Double broadband balun structure using CRLH TL for differential excitation of dual-polarized self-grounded bow-tie antenna

Konferensbidrag (offentliggjort, men ej förlagsutgivet), 2015

A broadband compact balun comprising two composite right-left handed transmission lines (CRLH TL) is designed to excite a self-grounded bow-tie antenna. The design is based on a fractal shaped CRLH TL balun modified to the frequency band of interest. This balun consists of one +90° branch and three-90° branches to produce the desired 180° phase difference at the output. The simulated results show an amplitude imbalance of less than 1dB and a phase imbalance of less than 10°over most of the target bandwidth, i.e., 1.6-3 GHz. Two of the designed baluns were integrated with the bow-tie antenna in such a way that the feeding network could totally fit at the back of the antenna. The performance of the whole structure was also evaluated showing a return loss below-10 dB. The radiation pattern and the gain of the antenna with baluns are in good agreement with the ideal differential excitation, with gain degradation of only about 0.5 dB in the worst case.