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A balanced planar quasi-Yagi antenna integrated with a bandpass filtering response is presented in this paper. The proposed balanced antenna consists of a balanced stepped-impedance microstrip-slotline transition structure, a driver dipole, a parasitic strip, and a bandpass filtering unit. A good differentialmode (DM) passband selectivity is formed by inserting a microstrip stub-loaded resonator (SLR) in the feed line of the quasi-Yagi antenna. This integration enables the antenna to achieve both compact size and high frequency selectivity. By controlling the dimensions of SLR, the central frequency and fractional bandwidth (FBW) can be easy to be adjusted. Meanwhile, the microstrip-slotline transition structure can achieve a good wideband common-mode (CM) suppression without affecting the DM ones, thus simplify the design procedure. The proposed antenna with low cross-polarization level and high CM rejection is found to be comparable to the conventional quasi-Yagi antenna. Furthermore, there are two radiation nulls on both sides of the passband to improve the selectivity effectively. In order to validate its practicability, the balanced antenna is designed and fabricated. The experimental results exhibit that the designed balanced filtering antenna features good filtering response, low cross-polarization level, and high CM rejection.INDEX TERMS Balanced antenna, filtering antenna, CM suppression, low cross-polarization.

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In this article, a new subwavelength element is introduced into the broadband folded reflectarray antenna (FRA). The element comprises a rectangular splitring resonator with two slits and a square patch located in the center of the rectangular ring. It can achieve superior cross polarization conversion (CPC) performance from 16.2 to 26.4 GHz with 1 dB bandwidth of 45.4%, and high orthogonal polarization isolation. Furthermore, changing the positions of two splits of the element can achieve two discrete reflection phases (0 and 180 ) with the high CPC efficiency and angular stability. To verify the feasibility, an FRA using the digitally quantized phase distribution method is designed and measured at 22 GHz. The measured results show that the 1 dB gain bandwidth of the proposed FRA is 30.8%, and the maximum aperture efficiency is 15.4%. This superior performance is comparable with the existing FRAs.