Compact Wideband and Low-Profile Antenna Mountable on Large Metallic Surfaces

This paper proposes a compact wideband and low-profile antenna mountable on large metallic surfaces. Six rows of coupled microstrip resonators with different lengths are printed on a Teflon block. The lengths of the microstrip resonators in different rows are gradually reduced along the end-fire direction. The first four rows of resonators provide four resonances at different frequencies for bandwidth enhancement. The last two rows of resonators are used as two directors to suppress sidelobe levels at high frequencies. A trapezoidal launcher is applied to serve as a reflector and provide one resonance at the lowest frequency. A trapezoid-shaped capacitive-feed (C-fed) strip is utilized and also printed on the Teflon block to globally optimize the wideband impedance matching. The proposed antenna covers a relative bandwidth of 109% for VSWR<2 with a height of 0.044 λL and a volume of only 0.03 λL3 (λL being the free-space wavelength at the lowest operating frequency). Within the operating band, the realized gain is better than 6.5 dBi and the radiation efficiency is higher than 95%.