A dual rhombic loop antenna for circular polarisation

It is reported that a rhombic loop antenna the perimeter of which is about 1.3λ₀(λ₀: centre wavelength) can radiate circular polarisation [Morishita and Hirashawa, 1994]. This antenna can have a traveling wave type current distribution, which has approximately a constant amplitude and a linearly changing phase. This current distribution is realized by making one point open or loading an infinitely large impedance on the proper position of the loop. In the present paper, two types of single feed dual rhombic loop antennas for circular polarization are proposed. Each antenna consists of two rhombic loops of the same size and is located above an infinite ground plane. The antenna characteristics including axial ratio, current distribution, radiation pattern and input impedance are calculated by the method of moments with respect to the gap position, the rhombus vertex angle and the feed type. The calculated results are in good agreement with the measured data