Bow-tie antenna fed by microstrip balun filter with designable bandwidth and extended stopband

A bow-tie antenna designed for 2.4-GHz ISM band with coplanar-strip (CPS) balanced input port is fed by a microstrip balun (balanced-to-unbalanced) filter thus possesses a designable bandwidth and the relatively wide stopband. The microstrip balun filter consisting of two uniform-impedance resonators (UIRs) and two stepped-impedance resonators (SIRs) designed from both differential- and common-mode (DM and CM) perspectives provides sharp selectivity, wide stopband, and differential output signal. Specifically, the proposed antenna possess the stopband ranging from 2.76 to 9.525GHz with the aid of the rejection provided by the attached balun filter. Experimental results verify the effect of the adopted feeding structure. Measured and simulated E- and H-plane radiation patterns show good agreement thus validates the presented design approach.