HIGH-PERFORMANCE ANTENNA ARRAYS FOR MULTIFUNCTION PHASED ARRAY RADAR (MPAR) APPLICATION

Abstract

There are interest and practical value in utilizing polarization diversity for a radar to obtain more target information or for a communication system to carry more signal information without occupying more frequency band. This is because frequency bands are getting crowded in microwave frequencies due to the recent advancements in cellular communications. For example, the Spectrum Efficient National Surveillance Radar Program (SENSR) is started to study the feasibility of replacing the four radar networks that service the U.S with a single network of Multifunction Phased Array Radar (MPAR). Candidates being considered for future MPAR include Cylindrical Polarimetric Phased Array Radar (CPPAR), and Planar Polarimetric Phased Array Radar (PPPAR). To have the desired accurate weather measurements with a PPPAR or CPPAR, a high-performance phased array antenna with dual-polarization capability is required. The array antenna is required to possess matched main beams, high input isolation, and low cross-polarization level at broadside and scan angles up to 45◦. The beam mismatch should be within 5% of the beamwidth, the input isolation needs to be better than 40 dB, and to have ZDR bias of less than 0.2 dB, the cross-polarization level along beam axis needs to be lower than -20 dB and -40 dB for alternate and simultaneous transmission, respectively. These are very stringent requirements for antenna design and development.

The primary objective of this dissertation is to propose high-performance dual-polarized antenna arrays with high input isolation and low cross-polarization level for multifunction phased radar application. To do so, four different types of dual-polarized microstrip patch antenna arrays are presented. In the proposed patch antennas, different feeding techniques such as, aperture coupling method, balanced feed method and the combination of these methods which is called hybrid feeding technique are used. The proposed antenna arrays in this dissertation are configured according to image configuration for improving the cross-polarization level. The issues and challenges of implementing image arrangement is discussed, and precise procedure for design and predicting the final array radiation characteristics is proposed.

The CPPAR demonstrator antenna is redesigned to achieve matched horizontal and vertical polarization beam pointing angels. A method of beam matching between two linearly polarized radiation patterns of a dual-polarized frequency scanning antenna is proposed, implemented, and tested. A meticulous phase match process between the outputs of both individual cells and the whole corresponding horizontal and vertical feed lines is carried out. To verify the simulation results and to take the coupling effect into account, the radiation patterns of an isolated column, as well as those of three columns, are measured. In agreement with the design and simulation results, horizontal and vertical polarization beams with a pointing angle mismatch of less than ±0.2◦ within the resonant frequency bandwidth of 2.75–2.95 GHz are achieved.