A novel spoof SPP-fed circular patch antenna with wideband harmonic rejection

The spoof SPP waveguide that is directly connected to the patch acts as the filter element which can provide the suppression of higher order modes up to fourth harmonics of the fundamental operating frequency of CPA. The spoof SPP waveguide is realized by etching the two grounds of coplanar waveguide (CPW) with periodic grooves, which has the advantages of compact size and low insertion loss. The cutoff frequency of the spoof SPP coincides with its asymptotic frequency which can be tuned by the depth of the grooves. By properly choosing the cut-off frequencies of the spoof SPP, a very wide stop band has been achieved by this design. Meanwhile, taking the advantage of high confinement of spoof SPP, the proposed spoof SPP-fed CPA can be designed much closer to other microwave devices in communication systems without significant mutual coupling. To validate the operation principle and the design approach, a prototype antenna centered at 3.4 GHz is then designed on Rogers 5880 substrate with relative permittivity of ε_r = 2.2, loss tangent of tan δ = 0.0009 and thickness of 0.508 mm. The prototype antenna has an impedance bandwidth (|S₁₁ > -10dB) from 3.0 to 3.8GHz (24%) and suppress the second, third and fourth harmonic up to - 1dB. The proposed spoof SPP-fed CPA antenna can be employed in the SPP communication systems and integrated circuits for its compact size, easy fabrication, and good out-of-band rejection.