Harmonics and size reduced microstrip branch-line baluns using shunt open-stubs

This article presents the design of harmonic suppressed compact microstrip balun, using shunt open-stubs. Two approaches using Π-shaped and T-shaped open-stub configurations are investigated. Because of the stopband effect of the open-stubs, the harmonic passband responses are suppressed effectively. A compact-size balun is realized because both kinds of structures have slow wave characteristics. To validate theoretical predictions, two prototype baluns operating at f0 = 1 GHz, showing size reduction up to 75% and no spurious passband up to 4f0 compared with the conventional design are fabricated in microstrip form. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011. © 2011 Wiley Periodicals, Inc.