Harmonic suppressed compact wideband branch‐line coupler using unequal length open‐stub units

In this article, the design of a broadband branch‐line coupler (BLC) with reduced size and suppressed harmonic passband response is presented. The proposed approach can be used to replace the low impedance λ/4 lines of the conventional BLC by an equivalent structure almost λ/12 in length. The main advantage of the proposed BLC is that, it has approximately the same bandwidth as that of a conventional BLC. A prototype broadband coupler having fractional bandwidth >50% at 1.1 GHz and of size less than one third of a conventional three‐section wideband BLC topology is realized. In addition, at least 20 dB suppression of up to fourth harmonics is achieved. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.