Slotline, CPW ring circuits and waveguide ring cavities for coupler and filter applications

Abstract

Slotline and coplanar waveguide (CPW) ring elements have been developed as circuit components for resonator, filter, and coupler applications. Transitions from CPW to slotline and coplanar strip (CPS) using uniform and non-uniform CPWs, slotlines, or CPSs which fully utilize the advantages of the uniplanar structures are discussed. These transitions are uniplanar and simple to fabricate. No via-holes are needed for ground connections, and integration with solid-state devices is easy. A new double-sided slotline hybrid-ring coupler using the resistively-coupled slotline ring was demonstrated with fairly good power dividing and isolation over a wide bandwidth. Novel uniplanar 180° and 90° hybrids suitable for MIC and MMIC were also developed. A new uniplanar 2-branch directional coupler using a coupled rectangular slotline ring has also been developed that has over 20 dB isolation over a bandwidth of more than 40% centered at 3 GHz with +1 dB power dividing balance. One double-sided planar magic-T and two uniplanar magic-Ts were developed by using the 180° reverse-phase slotline or CPW/slotline tee junction. Experimental results showed that the double-sided and uniplanar magic-Ts have a bandwidth of one octave from 2 to 4 GHz. The mutual isolation between the E- and H-arm is over 30 dB from 2 to 4 GHz. Their performance in terms of insertion loss, mutual isolation, amplitude and phase balance is comparable with the commonly used waveguide magic-Ts. A new type of rectangular waveguide ring cavity has been developed for applications of resonators, filters, and multiplexers. H-plane and E-plane waveguide ring cavities have been investigated thoroughly in single-mode and dual-mode operations. Mechanically-tuned and electronically-tuned resonators built by adjusting the resonant modes between regular resonant modes and forced resonant modes have been demonstrated. A dual-mode filter using a single H-plane ring cavity has been built with a bandwidth of 0.77%, a stop-band attenuation of more than 40 dB. Theoretical analyses based on circuit modeling and transmission line theory were developed to predict the performance of these components. The agreement between the theory and experiments is fairly good.