60-GHz Polarization-Adjustable Antenna Arrays

This paper proposes 2 × 2 and 4 × 4 polarization-adjustable millimeter-wave antenna arrays. The antennas were designed to function at 60 GHz and are planar and vialess. The proposed antenna designs contain two input ports; if the input phases and magnitudes of the two input ports can be controlled, enabling the proposed antenna to generate six types of polarization: right-handed circular polarization, left-handed circular polarization, and linear polarization along the φ = 0°, φ = 45°, φ = 90°, and φ = 135° axes. The achieved antenna gain of the 2 × 2 polarization diversity array was approximately 12 dBi, whereas that of the 4 × 4 array was 16 dBi. Prototypes of both the 2 × 2 and 4 × 4 arrays were fabricated and tested. The operating mechanism and design steps are described in detail in this paper.

I. Introduction

Polarization diversity antennas provide numerous advantages for wireless communication systems. This type of antenna can enable frequency reuse, eliminate multipath fading, and prevent polarization mismatch caused by unpredictable orientation of devices. Numerous polarization diversity antennas that feature switchable dual polarization have been presented in the literature [1]–[10], and several types of polarization diversity antenna feature switchable quadripolarization [9], [10]. In these designs, the antenna polarization can be reconfigured by adjusting the on/off states of the diodes, thereby changing the current path. However, this procedure requires integrating diodes in the antenna structure, which is not feasible at 60 GHz because, at this high frequency, the antenna dimensions are extremely small and integrating an active circuit and a passive circuit is difficult. In [11], a polarization-switchable antenna was presented. The polarization of the antenna can be varied among right-handed circular polarization (RHCP), left-handed circular polarization (LHCP), horizontal linear polarization, and vertical linear polarization by adjusting the inputs. A quadripolarization diversity antenna consisting of four circular polarized patches was proposed in [12]. This design formed a two-element sequentially rotated array when operates in a circular polarized mode; therefore, the axial ratio bandwidth can be improved.