Analysis and design of compact wideband baluns on multilayer liquid crystalline polymer (LCP) based substrates

Although the Marchand topology has been used extensively to implement wideband baluns, its size is prohibitively large at low frequencies. Several methods have been proposed in the past to reduce the balun size, but they also result in a reduction of the percentage bandwidth. This paper presents an approach to implement compact wideband baluns, by employing two additional lumped reactances at the output of the Marchand balun. A design methodology for the baluns is proposed that allows simultaneous optimization of size and bandwidth. Using a multilayer LCP packaging technology, a wideband balun operating in the 5GHz band has been designed and fabricated. Measurements show a percentage bandwidth of 53% centered around 6.2GHz (for S11 < -10dB) at the same time effecting a size reduction of 64% over a conventional Marchand balun.