FEATURES OF WIDEBAND DEVELOPMENT OF RESISTANCE TRANSFORMERS IN HF RANGE, LOADED ON LOW-IMPEDANCE ABSORBERS

A device based on a resistance transformer for matching a low-resistance load, including an electrically small short-wave antenna, with a transceiver equipment is described. The results of prototyping and modeling of broadband matching transformers with ferrite cores with transformation ratios 4:1, 9:1, and 25:1 are presented. A model of a matching transformer operating on a low-resistance absorber is proposed. The results of measurements and modeling of the effect of frequency dependences of the complex resistance of low-resistance resistors of various types used as loads on the measured characteristics of transformers are presented. An increase in the influence of parasitic parameters of the load, winding terminals, compensating reactivity of elements and the transformer itself on its characteristics with a decrease in the load resistance is shown.

Method for the synthesis of broadband devices with an optimal characteristic of the power conversion factor, matching the time-varying load impedance.

A method is proposed for the synthesis of broadband matching devices that adapt radio engineering systems to the changing load impedance in a wide range of natural conditions of their operation. The results of experimental studies of the effect of operating conditions on the impedance of VHF and UHF radio antennas with matching devices are presented. An invariant of the sensitivity of the reflection coefficient function to changes in the load impedance is obtained, on the basis of which a complex criterion for the synthesis of broadband matching devices is developed. A broadband matching circuit was synthesized for the AD-44/CW-TA-30-512 antenna device, which provides a gain in the potentially achievable radio line range of up to 5% in relation to the standard matching device. An analytical mathematical model of a broadband matching device is developed and based on it, a matching device adaptive to the changing impedance of the AD-25/CW-3512 antenna is synthesized, providing an average gain in the potentially achievable range of the radio line from 2% to 15% in the framework of the presented experimental studies.

Methods for synthesis of matching circuits for broadband radio devices with unstable load impedance

The aim of this work is to select a synthesis method for a broadband matching circuit that provides maximum power transfer from a signal source to a load in the presence of a changing load impedance of a radio engineering device. To achieve this goal, an analysis of the main directions of designing broadband matching circuits (analytical, numerical, graphic-analytical synthesis methods) was carried out. Based on the results of a comparison of synthesis methods, their features (advantages and disadvantages) were indicated. The analysis of methods of synthesis of broadband matching circuits was carried out. For the analysis, the generalized Darlington method, the method of real frequencies, the structural-parametric synthesis method based on the T-matrix apparatus, and the graphic-analytical method based on the Volpert-Smith diagram were chosen). Using these synthesis methods, broadband matching circuits were obtained for various types of loads. Comparison of the results obtained was carried out according to several indicators: the level of the power transfer coefficient in the operating frequency range, the sensitivity of the power transfer coefficient to the change in the ratings of the elements of the matching circuit and the load impedance, provided that the number of elements of the matching circuit is no more than six. Based on the comparison and analysis, it was found that the most preferable synthesis method for solving the problem posed is the method of real frequencies. Its advantage is the use of a combination approach (iterative determination of the parameters of the resistance function with an analytical representation of the transfer function). Matching circuits obtained using this synthesis method provided the highest level of power transmission coefficient, as well as the lowest sensitivity value in a given frequency band for the considered types of loads.

Conditions for the physical realizability of a typical component z(y)-matrix of a matching quadrupole of a general form in a concentrated elemental basis

When solving problems of broadband matching, very often there is a need for a certain form of the amplitude-frequency characteristic. In connection with this, the problem comes up of synthesizing broadband matching devices that simultaneously have correcting properties, i.e. having a given frequency dependence of the power conversion coefficient in the operating frequency band. The use of broadband reactive matching - correcting circuits in most practical cases is difficult because of the reflected power. This leads to the problem of the synthesis of broadband matching-correcting circuits with arbitrary immittances of the signal source and load in an elemental basis of a general form, containing along with reactive and active elements, which has not been adequately solved. Therefore, it becomes necessary to find the conditions for the physical realizability of a typical component of the immitance matrix of a two-port network of general form containing poles in the left half-plane of complex frequencies. In this paper the necessary and sufficient conditions are defined for the physical realizability of the immitance matrix of a typical component of a subclass of two-terminal networks of general form in a lumped elemental electric basis, when the poles of the Eigen functions in the Foster representation can be in the left half-plane of complex frequencies, excluding the imaginary and real axes. This allows to synthesis of broadband dissipative matching, matching-correcting circuits and matched attenuators in an elemental basis of a general form with arbitrary immitances of the signal source and load from a single point of view.

Own parameters of an ideal two-port for low noise matching

The problem of broadband matching of active elements in terms of noise figure is inevitably encountered in the design of broadband low-noise microwave amplifiers. Despite the fact that this problem differs from the classical problem of broadband matching of signal source and load, it can be reduced to a form suitable for applying methods for solving the classical problem. For this purpose, in this work, the own parameters of a reactive two-port network are derived that match active elements in terms of noise figure in the entire frequency band, where the data for calculating this coefficient are determined. The own parameters of such a two-port network, on the one hand, make it possible to construct methods for the synthesis of input matching circuits of low-noise amplifiers and other devices where low noise matching is required. On the other hand, the own parameters allow one to construct estimates of the maximum achievable bandwidth for a matching circuit of a given complexity.