This work presents a filtenna concept based on cascaded singlet filters, which inherits independent controllability of attenuation poles from the filter design and has high stopband performance. Two fourth-order filters with a center frequency of 270 GHz, a 14 GHz bandwidth, and in-band return losses of 15 dB and 18 dB, respectively, are manufactured and measured to verify the proposed concept. The filtennas with a single-slot and a double-slot configuration are fabricated by the silicon deep reactive ion etching technology and have the size of 3.65x2.6 mm2. Detailed explanations of the synthesis procedure, which was validated through EM simulation, and measurement results are provided. The measured single-slot and double-slot filtennas exhibit broadside radiation gains of approximately 4.5 dBi and 6.5 dBi at 270 GHz, respectively. Moreover, the challenges and details of silicon micromachining in fabricating the two filtering antennas are discussed.

This communication introduces a graded index (GRIN) Fresnel zone planar lens (FZPL) antenna operating with high gain in the 500–750-GHz frequency range. The main innovation involves achieving a gain of 35.9 dBi by incorporating a GRIN dielectric perforated disk. This perforated disk acts as a distributed spatial delay for beam focusing, ensuring gain improvement and circular polarization simultaneously without needing an extra polarizer. The antenna exhibits high efficiency, with an average radiation efficiency of −1.05 dB, achieved through the optimization of a modified FZPL for silicon-on-insulator (SOI) micromachining technology. The antenna maintains a return loss below −15 dB across the entire 500–750-GHz band, achieving a 40% fractional bandwidth, with circular polarization maintained and an axial ratio consistently below 2.8 dB. The fabricated chip, sized 12.18×12.18 mm with a thickness of 526 μ m, enhances practicality. The feeding arrangement involves a standard open waveguide, and direct mounting into a standard WM-380 waveguide flange is facilitated. This communication discusses the prototype’s design, fabrication, and measurement, emphasizing the excellent agreement between the antenna’s performance and simulated data.

The development of future 6G communication systems necessitates advanced materials for efficient electromagnetic interference shielding in the sub-terahertz frequency range. This study presents the preparation, porosimetry analysis, compositional and electromagnetic characterization of a highly efficient hierarchically porous carbon-silica composite suitable for shielding and stealth applications in this frequency regime. The composite, fabricated using a mixture of carbon powder and tetraethoxysilane, possesses a highly porous structure with high surface area, which facilitates multiple reflections and scattering of electromagnetic waves. Electromagnetic characterization was conducted using a free-space semi-optical method at 140-220 GHz, focusing on reflection-only measurements due to the sample's large thickness. The results demonstrate that the composite exhibits a qualified bandwidth of 83% over the measured frequency band, with a maximum reflection loss of 35 dB at 187 GHz. Furthermore, measurements demonstrate that electromagnetic power within the sample's volume is effectively attenuated. The composite's shielding efficiency due to reflection is on average 0.26 dB across the band, highlighting its potential for high frequency EMI shielding and stealth applications.

This paper presents a sub-THz 3D computational imaging system utilizing compact wideband cavity-backed frequency-diverse antennas fabricated by silicon micromachining. The antennas are integrated with a novel two-section direct waveguide transition feed. A pair of fabricated Mills-Cross transmitter and receiver antennas, generating pseudo-random frequency-diverse patterns within an 18 cm × 18 cm scanning aperture, achieve high-resolution imaging in the 220-330 GHz frequency range, with range and cross-range resolutions of 1.36 mm and 3 mm, respectively. The image reconstruction is done with a Fast Iterative Shrinkage-Thresholding Algorithm (FISTA). The system performance is evaluated by emulated experiments using the measured radiation patterns of the frequency-diverse antennas in the forward model and investigated under various signal-to-noise conditions. The hardware/signal-processing combination performs excellently when the signal-to-noise ratio is 10 dB or better. Already, an image with a signal-to-noise ratio of 10 dB is not distinguishable from an image without noise.

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, it is demonstrated that 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 analyze the trade-off between computational complexity and imaging accuracy. Sparsity investigations in spatial antenna population and frequency samples are comprehensively explored in this paper. The results show that 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 presents an in-depth investigation of optical wireless communication through water-filled PVC pipelines using high-brightness light-emitting diodes (HB-LEDs) operating at visible wavelengths: 475 nm (blue), 528 nm (green), 583 nm (yellow), and 625 nm (red). Simulations were conducted in Ansys Zemax OpticStudio using ray-tracing techniques and Bidirectional Scattering Distribution Function (BSDF) models to evaluate the effects of surface roughness, interface reflection, and wavelength-dependent absorption. A custom experimental setup was developed using a 375 mm long, 50 mm diameter PVC pipe and a Thorlabs S121C photodiode sensor to validate the simulation. Optical power was measured under five water fill conditions (0%, 25%, 50%, 75%, and 100%). Results show that the greatest transmission loss occurs at the 50% water level, where multiphase scattering dominates, with experimental power decreasing to −11.82 dBm at 583 nm (yellow). Full immersion improves transmission, with recovered power levels up to −2.3 dBm at 475 nm (blue). Absorption coefficients were calculated using the Beer–Lambert Law, with peak values exceeding 0.09 cm⁻¹ at 50% fill. Simulation results aligned with experimental measurements within 1–2 dB, validating the model’s reliability. These findings support the development of adaptive gain control strategies and wavelength-optimized optical links for autonomous robotic inspection in submerged or semi-submerged pipeline environments.

This paper presents the first demonstration of a high-gain planar THz lens antenna with beam-steering capability by frequency-orthogonal spatial spreading, operating in the 610–685 GHz range. The antenna is based on integrating a Fresnel zone planar lens with a graded-index silicon interposer. The concept enables passive beamforming of four simultaneous beams from a single feeding port, covering a field of view from -30° to -14° for 20 GHz bandwidth with a 4° separation of the beam direction. The beams can be swept continuously over that field of view by mapping the signal to different frequencies. Furthermore, when using four feeds, 16 simultaneous beams can be created, of which two frequency-orthogonal beams are separated by 40 GHz in frequency can be mapped into the same spatial direction. Thus, it is demonstrated that high-gain multibeam beam steering can be achieved without the hardware complexity of conventional phased-array antenna systems requiring a large number of RF chains. An antenna prototype is implemented using silicon micromachining, resulting in a compact 15.8 mm × 15.8 mm device with a thickness of 526μm, which is directly mounted on a standard WM-380 waveguide feed. Measurement results include a realized gain of 32.1 dBi, only a 0.8 dB beam steering loss across the field of view, an effective side-lobe suppression better than -22 dB, and a high radiation efficiency of -1.25 dB. The measurements are in excellent agreement with simulations, and the worst-case deviation of the measured beam direction from the simulated one is only 0.1° out of 16 beams.

This paper presents, for the first time, a novel highgain beam-steering lens antenna operating in the 610 to 645 GHz range. The antenna, fabricated using silicon micromachining, is based on incorporating a Fresnel lens layer in combination with a frequency-dependent graded-index interposer that acts as a passive beamformer. Frequency-dependent narrow beams are generated using an open waveguide feed. The prototype implemented in this paper features the generation of 8 frequencydependent narrow beams with just two open waveguide feeds. These beams can be steered from -30° to 2° in the azimuth. The prototype achieves a measured realized gain of 32.1 dBi with low beam-steering losses of just 0.8 dB. The antenna also exhibits a high radiation efficiency of -1.25 dB. The lens antenna is very compact, measuring only 15.8 mm × 15.8 mm × 0.526 mm. This beam-steering antenna offers a promising solution for future high-gain, multi-beam THz communication systems.

Ferrites, traditionally used for non-reciprocal microwave devices, have so far mainly been limited to sub-100GHz frequencies due to lack of low-loss high-frequency ferrite materials and due to missing high-frequency characterisation data of recently appearing sub-THz soft-magnetic materials. In this study, we investigate the electromagnetic properties of the commercially available soft ferrite TT2-111 in the 69-110 GHz frequency range, with and without a magnetic bias, by mapping a parameterized model to the measurement data by minimizing a multi-variable error function over the whole frequency band. We are using, to the best of our knowledge for the first time in this frequency range for magnetic materials, a waveguide-based characterization method, which, as shown in this paper, is superior to free-space quasi-optical material characterization methods previously used in this frequency range. The material was characterized to a relative permittivity of 12.6, a dielectric loss tangent of 0.006, and a transverse permeability ranging from 0.86 to 0.99 in the investigated frequency band, which asserts the suitability of soft magnetic materials for this frequency range. The parameter-matched simulation model is excellently able to reproduce the behaviour of the measured data.

In this article, a novel and innovative approach to characterize THz Bragg fibers using a horn-type adapter is presented, enabling a two-tier calibration method for a direct, efficient, and reliable way to measure THz Bragg fibers, including return loss (RL) and insertion loss (IL). The proposed approach is robust, accurate, and repeatable, making it suitable for designing and optimizing THz Bragg fibers and systems and enabling continued research and development. This study employs a calibration approach, utilizing short-short-load-thru (SSLT) and thru-reflect-line (TRL) calibrations. The horn-type adapter connects a standard WR-3.4 rectangular waveguide and a THz Bragg fiber, allowing the mode conversion from the TE10 mode in the rectangular waveguide to the HE11 mode in the Bragg fiber, with a middle stage of the TE11 mode in the tapered horn region. Additionally, the highly accurate measurement quality presented advantages compared to the existing THz measurement setups, for example, setup complexity, coupling efficiency, impedance adjustability, and less sensitivity to measurement environments, etc. The present approach shows advantages in experimental setup complexity, coupling efficiency, impedance adjustability, measurement repeatability, operator experience required, and setup tool cost compared to other existing THz measurement techniques.