Millimeter Wave Omnidirectional High Gain Transmit-Array Antenna

This paper proposes a high-gain omnidirectional transmit-array (TA) antenna that achieves both high gain and omnidirectionality in the millimeter-wave frequency range. The TA comprises a monopole antenna as the feed source, a conical metal reflector, and an annular TA surface composed of periodic unit cells surrounding the feed source. Each unit cell is designed with two back-to-back dipoles and an in-between delay line. The dipole facing the monopole receives waves from the monopole, and the other dipole radiates waves with modulated phase intended for a high gain beam. Continuous phase variation between 0 and 180 degrees can be realized by changing the length of the delay line. Additionally, flipping the dipole arms allows for 1-bit phase adjustment, thus enabling a total continuous phase variation from 0 to 360 degrees. By controlling the length of the delay lines and the orientation of the dipole arms, a low-gain conical beam from the monopole is compressed into a high-gain omnidirectional beam in the azimuth plane. The proposed antenna operates in the frequency range from 26.1 to 30.1 GHz with a bandwidth of 14.2%, exhibiting a high gain of 8.0 dBi and a stable omnidirectional beam.