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Steven Gao


Prof. Steven Gao
Chair of RF and Microwave Engineering
School of Engineering and Digital Arts
University of Kent
Canterbury CT2 7NZ, UK
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Low-Cost Smart Antennas

Smart antennas are the key technology for wireless communications and radars. They can adjust their radiation patterns adaptively, i.e., forming maximum radiation towards the desired users and nulls towards the interference sources. Thus, they can improve the capacity of wireless communication networks significantly, increase the spectrum efficiency and reduce the transmit power. Traditionally, smart antennas are, however, too complicated, bulky, heavy and expensive for civil applications. For commercial applications, it is very important to reduce the cost, size, mass and power consumption of smart antennas.

This lecture will first give an introduction to smart antennas and their types such as passive and active phased arrays, digital beamforming smart antennas, adaptive arrays, multi-beam antennas, beam-switching antennas, multiple inputs and multiple outputs (MIMO) antenna systems, etc. The basic principles of each type of smart antennas will be explained. The advantages and disadvantages of each type of smart antennas will be highlighted.

The lecture will then describe different types of low-cost smart antenna technologies, such as Electrically-Steerable Parasitic Array Radiator (ESPAR) antenna, compact MIMO antennas, beam-switching array antennas and low-cost phased arrays. Many practical examples of antenna configurations and designs will be shown, explained and their performance discussed. These will include folded-monopole ESPAR (FM-ESPAR) for wireless communications, high-gain ESPAR using small director array, small-size MIMO, beam-switching reflectarray antennas for satellite communications, low-cost phased array antennas, etc.

Space Antennas
Due to the special environment of space and the launch vehicle dynamics to get there, spacecraft antenna requirements and designs are quite different from those of terrestrial antennas. Onboard a satellite, there are a number of different antennas and arrays for various functions, such as Telemetry, Tracking and Command (TT&C), high-speed data downlink, GPS navigation and positioning, remote sensing, inter-satellite links, deep-space communications, etc. Since the launching of 1st man-made satellite “Sputnik” in 1957, a large variety of antennas and arrays have been developed for space applications and the antennas employ different frequency bands including UHF/VHF, L, S, C, X, Ku, Ka and V band.

This lecture will first explain the satellites, orbits, the space environment and special requirements of space antennas. Different types of satellites and orbits will be explained. Space environments such as extreme thermal conditions, materials outgassing, radiation environment, multipaction effects, passive inter-modulation, corona phenomenon, electro-static charging, atomic oxygen, etc, will be discussed and their impact on the antenna designs will be explained. Other issues, e.g., the interactions amongst antennas, satellite bodies and solar panels, will also be described. Key challenges for space antenna designs will be illustrated.

The lecture will then provide an overview of space antennas developed for different applications. This part will show many examples of the real-world space antennas for different applications such as TTC, navigations, high-speed data downlink, GPS reflectometry remote sensing, inter-satellite links, deep-space communications, etc. The operating principles of each antenna will be explained and their performance will be discussed.  Finally, an outlook to the future development of space antennas will be presented.

Multi-Band Antennas for Global Navigation Satellite Systems (GNSS) Receivers
Global Navigation Satellite System (GNSS) is a satellite based radio navigation system that provides precise information about the spatial coordinates (longitude, latitude and altitude) of an object anywhere on the earth or in the air. Global Positioning System (GPS) is the single fully operational navigation system available for commercial and military users around the globe while Galileo, GLONASS and COMPASS (European, Russian and Chinese respectively) are in the development stage with GLONASS operating with partial capability. GNSS operates at different frequency bands including L1, L2, L5, E5, etc. The use of a compact multi-band antenna instead of multiple single-band antennas can reduce the size, mass and cost of GNSS receivers significantly. During recent years, a variety of multi-band antennas have been developed for GNSS receivers.

This lecture will give an introduction to the GNSS system and the antenna design requirements for GNSS receivers. Various issues such as multipath mitigation, phase center stability, compact size, multi-band operation, etc, will be discussed. Techniques of multipath mitigation such as choke rings, electromagnetic-band-gap (EBG) antennas, etc, will be presented and their principles will be explained.

The lecture will then give a review of compact multi-band antennas and arrays for GNSS receivers. Many examples of GNSS antenna designs will be shown, and the antenna configurations and design principles will be explained. These will include the dual-band multipath mitigating GNSS antenna using the cross plate reflector ground plane (CPRGP), multi-band QHA antennas, active multi-band antennas, small multi-band GNSS array antennas, high-gain beam-switching multi-band GNSS arrays, etc. The performance of each antenna will be described.

Antennas for Synthetic Aperture Radars
Synthetic aperture radars (SAR) is an imaging radar which produces high resolution radar images of the earth’s surface by using microwave signals. Unlike optical sensors which are limited by day lights and weather conditions, SAR can be used day and night and can see through clouds. SAR has important wide-ranging applications for earth observations in remote sensing and mapping of the surfaces of both the Earth and other planets. SAR is used in various fields of research ranging from oceanography, geology, to archaeology. Antenna for SAR is usually very complicated and expensive. SAR antenna is often one of the most expensive components onboard the aircraft or spacecraft.

This lecture will first give an introduction to SAR systems and how SAR works. Key parameters of SAR systems such as range resolution, azimuth resolution, frequency bands, etc, will be explained. Different SAR modes such as stripmap, scanSAR, spotlight and interferometric SAR (InSAR) will be described. SAR system design considerations and key challenges for SAR antenna designs will also be presented.

The lecture will then provide a review of antennas for SAR. An overview of antenna development for space-borne SAR will be illustrated and some examples will be given. The design principles of each example antenna will be explained and their performance discussed. Finally the lecture will give a discussion of future development such as the digital beam-forming SAR for satellite constellations, etc.

Steven (Shichang) Gao was born in Anhui, P.R. China. He received a PhD from Shanghai University, China, in 1999. He is a Professor and Chair of RF and Microwave Engineering at School of Engineering and Digital Arts, University of Kent, UK. His research covers antennas, smart antennas, phased arrays, space antennas, RF/microwave and mm-wave circuits and systems, satellite communications, synthetic-aperture radars, UWB radars and GNSS receivers.

He started his career at China Research Institute of Radiowave Propagation in 1994-1996. Afterwards, he worked as a Post-doctoral Research Fellow at National University of Singapore in 1999-2001, a Research Fellow at Birmingham University (UK) in 2001-2002, a Senior Lecturer (2002-2006), Reader (2006-2007) and Head of Active Antenna and RF Group (2002-2007) at Northumbria University (UK) and a Senior Lecturer and Head of Space Antennas and RF System Group (2007-2012) at Surrey Space Center, University of Surrey, UK. Also he was a Visiting Scientist at Swiss Federal Institute of Technology (ETHZ, Switzerland) in 2003, a Visiting Professor at University of California at Santa Barbara (US) in Jan-July 2005, and a Visiting Fellow at Chiba University (Japan) in Aug-Sept 2005 and June-July 2013. Since Jan. 2013, he joined the University of Kent as a Full Professor and became a Chair of RF and Microwave Engineering since Feb. 2014.

He is General Co-Chair of Loughborough Antennas and Propagation Conference (LAPC), UK, 2013, and Chair of Special Session on “Satellite Communication Antennas” in IEEE/IET International Symposium on Communication Systems and Networks, 2012, etc. He is a Guest Editor of IEEE Transactions on Antennas and Propagation for a Special Issue on "Antennas for Satellite Communication"(Feb. 2015 issue). He is an Invited Speaker at IWAT'2014 (Sydney, 2014), SOMIRES'2013 (Japan, 2013), APCAP'2014 (Harbin, 2014), etc. He is an Associate Editor of Radio Science and also the Editor-in-Chief of Wiley Book Series in Microwave and Wireless Technologies. He is a Fellow of Institute of Engineering and Technology (IET), UK.

He has two book including Space Antenna Handbook (Wiley, 2012, co-editors: Imbriale and Boccia) and Circularly Polarized Antennas (Wiley-IEEE Press, 2014, co-authors: Luo and Zhu), published over 180 technical papers, 10 book chapters and holds three patents in smart antennas and RF. He received "URSI Young Scientist Award”, 2002, “JSPS Fellowship Award”, Japan, 2005, “Best Paper Award”, LAPC, UK, 2012, “JSPS Fellowship Award”, Japan, 2013, etc. He has been a leader and principal investigator of a number of research projects in areas of smart antennas for satellite communications on the move, space antennas, compact-size low-cost smart antennas for wireless communications, phased arrays for synthetic aperture radars, active integrated antennas for mobile communications, millimeter-wave antennas arrays, high-efficiency RF/microwave power amplifiers, UWB radars, GNSS receiver front end, adaptive small-size multi-band antennas for mobile phones, etc.