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.
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