A wideband balanced filtering coupled‐line coupler with improved directivity based on coupled microstrip–slotline

Abstract

In this article, a wideband balanced filtering coupled‐line coupler (BFCLC) with improved directivity is designed. By using coupled microstrip–slotline, the proposed BFCLC realizes tight coupling while maintaining good isolation. A lattice equivalent circuit is introduced for the coupled microstrip–slotline. Good differential‐mode transmission and high common‐mode suppression are achieved through the application of microstrip/slotline transition structures. Additional stubs are taken to compensate for the odd‐ and even‐mode phase velocities of the coupled microstrip–slotline. Transmission zeros can also be adjusted to improve selectivity. Based on the proposed BFCLC, a coupler with a smaller size using solely the slotline is designed. Two proposed couplers are manufactured to validate the theoretical design, and a good agreement between the simulation and measurement is presented.