Anders Skalare

Penetrating 3-D Imaging at 4- and 25-m Range Using a Submillimeter-Wave Radar

We show experimentally that a high-resolution imaging radar operating at 576-605 GHz is capable of detecting weapons concealed by clothing at standoff ranges of 4-25 m. We also demonstrate the critical advantage of 3-D image reconstruction for visualizing hidden objects using active-illumination coherent terahertz imaging. The present system can image a torso with <1 cm resolution at 4 m standoff in about five minutes. Greater standoff distances and much higher frame rates should be achievable by capitalizing on the bandwidth, output power, and compactness of solid state Schottky-diode based terahertz mixers and multiplied sources.

A High-Resolution Imaging Radar at 580 GHz

We have developed a high-resolution imaging radar at 580 GHz. Coherent illumination in the 576-589 GHz range and phase-sensitive detection are implemented in an all-solid-state design based on Schottky diode sensors and sources. By employing the frequency-modulated continuous wave (FMCW) radar technique, we achieve centimeter-scale range resolution while utilizing fractional bandwidths of less than 3%. Our high operating frequencies also permit centimeter-scale cross-range resolution at several-meter standoff distances without large apertures. Scanning of a single-pixel transceiver enables targets to be rapidly mapped in three dimensions, and here we apply this technology to the detection of concealed objects on persons.

InP HBT IC Technology for Terahertz Frequencies: Fundamental Oscillators Up to 0.57 THz

We report on the development of a 0.25-μm InP HBT IC technology for lower end of the THz frequency band (0.3-3 THz). Transistors demonstrate an extrapolated fmax of >;800 GHz while maintaining a common-emitter breakdown voltage (BVCEO) >;4 V. The transistors have been integrated in a full IC process that includes three-levels of interconnects, and backside processing. The technology has been utilized for key circuit building blocks (amplifiers, oscillators, frequency dividers, PLL, etc), all operating at ≥300 GHz. Next, we report a series of fundamental oscillators operating up to 0.57 THz fabricated in a 0.25-μm InP HBT technology. Oscillator designs are based on a differential series-tuned topology followed by a common-base buffer, in a fixed-frequency or varactor-tuned scheme. For ≥400 GHz designs, a subharmonic down-conversion mixer is integrated to facilitate spectrum measurement. At optimum bias, the measured output power was -6.2, -5.6, and -19.2 dBm, for 310.2-, 412.9-, and 573.1-GHz designs, respectively, with PDC ≤ 115 mW. Varactor-tuned designs demonstrated 10.6-12.3 GHz of tuning bandwidth up to 300 GHz.

Length scaling of bandwidth and noise in hot‐electron superconducting mixers

Mixing experiments have been performed at frequencies from 4 to 20 GHz on Nb thin‐film superconducting hot‐electron bolometers varying in length from 0.08 to 3 μm. The intermediate frequency (IF) bandwidth is found to vary as L−2, with L the bridge length, for devices shorter than √12 Le−ph≊1 μm, with Le−ph the electron‐phonon length. The shortest device has an IF bandwidth greater than 6 GHz, the largest reported for a low‐Tc superconducting bolometric mixer. The conversion efficiencies range from −5 to −11 dB (single sideband, SSB). For short bridges, the mixer noise temperature is found to be as low as 100 K (double sideband, DSB), with little length dependence. The local oscillator power required is small, ≊10 nW. Such mixers are very promising for low‐noise THz heterodyne receivers.

Large bandwidth and low noise in a diffusion‐cooled hot‐electron bolometer mixer

Heterodyne measurements have been made at 533 GHz using a novel superconducting hot‐electron bolometer in a waveguide mixer. The bolometer is a 0.3 μm long niobium microbridge with a superconducting transition temperature of 5 K. The short length ensures that electron diffusion dominates over electron‐phonon interactions as the electron cooling mechanism, which should allow heterodyne detection with intermediate frequencies (if) of several GHz. A Y‐factor response of 1.15 dB has been obtained at an if of 1.4 GHz with 77 and 295 K loads, indicating a receiver noise temperature of 650 K DSB. The −3 dB rolloff in the if response occurs at 1.7 GHz.

InP HBT Integrated Circuit Technology for Terahertz Frequencies

We report on the development of an InP DHBT integrated circuit technology for applications at the lower range of the THz frequency band (0.3-3 THz) 0.25um HBTs demonstrate an extrapolated fmax of >800GHz while maintaining a common-emitter breakdown voltage of >4V. The transistors have been integrated a full IC process that includes three-levels of interconnects, backside wafer thinning to 50um with a through-wafer via process, and a backside etch singulation process that allows for the formation of free standing integrated waveguide probes. The technology has been utilized to demonstrate amplifiers, oscillators and dynamic frequency dividers all operating at >300GHz.

Novel Terahertz Antenna Based on a Silicon Lens Fed by a Leaky Wave Enhanced Waveguide

We introduce a novel antenna concept suitable for future integrated arrays at terahertz frequencies. The antenna consists of an extended hemispherical lens antenna fed by a leaky wave waveguide feed that can be integrated with sensors and detectors such as Schottky diodes. In this antenna architecture, a couple of TE/TM leaky wave modes are excited in a resonant cavity formed by a waveguide opening ground plane and a silicon lens. Due to these modes, the field radiated by the waveguide inside the lens is a very directive pattern that illuminates the upper part of the lens. Having a directive primary field helps to increase the f-number of the lens improving several factors as spill over, off axis distortions and coating layer fabrication. The antenna structure is compatible with modern semiconductor fabrication technology and lends itself nicely for large format imaging arrays. In this contribution, we investigate the important parameters of a single antenna such as reflection coefficient, directivity, Gaussicity, phase center and off-axis displacement tolerances, and we validate our simulations by measuring the far field radiation patterns of a 545 GHz prototype.

MIXING AND NOISE IN DIFFUSION AND PHONON COOLED SUPERCONDUCTING HOT-ELECTRON BOLOMETERS

We report a systematic, comprehensive set of measurements on the dynamics and noise processes in diffusion and phonon-cooled superconducting hot-electron bolometer mixers which will serve as ultralow noise detectors in THz heterodyne receivers. The conversion efficiency and output noise of devices of varying lengths were measured with radio frequency between 8 and 40 GHz. The devices studied consist of 100-A-thin film Nb bridges connected to thick (1000 A), high conductivity normal metal (Au) leads. The lengths of the devices studied range from 0.08 to 3 μm. For devices longer than the electron–phonon interaction length Le–ph≡Dτe–ph, with D the diffusion constant and τe–ph−1 the electron–phonon interaction rate, the hot electrons are cooled dominantly by the electron–phonon interaction, which in Nb is too slow for practical applications. If the device length is less than πLe–ph(≈1 μm at 4.2 K), then out diffusion of heat into the high conductivity leads dominates the cooling process. In this limit, the in...

600 GHz Imaging Radar with 2 cm Range Resolution

We report the first submillimeter-wave imaging system that has radar ranging capabilities. By frequency-modulating the K-band synthesizers of a single-pixel 630 GHz scanning vector imager and applying a distortion compensation technique in software, we have achieved a range resolution of approximately 2 cm for targets at a range of several meters. Relief images of test objects obtained with our system demonstrate that three-dimensional THz imaging of scanned targets is feasible using a room temperature, all solid-state approach.

InP HBT amplifier MMICs operating to 0.67 THz

Two indium-phosphide (InP) double-heterojunction bipolar transistor (DHBT) based terahertz monolithic integrated circuit (TMIC) amplifiers are reported with record operating bandwidths up to 694 GHz. The first amplifier uses 3 μm long emitter transistors, has 24 dB gain at 670 GHz, and a saturated output power of -4 dBm at 585 GHz. The second amplifier uses 6 μm long emitter transistors, has 20 dB gain at 655 GHz, and a saturated output power of -0.7 dBm at 585 GHz. Both TMICs use Teledynes 130nm InP DHBT transistors in a common base configuration and are matched using inverted CPW transmission lines realized using a three-metal-layer high-density thin-film interconnects system. These results demonstrate the capability of 130nm InP DHBT technology to enable sophisticated TMIC circuits for operation in the terahertz band.