Trapezoid-shaped resonators to design compact branch line coupler with harmonic suppression

Abstract

This article proposes a new branch-line coupler design using two trapezoid-shaped resonators, applied in side and center. The standard 35 and 50 Ohms λ/4 transmission lines (TLs) are attained through the variations of the resonator’s TLs width. Since there are not explicit formulas for the suggested trapezoidal shape resonator, the design procedure will include the derivation of new formulas to configure the LC equivalent circuit. The proposed branch-line coupler, operating at 0.95 GHz, has achieved 79% of size reduction if compared to the conventional designs. Furthermore, the suggested design has successfully diminished the first six harmonics with a suppression level of (41, 29, 29, 28, 20, and 20) dB, respectively. The bandwidth is from 800 MHz to 1 GHz and The fractional bandwidth is 22.2%.