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An All-Port Matched Impedance-Transforming Marchand Balun and Its Mixer Application
Mitchai CHONGCHEAWCHAMNAN Kamorn BANDUDEJ Apisak WORAPISHET Choon Yong NG Ian D. ROBERTSON
IEICE TRANSACTIONS on Electronics
Publication Date: 2003/08/01
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on Microwave and Millimeter Wave Technology)
Marchand balun, impedance transforming, all-port matching, coupled-line phase-inverter, ring-diode mixer,
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A new technique to reduce the isolation network's size in a Marchand balun needed for perfect all-port matching and isolation is proposed. The proposed isolation circuit is realized using a coupled-line phase-inverter in place of the bulky 180line section that has been previously proposed. Analysis of the proposed circuit yields the required relationship between coupling coefficient and electrical length of the coupler. Based on the design equations, the circuit is experimentally demonstrated at 1.8 GHz and has shown excellent results. The obtained output return loss and isolation loss are more than 18 dB and 40 dB, respectively. The proposed balun was then applied to the application of a doubled-balanced ring-diode mixer. The designed mixer achieves a low conversion loss of 6 dB at its operating frequency, which is 1.5 dB lower than for a doubled-balanced diode mixer using a conventional impedance-transforming Marchand balun. The RF-IF and LO-IF isolations are well below 25 dB and 18 dB across 1 GHz RF operating bandwidth, respectively.