Polarization-Adjustable Planar Array Antenna With SIW-Fed High-Order-Mode Microstrip Patch

This communication presents a high-order-mode microstrip patch antenna driven by substrate integrated waveguide (SIW) for millimeter-wave polarization-adjustable applications. Different polarization status can be yielded from variable excited signals, including vertical and horizontal linear, right-handed and left-handed circular polarizations. In the patch antenna configuration, an enlarged aperture coming from high-order mode makes it easy to be fed by orthogonal SIWs for dual polarizations. Loaded slots on the patch significantly improve the radiation patterns. The impedance bandwidth with dual resonances is originated from the SIW slot and patch modes. A Ka-band 2 ×2 antenna array integrated with single-layer SIW feeding network is designed and tested to illustrate this technique. The results manifest that the planar integrated 2×2 antenna array features adjustable polarization with considerable gain. Furthermore, a two-layer scheme of orthogonal SIW feeding is developed, which would provide a more flexible topology for the scale-expandable array antenna with adjustable polarizations.

I. Introduction

With emerging system architecture of millimeter wave, for example, future 5G communications and high-resolution identification, special interests are directed toward various multifunctional planar integrated antennas. As a typical example, antenna is expected to manifest a flexible polarization utilizing shared aperture, which can upgrade channel capacity and weaken the influence of polarization misalignment [1], [2]. Microstrip patch antennas are popularly employed for such a polarization diversity, by virtue of low cost and feasible integration with the control components. Single-port two- or multiple-polarization microstrip antennas were presented in [1]–[3]. Switchable states of diode are set to tune the current distribution on radiator, different polarizations are thus generated. Most of them are implemented at low microwave frequency and achieve a gain around 5 dBi. Two-port antennas feature dual polarizations by each port allocating an independent polarization [4]–[6]. Two- or four-port multiple-polarization microstrip antennas were also developed in [7]–[10]. Among them, an adjustable polarization was introduced by altering the manner of excitation in [8]–[10], which is more suitable for millimeter-wave operations [9]. For gain improvement, a polarization-adjustable array antenna was employed based on a microstrip feeding network [9], [10]. However, microstrip line may be not an ideal choice at higher frequencies for its undesired line-to-line coupling and potential transmission loss. Recently, substrate integrated waveguide (SIW) has acquired noticeable development, owing to its inherently shielded construction with ignorable crosstalk, minimum radiation loss, and planar integrated ability. Some reports on SIW-fed microstrip antennas were proposed for single polarization [11]–[14]. The SIW’s surface wall is relatively large and it occupies the whole of footprint underneath the patch, so it is difficult to build two orthogonal SIWs for dual polarizations like the microstrip-fed counterpart [4]–[6], in consideration of the geometrical limitation. Different radiation patches [15] or apertures were utilized for dual-band dual polarizations. On the other hand, all the above-mentioned designs are deployed on the dominant-mode microstrip patch antenna. Alternatively, high-order-mode microstrip antennas were successfully explored for dual-band [16], wideband [17], or enhanced-gain [18] applications.