M.Yu. Zakharchenko – Ph.D.(Eng.), Associate Professor, Head of Departament,

Yuri Gagarin State Technical University of Saratov

E-mail: ppk_spo@sstu.ru

Yu.F. Zakharchenko – Ph.D.(Phys.-Math.), Senior Research Scientist,  Saratov branch of the Kotel’nikov IRE of RAS

E-mail: zaharchenko@mail.ru

K.M. Al Ali Abdul’ – Student, 

Yuri Gagarin State Technical University of Saratov E-mail: ppk_spo@sstu.ru

To realize a large gain in power output stage with a bipolar or field-effect transistor in its input and output circuits in receiving and transmitting radio devices of the high-frequency and ultra-high-frequency ranges resonant LC-circuits are used. Depending on the operating frequency range, LC circuits can be made on the basis of lumped-constant capacitors and inductances, or on the basis of symmetrical and asymmetrical strip lines. The quality factor of such circuits is within the limits of 300…1500. Such quality factor values determine the bell-shaped frequency-response characteristic of the LC-circuit with a bandwidth of not more than a few percent. But for the back ends a pi-section resonance characteristic of the gain is required. This characteristic is realized by detuning the resonant frequency of the LC-circuits in the input and output circuits of the stage in different directions from the band center of the transistor resonance band. However, in this case, the bandwith of amplified frequencies is less than 10…15%. Herewith the adjustment of the stage parameters becomes much more complicated, first of all, in the range of ultrahigh frequencies due to a decrease in its resistance to self-excitation.

A LC-circuit with a concentrated capacitance C and inductive loss L which form a parallel resonant circuit connected in series through a resistor to an alternating voltage source is considered. A phase shifting element in the form of a two-terminal-pair network chain with a negative phase-frequency characteristic is included in the circuit in series with L. The study of the parameters of the proposed LC circuit, providing a pi-section resonance characteristic in the frequency band more than 20%. For the analysis of the basic regularities of the circuit Kirchhoff laws for electrical circuits of alternating current are used. The calculation of the frequency dependence of the transmission coefficient in the form of the ratio of the voltage in the LC-circuit to the voltage of the AC voltage source is carried out using Mathematica 7.0 computing system. The diagrams of the frequency dependence of the transmission coefficient for a range of values of the number N of a two-terminal-pair network in the chain of the phase-shifting element and the ratio of the wavenumber of the two-terminal-pair network to the wavenumber of the LC-circuit have been obtained.

In the LC-circuit containing a phase-shifting element with a negative phase-frequency characteristic in the form of a chain of N twoterminal-pair network with high resonant impedance a pi-section resonance characteristic in the frequency band more than 20% can be realized. The optimal parameters of the proposed LC-circuit model are ensured with equal resonance frequencies of the LC-circuit and the phase-shifting element. In this case the impedance of the LC-circuit must be N times high than the impedance of a twoterminal-pair network in the phase-shifting element. The bandwidth of a pi-section resonance characteristic of the LC-circuit is 20…50% depending on the number of the resonant frequency of the phase-rotation element. Herewith the width of the strip slightly depends on N. The research results can be used in the implementation of a pi-section resonance characteristic with a frequency band more than 20% in high-frequency and ultra-high-frequency resonant lamp and transistor amplifiers. The proposed principle of construction of a wideband LC-circuit with a high impedance is of interest as an ideological basis for the development of wideband microwave resonators of planar design for transistor amplifiers of the long wavelength part of super high frequency (SHF) band as well as for the development of wideband cavity resonators with high impedance for vacuum microwave devices like tristron and klystron in the entire SHF wavelength range

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