Collaborative Design of a New Dual-Bandpass 180$^{\circ}$ Hybrid Coupler

A new dual-bandpass 180° hybrid coupler, based on four properly designed shorted-stub loaded stepped-impedance resonators, is proposed in this paper. In order to construct the collaboratively designed coupler/filter, the resonators are coupled magnetically and electrically with each other through three shorted stubs and an open coupled line, respectively. According to the approach of filter synthesis and the derived design equations, the characteristic admittances and electrical lengths of the resonators and coupling sections are determined to achieve the desired resonant frequencies, external
Q
factors, and internal coupling coefficients for dual passbands. A design procedure is provided. The design flexibilities for ratios of central frequencies and achievable bandwidths are explored. The component shows both filtering and power dividing functions within two specific passbands, whose good performances are demonstrated by the simulated and measured results. The two second-order passbands of a fabricated prototype are located at 2.42 and 5.84 GHz, with 4.6% and 5.2% bandwidths, respectively. The insertion losses are 1.0 and 1.4 dB over 3-dB power division. The isolations are better than 23.5 and 32.8 dB. In both the in-phase and out-of-phase responses, the in-band amplitude and phase imbalances are always within -1.6-0.6 dB and -6.5°-9.5°, respectively.