Highly compact and harmonic suppressed branch line balun using artificial transmission lines

Abstract

In this article, a compact and harmonic suppressed microstrip branch line balun is designed using artificial transmission line (ATL) units. The stopband response of open-stubs present in the ATL units has been utilized to suppress the spurious passbands. Design guidelines are given with graphs and equations based on the lossless transmission line model and an even-odd mode technique. To demonstrate the proposed design theory, an experimental prototype branch line balun operating at 0.9 GHz, having 10% relative circuit area and up to 5th harmonic suppression is presented.