RF Circuitry Research Articles

Cross‐talk reduction in metamaterial and non‐uniform transmission lines

AbstractThe electromagnetic compatibility analysis of RF circuitry is essential due to the adverse effects on sensitive components. Two metamaterial unit cells with slow‐wave properties are presented for cross‐talk reduction in transmission lines. The analytical expressions for computing equivalent lumped elements of the lines are then provided. The dispersion diagram is obtained from the parameters extracted from the measurement. A microstrip as the generator line and five identical CRLH unit cells as the receptor line are then used and a significant reduction in cross‐talk is observed in comparison to conventional lines. A non‐uniform transmission line with two different CRLH unit cells as the receptor line is then employed and found effective in further cross‐talk reduction between the lines. The lengths of the lines and numbers of cells are kept the same in all lines for comparison. The simulated results are validated by measurements.

Joint DoA and CFO Estimation Scheme With Received Beam Scanned Leaky Wave Antenna for Industrial Internet of Things (IIoT) Systems

Direction-of-arrival (DoA) estimation is essential in many industrial internet of things (IIoT) applications where IoT users may require a high-resolution estimation algorithm for features limited to positioning and device localization. The conventional DoA estimation is challenging as the number of antenna arrays increases leading to an increase in design complexity and cost in RF circuitry. As a result, the conventional DoA estimation algorithms may not be suited for IIoT applications. In this work, a joint DOA and carrier frequency offset (CFO) schemes is introduced for typical uplink IIoT systems by equipping the receiver with a leaky-wave antenna (LWA). By considering that the LWA can simultaneously steer its beam direction towards the active user. As a result, each user is estimated independently. The joint algorithm is developed based on the high-resolution MUSIC scheme, which utilizes the LWA properties to compute the DoA spectrum. Furthermore, we develop an iterative CFO estimation approach as the desired solution to a multi-dimensional search. Subsequently, we further formulate the Cramer–Rao lower bounds (CRLB) to serve as a performance benchmark for the accuracy of the proposed scheme. The SDR platform is provided to validate the proposed algorithm in real-time. Finally, the simulation results and the SDR experiments justify that the proposed scheme offers more robustness than conventional counterparts with linear array antenna, which achieves a root mean square error (RMSE) approach to the derived CLRB, especially at a medium signal-to-noise ratio (SNR) range which suited for IIoT applications.

Digitally Based Precision Time-Domain Spectrometer for NMR Relaxation and NMR Cryoporometry

NMR Relaxation (NMRR) is an extremely useful quantitative technique for material science, particularly for studying polymers and porous materials. NMR Cryoporometry (NMRC) is a powerful technique for the measurement of pore-size distributions and total porosities. This paper discusses the use, capabilities and application of a newly developed compact NMR time-domain relaxation spectrometer suitable for studying both solid and liquid samples (Mk3 NMR Relaxation spectrometer & Cryoporometer, Lab-Tools (nano-science), Ramsgate, Kent, UK. (2019)). This highly compact precision NMR Spectrometer is based on a Field Programmable Gate array (FPGA) module and custom surface mount low-noise NMR receiver and NMR linear transmitter. A high proportion of the RF circuitry is in a digital form, implemented as firmware in the FPGA, which gives the instrument an excellent long-term stability. It also includes an on-chip Linux computer. The FPGA module is credit-card sized, and both the NMR receiver and NMR transmitter are even smaller. The software, including the top-level NMR pulse sequence definitions, are written in an array processing language, Apl. The spectrometer comes complete with a Graphical User Interface (GUI) for control and on- and offline curve fitting and data analysis. The recent development of the Lab-Tools Peltier thermo-electrically cooled NMR variable-temperature (V-T) probe that cools the sample below −60 °C is also discussed. This Peltier cooling gives the precision temperature control and smoothness needed by NMR Cryoporometry (10 mK near the probe liquid bulk melting point). This enables the NMRC measurement of pore-size distributions in porous materials, for the unusually wide pore-size range of sub-nano to over 1 micron-sized pores. The NMR Spectrometer’s unusually small size, ability to measure solids, low noise and high performance make it particularly suitable for material science studies both in the field and in university, research institute, company and even school laboratories. A human portable version now exists. Use of the controlling GUI is described, and results from example NMR Relaxation and NMR Cryoporometric measurements are given.

Metasurface-Inspired Flexible Wearable MIMO Antenna Array for Wireless Body Area Network Applications and Biomedical Telemetry Devices

This article presents a sub-6GHz ISM-band flexible wearable MIMO antenna array for wireless body area networks (WBANs) and biomedical telemetry devices. The array is based on metasurface inspired technology. The antenna array consists of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times 2$ </tex-math></inline-formula> matrix of triangular-shaped radiation elements that were realized on 0.8 mm thick Rogers RT/duroid 5880 substrate. Radiation characteristics of the array are enhanced by isolating the surface current interaction between the individual radiators in the array. This is achieved by inserting an electromagnetic bandgap (EBG) decoupling structure between the radiating elements. The radiating elements were transformed into a metasurface by etching sub-wavelength slots inside them. The periodic arrangement of slots acts like resonant scatterers that manipulate the electromagnetic response of the surface. Results confirm that by employing the decoupling structure and sub-wavelength slots the isolation between the radiators is significantly improved ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;34.8$ </tex-math></inline-formula> dB). Moreover, there is an improvement in the array’s fractional bandwidth, gain and the radiation efficiency. The optimized array design for operation over 5.0-6.6 GHz has an average gain and efficiency of 10 dBi and 83%, respectively. Results show that the array’s performance is not greatly affected by a certain amount of bending. In fact, the antenna maintains a gain between 8.65-10.5 dBi and the efficiency between 77-83%. The proposed MIMO antenna array is relatively compact, can be easily fabricated on one side of a dielectric material, allows easy integration with RF circuitry, is robust, and maintains its characteristics with some bending. These features make it suitable for various wearable applications and biomedical telemetry devices.

Electrically detected electron nuclear double resonance in amorphous hydrogenated boron thin films

We report on electrically detected electron nuclear double resonance (EDENDOR) observations via spin dependent trap assisted tunneling (SDTAT) in amorphous boron thin films at 250 K. We observe EDENDOR from both 10B and 11B nuclei, likely interacting with carbon impurities. In SDTAT, electron paramagnetic resonance (EPR) is detected through a change in the trap assisted tunneling current through the thin film. As in conventional electron nuclear double resonance (ENDOR) the ENDOR response is detected through a modest change in the EPR response. Since SDTAT detection sensitivity is about seven orders of magnitude greater than that of conventional EPR, it, in principle, can provide an enormous boost in ENDOR sensitivity. This enormous potential sensitivity improvement can be compromised by a coupling of the RF electromagnetic field driving the nuclear spin response and the electrical leads which are utilized to monitor the resonance induced changes in device current. We overcome this difficulty with the introduction of proportional-integral-derivative (PID) control of the RF circuitry which greatly suppresses fluctuations in the amplitude of the RF magnetic field at the thin film structure under investigation.

Design of a Low-Cost Low-Profile Energy Efficient 64-QAM Load Modulator

The design of a 64-QAM I/Q modulator based on load modulation is presented. The modulator is designed to operate at 3 GHz. In any standard M-QAM modulation, the RF circuitry of the voltage source generates currents on the antenna corresponding to the transmitted signals. With load modulation, the waveforms of the M-QAM constellation points are generated by changing the internal parameters of the load modulator connected to the antenna. At the same time, the voltage source is kept constant. Thus, the power amplifier amplifies a constant signal all the time and does not need to operate in the back-off region. An optimization algorithm is developed to find the design parameters of the load modulator circuit. The design parameters obtained from the algorithm have been used in the advanced design system (ADS) software to design, simulate, and fully characterize the RF load modulator circuit. The hardware prototype of the load modulator circuit is realized using microstrip lines and a diode-based switching circuit. The measurements show that the load modulator can generate outputs on the <inline-formula> <tex-math notation="LaTeX">$S_{21}$ </tex-math></inline-formula>-parameter complex plane matched to the 64-QAM constellation diagram. A microcontroller is programmed to serve the required bias voltages to the p-i-n diodes in the load modulator based on a predetermined lookup table (LUT). The proposed architecture does not require a digital-to-analog converter (DAC). A credible agreement between the simulation results and measurements is obtained.

10 GHz regeneratively mode-locked thulium fiber laser with a stabilized repetition rate.

GHz pulsed thulium-doped fiber laser with stabilized repetition rate can enable a wide range of applications. By employing regenerative mode-locking and cavity stabilization technique, we have for the first time demonstrated a 10 GHz polarization-maintaining thulium-doped fiber laser, which has a long-term repetition-rate stabilization and picosecond timing-jitter. In our experiment, a RF circuitry is designed to extract the 10 GHz longitudinal clock signal so that stable regenerative mode-locking is achieved. A piezo actuator-based phase-lock-loop is used to lock the regeneratively mode-locked pulses to a local reference synthesizer. The regeneratively mode-locked pulses with picosecond pulse width exhibit a high super-mode suppression ratio of 60 dB. In addition, the repetition rate of the laser shows good long-term stability with a variation of 8 Hz in 8 hours, corresponding to a cavity free spectral range fluctuation of less than 16 mHz. Meanwhile, the Allan deviation of the stabilized 10 GHz regeneratively mode-locked pulses is measured to be as low as 2 × 10-12 over 1000 s average time, which is only limited by the stability of the reference synthesizer. Such an ultra-stable 10 GHz pulsed thulium fiber laser may find potential application in 2 µm optical communication, material processing and spectroscopy.

(Invited) Defect Engineering for Monolithic Integration of III-V Semiconductors on Silicon Substrates

Optimization of heterogeneous epitaxial techniques such as aspect ratio trapping and nano-ridge engineering strongly triggered the commercial breakthrough of III-V on Si devices for a variety of applications in fields like optoelectronics, lighting, telecommunication, power devices, RF circuitry etc. To achieve high device performance defect engineering is crucial to avoid increased leakage current, lifetime degradation and/or increased low frequency noise. The aim of this review is to discuss the present understanding of defects in III-V materials and devices and their impact on the device performance. This is illustrated by analyzing three important types of devices, including InxGa1-xAs p+n diodes, GaN/AlGaN/Si transistors (MOSFETs, HEMTs and MOSHEMTs) and GaAs/InGaP Heterojunction Bipolar Transistors (HBTs). It will be pointed out that by an appropriate defect control the further development of the monolithic III-V integration on Si will not be hampered and is facing a bright future.

A Must-Have Reference on Antenna Technology [Book/Software Reviews

This handbook is intended to provide a collection of design data for radar and communication system and array designers. As such, it only briefly addresses the details of electromagnetic analysis. Additional materials in this third edition include the areas of fabrication and computation, addressing array control, RF circuitry, and array elements on the same substrate or even incorporated into monolithic microwave integrated circuit packaging. This edition also introduces recent changes in fabrication capability, describing the huge impact of high-performance computational tools on antenna technology—from element design to synthesis. Overall, this book is the bible of array antenna design, development, and research and a must-have reference for those pursuing higher education in antenna technology. Unfortunately for such a valuable resource, this third edition could use a good proofreading.

Toward high voltage radio frequency devices in β-Ga2O3

The path to achieving integrated RF and power conversion circuitry using the β-Ga2O3 material system is described with regard to the materials high Johnson's RF figure of merit. Recent results, including large signal data at VD = 50 V, are provided, showing progress in achieving high-voltage RF operation. Additionally, progress in achieving high-gain devices through gate length scaling is also benchmarked by a record RF power device with a gate length of 0.5 μm achieving a 2.1 GHz μm fT−LG product. These results are compared with state-of-the-art RF devices, and the expectations for β-Ga2O3 at this point in its maturity throughout this Letter with future milestones laid out to measure progress. The conclusion includes near- and long-term projections for β-Ga2O3 devices for RF based on the results and projected milestones presented.

Characteristics and Applications of CAAC-IGZO FET with Gate Length of 13nm

A field-effect transistor (FET) with a gate length of 13 nm having a c-axis aligned crystalline In-Ga-Zn oxide (CAAC-IGZO) channel was fabricated. The CAAC-IGZO FET has an off-state leakage current of 200 yA/μm, a cutoff frequency of 60GHz, and a maximum oscillation frequency of 16GHz. A CAAC-IGZO FET, though it is a small transistor, withstands voltages up to approximately 2.5 V. It also has stable current characteristics with less temperature dependence than Si devices. We have constructed an equivalent-circuit model of the CAAC-IGZO FET and designed an RF amplifier to show CAAC-IGZO FET's applicability to the GHz-range RF circuitry.

Amplitude-Modulating Analog/RF Hardware Trojans in Wireless Networks: Risks and Remedies

We investigate the risk posed by amplitude-modulating analog/RF hardware Trojans in wireless networks and propose a defense mechanism to mitigate the threat. First, we introduce the operating principles of amplitude-modulating analog/RF hardware Trojan circuits and we theoretically analyze their performance characteristics. Subject to channel conditions and hardware Trojan design restrictions, this analysis seeks to determine the impact of these malicious circuits on the legitimate communication and to understand the capabilities of the covert channel that they establish in practical wireless networks, by characterizing its error probability. Next, we present the implementation of two hardware Trojan examples on a Wireless Open-Access Research Platform (WARP)-based experimental setup. These examples reside in the analog and the RF circuitry of an 802.11a/g transmitter, respectively, where they manipulate the transmitted signal characteristics to leak their payload bits. Using these examples, we demonstrate (i) attack robustness, i.e., ability of the rogue receiver to successfully retrieve the leaked data, and (ii) attack inconspicuousness, i.e., ability of the hardware Trojan circuits to evade detection by existing defense methods. Lastly, we propose a defense mechanism that is capable of detecting analog/RF hardware Trojans in WiFi transceivers. The proposed defense, termed Adaptive Channel Estimation (ACE), leverages channel estimation capabilities of Orthogonal Frequency Division Multiplexing (OFDM) systems to robustly expose the Trojan activity in the presence of channel fading and device noise. Effectiveness of the ACE defense has been verified through experiments conducted in actual channel conditions, namely over-the-air and in the presence of interference.

Post-process porous silicon for 5G applications

The interest of 5G in centimeter and millimeter waves relies on large blocks of available spectra and thus increased bandwidth. At these frequencies, the dielectric and conductive losses of the substrate can greatly degrade the performances of RF circuits. With high electrical resistivity and low relative permittivity, porous silicon is an ideal candidate as a high-quality RF substrate. This paper presents an innovative technique of post device fabrication integration of porous silicon (POST-PSi) with the substrate. The frontside is not involved in porous layer growth and therefore the integrity of the RF circuitry is not impacted by the POST-PSi process. A comparison of the RF performances with benchmark trap-rich (TR) RF silicon substrate is presented. In addition to its compatibility with standard microfabrication processes and stable final structure, POST-PSi provides characteristics of low losses, high isolation and very high linearity, unmatched by any other silicon-based substrate. Finally, the substrate’s RF performance is evaluated at high temperature, and POST-PSi substrate linearity is shown to remain sufficiently high for RF and 5G applications up to 175 °C.

Evolutionary trends in Transmit/Receive Module for Active Phased Array Radars

&lt;p&gt;Worldwide, defense technologies are rapidly evolving and are currently aiming at integrating diverse functionalities like Radar, Electronic Warfare, Communications, etc., on a singular miniaturized platform. Hence, it cannot be denied that the advancements in modern Active Phased Array Radar technologies assume a critical role towards the achievement of this goal. A typical Active Phased Array Radar comprises of an Active Antenna Array Unit (AAAU) consisting of a large number of radiating elements, Transmit/Receive (T/R) Modules with other associated RF and digital circuitry and power electronics. This paper presents mainly the developments in Transmit/Receive (T/R) Module technology, which assimilates various stages of the technological evolution - past, current and futuristic. It discusses how these technologies contribute towards the improvement of efficiency, miniaturization and reliability without compromising its performance parameters.&lt;/p&gt;

A High-Fractional-Bandwidth, Millimeter-Wave Bidirectional Image-Selection Architecture With Narrowband LO Tuning Requirements

An image-selection, two-element transceiver is presented that operates over a large fractional bandwidth (FBW) covering both 71–76 and 81–86 GHz while requiring only 3 GHz of local oscillator (LO) tuning range at the RF mixer. A bidirectional sliding-intermediate frequency (IF) Weaver architecture allows operation in either transmit (TX) or receive (RX) modes. The sliding IF and narrow LO tuning range allow wideband image rejection using only a single-stage polyphase filter. The circuit is implemented in a 90-nm SiGe BiCMOS process and the RF and LO circuitry consume at most 150 and 250 mW, respectively. Measurements show less than ±0.75-dB gain variation over 10 GHz in the TX mode and less than ±1-dB variation over 10-GHz bandwidth in the RX mode. With 16- and 64-quadrature-amplitude modulation (QAM), the error vector magnitude is below −22 and −28.5 dB at the data rates of 12 and 9 Gb/s, respectively.

Bubble inductors: Pneumatic tuning of a stretchable inductor

From adaptive matching networks in power systems to channel selectable RF filters and circuitry, tunable inductors are fundamental components for circuits requiring reconfigurability. Here we demonstrate a new continuously tunable inductor based on physically stretching the inductor traces themselves. Liquid-metal-based stretchable conductors are wrapped around a pneumatic bubble actuator, allowing the inductor to be collapsed or expanded by application of pressure. In vacuum the bubble collapses, bringing the loop area to nearly zero, while positive pressure brings a dramatic increase in area and loop inductance. Using this approach, the inductor demonstrated in this work was able to achieve a tuning ratio of 2.6 with 1-2 second response time. With conductors available that can stretch by hundreds of percent, this technique is promising for very large tuning ratios in continuously tunable inductors.

All-Digital LTE SAW-Less Transmitter With DSP-Based Programming of RX-Band Noise

We present the first all-digital LTE transmitter (TX) using programmable digital attenuation of receive band (RX-band) noise. The system is architectured to fully exploit the speed and low cost of DSP logic in deep-submicrometer CMOS processes, without increasing at all the design effort of the RF circuitry. To achieve operation without surface acoustic wave filter, the TX uses digital bandpass delta–sigma modulation and mismatch-shaping to attenuate the DAC noise at a programmable duplex distance. These functions can be implemented entirely within DSP, thus taking advantage of the standard digital design methodology. Furthermore, the fully digital RX-band noise shaping significantly relaxes the performance requirements on the RF front-end. Therefore, 10 bits of resolution for the D/A conversion are sufficient to achieve −160 dBc/Hz out-of-band (OOB) noise, without need for digital predistortion, calibration, or bulky analog filters. The TX was fabricated in 28-nm CMOS, and occupies only 0.82 mm2. Besides low OOB noise, our system also demonstrates state-of-art linearity performance, with measured CIM3/CIM5 below −67 dBc, and adjacent-channel leakage ratio of −61 dBc with LTE20 carrier. The circuit consumes 150 mW from 0.9-/1.5-V supplies at +3 dBm output power.

Driving frequency fluctuations in pulsed capacitively coupled plasmas

We report time resolved measurements of the RF current, voltage and complex impedance for pulsed plasmas through electropositive (Ar) and electronegative (CF4, O2) gases and gas mixtures. In addition, we report measurements of the effective frequency versus time at various locations within the RF circuitry. The frequency is found to fluctuate away from that sourced by the RF generator when the plasma re-ignites. Plasma re-ignition induces abrupt impedance changes due to the re-formation of the plasma sheath and bulk. These fast changes in the plasma impedance cause the measured changes in the voltage and current frequencies. As a result, the frequency of the RF power at the plasma electrodes was found to be as much as 250 kHz different from that being sourced by the RF generator for short periods of time. These frequency fluctuations are of particular interest to the application of frequency tuned matching networks.

Dual material gate doping-less tunnel FET with hetero gate dielectric for enhancement of analog/RF performance

In this paper, charge-plasma-based tunnel FET is proposed by employing dual material gate with hetero gate dielectric technique and it is named hetero-dielectric dual material gate doping-less TFET (HD_DMG_DLTFET). It is compared with conventional doping-less TFET (DLTFET) and dual material gate doping-less TFET (DMG_DLTFET) on the basis of analog and RF performance. The HD_DMG_DLTFET provides better ON state current (), , and average subthreshold slope (). The proposed device offers low total gate capacitance (Cgg) along with higher drive current. However, with a better transconductance (gm) and cut-off frequency (fT), the HD_DMG_DLTFET can be a good candidate for RF circuitry. The early voltage (VEA) and output conductance (gd) are also moderate for the proposed device with comparison to other devices and therefore can be a candidate for analog devices. From all these simulation results and their study, it is observed that HD_DMG_DLTFET has improved analog/RF performance compared to DLTFET and DMG_DLTFET.

Heterogeneous Packaging of Organic Electro-Optic Modulators With RF Substrates

As organic-based electro-optic (EO) modulators continually improve toward meeting the high performance required by new and developing photonic technologies, the challenge of compact and low loss packaging needs to be addressed.Because organic-based EO modulators and RF circuitry are traditionally built on different substrates homogeneous integration would require developing new designs and fabrication processes. In addition, the organic-based EO modulators most often implement microstrip transmission lines for optimal poling and modulation field overlap meaning the ground plane is encapsulated and unavailable for direct contact. In this letter, a heterogeneous RF packaging scheme featuring a wire bond transition between a ceramic feed coplanar waveguide and a thin-film polymer microstrip is presented. The transition introduces less than 1 dB of RF loss at 50 GHz and was demonstrated on an organic-based EO phase modulator which generated optical sidebands out to 40 GHz.