DESIGN AND IMPLEMENTATION OF A COMPACT PRACTICAL PASSIVE BEAM-FORMING MATRIX FOR 3D S-BAND RADAR

In this paper a compact two-layer microstrip passive beam-forming matrix in the 2.9-3.1GHz frequency band is designed, fabricated, and measured. This 13 X 6 matrix is a passive circuit that can transform the 13 patterns of an antenna array into six possible beams to decrease the complexity for multiplexing/demultiplexing operation in three dimensional Radar. The 90 degrees hybrid couplers with high isolation between two signals and phase shifters between the couplers are used to provide proper signals in outputs. The matrix structure consists of metal walls around transmission lines to eliminate the surface waves. Also, a coaxial to microstrip transition is used to extract accurate measurement results. A special box is designed to cover matrix which has many design considerations such as cutoff frequency, destructive effects on couplers and other parts of matrix, and all of these effects are analyzed and considered to achieve the optimum performance in this paper. The matrix is designed on a substrate Rogers RT5880 with [[epsilon].sub.r] = 2.2, substrate height = 0.787 mm, and loss tangent = 0.0009. Also the thickness of the copper cladding layer is 17 [micro]m. The maximum amplitude and phase errors in outputs are 0.6 dB and 7[degrees], respectively, and VSWRs are less than 1.35 in the matrix bandwidth with at least 20 dB isolation between all ports.