A High‐Performance Microstrip Bandpass Filtering Coupler with Low‐Loss and Compact Size

In this letter, novel spiral‐coupled transmission lines are used to obtain a high‐performance microstrip coupler. The advantages of the proposed microstrip coupler are novel structure, filtering frequency response, suppressed harmonics up to second harmonics, transmission poles, low losses, compact size, and good phase balance. The proposed structure is novel and different from the previous coupler designs such as rate‐races, rings, and branch‐lines types. It is presented for the first time in this work with a very small size and good performance. The size of this coupler is only 82.6 mm 2 (0.004 λg 2 ). The common port return loss is 33 dB and the insertion losses at port 2 and port 3 are 2.2 and 2.7 dB, respectively. To prove the accuracy of the design method and simulation results, the proposed coupler is fabricated and measured where the measurement results confirm the simulation results and the proposed design method.