Size-reduction and band-broadening design technique of uniplanar hybrid ring coupler using phase inverter for M(H)MIC's

The hybrid coupler is one of the most fundamental building blocks in microw ave and millimeter-wave systems. Ring topology can be often found in the hy brid microwave integrated-circuit design of narrow and broad-band integrate d couplers and mixers. In this paper, we propose a new design theory using a phase inverter for systematic size reduction and band broadening of a uni planar hybrid ring coupler, The features and design criteria of broad-band reverse-phase hybrid ring couplers are presented. Effective bandwidth of a new reverse-phase hybrid ring coupler can be increased by 28% with a return loss of 20 dB, In addition, we present a class of uniplanar phase inverter s and discuss their technical aspects. Experimental results show that the b andwidth of the proposed phase inverter is greater than 1.9 octaves with in sertion loss below 1 dB and phase shift error of less than +/-20 degrees. M easurements confirm that the new uniplanar hybrid ring coupler provides att ractive features, Its isolation is better than 20 dB over a 1.8-octave band width attributed to the phase inverter providing almost a frequency-indepen dent phase shift.