This article investigates the validity of the physical optics/geometrical optics (PO/GO) approximation in modeling low-permittivity integrated lens antennas when there is significant illumination of the shadow region as a function of the feed and lens geometry. The comparative analysis reveals that for certain extended hemispherical lenses, feed illumination of the lens surface beyond the critical angle leads to significant discrepancies in radiation pattern and antenna gain between PO/GO predictions and full-wave simulations. These discrepancies are traced to the constructive far-field contribution of the shadow region currents relative to those originating from the top lens region below the critical angle. The measurements of fabricated extended hemispherical lenses confirm these findings, showing up to 2-dB gain enhancement over PO/GO predictions and showcasing the limitations of traditional high-frequency modeling techniques in capturing this phenomenon. The significant gain enhancement, along with the clean measured radiation patterns, highlights the potential of using lens antenna designs with feeds that provide strong shadow region illumination. These findings provide new insights into the development of high-performance integrated lens antennas for advanced communication and sensing applications.

Future space-based far infrared astronomical observations require background limited detector sensitivities and scalable focal plane array solutions to realize their vast potential in observation speed. In this work, a focal plane array of lens absorber coupled kinetic inductance detectors (KIDs) is proposed to fill this role. The figures of merit and design guidelines for the proposed detector concept are derived by employing a previously developed electromagnetic spectral modeling technique. Two designs operating at central frequencies of 6.98 and 12 THz are studied. A prototype array of the former is fabricated, and its performance is experimentally determined and validated. Specifically, the optical coupling of the detectors to incoherent distributed sources (i.e., normalized throughput) is quantified experimentally with good agreement with the estimations provided by the model. The coupling of the lens absorber prototypes to an incident plane wave, i.e., aperture efficiency, is also indirectly validated experimentally matching the expected value of 54% averaged over two linear polarizations. The noise equivalent power of the KIDs is also measured with limiting value of 8 × 10-20W\√Hz at the bath and radiator temperatures of 130 mK and 2.7 K, respectively, under negligible optical loading.

Radiative near-field links have gained noticeable interests recently for high-data-rate wireless communication. Unlike far-field links, near-field links can have negligible path loss within hundreds of meters for electrically large antennas at high frequencies. In this work, we propose a multi-lens quasi-optical (QO) system for 100-m near-field backhaul communication at H-band. The QO system is designed with compact size (aspect ratio of 1.3:1) and high coupling efficiency of 82%. Moreover, the rotation of an auxiliary lens realizes beam scanning for the link alignment. The scan range is in the order of 1 m with less than 2 dB scanning coupling loss and scanning magnification of 14.5:1.

In this work, we present the development of a low-power and high-sensitivity electromagnetic field (EMF) sensor operating in the n258 FR2 band. The design of the sensor architecture and its sub-systems are discussed, and the sensor performance is characterised using over-the-air measurements. For the front end, a dual-polarised leaky-wave antenna feed is coupled to a dielectric lens and implemented in a multilayer PCB stack. The elliptical lens is 3D-printed using commercially available ABS. The back-end RF electronics are integrated on the same PCB to realise low-power direct down conversion sensing. The components include low noise amplifiers (LNA), digital step attenuators (DSA) and root-mean-square (RMS) detectors. An onboard 12-bit digitiser provides signal quantisation. The measured radiation patterns of the lens antenna agree well with the simulations with 17.18 dBi directivity. The responsivity is −57.7 dBm and the power consumption is about 0.6 W for a single polarisation.

We introduce the design of an array-fed dielectric lens antenna that enables electronic beam steering within a large Field of View (FoV). The feed array consists of eight cavity-backed double-slot antenna elements, fed by a microstrip feed structure that tilts the beam of each double slot toward the lens center. The slots are loaded with a two Artificial Dielectric Layers (ADL) to increase the front-to-back ratio. The elements are placed closer to the lens surface with respect to the nominal focal plane and are combined with proper weights to reduce the scan loss. Metallic reflectors are positioned along the sides of the array edges to further improve the scanning performance, especially at large scan angles. Full-wave simulations show that the designed antenna realizes a stable gain around 20 dBi within a ±50° FoV coverage, for a lens diameter of 5 wavelengths.

This work presents an electrically-small lens that has been redesigned towards a flat interface. This way, the lens is easier to integrated, compared to an earlier introduced spherical core-shell lens concept. The lens is created from a single dielectric host material by conformally machining holes into the material. In this process, two artificial dielectric layers are created; The first layer is used for anti-reflection purposes, whereas the second is used to convert the spherical interface to a flat interface. The two layers enable the use of holes with lower aspect ratio drilling, compared to classical gradient-index lenses. The lens is designed to operate in the 140-170 GHz bandwidth, and a prototype with height of only 2.2 mm and diameter of 6.6 mm was fabricated and characterize. The prototype is small enough to fit in many integrated circuit packages. The flat lens was compared to a non-flat core lens in terms of pattern quality, return loss and dielectric loss, with only negligible performance degradation.

This paper presents a distributed radar system architecture designed for sensing applications above 100GHz. The proposed radar system leverages high-gain lens arrays to generate extremely narrow beams, enabling high angular resolution. A hybrid beamforming approach is proposed in both the transmitter and receiver arrays, allowing for continuous scanning across a moderate field of view. Additionally, an ideal estimation of radar range is conducted assuming a simplified radar equation for this architecture, showing its potential to detect targets at very long distances.

The THz spectrum is being explored due to its inherent large bandwidth to fulfill the throughput requirements for future wireless systems. However, there are intrinsic challenges for the exploitation of this spectrum for wireless communications, particularly concerning current technological capabilities. Moreover, it remains a big question if THz systems can be made efficient. In this contribution, we present a system analysis to show the potential of overcoming these challenges using quasi-optical antennas integrated with wideband SiGe-BiCMOS electronics and a suitable baseband design that can lead to the Tbit/sec and energy-efficient wireless transmission.

Transition metal-doped InGaAs material has proven to be extremely efficient when used as photoconductor in photoconductive antennas excited with a 1550 nm wavelength laser. In this contribution, we apply a time-domain modeling procedure to predict the radiated power by InGaAs:Fe strip-line antennas. The simulations are verified with measurements, showing an excellent match between them. Additionally, we model the reconstructed current when such a strip-line antenna is coupled with a receiver through a Quasi-Optical (QO) link.

This contribution presents the measurement strategy to accurately characterize probe-fed high-gain antennas operating in the sub-THz band. First, a near-field technique employing a quasi-optical system is introduced to enable characterization of backside radiating antennas (with respect to the landing pads). The proposed setup employs classical manipulators for probe landing (i.e., above the structure) and linear xyz CNC controlled translation stage. After, the calibration and modelling techniques to allow for an accurate input reflection-coefficient at the antenna input plane, and the estimation of the antenna gain, in a near field planar scanning system, are described in details. The experimental data of an high-gain backside-radiating lens antenna operating in D-band are presented to validate the proposed approach and characterization bench.

This article introduces a novel transmit lens array with beam-steering capabilities for submillimeter-wave space instruments. The transmit array consists of two sparse silicon lens antenna arrays connected by a waveguide array, in which active components can potentially be integrated, arranged in a hexagonal grid. The upper lens array is mechanically actuated to achieve dynamic beam-steering. The bottom lens array is fed coherently by a quasi-optical (QO) power distribution lens antenna. This antenna is capable of distributing power to a multipixel lens array in a hexagonal configuration with a power coupling efficiency of approximately 60%. The transmit lens array and QO power distribution lens antennas are based on a recently developed multimode leaky-wave feed, which results in lens antenna aperture efficiencies of nearly 80%. A model based on high-frequency techniques has been implemented to design and optimize the complete architecture, allowing to evaluate its directivity and gain. We have fabricated and measured a prototype based on seven-lens elements with excellent agreement to the performances estimated by the model. This article demonstrates for the first time an array architecture that reaches 36 dBi directivity, 32 dBi gain, and +/-25° scanning with 3 dB scan loss over a 450-650 GHz band.

The use of lens arrays in (sub)-millimeter sensing and communication applications will enable the development of integrated antenna front-ends with multiple independent beams as well as dynamic scanning capabilities. In applications such as MIMO communications, interferometric arrays, and Tx/Rx duplexing capabilities, a key parameter is the mutual coupling between the integrated antenna front-ends. In this work, we model such mutual coupling using a geometrical optics (GO) technique combined with bi-directional forward ray tracing. In this model, the mutual coupling is estimated by considering up to secondary reflections in lens array geometries. The proposed technique is then used to investigate the mutual coupling for low and high-density lens arrays as a function of feed locations. The accuracy of the model is also investigated in comparison to full wave simulations and measured data reaching a sufficient agreement to identify the regions within lens arrays with critical mutual coupling levels.

Photoconductive antennas (PCAs) are promising candidates for sensing and imaging applications. In recent years, our group has investigated their properties under pulsed laser illumination in transmission using a time-domain (TD) Norton equivalent circuit. Here, we extend this analysis to the link between a photoconductive source and a receiver introducing for the latter a second TD Norton equivalent circuit. We also evaluate the transfer function of a dispersive quasi-optical (QO) link. Specifically, a field correlation approach based on the high-frequency techniques is used to evaluate the spectral transfer function between two bow-tie-based PCAs, including the QO link. The detected currents in the receiving circuit are reconstructed using stroboscopic sampling of the modeled THz pulses, equivalent to what is actually performed by THz TD systems. Both the amplitude and the waveforms of these currents are evaluated. The QO link is then experimentally characterized to validate the proposed methodology. The comparison between the simulations and the measurements is excellent.

In this contribution, we describe a reconfigurable surface, designed in 130um SiGe technology, to realize a fully-electronic, planar chopper aiming at passive terahertz imaging applications. This surface consists of subwavelength metallic patches that are interconnected using FET-based varactors. By switching the bias voltage of the varactors between 0V and 1.2V, the reconfigurable surface can switch between a transmissive and opaque state, respectively. The expected transmissivity is simulated to be between 0.2 and 0.9 over a wide frequency band, from 250 GHz to 550 GHz. This chopping solution would enable a high degree of system integration for future passive terahertz cameras.

Large format focal plane arrays (FPAs) of dielectric lenses are promising candidates for wide field-of-view submillimeter imagers. In this work, we optimize the scanning gain of such imagers via shaping lens surfaces. We develop an optimization procedure using a field correlation technique between the fields generated by a reflector on the top of the lenses and those generated by the lens feeds. Based on this procedure, an FPA of quartz lens antennas combined with leaky-wave feeds is designed to efficiently illuminate the reflector, achieving a directivity of 50.5 dBi up to scanning 20.3°. The obtained scanning gain loss of 2.6 dB is much lower than that associated with the direct fields coming from the reflector (about 6 dB). The proposed FPA is validated by full-wave simulations with excellent agreement. We have fabricated and measured an example shaped quartz lens optimized for the scanning angle of 20.3° at 180 GHz. The comparison between the simulations and the measurements also shows excellent agreement.

Lens based focal plane arrays (FPAs) with thousand elements are promising candidates for wide scanning sub-millimeter security imaging systems. To analyze such arrays, a field correlation approach is employed to design an FPA of quartz lenses coupled to a reflector. We consider quartz as the lens material due to its lower cost compared to silicon lenses. Here we focus on the design of the lens element at the edge of the FPA. The reflector’s scanning angle at the edge of its FPA is 20.3°, and the lens surface is shaped to couple better to the reflector. The far-field performance of the optimized shaped lens is validated by full-wave simulations with excellent agreement. The simulated scan loss of the system is 2.6 dB. A prototype was fabricated and will be measured to validate the simulation.

In this paper, we present a quasi-optical power distribution architecture based on the use of an integrated lens antenna that generates a uniform aperture field distribution. By using such distribution in combination with an integrated lens array, an efficient and scalable quasi-optical power distribution can be achieved at THz frequencies. The proposed architecture is based on a leaky-wave waveguide feed that illuminates an elliptical lens with a top-hat distribution. This method can distribute the power from one antenna to a 7-pixel lens array in a hexagonal configuration with a power coupling efficiency of nearly 60%. This scheme could be potentially used for the local oscillator power distribution in heterodyne THz arrays. A prototype at 450-615GHz has been developed and characterized, achieving an aperture efficiency higher than 80%.

This contribution presents the development of an electrically small lens antenna using an artificially loaded thermoplastic at 140-170GHz. We will present the on-going development of the Fly’s Eye front end antenna concept that was presented in [1]. The antenna is composed on a dual plastic lens, a core lens and a shell lens, fed by a double slot. The core-lens, being presented in this contribution, is a spherical lens made from an artificially loaded plastic of permittivity 9.5. To the best of our knowledge, this thermoplastic material has not been used for lens antennas in this frequency range before. A 4mm lens prototype has been developed using this material, which includes an antireflective layer synthesized by drilling sub-wavelength holes on the lens contour. Full-wave simulations show a negligible degradation of the performance of the anti-reflection layer compared to an ideal homogeneous matching layer. Physical measurements and antenna measurements confirm that the antenna's performance matches the design specifications.