RF Frequency Range Research Articles

INCAPE23-A Fully Differential Active Inductor with Cascode Current Mirror Using 0.18-um Technology for RF Frequency

This paper introduces a fully differential CMOS active inductor integrated with a cascoded current mirror, tailored for applications within the RF frequency range. The active inductor design is meticulously realized using CMOS 0.18-µm technology. The circuit implementation comprises a fully differential cross-coupled pair of transistors, strategically employed to impart negative feedback, thereby enhancing the quality factor (Q). The cascoded current mirror functions as a pivotal biasing component, facilitating control over the current source to modulate negative feedback and Q factor tuning. Simultaneously, two resistors integrated into the differential structure are crucial in managing the frequency spectrum. Simulation results substantiate a Q factor of 16k, coupled with an inductance of 14 nH, prominently achieved at 3 GHz frequency. Additionally, the objective of achieving a robust Q factor at 3.5 GHz, amounting to 500, is successfully realized. Noteworthy is the adaptability in achieving a frequency range spanning 2 GHz to 3.6 GHz by manipulating resistor values. Furthermore, the study observes that manipulation of supply voltage and current source enables the tuning of Q factor values from 70 to 16k. A performance assessment, juxtaposed with previously published works, underscores the viability of the proposed active inductor for applications within the gigahertz frequency range of RF.

Numerical Simulation of the Dynamics of RF Capacitive Discharge in Carbon Dioxide

In this research, the one-dimensional fluid code SIGLO-rf was used to study the internal parameters of RF capacitive discharge in carbon dioxide, focusing mainly on time-averaged and spatio-temporal distributions of discharge parameters. With the help of this code, in the range of distances between electrodes d = 0.04 – 8 cm, RF frequencies f = 3.89 – 67.8 MHz, and values of carbon dioxide pressure p = 0.1 – 9.9 Torr, averaged over the RF period axial profiles of the density of electrons, positive and negative ions were calculated as well as potential and electric field strength. It is shown that the discharge plasma in CO2 contains electrons, positive ions, as well as negative ions. The negative ions of atomic oxygen are formed by the dissociative attachment of electrons to CO2 molecules. Studies of the spatio-temporal dynamics of plasma parameters (electron density, potential and electric field strength, as well as ionization and attachment rates) in RF capacitive discharge in CO2 showed that during half of the RF period, 1 to 3 ionization bursts are usually observed. They correspond to stochastic heating in the near-electrode sheath and the formation of passive and active double layers near the sheath boundaries. The passive double layer appears in the cathode phase and maintains the discharge plasma. The active layer is formed in the anodic phase and ensures a balance of positive and negative charges escaping to the electrode during the RF period. It was found that when the conditions pd = 2 Torr cm and fd = 27.12 MHz cm are met simultaneously, during half of the RF period, 4 intense ionization peaks are observed: resulting from stochastic heating, passive, active, and additional (auxiliary) double layers. The auxiliary double layer helps bring electrons to the surface of the temporary anode and occurs near its surface inside the near-electrode sheath. Using the similarity law, the conditions for the existence of these 4 ionization peaks in a wide range of RF frequencies, carbon dioxide pressures, and distances between electrodes were verified.

Ion transmission in an electrospray ionization-mass spectrometry interface using an S-lens.

We present the design and performance of an in-house built electrospray ionization-mass spectrometry (ESI-MS) interface equipped with an S-lens ion guide. The ion source was designed specifically for our ion beam experiments to investigate the chemical reactivity and deposition of the clusters and nanoparticles. It includes standard ESI-MS interface components, such as nanoelectrospray, ion transfer capillary, and the S-lens. A custom design enables systematic optimization of all relevant factors influencing ion formation and transfer through the interface. By varying the ESI voltage and flow rate, we determined the optimal operating conditions for selected silica emitters. A comparison of the pulled silica emitters with different tip inner diameters reveals that the total ion current is highest for the largest tip, whereas a tip with the smallest diameter exhibited the highest transmission efficiency through the ESI-MS interface. Ion transmission through the transfer capillary is strongly limited by its length, but the loss of ions can be reduced by increasing the capillary voltage and temperature. The S-lens was characterized over a wide range of RF frequencies and amplitudes. Maximum ion current was detected at RF amplitudes greater than 50 V peak-to-peak (p/p) and frequencies above 750 kHz, with a stable ion transmission region of about 20%. A factor of 2.6 increase in total ion current is observed for 650 kHz as RF amplitudes reach 400 V p/p. Higher RF amplitudes also focus the ions into a narrow beam, which mitigates their losses when passing through the ion guide.

Performance Comparison Of Three Antennas With Passive Reflecting Walls For Wireless Power Transmission

This paper presents a novel wireless power transmission system through reflecting walls for enhancing received signal strength. The study has been conducted with an objective to achieve a novel system for the energy harvesting and subsequent wireless power transmission for mobile phone charging applications. The work is carried out at the well-known RF frequency range from 469.5 MHz to 773.5 MHz. We have employed three different antennas for the proposed system. Multiple changes in antenna orientations have also been accounted for including azimuthal variations. The results show substantial enhancement in the received signal strength (RSS) due to use of these reflecting walls

ICRF heating schemes for the HL-2M tokamak

The HL-2M tokamak is a new medium-sized tokamak at SouthWestern Institute of Physics. Two of its key missions are to achieve 10 keV ion temperature and investigate the behavior of energetic particles relevant to burning plasmas. A 6 MW ion cyclotron range of frequencies (ICRF) heating power is embedded in the next upgrade program of HL-2M. In order to facilitate the engineering design of the ICRF system, this paper analyses the main ICRF heating schemes for HL-2M, in terms of ion heating and energetic ion generation in particular. D(H) minority heating and the 2nd harmonic D will act as the main ion heating schemes, for which the optimal RF frequency range 27–33 MHz, antenna parallel wavenumber k // ∼ 8 m−1 are proposed and strong single pass absorption is expected under typical HL-2M plasma parameters. Full wave simulations carried out via TORIC/steady-state Fokker–Planck quasilinear solver and TRANSP codes suggest that by adopting three ion scheme or synergetic heating on neutral beam injection D ions by the 2nd harmonic D, energetic ions with energy at MeV level can be produced. This study shows that ICRF heating could play significant roles in ion heating, energetic ion generation in HL-2M.

Virtual-carrier-assisted 12 Gb/s 64QAM millimeter-wave signal transmission at 30 GHz using a 4-bit digital-to-analog converter.

We propose and experimentally demonstrate a radio-frequency digital resolution enhancer (RF-DRE) to mitigate the quantization noise of the RF signal induced by the low-resolution digital-to-analog converter (DAC) in the virtual-carrier-assisted millimeter-wave (mm-wave) signal transmission system. By introducing a bandpass filter (BPF) as the reference for the RF-DRE algorithm, we can design the quantization noise and shape its spectrum inversely to the bandpass filter. By these means, the quantization noise in the target RF frequency range can be effectively mitigated. In the simulation, the bit error rate (BER) of a 4-bit DAC-quantized 16 Gb/s 256QAM signal at 30 GHz is improved from 3.36e-2 to 7.43e-3 by using the RF-DRE. In our experiment, 30 GHz virtual-carrier-assisted mm-wave transmission of 12 Gb/s 64QAM signals over 25 km of standard signal mode fiber (SSMF) is realized. By using the RF-DRE, the BER of a 4-bit DAC-quantized signal can be improved from 6.88e-3 to 1.49e-3, and a 5-bit DAC exhibits a similar performance to an 8-bit DAC without the RF-DRE. Therefore, low-resolution and low-cost DACs can be used for mm-wave signal generation with the help of the proposed RF-DRE.

Parasitic-Aware Simulation-Based Optimization Design Tool for Current Steering VGAs

Designing millimeter-wave variable gain amplifiers (VGAs) is very challenging owing to the parasitic effects of the interconnects of both active and passive devices. An automated parasitic-aware optimization RF design tool is proposed in this paper to address this challenge. The proposed tool considers the parasitic effects prior to layout. It employs a knowledge-aware optimization technique. The augmentation between parasitic-aware and knowledge-aware techniques speeds up the design process and leads to a design as close to the final design after finalizing the layout. The proposed tool gives limitless and guaranteed converged solutions in a wide range of RF frequencies. A four-bits current steering VGA design is used as a validation of the tool. The tool is tested on three different frequencies using the 65 nm-technology node. The three tested frequencies (7, 10, and 13 GHz) show a root mean square gain error at approximately 0.1 dB and a phase variation at approximately 3.5° within a 16-dB gain control range. To our knowledge, it is the first reported automated design tool for a current steering VGA.

High-power UTC-photodiodes for an optically pumped subharmonic terahertz receiver.

In this work, we present an optically subharmonic pumped WR3-mixer for enabling photonic coherent frequency-domain terahertz (THz) imaging and spectroscopy systems in the future. The studied mixer operates within the upper range of the WR3-band from 270 GHz to 320 GHz. High-power uni-travelling carrier photodiodes (UTC-PDs) are developed for providing the subharmonic local oscillator (LO) signal within the corresponding WR6-band in the range between 135 GHz and 160 GHz. The proposed THz mixer module consists of a gallium arsenide (GaAs)-based low barrier Schottky diodes (LBSDs) chip and an indium phosphide (InP)-based UTC-PD chip. For integrating the UTC-PD with the WR6 at the mixer's LO input, an E-plane transition and a stepped-impedance microstrip line low pass filter (MSL-LPF) are developed and monolithically integrated with the UTC-PD chip on a 100 µm thick InP substrate. The E-plane transition converts the quasi-TEM mode of the grounded coplanar waveguide (GCPW) to the dominant TE10 mode of the WR6 and matches the GCPW's impedance with the WR6's impedance. According to full-wave EM simulations, the transition exhibits a 1 dB bandwidth (BW) of more than 30 GHz (138.8-172.1 GHz) with a corresponding return loss (RL) better than 10 dB, whereas the minimum insertion loss (IL) is 0.65 dB at a frequency of 150 GHz. Experimentally, the 1 dB BW of the fabricated transition is found to be between 140 GHz and 170 GHz, which confirms the numerical results. The minimum measured IL is 2.94 dB, i.e., about 2 dB larger than the simulated value. In order to achieve the required LO power for successfully pumping the mixer in a direct approach (i.e., without an additional LO amplifier), the design of the epitaxial system of the UTC-PD is optimized to provide a high output power within the WR6-band (110-170 GHz). Experimentally, at 150 GHz, the output power of the fabricated UTC-PD chip is measured to be +3.38 dBm at a photocurrent of 21 mA. To our knowledge, this is the highest output power ever achieved from a UTC-PD at 150 GHz. Finally, the developed high-power UTC-PDs are used as LO source to pump the subharmonic WR3-mixer. Experimentally, the conversion loss (CL) is determined in dependency of the LO power levels within the RF frequency range between 271 GHz and 321 GHz for a fixed IF at 1 GHz. The achieved results have revealed an inverse relation between the CL and LO power level, where the average minimum CL of 16.8 dB is achieved at the highest applied LO power level, corresponding to a photocurrent of 10 mA. This CL figure is promising and is expected to reach the CL of electronically pumped and commercially available THz mixers (∼12 dB) after packaging the LO source with the mixer. Furthermore, an average CL of 17.2 dB is measured at a fixed LO frequency of 150 GHz and a tuned RF frequency between 301 GHz and 310 GHz, i.e., IF between 1 GHz and 10 GHz.

Numerical Investigation of Signal Launch Imperfections for Edge Mount RF Connectors

In this paper, common practice RF design guidelines for SMA edge mount connectors are investigated in terms of numerical simulations and VNA measurements. These guidelines are used in a variety of applications for coaxial-to-planar interfaces but often do not provide information regarding the physical origins of increased insertion and transmission losses. The presented results in this work focus on different RF PCB design features and their impact on electromagnetic field distributions in the launching zone. The presented investigations should raise awareness on the issue of electromagnetic field resonances occurring in the RF frequency range and assist PCB design engineers to identify potential issues occurring at an coaxial-to-planar interface. The investigated PCB features facilitate a high performance RF PCB design up to a frequency of 26 GHz.

Broadband RCN-based RF-rectifier with a large range of power for harvesting ambient wireless energy

In this paper, a broadband RF-rectifier with a wide scale of RF input power levels, using FR-4 substrate, is proposed. A wideband resistance compression network (RCN) is applied to achieve the unique RF-rectifier design approach. The method improves the matching performance of the circuit over a broader range of the available input RF signals and frequency. The RF-rectifier circuit is configured in two sections. The two sections are configured using a modified L-section matching network (MN) through a series impedance transformer (ITx). A wideband RCN integrates the two RF-rectifier segments to a 50 Ω transmission line (TL). The design provides a wider span of accessible RF power from −15 to 15 dBm via a 2 kΩ load terminal. The proposed RF-rectifier achieved a simulated and measured fractional percentage bandwidth (FBW) of 38.5% and 38% from 1.780 to 2.620 GHz and 1.780 to 2.610 GHz, respectively. The maximum measured RF-to-DC PCE and output DC voltage (Vdc) realized by the proposed RF harvester are 75.5% and 3.2 V, respectively. The design also reached a high PCE of 88.25% and 15.10%, respectively, from the quad-tone signals at 10 and −20 dBm RF input power. The proposed RF-rectifier’s ambient evaluation produces a Vdc of 0.322 V and also activated a low-power bq25504-674 evaluation module (EVM) at 0.682 V.

A V-Band Integrated Receiver Front-End Based on 0.15 μm GaAs pHEMT Process for Passive Millimeter-Wave Imaging

The design, analysis, implementation and measurement of an integrated V-band receiver front-end based on 0.15 μm GaAs pHEMT process are presented in this paper. The front-end chip uses the super-heterodyne topology which consists of a low noise amplifier, an image reject mixer, and a multiply-by-four (×4) LO chain. In order to minimize the power consumed by LO chain, an active single-ended mixer is designed which requires extremely low LO power of -5 dBm. Meanwhile, the effect of signal coupling in the integrated chip is analyzed and solutions are proposed. By introducing appropriate filters into the circuit and optimizing the overall layout, the imbalance of in-phase and quadrature signals caused by unwanted coupling can be effectively mitigated, thus enhancing the image rejection of the chip. Probe and module tests are applied to the receiver front-end, and the measurement results reveal that the chip achieves -3 ± 0.7 dB conversion gain, 7 dB noise figure and more than 25 dB image rejection ratio in the RF frequency range of 52-56 GHz. Only one supply voltage of 3 V is required for the chip, and total power consumption is 312 mW. Moreover, with a continuously adjustable phase control of 360° and very broadband IF characteristics, the front-end chip is suitable for passive millimeter-wave imaging applications.

Development of mock-up Ion cyclotron resonance heating system with a new algorithmic approach for automatic impedance matching

This paper presents the development of a mock-up Ion Cyclotron Resonance Heating (ICRH) system along with a new algorithmic approach for fast automatic impedance matching. The mock-up is developed for low power (few watts) and frequency (182.5 MHz) i.e. five times the ICRH frequency of SST-1. The size of the mock-up is considerably reduced to be fit on the test bench using it. The main objective of the work is to develop different matching approaches in order to get the optimum speed of matching. Reducing the size of the mock-up allows frequent implementation and testing of new algorithms which is generally difficult to implement in the real system of tokamak because of its size and complexity. The system consists of indigenously developed components such as 3 dB hybrid coupler, 20 dB directional coupler, tapped transmission line, rigid coaxial stub tuners, line stretcher, service stub, RF antenna, movable water tank based load. The developed system is capable of automatically match any arbitrary load in the range, (35–260)Ω, resistive + (-j25 to +j220)Ω, reactive or VSWR in the range 1.5–4.0 within 200 ms. The matching system also consists of power detectors which automatically sense the forward and reflected power using coupler and the feedback controlled moving coaxial stubs, line stretchers respond as per developed algorithms. The matching algorithm incorporates the various matching steps based on VSWR which have been interpreted for the controller program to control the devices used in the matching network. The developed system is tested using an RF antenna facing the movable saltwater tank that emulates the plasma-like loading behavior. The developed setup is also useful for various high power RF applications like RF heating, sputtering, plasma generation, RADAR, etc. in the RF frequency range.

Realization of LNA and Mixer Using CMOS 0.18μm Technology for 3.1 to 10.6 GHz

In this paper, low noise amplifier and mixer circuits are realized using 0.18μm CMOS technology in the frequency range of 3.1 to 10.6 GHz. LNA circuit uses the cascade topology with source degeneration technique, which help in reducing the non-linearity in the circuit. The current reuse topology is used to decrease the biasing voltage and hence to decrease the power consumption in the circuit. Realized circuit simulated in 0.18μm technology and various results shows highest gain S21 is 19.982dB and has the positive value in the entire frequency band, minimum NFmin is 1.270dB occurs at 1.27GHz and the highest NFmin is 3.4dB. S11 i.e. input reflection coefficient is -31.670dB and it is negative throughout the entire frequency range while the reflection at output port is report to be -7.449 dB. The resistive feedback topology helps in getting the flat gain in the frequency. Mixer circuit is also realize in 0.18μm CMOS technology, which uses current bleeding topology. Transformer help in converting the single ended signal into differential format. Maximum value of gain is 6.584dB, gain is positive in the entire RF frequency range, S11 i.e. the reflection at port1, which give the negative values in the entire frequency band, simulation of S12 i.e. leakage between the port 1 and 2 has negative values in the entire frequency band means proper isolation between the ports. The future work can the realization of the superheterodyne receiver in UWB band.

RESEARCH ON A MAGNETIC FIELD SENSOR WITH A FREQUENCY OUTPUT SIGNAL BASED ON A TUNNEL-RESONANCE DIODE

Based on the consideration of physical processes in a tunnel-resonant diode under the action of a magnetic field, the construction of an autogenerating magnetic field sensor with a frequency output signal is proposed. The use of devices with negative differential resistance makes it possible to significantly simplify the design of magnetic field sensors in the entire RF frequency range. Depending on the operating modes of the sensor, an output signal can be obtained in the form of harmonic oscillations, as well as in the form of pulse oscillations of a special form.
 The study of the characteristics of the magnetic field sensor is based on the complete equivalent circuit of the tunnel-resonant diode. The equivalent circuit takes into account both the capacitive and inductive properties of the tunneling resonant diode. The inductive component exists under any operating conditions, as a result of the fact that the current flowing through the device is always lagging behind the voltage that caused it, which corresponds to the inductive response of a tunnel-resonant diode.

A 0.7–5.7 GHz Reconfigurable MIMO Receiver Architecture for Analog Spatial Notch Filtering Using Orthogonal Beamforming

A highly reconfigurable direct-conversion software-defined multiple-input multiple-output (MIMO) receiver with four RF inputs and four I/Q baseband outputs is proposed. It allows for digital MIMO but also analog interference rejection by spatial notch filtering through four flexible and simultaneous orthogonal beams. A segmented constant-Gm vector modulator (VM) with improved interference tolerance and wide RF frequency range targeting the sub-6-GHz bands is proposed. It exploits current-domain beamforming before $I$ – $V$ conversion by transimpedance amplifiers. A 0.7–5.7-GHz 22-nm fully depleted silicon-on-insulator (FD-SOI) prototype chip achieves >29 dB spatial filtering for a single notch and an ultrawideband 20-dB notch suppression bandwidth of 2.3 GHz at broadside excitation at an local oscillator (LO) frequency of 2.5 GHz. In the notches, an IIP3 of +16 dBm and B1dB of −11.5 dBm at a 41-dB gain is achieved, improving IIP3 and B1dB by 35 and 27 dB, respectively, by spatial filtering. A single-element noise figure (NF) of 5.5–7 dB is achieved on the VM constellation corners, degrading about 2 dB on the points nearby the biggest circle fitting into a square constellation. However, sub-3-dB system NF is potentially achievable, taking into account up to 6-dB improvement by the four-element beamforming. Given both gain and phase control provided by the VM, spatial patterns with up to three independent nulls can be synthesized with the four-element antenna array. The chip of 0.52 mm2 active area consumes 77–139 mW at an LO-frequency of 0.7–5.7 GHz from a 0.8-V supply.

Design of reconfigurable antenna by capacitive type RF MEMS switch for 5G applications

This paper presents the design and simulation of RF-MEMS shunt switch and microstrip patch antenna for reconfigurability and high-frequency applications. Here, the RF-MEMS capacitive switch is designed to establish communication between the main and assistant patches of the antenna, which controls the wavelength of the propagating signal. The performance of the switch has been analyzed at RF frequency range and also reconfigurability in the frequency of antenna at four different conditions (by the combination of two switches) is simulating by using COMSOL and HFSS tools. The operating voltage of the proposed switch is 12 V with a quality factor of 0.3. The capacitance ratio and switching time are 12.72 and 12.06 µs, and it is obtained at the resonant 34.6 kHz. The switch shows the good insertion loss of − 0.009 dB, reflection and isolation losses are − 59 dB, − 36.5 dB at the 39 GHz frequency. The proposed switch is integrated with the patch antenna and it is invented to achieve a resonant frequency of 39 GHz by operating four conditions. The device shows the shift in frequency as 4 GHz, it is recognized from condition 1 to condition 2 and 3 and 10 GHz shift in condition 4. Finally, the proposed device can be useful in space technology and high frequency applications (5G).

Triply resonant coupled-cavity electro-optic modulators for RF to optical signal conversion.

We propose an on-chip triply resonant electro-optic modulator architecture for RF-to-optical signal conversion and provide a detailed theoretical analysis of the optimal "circuit-level" device geometries and their performance limits. The designs maximize the RF-optical conversion efficiency through simultaneous resonant enhancement of the RF drive signal, a continuous-wave (CW) optical pump, and the generated optical sideband. The optical pump and sideband are resonantly enhanced in respective supermodes of a two-coupled-cavity optical resonator system, while the RF signal can be enhanced in addition by an LC circuit formed by capacitances of the optical resonator active regions and (integrated) matching inductors. We show that such designs can offer 15-50 dB improvement in conversion efficiency over conventional microring modulators. In the proposed configurations, the photon lifetime (resonance linewidth) limits the instantaneous RF bandwidth of the electro-optic response but does not limit its central RF frequency. The latter is set by the coupling strength between the two coupled cavities and is not subject to the photon lifetime constraint inherent to conventional singly resonant microring modulators. This feature enables efficient operation at high RF carrier frequencies without a reduction in efficiency commonly associated with the photon lifetime limit and accounts for 10-30 dB of the total improvement. Two optical configurations of the modulator are proposed: a "basic" configuration with equal Q-factors in both supermodes, most suitable for narrowband RF signals, and a "generalized" configuration with independently tailored supermode Q-factors that supports a wider instantaneous bandwidth. A second significant 5-20 dB gain in modulation efficiency is expected from RF drive signal enhancement by integrated LC resonant matching, leading to the total expected improvement of 15-50 dB. Previously studied triply-resonant modulators, with coupled longitudinal [across the free spectral range (FSR)] modes, have large resonant mode volume for typical RF frequencies, which limits the interaction between the optical and RF fields. In contrast, the proposed modulators support maximally tightly confined resonant modes, with strong coupling between the mode fields, which increases and maintains high device efficiency across a range of RF frequencies. The proposed modulator architecture is compact, efficient, capable of modulation at high RF carrier frequencies and can be applied to any cavity design or modulation mechanism. It is also well suited to moderate Q, including silicon, implementations, and may be enabling for future CMOS RF-electronic-photonic systems on chip.

An Innovative Joint-Injection Mixer With Broadband If and RF for Advanced Heterodyne Receivers of Millimeter-Wave Astronomy

An innovative mixing unit of the proposed mixer named joint-injection-mixer (JIM) features both wide IF and RF bandwidths (BWs) for next-generation advanced heterodyne receivers of millimeter-wave astronomy. This proposed mixer demonstrates an RF frequency range from 60 to 148 GHz and an IF frequency range from dc to 36 GHz. The dc power consumption of the JIM mixer is 2 mW with LO driving power of 0 dBm. All the measured results are under 0-dBm LO power. The conversion gain (CG) of the JIM mixer is from −8 to −14 dB. The JIM mixer in this work is implemented for fundamental mixing as downconversion. By utilizing the proposed modified Marchand balun with ultrabroad BW, the LO-to-RF isolation of the JIM mixer achieves better than 40 dB from 60 to 140 GHz. The fabricated process for the JIM mixer is the 40-nm CMOS process. The chip sizes, excluding and including pads, are 0.144 and 0.22 mm2, respectively. The proposed JIM mixer features the state-of-the-art mixer with the widest IF BW compared with all the prior works. Compared with the present capability of world-leading receivers for radio astronomy, the 36-GHz IF BW of the mixer in this work can construct a next-generation receiver for astronomy to provide received data rate by at least three times.

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.

Capacitively coupled radio-frequency discharge in alpha-mode as a variable capacitor

In many cases, the capacitance of a plasma discharge is determined by the sheath capacitance, and therefore controlling the sheath thickness can result in a novel plasma-tunable capacitor. In this work, experiments were conducted with capacitively-coupled RF discharge in the alpha regime using parallel-plate electrode geometry in air at 1 Torr with an RF amplifier operating at a constant voltage in a wide range of frequencies, 20–120 MHz. The impedance characteristics and the sheath and plasma parameters were inferred from the current and voltage measurements supplemented with optical imaging. The experimental data show that the sheath thickness is approximately inversely proportional to the excitation RF frequency, so that the capacitance is proportional to the frequency, in agreement with a simple theory. In applications, tuning the sheath thickness by varying the excitation RF frequency could be used to control the impedance variation in a different range of probing RF frequencies, including control of the transition from capacitive to inductive behaviour.