Radio Frequency Choke Research Articles

High-Sensitivity RF Choke-Enhanced Dipole Antenna-Coupled Nb5N6 THz Detector

In this study, we demonstrate an Nb5N6 terahertz (THz) detector with radio frequency (RF) choke-enhanced dipole antenna structure for 0.3 THz detection. The maximum electric field intensity of 218 V/m is obtained by optimizing the parameters of the dipole antenna with RF choke. Compared to a dipole antenna without RF choke, the electric field intensity of that with RF choke is improved by 2.6 times. The RF choke-enhanced dipole antenna-coupled Nb5N6 THz detector is fabricated and characterized. The measured maximum responsivity of the detector is 1100 V/W at 0.308 THz, and the corresponding noise equivalent power (NEP) is 6.4 × 10–12 W/Hz1/2. The measured response time of the Nb5N6 THz detector is as low as 8.46 μs. Furthermore, the Nb5N6 THz detector is applied to a homemade THz transmission imaging system for demonstrating its performance. The THz imaging results of a blade and access card show that the contrast of the blade image is sharp and the components hidden within the access card are clearly visible. This indicates that the Nb5N6 THz detector can be used in THz imaging, particularly in THz active imaging, which will have greater application prospects.

Power efficiency enhancement analysis of an inverse class D power amplifier for NB-IoT applications

The power amplifiers (PAs) are generally the most power-consuming building blocks in Radio Frequency (RF) transceivers. This paper presents a high efficiency fully integrated inverse class D power amplifier for the narrowband Internet of Things (NB-IoT) applications. In this design, the PA's power added efficiency (PAE) is improved by inserting two auxiliary PMOS transistors into the conventional topology of class D−1 PA, and the chip area is reduced by proper selection of the RF choke. An on-chip balun is designed to combine the output power of the two transistors, while its primary equivalent inductor resonates with a capacitor at the fundamental frequency. Based on simulation results, the proposed PA achieves 16.5 dBm output power with a peak power added efficiency (PAE) of 51.3%, while operating from a 1-V supply. Moreover, the proposed PA demonstrates the power gain of 21.6 dB and drain efficiency of 57% at the frequency band of 1.85–1.91 GHz. By using 180 nm TSMC technology, the proposed PA occupies a total chip area of 1.19 mm2 (0.85 mm × 1.4 mm), including pads.

Design and modeling of a wearable textile rectenna array implemented on Cordura fabric for batteryless applications

This paper presents a wearable rectenna array fabricated using Cordura textile material for harvesting low-power radio frequency (RF) energy. The dielectric properties of the textile were thoroughly investigated for circuit and antenna design. The rectenna element comprises a linearly polarized patch antenna and a single-stage full-wave Greinacher rectifier. The proposed stack topology helps reduce the size of the elements in the rectenna array. An RF choke is added to the array to prevent impedance mismatch due to changes in load impedance, and a foam with a shielding ground is inserted between the rectifier circuit and the human body to eliminate the body-proximity effect. A maximum output voltage of 1.05 V is achieved when the 2 × 2 rectenna array attached to a human body and 150 cm from the indoor Wi-Fi access point whose output power is 20 dBm and the antenna gain is 5 dBi.

Switchable differential filter using dual‐mode dielectric resonator

The invention discloses a switchable differential filter based on a dual-mode dielectric resonator. The filter comprises a metal cavity, the dielectric resonator, four feed probes, two differential input ports and two differential output ports; the tail ends of the feed probes are grounded through a switch circuit; the switch circuit comprises a blocking capacitor and a diode which are sequentially connected in series with the tail ends of the feed probes; the negative electrode of the diode is grounded; and the positive electrode of the diode is connected with a bias voltage for controlling the on/off of the diode through a radio-frequency choke coil inductor. The diode at the tail end of the feed probe is controlled to be on/off, so that a differential mode pass band is controlled to bein an on/off state. The filter has the characteristic of low loss in the on state, and has relatively high isolation degree in the off state. Meanwhile, in the two states, common mode rejection is larger than 20 dB. The switchable differential filter based on the dual-mode dielectric resonator has excellent performance, and has important application values in current and future communication systems.

Compact and Wideband Millimeter-Wave Antenna-Coupled Detector

This paper presents a compact and wideband millimeter-wave antenna-coupled detector, with a Schottky diode directly integrated across the feeding terminals of a planar dipole. An integrated wideband dipole is proposed, as a radiator as well as a radio frequency choke. It contains a pair of folded strips for broadening the bandwidth and a pair of U-slot resonators for sidelobe reduction, both of which facilitate the compact design. To form unidirectional radiation with a low profile, a hybrid reactive impedance surface is presented, which can simultaneously enhance the gain and impedance bandwidths covering the full Ka-band. An equivalent circuit model is provided to illustrate the operating mechanism of this antenna-coupled detector, and the mounting effect caused by the diode is examined. A Ka-band prototype with dimensions of about $1.12\lambda _{0}\times 1.12\lambda _{0}\times 0.08\lambda _{0}$ is fabricated and characterized, exhibiting a responsivity between 1500 and 3800 V/W over the full Ka-band. The proposed design has the advantages of broad bandwidth, low profile, small footprint, and mechanically stable structure. It can be fabricated using low-cost printed circuit technology, and can easily be configured into a planar 2-D array, making it suitable for low-cost sensing and imaging applications based on small unmanned aerial vehicles.

Miniaturized Radio Frequency Choke Using Modified Stubs for High Isolation in MIMO Systems

In this paper, a miniaturized radio frequency choke (RFC) using modified stubs is proposed to improve isolation characteristics in a multiple-input-multiple-output (MIMO) antenna system. The proposed RFC, based on the LC resonance, is designed to suppress the leakage current that leads to the degradation of antenna diversity performances in the MIMO antenna configuration. The proposed RFC is composed of two open stubs that are implemented on the top of the ground plane and miniaturized by adding a slit structure on the ground plane. The MIMO antennas are also designed to verify isolation performance in the LTE 2300 band (2,300?2,400 MHz). The MIMO antennas perform well with low reflection coefficient characteristics and high isolation characteristics in the whole LTE 2300 band. To evaluate the isolation in the MIMO system, the envelope correlation coefficient (ECC) is calculated, and the value is less than 0.08. The achieved ECC is regarded as a reasonable result for improving isolation performance in the frequency range of 2,300?2,400 MHz; also, radiation patterns of antenna elements are maintained regardless of the presence of RFC.

Characterization and Implementation Methods of Multilayer Inductors with Ni-Zn Ferrite and Carbonyl SF Powder Iron on Ceramic Substrates for RF Amplifers

Characterization and implementation of multilayer inductors constructed with Ni-Zn ferrite and Carbonyl SF powder iron on ceramic substrates for radio frequency (RF) power amplifier applications are presented for the first time. The multilayer inductor has a base material with high permittivity and low loss ceramic substrate, which has spiral inductor configuration and overlay magnetic substrate that is used to increase the effective permeability of the multilayer structure. High permittivity and low loss ceramic substrate gives the inductor a lower profile and better thermal performance for radio frequency applications. Ni-Zn ferrite and Carbonyl SF powder iron magnetic layers are used as an overlay magnetic substrate to increase effective permeability of the multilayer structure where magnetic flux flows through without degrading the performance of the inductor. The multilayer inductors that are designed are used as resonator inductor in the load line, RF choke, and combiner output inductor for RF power amplifiers carrying a large amount of current. Several different multilayer inductors are simulated, implemented, and measured. Various characteristic curves such as quality factor, inductance, resonance, return loss, and impedance versus frequency for different permeability and thickness of the magnetic substrate using Ni-Zn ferrite and powder iron core are measured, simulated, and presented. Measured and simulated results have been compared and found to be close. The multilayer inductors are then integrated to the RF amplifier, and the amplifier is tested for performance when it is interfaced with matched load at the rated power. It has been shown that the proposed multilayer inductor design can be used for radio frequency amplifier applications when high current flow and lower profile are required.

Design of a multi-input multi-output antenna with improved isolation using RF choke for long-term evolution mobile application

A multi-input multi-output (MIMO) antenna with improved isolation using radio frequency choke (RFC) is proposed.The proposed MIMO antenna consists of two radiating elements and an RFC that is located in between the two radiating elements. To improve the isolation between the two radiating elements of the MIMO antenna, the RF signal is suppressed at the desired frequency band by utilizing an RFC. The isolation is improved by ∼20 dB at the center frequency. The fabricated antenna satisfies the 6 dB return loss in long-term evolution band 13 from 746 to 787 MHz. The measured average efficiency and gain of the MIMO antenna are about 30.5% and −1.5 dBi, respectively. The measured envelope correlation coefficient is less than 0.4 over the frequency band of interest. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1569–1574, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27623

A Three-Stage Inverter-Based Stacked Power Amplifier in 65 nm Complementary Metal Oxide Semiconductor Process

A three-stage inverter-based stacked power amplifier (PA) in complementary metal oxide semiconductor (CMOS) process is proposed to overcome low breakdown voltage problem of scaled CMOS technologies. Unlike previous reported stacked PAs which radio frequency choke (RFC) was inevitable, we proposed stacked nMOS and pMOS transistors which effectively eliminates use of RFC. By properly setting self-biased circuits' and transistors' parameters, output impedance could reach up to 50 Ω which together with not employing the RFC makes this topology very appealing for the scalable PA realization. As a proof of concept, a three-stage PA using 65 nm CMOS technology is implemented. With a 6 V power supply for the third stage, the fabricated PA shows a small-signal gain of 36 dB, a saturated output power of 16 dBm and a maximum power added efficiency of 10% at 1 GHz. Using a 7.5 V of power supply, saturated output power reaches 18 dBm. To the best of our knowledge, this is the first reported inverter-based stacked PA.

Transmission-Line Class-E Power Amplifier With Extended Maximum Operating Frequency

A novel Class-E power amplifier (PA) topology with transmission-line load network is presented in this brief. When compared with the classic Class-E topology, the new circuit can increase the maximum operating frequency up to 50% higher without trading the other Class-E figures of merit. Neither quarterwave line/massive radio-frequency choke for collector/drain biasing nor additional fundamental-frequency output matching circuit are needed in the proposed PA, thus resulting in a compact design. Closed-form formulations are derived and verified by simulations with practical design limitations carefully taken into consideration and good agreement achieved.

Potential heating caused by intraparenchymal intracranial pressure transducers in a 3-tesla magnetic resonance imaging system using a body radiofrequency resonator: assessment of the Codman MicroSensor Transducer

Magnetic resonance imaging and spectroscopy may provide important clinical information in the acute stages of brain injury. For this to occur it must be ensured that intracranial pressure (ICP) monitoring devices are safe to bring into the MR imaging suite. The authors tested a Codman MicroSensor ICP Transducer (Codman & Shurtleff, Inc.) within a 3-T MR imaging system using the transmit body coil and receive-only coils and the transmit-and-receive head coil. Extreme and rapid heating of 64 degrees C was noted with the transducer wire in certain positions when using the transmit body coil and receive-only head coil. This is consistent with the phenomenon of resonance, and the probe was shown to have a distinct resonant response when coupled to HP 4195A Network Analyzer (Hewlett Packard). Coiling some of the transducer wire outside of the receive-only head coil reduced the generated current and so stopped the thermogenesis. This may be due to the introduction of a radiofrequency choke. The ICP transducer performed within clinically acceptable limits in both the static magnetic field and during imaging with high radiofrequency power when the excess wire was in this configuration. No heating was observed when a transmit-and-receive head coil was used. This study has shown when using a high-field magnet, the Codman ICP probe is MR conditional. That is, in the authors' system, it can be safely used with the transmit-and-receive head coil, but when using the transmit body coil the transducer wire must be coiled into concentric loops outside of the receive-only head coil.

Investigation on the resonance observed in the embedding-impedance response of an 850-GHz waveguide HEB mixer

A resonance is observed while simulating the embedding-impedance response of an 850-GHz waveguide hot-electron-bolometer (HEB) mixer. At the resonance frequency strong electric field is found distributed in the dc-grounded branch of the mixer's radio frequency (RF) choke filter. In fact, the phase response of the input reflection coefficient of the dc-grounded branch demonstrates the same resonance. Furthermore, the resonance frequency shifts with the change of the dc-ground position. A 254-times scale model of the dc-grounded branch of the mixer's RF choke filter is fabricated and measured. Experimental results are found in good agreement with the simulation results.

A Comparative Study of Single and Double Langmuir Probe Techniques for RF Plasma Characterization

AbstractIn this study, the plasma density and electron temperature of Radio Frequency (RF) plasmas were determined by three types of Langmuir probes, namely a conventional double probe, a single probe with RF choke and a single probe with RF choke and compensating electrode. The same plasmas were characterized by the three probes, each performing three measurements per plasma condition, in order to determine the precision of the measurement results. After performing a comparative analysis, which looked at the precision and the accuracy of these results, the conclusion is that the double probe, which has already the advantage of the simplest construction, yields the most reliable results for both capacitively and inductively coupled RF plasmas. The single probe with RF choke and compensating electrode has a similar precision as the single probe without compensating electrode, but its accuracy is better.

Class E Power Amplifiers and Frequency Multipliers with finite DC-Feed Inductance

Previous descriptions of class E amplifiers and frequency multipliers have required a radio frequency choke between the dc power supply and the active device switch. In this paper, it is shown that class E operation may be maintained with the RF choke replaced by a smaller reactance. The analysis technique used is similar to that used by Raab in his description of class E amplifiers in that the equations describing circuit operation are obtained from Fourier series methods and the assumption of an infinite output network Q . The equations so obtained are used to determine (1) optimum operation (maximum power output capability at 100-percent efficiency) at any harmonic and (2) design equations that yield the requisite component values for optimum operation. The equations show that class E circuits may be configured to accommodate devices with arbitrary output capacitance and that class E amplifiers may be configured to provide greater power output capability than can be obtained using an RF choke design. Class E circuits with moderate values of output network Q were constructed and tested. The measured performance of these experimental circuits shows excellent agreement with the theoretical performance predicted by the equations.

The Design of Radio-Frequency Choke Coils

The selection of a choke coil without regard for overtones is likely to permit kinks in the curve of apparent capacitance. These kinks represent overtones, at whose frequencies the choke coil has maximum values of excess shunt conductance, and therefore is unsuited for connection across a sharply selective tuned circuit. These overtones occur near even multiples of the fundamental frequency, in the absence of an iron core. Choke coils of two equal or unequal sections are proposed, and rules are given for proportioning the dimensions to suppress the first and second overtones. Examples are described, in which the remaining effect of the third overtone is small and that of higher overtones is negligible. Iron cores for choke coils have some advantages, in reducing the excess conductance, as indicated by the performance of an example described.