Low-Loss Circularly Polarized Periodic Leaky-Wave Antenna

This letter presents a periodic leaky-wave array antenna with circular polarization at millimeter-wave frequencies. The antenna is designed on the low-loss planar Goubau transmission line to maximize the radiation efficiency of the antenna. The unit cell of the array is formed by four dipoles located on both faces of the Goubau line’s substrate. A prototype has been fabricated and measured. Experimental results show an impedance bandwidth above 15% for
$\vert{S_{11}}\vert < - 10~\hbox{dB}$
and a 3-dB axial-ratio bandwidth of 7.6%. The radiation efficiency and maximum gain of the prototype are above 90% and 15.6 dBi, respectively, from 38 to 41 GHz. The maximum gain and the minimum axial ratio present the characteristic steering behavior of leaky-wave antennas.