Double-sideband Noise Temperature Research Articles

Terahertz high-sensitivity SIS mixer based on Nb–AlN–NbN hybrid superconducting tunnel junctions

The terahertz band, a unique segment of the electromagnetic spectrum, is crucial for observing the cold, dark universe and plays a pivotal role in cutting-edge scientific research, including the study of cosmic environments that support life and imaging black holes. High-sensitivity superconductor–insulator–superconductor (SIS) mixers are essential detectors for terahertz astronomical telescopes and interferometric arrays. Compared to the commonly used classical Nb/AlO x /Nb superconducting tunnel junction, the Nb/AlN/NbN hybrid superconducting tunnel junction has a higher energy gap voltage and can achieve a higher critical current density. This makes it particularly promising for the development of ultra-wideband, high-sensitivity coherent detectors or mixers in various scientific research fields. In this paper, we present a superconducting SIS mixer based on Nb/AlN/NbN parallel-connected twin junctions (PCTJ), which has a bandwidth extending up to 490 GHz–720 GHz. The best achieved double-sideband (DSB) noise temperature (sensitivity) is below three times the quantum noise level.

Efficiency Assessment of Traditional GaAs and Low-Power InGaAs Schottky Diodes in Full-Band Mixers at 0.3 THz

In this paper, we present and compare two different full-band WR3.4 Sub-Harmonic Mixers (SHMs), featuring traditional GaAs and the novel low-barrier InGaAs discrete diodes. In this study, an Active Multiplier Chain (AMC) is used as a Local Oscillator source, which provides peak powers beyond 20 mW. The GaAs mixer presents Single-Sideband (SSB) Conversion Loss (CL) of 10 dB and Double-Sideband (DSB) Noise Temperature (NT) of 3000 K across the entire RF and IF bands when an LO power of 6–10 mW is applied. The low-barrier mixer featuring the new and improved batch of InGaAs diodes performs SSB Conversion Loss of 15 dB and DSB Noise Temperature of 9000 K, using LO powers of 0.5 mW. In this work, a comparison of the CL and NT of both mixers is carried out, highlighting the excellent performances of GaAs diodes and the minimum LO power requirements needed by InGaAs counterparts, as well as future perspectives in InGaAs mixer performances. The mixers and diodes were fully designed, fabricated, and tested at ACST GmbH.

SiGe BiCMOS Heterodyne Receiver Frontend for Remote Sensing With Small Satellites

Molecular spectroscopy with terahertz heterodyne receivers is an important and widely used method for remote sensing of gases in space, in the Earth's and planetary atmospheres, as well as in the coma of comets. For the use on small satellites, compact and lightweight receivers are needed. We have developed an integrated SiGe BiCMOS receiver frontend that is tunable from 225 to 255 GHz and have characterized it for heterodyne spectroscopy. The double-sideband noise temperature is 11000 K at a local oscillator frequency of 240 GHz and the Allan time is 1 s. With this receiver, we successfully performed heterodyne absorption and emission spectroscopy of acetonitrile in laboratory experiments.

340 and 250 GHz Schottky solid‐state heterodyne receiver arrays for passive imaging systems

AbstractReal‐time terahertz passive imaging systems are highly demanded in security checking application. In this paper, two four‐pixel receiver arrays for 340 and 250 GHz passive imaging systems are presented. As the core device of the front‐end of the receiving array, the low noise terahertz mixer is realized based on the enhanced Schottky diode model and low‐loss circuit structure. The minimum double side band (DSB) noise temperature of the separated 340 and 250 GHz mixers is 900 and 580 K, respectively, within the operational band‐width. Without considering fluctuation in the power gain, the calculated temperature sensitivity of 340 GHz receiver is 0.8 K with 40 GHz RF band. Finally, based on all‐solid‐state millimeter‐wave drive front end and reflector optics, a passive terahertz imaging system is completed. Less than 1 cm space resolution is achieved for 1–3 m object distances, and the distinct imaging to hidden threats is produced and made contrast among the two receiver arrays. The perfect imaging performances of the system verify the low noise characteristic of terahertz mixer. The Schottky solid‐state receiver array provides a cheap and feasible option for personal security screening.

10-Gbps real-time wireless link over 1.5 km at 220-GHz band based on Schottky-diode transceiver and 16-QAM modulation

A wireless link working at 220-GHz band is proposed for point-to-point high-speed communication. The system is primarily composed of sub-terahertz transceivers and baseband data processing platforms. Subharmonic mixers based on Schottky diode are developed and measured with a double-sideband (DSB) noise temperature of lower than 1100 K from 205 GHz to 230 GHz. High-selectivity waveguide bandpass filters are designed to reject the image sideband noise from entering the receiver. Two 58-dBi Cassegrain antennas are used to compensate for the large energy losses contributed by free space path and atmospheric absorption. Besides, sub-THz amplifiers based on InP HEMT technology are developed to further increase the transmitting power. To improve spectrum efficiency, 16 quadrature amplitude modulation is adopted. Forward error correction is implemented by using Reed-Solomon codes to reinforce the reliability of signal transmission. An outdoor wireless link is finally established within 1.5 km, and a data rate of 10 Gbps is achieved in real-time mode with an EVM of 9.53% (BER 1.4×10-9). For demonstration, uncompressed ultra-HD videos are successfully transmitted. Note that any auxiliary electronic testing and measurement equipment is not required while communicating. It is believed that this article provides an effective and practical solution for future long-distance high-speed communication.

Dual-Band Transmitter and Receiver With Bowtie-Antenna in 0.13 μm SiGe BiCMOS for Gas Spectroscopy at 222 - 270 GHz

This paper presents a transmitter (TX) and a receiver (RX) with bowtie-antenna and silicon lens for gas spectroscopy at 222-270 GHz, which are fabricated in IHP’s $0.13~\mu \text{m}$ SiGe BiCMOS technology. The TX and RX use two integrated local oscillators for 222 – 256 GHz and 250 – 270 GHz, which are switched for dual-band operation. Due to its directivity of about 27 dBi, the single integrated bowtie-antenna with silicon lens enables an EIRP of about 25 dBm for the TX, and therefore a considerably higher EIRP for the 2-band TX compared to previously reported systems. The double sideband noise temperature of the RX is 20,000 K (18.5 dB noise figure) as measured by the Y-factor method. Absorption spectroscopy of gaseous methanol is used as a measure for the performance of the gas spectroscopy system with TX- and RX-modules.

Development of 340-GHz Transceiver Front End Based on GaAs Monolithic Integration Technology for THz Active Imaging Array

Frequency multipliers and mixers based on Schottky barrier diodes (SBDs) are widely used in terahertz (THz) imaging applications. However, they still face obstacles, such as poor performance consistency caused by discrete flip-chip diodes, as well as low efficiency and large receiving noise temperature. It is very hard to meet the requirement of multiple channels in THz imaging array. In order to solve this problem, 12-μm-thick gallium arsenide (GaAs) monolithic integrated technology was adopted. In the process, the diode chip shared the same GaAs substrate with the transmission line, and the diode’s pads were seamlessly connected to the transmission line without using silver glue. A three-dimensional (3D) electromagnetic (EM) model of the diode chip was established in Ansys High Frequency Structure Simulator (HFSS) to accurately characterize the parasitic parameters. Based on the model, by quantitatively analyzing the influence of the surface channel width and the diode anode junction area on the best efficiency, the final parameters and dimensions of the diode were further optimized and determined. Finally, three 0.34 THz triplers and subharmonic mixers (SHMs) were manufactured, assembled, and measured for demonstration, all of which comprised a waveguide housing, a GaAs circuit integrated with diodes, and other external connectors. Experimental results show that all the triplers and SHMs had great performance consistency. Typically, when the input power was 100 mW, the output power of the THz tripler was greater than 1 mW in the frequency range of 324 GHz to 352 GHz, and a peak efficiency of 6.8% was achieved at 338 GHz. The THz SHM exhibited quite a low double sideband (DSB) noise temperature of 900~1500 K and a DSB conversion loss of 6.9~9 dB over the frequency range of 325~352 GHz. It is indicated that the GaAs monolithic integrated process, diodes modeling, and circuits simulation method in this paper provide an effective way to design THz frequency multiplier and mixer circuits.

220 GHz wideband integrated receiver front end based on planar Schottky diodes

AbstractIn this article, a 220 GHz wideband receiver front end is proposed, featuring a 220 GHz subharmonic mixer and a 110 GHz wideband tripler integrated in one single block. The 220 GHz subharmonic mixer and 110 GHz tripler are firstly developed separately with proper planar Schottky diodes. According to the simulated and experimental results, the direct combination of independent mixer and tripler will lead to deterioration of the front end's performances, especially for wideband receivers. This indicates the necessity of building matching network between the cascade circuits in wideband submillimeter receivers. To improve the integral performances of the receiver front end and reduce its size, the combination of the subharmonic mixer and the tripler was optimized with load‐pull techniques and realized in one block. Measured results reveal that the single sideband (SSB) conversion loss of the integrated receiver front end is 7.5‐11 dB from 185 to 250 GHz, while the double sideband (DSB) noise temperature is 750‐1600 K within this frequency range. The integrated front end features half size of the combination of independent modules and better performances. Good agreement between the simulated and measured results shows that the integration and optimization techniques can be applied to realize compact terahertz systems in the future.

Development of a Wideband 220-GHz Subharmonic Mixer Based on GaAs Monolithic Integration Technology

A wideband 220 GHz subharmonic mixer based on monolithic integration technology is proposed in this paper. It features 12 Mm-thick GaAs membrane with anti-parallel Schottky diodes working at THz band monolithically integrated on the membrane. The optimization principles of low-parastics Schottky diodes and the fabrication process of GaAs MMIC membrane diodes are elaborated. To realize optimum performances of the mixer, the dimensions of the integrated diodes and the matching network are optimized with harmonic balance simulation and load-pull techniques. An IF low pass filter with compact microstrip resonance cell (CMRC) configuration and an improved perpendicular coax-to-microstrip connection are used to realize wide IF band. The measured results show that the single sideband (SSB) conversion loss of this mixer is less than 10.5 dB from 185 to 255 GHz with fixed IF of 1 GHz, while the double sideband (DSB) noise temperature is better than 1400 K in this frequency range. Using fixed local oscillator (LO) frequency of 110 GHz, the measured SSB conversion loss is 7.4-10.7 dB within 185-255 GHz, indicating the good performances of the mixer with IF from DC to 35 GHz. The GaAs monolithic integration technology provides an approach for massive manufacturing of identical circuits and the proposed mixer with wideband characteristics will be applied in 220 GHz imaging systems in the near future.

A 200–240 GHz Sub-Harmonic Mixer Based on Half-Subdivision and Half-Global Design Method

For the terahertz harmonic mixer, a design model based on Half-Subdivision and Half-Global Design Method (HS-HGDM) with a single functional unit is proposed. The single functional unit circuit of the mixer, such as LO or IF Low Pass Filter (LPF), is designed by Subdivision Design Method (SDM), and the rest circuits of the mixer are designed by Global Design Method (GDM). The harmonic mixer based on this model is characterized by simple circuit structure, low conversion loss, small circuit size and high stability. In this paper, an improved Compact Suspended Micro-strip Resonators (CSMRs) filter is developed for the IF part of sub-harmonic mixer. The remaining circuits consist of some basic transmission units, such as the High-Z Low-Z impedance Transmission Lines (H-Z L-Z TLs) applied for main circuit, and full/reduced height WR4.3/WR8 applied for providing RF/LO signal. In RF frequency range 200–240 GHz, a Single Sideband (SSB) conversion loss of 7.36±0.76 dB operating at IF frequency 1.8 GHz, and a Double Sideband (DSB) noise temperature below 1034 K with the LO power of 2–5 mW and the LO frequency of 107 GHz were achieved. This broadband sub-harmonic mixer operates at room temperature, which makes it applicable to sub-millimeter wave or terahertz wireless communication systems and imaging inspection systems.

Design and Performance of a Sideband Separating SIS Mixer for 800–950 GHz

We present the design and results of characterization of a new sideband separating (2SB) mixer for 800–950 GHz, based on superconductor–insulator–superconductor (SIS) junctions. This is the first waveguide 2SB SIS mixer demonstrated at such a high frequency. The design is following the classical quadrature hybrid architecture, meanwhile additional attention was put on the reduction of reflections in the RF structure in order to minimize the RF imbalance, to achieve a high image rejection ratio (IRR). The RF waveguide block was manufactured by micromilling and populated by single-ended SIS mixers developed earlier for upgrade of the CHAMP+ high-band array on the APEX telescope. These SIS mixers have double-sideband (DSB) noise temperatures from 210 to 400 K. The assembled 2SB mixer yields a SSB noise temperature from 450 to 900 K, with an IRR above 15 dB in 95% of the band. Comparing the DSB and the SSB sensitivities, we find that the waveguide losses are as low as expected and do not exceed 0.6 dB. The presented mixer is a prototype for use in a 2SB dual polarization receiver planned for deployment on the APEX telescope.

A broadband 630–720 GHz Schottky based sub-harmonic mixer using intrinsic resonances of hammer-head filter

An room temperature low noise anti-parallel Schottky diode based 630–720GHz sub-harmonic mixer (SHM) is designed, built and measured. Intrinsic resonances in low-pass hammer-head filter have been adopted to prevent the LO and RF power leak from the IF channel, while greatly minimizing the transmission line size. The mixer consists of 15um quartz terahertz circuit and 127um Al2O3 IF transformer circuit. An improved lumped element equivalent noise model of SBDs guarantees the accuracy of simulation. The measurement indicates that with local oscillating (LO) signal of 2–8 mW, the lowest double sideband (DSB) conversion loss is 8.2 dB at 645 GHz, and the best DSB noise temperature is 2800 K at 657GHz. The 3 dB bandwidth of conversion loss is 75 GHz from 638 to 715 GHz. The work IF frequency band is above 20GHz ranging from 1 to 20 GHz with −10dB return loss.

THz Mixing with High-TC Hot Electron Bolometers: a Performance Modeling Assessment for Y-Ba-Cu-O Devices

Hot electron bolometers (HEB) made from high-TC superconducting YBa2Cu3O7–x (YBCO) oxide nano-constrictions are promising THz mixers, due to their expected wide bandwidth, large mixing gain, and low intrinsic noise. The challenge for YBCO resides, however, in the chemical reactivity of the material and the related aging effects. In this paper, we model and simulate the frequency dependent performance of YBCO HEBs operating as THz mixers. We recall first the main hypotheses of our hot spot model taking into account both the RF frequency effects in the YBCO superconducting transition and the nano-constriction impedance at THz frequencies. The predicted performance up to 4 THz is given in terms of double sideband noise temperature TDSB and conversion gain G. At 2.5 THz for instance, TDSB  1000 K and G 6 dB could be achieved at 12.5 W local oscillator power. We then consider a standoff target detection scheme and examine the feasibility with YBCO devices. For instance, detection at 3 m through cotton cloth in passive imaging mode could be readily achieved in moderate humidity conditions with 10 K resolution.

A 220 GHz Broadband Sub-Harmonic Mixer Based on Global Design Method

A terahertz mixer is one of terahertz key components and widely used on terahertz wireless communication, remote sensing, aerospace exploration, and biomedical system. The performance of the terahertz mixer has a great effect on the entire terahertz transceiver system performance. This paper proposes a 220 GHz broadband sub-harmonic mixer based on global design method (GDM), which is different from the traditional subdivision design method of which the mixer circuit is composed of functional unit circuits. Instead, the GDM adopts the overall performance of the mixer (conversion loss) as an optimization goal. The continuous structures of the circuit are described by ideal transmission line models and waveguide models, meanwhile, the S-parameters of the de-embedded model are used to describe the discontinuous structures. The measured single-sideband (SSB) conversion loss is basically consistent with the simulation results, which verifies the accuracy and reliability of the GDM. When local oscillator (LO) frequency is fixed at 110 GHz, the measured SSB conversion loss is less than 10 dB with the average value of 8.1 dB from 198 to 238 GHz. The minimum conversion loss of the mixer is 6.35 dB at 207 GHz. The measured double-sideband noise temperature of the mixer is less than 924 K at an intermediate frequency of 1.6 GHz. The GDM has the characteristics with a wide frequency band, small circuit size, simple structure, low LO power, and stable performance, and can also be applied to other terahertz components.

Low noise 874 GHz receivers for the International Submillimetre Airborne Radiometer (ISMAR).

We report on the development of two 874 GHz receiver channels with orthogonal polarizations for the International Submillimetre Airborne Radiometer. A spline horn antenna and dielectric lens, a Schottky diode mixer circuit, and an intermediate frequency (IF) low noise amplifier circuit were integrated in the same metallic split block housing. This resulted in a receiver mean double sideband (DSB) noise temperature of 3300 K (minimum 2770 K, maximum 3400 K), achieved at an operation temperature of 40 °C and across a 10 GHz wide IF band. A minimum DSB noise temperature of 2260 K at 20 °C was measured without the lens. Three different dielectric lens materials were tested and compared with respect to the radiation pattern and noise temperature. All three lenses were compliant in terms of radiation pattern, but one of the materials led to a reduction in noise temperature of approximately 200 K compared to the others. The loss in this lens was estimated to be 0.42 dB. The local oscillator chains have a power consumption of 24 W and consist of custom-designed Schottky diode quadruplers (5% power efficiency in operation, 8%-9% peak), commercial heterostructure barrier varactor (HBV) triplers, and power amplifiers that are pumped by using a common dielectric resonator oscillator at 36.43 GHz. Measurements of the radiation pattern showed a symmetric main beam lobe with full width half maximum <5° and side lobe levels below -20 dB. Return loss of a prototype of the spline horn and lens was measured using a network analyzer and frequency extenders to 750-1100 GHz. Time-domain analysis of the reflection coefficients shows that the reflections are below -25 dB and are dominated by the external waveguide interface.

Noise and IF Gain Bandwidth of a Balanced Waveguide NbN/GaN Hot Electron Bolometer Mixer Operating at 1.3 THz

In this paper, we present the comprehensive characterization of a waveguide balanced phonon-cooled NbN hot electron bolometer (HEB) mixer on a GaN buffer-layer operating at approximately 1.3 terahertz (THz). The measured uncorrected double sideband noise temperature was as low as 750 K at 1 GHz intermediate frequency (IF) and 900 K at 4 GHz IF, respectively, and suggests a noise bandwidth of 7 GHz. Moreover, the IF gain bandwidth of the HEB itself was deduced from a mixing experiment with a second monochromatic THz signal source and has shown a 3 dB roll-off at 5.5 GHz. The contribution of the HEB mixer on the overall receiver noise temperature was determined to be in the order of 300 K or 5 hf/k considering losses in the RF transmission path and the waveguide components as well as accounting for the receiver conversion loss, which was deduced from the U-factor method. The achieved performance sets a new benchmark for future THz instruments and emphasizes the technological readiness of waveguide-based NbN HEB mixers employing a GaN buffer-layer featuring significantly improved IF bandwidth without compromising on the receiver's noise temperature.

A compact 220 GHz heterodyne receiver module with planar Schottky diodes

This letter presents the development of a compact 220 GHz heterodyne receiver module for radars application in which a novel low pass wide stop band intermediate frequency (IF) filter is integrated. The planar Schottky anti-parallel mixing diode based subharmonic mixer (SHM) is used as the receiver’s first stage. The diode is flip-chip mounted on a 50 μm thick quartz substrate. The accurate modeling of the self and mutual inductance of the diode’s air-bridges are discussed. The measured conversion loss (CL) of the SHM has a minimum value of 6.2 dB at 210.5 GHz, and is lower than 8.4 dB in the frequency range 209.4–219.6 GHz with a 10 mW input power from a local oscillator (LO). The LO chain consists of a 110 GHz passive tripler, two Ka-band amplifiers and a Ka-band active tripler. The tested minimum double side band (DSB) noise temperature of the integrated 220 GHz heterodyne receiver is 725 K at 205.2 GHz and lower than 1550 K in the frequency range 199–226 GHz.

Noise and conversion performance of a high-Tc superconducting Josephson junction mixer at 0.6 THz

This letter presents both theoretical and experimental investigations on the noise and conversion performance of a high-Tc superconducting (HTS) step-edge Josephson-junction mixer at the frequency of 0.6 THz and operating temperatures of 20–40 K. Based on the Y-factor and U-factor methods, a double-sideband noise temperature of around 1000 K and a conversion gain of −3.5 dB were experimentally obtained at 20 K. At the temperature of 40 K, the measured mixer noise and conversion efficiency are around 2100 K and −10 dB, respectively. The experimental data are in good agreement with the numerical analysis results using the three-port model. A detailed performance comparison with other reported HTS terahertz mixers has confirmed the superior performance of our presented mixer device.

Terahertz Direct Detectors Based on Superconducting Hot Electron Bolometers with Microwave Biasing**Supported by the National Basic Research Program of China under Grant No 2014CB339800, the National Natural Science Foundation of China under Grant Nos 61521001, 11173015 and 11227904, the Fundamental Research Funds for the Central Universities, and the Key Laboratory of Advanced Techniques for Manipulating Electromagnetic Waves of Jiangsu Province.

Terahertz (THz) direct detectors based on superconducting niobium nitride (NbN) hot electron bolometers (HEBs) with microwave (MW) biasing are studied. The MW is used to bias the HEB to the optimum point and to readout the impedance changes caused by the incident THz signals. Compared with the thermal biasing method, this method would be more promising in large scale array with simple readout. The used NbN HEB has an excellent performance as heterodyne detector with the double sideband noise temperature (TN) of 403 K working at 4.2 K and 0.65 THz. As a result, the noise equivalent power of 1.5 pW/Hz1/2 and the response time of 64 ps are obtained for the direct detectors based on the NbN HEBs and working at 4.2 K and 0.65 THz.

Low-noise integrated balanced SIS mixer for 787–950 GHz

We developed a low-noise, compact, balanced superconductor–insulator–superconductor (SIS) mixer, operating in the 787–950 GHz radio frequency range. A waveguide mixer block was designed to integrate all the key components, such as a radio frequency (RF) 90° hybrid coupler, two identical SIS mixer chips, bias-tees, and an intermediate frequency power-combiner. The RF waveguide 90° hybrid coupler consists of branch lines with wide slots optimized by numerical simulation, for ease of fabrication. The balanced mixer was installed into a cartridge type receiver, originally developed for the Atacama Large Millimeter/submillimeter Array Band 10 (787–950 GHz). The receiver demonstrated double sideband noise temperatures of approximately 200 K for most of the band, without any correction for loss in front of the receiver. The local oscillator noise rejection ratio was estimated to be more than 15 dB within the measured frequency range.