Ultra-Thin Singly-Fed Dual-Wideband Antenna With Large Frequency Ratio Using a Dual-Mode Feeding Network

In this letter, an ultra-thin large frequency ratio dual-band antenna singly-fed by a dual-mode feeding network is proposed. The dual-mode feeding network can excite even mode in the microwave band and odd mode in the millimeter-wave (mm-wave) band, respectively, through a microstrip-to-coplanar waveguide (CPW) transition with an asymmetrical T-junction. The integration of dual-band radiation is realized by reusing a grooved metal strip as radiators for both the microwave monopole antenna and the mm-wave spoof surface plasmon polaritons (SSPPs) antenna. Moreover, six paralleled strip directors are added ahead of the front end of the metal strip to enhance the endfire radiation performance of the SSPPs antenna which has been originally restricted by the design of the monopole antenna. The fabricated antenna achieves wideband operation in both microwave and mm-wave bands, with impedance bandwidths (|S₁₁|<−10 dB) of 69.2% and 42.0%, respectively. In addition, a high realized peak gain of 12.75 dBi and a large front-to-back ratio of 25 dB can be obtained in the mm-wave band.