RF Leakage Research Articles

Automatic RF Leakage Cancellation for Improved Remote Vital Sign Detection Using a Low-IF Dual-PLL Radar System

Remote vital sign detection using Doppler radar has gained increasing interest over the years. However, challenges remain in improving radar system sensitivity to extend the detection range. In this article, we analyze noise contributions in a dual-PLL low-IF Doppler radar system and identify RF leakage/coupling as a major component of the system noise floor. This effect results in negligible SNR improvement when the transmit output power is increased beyond a certain threshold. By applying RF leakage/coupling cancellation through phase and magnitude adjustments, we demonstrate significant improvements to radar system performance. Furthermore, we propose and validate an automatic RF leakage cancellation scheme. The proposed technique is shown to achieve a vital-sign-sensing range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4$</tex-math> </inline-formula> m under a very low transmit power of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 31 dBm and with a high confidence level of three beats per minute against the ground truth measured by an oximeter sensor.

Quasi-Physical Equivalent Circuit Model of RF Leakage Current in Substrate Including Temperature Dependence for GaN-HEMT on Si

This article proposes a quasi-physical equivalent circuit model of RF leakage current in the substrate including temperature dependence for GaN-high-electron-mobility transistor (HEMT) on Si. In the proposed model, the effects of electrons and holes near the interface between the buffer layer and the Si substrate are considered to model the RF leakage current. Furthermore, the physical mechanism of the RF leakage current is analyzed using technology computer aided design (TCAD) simulation. Through the analysis, it was found that the RF leakage current increased at a high drain voltage and high temperature; this is because electrons were generated in the inversion layer at the interface between the buffer layer and the Si substrate with a low acceptor concentration. To model the RF leakage current, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C$</tex-math> </inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R$</tex-math> </inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C$</tex-math> </inline-formula> circuit corresponding to the physical structure of GaN-on-Si between the drain and the source terminal was added to Angelov-GaN large-signal model. Moreover, the resistance and capacitance in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C$</tex-math> </inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R$</tex-math> </inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C$</tex-math> </inline-formula> circuit were derived from the physical equation of the electron and hole densities in the Si substrate to consider the temperature and bias dependence of the RF leakage current. Upon the verification of the proposed model, it was proven to accurately reproduce the measurement of the temperature characteristics of the power sweep. The large-signal model with the proposed quasi-physical model of RF leakage current can simulate the degradation of the RF performance due to the extrinsic RF leakage current generated by the electrons and holes in the Si substrate. Moreover, the model also agreed with the measured dependence of large-signal characteristics on the drain electrode width. The proposed model was confirmed to be useful for the design of the transistor and amplifier.

FPGA Implementation of a Linearization System for Wideband Envelope Tracking Power Amplifiers

This article focuses on the implementation of a linearization system for envelope tracking (ET) power amplifiers (PAs) in field-programmable gate array (FPGA). The ET PA linearization system includes a slew-rate reduction envelope generator, a RF leakage cancellation system in the supply envelope path and a baseband <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I - Q$ </tex-math></inline-formula> digital predistorter (DPD). This work targets the implementation of an ET PA linearization system on a radio frequency system-on-chip (RFSoC) device running under a demanding baseband sampling frequency of 614.4 MHz, which allows handling communication signals with up to 200 MHz bandwidth, considering a DPD bandwidth expansion by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3\times $ </tex-math></inline-formula> . The detail of the FPGA implementation is presented to illustrate the trade-off between hardware resources and linearization performance, i.e., adjacent channel power ratio (ACPR) and error vector magnitude (EVM), under different bit configurations for the arithmetic. The power consumption is also evaluated since it is another relevant performance indicator to be considered in the FPGA implementation of the linearization system.

Intelligent MRI Room Design Using Visible Light Communication with Range Augmentation

Radio waves and strong magnetic fields are used by Magnetic Resonance Imaging (MRI) scanners to detect tumours, wounds and visualize detailed images of the human body. Wi-Fi and other medical devices placed in the MRI procedure room produces RF noise in MRI Images. The RF noise is the result of electromagnetic emissions produced by Wi-Fi and other medical devices that interfere with the operation of the MRI scanner. Existing techniques for RF noise mitigation involve RF shielding techniques which induce eddy currents that affect the MRI image quality. RF shielding techniques are complex and lead to RF leakage. VLC (Visible light Communication) is an emerging and efficient technology to avoid RF interference near MRI scanners. Range augmentation with power conservation of the LED is a big challenge in existing VLC systems. The major objective of the proposed work is to develop an intelligent-MRI room design without RF interference using visible light communication and enhance the distance between VLC transmitter and VLC receiver. In this paper, it is proposed to implement VLC using On-Off keying modulation and enhance distance using large active area photodiodes with Automatic Gain Control Circuit (AGC) using software and hardware. The performance of the proposed intelligent MRI-VLC system is analyzed by calculating Bit Error Rate at an inclined distance of 50 cm away from line of sight of the LED. The Experimental results showed that the maximum distance achieved was 400 cm at Bit Error Rate (BER) of 1.5 × 10−5.

A 37-GHz Asymmetric Doherty Power Amplifier With 28-dBm P sat and 32% Back-Off PAE in 0.1-μm GaAs Process

In this article, the analysis, design, and development of a 37-GHz asymmetric Doherty power amplifier (DPA) are presented. In a practical DPA, the main power amplifier (PA) shows nonideal characteristic, which varies the effect of the load modulation. Based on the theoretical analysis, we derive the relationship among the efficiency, power back-off (PBO) level, and the corresponding load impedance in a nonideal load modulation. The result suggests that a Class-AB main PA shows a decreased PBO efficiency during the load modulation. To achieve a good compromise between PBO level and PBO efficiency of the main PA, the load modulation scheme is redesigned in this work. A 2-dB PBO of the main PA is chosen to maintain the high efficiency during the load modulation. An asymmetric DPA topology is employed to compensate the inadequate PBO of the main PA so that a desired 6-dB PBO is achieved. Generally, the RF leakage at the DPA output degrades its performance. To solve this issue, we propose a modified low characteristic impedance DPA output network. The output matching network of the auxiliary PA is particularly designed to enlarge its output impedance. Through these design techniques, the leakage loss is significantly reduced to 0.2 dB, which improves the gain and power-added efficiency (PAE) at PBO. To validate the proposed techniques, a DPA chip is designed and fabricated in a D-mode 0.1- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> GaAs pHEMT process. At 37 GHz, the 1.6 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times1.8$ </tex-math></inline-formula> mm integrated chip exhibits a measured small-signal gain of 15.6 dB and a saturated power ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\mathrm{sat}}$ </tex-math></inline-formula> ) of 28.0 dBm, with an associated 33.2% peak PAE and a 32.0% PAE at 6-dB PBO. To the best of our knowledge, the proposed chip exhibits the state-of-the-art overall performance among DPAs operating around 37 GHz for 5G n260 millimeter-wave (mm-wave) band.

4.2\xa0K sensitivity-tunable radio frequency reflectometry of a physically defined p-channel silicon quantum dot

We demonstrate the measurement of p-channel silicon-on-insulator quantum dots at liquid helium temperatures by using a radio frequency (rf) reflectometry circuit comprising of two independently tunable GaAs varactors. This arrangement allows observing Coulomb diamonds at 4.2 K under nearly best matching condition and optimal signal-to-noise ratio. We also discuss the rf leakage induced by the presence of the large top gate in MOS nanostructures and its consequence on the efficiency of rf-reflectometry. These results open the way to fast and sensitive readout in multi-gate architectures, including multi qubit platforms.

Subharmonic single-balanced LMV with bottom LO injection

This paper proposes a subharmonic single-balanced RF receiver front-end (called LMV) where low noise amplifier is stacked on top of a differential voltage-controlled oscillator (VCO) to re-use the dc bias current. In this subharmonic (SH) LMV, the VCO itself plays the role of the single-balanced subharmonic mixer while generating an LO signal. This bottom LO SH LMV has good LO to IF and LO to RF leakage performances. Also, it can reduce the die size on a chip since it requires only one inductor for the VCO instead of two in the case of top LO LMV.Oscillating at around 2.4 GHz band, the proposed SH LMV is designed using a 65 nm CMOS technology and compared to the top LO SH LMV in terms of phase noise, conversion gain and double sideband noise figure. The SH LMVs consume about 160 μW dc power from a 1-V supply.

A Temperature Stable Amplifier Characteristics of AlGaN/GaN HEMTs on 3C-SiC/Si

A high temperature stable amplifier characteristics for L-band or 2 GHz was studied using AlGaN/GaN high electron mobility transistors (HEMTs) on 3C-SiC/Si substrate. A crack free, high quality AlGaN/GaN heterostructure on a 6-inch Czochralski (Cz)-Si substrate was realized by metal oxide chemical vapor deposition (MOCVD). The epitaxial structure comprises an $8~\mu \text{m}$ thick nitride layer and a $1~\mu \text{m}$ thick 3C-SiC intermediate layer. The fabricated AlGaN/GaN HEMT achieved excellent electron transport characteristics along with a comparable cutoff frequency ( ${f}~_{\text {T}}$ ) of 4.8 GHz for $2~\mu \text{m}$ gate length device. Temperature dependent S-parameter measurement of open pad structures achieved outstanding temperature stability up to $125~^\circ \text{C}$ . Continuous wave power measurements showed a 2 GHz continuous wave power density of 2 W/mm, a maximum power added efficiency (PAE) of 47% along with a linear gain of 17.2 dB for class A amplifier operation. Moreover, at elevated temperature of up to $125~^\circ \text{C}$ , the minimal power performance degradation was mainly attributed to the intrinsic property of the device, thus elimination of RF leakage from the buffer or epitaxial layers at high temperatures was confirmed.

Development of a DC bias structure with reduced RF leakage for suppressing the multipacting effect in the high power coaxial couplers

Coaxial power couplers are being employed for RF power transmission to the low beta superconducting cavities used for proton beam acceleration in the 25 MeV superconducting linear accelerator (linac) demonstration facility of the China Initiative Accelerator Driven System (CiADS) project. However, the operation stability of the coaxial couplers was mainly limited by the multipacting effect, which can be suppressed by applying DC bias voltage between the inner and the outer conductors. In this paper, we found an RF leakage problem that the electromagnetic (EM) field inside the couplers can penetrate the bias capacitor and then propagate along the DC bias cable, thus disturbing the stability of the DC power supply and finally disabling the RF system. Therefore, a simple DC bias “T” transition part has been developed, where the series resistors are introduced to reduce the electromagnetic field propagating along the cable and make the structure intensely stable. The test results indicate that the blocking effect of the resistive solution is better than that of the conventional inductive method. The equivalent circuits of the resistive structure and the inductive structure are established and analyzed. The detailed test and analysis results of the new DC bias structure will be reported.

A compact, dual-polarized patch antenna with improved Tx–Rx isolation for 2.4 GHz single frequency full-duplex applications

AbstractA compact dual-polarized monostatic antenna (single radiator for transmit and receive modes) is presented with differential receive mode operation to achieve excellent interport isolation for 2.4 GHz single frequency full-duplex or in-band full-duplex applications. The presented antenna comprises three ports radiating element (patch) and a simple 3 dB/180o ring hybrid coupler has been utilized for differentially excited receive mode operation. The 3 dB/180o ring hybrid coupler acts as a self-interference cancellation (SIC) circuit for effective suppression of RF leakage from the transmit port to provide very high interport decoupling between transmit and receive ports. A compact antenna structure has been realized by using two-layered printed circuit board through vias interconnections of both receive ports of the antenna with inputs of SIC circuit. The validation model of proposed antenna offers more than 95 dB peak interport isolation. Moreover, the experimentally measured interport isolation is better than 70 dB throughout the antenna's 10 dB return-loss impedance bandwidth (BW) of 50 MHz (2.38–2.43 GHz). Furthermore, the recorded isolation is more than 80 dB in 20 MHz BW. The implemented antenna has good radiation characteristics including nice gain and low cross-polarization levels as endorsed by measurements. Same antenna structure with microstrip-T feeds can provide DC isolated ports with same interport RF isolation performance for active antenna applications. Such antenna with DC interport isolation will avoid the requirements of additional series capacitors on transmit and receive ports of antenna.

A Slotline DC Block for Microwave, Millimeter, and Submillimeter Circuits

DC blocks are used frequently in planar circuits to enable separate dc voltage/current biasing of active components inserted along the transmission lines. In this letter, we present a slotline dc block design where the conductors of the transmission line can be physically broken while allowing the propagation of the RF signal across the discontinuity with negligible insertion loss. The dc block comprises two breaklines with narrow gaps, patterned on the two ground planes of a slotline with each breakline connected to an RF choke. The RF chokes present open circuit nodes that prevent the RF power from leaking into the breaklines gaps. We have fabricated and tested the dc block and demonstrated that the measured performance agrees very well with simulated results. The insertion loss was close to −0.5 dB in the designated range of 12–16 GHz, demonstrating that the RF leakage through the dc block is indeed negligible.

Differential Fed Antenna With High Self-Interference Cancellation for In-Band Full-Duplex Communication System

This paper presents a novel design of high self-interference cancellation (SIC) technique for microstrip antennas. The proposed antenna consists of two closely-spaced orthogonal antennas with differential feeding as SIC circuit so as to achieve high interport isolation between the transmitter and receiver. In order to achieve high RF leakage cancellation, a novel differential feeding network (DFN) is also proposed in this paper, which provides amplitude and out-of-phase imbalances within 0.12 ± 0.03dB and -180 ± 1°, respectively, for the bandwidth of 500 MHz at a center frequency of 2.50 GHz. General analytical design equations are derived for achieving high SIC over the wide bandwidth. For experimental validation, prototypes are designed and fabricated at the center frequency of 2.50 GHz using an FR-4 substrate with dielectric constant of 4.4 and loss tangent of 0.02. A good agreement is observed among the theoretical analysis, and the simulation and measurement results. The first fabricated prototype provides more than 64 dB SIC for the bandwidth of 110 MHz, while the second prototype achieved more than 60 dB SIC for 160 MHz bandwidth. In addition, the SIC of the antenna using the proposed DFN is high over the wideband frequency bandwidth as compared to conventional 180° ring hybrid feeding network. Due to ease of implementation and excellent performances, the proposed antennas have potential application for wideband in-band full duplex systems.

Co‐polarized monostatic antenna with high Tx–Rx isolation for 2.4 GHz single channel full duplex applications

AbstractThis article presents a linear co‐polarized (same polarization for transmit and receive modes), proximity coupled monostatic patch antenna with high port to port RF isolation for 2.4 GHz single channel full duplex (SCFD) wireless applications. The presented proximity coupled monostatic patch antenna deploys differential feeding for receive (Rx) mode to significantly suppress RF leakage from transmit (Tx) port and external single‐tap self‐interference cancellation (SIC) circuit provides additional interport isolation. The measurements for implemented prototype of antenna in lab environment provide around 50 dB Tx–Rx isolation for 50 MHz bandwidth in addition to better than 75 dB peak isolation. Moreover, the deployed single‐tap RF SIC circuit can be used to suppress SI resulted from environmental reflections and 50 MHz SIC bandwidth with 50 dB isolation can be tuned within antenna's 10 dB return loss impedance bandwidth of 150 MHz.

On the Split-Block Realization of Millimeter-Wave Ridge Waveguide Components

A method to reduce RF leakage in split-block fabricated metallic ridged waveguide is presented. By placing a pin wall into the split-block seam, RF leakage and detrimental performance spikes are significantly reduced. Three different split-block double-ridge waveguide components of varying design complexity operating over 18–45-GHz bandwidth are fabricated and measured. It is shown that the addition of the pin wall improves the performance of each component such that results correlate well to simulated models with no split.

Integrated Quasi-Circulator With RF Leakage Cancellation for Full-Duplex Wireless Transceivers

An integrated reconfigurable CMOS quasi-circulator operating at 2.4 GHz is presented. A passive structure delivers transmit power amplifier (PA) output signal to the differential low-noise amplifier (LNA) input as a common-mode signal and simultaneously delivers received signal as a differential-mode signal at the LNA input. The leakage of the PA output signal at the LNA input is reduced in two steps. First, the use of a reconfigurable impedance matching circuit, instead of a fixed 50- $\Omega $ resistance reduces the leakage by compensating the antenna impedance mismatch, and improves transmitter–receiver isolation. Second, a reconfigurable summing stage adds amplitude and phase adjusted PA output signal to LNA output to cancel the residual PA output leakage. Measurement results show that the receiver achieves a reduction of 90 dB for a single tone and more than 50 dB for a QPSK modulated 40-MHz bandwidth transmit signal. The receiver gain is more than 10 dB and the noise figure in the receiver path is 4.5 dB. The reconfigurable quasi-circulator along with the receiver LNA is designed and fabricated on a 130-nm CMOS technology. The cancellation circuitry occupies 0.27 mm2 and consumes 30-mW quiescent power, while the total active area of the chip is 1 mm2, and it consumes 65-mW power.

Double-Differential-Fed, Dual-Polarized Patch Antenna With 90 dB Interport RF Isolation for a 2.4 GHz In-Band Full-Duplex Transceiver

This letter presents a 2.4 GHz, dual-polarized microstrip patch antenna with extremely high interport isolation for a shared antenna architecture-based in-band full-duplex transceiver. The presented antenna configuration is based on four-ports linearly polarized single radiating element with differential feeding for both transmit $(T_{x})$ and receive $(R_{x})$ operation. The double-differential feeding using two identical 3 dB/180° ring hybrid couplers with nice amplitude and phase balance effectively suppresses the interport RF leakage to achieve very high isolation. The prototype of the proposed antenna architecture is implemented using a 1.6 mm thick general-purpose FR-4 substrate. The implemented antenna provides more than 90 and 80 dB interport RF isolation for 20 and 40 MHz bandwidths, respectively, in addition to more than 98 dB port-to-port peak isolation when measured inside an anechoic chamber. To the best of our knowledge, this is the highest amount of RF isolation reported for a single dual-polarized patch antenna.

Low‐power SOI CMOS antenna switch driver circuit with RF leakage suppression and fast switching time

A low-power antenna switch driver circuit with RF leakage suppression and fast switching time is implemented in a 0.25 μm silicon-on-insulator (SOI) CMOS process. It is composed of a three-stage current starved ring oscillator with a clock buffer, a charge pump and a latch-based three-state logic driver. The negative voltage from the charge pump is fed into the latch-based three-state logic driver, and it generates three states of logic level (+VDD, GND and −VDD) according to the decoder signal without any reliability issue. In addition, the proposed three-state logic driver with an optimal negative resistance value reduces the amount of the RF leakage coupling into the charge pump while maintaining its switching time fast. In the measurement, the designed switch driver circuit shows 30 dB of isolation over 100 MHz to 3 GHz frequency range.

RF Control Optimization and Automation for Normal Conducting Linear Accelerators

Normal conducting linear accelerators are widely used in many free-electron laser (FEL) machines all over the world. They normally consist of multiple RF stations either with standing wave cavities (e.g., RF Gun) or with traveling wave accelerating structures working at different frequencies. Low-level radio frequency (LLRF) systems are used to measure the RF fields in cavities or structures and correct the fluctuations in RF fields with pulse-to-pulse feedback controllers. To facilitate the operations of multiple RF stations, the LLRF system should also provide algorithms and procedures to automate the setup, calibration, and optimization of the RF systems. In this paper, several typical algorithms and procedures will be described, such as calibrating the digital-to-analog converters offset to reduce the RF leakage from vector modulator, calibrating the RF signal group delay, and flattening the intrapulse phase distribution with an adaptive feed forward. The algorithms and procedures have been implemented as an LLRF high-level applications (HLAs) software for SwissFEL, which is an FEL machine under commissioning at Paul Scherrer Institut, Switzerland. The architecture of the LLRF HLA software will be introduced, and the test results at SwissFEL will also be described.

A High-Power Waveguide Phase Shifter With Periodic RF Chokes for Subgigawatt Nanopulse Transmission

A high-power handling waveguide phase shifter with a high RF leakage attenuation is proposed at S-band. It uses the periodic RF chokes as a moveable noncontacting short circuit and a compact narrow-wall hybrid coupler in order to improve the RF leakage attenuation and the power handling capacity in low-profile beam-forming networks, respectively. This geometry is attractive, since it does not need a capacitive loading button and a contacting short circuit, which reduce the power handling capacity of the phase shifter. The results shows that the phase shifter could handle the high-power pulse energy of subgigawatt levels, and the phase can be adjustable in a range of 0°–360° over the 0.5-GHz bandwidth for −15-dB return loss in a numerical simulation. In addition, it has a high RF-leakage attenuation of −110 dB, which is a significant improvement compared with that of the single RF choke of −50 dB over the frequency range of 2.7–3.2 GHz.

A 1.9 GHz CMOS High Isolation Absorptive OOK Modulator

This letter presents a high-isolation absorptive 1.9 GHz on-off keying (OOK) modulator in 90 nm CMOS process. The RF leakage-canceling technique is developed to suppress the RF leakage by combining it with its inverse replica at the output. The transform-typed baluns are used for the input and output matching such that the modulator input and output return losses change only slightly between the on and off states. The measured off-isolation of the CMOS OOK modulator is higher than 39.2 dB and the modulator has the on-state signal gain of 3.6 dB.