Compact Dual-Polarized Filtenna With Steep Roll-Off Rate for Base Stations

This letter presents a dual-polarized, band-pass filtering antenna, or “filtenna” with a steep roll-off rate and a compact size. To simultaneously support multiple communication standards in a shared aperture, base station antenna arrays need to operate in multiple closely-spaced frequency bands. However, each filtenna has a limited space in the aperture-shared array; therefore, it is challenging to achieve a high roll-off rate. To resolve this problem, we proposed a filtenna that consists of four stacked X-shaped patches, of which the second from the bottom is the driven patch and the rest are parasitic ones. These closely coupled parasitic patches switch rapidly from resonance to antiresonance; however, their radiations change because they together cancel one another and create a very steep roll-off rate. The aperture dimension of the proposed antenna is $0.2 \, \lambda _{0} \times 0.2 \, \lambda _{0} \times 0.14 \, \lambda _{0}$ , where $\lambda _{0}$ is the wavelength in free space at the center frequency. The measurement results demonstrate a very steep roll-off rate up to 1795 dBi/GHz at the lower cutoff frequency of 1.8 GHz. The measured average gain was 8 dBi over the operating frequency band of 1.805–1.88 GHz, which makes the proposed filtenna a good candidate for multiband and multistandard base stations.