Skip to main content
To KTH's start page

Signal Processing and Antenna Design for Sub-Terahertz Radar Using Frequency

Diverse and Scanning Notch-Beam Antennas

Time: Thu 2025-01-23 09.00

Location: F3 (Flodis), Lindstedtsvägen 26 & 28, Stockholm

Language: English

Subject area: Electrical Engineering

Doctoral student: Mohammad-Reza Seidi Goldar , Mikro- och nanosystemteknik

Opponent: Assistant professor Thomas Fromentèze, University of Limoges, Limoges, France; Xlim Research Institute, UMR CNRS 7252, Limoges, France

Supervisor: Professor Joachim Oberhammer, Mikro- och nanosystemteknik

Export to calendar

QC 20241218

Abstract

This thesis explores the design, fabrication, characterization, and performance of frequency-diverse antennas and frequency-scanning notch-beam antennas for high-resolution radar detection and imaging at sub-THz frequencies ranging from 220 to 330 GHz. 

Utilizing cutting-edge silicon micromachining techniques, the body of work presents innovative solutions that address the challenges of high-resolution radar imaging, focusing on improving imaging performance, reducing hardware complexity, and enhancing signal processing techniques.

At the heart of this research is analyzing, characterizing, and evaluating a minimalistic beam-shape switching frequency-scanning notch and broad-beam radar systems. A two-antenna system was designed to switch between broad and notch beam patterns, improving imaging resolution and hardware efficiency. The system's ability to operate with fewer components while maintaining high performance was further augmented through advanced signal processing algorithms like TwIST and MUSIC, which offered superior image reconstruction in noisy scenarios.

A key aspect of this research was the experimental validation of the scanning notch antenna, which demonstrated its capability for sub-THz imaging. This work evaluated various algorithms, including FISTA, MUSIC, and matched filter methods, highlighting MUSIC's limitations when multiple targets were present. To overcome the challenge of multi-target scenario failure, a novel adaptive IFFT range-gating method was introduced, which markedly enhanced the radar’s ability to distinguish closely spaced targets by separating the return signals more effectively.

Further advancing in sub-THz imaging systems, we explored designing and fabricating a Mills-cross frequency-diverse antenna using slot radiators and a direct waveguide feed network. This configuration allows for efficient radiation pattern diversity over the operating bandwidth, contributing to enhanced imaging resolution without complex mechanical scanning or phase shifters. 

Following this, we developed a more advanced wideband frequency-diverse antenna for 220 to 330 GHz, featuring an array of silicon-micromachined cross-slot radiators. The frequency-diverse antenna using a cross-slot is incorporated with direct and distributed feed networks. This configuration, which utilizes cross-slot radiators and a distributed feed network, significantly improved radiation pattern diversity and imaging resolution. The performance of these frequency-diverse antennas was evaluated using advanced imaging algorithms, with FISTA and CoSaMP emerging as the preferred algorithms for efficient, high-resolution image reconstruction under various noise conditions. These antennas are designed for short-range, high-resolution imaging and eliminate the need for phase shifters or mechanical scanning, achieving diverse radiation patterns across a broad frequency range.

Finally, this work culminated in a detailed investigation of imaging performance using these frequency-diverse antennas, where the comparison of direct and distributed feed networks provided key insights into optimizing feed designs for enhanced imaging quality and spatial resolution. Furthermore, we investigated the influence of sparse data collection on imaging performance, considering sparsity in three major areas: 1) when the imaging antenna array is sparsely populated, 2) when sparse frequency sampling is applied across the total available bandwidth, and 3) when the bandwidth is divided among multiple transmitters, each operating over a partial bandwidth, while the receiver utilizes the full bandwidth. 

These scenarios provided a comprehensive understanding of how sparsity affects overall imaging performance and resolution, enabling more efficient data acquisition without compromising image quality.

This thesis substantially contributes to advancing sub-THz radar detection and computational imaging. By integrating innovative antenna designs, adaptive signal processing techniques, and advanced fabrication methods, this research presents a comprehensive solution for achieving high-resolution radar imaging with minimal hardware complexity, paving the way for practical applications in security, medical diagnostics, and structural monitoring.

urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-357769