A Wideband 90-Degree 3 dB Hybrid Coupler Design for Ku-Band Space Applications

This paper presents the design and analysis of a miniaturized 90-degree hybrid coupler for Ku-band applications with a wideband operation. The coupler features a ring-shaped microstrip structure and has been optimised for a 14.3 GHz on a Rogers RO4003C substrate. First, the hybrid coupler is designed without modifying any ground planes, achieving a return loss of 44.61 dB and a bandwidth of 4.6 GHz. To enhance performance, a concentric circular slot with inner and outer radii of 0.18 mm and 0.44 mm, respectively, is added to the ground plane, which is a defected ground structure (DGS). This structure enhances impedance matching and amplitude balance to a large extent, with a return loss of 72 dB, an amplitude imbalance of 0.5 dB over 13.45-15.4 GHz, and an isolation of 38.54 dB. Additionally, the coupler achieves the required 9 0 phase difference with minimal variation. The compact packaging, with a configuration dimension of 0.48 λ × 0.48 λ₀, offers high performance and can therefore be used for advanced Ku-band applications such as satellite subsystems and phased arrays.