Sudhakar K. Rao

Parametric design and analysis of multiple-beam reflector antennas for satellite communications

This paper presents the parametric design and analysis of multiple-beam reflector-antenna systems employed for satellite communications. It is based on extending the earlier work of Rao (see IEEE Antennas and Propagation Magazine, vol.41, no.4, p.53-59,1999) by taking into account the efficiency of the horn and pointing error of the satellite in the design of the multiple-beam antennas (MBAs), and by analyzing the edge-of-coverage directivity and co-polar isolation (C/I) performance. Design and analysis equations are developed for the multiple-beam antennas using offset parabolic-reflector antennas by including various design parameters such as the number of reflectors, the number of frequency cells, the focal-length-to-diameter (F/D) ratio, the horn efficiency, and the pointing error. The analysis employs a quasi-Gaussian beam representation for the primary and secondary patterns in order to take into account the effect of the sidelobes. Results of the analysis given in this paper agree well with rigorous computations based on physical optics analysis of the antenna radiation. Design curves showing the impact of horn efficiency on the C/I performance of multiple-beam antennas are presented for various frequency-reuse schemes.

Miniature implantable and wearable on-body antennas: towards the new era of wireless body-centric systems [antenna applications corner]

Wireless body-centric sensing systems have an important role in the fields of biomedicine, personal healthcare, safety, and security. Body-centric radio-frequency identification (RFID) technology provides a wireless and maintenance-free communication link between the human body and the surroundings through wearable and implanted antennas. This enables real-time monitoring of human vital signs everywhere. Seamlessly integrated wearable and implanted miniaturized antennas thus have the potential to revolutionize the everyday life of people, and to contribute to independent living. Low-cost and low-power system solutions will make widespread use of such technology become reality. The primary target applications for this research are body-centric sensing systems and the relatively new interdisciplinary field of wireless brain-machine interface (BMI) systems. Providing a direct wireless pathway between the brain and an external device, a wireless brain-machine interface holds an enormous potential for helping people suffering from severely disabling neurological conditions to communicate and manage their everyday life more independently. In this paper, we discuss RFID-inspired wireless brain-machine interface systems. We demonstrate that mm-size loop implanted antennas are capable of efficiently coupling to an external transmitting loop antenna through an inductive link. In addition, we focus on wearable antennas based on electrically conductive textiles and threads, and present design guidelines for their use as wearable-antenna conductive elements. Overall, our results constitute an important milestone in the development of wireless brain-machine interface systems, and a new era of wireless body-centric systems.

Design and analysis of multiple-beam reflector antennas

Simplified design and analysis equations are presented for multiple-beam reflector antennas based on the Gaussian-beam analysis of the primary and secondary patterns. The derived equations are useful for the quick design and performance analysis in terms of the coverage-area directivity and the inter-beam isolation of multiple-beam antenna systems. Results of the analysis given in this paper agree well with rigorous computations based on physical-optics analysis of the reflector-antenna radiation patterns. Extension of the analysis to multiple-beam lens antennas, and to shaped/contoured-beam antennas, is also presented.

A Novel Method for High-Power Thermal Vacuum Testing of Satellite Payloads Using Pickup Horns

This paper presents the development of a novel method for high-power thermal vacuum (TVAC) testing of satellite payloads using pickup horns (PUH). It describes the design, manufacture, and qualification results for a Ku-band pickup horn, followed by high-power thermal vacuum test results of a Ku-band satellite for fixed satellite service. Based on the successful demonstration of this method, a generic pickup horn (GPUH) - with improved performance over a large bandwidth, covering 7.0 GHz to 21.0 GHz - was developed for testing of X-band, Ku-band, and Ka-band satellite payloads. Detailed design and qualification aspects of the generic pickup horn are addressed, including measured results. This method has been successfully employed for high-power thermal vacuum testing of three different satellites at Lockheed Martin Commercial Space Systems (LMCSS), and is the planned testing method for all future payloads.

Low gain antenna performance impact due to spacecraft scattering

This paper presents impact of spacecraft scattering on the RF performance of low gain antennas used for communications satellites. The scattering analysis includes nadir deck structures, other spacecraft structures, large reflector used for high gain communication antennas, and solar panels. Impact of these spacecraft structures on both gain and cross-polar isolation of the low gain antennas is analyzed using ray-tracing analysis combined with physical optics (PO) integration of induced currents on these structures.

Pick-up horn for high power TVAC test of spacecraft payloads for communication satellites

This paper presents a novel method for high power thermal vacuum tests of spacecraft payloads using pick-up horns (PUH). The PUH method has benefits of being cost-effective, compact, easy to implement, does not require breaking the vacuum several times and avoids physical contact with flight hardware. It is designed with four oversized slots to receive the high RF power from the flight horns, absorb almost all the power and efficiently transfer the heat outside the TVAC chamber with minimal reflections back to the horn and minimal RF leakage outside the PUH. The PUH has been successfully used for high power TVAC testing and validation of a Ku-band payload for satellite communications

Parametric design of multiple beam reflector antennas

There has been a tremendous growth over the last few years in the use of multiple beam antennas (MBAs) for direct broadcast satellites and personal communication satellites. The MBAs provide a contiguous or non-contiguous coverage over a specified field-of-view on Earth by using high gain multiple spot beams for downlink and uplink coverage. Design of these MBAs using conventional feeds has been discussed earlier (see Rao, S., IEEE Antennas and Propagation Magazine, vol.41, no.4, p.53-9, 1999; IEEE AP-S Digest, vol.4, p.2078-81, 1998). This paper presents a parametric design approach using the horn efficiency as a variable. It is shown that the electrical performance of the MBAs in terms of coverage gain and copolar isolation can be significantly improved by selecting optimum efficiency for these multi-mode feed horns. Analytical results of the MBA with horn efficiency as parameter are presented here including comparisons with computed values.

Common aperture satellite antenna system for multiple contoured beams and multiple spot beams

This paper presents a novel satellite antenna that generates simultaneously multiple contoured beams at Ku-band and multiple spot beams at Ka-band using a common aperture reflector antenna. It employs a shaped reflector that optimizes the RF performance of the desired Ku-band contoured beams on the ground by employing multiple corrugated horns that are located along the focal-plane of the reflector. The synthesized reflector surface at Ku-band is employed to generate the Ka-band spot beams by “un-folding” the large quadratic phase distribution using an optimized location for the Ka feeds that is far from the focal-plane and by placing the feeds on a spherical arc. The common aperture antenna replaces three or more large reflectors on the spacecraft and provides significant cost and mass reductions for future communications satellites.

Report on the chicago antenna workshop

The Chicago Joint Chapter of the IEEE Antennas and Propagation Society (AP-S) and Microwave Theory and Techniques Society (MTT-S), the Industry Initiatives Committee of AP-S, and Motorola Mobility organized a full-day workshop entitled “Advanced Antennas for Satellites, Air craft, and Remote Sensing Applications” on Saturday, Sep tember 13, 2014. The workshop was a great success, with about 80 attendees. It took place at Motorola Mobility, located within the Merchandise Mart building in downtown Chicago.

A generic pick-up horn for high power thermal vacuum test of X, Ku, and Ka band satellite payloads

This paper presents development results of a generic pick-up horn (GPUH) for high power thermal vacuum (TVAC) test of satellite communications payloads. The GPUH is an improved method than the PUH that was presented earlier. It has much wider bandwidth of more than three octaves covering X-band, Ku-band, and Ka-band, can handle more power than the PUH, has better return loss, and is insensitive to polarization. Design and measured results of the GPUH are given here and are also discussed in an earlier publication.