A wideband MMIC-compatible balun using offset broadside air-gap coupling

A compact ultra-broadband MMIC-compatible uniplanar balun has been developed using offset air-gap coupler. The offset air-gap coupler presents tight coupling and low conductor loss, and thus allows the balun to show low loss at mm-wave frequencies. The measured insertion loss was less than 2 dB from 26 to 55 GHz, and amplitude and phase imbalance was less than /spl plusmn/1dB and 5/spl deg/, respectively over a wide frequency range from 27 to 69 GHz.

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