Printed Circularly Polarized Spiral Antenna Array for Millimeter-Wave Applications

A novel circularly polarized (CP) antenna element based on spiral antenna is proposed in this paper. It is differentially fed with an aperture through two vias locating at opposite sides of the aperture. This element can be easily integrated with the low loss substrate integrated waveguide and fabricated with the low cost printed circuit board technology. It can achieve 23.0% impedance bandwidth and 21.9% 3-dB axial ratio (AR) bandwidth with a maximum gain of 7.9 dBic. In order to broaden the AR bandwidth and lower the AR values of the antenna array, sequential rotation is applied to make a 2 × 2 subarray. The subarray covers an impedance bandwidth of 21.3%, with AR values lower than 1.1 dB across the whole impedance matching band. Thereafter, by employing the designed subarray, a 4 × 8 antenna array is composed and fabricated. The measured impedance bandwidth covers 14.1%, from 56.55 to 65.13 GHz, and the measured 3-dB AR bandwidth covers 21.1%, from 55 to 68 GHz. The maximum measured gain is 19.5 dBic. It also demonstrates that the proposed antenna element is a promising candidate to design high gain CP antenna arrays in millimeter-wave band.