Analysis and Comparison of Marchand and Transformer Baluns Applied in GaAs

Abstract

Analysis and measurement validation of Marchand and Transformer baluns is presented in this brief that compares key performance metrics including amplitude and phase balance, circuit size, bandwidth and impedance match. Whilst novel variants of these circuits have been published in the open literature to improve their performance by direct compensation, there yet remains a fundamental comparison of the core coupled-line structures to reveal a systematic design procedure for baluns. Simple analytical equations are derived for both the baluns to reveal a deep analytical insight and a basis for performance comparison. It is then validated by measurement on the same gallium arsenide wafer, which is demonstrated for the first time. A systematic design approach is summarized that can be followed by other designers that has resulted in state-of-the-art performance for both balun types without the need for additional compensation and or tuning techniques at the output ports. The Marchand balun covers a frequency range of 30-65 GHz with a measured amplitude and phase imbalance less than 0.7 dB and 1.2° respectively. The transformer balun covers a frequency range of 30-45 GHz with a measured amplitude and phase imbalance less than 0.2 dB and 0.9° respectively.