This research investigates a unique radar concept based on a frequency-sweeping stepped-frequency continuous-wave (SFCW) radar with a two-element antenna array. The suggested array can switch between a notched and a broad beam shape. Regarding target discrimination and locating accuracy, we compare this radar system to three-element and four-element frequency-sweeping SFCW radars. Compressed sensing methods are used to reconstruct images and evaluate the performance of various antenna arrays. The range resolution for the proposed two-element beam shape switching antenna system with a bandwidth of 10 GHz is noteworthy-10 mm for point targets and 20 mm for extended targets. This range resolution is two times that of the larger aperture three-element array and four times that of the four-element array. Notably, the range resolution beats the theoretical range resolution due to the use of compressed sensing to combine information from the two beam shapes. Furthermore, the suggested system outperforms previous antenna arrays regarding angular resolution, especially when targets are close in range and angle. With a 10 mm range distance and a 2(degrees )angle difference, the system effectively discriminates three targets. In a triple-target scenario, the suggested two-element beam shape switching system outperforms a standard four-element phased array radar with the same bandwidth even with restricted computational resources.

This article experimentally demonstrates a frequency-sweeping notch-beam sub-THz radar frontend based on a two-line array antenna featuring computational imaging. Operating within 237.5 GHz and 250 GHz with 12.5 GHz bandwidth, the radar utilizes a 12 λc delay line to achieve frequency-sweeping capabilities. This configuration allows dynamic notch-beam scanning across angular ranges from − 26.5 ∘ to 28 ∘ . The radar frontend is highly compact with a total size of 20 mm× 14.3 mm× 1.2 mm, including the beam-steering network, a magic-tee for creating the 180 ∘ phase shift required for creating the notch-beam, and the antenna array, and is implemented by silicon micromachining. The radar was evaluated with single and dual-target scenarios utilizing and benchmarking different computational imaging algorithms, i.e., matched filter (MF), fast iterative shrinkage-thresholding algorithm (FISTA), and multiple signal classification (MUSIC). It was found that the MUSIC algorithm outperforms MF and FISTA in range and angular resolution in single-target scenes, achieving a range resolution of 7.8 mm and an angular resolution of 15.7 ∘ , with detection errors of less than 6.6 mm and 3.5 ∘ , respectively. Although the MUSIC algorithm maintains reliable range resolution in dual-target scenarios, it performs poorly in providing angular information.

This paper presents a novel adaptive IFFT range-gating method for enhanced radar imaging performance, validated experimentally using a minimalistic frequency-scanning notch-beam radar frontend operating at sub-THz frequencies. Since the bandwidth is utilized to derive both the range and angular information in a frequency-scanning radar, the proposed technique is particularly effective in improving the performance of frequency-scanning types of radars. The frequency-steeringantenna covers an angular range of -26.5 ◦ to 28◦ within the237.5 to 250 GHz frequency range, with 12.5 GHz of bandwidth. The performance enhancement of the proposed adaptive IFFT range-gating method is evaluated using different computational imaging algorithms, such as Matched Filter, FISTA, and MUSIC. The experimental verification indicates that the adaptive IFFT algorithm performs best, achieving an angle error with a root mean square error (RMSE) of only 1.58◦. In addition, combining the MUSIC algorithm with the adaptive IFFT significantly improves angular RMSE, reducing it from 10.11◦ to 4.9◦. Besides, utilizing the adaptive IFFT method combined with MF and FISTA further improves their performance. Furthermore, this paper mathematically demonstrates that the optimal beam-shape configuration for the proposed imaging radar system is to use a frequency-scanning notch-beam as the receiver and a fixed broad-beam as the transmitter, outperforming other combinations of beam shapes.

This paper presents the first compact, wideband,silicon-micromachined frequency-diverse antenna, operating across the 220-330 GHz range, designed explicitly for sub-THzimaging applications. The antenna consists of 80 slot radiating elements of twelve distinct sizes corresponding to half of the uniformly sampled wavelengths within the operating bandwidth. These elements are arranged in a Mills-Crossconfiguration for antenna designs A and B, supported by an innovatively shaped air-filled cavity. The cavity is engineered to support multiple higher-order, high-Q resonance modes, generating highly frequency-diverse, pseudo-random radiation patterns. The frequency-diverse antenna is fed by a three-sectionimpedance-matching transitional direct waveguide and isfabricated using advanced silicon micromachining technology. This paper comprehensively analyzes the antenna’s radiation patterns and impedance matching across the entire waveguide band. The compact prototype, with an overall size of 18mm × 16 mm × 0.933 mm (effective antenna dimensions of11λ×11λ×0.85λ), is the most compact air-filled, cavity-backed frequency-diverse antenna reported to date. It demonstrates high radiation efficiency and is designed for direct mounting on a standard WR-3.4 waveguide flange. The antenna achieves a fractional bandwidth of 34%, with a return loss better than 10 dB, extending to 40% with a return loss better than 5 dB.

This paper presents the design, fabrication, and evaluation of a compact, dual-polarized, wideband, sub-THz frequency-diverse antenna with a novel distributed feed configuration and cross-slot radiation elements implemented by silicon-micromachining. The distributed feed is based on a spiral-shaped waveguide network with multiple Morenocross-couplers for stimulating the overloaded resonance cavity backing the antenna with 140 cross-slot radiation elements optimized for 16 frequencies, which generates pseudo-random radiation patterns over the full waveguide bandwidth of 220–330GHz, with applications to sub-THz imaging. As experimentally verified by comparisons of prototype devices, one with the novel distributed feed and a reference design with an optimized conventional direct feed, the novel feed design reduces the radiation pattern dependence over frequency by at least 48.5%, and up to 83.4%, over the entire frequency range. This clearly demonstrates the effectiveness of the novel distributed feed structure and implies, to a sub-THz imaging system, an improvement of the resolution or a reduction of the necessary number of measurements. Additionally, the distributed feed significantly improves the spatial coverage of the radiation patterns, as demonstrated in the paper. The overall design is very compact, with an active volume of 11×11×0.85λ3c, including the cavity, and the distributed feeding network. The measured return loss of the antenna with the distributed feed is better than 10 dB across the operating bandwidth.

This paper investigates sub-THz computational imaging using compact, wideband, cavity-backed frequency-diverse antennas fabricated through silicon micromachining techniques. This paper presents a forward model based on pseudo-random frequency-diverse patterns using a Mills-Cross transmitter and receiver pair, which provides high-resolution imaging capabilities in the 220-330 GHz frequency range. The model is coupled with advanced compressed sensing algorithms, specifically Compressive Sampling Matching Pursuit (CoSaMP)and Fast Iterative Shrinkage-Thresholding Algorithm (FISTA), to enhance imaging performance under limited data acquisition. Through emulated simulation and experimental data, the system’s ability to achieve range resolutions down to 1.4 mm and angular resolutions of 0.35°, even in the presence of noise, and analyzes the trade-off between computational complexity and imaging accuracy. Sparsity investigation in spatial antenna population and frequency samples are comprehensively explored in this paper. The results show using only 6.7% of the data, the CoSaMP algorithm can reconstruct a discernable image of the KTH logo. Results show that CoSaMP provides lower reconstruction error for sparse target distributions, while FISTA achieves superior noise resilience. The study highlights the practical implications of using frequency-diverse antennas in security screening and industrial inspection, where high-resolution imaging at sub-THz frequencies is demanded.

This paper explores novel aspects of sparsity in sub-THz computational imaging using dual-polarization, wideband,frequency-diverse antennas fabricated through silicon micro-machining techniques. These antennas—one with a distributed feed and the other with a direct feed—operate at 220-330GHz frequency range, generating pseudo-random radiation patterns. This makes them well-suited for high-resolution imaging with reduced hardware complexity compared to traditional radar imaging setups. A forward model based on these antennas' radiation patterns is integrated with compressed sensing techniques, specifically the Compressive Sampling MatchingPursuit (CoSaMP) and Fast Iterative Shrinkage-ThresholdingAlgorithm (FISTA). The computational imaging investigation, involving three configurations of the two antennas, shows that deploying the distributed feed antenna significantly enhances imaging performance in scenarios with sparse measurement data. Furthermore, the paper comprehensively investigates two types of sparsity: the number of Tx-Rx measurements and sub-bandwidth division. Sparsity analysis on several emulation results reveals that under high SNR conditions, using only the distributed feed antenna as both Tx and Rx requires just 25% of the measured data to successfully reconstruct an image of the scene. Additionally, the sub-bandwidth allocation technique drastically reduces the complexity of wideband hardware, requiring only 2% of the data when using the distributed feed antenna. The system demonstrates impressive performance through both simulations and experimental validation, achieving range resolutions as satisfactory as 1.4 mm and angular resolutions down to 0.35°.