Design and fabrication of a compact microstrip hybrid ring coupler with harmonic reduction for L band radar system.

In this paper, a compact hybrid ring coupler is designed, simulated, and fabricated to achieve both size reduction and unwanted harmonic suppression in the L-band frequency range. As the demand for miniaturized and high-performance microwave components increases, reducing the footprint of passive devices such as couplers has become a key objective in modern electronic design. The proposed coupler integrates a specially designed resonator between its ports to effectively suppress unwanted harmonics, ensuring improved signal integrity and enhanced operational efficiency. Through this approach, 2nd to 10th harmonics are successfully eliminated, minimizing interference and improving overall system performance. The proposed design operates at a center frequency of 1.4 GHz, achieving an exceptionally low insertion loss of 0.3 dB. Additionally, it demonstrates a remarkable 70% reduction in size compared to conventional couplers while maintaining excellent isolation and phase balance. The design and simulation of the rat-race coupler were conducted using Advanced Design System (ADS) software, and the device was fabricated using a Rogers RT/duroid 5880 substrate with a thickness of 20 mil and a dielectric constant of 2.2. Experimental validation confirms strong agreement between simulated and measured results, highlighting the effectiveness of the proposed structure in achieving compactness and superior performance. This novel design presents a promising solution for modern microwave applications requiring highly efficient, compact, and low-loss couplers.