The development of a low focal number and low-mass lens antenna is presented that enables terahertz spectroscopy applications on ultracompact platforms. The antenna operates efficiently over a 20% fractional bandwidth, from 450 to 550 GHz, with a gain of 50 dBi at 500 GHz. The antenna consists of a hyperbolic silicon lens that is placed in a record low focal number configuration (f_#=0.27) with respect to an advanced waveguide feed. An incident field-matching analysis is applied to investigate the optimal feed radiation pattern that maximizes the lens aperture efficiency, which would result in a 20% increase in aperture efficiency (> 80%) with respect to a standard open-ended waveguide (< 60% aperture efficiency). A multilayer leaky-wave (LW) stratification is quasi-analytically optimized to approximate the optimal feeding pattern, resulting in a >70% lens aperture efficiency. An example LW stratification is synthesized using silicon micromachining technology and is fully characterized in combination with the dielectric lens.

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This article presents the development of a focal plane array (FPA) for terahertz imaging applications with a near diffraction-limited resolution achieved through a very tight sampling of the focal plane. The antenna array is integrated with direct detectors in a 22-nm CMOS technology and operates from 200 to 600 GHz. The tight sampling of the focal plane is realized by using a combination of leaky-wave radiation and a dual-polarized connected array configuration that closely resembles a chessboard. By utilizing both the polarizations in the chessboard design, the number of array elements per unit area is effectively doubled. The geometry of the chessboard array was co-optimized together with that of a silicon elliptical lens to achieve both high aperture efficiency and beam overlap. Measurements in the WR2.2 band of a fabricated demonstrator showed that an aperture efficiency of −4.1 dB was realized at 400 GHz. The average gain roll-off between two diagonally adjacent array elements was measured to be −1.5 dB at 400 GHz. Compared to the reference configuration of an idealized, equivalently sampled hexagonal FPA, the improvement in gain at the edge of coverage yields 1.2 dB, which includes 1.9 dB of ohmic losses in the chessboard array. The agreement between measurements and simulations proved to be within 1 dB from 325 to 475 GHz.

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In this contribution we will present the diffraction-limited imaging capabilities of a focal plane array (FPA) of antenna-coupled direct-detectors at submillimeter wavelengths. The FPA prototype is a tightly sampled, 12-pixel array that was developed in a 22 nm CMOS technology and it covers a band from 200 GHz to 600 GHz. A quasi-optical (QO) setup was developed to actively illuminate this FPA in order to perform imaging with > 40 dB SNR. The resulting images will be the first that have diffraction-limited angular resolution at these wavelengths, which demonstrates that this FPA design can be very attractive for future passive THz imaging applications.@en

A complete system modeling and characterization of a wideband differential terahertz (THz) direct detector, integrated in a commercial CMOS technology, is presented. The detector consists of a recently developed double leaky-slot lens antenna that operates from 200 to 600 GHz in combination with a differential Schottky barrier diode (SBD) direct detection circuit. The proposed methodology, starting from low-frequency measurements on a standalone SBD, is able to adequately model the spectral radiometric performance. The system noise-equivalent power (NEP) is characterized from 325 to 500 GHz in excellent agreement with the proposed system model. The measured NEP, 20 pW/√Hz minimum and 90 pW/√Hz frequency averaged, is compromised with respect to the average NEP of 2.7 pW/√Hz that was initially predicted by simulations using the process design kit (PDK) model, since the available SBDs are operating beyond their cutoff frequency. The diodes and models provided by the PDK proved to be inaccurate in predicting circuit behavior at these high frequencies. By using the proposed analysis and modeling approaches, an accurate wideband antenna–detector codesign could be applied for future passive THz imaging applications based on CMOS technologies.@en

The design and performance of two wideband double leaky slot lens antennas, suitable for integration in commercial CMOS technologies, are presented in this article. It is shown that antennas that are of leaky-wave nature are extremely suitable for CMOS integration as the impact of the metal density rules is minimized while simultaneously a dielectric lens can be efficiently illuminated. One antenna, operating over an ultrawide bandwidth from 200 to 600 GHz with a state-of-the-art simulated average efficiency of 57%, is suitable for center-fed direct detection scenarios. As a means of antenna performance verification, a coplanar waveguide (CPW)-fed antenna, which operates from 250 to 500 GHz with an average efficiency of 47%, is designed, fabricated, and characterized. This antenna, which potentially could be interfaced to other on-chip active elements, is fabricated and characterized in terms of S -parameters and gain patterns with excellent agreement with simulation, thanks to the use of an ad hoc quasi-optical measurement setup.@en

We present the design, fabrication, and characterization of a broadband leaky lens antenna for broadband, spectroscopic imaging applications. The antenna is designed for operation in the 300-900 GHz band. We integrate the antenna directly into an Al-NbTiN hybrid microwave kinetic inductance detector (MKID) to measure the beam pattern and absolute coupling efficiency at three frequency bands centered around 350, 650, and 850 GHz, covering the full antenna band. We find an aperture efficiency \eta _{ap} \approx 0.4 over the whole frequency band, limited by lens reflections. We find a good match with simulations for both the patterns and efficiency, demonstrating a 1:3 bandwidth in the submillimeter wavelength range for future on-chip spectrometers.

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In the design of millimeter and sub-millimeter wave radiometric imaging systems a persistent goal is the increase in the speed of acquisition of the image while maintaining a high sensitivity. Typically, the highest sensitivity is achieved by cryogenically cooling the detectors, specifically in astronomical applications. However, for the purpose of low-cost imaging applications it is desirable to operate at room temperature. Without cryogenically cooling, the electronic noise introduced by the detectors becomes dominant, making the detectors less sensitive. Resorting to detection architectures containing amplification circuitry might be impractical for implementation in large focal plane arrays (FPAs) fabricated in integrated technologies. This work derives the focal plane architecture that maximizes the imaging speed of radiometers operating at room temperature without using any amplification circuitry. It is shown that in such scenario a practical image acquisition speed can still be achieved when a very broad portion of the THz-band is exploited. Ultimately the imaging speed is maximized when the FPA is undersampled, implying a trade-off in the size of the optics. The analysis is substantiated by a case study using wideband leaky lens antenna feeds operating over a 3:1 relative frequency band. ..@en

The predicted Noise Equivalent Power (NEP) of a THz direct detector is validated by means of a noise- and a system responsivity measurement. The direct detector consists of a double leaky slot lens antenna that operates from 200 GHz to 600 GHz in combination with a differential pair of Schottky Barrier Diodes (SBDs). The model is derived from low-frequency measurements.@en

A 12-pixel THz Focal Plane Array (FPA), integrated in Global Foundries 22nm CMOS technology, enabling high resolution passive THz imaging, is presented. The array efficiently couples blackbody radiation from 200 GHz to 600 GHz to Schottky Barrier Diodes (SBDs) in a differential topology. An antenna-detector co-design results in an average Noise Equivalent Power (NEP) of 0.9 pW/ sqrt{ text{Hz}}. An extremely small array periodicity is achieved by using two orthogonal polarizations. Such configuration enables passive imaging with a near-diffraction limited resolution while simultaneously maintaining a high optical efficiency of 42%. The array is currently in tape-out and measurements will be presented at the conference.

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The optical performance of a wideband double bowtie slot antenna, implemented in 28nm CMOS technology, is evaluated. The antenna serves as a verification antenna for an uncooled single-pixel radiometer operating from 200 GHz to 600 GHz. The performance is evaluated in terms of radiometric pattern that is derived from the measured radiation patterns and simulated optical efficiency.

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A new family of pulses is introduced. It consists of a windowed-power (WP), unipolar prototype, a unicycle, and a pulse with almost rectangular spectral diagram. These pulses have finite temporal support, controlled continuity at onset and end, and are tailored via simple design rules. The WP prototype has a very low spectral leakage. The WP monocycle's effectiveness as excitation in computational schemes is demonstrated via numerical experiments. Its signature is also shown to practically overlap one generated by readily available circuitry. The WP pulses are opportune as excitation in electromagnetic analysis, for time-windowing purposes, and for feeding pulsed-field or timed antenna arrays.

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In millimeter and submillimeter-wave radiometric imaging systems, a persistent goal is the increase in the speed of acquisition of the image while maintaining a high sensitivity. Typically, the highest sensitivity is achieved by cryogenically cooling the detectors, specifically in astronomical applications. However, for the purpose of low-cost imaging applications, it is desirable to operate at room temperature. Without cryogenically cooling, the electronic noise introduced by the detectors becomes dominant, making the detectors less sensitive. Resorting to detection architectures containing amplification circuitry might be impractical for implementation in large focal plane arrays (FPAs) fabricated in integrated technologies. This contribution derives the focal plane architecture that maximizes the imaging speed of radiometers operating at room temperature without using any amplification circuitry. It is shown that in such scenario a practical image acquisition speed can still be achieved when a very broad portion of the THz-band is exploited. Ultimately, the imaging speed is maximized when the FPA is undersampled, implying a tradeoff in the size of the optics. The analysis is substantiated by a case study with recently developed wideband leaky lens antenna feeds operating from 200 to 600 GHz.

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The design and performance analysis are presented for a passive uncooled radiometer pixel suitable for integration in 28 nm CMOS technology. In the configuration a single wideband antenna, operating from 200 GHz to 600 GHz, is connected to a pn-junction diode. Including the antenna-detector impedance mismatch, the detector shows an average NEP of 2.71 pW/√Hz such that, together with the antenna, the radiometer promises fully passive and uncooled imaging capabilities with 2.6 K temperature sensitivity at a 10 Hz refresh rate. The design is planned for fabrication and measurement.@en

A number of model-pulses to be used for feeding purposes in time-domain, electromagnetic simulations are compared. The pulses' causality and temporal support are employed as discriminating features. CST Microwave Studio® simulations of a canonical configuration are employed for assessing the pulses' suitability. In view of their entailing numerical accuracy and short temporal signatures, the time-differentiated windowed-power (∂tWP) and the time-differentiated power-exponential (∂tPE) are shown to represent opportune alternatives to the standard CST Microwave Studio® (Gaussian) pulse for performing simulations.@en

In this article, we present a freely accessible software tool that allows for fast characterization of dynamic phenomena in a wide variety of transmission lines that include characteristic impedance, effective dielectric constant, and losses, such as radiation into space and surface waves. For printed transmission lines, the radiation effects are of particular importance when the transverse dimensions of the transmission lines become significant in terms of wavelength. Generally, dispersion and losses of the line due to these dynamic phenomena are predicted by full-wave simulations as quasi-static formula do not suffice. The presented software tool, freely downloaded from http://terahertz.tudelft.nl, is capable of accurately analyzing the most widely used transmission lines at high frequencies.@en