Design of a programmable wideband microwave feed network

Abstract

The design and fabrication of a wide-band programmable microwave feed network is proposed. The design architecture is composed of four main stages, switching, phase shifting, amplication/attenuation and control. The proposed feed network is designed to cover a wide band from 2.5 to 6 GHz over two separate branches, one covers from 2.5 to 3 GHz and the other covers from 3 to 6 GHz. Digitally controlled phase shifters are used to control the phase. A digital control unit is used to provide the required control signals for all the feed network stages. Digitally controlled wide-band variable gain ampliers are used to set the appropriate amplitude to the signal in both paths. The feed network is simulated and fabricated on an FR-4 substrate with thickness of 0:8mm. Good matching between simulation and measurement results is achieved.The measured amplitude resolution was 0.5 dB with an error of less than +0.22/−0.12 dB. The measured phase resolution was approximately 5.625° with an error of less than ±1°. This value of phase resolution can achieve a scanning beam resolution of 1:8 for a linear antenna array. Also, the sidelobe levels can be controlled by amplitude tapering functionality of the proposed network. The proposed network is a generic two-path design that can be used as a standalone network to feed any kind of array system. The size of the two-path feed network was 110 × 63 × 0:8mm 3. Since the feed network needs a kind of combiner circuit to combine all the outputs from the network to the input of a transceiver, a compact size 12-port microwave combiner with phase compensation is designed and fabricated. The combiner covers the band from 2.3 to 3 GHz. Its size was 78:5 × 61 × 0:8mm3.