Design approach for simultaneously achieving impedance matching and enhancing the isolation of multiplexer has been proposed. The channel filters constituting the multiplexer utilize the T-shaped short-circuited resonators as resonant components and short-circuited parallel-coupled lines as interstage couplings. The embedded open-ended stubs of resonators intentionally placed along the main transmission path of each channel contribute the virtual-shorts by creating transmission zeros thereby making the matching and isolation improvement possible. A triplexer with satisfactorily high output isolation is designed and implemented to validate the concept.

Abstract-Benefitting from the simultaneous utilization of quarterwave (λ/4) and half-wave (λ/2) microstrip resonators, a via-free balanced bandpass filter (BPF) with direct-coupled scheme is presented in this study. In the beginning, a single-ended filter with transmission zeros (TZs) is newly proposed and the mechanism of creating two TZs around the passband without necessitating cross couplings is adopted. The TZs can be made structure-inherent based on the coexisted out-of-phase couplings among a coupled-resonator pair. On the foundation of the presented single-ended filter, a balanced filter featuring extended differential-mode (DM) stopband, good commonmode (CM) suppression, and improved passband selectivity has been designed and implemented. The DM stopband extension is achieved by misaligning the higher-order harmonic frequencies of each resonator in the DM bisected circuit while the CM suppression is accomplished by both harmonic misalignment and careful designed coupled structure in the CM bisected circuit. Eventually, a demonstrated balanced filter centering at 1.5 GHz possesses DM stopband extended up to 8f d 0 , where f d 0 denotes the DM operation frequency, and its CM rejection ratio (CMRR) within DM passband better than 51.9 dB is attained. For measurement convenience, the DM characterizations have been accomplished by 2-port network analyzer with simple rat-race baluns and are found relatively accurate within the −15 dB bandwidth of the utilized baluns.

No abstract

No abstract