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A reduced size rat-race coupler incorporating a bandpass frequency response characteristic is presented and designed based on substrate-integrated waveguide (SIW) technology. By use of electric- and magnetic-coupling structures between adjacent SIW cavity resonators, a conventional rat-race coupler and a bandpass filter with a 200-MHz bandwidth at a centre frequency of 7.75 GHz can be integrated as one component resulting in miniaturisation. A design process based on the coupled-resonator network is introduced to synthesise such a bandpass coupler with desired bandwidth, return loss and coupling. A Butler matrix and a six-port junction with bandpass response are then developed based on the proposed rat-race coupler. They represent excellent candidates for miniaturised transceiver and direct conversion systems. The measured results are in good agreement with the simulated predictions. [ABSTRACT FROM AUTHOR]

In this study, a new type of substrate integrated waveguide (SIW) beamforming network (BFN) based on the principle of the modified R-KR lens has been proposed and experimentally verified. Through the detailed analysis of such a structure, a prototype lens with 15 input ports is implemented together with an SIW slot array antenna at 30 GHz, which is able to cover a wide angle of (-59°, 59°) with its 3 dB beam-width. The measured radiation efficiencies of the lens excited at different ports range from 21.6 to 40.8%. This type of BFN takes the advantages of low profile, low cost and high performance, and may be applied to millimetre-wave mobile communications and radars with beam switching technology. [ABSTRACT FROM AUTHOR]