All-Metal Evanescent Wave Filtenna With Small Frequency Ratio Between Radiation Null and Transmission Pole for Narrow-Band Diplex Applications

An all-metal evanescent wave filtenna (EWF), which operates below the cutoff frequency of the rectangular waveguide (RWG), and exhibits a small frequency ratio (FR) of 1.06 between the radiation null (RN) and transmission pole (TP) is developed in this communication. By partially filling a capacitive metasurface (CMS) with two slits in the cross section of RWG, the transverse and vertical electric resonant modes in the cross section can be generated at different frequencies. For the former, it is orthogonal to the TE10 mode of the RWG, and can introduce the RN due to the mode-mismatch. For the latter, the TP can be obtained due to the evanescent wave (EW) coupling principle. Several key parameters of the CMS are studied based on the mode analysis to illustrate the independent controllability of the RN, TP, and resultant FR. By properly adjusting the design parameters of CMSs, a diplex EWF working in S-band is designed, prototyped, and tested, which exhibits advantages of small FR, all-metal design, and small size over the reported counterparts. The developed diplex EWF is suitable for narrow-band diplex scenarios with the high-power and high-temperature characteristics, such as the direct satellite communication, wireless power transfer (WPT), and vehicular communication.