A Polarisation-Agile Phased-Array Antenna for Satellite and beyond-5G Communications

Abstract

A dual-linear polarised 8-by-8 array of stacked patches is proposed as a flexible, UAV-based, gateway node for Satcom and 5G. The array uses a triangular grid with sequential rotation for a frequency range of 37 GHz to 42 GHz. The scan range extends from −50 • to 50 • on all ϕ-planes while maintaining a scan-loss below cos(θ) 1.1 for most of these scan angles. Moreover, the broadside total active reflection coefficient is below −11.5 dB for the whole frequency range. Circular polarisation is achieved by reconfiguring the two linear polarised ports utilising the beamforming integrated circuits on the phased array to provide the phase difference. The axial ratio is maintained below 3 dB for the whole scan range in the ϕ0 = 0 and ϕ0 = 90 cut. Furthermore, an axial ratio compensation mechanism is presented. This mechanism will use the vector modulators embedded on each antenna port to minimise the axial ratio. The compensation mechanism is experimentally verified on an 8-by-8 active antenna array with similar specifications, where an axial ratio of 0.5 dB is achieved. I. INTRODUCTIONT HE ever-growing market for connected devices has increased the demand for bandwidth and flexibility of communication systems. In order to accommodate the required bandwidth, moving towards millimetre-wave (mm-Wave) frequencies is required. However, mm-Wave frequencies suffer from significant path loss, attenuation, and blockage [1]. Phased-array antennas (PAAs) will be used to compensate these losses, whereas gateway (GtW) nodes [2], a system category between a base station and user terminal, are proposed to prevent blockages by functioning as signal repeaters. Unmanned aerial vehicles (UAVs) have been investigated as flexible GtW nodes in [3] for the fifth generation of mobile communication (5G) and beyond systems.This system, UAV based, is also proposed as a flexible communication interface between satellite communication (Satcom) systems and mobile technologies. A schematic view of this use-case is shown in Fig. 1. In order to serve as a GtW between Satcom and mobile communication systems, UAV based PAAs need to provide both circular-polarised (CP) and linear-polarised (LP) beams -as Satcom uses CP and most mobile communication systems require LP. A possible means to achieve both communication systems is by implementing two separate antenna architectures on a single GtW. However, the system should comply with the stringent swap-c (Size, Weight, Power, and Cost) requirements of . A flexible way to achieve both communication systems is by using a reconfigurable dual-LP antenna element.