A Series-Fed Loop Array Antenna with Wideband Circular Polarization and Enhanced Gain

We analyze a loop antenna array proximity coupled to a coplanar feed line using the method of moments. First, a novel-loop array at a uniform proximity distance (PD) from the feedline is investigated versus loop height above the ground plane. It is found that when the loop height is
$\lambda/5 \lambda$
: wavelength), a 3 dB axial-ratio bandwidth reaches 11%, which is 3.5 times as wide as that of a conventional-loop array. Subsequently, we transform the uniform PD into multiform PD's to enhance the gain of the novel-loop array. It is revealed that the array has a gain enhancement of 1.8 dB compared with that at a uniform PD and still shows an axial ratio bandwidth of 7%.