In this dissertation, a 38 GHz waveguide-fed microstrip antenna array using a novel beam-steering technique was first proposed. The array is composed of 15 sub-arrays fed by a rectangular waveguide through apertures on the waveguide’s top wall. Each sub-array contains two parallel series-fed microstrip antenna arrays.
The array has a fixed beam in the E plane and a variable beam in the H plane. The phase difference between adjacent sub-arrays is controlled by changing the waveguide width so as to steering the array beam. The measured gain of the array is about 22 dBi. The main beam scanning angle is 5.4o.
Next, a dual-mode folded microstrip reflectarray antenna was developed and demonstrated in this paper. The proposed folded reflectarray antenna contains three parts: a planar main reflector, a planar sub-reflector, and printed feed antennas. The main reflector is used to produce twisted re-radiated fields and to provide phase compensation for focusing. The sub-reflector parallel with the main reflector is made of a substrate printed with high-density metal grid lines, which is transparent to perpendicularly polarized fields, but would reflect the parallel ones. Three fixed-position patch antennas with polarization parallel to the grid lines are created for the radar mode, so that the radiation beam is switchable. Another patch with perpendicular polarization is designed for communication. A simple approach was proposed for simulating and designing the folded reflectarray. In the radar mode, the total beam switching angle is 29.5o. At 38.5 GHz, the finished folded reflectarray antenna possesses an antenna gain of larger than 20 dBi within the beam switching range. A maximum gain of 27.4 dBi and the corresponding aperture efficiency of 33.9% were achieved. While in the communication mode, the ripple in the pattern
was improved by enclosing the feed patch with a square metal frame, the beamwidth is much broader, and thus provides communications over a wide angular range.
Then, a 60 GHz RHCPSS was investigated. The structure of the CPSS presented is very simple, so that printed circuit technology could be used to realize it.
Method of moments was utilized to extract the currents on a single circular polarization selective structure. Using periodic Green’s function together with the currents, a 2 dimensional infinite CPSS can be simulated. From which, scattered field for different circularly polarized incident waves were obtained. The optimal design parameters were found in this study. The respective simulated isolation and transmission loss at 60 GHz are 26.4 dB and -0.43 dB. While for the finished RHCPSS, the maximum measured isolation of 23.89 dB and the minimum measured transmission loss of -2.25 dB occur at 58.4 GHz,
Investigations into a new type of CPSSs were also carried out. It is of simple planar structure without any vertical conductive segments. Couplings, through the use of L-shaped traces, were produced to replace the vias. Operational principle and design procedure are developed, thus the optimal design parameters are found. The measured data of the finished LHCPSS have an isolation of larger than 13 dB for an incident LHCP wave at 30 GHz, with transmission loss of -2.28 dB for the RHCP wave. This example demonstrates the performances of the design and the attractiveness the new type of CPSSs.
Lastly, a corner reflector antenna with pattern diversity was developed. It supports multiple patterns with the maximum measured gain of 6.77 dBi. By controlling the switch states, the pattern can be steered in 45o increment to cover the whole H plane. This design provides a simple and flexible way for pattern beam-forming.
The proposed CPSSs and FSS can be modified or integrated to contribute to more advanced planar reflector antennas, such as corner reflector antenna, reflectarray antenna, folded reflectarray and so on. For example, the method of simultaneously control the switching states of a group of microwave elements with one switch can be utilized to design a multi-band reconfigurable FSS. It is also feasible to be applied to handle the characteristics of a CPSS.
Besides, a good CPSS could raise many new applications, especially the reflectarray antenna. For a conventional folded microstrip reflectarray antenna, the main-reflector provides the 90o polarization twisting of the re-radiation and phase compensation for the in-phase array. The sub-reflector parallel to the main-reflector is transparent to one linear polarization but would reflect the other one. The electromagnetic wave radiated from the feed antenna located at the center of the main reflector is linearly polarized. Hence the wave would be reflected when it confronts the sub-reflector. The main reflector then receives the field and re-transmits it. The re-transmitted field could penetrate the sub-reflector and focus in the far field region.
With the emergence of excellent CPSSs, the concept of the folded reflectarray antennas could be extended to circular polarization applications. Figure 7.1 illustrates the concept of the circular polarization folded reflectarray antenna. The linear polarizor in the original linear polarization folded reflectarray antenna is replaced by the CPSS. Nevertheless, the main reflector design is not applicable to the circular polarization case; we use just a simple flat conducting plate instead.
Phase compensating is no longer carried out by tuning the elements on the main reflector of the linear polarization folded reflectarray antenna, but by adjusting adequate amounts of rotation on the elements of the CPSS around the z-axis. With reference to Figure 7.1(b), a simple trigonometric relation is used to compensate the
additional path lengths across the array’s surface.
Assume a LHCP wave emitted from the feed on the conducting plate, it undergoes various path length to each element of the LHCPSS and makes different phase shifts among the elements. Take the distance from the feed to the centermost element as reference, element with lager path length should be rotated clockwise to offset the phase delay. Thus the elements of the LHCPSS re-radiate in-phase and the reflection wave resulted. When the reflected LHCP wave impinges the conducting plate and get reflected again, the sense of polarization changes. Then the consequent RHCP wave will pass through the LHCPSS with an enhanced gain in the boresight (+z) direction.
(a)
LHCP RHCP RHCPSS
Conducting Plate
(b)
x z
Figure 7.1 Schematic diagram of circular polarization folded reflectarray antenna.
(a) Topology, (b) Phase compensation method.
Vita
I-Young Tarn was born in Taipei in 1970. He received the B.S. and M.S.
degrees in electrical engineering from Yuan-Ze University, Tao-Yuan, Taiwan, R.O.C., in 1993 and 1995, respectively. From 1995 to 1999, he was an Assistant Researcher in Systems Engineering Project, National Space Program Office, Hsinchu, Taiwan, R.O.C.. Since 2000, he has been with the Electrical Engineering Division of the National Space Program Office, where he has been involved in satellite communications and antenna design. In the same year, he entered the Ph.D. program in Department of Communication Engineering at National Chiao Tung University, Hsinchu, Taiwan, R.O.C.. His research interests include microwave/mm-wave microstrip antennas, reflectarray antennas, frequency selective surfaces and circular polarization selective structures.
Publication List
Journal Papers
I-Young Tarn, and Shyh-Jong Chung, “A New Advance in Circular Polarization Selective Surface – A Three Layered CPSS without Vertical Conductive Segments,”
IEEE Trans. Antennas Propagat., vol. 55, no. 2, pp. 460 - 467, Feb. 2007.
Chong-Yu Hong, Ching-Wei Ling, I-Young Tarn, and Shyh-Jong Chung, “Design of a Planar Ultra-Wideband Antenna with a New Band-Notch Structure,” IEEE Trans.
Antennas Propagat., vol. 55, iss. 12, pp. 3391 - 3397, Dec. 2007.
I-Young Tarn, and Shyh-Jong Chung, “A Dual-Mode Millimeter-Wave Folded Microstrip Reflectarray Antenna,” IEEE Trans. Antennas Propagat., vol. 56, iss. 6, pp.
1510 - 1517, Jun. 2008.
I-Young Tarn , and Shyh-Jong Chung, “A Novel Pattern Diversity Reflector Antenna Using Reconfigurable Frequency Selective Surfaces”, submitted to IEEE Trans.
Antennas Propagat., 2008
Conference Papers
I-Young Tarn, and Shyh-Jong Chung, "A Beam-steering Waveguide-fed Microstrip Antenna Array", TSMMW2002.
I-Young Tarn, and Shyh-Jong Chung, "A Dual-modes Folded Microstrip Reflectarray Antenna ", PIERS2003.
I-Young Tarn, and Shyh-Jong Chung, "A 60 GHz Circular Polarization Selective Surface by Printed Circuit Technology", MINT-MIS2005/TSMMW2005.