High Millimeter-wave Frequencies Research Articles

A compact and fully integrated FMCW radar transceiver combined with a dielectric lens

Abstract Electronic measurement systems in the THz frequency range are often bulky and expensive devices. While some compact single-chip systems operating in the high millimeter-wave frequency range have recently been published, compact measurement systems in the low THz frequency range are still rare. The emergence of new silicon-germanium (SiGe) semiconductor technologies allow the integration of system components, like oscillators, frequency multipliers, frequency dividers, and antennas, operating in the low THz frequency range, into a compact monolithic microwave integrated circuits (MMIC), which contains most components to implement a low-cost and compact frequency-modulated continuous-wave-radar transceiver. This article presents a single transceiver solution containing all necessary components. It introduces a $0.48\,\mathrm{THz}$ radar transceiver MMIC with a tuning range of $43\,\mathrm{GHz}$ and an output power of up to $-9.4\,\mathrm{dBm}$ in the SG13G3 $130\,\mathrm{nm}$ SiGe technology by IHP. The MMIC is complemented by a dielectric lens antenna design consisting of polytetrafluoroethylene, providing up to $39.3\,\mathrm d\mathrm B\mathrm i$ of directivity and half-power beam widths of 0.95∘ in transmit and receive direction. The suppression of clutter from unwanted targets deviating from antenna boresight more than 6∘ is higher than $24.6\,\mathrm d \mathrm B$ in E- and H-Plane.

Phenomenological Study of Radar Scattering at High Millimeter-Wave Frequencies in Support of Autonomous Vehicles

Phenomenological Study of Radar Scattering at High Millimeter-Wave Frequencies in Support of Autonomous Vehicles

Impact of Ground Via Placement in On-Wafer Contact Pad Design up to 325 GHz

The design of RF contact pads is a challenging task, especially when operating in the high millimeter-wave frequency range up to 325 GHz. The pads need to fulfill low loss, low distortion, probe ability, and packagability. Compared to the dimensions of the circuit components, the contact pads are rather large because the pad miniaturization is limited by the available probing and packaging technologies. This large spatial extent makes the contact pads prone to the excitation of parasitic modes, which deteriorate the overall circuit performance. This paper presents a comprehensive study on these parasitic modes and acquires analytical and numerical solutions to estimate the critical frequencies. For verification, two different contact pad structures were realized using an indium gallium arsenide (InGaAs) monolithic microwave integrated circuit process, with a substrate thickness of 50 $\mu \text{m}$ . The test structures were characterized up to 325 GHz in an on-wafer measurement setup. Despite the good agreement between measurement and simulation, detailed investigations of fabrication and measurement tolerances were carried out to estimate the robustness of the electrical performance. The optimized via configuration achieves resonance-free behavior of the pad over the full measurement frequency range with less than 1.8-dB loss per probe-to-pad contact at 325 GHz.

Efficiency Optimized Distributed Transformers for Broadband Monolithic Millimeter-Wave Integrated Power Amplifier Circuits

This paper revises the efficiency optimization equations for magnetic-transformer-based power combiner/ divider impedance transformation networks (e.g., distributed active transformer). It evaluates their usability for high millimeter-wave frequencies, where the distributed behavior of a transformer and its loss become relevant. As is demonstrated, the standard optimization equations do not lead to an optimum result. To enable the optimization of distributed transformers, an extended lumped equivalent circuit model is proposed and used for the derivation of new optimization equations. The novel equations enable the design of magnetic transformers with maximum efficiency. To demonstrate the performance that can be achieved with optimized distributed magnetic transformer networks at millimeter-wave frequencies, measurement results of an R-band (i.e., 170–260 GHz)/H-band (i.e., 220–325 GHz) power amplifier (PA) are presented. With an output power of approximately 6.2 dBm at 260 GHz, the amplifier is among the state of the art for mHEMT PAs operating in this frequency range. With its relative 3-dB bandwidth of 29%, however, it surpasses all those reported mHEMT PAs to date.

A Novel Unit Cell for Active Switches in the Millimeter-Wave Frequency Range

This paper presents a novel transistor unit cell which is intended to realize compact active switches in the high millimeter-wave frequency range. The unit cell consists of the combination of shunt and common gate transistor within a four-finger transistor cell, achieving gain in the amplifying state as well as good isolation in the isolating state. Gate width-dependent characteristics of the unit cell as well as the design of actual switch implementations are discussed in detail. To verify the concept, two switches, a single pole double throw (SPDT) switch and single pole quadruple throw (SP4T) switch, intended for the WR3 frequency range (220–325 GHz) were manufactured and characterized. The measured gain at 250 GHz is 4.6 and 2.2 dB for the SPDT and SP4T switch, respectively. An isolation of more than 24 dB for the SPDT switch and 12.8 dB for the SP4T switch was achieved.

A 190-GHz VCO With 20.7% Tuning Range Employing an Active Mode Switching Block in a 130 nm SiGe BiCMOS

A voltage controlled oscillator (VCO) incorporating a system of coupled oscillators with two active mode switching (AMS) blocks is presented. The AMS blocks excite the main VCOs to operate in two distinct frequency bands. An overlap between the two frequency bands has extended the tuning range of the VCO. By turning the AMS blocks off, low-loss and low-capacitance behaviors of these blocks result in wide tuning range and high harmonic output power at high millimeter-wave frequencies. On the other hand, by turning the AMS blocks on, their loss-canceling and capacitance-tuning behaviors yield to higher power and wider tuning range with a lower center frequency. By having sufficient frequency overlap between the two modes, the implemented VCO achieves record tuning range of 20.7% at 190.5 GHz with a maximum output power of –2.1 dBm. This tuning range is significantly higher than reported silicon-based VCOs with center frequencies higher than 120 GHz.

Evaluation of cross-connected waveguides as transfer standards of transmission at high millimetre-wave frequencies

At the present time, transfer and verification standards of transmission coefficient (or, equivalently, transmission loss) are not readily available at high millimetre-wave frequencies (i.e. at frequencies ranging typically from 100 GHz to 300 GHz). In recent years, cross-connected waveguide devices have been proposed to provide calculable standards of transmission loss at these frequencies. This paper investigates the viability of these cross-connected waveguides as transfer standards of transmission for inter-laboratory measurement comparison exercises. This relates to their potential use in activities such as international key comparison exercises and measurement audit programmes. A trial inter-laboratory comparison involving four laboratories using two cross-connected waveguides in the WR-05 waveguide size (covering frequencies from 140 GHz to 220 GHz) is described and includes an analysis of the measurement results obtained during the comparison exercise.

Design of a W-band Groove Polarizer

원형 도파관 그루브 편파기는 구조가 단순하고 비교적 광대역 특성을 가지므로 가공공차가 중요한 고역 밀리미터파 주파수에서 특히 유용하다. 본 논문에서는 직경 2.2mm 원형 도파관에서 구현된 W-대역 그루브 편파기의 설계, 제작 및 측정 결과를 제시하였다. 우선 최적성능을 위한 편파기의 설계절차를 제시하였다. 다음으로 낮은 축비와 우수한 임피던스 정합특성을 가지도록 W-대역 그루브 편파기를 설계하였다. 설계한 편파기를 수치제어 머시닝센터에서 제작하였다. 제작된 편파기의 측정으로부터 설계결과와 측정결과의 일치도가 양호함을 확인하였다.

Experimental Characterization of Polarimetric Radar Backscatter Response of Distributed Targets at High Millimeter-Wave Frequencies

Subterahertz frequencies between 100 and 300 GHz remain an untapped portion of the frequency spectrum for many radar- and radiometer-based remote sensing applications. This can be attributed in part to the lack of knowledge of the phenomenology of signal interaction with terrain at these frequencies. This paper examines recently acquired polarimetric radar backscatter data of different types of surfaces using a newly constructed polarimetric instrumentation radar operating at 222 GHz. At this frequency bare surfaces such as asphalt and dirt are electrically rough with subsurface aggregate sizes comparable with the wavelength resulting in substantial volume and surface scattering. The data show strong backscatter responses from bare surfaces with angular dependence proportional to the cosine square of the incidence angle along with significant depolarization (between −8 and −4 dB). The data for vegetation-covered surfaces show weak dependence on incidence angle and appreciable depolarization (between −12 and −6 dB). Empirical models for bare and vegetation-covered surfaces are proposed.

A High-Dynamic Range Heterodyne Microwave Receiver for Modulated Scattering Measurements

This paper presents the design of a high-dynamic range heterodyne receiver specifically designed for modulated scatterer technique (MST) applications. Due to the amplitude-modulated nature of the signal, several unique receiver architectures have been reported and implemented for MST measurements, with the most widely used being the homodyne receiver. The proposed design offers a higher dynamic range compared with the homodyne receivers, particularly at high microwave and millimeter-wave frequencies. A prototype 24-GHz receiver, based on the proposed design, was built for an MST-based microwave imaging device, and its performance characteristics are presented in this paper.

Design and model studies for solid-state power amplification at 210 GHz

The high millimeter-wave (mmW) frequency range offers new possibilities for high-resolution imaging and sensing as well as for high data rate wireless communication systems. The use of power amplifiers of such systems boosts the performance in terms of operating range and/or data rate. To date, however, the design of solid-state power amplifiers at frequencies about 210 GHz suffers from limited transistor model accuracy, resulting in significant deviation of simulation and measurement. This causes cost and time consuming re-design iterations, and it obstructs the possibility of design optimization ultimately leading to moderate results. For verification of the small-signal behavior of our in-house large-signal transistor model, S-parameter measurements were taken from DC to 220 GHz on pre-matched transistors. The large-signal behavior of the transistor models was verified by power measurements at 210 GHz. After model modification, based on process control monitor (PCM) measurement data, the large-signal model was found to match the measurements well. A transistor model was designed containing the statistical information of the PCM data. This allows for non-linear spread analysis and reliable load-pull simulations for obtaining the highest available circuit performance. An experimental determination of the most suitable transistor geometry (i.e. number of gate fingers and gate width) and transistor bias was taken on 100 nm gate length metamorphic high electron mobility transistor (mHEMT) transistors. The most suitable combination of number of fingers, gate width and bias for obtaining maximum gain, maximum output power, and maximum power added efficiency (PAE) at a given frequency was determined.

An Improved Triple-Tunable Millimeter-Wave Frequency Synthesizer with High Performance

In this letter, an improved triple-tunable frequency synthesizer structure to achieve both high frequency resolution and fast switching speed without degradation of spurious signals (spurs) level performance is proposed. According to this structure, a high performance millimeter-wave frequency synthesizer with low spurious, low phase noise, and fast switching speed, is developed. This synthesizer driven by the direct digital synthesizer (DDS) AD9956 can adjust the output of a DDS and frequency division ratios of two variable frequency dividers (VFDs) to move the spurious components outside the loop bandwidth of the phase-locked loop (PLL). Moreover, the ADF4252 based microwave PLL can further suppress the phase noise. Experimental results from the implemented synthesizer show that remarkable performance improvements have been achieved.

Electrical Prism: A High Quality Factor Filter for Millimeter-Wave and Terahertz Frequencies

A 2-D electrical filter is introduced that is compatible with today's conventional integrated circuit processes. The rich 2-D propagation properties of the medium are used to introduce a novel high quality factor filter called an electrical prism. The proposed filter shows a quality factor much larger than the quality factor of the individual components at high millimeter-wave and terahertz frequencies. This structure also provides a negative effective index in a low-pass LC lattice. Based on this idea, we show filters with quality factors of 130 at 230 GHz and 420 at 460 GHz consisting of elements with the quality factor of 10 and 20, respectively. The effect of component loss on the filter quality factor is discussed in this paper. The negative effective index and the filter behavior of the lattice is verified by measuring a prototype on a CMOS process at 32-40 GHz. There is good agreement among the theory, simulation, and experimental results.

Millimeter Wave Substrate Integrated Waveguide Antennas: Design and Fabrication Analysis

The paper presents a new concept in antenna design, whereby a photo-imageable thick-film process is used to integrate a waveguide antenna within a multilayer structure. This has yielded a very compact, high performance antenna working at high millimeter-wave (mm-wave) frequencies, with a high degree of repeatability and reliability in antenna construction. Theoretical and experimental results for 70 GHz mm-wave integrated antennas, fabricated using the new technique, are presented. The antennas were formed from miniature slotted waveguide arrays using up to 18 layers of photo-imageable material. To enhance the electrical performance a novel folded waveguide array was also investigated. The fabrication process is analyzed in detail and the critical issues involved in the fabrication cycle are discussed. The losses in the substrate integrated waveguide have been calculated. The performance of the new integrated antenna is compared to conventional metallic, air-filled waveguide antennas, and also to conventional microstrip antenna arrays operating at the same frequencies.

Ceramics to 100 GHz: Including a novel free space dielectric measurement technique

Data are presented for transmission measurements on ceramic coplanar lines over the frequency range 50 MHz to 100 GHz. The data has been analysed to separate the loss due to the conductor and the loss due to the dielectric. The results of a novel technique to reduce surface losses by flash etching the surfaces of the conductors are also presented. In addition, a new free-space technique for measuring the loss tangent and relative permittivity of dielectric layers at high millimetre-wave frequencies is introduced.

220-GHz metamorphic HEMT amplifier MMICs for high-resolution imaging applications

In this paper, the development of 220-GHz low-noise amplifier (LNA) MMICs for use in high-resolution active and passive millimeter-wave imaging systems is presented. The amplifier circuits have been realized using a well-proven 0.1-/spl mu/m gate length and an advanced 0.05-/spl mu/m gate length InAlAs/InGaAs based depletion-type metamorphic high electron mobility transistor technology. Furthermore, coplanar circuit topology in combination with cascode transistors was applied, leading to a compact chip size and an excellent gain performance at high millimeter-wave frequencies. A realized single-stage 0.05-/spl mu/m cascode LNA exhibited a small-signal gain of 10 dB at 222 GHz, while a 0.1-/spl mu/m four-stage amplifier circuit achieved a linear gain of 20 dB at the frequency of operation and more than 10 dB over the bandwidth from 180 to 225 GHz.

Material Processing with a High Frequency Millimeter-Wave Source

A millimeter-wave beam based on a 15-kW, continuous-wave, 83-GHz gyrotron with superconducting magnets system is being investigated for use in material processing. The millimeter-wave beam can be focused to a few millimeters and manipulated quasi-optically and has been used in the following experiments: joining of ceramics (both similar and dissimilar materials), brazing of poled piezoelectric ceramics without significant heating and depoling, and coating of metals and polymers. Joining has been done directly and with reactive brazes. In coating, the beam's short wavelength and absorption depth permit effective ceramic-coating deposition on lower temperature materials, e.g., polymers and metals, without significant substrate heating, and localized deposition of coatings as well. Finally, the millimeter-wave source has been used in the efficient production of nanophase metal and ceramic powders, via a greatly accelerated modified polyol process producing smaller powders of greater uniformity. The results and implications of the various experiments will be discussed with some theoretical calculations and modeling.

A novel low noise IMPATT diode

IMPATT diodes are currently the main solid state source of power at the higher millimeter-wave frequencies, but can suffer from high noise levels, low efficiency and low reliability, particularly when driven for high power. In the present paper a new concept is proposed which can yield essentially noise free avalanche multiplication at high frequency and should improve both efficiency and reliability. The proposed structures require a layer of narrow gap material adjacent to a wide gap avalanche zone.

Performance of NbN superconductive tunnel junctions as SIS mixers at 205 GHz

Small area (<or=1- mu m/sup 2/), high-current-density NbN-MgO-NbN tunnel junctions with I-V characteristics suitable for high-frequency mixers have been fabricated. Mesa-geometry junctions with an area of about 1 mu m/sup 2/ and critical current density of 5-10 kA/cm/sup 2/ are integrated with superconducting microstrip lines designed to resonate out the junction capacitance. Accurate values of junction capacitance and magnetic penetration depth are required for the proper design of the microstrip. A study was made of the mixer gain and noise performance near 205 GHz as a function of the inductance provided by the microstrip line. This has confirmed, at a high millimeter-wave frequency, values of junction capacitance of 85 fF/ mu m/sup 2/ and recently measured values of a magnetic penetration depth of 380 nm. Mixer noise temperatures as low as 134 K at 1.5 K have been obtained for properly tuned junctions. A significant improvement in mixer performance on cooling from 4.2 K to 1.5 K was observed. Edge-geometry junctions with an area of 0.3 mu m/sup 3/ and critical current density of 18-25 kA/cm/sup 2/ have also been fabricated. These junctions give a mixer noise temperature of 145 K at 4.2 K without the use of integrated tuning elements. These are the best results ever achieved for NbN-based SIS mixers.

A new transit-time device using quantum-well injection

The use of such techniques as molecular beam epitaxy has allowed the fabrication of devices in which tunneling is the dominant transport mechanism. In this paper a new transit-time device which uses resonant tunneling through a quantum well is proposed and analyzed. Depending on the bias level, this device may permit injection of carriers into the drift region at more favorable phase angles (hence higher efficiencies) than other transit-time devices. The device promises low noise performance and should be capable of operating at high millimeter-wave frequencies with higher output power than other transit-time devices or pure quantum-well oscillators. Since the device uses quantum-well injection and transit-time effects, it is called a QWITT diode.