180-Degree Branch Line Coupler Composed of Two Types of Iris-Loaded Waveguides

Abstract

We propose a 180-degree branch line coupler composed of two types of iris-loaded waveguides. The proposed coupler consists of two main transmission lines and branch lines with different electrical lengths. Based on optimal electrical lengths, a 180-degree output phase difference can be achieved without additional phase shifters. The two main lines with different electrical lengths are realized by capacitive and inductive iris-loaded waveguides. The size of the proposed coupler is nearly half that of the conventional 180-degree branch line coupler with additional phase shifters. Thus, the proposed coupler is of advantage with respect to the conventional one. We designed a proposed coupler in the K-band for satellite communication systems. The measurement results demonstrate a reflection of -20 dB, isolation of -20 dB, coupling response of -3.1+0.1 dB/-0.1 dB, and phase differences of 0+0.1 deg/-1.4 deg and -180+0.5 deg/-2.3 deg at a bandwidth of 8% in the K-band.