been verified at C-Band linear frequencies for transmission at 5.85-6.725 GHz and receiving at 3.4-4.2 GHz.