A new compact 30:1 bandwidth ratio balun and its application to balanced antennas are presented in this paper. To realize the balun-type function, two different types of wideband transition structures are adopted for unbalanced and balanced outputs of the balun. Further, a Vivaldi antenna integrated with the proposed balun is designed and fabricated to validate the feasibility of the new approach. Results indicated that the proposed balun can operate from 0.2 GHz to 6 GHz (a bandwidth ratio of 30:1). And it exhibits a good balanced performance within 0.5 dB magnitude imbalance and less than 6 degree phase imbalance between the two balanced outputs. In addition, the antenna can operate from 0.9 GHz to 6 GHz with good unidirectional radiation patterns.
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