A Low-Profile Wideband Planar Antenna

A wideband planar antenna with a low profile of, where is the wavelength referring to the center frequency of the operating band, is proposed. Using the concept of complementary antenna, two shorted quarter-wave microstrip patch antennas, operating as magnetic dipoles, and two planar electric dipoles are connected together and excited simultaneously by a coaxial-to-microstrip impedance transformer. For further size reduction and back radiation suppression, a U-shaped reflector is employed. Experimentally, the proposed antenna exhibited an impedance bandwidth of 51.5% with SWR <= 1.5 from 1.96 to 3.32 GHz, a boresight gain of 6.9 +/- 1.1 dBi and a unidirectional radiation pattern with low cross-polarization and back radiation levels. Moreover, the dc grounded structure fulfills the requirement for lightning protection in outdoor applications.