A Duplexing Filtering Antenna With Small Frequency Ratio and High Isolation Using Hanging Resonators

A duplexing filtering antenna based on hanging resonators is presented. The antenna is mainly composed of seven cavities. A square cavity operating in TE101 and TE011 modes is located at the top, and a pair of metal posts is introduced at the diagonal line to control the coupling between the two modes. Then, by utilizing slots along the x-axis, only the TE101 mode radiates and is coupled to both the low- and high-frequency channels. Therefore, the TE011 mode is hanging from the TE101 mode, and a transmission zero can be generated between the two channels. Each of the two channels consists of three cavities placed under the square cavity. The three cavities are sequentially coupled through inductive irises and the middle cavity is excited by a coaxial input port. The bottom cavity acts as a hanging resonator and produces a transmission zero when it resonates. To verify the design, a prototype is manufactured and tested, whose measured results show a good agreement with the simulated ones. Three transmission zeros can be observed and the interport isolation is above 39.4 and 34.5 dB in the low- and high-frequency bands, respectively.