volume | PIER Journals

Abstract

This paper presents a class of wideband hybrid couplers with enhanced isolation, based on an N-section phase shift filter network integrated into an unequal-split, multi-section branch-line hybrid architecture. The key innovation lies in the incorporation of the N-section phase shift network, which significantly enhances the fractional bandwidth with each increase in section and isolation performance compared to conventional designs. A detailed design methodology applicable for any N is developed and validated through the fabrication and testing of two microstrip prototypes for N = 3 and N = 4 at a center frequency of 1 GHz. Both simulated and measured results confirm consistent tight coupling, insertion loss better than 6 dB, and isolation exceeding 15 dB across all prototypes. Furthermore, N = 3 and N = 4 hybrids shows peak isolation of 87.4 dB, 96.8 dB in simulation and 66.5 dB, 72.7 dB in measurement respectively, at the center frequency of 1 GHz. Notably, the designs demonstrate a progressive improvement in the fractional bandwidth, achieving 73.68% and 91.89% for N = 3 and N = 4, respectively. This scalable and frequency-flexible design approach makes the proposed class of hybrid couplers highly suitable for modern microwave systems such as vector network analyzer (VNA) test set, applications in radar, communication receivers, and phased array antennas.

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Mr. Shubham Tirmanwar

Dr. Debapratim Ghosh