RU2626296C2 - Resistance transformer - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: resistance transformer contains three cascaded sections of the quarter-wave line segments. Parallel to the three sections of the quarter-wave segments of the transmission line, one quarter-wave section is included, and one short-circuited quarter-wave section of the transmission line is connected parallel to the input.

EFFECT: reducing the relative non-uniformity of the group delay function in a given bandwidth with a given resistance transformation coefficient and a specified maximum standing wave ratio and expanding the bandwidth with less stringent requirements for the relative non-uniformity of the group delay function at a given maximum standing wave ratio.

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Description

The invention relates to electronics and can be used to match the active resistances without distorting the waveform in radio devices, television, communication systems and radio channels for transmitting telecommunications data.

A known resistance transformer based on a low-pass filter (see Matthaei GL Tables of Chebyshev Impedance-Transforming Networks of Low-Pass Filter Form. - Proceedings of the IEEE, August 1964, pp. 939-963), consisting of a cascade connection of L-shaped links containing inductance and capacitance. Such a transformer can be made on elements with lumped parameters in the form of a ladder chain at low frequencies or on elements with lumped parameters at frequencies of the microwave range.

The calculation of transformers in the form of a low-pass filter is performed using special tables based on such parameters as:

resistance transformation coefficient

,

,

where R _H is the load resistance, R _G is the generator resistance;

relative bandwidth

,

,

where ƒ _a is the lower limit of the passband, ƒ _b is the upper limit of the passband;

expressed in decibels, the amplitude of the attenuation pulsations in the passband L _Ar .

After determining the value of the transformation coefficient r, the relative bandwidth w and the maximum value L _Ar admissible for the given conditions, from the tables the number of reactive elements of the circuit is found to ensure the fulfillment of the given requirements. Then, also from the tables, the normalized values of the parameters of the circuit elements are determined, from which, by recounting, the values of the circuit elements corresponding to the specific application are obtained.

The disadvantage of a transformer based on a low-pass filter with lumped parameters is the nonlinearity of the phase-frequency characteristic, and, consequently, the unevenness of the group delay function (GB), which is the cause of the distortion of the waveform.

The relative non-uniformity of the group delay function is determined from the expression

,

,

where GD _min and GD _max are the minimum and maximum group delay times in the passband.

In addition, since a transformer based on a low-pass filter is a minimum-phase circuit, it is not possible to vary the relative non-uniformity of the GB function without increasing the maximum SWR level in a given frequency band.

Also known is a resistance transformer, consisting of a cascade connection of sections of quarter-wave transmission lines (see Mattey G.L., Young L., E.M. T. Jones. Microwave filters, matching circuits and communication circuits. - M .: Communication 1971, 217 p., Fig. 6.02.1). The resistance transformer, consisting of three cascade-connected sections of quarter-wave segments of transmission lines, is a prototype of the invention. Such a transformer, with a wide range of resistance transformation coefficient values, provides a relative bandwidth sufficient to solve most coordination problems. So, for the resistance transformation coefficient r = 10, the relative bandwidth is w = 78% at the level of SWR = 1.2. With lower transformation ratios, the relative bandwidth will be even greater.

The calculation of the wave impedances of the sections of the transmission line of the prototype transformer is performed using tables based on such parameters as the coefficient of transformation of the resistance (r) and the relative bandwidth (w).

From the table determine the value of the wave impedance of the first section. The wave impedances of the second and third sections are determined from the relations:

where r is the transformation coefficient of the resistances, Z _i is the wave impedance of the i-th section.

The disadvantage of the prototype is the non-uniformity of the GB function, the lack of the ability to vary the relative unevenness of the GB function without increasing the maximum level of SWR in a given frequency band.

So, with the resistance transformation coefficient r = 10, the relative bandwidth at the level of SWR = 1.2 is 78%, in which the relative non-uniformity of the GB function is 9.4%. In this case, the greatest non-uniformity of the GB function occurs at the edges of the passband.

The objective of the invention is to reduce the relative unevenness of the GB function in a given passband at a given resistance transformation coefficient and the maximum SWR level, as well as expanding the passband with less stringent requirements (or in the absence of requirements) to the relative unevenness of the GB function at a given maximum SWR level.

The task is achieved in that in the resistance transformer, which contains three cascade sections of the quarter-wave segments of the transmission line, parallel to the three sections of the quarter-wave segments of the transmission line, one quarter-wave section is included, and one short-circuited quarter-wave segment of the transmission line is included in parallel with the input.

In FIG. 1 shows an electrical schematic diagram of the proposed resistance transformer. In FIG. 2 shows a graph of the SWR of the proposed transformer (solid curve) and a graph of the SWR of the prototype (dashed curve). In FIG. 3 shows a graph of the GB function of the proposed device (solid curve) and a graph of the GB function of the prototype (dashed curve).

The proposed resistance transformer (Fig. 1) contains three cascade-connected sections of transmission line segments 4, 5 and 6. A section of transmission line 3 is connected in parallel to these sections. A short-circuited section of transmission line 2 is connected in parallel to the input. The electrical lengths of all segments of transmission lines at the central frequency are

.

.

The proposed resistance transformer operates as follows. As can be seen from the consideration of the structure shown in figure 1, the proposed transformer is a prototype transformer 1 on the quarter-wave segments 4, 5, 6. To give the prototype non-minimum phase properties parallel to three sections of the quarter-wave segments of the transmission line 4, 5 and 6 included one quarter-wave segment 3, which allows to reduce the relative non-uniformity of the GB function without significantly reducing the relative bandwidth and increasing the maximum level of SWR in the passband. The inclusion of a short-circuited quarter-wave segment of transmission line 2 parallel to the input allows you to expand the passband and reduce the uneven function of the GB at the borders of the passband.

Table 1 for the proposed resistance transformer with a maximum SWR level of ≤1.2 in the working frequency band, for three values of the resistance transformation coefficient and for various specified relative bandwidths (w), the values of the relative non-uniformity of the GB function (AGD) in the passband , values of wave impedances of segments of transmission lines (ρ _a , ρ _b , ρ _c , ρ _d , ρ _s ) obtained using optimization and computer simulation in the AWR Microwave Office program. The values of wave impedances are normalized relative to R _G = 1 Ohm.

Table 2 for the proposed resistance transformer with a maximum SWR level of ≤1.2 in the operating frequency band, for three values of the resistance transformation coefficient, the values of the maximum relative bandwidth are given in the absence of requirements for the heterogeneity of the GB function, the wave impedances of the transmission line segments (ρ _a , ρ _b , ρ _c , ρ _d , ρ _s ) obtained using optimization and computer modeling in the AWR Microwave Office program. The values of wave impedances are normalized relative to R _G = 1 Ohm.

Table 3 for a prototype having an SWR level of ≤1.2 in the operating frequency band, for three values of the resistance transformation coefficient and for various specified relative bandwidths, the values of the relative non-uniformity of the GB function (∆GD) normalized relative to R _Г = 1 Ohm values of wave impedances of sections of quarter-wave segments of a transmission line calculated using tables and expressions (1) and (2). In table 3, with the transformation coefficient r = 10, the relative bandwidth of the prototype w = 80% is taken at the level of SWR = 1.21.

In table 3, the symbol “-” indicates cases where the prototype does not provide a given relative bandwidth at the level of SWR = 1.2.

A comparison of tables 1 and 3 shows that the proposed transformer with stringent requirements for the heterogeneity of the function of the GB has a smaller relative uneven GB in the passband and is able to provide a large relative bandwidth with a large value of the resistance transformation coefficient.

From a comparison of tables 2 and 3 it can be seen that in the absence of requirements for the uneven function of the GB, the proposed transformer is able to provide a larger relative bandwidth than the prototype.

In FIG. Figures 2 and 3 present the results of computer simulations of the SWR and GZ of the proposed transformer (solid curve) and prototype (dashed curve). The results were obtained for the following initial data: r = 10, w = 80%. For this example, values normalized with respect to _r = R 1 ohm impedances quarter segments of the proposed transformer of FIG. 1: ρ _a = 37.1, ρ _b = 1.63, ρ _c = 4.48, ρ _d = 7.41, ρ _s = 3.04. The values of wave impedance sections of the quarter-wave segments of the prototype transformer, normalized relative to R _G = 1 Ohm: Z ₁ = 1,504, Z ₂ = 3,1623, Z ₃ = 6,6491.

For a given relative bandwidth of 80%, the prototype has a maximum SWR level of 1.21 in the passband, and the maximum SWR level of 1.2 for the proposed transformer. Due to the inclusion of additional quarter-wave segments of the transmission line, the heterogeneity of the GB function in the passband of the proposed transformer is more than three times less than the prototype: 2.3% of the proposed transformer versus 9.4% of the prototype.

A comparative analysis of the data given in the tables showed that the inclusion of one quarter-wave length of the transmission line parallel to three cascade sections of the quarter-wave length of the transmission line and one short-circuited quarter-wave length of the transmission line parallel to the input reduces the relative unevenness of the GB function in a given passband for a given resistance transformation ratio and the maximum level of SWR, and also allows you to expand the bandwidth with less hard x requirements (or there is no requirements) relative to PP function unevenness at a predetermined maximum level SWR.

The technical result is to reduce the relative unevenness of the GB function in a given bandwidth at a given maximum level of SWR = 1.2, the expansion of the bandwidth with less stringent requirements for the relative unevenness of the GB function (or the absence of such requirements) at a given maximum level of SWR = 1.2, the ability to vary the relative non-uniformity of the GB function without increasing the maximum level of SWR in a given frequency band.

Claims (1)

A resistance transformer containing three cascade-connected sections of quarter-wave segments of a transmission line, characterized in that one quarter-wave segment is included in parallel to three sections of quarter-wave segments of a transmission line, and one short-circuited quarter-wave segment of a transmission line is included in parallel with the input.

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