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Due to an increasing demand in channel capacity and bandwidth, there has been a growing interest in the millimeter wave (mmWave) spectrum [1]-[3]. Many researchers overcame the challenges of implementing extremely high frequency systems and secured large bandwidths comparable to that of fiber optics [4]. The mmWave spectrum offers numerous advantages not only in the wireless communication field but also in the field of sensors and radar technology [5]. Indeed, transmitting shorter wavelengths helps radars achieve higher range accuracy with smaller antenna footprints.

Funding Information: This research has been supported by Academy of Finland, grant number 310880. Publisher Copyright: © 2021 IEEE This paper describes the design of a 140-GHz low-noise amplifier in 130-nm SiGe BiCMOS technology. The circuit is aimed for a high integration-density imaging radiometer, where several receivers are integrated on the same die. Thus, we particularly focus on minimizing the die area and power consumption. The two-stage amplifier is composed of cascode stages with gain boosting base resonators. The performance of a single cascode stage is optimized by correctly sizing the base resonator to avoid instability and optimizing the compact transistor layout without typically used interstage matching between the cascode stages. The circuit features gain of 19 dB at 140 GHz, and noise figure of 7 dB, while consuming only 15 mW with the supply voltage of 2 V and occupying a die area of 0.1 mm2

In this article, a 60-GHz frequency-modulated continuous-wave (FMCW) multiple-input multiple-output (MIMO) radar system using frequency-division multiplexing for TX signal separation is presented. Four-channel transmitter and receiver chips were designed using 130 nm SiGe process. The total number of TX and RX channels can be scaled by the number of chips in the system while still maintaining phase coherence between the channels. 2-D and 3-D object localization measurements are made with four TX and eight RX channel systems. In the 2-D configuration, the radar system is capable of a 5-cm range resolution and 3.5° angular resolution.

This paper presents thermal characterization results for three high-power THz Schottky frequency multipliers in the temperature range of 20–380 K. All measured multipliers have different substrates: a 5- $\mu\hbox{m}$ -thick GaAs membrane, a 40- $\mu\hbox{m}$ -thick GaAs substrate, and a 5- $\mu\hbox{m}$ -thick GaAs membrane glued to a 20- $\mu\hbox{m}$ -thick CVD diamond substrate with polymer bonding agent. The thermal characterization results include such parameters as the maximum average junction temperature of the anodes, device total thermal resistance, and device cooling (or heating) times. The results enable designers to better optimize their devices for the maximum power level and temperature range and system engineers to better predict the overall performance of the system in an environment, where the ambient conditions might change. For example, from the thermal resistance point of view the GaAs membrane on diamond substrate clearly outperforms the device on GaAs membrane alone at room temperature or above. However, perhaps surprisingly, at temperatures below 125 K, the GaAs membrane is on par, or even has lower thermal resistance than the membrane on diamond.

We present clinical investigation results of a novel, wearable, orientation and mobility assistive device that uses radar technology. The radar device sends radio signals, detects objects in the environment, and conveys this information to the users by way of sound or vibration feedback. The aim of this investigation is to assess the effectiveness of the device for the visually impaired. During a two-week period of the investigation, 25 visually impaired participants used the device in their everyday activities and kept a diary of their experiences. The investigation included a training session as well as opening and closing interviews, including a standard QUEST 2.0 form to evaluate user satisfaction with assistive technology devices. 92 percent of the participants observed that the device improved their ability to perceive their environment, and 80 percent observed that it increased their confidence in independent mobility.

This paper presents an alternative characterization method to the traditional characterization methods of the millimeter-wave and terahertz Schottky diodes. The diodes can be characterized based on the mixer operation (conversion loss and noise temperature) under comparable conditions. The tuning of the embedding impedances and the easy changing of the diode under test allow the comparison of different diodes in their actual operating environment. A fundamental mixer test jig and a subharmonic mixer test jig are designed for the characterization and comparison of different single-anode and antiparallel Schottky diodes, respectively, at 183 GHz. For the antiparallel diodes, the traditional capacitance extraction is not possible, thus alternative and additional characterization data is valuable. The diode manufacturers can exploit the mixer-based characterization to test the mixer operation of their diode and to reveal possible problems with the diode during the diode development process.

This paper presents a new method for thermal characterization of THz Schottky diodes. The method is based on the transient current behavior, and it enables the extraction of thermal resistances, thermal time-constants, and peak junction temperatures of THz Schottky diodes. Many typical challenges in thermal characterization of small-area diode devices, particularly those related to self-heating and electrical transients, are either avoided or mitigated. The method is validated with measurements of commercially available single-anode Schottky varactor diodes. A verification routine is performed to ensure the accuracy of the measurement setup, and the characterization results are compared against an in-house measurement-based method and against simulation results of two commercial 3-D thermal simulators. For example, characterization result for the total thermal resistance of a Schottky diode with an anode area of 9 μm2 is within 10% of the average value of 4020 K/W when using all four approaches. The new method can be used to measure small diode devices with thermal time constants down to about 300 ns with the measurement setup described in the paper.

This paper presents the characterization measurements and simulations performed with ACST InGaAs low-barrier Schottky diodes for millimeter wave mixing applications. While these low-barrier Schottky diodes have been successfully used for millimeter wave detector design, their performance when acting as mixers has not been tested yet. This paper shows the performance for this type of diodes in a fundamental mixing configuration with evaluation of conversion loss and noise temperature. A fundamental mixer test-jig is used as the measurement platform with low-loss E-H impedance tuners for RF and LO signal matching. In addition to the measurements, 3D HFSS and ADS circuit simulations are also performed and results are presented. Conversion loss of less than 5 dB is obtained for 0.1 mW LO power in mixer operation at 181-183 GHz.

In this paper, a 24 GHz frequency-modulated continuous wave radar is used to detect and localize both stationary and moving targets. Depending on the application, the implemented software offers different modes of operation. For example, it can simply output raw data samples for advanced offline processing or directly carry out a two dimensional fast Fourier transform to estimate the location and velocity of multiple targets. To suppress clutter and detect only moving targets, two methods based on the background reduction and the slow time processing techniques are implemented. A trade-off between the two methods is presented based on their performance and the required processing time.

This paper presents a 24 GHz FMCW radar system for detection of movement and respiration using change in the statistical properties of the received radar signal, both amplitude and phase. We present the hardware and software segments of the radar system as well as algorithms with measurement results for two distinct use-cases: 1. FMCW radar as a respiration monitor and 2. a dual-use of the same radar system for smart lighting and intrusion detection. By using change in statistical properties of the signal for detection, several system parameters can be relaxed, including, for example, pulse repetition rate, power consumption, computational load, processor speed, and memory space. We will also demonstrate, that the capability to switch between received signal strength and phase difference enables dual-use cases with one requiring extreme sensitivity to movement and the other robustness against small sources of interference.

A new method for extracting the series resistance and thermal resistance of a Schottky diode is presented. The method avoids the inaccuracies caused by the temperature dependence of the saturation current and ideality factor. These are a major concern for traditional extraction methods, especially when the diode under test has a submicrometer anode diameter and is significantly heated up by the bias current. The method uses theoretical models validated with measurements for the temperature-dependent saturation current and ideality factor, and the series resistance values extracted from low-frequency scattering parameter measurements in the high bias current regime. The main focus of this paper is the accurate extraction of the series resistance. For example, the series resistance value extracted with our method for a discrete diode with a 0.8-μm anode diameter is 88% larger than the series resistance extracted using traditional techniques. As a by-product from the extraction algorithm, an estimate for the thermal resistance of the diode is obtained. The method is validated with extensive current-voltage (I-V) and scattering parameter measurements of two different commercially available discrete single anode mixer diodes optimized for terahertz operation. I-V measurements are performed at several controlled ambient temperatures and scattering parameter measurements at one known ambient temperature.

We present the design, simulations, fabrication, and measurements of a W-band waveguide impedance tuner. The design consists of a WR-10 waveguide with two E-plane arms for tunable dielectric-based backshorts. The impedance tuner is fabricated using a simple split-block technique and is easily scalable to submillimeter wavelengths. Our design shows an excellent input impedance range, tuning accuracy, repeatability, and a high attainable maximum reflection coefficient over the frequency band of 75-110 GHz. Our tuner applies dielectric-based backshorts, which provide a tuning accuracy better than that of other waveguide backshorts.

Efficient characterization and modelling techniques have a key role in the development of Schottky diode-based devices with state-of-the-art performance. This paper makes an effort to introduce such techniques and to provide examples of how they are used by the Schottky community. The modelling techniques covered in the paper are circuit simulator and electro-magnetic modelling. Characterization methods include current-voltage, capacitance-voltage, S-parameter, test jig-based, and thermal measurement techniques.

This paper presents the design and measurements of a 60-GHz semipassive MMID transponder for high data rate applications. The transponder consists of an antenna array that is connected to a millimeter wave diode on liquid crystal polymer. The diode acts as a detector as well as a backscattering modulator. The transponder functionality is demonstrated with laboratory equipment. The measured diode sensitivity is 560 V/W. A signal-to-noise ratio of over 20 dB in the received backscattered signal is measured at a distance of 30 cm.

Stand-off detection for concealed weapons is one of the applications for passive submillimetre-wave imaging. The operating frequency (neglecting technology limitations) is often a compromise between the diffraction-limited angular resolution for a fixed maximum aperture diameter, and the extinction of the signal in obscurant layers: At high frequencies towards the 1 THz mark, excellent angular resolution is readily achievable with modest aperture diameters, while scattering and attenuation by clothing is high which creates potentially more clutter rather than improving detection capability. At lower frequencies towards 100 GHz, attenuation and scattering by clothing is much less pronounced, albeit at significantly reduced spatial definition thanks to increased diffraction. In order to avoid the above-mentioned compromise, we have constructed a three-band passive imaging system operating at effective centre frequencies of 250 GHz, 450 GHz and 720 GHz. Aspects of the system will be presented.

Imaging at submillimetre-wave (SMMW) frequencies is of considerable interest for security applications due to potentially superior performance at longer stand-off ranges in comparison to mm-wave imaging thanks to reduced diffraction. We have demonstrated passive broad-band video rate imaging system operating at a centre frequency of about 600 GHz, capable of 10 frames/second imagery of a 2 m × 1 m field-of-view at a stand-off distance of 5 meters. In addition, a multi-band system centred around 250, 450 and 720 GHz will be discussed. Multi-band imagery is interesting given its potential for rudimentary materials differentiation, a capability that would substantially benefit e.g. security imaging applications. The passive imaging activities are complemented by activities towards developing rapid electronic beam steering capability for imaging submm-wave radars. Results from two projects aiming at constructing such beam steering systems at 120 GHz and at 650 GHz are presented.

By taking reciprocity of the error network into account, full and accurate calibration of a 16-term error model can be performed using only four two-port calibration standards or termination pairs. Moreover, there is no need for a nonsymmetrical calibration standard that is strictly required in a more conventional five-standard calibration. Commercially available standard substrates can thus be used. Detailed theory of the reciprocal 16-term error model and a new calibration method are presented. Reciprocity assumption is valid in on-wafer and other measurements when two-tier calibration is applied. However, the calibration scheme allows measurement of nonreciprocal devices too. The usefulness of the new method is confirmed by practical wideband on-wafer measurements.

This paper describes the design, electromagnetic (EM) modeling and experimental results obtained for a 160 GHz double folded slot antenna array processed through silicon micromachining. Initial simulations showed reflection losses (RL) of -17 dB at 160 GHz and a fractional bandwidth of ~18.7% (with RL

A combined full-wave/circuit simulator model for a coaxial cavity Gunn oscillator is developed. The Gunn oscillator utilizes the second harmonic for the output power generation at 76 GHz. The model is validated with reflection coefficient and output power measurements. This combined model provides accurate and fast Gunn oscillator cavity design.