Filter-Antenna Module Using Substrate Integrated Waveguide Cavities

A design procedure for filter-antenna modules based on substrate integrated waveguide cavities is presented in this letter. The filter-antenna module is modeled as an asynchronously tuned coupled-resonator circuit in which the last resonator also contains the radiating element. The design of the filter-antenna module is based on the classical process applied to obtain filters through the use of coupled resonators. The designed filter-antenna module is manufactured and measured, obtaining the following: a central frequency (f_o) of 1.94 GHz, a -3-dB fractional band- width (FBW) of 5.57%, a gain (G) of 4.87 dBi, a front-to-back ratio (FTBR) of 25.60 dB, and a co-to-cross-polarization ratio of 22.86 dB in the direction of maximum radiation. The integration of the filter and the antenna into just one module leads to a reduction of size and weight in the RF front-end, while the implementation by means of the substrate integrated waveguide technique makes the integration with planar circuits easier.