Abstract
This paper presents a novel design of a wideband circular polarization 2 × 2 microstrip antenna array working at Ka-band frequencies, from 27.5 to 31 GHz. This module is highly integrable with new silicon beamformer chips, creating a unit cell that can be part of a large electronically steerable antenna for compact, ultra-low-profile, Satcom-on-the-move (SOTM) platforms. A multi-layer structure fabricated in standard printed circuit board (PCB) technology with high-yield substrates has been used. The radiating elements consist of double-stacked circular patches housed in a cavity and fed by H-shaped aperture coupling. It achieves a bandwidth of 16.5 % with a wide beam-width of 95° in the desired band, which is necessary for wide scanning angles in a large phased array. In the 2 × 2 unit cell, the antenna elements are distributed by means of a sequential rotation technique where the separation between two of them is 5.3 mm in the XY-plane. Broadside beam-widths ranging from 53.4° at 27.5 GHz to 42.1° at 31 GHz are achieved, with boresight directivities from 10.7 to 12.9 dBi, respectively, in both the RHCP and LHCP polarization. Moreover, mutual coupling levels below −20 dB and an axial ratio less than 3 dB in the whole band guarantee a good circular polarization purity.
Highlights
The interest in satellite communications has grown exponentially in recent years.With the massive deployment of non-geostationary orbit (NGSO) LEO/MEO satellite constellations, a great variety of high-speed and low-latency communication applications are showing up [1,2,3,4]
In [11,12], dual-band phased arrays are presented to cover Tx/Rx satellite communications, interleaving in the same space K/Kaband radiating elements with Ka-band elements, but introducing new integration problems that they will have to solve and with reduced bandwidths of 4.3% in Tx (29.5–30.8 GHz) and 4.8% in Rx (20.2–21.2 GHz). Focusing on this type of radio frequency (RF) beamforming structure, in the literature we find state-ofthe-art beamformers which include low-noise amplifiers (LNA), power amplifiers (PA), phase shifters, variable gain amplifiers (VGAs), power combiners, simple pole double throw (SPDT) switches, together with serial-peripheral interface (SPI) control and even biasing networks all in a single chip, working at frequencies up to 95 GHz, for 4, 8 or 16 channels, and with a high yield [13,14,15]
The prototypes have been fabricated in a multilayer printed circuit board (PCB) with the highest perforThe prototypes have been fabricated in a multilayer PCB with the highest performance mance and tolerances provided by the manufacturer Lab Circuits
Summary
The interest in satellite communications has grown exponentially in recent years. With the massive deployment of non-geostationary orbit (NGSO) LEO/MEO satellite constellations, a great variety of high-speed and low-latency communication applications are showing up [1,2,3,4]. The upcoming scenario is driving the development of new antenna front-ends capable of tracking one or more satellites while providing a high data rate and low-latency two-way communications. The antenna front-end configuration is not that simple for NGSO networks, where satellites are moving with respect to the land-terminal. Tracking the satellite as it moves may seem solved with a mechanical structure that follows its movement, which is the basic principle of Satcom-on-the-move (SOTM), the satellite eventually crosses the horizon and the antenna must perform a handover to track a new satellite in the line of sight. Mechanical systems show very poor behavior at switching between satellites, with very slow responses that imply periodic losses of the communication link, greatly reducing their reliability
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