A Third-Order SIW-Integrated Filter/Antenna Using Two Resonant Cavities

A third-order substrate integrated waveguide (SIW) integrated filter/antenna is presented in this letter. The filter/antenna is composed of two cavity resonators with a slot antenna in the second cavity. The slot antenna excites two modes in the slot cavity, creating a third-order filtering response while preserving the radiating characteristics. A transmission zero can be arbitrarily placed below or above the passband. The filter/antenna operates at a center frequency of 3.71 GHz and has an 8.29% fractional bandwidth with a 5.10 dBi antenna gain.