Diode Mixer Research Articles

Analysis of diode mixers using the method of node potentials in generalized matrix form in the frequency domain. Part 2. Isolation between ports, miscondition effect, noise level

A method for theoretical analysis of “input-output” and “local oscillator-output” decouplings of three types of diode frequency converters is presented: balanced, double balanced, triple balanced. For two operating modes of the local oscillator – “non-intensive” and “intensive” – the dependences of the “input-output” decoupling of the balanced mixer on the load conductivity and on the amplitude of the local oscillator voltage were obtained. Theoretical analysis and modeling were carried out. It is shown that the error between the calculated results and the simulation results does not exceed 3 dB. Expressions are obtained for errors introduced by the technological spread of diode parameters, which make it possible to estimate the maximum achievable values of the mixer characteristics (transmission coefficient and port isolation). A method for analyzing the noise properties of mixers is presented, the output noise spectra are calculated for each of the circuit elements (input resistance, diodes and output resistance), and analytical expressions for noise coefficients are obtained. Theoretical noise figure estimates are confirmed by simulation results with an accuracy of 1 dB.

Sensitivity evaluation of optical receiver mixers

In optical receivers for realisation of procedures of heterodyning of a signal, both at a stage of formation, and at reception, as a rule, diodes are used. At the same time diodes, being electronic devices, are characterised by internal noises, which limit the sensitivity of reception. The nature of internal noise of electronic devices is determined by thermal processes and shot effect, which in their turn are determined not only by the ambient background temperature, but also by the frequency of received radiations. To present the results of estimation of the threshold sensitivity of diode mixers in heterodyning paths of optical receivers. Results are presented on the development of an approach to sensitivity estimation of heterodyne receiver mixer estimation. Estimation expressions for calculating the internal noise level of an optical mixer are obtained. The approach of shot noise estimation characterising the threshold sensitivity from the position of noise temperature is proposed. Simplified expressions of dependence of threshold sensitivity as a function of radiation frequency at a given temperature are obtained. Noise values in terms of temperature for different frequencies are calculated. A practical method of measuring the noise temperature, which characterises the sensitivity of reception, based on measuring the output voltage when receiving signals from sources with known temperatures of emitters, is substantiated. The values of the signal-to-noise ratio of the threshold sensitivity for different frequency ranges are presented. The obtained analytical expressions allow us to conclude that the rational solution is the choice of the frequency range in the region of 0.1…1 THz, because it is characterised by a relatively low noise temperature, but at the same time it is able to provide a high speed of message transmission.

Phase Locking of a THz QC-VECSEL to a Microwave Reference

High resolution frequency study and phase-locking have been performed on a terahertz quantum-cascade vertical-external-cavity surface-emitting-laser operating around 2.5 THz. A subharmonic diode mixer is used to down convert the THz signal to a 100 MHz intermediate frequency that is phase locked to a stable 100 MHz microwave reference. Between 90-95% of the QC-VECSEL signal is locked within 2 Hz of the multiplied RF reference, and amplitude fluctuations on the order of 1-10% are observed, depending on the bias point of the QC-VECSEL. The bandwidth of the locking loop is ∼1 MHz. Many noise peaks in the IF signal are observed, likely corresponding to mechanical resonances in the 10 Hz-10 kHz. These peaks are generally -30 to -60 dB below the main tone, and are below the phase noise level of the multiplied RF reference which ultimately limits the phase noise of the locked QC-VECSEL.

Optical injection locking of a THz quantum-cascade VECSEL with an electronic source.

Optical injection locking of a metasurface quantum-cascade (QC) vertical-external-cavity surface-emitting laser (VECSEL) is demonstrated at 2.5 THz using a Schottky diode frequency multiplier chain as the injection source. The spectral properties of the source are transferred to the laser output with a locked linewidth of ∼1 Hz, as measured by a separate subharmonic diode mixer, and a locking bandwidth of ∼300 MHz is achieved. The large locking range is enabled by the microwatt power levels available from modern diode multipliers. The interplay between the injected signal and feedback from external reflections is studied and demonstrated to increase or decrease the locking bandwidth relative to the classic locking range depending on the phase of the feedback.

Optical design and synthetic analysis of the electron cyclotron emission imaging diagnostic of HL-2M tokamak

The electron cyclotron emission imaging (ECEI) diagnostic is a powerful tool to study the MHD and turbulent transport in magnetically confined fusion plasmas. In this work, the optical system including the local oscillator (LO) coupling and radio frequency (RF) receiving optics, has been designed and analyzed for the HL-2M ECEI diagnostic. The LO optics can illuminate the antenna array and drive the mixer diode to work efficiently, with more than 36% of the beam intensity for the channels which probe the plasma edge relative to those of channels which probe the plasma core. The RF optics aims at guiding the plasma emission signal to the antenna array. To meet different physical requirements, three types of field of view have been achieved for the plasma imaging, with zoom factors of around 1, 1.5 and 2, respectively. The focal surfaces are almost flat, with a maximum off-mapping (defined as the radial distance between the beam waists of the lower-/uppermost antennas and electron cyclotron emission layer) less than 2.5 cm, which can match the electron cyclotron emission layer quite well and suppress the image distortion in the plasma edge region. The impact of possible vibrations and installation error on the focal plane has been evaluated. In addition, the predefined MHD and turbulence perturbations are well reproduced by combining the optical simulation results and synthetic ECEI modeling, which further verifies the good performance of the RF optics.

Silicon Micromachined Waveguide Circuit for a 2 THz Schottky Receiver: Progress and Challenges

Space instruments that operate in the THz range can enable unique measurements for a better understanding of the chemical and physical processes taking place in our Universe. One such application of this technology is a compact 2.06 THz receiver that can measure the ionized oxygen line to determine wind velocity in Earth's upper atmosphere. Metal machined waveguide circuits have long been utilized to build and demonstrate functional receivers in the submillimeter-wave range. However, as the operational frequency is increased, extremely challenging requirements are placed on metal machining in terms of the required precision, surface roughness, and alignment tolerance. This work describes the design and implementation of the first-of-its-kind, vertically-integrated, 2-THz Schottky diode mixer using precise silicon micromachine technology. A traditional e-plane split waveguide package is re-designed to utilize the three-dimensional (3-D) capability of stacking silicon micromachined parts. The silicon microfabrication process has been optimized to produce smooth and precise features for packaging a 2 THz subharmonic GaAs Schottky diode mixer, providing surface roughness better than 1-micron rms with less than 5% variation on critical dimensions. The subharmonic mixer and a fully solid-state local oscillator (LO) chain is currently being implemented to validate silicon micromachining for THz packaging. The impact of micromachining variation on mixer performance is explored through simulations over a range of dimensions on the most sensitive regions of the Si module.

TeraHertz desorption emission spectroscopy (THz DES) of space relevant ices

ABSTRACT We present an experimental instrument that performs laboratory-based gas-phase Terahertz Desorption Emission Spectroscopy (THz-DES) experiments in support of astrochemistry. The measurement system combines a terahertz heterodyne radiometer that uses room temperature semiconductor mixer diode technology previously developed for the purposes of Earth observation, with a high-vacuum desorption gas cell and high-speed digital sampling circuitry to enable high spectral and temporal resolution spectroscopy of molecular species with thermal discrimination. During use, molecules are condensed on to a liquid nitrogen cooled metal finger to emulate ice structures that may be present in space. Following deposition, thermal desorption is controlled and initiated by means of a heater and monitored via a temperature sensor. The ‘rest frequency’ spectral signatures of molecules released into the vacuum cell environment are detected by the heterodyne radiometer in real-time and characterized with high spectral resolution. To demonstrate the viability of the instrument, we have studied Nitrous Oxide (N2O). This molecule strongly emits within the terahertz (sub-millimetre wavelength) range and provide a suitable test gas and we compare the results obtained with more traditional techniques such as quadrupole mass spectrometry. The results obtained allow us to fully characterize the measurement method and we discuss its potential use as a laboratory tool in support of astrochemical observations of molecular species in the interstellar medium and the Solar System.

Development of the HCN heterodyne collective scattering system on J-TEXT

A heterodyne collective scattering system has been designed and developed to investigate the turbulent transport of core plasma on J-TEXT. A dual-HCN laser which consists of two separately pumped HCN gas lasers at 337 μm has been developed as the laser source of the scattering system. The intermediate frequency (IF) is ∼1 MHz when there is a 4 μm cavity length difference and capable to maintain stability more than 5 h without manual operation. Detection channels at three different angles (2 ≤ k ⊥ ≤ 12 cm−1) have been installed with Schottky barrier diode mixers of 893 GHz. The sampling frequency of the acquisition system is 6 MHz to observe low-frequency density fluctuations. Initial experimental results have been detected and more results can be expected in future experiments.

Analysis of Diode Mixers Using Nodal Voltage Method in Generalized Matrix Form in Frequency Domain. Part 1: Transfer Function

Analysis of Diode Mixers Using Nodal Voltage Method in Generalized Matrix Form in Frequency Domain. Part 1: Transfer Function

A 3.5-THz, ×6-Harmonic, Single-Ended Schottky Diode Mixer for Frequency Stabilization of Quantum-Cascade Lasers

Efficient and compact frequency converters are essential for frequency stabilization of terahertz sources. In this article, we present a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${3.5}$</tex-math></inline-formula> -THz, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\times 6}$</tex-math></inline-formula> -harmonic, integrated Schottky diode mixer operating at room temperature. The designed frequency converter is based on a single-ended, planar Schottky diode with a submicron anode contact area defined on a suspended 2- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\mu }$</tex-math></inline-formula> m ultra-thin gallium arsenide substrate. The dc-grounded anode pad was combined with the radio frequency E-plane probe, which resulted in an electrically compact circuit. At <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{200}$</tex-math></inline-formula> -MHz intermediate frequency, a mixer conversion loss of about <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{59}$</tex-math></inline-formula> dB is measured resulting in a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${40}$</tex-math></inline-formula> -dB signal-to-noise ratio for phase locking a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${3.5}$</tex-math></inline-formula> -THz quantum-cascade laser. Using a quasi-static diode model combined with electromagnetic simulations, good agreement with the measured results was obtained. Harmonic frequency converters without the need of cryogenic cooling will help in the realization of highly sensitive space and air-borne heterodyne receivers.

A Millimeter-Wave 4th-Harmonic Schottky Diode Mixer with Integrated Local Oscillator

In this paper the design and experimental validation of a fourth-harmonic mixer based on Schottky diodes working around 300 GHz is presented. The main novelty of this work consists in the integration of an MMIC-based local oscillator, working around 75 GHz, and a mixer in the same metallic block housing. A prototype has been characterized using the Y-Factor method and yields a best measured conversion loss and an equivalent noise temperature of 14 dB and 9600 K, respectively. This performance is comparable to the state-of-the-art for this type of mixer.

Harmonic Dual-Band Diode Mixer for the X- and K-Bands

This paper presents a new dual-band diode mixer for the X- and K-bands. The proposed mixer consists of a pair of series-connected diodes and a frequency-dependent delay line that operates at 180° and 360° at the X-band of 10.525 GHz and at the K-band of 24.15 GHz, respectively. Without reconfigurable devices such as switches, the proposed mixer operates as a single-balanced diode mixer at the X-band and a subharmonically pumped antiparallel diode mixer at the K-band simultaneously. The designed circuit was implemented in a hybrid microwave integrated circuit using discretely packaged RF components on a microwave printed circuit board. The measurement results showed conversion losses of 6.5 dB and 16.6 dB at the X- and K-bands, respectively.

Phase Shift and Amplitude Array Measurement System Based on 360° Switched Dual Multiplier Phase Detector

This article presents an amplitude and 360° phase shift array measurement system. The basic cell of the measurement system uses a novel amplitude and phase detector based on switched dual multipliers. The phase shift measurement is characterized using an analog phase detector (mixer), detecting a maximum range of ±90°, and a double multiplication of the input signals, in phase and phase shifted. This method broadens the frequency and amplitude range beyond other solutions that require fulfilling the quadrature condition. This method broadens the frequency and amplitude beyond other solutions requiring fulfilling the quadrature condition or phase and amplitude balance. Thus, it enables to compensate significant phase imbalance in the 90° hybrid or use amplitudes out of the range that ensures the switching operation of mixer diodes. The circuit calibration that allows compensation for errors (amplitude, phase shift, mismatching, etc.) is detailed, and its relation to the required measurement accuracy is discussed. The design can be easily extrapolated to other frequency ranges because it uses commercial RF devices available in a wide frequency range and avoids the need of crossing lines or complex 90° hybrid. A prototype with $3 \times 3$ cells has been built to evaluate various test conditions on $1 \times 3$ cell configurations that show the advantages of the procedure. It should be highlighted that the cell prototype uses devices that will be operating outside the frequency and amplitude ranges recommended by their manufacturers. A calibration from 2.6 to 6 GHz and −15 to −3 dBm was performed to evaluate the measurement errors. An analysis of the isolation between cells and different calibration configurations is performed to analyze the measurement errors. Measurements show compensation of +30°/−25° phase imbalance and 13-dB power lower than mixer manufacturer recommendation.

W-band system-on-chip electron cyclotron emission imaging system on DIII-D.

Monolithic, millimeter-wave "system-on-chip" (SoC) technology has been employed in heterodyne receiver integrated circuit radiometers in a newly developed Electron Cyclotron Emission Imaging (ECEI) system on the DIII-D tokamak for 2D electron temperature profile and fluctuation evolution diagnostics. A prototype module operating in the E-band (72 GHz-80 GHz) was first employed in a 2 × 10 element array that demonstrated significant improvements over the previous quasi-optical Schottky diode mixer arrays during the 2018 operational campaign of the DIII-D tokamak. For compatibility with International Thermonuclear Experimental Reactor relevant scenarios on DIII-D, the SoC ECEI system was upgraded with 20 horn-waveguide receiver modules. Each individual module contains a University of California Davis designed W-band (75 GHz-110 GHz) receiver die that integrates a broadband low noise amplifier, a double balanced down-converting mixer, and a ×4 multiplier on the local oscillator (LO) chain. A ×2 multiplier and two IF amplifiers are packaged and selected to further boost the signal strength and downconvert the signal frequency. The upgraded W-band array exhibits >30 dB additional gain and 20× improvement in noise temperature compared with the previous Schottky diode radio frequency mixer input systems; an internal 8 times multiplier chain is used to bring down the LO frequency below 12 GHz, thereby obviating the need for a large aperture for quasi-optical LO coupling and replacing it with coaxial connectors. Horn-waveguide shielding housing avoids out-of-band noise interference on each individual module. The upgraded ECEI system plays an important role for absolute electron temperature evolution and fluctuation measurements for edge and core region transport physics studies.

Dual Lumped Ports Technique and Its Applications in Modeling of Planar Schottky Diode in THz Band

Micro-coaxial probe technique (MCPT) is widely used in three-dimensional electromagnetic (3-D EM) modeling of planar Schottky barrier diodes (SBDs) for the design of terahertz multipliers and mixers. However, the inconsistency of port numbers between 3-D EM model and intrinsic model of diode has been pended for years due to the lack of alternative internal port techniques. In this paper, after investigating port techniques available for field simulation software, a novel dual lumped ports technique (DLPT) is proposed to replace the MCPT for removing its non-physical grounding requirement, which makes the defined internal ports have definite physical meaning. Moreover, the proposed DLPT possesses higher accuracy than MCPT for the elimination of epitaxial layer penetration and additional consideration of port coupling effect. Detail technical procedures for DLPT are presented for internal double ports implementation. To verify its feasibility and accuracy at terahertz band, a 110 GHz broadband tripler was designed utilizing the proposed DLPT and the measured results agree well with the simulated ones. Furthermore, a series of frequency multipliers designed by MCPT are post-analyzed with the same models derived from DLPT. Finally, a slight discrepancy is observed between MCPT and DLPT, and the latter coincides better with the measured results. All these results indicate that the proposed DLPT is validated to be effective and accurate for the design of diode frequency multipliers and mixers in terahertz region.

Wave Equation-Based Discontinuous Galerkin Time Domain Method for Co-Simulation of Electromagnetics-Circuit Systems

In this article, a hybrid electromagnetic (EM)-circuit solver incorporated with wave equation-based discontinuous Galerkin time domain (DGTD-WE) method is developed to simulate microwave antennas and devices comprised of lumped circuit networks including arbitrary ports and both linear and nonlinear components. The computational domain is divided into two subsystems: one is the distributive part of the model which is modeled by the DGTD-WE method and the other is the lumped circuit networks which are analyzed by a SPICE-like transient circuit solver. In addition, a general impedance transmission boundary condition (ITBC) is introduced for the DGTD-WE method to model the interactions between the EM fields and the circuit networks. With the help of the proposed ITBC, coupling matrices between the two subsystems are small and highly sparse, and thus can be efficiently solved. Moreover, an average evaluation technique for the port voltage has been proposed to obtain a stable solution in the EM-circuit co-simulation. Numerical examples are presented to demonstrate stability, accuracy, and applications which extend the capability of the current DGTD-WE method to model hybrid field-circuit problems. Finally, the proposed method is validated experimentally using a diode mixer.

Forward Scattering Measurement Based on Terahertz Microwave Interferometer on KTX Reversed Field Pinch

Electron density fluctuation has been measured based on the collect forward scattering method using a single-chord microwave interferometer system on the Keda Torus eXperiment (KTX) reversed field pinch. The interferometer system is a heterodyne one with two terahertz solid-state sources with frequency around 650 GHz, and the transmitted beam and forward scattering beam are received simultaneously by a Schottky planar diode mixer with sensitivity about 500 mV/mW. Constrained by the beamwidth and geometry limitation, the measurable wave vector range is $k_{w}\le 5 {\mathrm {cm}}^{-1}$ with a resolution $\Delta k\approx 2.07\,{\mathrm {cm}}^{-1}$ . MHD activities are detected via this forward scattering technique. The results are consistent with other diagnostics, such as the chord averaged electron density, the edge magnetic probe, and high-speed charge-coupled device (CCD) camera.

A coupled-line balun for ultra-wideband single-balanced diode mixer

A multi-section coupled-line balun design for an ultra-wideband diode mixer is presented in this paper. The multi-section coupled-line balun was used to interface with the diode mixer in which it can deliver a good impedance matching between the diode mixer and input/output ports. The mixer design operates with a Local Oscillator (LO) power level of 10 dBm, Radio Frequency (RF) power level of -20 dBm and Intermediate Frequency (IF) of 100 MHz with the balun characteristic of 180° phase shift over UWB frequency (3.1 to 10.6 GHz), the mixer design demonstrated a good conversion loss of -8 to -16 dB over the frequency range from 3.1 to 10.6 GHz. Therefore, the proposed multi-section coupled-line balun for application of UWB mixer showed a good isolation between the mixer’s ports.

Metal–Insulator–Graphene Diode Mixer Based on CVD Graphene-on-Glass

In this letter, we present for the first time a mixer circuit based on Metal–Insulator–Graphene (MIG) diodes fabricated with large-scale monolayer graphene grown by chemical vapor deposition. A small-signal model extracted from the diode physical structure is used together with a large-signal model extracted from the dc characteristics of the MIG diode to build a down-conversion mixer. The measured conversion loss at a local oscillator power ( ${P}_{\text {LO}}$ ) of 5 dBm is lower than 15 dB, while RF-to-IF isolation is 36 dB with an input return loss and RF-to-LO isolation better than 10 dB over the frequency band from 1.7–6 GHz. Promising mixer results in combination with the CVD-based process promote the MIG diode-based mixer to be used in low-power, low-cost, microwave, and millimeter-wave circuit applications.

Wave-Port Technique in Design of Diode Mixers and Multipliers at Low THz Region

In this paper, the port techniques including lumped port, boundary wave-port and internal wave-port for design of the diode mixers and multipliers at low THz region are discussed. A mini-coaxial probe is proposed for exciting the field-polarization-based differential circuits and reducing the discontinuity of boundary wave-port. Then, the equivalent procedure from boundary wave-port to internal wave-port of diode device is demonstrated, which can speed up the simulation by reducing the number of ports of the passive network. And then, a mini-coaxial lead is presented as the simplified diode structure for internal wave-port implementation. Finally, a multiplier, a fundamental mixer and two sub-harmonic mixers at low THz region were designed by using the wave-port technique. The measured results are in good agreement with the simulated ones.