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-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 end-fire 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 (FBR) of 25 dB can be obtained in the mm-wave band.