Compact Dual-Band Filtering Microstrip Antenna Using Spoof Surface Plasmon Polaritons Feed line

In this letter, a compact dual-band microstrip antenna with filtering frequency response is proposed. Firstly, a novel dual-band microstrip antenna with miniaturized size is presented by loading two pairs of L-shaped open-ended stubs along the non-radiating edges to excite two modes, namely the quasi-TM10 mode and TM10 mode. The two resonance modes operate independently at different bands, depending on whether the current on the stubs and patch is in phase. Meanwhile, a natural stopband is generated with two deep radiation nulls located between these two bands. Then, a long metal strip is printed underneath the patch and connected with the feeding via, producing a radiation null at the lower edge of lower passband. Finally, a spoof surface plasmon polaritons (SSPPs) feed line working at fundamental mode is innovatively explored to achieve an upper stopband with high rejection. As a proof of concept, a prototype with a compact size of 0.41 λ0 × 0.28 λ0 × 0.05 λ0 (λ0 is free-space wavelength at center frequency of lower band) is fabricated, assembled and tested. The measured results show that the proposed antenna realizes a bandwidth of 3.49-3.60 GHz (3.1%) and 4.90-5.37 GHz (9.2%), and peak realized gains of 8.0 and 9.2 dBi, respectively.