Antenna Tuning Unit Research Articles

Adaptive Matching of Discrete Antenna Tuning Units of High Frequency Band to Varying Load Impedance

The issue of matching the antenna with thetransmitter-receiverplays a primary role in radio communications. The matching problem is relevant for different ranges and is solved in many ways. In the high frequency wave range, matching has a number of features when using an antenna coupler based on discrete elements consisting of capacitance and inductance boxes. The article discusses the concept of fast matching of high-frequency amplifying paths ofdecametric wavestransceivers with non-stationary loads using discrete antenna couplers. An innovative approach has been developed to the tuning process when changing the operating frequency and ensuring self-adaptation of the antenna coupler when changing the impedance, based on methods for quickly searching for the geometric proximity of points. A quick method for configuring the antenna coupler is proposed, eliminating the procedure for recalculating the input impedance based on the results of measuring the input impedance of the antenna coupler. When using it, the speed of setting the antenna coupler at the current operating frequency is limited only by the time of a single state change of the discrete power circuit, which in the case of electromagnetic relays is numerically equal to their switching time. The configuration of the antenna coupler using the method of fast search for the geometric proximity of points is based on a set of frequency cards with settings options. Such cards can be recalculated for the reference plane between the generator and the antenna coupler input for all combinations of discrete elements in accordance with the known matrix model of a discrete power circuit. This eliminates the complicated procedure of recalculating the input impedance of the antenna using complex numbers. The technical result of the proposed innovative method of antenna coupler configuringis simplification, tracking of systematic errors of the impedance meter, elimination of time-consuming calculations with complex numbers, expansion of the method functionality, reduction of the tuning duration and improvement its quality. The practical significance lies in the fact that the implementation of the proposed technical solutions in the high frequency range communications means can significantly (about 100 times) limit the duration of preparation for a radio communication session, eliminate the procedure for recalculating the antenna input impedance and reduce the resource requirements of switching elements.

Advanced Algorithms for Configuring Discrete Antenna Tuning Units of High Frequency Band Using a Quick Search Method for the Points’ Geometric Proximity

Advanced Algorithms for Configuring Discrete Antenna Tuning Units of High Frequency Band Using a Quick Search Method for the Points’ Geometric Proximity

Matrix model parametric identification of antenna tuning units

HF radiocommunication modern development trends provide for improved handling and increased speed of antenna tuning units (ATU) functioning. The need to control the tuning process using a microcontroller based on the measurement results of antenna input impedance in the “on-line” mode requires an increase in the accuracy of modeling the transformative properties of these devices and subsequent calculations for the development of control commands by discrete tuning bodies. The more reliable the data in the memory of the microcontroller will characterize the real properties of the device's tuning bodies, the better their regulation will be. Based on the results of a full-scale experiment, the issues of parametric identification of the previously proposed conceptual matrix model of discreet power circuit are considered. Due to the complexity of technological modeling of circuits transformative properties, the task is to increase the accuracy of its numerical results for each device. With the found set of solutions for the model with the selected structure and a significant number of unknown parameters, its identification by the objective function extremum is not possible. Accordingly, the analysis of a priori identifiability (theoretical, with unambiguous definition of parameters) is carried out on the basis of a qualitative study of the structure of the model and the scheme of the “ideal” experiment (with determinism of all unmistakably measured values). The identifiability of the proposed power circuit model has been confirmed. The variants of the experiment, the algorithm for processing its results, as well as ways to obtain their guaranteed quality with the help of a vector circuits analyzer for a certain time at a given cost are described. The criterion for assessing the conformity of the model to a real power circuit is a measure of the number of its errors after measuring complex coefficients on a set of frequencies. Processing the results using the least squares method with interpolation for the entire frequency band reduces the errors and complexity of the experiment. Modeling of a 9-bit matching inductive body confirmed the correctness and effectiveness of the matrix description of the transforming properties of the wide band ATU and other solutions presented, as well as the possibility of full automation of this experiment.

The Matrix Model of Discrete Matching Elements for HF Computational Automatic Tuning Units

The article is devoted to a new and relevant direction in the HF communication technology - the construction of high-speed computational antenna tuning units (ATU). The implementation of automatic ATU requires the designing of power circuits models adequate, as practice shows, the construction of models to physical reality in order to ensure their controllability. Practically powerful device elements are not in fact concentrated, the distributed nature of their parameters is noticeably manifested in the HF range. Matching ATU on the base of antenna input impedance measuring involves forming of accurate control commands for the elements, especially in conditions where the settings are narrow-band. A new approach to the description of a power circuit discrete elements transforming properties using the theory of linear passive four-pole and matrices, which has the ultimate accuracy, is proposed. A method to form a matrix description of on-off discrete elements of a power circuit based on the results of characteristic field measurements of the mounted device is presented. This approach made it possible to significantly reduce the amount of tabulated data describing the functional dependences of the complex coefficients of wave transmission matrices and to “smooth out” the experimental error. Complex cases are considered, which are of the greatest interest for practice - options for a four-pole cascade and parallel connection of reactive elements in the branches of the power circuit. The current state of computer technology makes it possible to sharply increase the complexity of the mathematical models used. The matrix model takes into account a significant variety of operating factors and does not require them to be “customized” to existing analytical methods. The adequacy, in this simulation, is determined by practical needs that arise in the design of power circuits of matching antenna devices and their tuning algorithms. In fact, the model is considered adequate if the errors in the calculation of the response function according to the model do not exceed the errors in its experimental determination. The proposed matrix approach made it possible to significantly improve the accuracy of modeling, while the error does not exceed 1 %. Also, this approach allows to find several options for setting a given quality and choose the best one for any parameter, while reducing the duration of the process up to 25 times. At the additional metrological advantages appeared in such devices serial production.

A Cavity Balun for High-Power Shortwave Transmission

Compared with conventional systems, high power puts forward more requirements on the balun: the materials and structures should be more reliable, able to withstand high power, and have extremely high transmission efficiency. Based on the electromagnetic field theory and the visual optimization method by CST MW Studio, a parallel-connected coaxial cavity balun is proposed in this article that can realize the balance–unbalance conversion in almost the entire shortwave frequency band (4.4–27 MHz). For further improvement of the transmission efficiency and the reduction of voltage standing wave ratio (VSWR), an antenna tuning unit (ATU) was added to the unbalanced port of the cavity, which lowered the VSWR from 1.5 to 1.1. The theoretical value of the breakdown power of the balun is also calculated, and it is much larger than the transmit power. The results of the scaled mode measurement are consistent with the simulation results: the amplitude imbalance of the balanced port is within ±0.5 dB, the phase difference is 180° ± 5°, and the withstand power is at least three times the transmit power, which fully demonstrates that the proposed balun is suitable for high-power shortwave transmitting systems.

Method for automatic antenna matching with transmitter output stage

This work is devoted to the study of automatic antenna tuning units of the short-wave range. Devices of narrowband matching based on discrete sets of reactive elements are considered. A classification of the most frequently used automatic matching methods has been made. The advantages and disadvantages of each method are analyzed. Examples of using different approaches in commercially available devices are given. Particular attention is paid to the calculation method of matching, as the most promising for use in modern communications. Assumptions are made about the reasons for its rare use in serial devices. Circuits have been developed to simulate the influence of parasitic parameters of the components of the matching circuit and the body of the tuning unit on the resulting standing wave ratio when using this method. Based on the simulation results, conclusions were drawn about the reasons for the low quality of the calculation method. As an alternative, a new method of automatic tuning is proposed, combining the advantages of computation and search methods, which is based on modeling the search process using a simulation model. The conditions for its application in automatic antenna tuning units are determined. Acomparative analysis of the features of both the known methods of automatic tuning and the newly proposed one ismade.

Triple-Band Concurrent Reconfigurable Matching Network

Reconfigurable Matching Networks (RMN) have found a wide range of applications, such as antenna impedance matching (Antenna Tuning Units -ATU-), the design of reconfigurable power amplifiers, applications in Magnetic Resonance Imaging (MRI), adjustable low noise amplifier design, etc. In this paper, we propose the experimental design and verification of a reconfigurable impedance synthesis network that can simultaneously work in three different bands and is completely independent so that the impedance variations in a frequency band are approximately transparent to the rest. The variable elements used in this paper are varactors. To verify its operation, it is applied to a process of matching a laser modulator in three different frequency bands for C-RAN (Cloud Radio Access Networks) applications. Experimental results demonstrate, as expected, that losses may depend on the state in which they are driven. Consequently, a state that can guarantee a good match could also imply greater losses, leading to a certain trade-off. The application of genetic algorithms in this context points out that it may be convenient to optimize the insertion losses of the complete chain instead of the return losses.

Automatic Antenna Tuning Unit to Improve RFID System Performance

Systems for radio-frequency identification (RFID) realize a bidirectional wireless communication between a reader device and cheap passive tags (e.g., an RFID chip with an antenna printed on badges for access-control systems) in the near field of an antenna. This paper deals with the automatic and fast tuning of the resonant reader antennas in the widely used 13.56-MHz frequency band, resulting in a performance improvement and an increased read/write range. A novel RFID reader system is proposed with a tuning transformer for the automatic adjustment of the resonant circuit center frequency. This is achieved by shifting the magnetic operating point (i.e., the biasing direct-current (dc) magnetization) of a Ni-Zn ferrite transformer by means of an additional dc winding. The operation principle and the performance potential of this device are demonstrated by measurements on a prototypical RFID system.

A Novel Method for Synthesizing an Automatic Matching Network and Its Control Unit

We present a novel method simplifying matching network synthesis and design based on a tunable low-pass π matching network topology. This method exploits the Smith chart in a novel way. Analytic expressions for calculating the optimal matching network for automatically adapting the load to the source impedance are derived. This work is applied to a new antenna tuning unit concept able to calibrate the system in a single iteration process reducing strongly both the speed and the overall consumption of the antenna calibration module. The obtained matching network nodal and load quality factors are analyzed and the matching network efficiency is evaluated to highlight the impact of the imperfection in the design. The simulation and experimental results are presented to validate the proposed method and to evaluate the obtained matching efficWe present a novel method simplifying matching network synthesis and design based on a tunable low-pass π matching network topology. This method exploits the Smith chart in a novel way. Analytic expressions for calculating the optimal matching network for automatically adapting the load to the source impedance are derived. This work is applied to a new antenna tuning unit concept able to calibrate the system in a single iteration process reducing strongly both the speed and the overall consumption of the antenna calibration module. The obtained matching network nodal and load quality factors are analyzed and the matching network efficiency is evaluated to highlight the impact of the imperfection in the design. The simulation and experimental results are presented to validate the proposed method and to evaluate the obtained matching efficiency. We perform reflection coefficients less than -30 dB, high efficiency matching networks with only 258 μs to calculate the proper state of the tunable matching network under a processor delivering 40 MIPS of performance.iency. We perform reflection coefficients less than -30 dB, high efficiency matching networks with only 258 μs to calculate the proper state of the tunable matching network under a processor delivering 40 MIPS of performance.

A Mixed-Signal Matching State Search Based Adaptive Antenna Tuning IC

A closed-loop adaptive antenna tuning unit operating from 850 MHz-2 GHz for multi-band, multi-mode radios is presented. Unlike previous approaches, the proposed module utilizes an analog mismatch detector and a closed-loop mixed-signal matching state search circuit, without the need for an A/D converter. The integrated module is designed and fabricated on a 0.18 CMOS process. When tested on a band-limited shorted patch antenna, the module can perform a scan of 4096 antenna matching states in 4.1 ms, and tune the antenna to a specified narrow instantaneous bandwidth over the entire frequency range.

Performance degradation due to antenna impedance variability in DVB-H consumer devices

The quality of DVB-H (Digital Video Broadcasting for Handheld) signals in a consumer receiver is usually analyzed by means of the BER (Bit Error Rate). This measure has been studied from a mobile channel perspective, and different signal processing algorithms have been proposed to mitigate its degradation. However, the effects of the hardware at the receiver are also important. The antenna can cause some degradation due to variations in field magnitudes, like the radiation pattern, but also in circuit magnitudes, as mismatching. In this paper, we propose an algorithm to evaluate the degradation on the BER due to consumer equipment effects which cause certain variability in the antenna impedance and consequently in the SNR (Signal to Noise Ratio). We also evaluate the theoretical improvement when a mitigation circuit (an ideal Antenna Tuning Unit) is included in the DVB-H receiver design.

A discussion on the performance of impedance matched antenna system and considerations for a better performance

AbstractImpedance matching networks are used extensively in radio communications. In this study, π‐matching circuit has been used as a matching network. The return loss level of several impedance matched microstrip antennas are compared as a function of matching techniques. The π‐matching device is used to construct the antenna tuning units, which is only used to match the front module and the antenna. This circuit impedance region has been investigated analytically under the variable load condition. When the mismatch is occurred, the result is an increase in the energy consumption or transmission quality deterioration. In addition, the input module in antenna system could be damaged if reflection of the signal levels is excessively high. This is interesting application because antennas cannot be considered alone as component with changing electromagnetic properties. The rectangular microstrip antenna was designed at 2.5 GHz frequency by using microstrip feed line. Better return loss level which is −16.86 dB has been obtained for this antenna using π‐matching circuit. It is shown that theoretical, simulation, and laboratory results are good agreement. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 410–415, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23101

Automatic antenna‐tuning unit for software‐defined and cognitive radio

AbstractThis paper discusses the implementation of an automatic antenna tuning unit system (ATU) for software‐defined and cognitive radio. The ATU simplifies radio frequency (RF) front‐end design for multi‐band, multi‐mode radios by allowing an electrically small reconfigurable antenna to become a frequency‐agile selective component (essentially a tunable filter). In implementing the ATU, impedance synthesizers (tunable matching networks) using RF MEMS switches as the control elements are used to match a more or less arbitrary load to a convenient impedance value. To generate feedback data that can be used to optimize the impedance synthesizer, the incident and reflected powers at the input to the impedance synthesizer are sampled using a power sensor block comprising directional coupler, logarithmic RF power detectors, analog‐to‐digital converters (ADCS), and return loss computation algorithms running on a field programmable gate array (FPGA). From a practical point of view, in order to be compatible with commercial wireless handset devices, we propose to design and ultimately implement a fully integrated ATU system. In this paper, a hard‐ ware implementation of the ATU prototype has been demonstrated to verify narrowband automatic tuning ability of the ATU under constantly changing environment conditions, and we present simulated results for a logarithmic power detector designed with 55 dB dynamic range over the 800 MHz–2 GHz frequency band using 0.25 µ CMOS technology. Copyright © 2007 John Wiley & Sons, Ltd.

Application of the genetic algorithm and simulated annealing to LC filter tuning

The paper discusses and compares the application of genetic algorithm and simulated annealing methods to LC filter tuning. Specifically, the paper is concerned with the application and implementation of these methods for the development of a fast microprocessor-based automatic antenna tuning unit, providing the facility to adapt to changes in load impedance, temperature or environment. A number of simulations were carried out to evaluate the relative performance of these algorithms. Finally, experimental results are presented where the simulated annealing algorithm was used to control a commercial impedance matching device in real time.

Fast antenna tuning using transputer based simulated annealing

A method of applying simulated annealing to the control of an antenna tuning unit (ATU) is presented. This includes implementation of the algorithm on a transputer architecture and a diagnosis procedure to calculate the load impedance in a timely fashion and to allow the system to adapt to changes in the environment.