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.