Candidate: Soroush Rasti Boroujeni
Title: Active-Antenna Front-Ends for Large Phased-Array Transmitters
Date: May 19, 2020
Time: 2:30 PM
Place: REMOTE PARTICIPATION
Supervisor(s): Safavi-Naeini, Safieddin
Active phased-arrays with as many as thousands of antenna elements are needed for satellite communication (SATCOM) and emerging 5G wireless communications systems. The cost and power consumption of these systems is one of the main challenges in the implementation of these systems. The required 10 dB amplitude tapering in the antenna aperture results in deep-back-off operation of thousands of active-antenna elements and severely degrade the efficiency of the whole system.
In this thesis, novel broadband millimeter-wave harmonic tuned power amplifier (PA) structures are proposed to enhance the efficiency of large phased-array systems. The proposed PA solutions which are based on 1:1 transformers have higher efficiency and smaller size compared to the state of the art solutions. This results in the implementation of smaller size and therefore lower cost RF beam-former solutions.
The adaptive supply voltage level is introduced as an effective way of enhancing the efficiency of the PA at backoff. Common base PA with adaptive supply voltage is found to have better backoff efficiency response compared to conventional linear PA structure. A harmonic tuned common-bases PA with high efficiency at back off is proposed. The efficiency of the PA at 10 dB backoff in the proposed solution has been improved from 14 % in the conventional PA structures (cascode structure) to 24 % in the proposed PA (common base structure). This will remarkably reduce the power consumption of the entire phased array system.
Furthermore, a power-efficient 27-30 GHz front-end architecture with 15 dB gain control and 360 phase shift and total efficiency of 26 % at 12 dBm output power is demonstrated. The implemented RF front end achieved the highest efficiency compared to the state of the art Ka-band SATCOM solutions available in the market and literature.
Another challenge in large phased-array transmitters is the large impedance variation of antenna elements with scan angle. This results in output power degradation and possible damages to the front-end system An off-chip low loss reconfigurable output matching network is proposed which minimizes the antenna impedance variation with minimum impact on the output power of the PA. Our fabricated prototype shows promising results in improving the impedance matching of the PA and antenna element.