A Broadband Circularly Polarized Multiloop Antenna for Millimeter-Wave Applications

In this letter, a broadband circularly polarized (CP) multiloop antenna is proposed for millimeter-wave (mm-wave) applications. The antenna is curved on one substrate with its radiating part etched on the upper surface and reflecting ground etched on the lower surface. Its radiating part is a four-element array with four nested dual loops (NDLs) operating as elements, which are sequentially fed by another loop located in the center. Thus, the antenna has self-similarity for wideband. In comparison to normal DL, depending on the coupling, a short microstrip line is adopted to connect the two loops of the proposed NDL. The current magnitude along the inside loop is enhanced by direct feeding, and the feeding phase can be controlled by the connection point on the outside loop, which has more effect in compensating the current variation on the outside loop for good CP radiation. Measurement results of the prototype reveal that the antenna achieves a wide overall bandwidth of 33.5% from 24.6 GHz to 34.5 GHz and a peak gain of 10.4 dBic. Besides, the antenna has a compact and planar structure, which makes it more suitable for integrated circuits.