Highly linear RF amplifying transmitarray unit-cell with varactor-based reconfigurable phase and amplitude

Abstract

This research proposes a novel reconfigurable transmitarray (RTA) RF unit-cell including varactor-based magnitude and phase control capabilities and an amplifying function while delivering highly linear RF signals at transmitters’ power levels. Moreover, the DC current consumption and the components count are minimized for maximum energy efficiency and maximum reliability. These novel features are made possible by proposing solutions to improve the performances of the key circuit blocks and networks involved in this RTA unitcell. These key circuit blocks are a varactor-based tunable impedance network (TIN) enabling the reconfiguration capabilities within both the following networks: a network controlling the phase and a network including a control of the magnitude and an amplification function. The proposed TIN in this work consists of a novel varactor-based circuit technique with improved linearity in the presence of parasitic capacitances and parasitic inductances. The mechanism causing linearity degradation in an anti-series varactor network that includes significant parasitic elements – a key aspect that, to our knowledge, has never been reported – is first studied using an analytical approach based on a multi-tone excitation. It is demonstrated analytically that simply optimizing the ratio of diode sizes is insufficient to circumvent this linearity degradation. The underlying linearity degradation concept serves as the basis for introducing a modified anti-series controllable capacitance (i.e., the proposed TIN) generating minimum distortions in the presence of parasitics. In the proposed RTA unit-cell, the network controlling the phase is a low-loss 360° varactorbased reflection-type phase shifter (V-B RTPS) network with improved linearity performances over the state-of-the-art when considering power, insertion loss (IL), frequency, and relative phase shift (Δϕ) range. The other reconfigurable network involved in the proposed RTA unitcell is a single-stage GaN RF amplifier including mechanisms to tune the gain over a wide range. Measured performances on both fabricated RF controllable networks and on a prototype RTA unit-cell at a carrier frequency of 3.6GHz demonstrate a relative phase shift up to 360°, a magnitude variation up to 10dB, and a delivered highly linear output power level ranging from 14.1dBm to 19.1dBm in response to a multi-tone excitation. Hence, the proposed amplifying RTA unit-cell and its controllable networks with such reconfiguration capabilities while achieving highly linear performances at transmitter-like power levels constitute a significant improvement with respect to the state-of-the-art in the fields of TINs, phase-shifters, and RTAs. In addition to improving the state-of-the-art by achieving unequaled performances, this RTA unit-cell provides many opportunities for new system-level functionalities. This is supported by measured-performance -based analyzes on RTA antenna systems. These analyses reveal that our proposed RTA unit-cell has the potential of 1) significantly enhancing the linearity performances at large power levels, in contrast with most reported varactor-based solutions limited to low-power applications, 2) compensating the insertion loss variation (ΔIL) of the phase shifter for a better quality of the scattered field, 3) significantly improving the antenna efficiency of a planar aperture, an aspect that was never demonstrated based on measured performances, and 4) reducing the negative impact of all the losses located upstream these RF amplifiers on the global system energy efficiency, an aspect that is not considered in most reported RTA systems, even for RTA systems employing amplifying functions.

Date	14 Feb 2022
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Nicolas Constantin (Supervisor)