Novel compact dual-narrow/wideband branch-line couplers using T-Shaped stepped-impedance-stub lines
This article presents a compact model to reduce the physical size and increase the frequency ratio between the second and first resonance frequencies of a dual-function stepped-impedance-stub (SIS) line, which was subsequently employed in the realization of dual-band branch-line couplers. The proposed model comprises of a loaded spiral T-shaped SIS that reduces the size of a conventional SIS line as well as improving its frequency ratio. The proposed model behaves exactly similar to the recently developed dual-band resonators with the advantage of size reduction of ?35% as well as having a wide range of realizable frequency ratios between 1.4 and 3.7 compared to 1.72.7 and 1.82.3 for the conventional SIS and T-shaped transmission-lines, respectively. Dual-narrowband and wideband branch-line couplers were developed based on the spiral T-shaped SIS lines. The dual-wideband device's bandwidth was enhanced by 2.7% accompanied by a size reduction of 58.6% in comparison with the conventional dual-wideband couplers operating at the same frequencies. The theoretical results were verified by measurement.  2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.
spiral t-shaped stepped impedance-stub dual narrow-band branch-line coupler dual wide-band branch-line coupler