Tunable Matching Circuit Research Articles

Matching of generators and gas-discharge loads with radio frequency pumping

The article considers the problem of matching power high-frequency generators and gas discharge loads. Variants of various types of tunable matching circuits are proposed. A method of adaptive continuous tuning is described and a variant of implementing tunable elements on varicaps is proposed.

Ferrite-Less Frequency-Tuned Printed-Coil Resonator With Rear Metallic Plate for RFID Applications

The communication distance of Radio Frequency Identification (RFID) system is affected by the environment. This study presents a compact ferrite-less frequency-tuned printed-coil (PC) resonator, which introduces the additional PC resonators as well as the tunable matching circuits to the coil-based antennas, to address the rear metallic effect and the impedance mismatch effect caused by the environment variation for RFID system. The tunable matching circuit using the proposed negative voltage generator achieves low power consumption of only 0.5 mW. The usefulness of the proposed technique is experimentally validated with the rear metallic plate and the interference of water. Measurements show that compared with the commercial PC resonator, the proposed technique reduces the gaps between the coil and the rear metallic plate from 2.9 mm to 1.1 mm when the detected distance is 4.1 mm and, furthermore, improves the detected distance of the system from 3 mm to 17 mm with the interference of water.

A Real-Time Range-Adaptive Impedance Matching Utilizing a Machine Learning Strategy Based on Neural Networks for Wireless Power Transfer Systems

In this article, the implementation of a machine learning (ML) strategy based on neural networks for the real-time range-adaptive automatic impedance matching of wireless power transfer (WPT) applications is discussed. This approach for the effective prediction of the optimal parameters of the tunable matching network and the selection of range-adaptive transmitter coils (Tx) is introduced in this article, aiming to achieve an effective automatic impedance matching over a wide range of relative distances. We propose a WPT system consisting of a tunable matching circuit and three Tx coils that have different radii and are simultaneously controlled by trained neural network models, returning an output set of matching capacitances as well as the optimal single transmitter among the three transmitters. In addition, a proof-of-concept prototype of the entire real-time range-adaptive automatic impedance-matching system is built and characterized. Finally, the proposed approach achieves a power transfer efficiency (PTE) of around 90% for ranges within 10–25 cm.

Automatic Adaptation of Multi-Loop Wireless Power Transfer to Variable Coupling between Transmit and Receive Coils

In the conventional wireless power transfer (WPT) using magnetic resonance coupling, power transfer efficiency (PTE) exhibits a peak only at a matched distance between transmitter (Tx) and receiver (Rx). That is, it rapidly degrades if the distance deviates from the matched distance. In order to achieve high PTE over a wide range of the distance, automatic range-adaptation technique is proposed in this work by using multi-loop technique and tunable matching circuit with digital capacitors. For automatic range adaptation, the microcontroller unit (MCU) in Rx runs an algorithm to find optimum loop and capacitance for best PTE based on the received power. Tx and Rx are synchronized by using low power Bluetooth wireless communications. Instead of the conventional relays, microelectromechanical system (MEMS) switches with low loss and high isolation are employed to minimize the power dissipation. The entire WPT system automatically maximize PTE with the distance, achieving high PTE of 80.5% at 30 cm and 29.7% at 100 cm.

Fragmented Antenna Realization Using Coupled Small Radiating Elements

This paper reports on the feasibility of formation of an electrically large antenna at low frequencies using a number of miniaturized antennas through electromagnetic coupling for achieving high bandwidth. The proposed fragmented antenna system is intended for a swarm of small unmanned aerial vehicles in a linear flight formation. Inductively end-loaded folded dipole antennas are used as radiating elements. The small antennas are designed so that they can individually radiate with small bandwidth when isolated. The overall dimensions and the total mass of these fabricated elements are $12 \times 10\times 10$ cm ( $0.096\lambda _{0}\times 0.08\lambda _{0}\times 0.08\lambda _{0}$ at 240 MHz) and 18 g (including the matching network), respectively. Each miniaturized antenna can only provide 2.4 MHz (~1%) bandwidth and $25~\Omega $ input impedance. Having proper electromagnetic coupling between a cluster of three of such elements, measurement results demonstrate that the middle element can provide 18.4 MHz bandwidth (7.7%, 7.7 fold improvement) and $126~\Omega $ input impedance when the other two elements are loaded with optimal reactive elements. Moreover, the proposed configuration shows 1 dB gain improvement at boresight direction. The effects of flight formation fluctuations on the coupled antennas are also investigated, and it is shown that as the separation distance between the coupled antennas increases, the input impedance and bandwidth enhancement decrease. To overcome this problem, a tunable matching circuit containing a single varactor is proposed. Measurement results are shown to be in good agreement with the simulation predictions.

High-efficiency resonant coupled wireless power transfer via tunable impedance matching

ABSTRACTFor magnetic resonant coupled wireless power transfer (WPT), the axial movement of near-field coupled coils adversely degrades the power transfer efficiency (PTE) of the system and often creates sub-resonance. This paper presents a tunable impedance matching technique based on optimum coupling tuning to enhance the efficiency of resonant coupled WPT system. The optimum power transfer model is analysed from equivalent circuit model via reflected load principle, and the adequate matching are achieved through the optimum tuning of coupling coefficients at both the transmitting and receiving end of the system. Both simulations and experiments are performed to evaluate the theoretical model of the proposed matching technique, and results in a PTE over 80% at close coil proximity without shifting the original resonant frequency. Compared to the fixed coupled WPT, the extracted efficiency shows 15.1% and 19.9% improvements at the centre-to-centre misalignment of 10 and 70 cm, respectively. Applying this technique, the extracted S21 parameter shows more than 10 dB improvements at both strong and weak couplings. Through the developed model, the optimum coupling tuning also significantly improves the performance over matching techniques using frequency tracking and tunable matching circuits.

High efficiency radio frequency power amplifier with dynamic load modulation for wireless communications

ABSTRACTIn this article, a radio frequency (RF) power amplifier (PA) with high efficiency and high linearity is presented by using dynamic load modulation (DLM) technique. To improve the average efficiency, the load impedance is dynamically modulated according to the input envelop using tunable matching circuit (TMC). The TMC using varactors is located at a low‐impedance region of the output matching network. This reduces the RF voltage swing across the varactors, which minimizes the performance degradation by the varactors. The measurement setup is constructed to generate a control signal for the TMC that is synchronized with an input envelope. For wideband code division multiple access (W‐CDMA) signal with a peak‐to‐average ratio of 7.4 dB and a bandwidth of 3.84 MHz at 1.85 GHz, the fabricated DLM PA shows a power‐added efficiency of 49.7% at an output power of 30.6 dBm with an adjacent channel leakage ratio of <–45 dBc © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2717–2722, 2016

Range-Adaptive Wireless Power Transfer Using Multiloop and Tunable Matching Techniques

In this paper, a range-adaptive wireless power transfer (WPT) system is proposed to achieve high efficiency over a wide range of distances by using tunable impedance matching techniques. A multiloop topology is employed to greatly reduce the variation in the input impedance of the WPT system with respect to the distance, where one of the four loops with a different size is selected, depending on the distance. It enables the design of a simple tunable matching circuit using a single variable capacitor. An algorithm is written to find the optimum loop and capacitance in the matching network, based on the measured input return loss using a directional coupler and rectifiers. The fabricated WPT system shows a range-adaptive operation with high efficiency over a wide range of distances. It attains 48% efficiency at a distance of 100 cm with a maximum efficiency of 92% at a distance of 10 cm.

Design and Implementation of Long Range UHF RFID Reader

Aiming at the problems how to realize long range, high speed identification and how to integrate web with the management system in the UHF RFID applications, a UHF RFID reader system based on S3C2440 microprocessor and AS3992 UHF Reader chip is designed and implemented in this paper. By designing the RF front-end power amplifier and signal isolation circuit, the transmit power detection circuit and the antenna impedance tunable matching circuit, the transmit power reaches up to 32 dBm and the receiver SNR is improved at the same time, resulting in the stable read range reaching up to 12 meters. In order to integrate web control into the RFID management system, the reader system is transplanted into the embedded Linux OS and a web management system that is based on web server and CGI is constructed. Device drivers are developed and RFID APIs are packaged, greatly facilitating the software development and maintenance. By using the Random-Slotted anti-collision algorithm, high speed identification of ISO18000-6C RFID tags has been achieved.

Dynamic real-time calibration for antenna matching in the transmitting and receiving modes

In this article, we introduce an effective approach for dynamic impedance tuning of antenna matching circuits in both the transmitting and receiving modes. The tuning problem is described mathematically by a system of two nonlinear equations. These nonlinear equations are constructed by perturbing the tunable components of the matching circuit. We introduce a closed form solution to the proposed system of equations in addition to a numerical one. The outcome of our algorithm is the exact calculation of the instantaneous antenna input impedance. This impedance is then used to determine the optimal matching circuit values. The proposed algorithm takes place on the handset in real-time. Additionally, it does not limit the number of tunable components of the tunable matching circuit as the computational overhead is independent of their cardinality. The proposed approach can also be expanded to the case of real-time broadband tuning of antennas in a dynamic environment. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.

A Linear Multi-Mode CMOS Power Amplifier With Discrete Resizing and Concurrent Power Combining Structure

Efficiency degradation effects of power combining transformers with partially disabled inputs are quantitatively analyzed. To improve efficiencies in lower-power modes of a multi-mode class-AB power amplifier (PA), a discrete resizing technique is introduced in combination with a parallel-combining transformer (PCT). The two-stage PA implemented in a 0.18-μm CMOS technology also includes varactor-based tunable matching circuits. The design method involves parallel-combining of two power stages, each of which are divided into three sub-cells to facilitate discrete resizing. The parallel-combining of concurrently resized power cells minimizes undesired power loss through the transformer and helps the PA to utilize the transformer efficiency maximally independent of the number of combining cells. When operating in the high-power mode, the PA exhibits a peak output power of 31 dBm with a PAE of 34.8%. Power back-offs are realized by discretely turning off parallel sub-amplifier cells concurrently, achieving output power levels of 26 dBm and 22.3 dBm with respective PAE of 22.5% and 15%. The EVM has been measured with IEEE 802.11g WLAN and 802.16e WiMAX modulated signals in three operation modes. In the high-power mode, the PA dissipates 590 mA from a 3.3 V supply.