Low-Profile Duplex Filtering Antenna With High Isolation and High Roll-Off Filtering Response

A filtering slot antenna with high isolation and high roll-off filtering response is proposed for duplex application. With a low profile of 0.007 lambda(H0), the proposed antenna only consists of a ground plane, two slot radiation elements, and two feeding networks. The feeding networks can improve the impendence matching to make each radiation slot produce additional two resonant modes, excite transmission zeros (TZ) to enhance the port-to-port isolation, and produce four band-edge radiation nulls (RNs) to realize sharp roll-off filtering response. Interestingly, one TZ corresponds to one RN, and they are almost at the same frequency, which is very useful to achieve high isolation and good filtering performance simultaneously, although the distance and band gap of the two radiation elements are only 0.027 lambda(0) and 0.1 GHz, respectively. The measured results show that the two operation bands are both 18.2%, and the isolation is higher than 29 dB and 39 dB for the low and high operation bands, respectively. Monopole-like radiation pattern is realized, they have stable in-band gains of about 4.6 dBi and 5.0 dBi, respectively, and the band-edge filtering roll-off rate of up to 215 dBi/GHz is obtained.