Sudhakar K. Rao, Philip Venezia, Jonathan R. Scupin, Clency Lee-Yow, Suzanna LaMar
IMAGE LICENSED BY INGRAM PUBLISHING
Future protected communications require soldiers on the ground to carry several antennas integrated with their manpacks to provide secure and reliable communications at a number of frequency bands. This article describes a novel quadband petal reflector antenna (QPRA) that combines four frequency bands into one using a quadruplexer. A dual-reflector antenna utilizing an axially displaced ellipsoid subreflector being fed with a quad-ridged horn provides communications at Ku-band transmit (Ku-Tx), Ku-band receive (Ku-Rx), K-band receive (K-Rx), and Ka-band transmit (Ka-Tx) frequencies simultaneously. The main reflector is made of six identical petals that can be quickly assembled and disassembled in the battlefield. The antenna is mounted on a lightweight gimbal to provide beam scanning over a hemispherical coverage. The antenna is mounted on a tripod structure for field operations and uses commercial off the shelf (COTS) components and 3D manufactured parts to minimize cost and mass. The novelty of the antenna presented in this article includes a wide bandwidth capability of 73%, the use of a petal reflector, a 3D manufactured quad-ridged horn, a high-performance quadruplexer, and the use of COTS gimbals for beam scanning. Antenna design, analyses, hardware, and test results are presented in this article. The measured results of the antenna agree well with the computed results validating the QPRA design.
An innovative, easy to deploy, ruggedized, lightweight QPRA has been designed and developed to provide high-band, full-duplex communications operations at Ku-Rx, Ku-Tx, K-Rx, and Ka-Tx. The QPRA design supports full-duplex operation and right-hand circular polarization (RHCP) for 14.4–14.83 GHz (Rx) and 15.15–15.35 GHz (Tx) with a minimum of 28 dBi antenna gain and K/Ka-bands at 20.2–21.2 GHz (Rx) and 30–31 GHz (Tx) with switchable RHCP and left-hand circular polarization (LHCP) with a minimum of 32-dBi antenna gain. The QPRA is integrated with a lightweight COTS gimbal and a small tripod to provide beam scanning of ±90° in elevation and ±90° in azimuth. Personnel on the ground require advanced antenna technologies, such as the novel QPRA, that can be integrated with emerging software defined radio communication devices to provide high capacity for communications at the halt as shown in Figure 1. The QPRA is used to communicate with unmanned intelligence, surveillance, and reconnaissance platforms; geostationary Earth orbit (GEO) satellites; and command headquarters. Currently, there are a great number of high-bandwidth applications that the QPRA could be used with, to include distribution of data, video and commercial command and control or data dissemination, or surrogate communications systems should control towers be compromised, e.g., in a national disaster scenario [1].
Figure 1. Quadband reflector antenna communications capability. LOS: line of sight; BLOS: beyond line of sight.
Reflector antennas are widely used in satellite communications, Earth stations, and aircraft applications requiring high data rates due to high gain and mature technology [2], [3], [4], [5], [6]. However, the reflector antennas used for space applications are moderately expensive and operate in either a single band (transmit or receive) or dual bands supporting both transmit and receive frequencies [7], [8], [9], [10], [11], [12], [13], [14]. They are made of composite graphite material due to its thermal stability, which is required to operate in space environments, and are up to 3 m in size. A triband feed working at 20/30/45 GHz has been reported by Granet and James [15]. A multiband antenna working at five frequency bands has been reported by Rao et al. [16] for space applications. The drawbacks are higher losses associated with reflect arrays and frequency selective surfaces (FSSs) and inability to scan the beams. For mobile satellite service payloads at L- and S-bands, mesh reflectors of 6 m to 22 m deployable in space are used to provide the required gain to close the communication link. The mesh is made up of gold molybdenum wires of 1 mil diameter. The reflectors are very expensive due to the size and the deployable features of the antenna [17], [18]. Ground antennas used for deep-space networks employ larger than 30 m reflectors to communicate with satellites at S- and Ka-bands. The main reflector is made of a number of aluminum panels and is heavy and expensive. Radio astronomy antennas such as Arecibo used 1,000-ft reflectors made up of thousands of metallic panels [4], [18], and these antennas are extremely expensive. Phased arrays have been used at Ku-, K-, and Ka-bands [19], [20], [21], [22]. However, four phased arrays are required due to the narrow bandwidth of phased array antennas. In addition, they are expensive and heavy and require hundreds of watts of dc power, making them unsuitable for mobile soldiers to carry in the battlefield for Communication At The Halt (CATH) applications. Deng et al. [23] presented a multiband reflectarray at Ku/K using an FSS. Reflectarrays have been used for narrow-bandwidth applications, and therefore, four reflectarrays are needed for our application [24], [25]. In addition, reflectarrays cannot scan over the coverage, and a mechanical gimbal system is required for each of the four reflectors.
A novel petal reflector antenna that works simultaneously at four frequency bands is presented in this article. A detailed trade study was carried out among four different antenna technologies, and the results are summarized in Table 1. Based on the trade study, the QPRA has been selected as the suitable candidate due to ease of deployment, low mass, low cost, low dc power requirement, and better gain performance over the scan range. Key components of the QPRA are the quadband feed having more than an octave bandwidth, a subreflector supported by the feed cone, a petal reflector where the main reflector is made of six identical petals that are easily and quickly assembled and disassembled on the ground, a wideband polarizer, two quadruplexers (one for each polarization) that are used to separate the four frequency bands with sufficient isolation among them, a COTS gimbal that can move the beam over a hemispherical coverage, and a tripod mount used to assemble it on the ground. The majority of the components are either 3D manufactured or COTS parts in order to reduce mass and cost. Design, analysis, fabrication, and test results of the QPRA are presented in this article. A recent patent [26] issued by the U. S. Patent and Trademark Office and a recent publication [27] describe some of the novel features of the QPRA. The complete details of the QPRA are given in this article.
Table 1. Comparison of different antenna technologies for ground applications.
The QPRA assembly is shown in Figure 2. The main components of QPRA are a 15-in-diameter main reflector, a subreflector supported by a feed cone, a feed assembly comprising a wideband ridged horn, a wideband polarizer, two quadruplexers, a two-axis COTS gimbal, and a tripod structure to mount the antenna assembly and the gimbal on the ground. The reflector focal length to diameter ratio is 0.21 in order to keep the antenna compact in size. The reflector design, subreflector surface profile optimization, and RF analysis were performed using TICRA Generalized Reflector Analysis Software Program (GRASP) [28], a commercial software package. GRASP is a very efficient tool that uses physical optics to accurately predict QPRA radiation patterns. The main reflector is made of six identical petals composed of plastic (rexolite) with metal coating on the top of the reflecting surface. The petal geometry is shown in Figure 3. The petals have an adjacent gap of 0.1 in so that they can be easily inserted into a common circular mounting structure in the field when the soldier is stationary and easily and rapidly removed and stored in a carrying case when the soldier is roaming. Analysis using TICRA’s GRASP software was performed to show that the gap between the petals would have minimal impact on performance over all frequency bands. The overall size of the QPRA in its assembled state is 15 in diameter with height adjustable to 40 in, and the overall mass is only 16 lb so that the soldier can carry it effortlessly in the battlefield. The antenna can scan over ±90° in elevation plane and ±90° in azimuth plane using the COTS two-axis gimbal procured from FLIR [Forward Looking Infrared (model PTU/5)]. It is mounted on a carbon fiber tripod structure, which is a COTS part procured from the vendor K&F Concept. The main advantages and novel features of the QPRA when compared to conventional phased arrays are 1) a single QPRA, 2) a 6-dB gain advantage due to avoidance of scan loss achieved by using gimbal mechanisms, 3) 3D manufactured parts and COTS items to reduce cost and delivery schedule, and 4) low dc power and low mass.
Figure 2. Mechanical design of (a) the QPRA and (b) the gimbal mechanism.
Figure 3. (a) Petal reflector (15-in diameter) made out of six petals with an adjacent spacing of 0.1 in between each petal for ease in assembly process. (b) View of one petal in the circular mounting structure. (c) Detailed view of the locking feature of the petal to the mounting structure.
The feed assembly includes a wideband quad-ridged horn with 73% bandwidth, a matching section, and an orthomode transducer to generate two orthogonal linear polarizations. The two linear polarization ports are connected to a COTS hybrid coupler to generate both RHCP and LHCP signals. The two circular polarization (CP) ports are connected to two quadruplexers using two 2.92-mm coaxial RF cables. The quadruplexers separate the four frequency bands with sufficient isolation among them. The feed has a total of eight output ports coming from the two quadruplexers and four RHCP and four LHCP ports. Figure 4 shows the geometry of the horn assembly. The horn performance has been analyzed using the Computer Simulation Technology (CST) software. Measured return loss of the horn is shown in Figure 5 and compared with simulation results over the 14–31 GHz frequency range. The agreement is reasonably good in spite of the increased dimensional tolerances due to 3D manufacturing of the horn using an AlSiMg metal alloy. The return loss measured is better than 10 dB at both the orthogonal linearly polarized ports of the horn. The measured isolation performance between the two ports of the feed assembly is shown in Figure 6 and compared with simulations. The isolation is better than 30 dB mostly, with the worst-case value of 28 dB at 30 GHz. Good agreement has been achieved between the two even with the increased tolerances associated with 3D manufacturing of the feed assembly. The radiation patterns of the feed assembly have been measured in an anechoic chamber using a source horn and compared with simulated results in Figure 7 at 14.4 GHz and 30.0 GHz. Only the two edge bands are shown, but the other two bands have similar behavior. Copolar and cross-polar radiation patterns are shown in the ${\varphi} = {45}^{\circ}$ plane in the plots. The horn patterns are well behaved over more than an octave bandwidth, and the agreement between measurements and simulations is good. The cross-polar patterns also agree well, and the minor differences are due to manufactured tolerances.
Figure 4. Quad-ridged wideband horn assembly with coaxial transitions showing two orthogonal ports.
Figure 5. Return loss (RL) performance of the quad-ridged horn and transition at the two orthogonal ports (measured versus computed).
Figure 6. Isolation (Iso) performance between the two orthogonal ports of the quad-ridged horn (measured versus computed).
Figure 7. Radiation patterns of the quad-ridged horn at (a) 14.4 GHz and (b) 30 GHz (measured versus computed shown in ${\varphi} = {45}^{\circ}$ plane).
The subreflector is supported by a foam radome machined out of a solid piece of General Plastics Dielectric Foam, RF-2203, which is typically used for radome applications. The foam radome and quad-ridge feed are analyzed using CST, to get the performance impact from the foam radome support. The data from the CST simulations of the feed horn and foam radome are then used together with the subreflector and main reflector geometries using the physical optics technique in the GRASP simulation to achieve the final performance of the QPRA. The horn, radome support, and subreflector assembly is shown in Figure 8.
Figure 8. The subreflector and the feed horn assembled together with the foam radome structure.
A pair of quadruplexers are required to interface between each of the two orthogonal CP ports of the antenna feed and the four radios per polarization within the manpack. The primary design drivers are the very wide total bandwidth that must be supported within the communication system and the high-power handling requirement, which makes the microstrip implementation undesirable. Low insertion loss and high isolation among the frequency bands, as well as low mass, are other key design drivers. The design criticality is to achieve high isolation between the closely spaced Ku-Rx and Ku-Tx frequency bands. The topology arrived at consists of the cascade of three diplexers as shown in Figure 9. A custom waveguide with reduced width and height has been selected as the internal transmission line media to minimize the occurrence of higher-order mode propagation within the structure. This waveguide allows TE10 to propagate at the lowest frequency (14.4 GHz) and allows only the TE20 mode to propagate at the highest frequency band (31 GHz). Excitation of this mode can be avoided using a side-to-side symmetric structure throughout the device, which has the additional benefit of simplifying the electromagnetic model.
Figure 9. Quadruplexer topology.
Diplexer1 consists of a cutoff waveguide, with reduced waveguide dimensions, selected to pass the TE10 mode at 30–31 GHz, with high attenuation at all lower frequencies, to extract the highest frequency band (Ka) at a T-junction while a corrugated low-pass structure passes the K and Ku bands through to the next diplexer. Diplexer2 consists of a cutoff waveguide, with reduced waveguide dimensions, selected to pass the TE10 mode at 20.2–21.2 GHz, which extracts the K band at a t-junction while a corrugated low-pass structure passes the Ku bands through to the next diplexer. Diplexer3 consists of a pair of traditional narrow bandpass inductive iris cavity filters with six poles for the low band and seven poles for the high band, to achieve high adjacent band rejection.
All three diplexers were designed using Microwave Wizard, a commercial software package developed for the design of complex waveguide components using mode matching, boundary contour mode matching, 2D finite element method, 3D finite element method, and the efficient cascading and intermixing of all of these electromagnetic techniques. This allows the user to use the most efficient method to simulate each element of a circuit, minimizing computation time. Additionally, Diplexer3 was optimized using an add-on filter optimization package, Equal Ripple Optimization, by DGS Associates, which is a highly efficient optimizer developed specifically for filters. The combination of Microwave Wizard and Equal Ripple Optimizer has proven very effective and efficient for the design of tuningless filters, diplexer, and multiplexers. The three diplexers were designed independently, then cascaded, with only minor optimization of connection lengths to improve the return loss. One end launcher and four side launcher coaxial connector transitions were designed using full wave mode matching techniques in Microwave Wizard and then integrated into the package. Southwest Microwave Inc. 2.92-mm thread-in Hi-Rel connectors were selected for this prototype. The quadruplexer was precision CNC machined from 6061-T6 Aluminum in two halves to create a split-block/clamshell construction, with no provision or need for tuning screws. The diplexers are laid out such that they can be parted at the waveguide zero current line to reduce RF leakage. The quadruplexer design layout and the fabricated hardware are shown in Figures 10 and 11, respectively.
Figure 10. Quadruplexer geometry.
Figure 11. Fabricated unit of the quadruplexer.
The return loss of the quadruplexer has been measured and compared with simulated results and is depicted in Figure 12. The measured results match well with simulations, and return loss specification of 15 dB is met at all four bands with margin. A high isolation of >40 dB is achieved among the frequency bands. Figure 13 shows the measured passband characteristics at 30 GHz band and the isolation achieved at Ku-Rx, Ku-Tx, and K-Rx bands. Isolation of better than 65 dB at the K-band and better than 80 dB has been accomplished for the quadruplexer with the passband at Ka. Isolation performance for the Ku-Tx passband at the other three bands is shown in Figure 14. Insertion loss has been measured at all four bands, and the typical results are plotted in Figure 15 for the low and high bands. Measured insertion losses are 0.8 dB, 0.9 dB, 0.5 dB, and 0.5 dB at Ku-Rx, Ku-Tx, K-Rx, and Ka-Tx frequency bands, respectively. Insertion loss is higher at the two Ku-bands due to close proximity of the two Ku-band frequencies. Two units of quadruplexer have been fabricated and tested. Measured test results show that return loss of better than 16 dB, insertion loss better than 0.9 dB, and rejection among the bands of better than 40 dB have been achieved over all four frequency bands. All requirements have been met for the two prototype quadruplexers.
Figure 12. Measured return loss performance of the quadruplexer compared with simulations.
Figure 13. Measured versus simulated isolation performance of the 30-GHz passband over the other three bands (K, Ku-Tx, and Ku-Rx).
Figure 14. Measured versus simulated isolation performance of the 15-GHz passband over the other three bands (Ka, K, and Ku-Rx).
Figure 15. Measured insertion loss of the quadruplexer compared with simulations at the four bands: (a) the 30-GHz band and (b) the 14-GHz band.
The integrated QPRA with the main reflector, feed assembly, hybrid coupler, subreflector, foam support radome, quadruplexer, two-axis gimbal, RF cables, and tripod mount and its components are shown separately in Figure 16. The foam radome support is machined out of a solid piece of General Plastics Dielectric Foam, RF-2203, typically used for antenna radome applications. The hybrid coupler is a COTS 90° hybrid coupler from dBWave that operates over the required bandwidth. Dimensional details of the QPRA are shown in Figure 17. For the prototype, the main reflector is fabricated with solid aluminum instead of petals and tested to demonstrate the antenna performance. Table 2 shows the computed performance comparison between the solid and petal reflectors. The antenna performance has been analyzed using TICRA’S GRASP software [28] based on physical optics integration of the surface currents. The gain difference between the two is negligible and within 0.07 dB. The slight drop in gain for petal reflector is due to the 0.1-in gap between the adjacent petals. The sidelobe level has been computed, and the maximum difference is 0.1 dB, as shown in Table 2.
Figure 16. (a) Mechanical design and (b)–(i) fabricated components of the integrated quadband reflector antenna. Components are as follows: (b) main reflector, (c) feed horn, (d) foam spacer, (e) cables, (f) subreflector, (g) gimbal, (h) hybrid coupler, and (i) support brackets.
Figure 17. Dimensions for the quadband reflector antenna.
Table 2. Comparison of the QPRA computed performance with solid AI main reflector antenna.
The integrated quadband reflector antenna patterns have been measured in a near-field antenna range facility with an 8 ft × 8 ft vertical scanner as shown in Figure 18. The near-field probe used is an open-ended waveguide. Near fields have been probed over a 7 ft × 7 ft scan area with two orthogonal orientations of the probe, vertical and horizontal. The amplitude and phase patterns have been transformed into far field by combining the vertical polarization and horizontal polarization fields using equal amplitude and phase quadrature to obtain the far-field circularly polarized RHCP and LHCP patterns. Measured copolar and cross-polar patterns of the antenna are shown at low and high bands in Figures 19 and 20 and compared with simulated results. The measured copolar patterns match very well with all the computed patterns. The cross-polar patterns also match reasonably well where minor differences noticed are due to increased dimensional tolerances of the feed assembly due to 3D manufacturing.
Figure 18. Integrated quadband reflector antenna in the near-field antenna range at Custom Microwave Inc.
Figure 19. Comparison of measured antenna RHCP and LHCP patterns with simulations at 14.4 GHz. (a) RHCP Patterns 14.4 GHz. (b) LHCP Patterns 14.4 GHz.
Figure 20. Comparison of measured antenna RHCP and LHCP patterns with simulations at 30 GHz. (a) RHCP Patterns 30 GHz. (b) LHCP Patterns 30 GHz.
The worst-case cross-polar levels match well between simulated and measured patterns. The mass budget of the QPRA including all components is summarized in Table 3. Total mass is 15.96 lb, which is much below the 25-lb requirement. Detailed loss budget and antenna gain performance are summarized in Table 4. The loss budget includes feed assembly loss, quadruplexer loss, cable loss, surface root mean square loss of the main reflector and subreflector, and thermal distortion loss. The total loss is subtracted from the measured antenna directivity to obtain the antenna gain. The measured antenna gain meets the requirements with margin at all four frequency bands. The prototype antenna has been successfully developed conforming to all the requirements. For field testing during the next phase of this development, the solid aluminum main reflector used in this prototype will be replaced with the petal reflector design without changing the remainder of the hardware components.
Table 3. Mass budget of the QPRA.
Table 4. Measured gain performance of the quadband reflector antenna and loss budget.
This article presents development results of a novel QPRA for soldiers on the ground communicating with other aircraft in hostile situations, satellites, and command headquarters. The antenna has more than an octave bandwidth, enabling it to operate simultaneously at Ku-Rx, Ku-Tx, K-Rx, and Ka-Tx bands. A single QPRA replaces conventional design using four phased arrays, one for each band, reducing the cost, mass, and production schedule significantly. The fabricated antenna has been tested, the measured results agree well with simulations, and it meets all the requirements with margin. The antenna beams are scanned over the hemispherical coverage region using COTS gimbals. There is no scan loss associated with beam scanning, unlike phased arrays. Key aspects of the antenna including low mass, low cost, and ease of deployment and stowage combined with significantly higher gain have been successfully demonstrated. This antenna is currently being field tested and later will be mass produced with thousands of units for ground applications with an emphasis on expeditious deployment in the battlefield. The QPRA has potential future space applications for low Earth orbit, medium Earth orbit, and GEO satellites. It will also have future applications in aircraft and unmanned air vehicles, where the QPRA can be placed either in the nose cone or as an aircraft point of descent.
This research is based upon work supported by the U.S. Air Force and Defense Advanced Research Projects Agency (DARPA) under Contract FA-8750-18-C-0058. Any opinions, findings and conclusions, or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the U.S. organizations or agencies.
Sudhakar K. Rao (skraoks@yahoo.com) is the president and chief executive officer of RaoS Consultants LLC, Rancho Palos Verdes, CA 90275 USA. He retired from Northrop Grumman in 2022. His professional interests include antennas for space, air, and ground systems. He is an IEEE Life Fellow.
Philip Venezia (venezia@custommicrowave.com) is the director of the Innovation Center of Excellence at Custom Microwave Inc., Longmont, CO 80501 USA. His research interests include reflector antennas, feeds, and waveguide components for space applications.
Jonathan R. Scupin (scupin@custommicrowave.com) is currently the principal RF engineer and manages the Antenna Product Test Laboratory at Custom Microwave Inc., Longmont, CO 80501 USA. He has been an RF/microwave engineer for 25 years, with expertise in advanced antenna feeds and components.
Clency Lee-Yow (clency@custommicrowave.com) is the president and chief executive officer of Custom Microwave Inc., Longmont, CO 80501 USA. His research interests include developing novel antenna products for space and other applications.
Suzanna LaMar (suzanna.lamar@ngc.com) received her Ph.D. in systems engineering at Colorado State University, Colorado, in 2022. She is the chief architect for the 3U software defined radios product line and is a Fellow at Northrop Grumman Mission Systems, San Diego, CA 92128.
[1] G. R. Walton, “Overcoming the odds: How the U.S. Army can achieve indirect fire superiority in a near-peer environment,” U.S. Army Command General Staff College, Leavenworth, KS, USA, Tech. Rep., Jun. 2018. [Online] . Available: https://apps.dtic.mil/sti/pdfs/AD1085634.pdf
[2] S. Rao, L. Shafai, and S. Sharma, Handbook of Reflector Antennas and Feed Systems – Applications of Reflectors, vol. 3. Norwood, MA, USA: Artech House, 2013.
[3] A. W. Love, “Some highlights in reflector antenna development,” Radio Sci., vol. 11, nos. 8–9, pp. 671–684, Aug./Sep. 1976, doi: 10.1029/RS011i008p00671.
[4] Y. Rahmat Samii and A. C. Densmore, “Technology trends and challenges of antennas for satellite communication systems,” IEEE Trans. Antennas Propag., vol. 63, no. 4, pp. 1191–1204, Apr. 2015, doi: 10.1109/TAP.2014.2366784.
[5] S. Rao, “Advanced antenna technologies for satellite communications payloads,” IEEE Trans. Antennas Propag., vol. 63, no. 4, pp. 1205–1217, Apr. 2015, doi: 10.1109/TAP.2015.2391283.
[6] C. Kumar et al., “Axially displaced ellipse reflector antenna for Chandrayaan-1 data transmission system,” in Proc. Int. Radio Symp. India (IRSI), Bangalore, India, Dec. 2009, pp. 1–4.
[7] N. Chahat et al., “CubeSat deployable Ka-band mesh reflector antenna development for earth science missions,” IEEE Trans. Antennas Propag., vol. 64, no. 6, pp. 2083–2093, Jun. 2016, doi: 10.1109/TAP.2016.2546306.
[8] S. Rao and M. Tang, “Stepped-Reflector antenna for dual-band multiple beam satellite communications payloads,” IEEE Trans. Antennas Propag., vol. 54, no. 3, pp. 801–811, Mar. 2006, doi: 10.1109/TAP.2006.869938.
[9] R. C. Gupta, S. K. Sagi, and M. Mahajan, “Parallel-shaping technique for a ring-focus reflector antenna: A multiband Gregorian ring-focus reflector antenna for the Satcom flyaway terminal,” IEEE Antennas Propag. Mag., vol. 61, no. 5, pp. 87–96, Oct. 2019, doi: 10.1109/MAP.2019.2932306.
[10] C. Granet, “Designing axially symmetric Cassegrain or Gregorian dual-reflector antennas from combinations of prescribed geometric parameters,” IEEE Antennas Propag. Mag., vol. 40, no. 2, pp. 76–82, Apr. 1998, doi: 10.1109/74.683545.
[11] S. Rao, P. Venezia, and C. Lee-Yow, “A reconfigurable reflector antenna system with a hybrid scanning method: Imaging antennas for simultaneous multiple spot and wide coverage beams,” IEEE Antennas Propag. Mag., vol. 61, no. 5, pp. 29–36, Oct. 2019, doi: 10.1109/MAP.2019.2932298.
[12] C. Hsu and S. Rao, “Horn antenna and system for transmitting and/or receiving radio frequency signals in multiple frequency bands,” U.S. Patent 8 164 533, Apr. 2021.
[13] S. Rao and M. Tang, “Stepped-reflector antenna for satellite communications payloads,” U.S. Patent 7 737 903, Jun. 2010.
[14] S. Rao, K. K. Chan, and M. Tang, “Dual-band multiple beam antenna system for satellite communications,” in Proc. IEEE Antennas Propag. Soc. Int. Symp., Washington, DC, USA, Jul. 2005, vol. 3A, pp. 359–362, doi: 10.1109/APS.2005.1552258.
[15] C. Granet and G. L. James, “Optimized spline-profile smooth-walled tri-band 20/30/44-GHz horns,” IEEE Antennas Wireless Propag. Lett., vol. 6, pp. 492–494, Nov. 2007, doi: 10.1109/LAWP.2007.907057.
[16] S. Rao, C.-C. Hsu, and K. K. Chan, “Antenna system supporting multiple frequency bands and multiple beams,” IEEE Trans. Antennas Propag., vol. 56, no. 10, pp. 3327–3329, Oct. 2008, doi: 10.1109/TAP.2008.929540.
[17] M. W. Thomson, “The AstroMesh deployable reflector,” in Proc. IEEE Antennas Propag. Soc. Int. Symp., 1999, vol. 3, pp. 1516–1519, doi: 10.1109/APS.1999.838231.
[18] I. Chiba and Y. Konishi, “Development of large earth-station reflector antennas in Japan,” IEEE Antennas Propag. Mag., vol. 53, no. 6, pp. 245–257, Dec. 2011, doi: 10.1109/MAP.2011.6157768.
[19] S. K. Rao and C. Ostroot, “Design principles and guidelines for phased array and reflector antennas,” IEEE Antennas Propag. Mag., vol. 62, no. 2, pp. 74–81, Apr. 2020, doi: 10.1109/MAP.2020.2969261.
[20] A. Samaiyar et al., “Phased array antenna for bi-static simultaneous transmit and receive (STAR) systems,” in Proc. IEEE Int. Symp. Phased Array Syst. Technol. (PAST), Oct. 2019, pp. 1–5, doi: 10.1109/PAST43306.2019.9021027.
[21] G. Oliveri et al., “Wide-angle impedance matching layer-enhanced dual-polarization sub-6 GHz wide-scan array for next-generation base stations,” IEEE Trans. Antennas Propag., vol. 70, no. 7, pp. 5506–5520, Jul. 2022, doi: 10.1109/TAP.2022.3161555.
[22] S. Rao, A. Pandya, and C. Ostroot, “Phased array antennas for aircraft applications,” in Proc. IEEE Indian Conf. Antennas Propag. (InCAP), Hyderabad, India, Dec. 2018, pp. 1–4, doi: 10.1109/INCAP.2018.8770894.
[23] R. Deng, S. Xu, F. Yang, and M. Li, “An FSS-backed Ku/Ka quad-band reflectarray antenna for satellite communications,” IEEE Trans. Antennas Propag., vol. 66, no. 8, pp. 4353–4358, Aug. 2018, doi: 10.1109/TAP.2018.2835725.
[24] P. Nayeri, F. Yang, and A. Elsherbeni, Reflectarray Antennas: Theory, Design and Applications. Hoboken, NJ, USA: Wiley, 2018.
[25] J. Huang and J. Encinar, Reflectarray Antennas. Hoboken, NJ, USA: Wiley, 2007.
[26] S. Rao et al., “Quad-band petal reflector antenna,” U.S. Patent 11 088 461, Aug. 10, 2021.
[27] S. Rao et al., “Quad-band petal reflector antenna for ground communications,” in Proc. IEEE Wireless, Antenna Microw. Symp. (WAMS), Rourkela, India, Jun. 2022, pp. 1–4, doi: 10.1109/WAMS54719.2022.9848186.
[28] “TICRA tools GRASP version 21.0,” TICRA, Copenhagen, Denmark, Jul. 2021. [Online] . Available: https://www.ticra.com/ticra-tools-21-0-is-released/
Digital Object Identifier 10.1109/MAP.2022.3229572