Ultrawideband Beam Steering at mm-Wave Frequency With Planar Dielectric Phase Transformers

In this article, a new method to design an ultrawideband beam-steering antenna system is presented. The system is completely passive and suitable for millimeter-wave applications, including some in defense, where both discrete beam steering and continuous beam steering in two dimensions (elevation and azimuth) are required at a reasonably fast speed. The beam-steering capability is achieved using a pair of distinct low-profile and planar phase transformers (PPTs) placed in the near-field region of a fixed-beam radiating source. The antenna system demonstrates a steering and impedance-matching bandwidth of 28.6%, from 30 to 40 GHz. A prototype of the new antenna system, including a pair of thin PPTs and a completely automated mechanical system to rotate each of the PPTs around the antenna axis, has been fabricated and tested. The pair of rotating PPTs, equivalent to a pair of 3-D dielectric PTs (DPTs), introduces a precalculated phase gradient to the input near field from the fixed-beam antenna and creates an output near field that will radiate toward a selected direction, which can be varied within a large conical region with a maximum apex angle of 108°. The system exhibits the predicted and measured peak gains of 21.5 and 21.7 dBi, respectively, and the measured gain variation over 2-D beam steering is less than 2.2 dB. This beam-steering method obviates the need for expensive phase shifters and distribution networks, which are also lossy at mm-wave frequencies. The measured results validate the predicted wideband matching and steering performance of the system with a close agreement.