Lower mode excitation in vertex-fed slotted hexagonal S-band antenna

Direct-fed hexagonal patch antenna are limited to |S11| ≥ −10 dB at lower modes, especially when fed at the vertex of the hexagon. This paper demonstrates a technique to compensate impedance mismatch at a lower mode in a vertex-fed slotted hexagonal antenna. A circular parallel-plate capacitor (PPC) is introduced to the antenna structure that improves impedance matching to excite a lower mode for a probe-fed hexagonal patch antenna. With an overall size of 50 × 50 mm2, the proposed antenna is compact and can operate at 2.4 GHz in presence of PPC with a gain of 2.11 dB and is suitable for various S-band applications.