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. First, a novel dual-band microstrip antenna with miniaturized size is presented by loading two pairs of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i>-shaped open-ended stubs along the non-radiating edges to excite two modes, namely the quasi-TM<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> mode and TM<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> 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 0.41λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.28λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.05λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> (λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> 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 GHz to 3.60 GHz (3.1%) and 4.90 GHz to 5.37 GHz (9.2%), and peak realized gains of 8.0 dBi and 9.2 dBi, respectively.