Dual‐band microstrip‐to‐coplanar stripline Wilkinson balun using composite right‐ and left‐handed transmission lines and its application in feeding dual‐band bow‐tie antenna

Using a composite right‐ and left‐handed transmission lines, a dual‐band microstrip‐to‐coplanar stripline balun is proposed that presents the benefits of bandwidth enlargement, excellent isolation and equal power split between output ports in the two passbands. Also, the dual‐band nature of the balun, close space between output ports and ease of integration with a printed antenna in a compact size make it well suited for feeding dual‐band planar two‐wire antennas. As an example of an application, the proposed balun is designed and fabricated to work at two arbitrary frequency bands, 0.9 and 1.8 GHz. There is a good agreement between the measured and predicted results, which verifies the proposed design methodology. The fabricated balun shows a measured differential output phase bandwidth (180° ± 10°) of 22.95% and 18.76% for the first and second frequency bands, respectively. Moreover, this device is shown to have enhanced bandwidth performance in both isolation and 3‐dB magnitude balance. To validate the performance of the proposed balun, the balun is employed to feed a dual‐band metamaterial‐loaded bow‐tie antenna. The experimental results show that the return losses for both the operating bands remain below 10 dB. Likewise, the dual‐band bow‐tie antenna provides quasi‐omnidirectional radiation over the frequency bands.