RU2513764C2 - Band-pass lc filter with reflection compensation in stop-band - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: disclosed device relates to radio electronics and can be used as input selecting circuits of professional-grade radio receivers. The band-pass LC filter with reflection compensation in the stop-band, having multiple cascade-connected links with an identical structure, each having a first inductance coil, the first lead of which is the input of the link, the second lead being connected to a first capacitor, the second lead of which is connected to second and third capacitors, the second lead of the second capacitor is connected to a common bus, the second lead of the third capacitor is connected to a second inductance coil, the second lead of which is the output of the link, wherein the first lead of the first inductance coil of the first link is connected to a fourth capacitor and a third inductance coil, wherein the second lead of a fourth capacitor is connected through a first resistor to the common bus, and the second lead of the third inductance coil is connected through a second resistor to the common bus.

EFFECT: improved standing wave ratio at the input of the band-pass circuit in stop-bands.

4 dwg

Description

The proposed device relates to radio electronics and can be used as input selector circuits of professional radio receivers.

Various types of LC bandpass filters are used as input circuits in radio receiving devices of the mainline radio communication, the task of which is to provide preliminary selection of the received signals, to ensure matching with the antenna at the maximum possible transmission coefficient in the passband of the filter.

One of the options for implementing a strip input circuit is a band filter, consisting of several links, each of which contains a first inductor, the first output of which is an input of the link, its second output is connected to the first capacitor, the second output of which is connected to the second and third capacitors, and the second the output of the second capacitor is connected to a common bus, the second output of the third capacitor is connected to the second inductor, while the second output of the second inductor is the output of a [1]. This filter is the closest analogue to the proposed solution and is selected as a prototype. It contains the smallest possible number of inductors, which allows to realize the maximum transfer coefficient of the input device. The necessary attenuation in the delay band is provided by an appropriate choice of the number of links.

The disadvantages of the filter prototype is that its input impedance in the delay bands is reactive and does not provide coordination with the active load of the signal source, which would provide any acceptable coefficient of the standing wave.

The objective of the invention is to improve the coefficient of a standing wave at the entrance of a strip circuit in the delay bands.

The problem is solved in that in a band-pass filter containing several cascade-connected, identical in structure links, each of which has a first inductor, the first output of which is the input of the link, its second output is connected to the first capacitor, the second output of which is connected to the second and third capacitors, while the second terminal of the second capacitor is connected to a common bus, the second terminal of the third capacitor is connected to the second inductor, the second terminal of which is the output of this Vienna, an additional fourth capacitor, a third inductor, first and second resistors are introduced, while a fourth capacitor and a third inductor are connected to the first output of the first inductor of the first link, the second output of the fourth capacitor connected to the common bus through the first resistor and the second output the third inductor through the second resistor is connected to a common bus.

Comparative analysis shows that the claimed solution differs from the prototype in that the fourth capacitor and the third inductor are connected to the first output of the first inductance coil of the first link, the second output of the fourth capacitor connected to the common bus through the first resistor, and the second output of the third inductance through the second the resistor is connected to a common bus.

When comparing the claimed device not only with the prototype, but also with other technical solutions known in science and technology, no solutions were found that have similar characteristics.

Figure 1 presents the electrical circuit of the claimed device. The filter contains several identical in structure links of the band-pass filter 1, each of the links contains a first inductor 2 connected to the first capacitor 3, the second output of which is connected to the second 4 and third 5 capacitors, the second output of the third capacitor is connected to the second inductor 6. In addition Moreover, the fourth capacitor 7 and the third inductor 8 are introduced into the filter circuit, the first terminals of which are connected to the first output of the first inductor. The second output of the fourth capacitor 7 through the first resistor 9 is connected to a common bus, the second output of the third inductor 8 through a second resistor 10 is connected to a common bus.

The device operates as follows.

The band-pass filter 1 forms the amplitude-frequency characteristic (AFC) of the device and has a characteristic resistance of the second class, the frequency dependence of which is presented in figure 2. In the frequency band from ω ₁ to ω ₂ its characteristic resistance is active, in the frequency band from zero to ω ₁ - capacitive, at frequencies from ω ₂ and above - inductive. With an increase in detuning from the edges of the passband, the filter input resistance module increases.

A circuit consisting of a capacitor 7, the capacitance of which is denoted by C ₁ , and a resistor 9 of value R ₁ will bypass the input resistance of the original filter. In this case, the conductivity of this circuit is

$$Y_{\mathrm{one}}=\frac{j\omega C_{\mathrm{one}}}{\mathrm{one}+j\omega C_{\mathrm{one}}{R}_{\mathrm{one}}}=\frac{j\omega C_{\mathrm{one}}+{\omega }^2{C}_{\mathrm{one}}^2{R}_{\mathrm{one}}}{\mathrm{one}+{\omega }^2{C}_{\mathrm{one}}^2{R}_{\mathrm{one}}^2}(\mathrm{one})$$

The real part of the conductivity Y ₁ and its modulus can be represented as

$$\mathrm{Re}{Y}_{\mathrm{one}}=\frac{\mathrm{one}}{R_{\mathrm{one}}}\cdot \frac{Q_{\mathrm{one}}^2}{\mathrm{one}+Q_{\mathrm{one}}^2}(2)$$

, где $$|\; |\; |Y_{\mathrm{one}}|\; |\; |=\frac{\mathrm{one}}{R_{\mathrm{one}}}\cdot \frac{Q_{\mathrm{one}}}{\sqrt{\mathrm{one}+Q_{\mathrm{one}}^2}}$$

where

Q ₁ = ωC ₁ R ₁ - reduced quality factor of the chain.

изменяются от нуля до величины $$\frac{1}{R_1}$$

с ростом частоты. На частотах, когда Q₁>1, входное сопротивление фильтра шунтируется этой цепью и приближается к величине R₁.ReY ₁ and $$|\; |\; |Y_{\mathrm{one}}|\; |\; |$$

vary from zero to magnitude $$\frac{\mathrm{one}}{R_{\mathrm{one}}}$$

with increasing frequency. At frequencies when Q ₁ > 1, the input impedance of the filter is bridged by this circuit and approaches R ₁ .

The second circuit, consisting of an inductance 9 of value L ₂ and a resistor 10, the value of which is equal to R ₂ , also shunts the input resistance of the filter. 1. The conductivity of this circuit is determined by the expression

$${\mathrm{<figure-callout\; id="2"\; label="Y"\; filenames="00000014.png,00000016.png"\; state="\{\{state\}\}">Y</figure-callout>}}_2=\frac{R_2-j\omega L_2}{R_2^2+{\omega }^2{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="00000014.png,00000016.png"\; state="\{\{state\}\}">L</figure-callout>}}_2^2}$$

$$\mathrm{Re}{\mathrm{<figure-callout\; id="2"\; label="Y"\; filenames="00000014.png,00000016.png"\; state="\{\{state\}\}">Y</figure-callout>}}_2=\frac{\mathrm{one}}{{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="00000014.png,00000016.png"\; state="\{\{state\}\}">R</figure-callout>}}_2}\cdot \frac{\mathrm{one}}{\mathrm{one}+{\mathrm{<figure-callout\; id="2"\; label="Q"\; filenames="00000014.png,00000016.png"\; state="\{\{state\}\}">Q</figure-callout>}}_2^2}(3)$$

, где $$Q_2=\frac{\omega L_2}{R_2}$$

. $$|\; |\; |{\mathrm{<figure-callout\; id="2"\; label="Y"\; filenames="00000014.png,00000016.png"\; state="\{\{state\}\}">Y</figure-callout>}}_2|\; |\; |=\frac{\mathrm{one}}{{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="00000014.png,00000016.png"\; state="\{\{state\}\}">R</figure-callout>}}_2\sqrt{\mathrm{one}+{\mathrm{<figure-callout\; id="2"\; label="Q"\; filenames="00000014.png,00000016.png"\; state="\{\{state\}\}">Q</figure-callout>}}_2^2}}$$

where $${\mathrm{<figure-callout\; id="2"\; label="Q"\; filenames="00000014.png,00000016.png"\; state="\{\{state\}\}">Q</figure-callout>}}_2=\frac{\omega L_2}{{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="00000014.png,00000016.png"\; state="\{\{state\}\}">R</figure-callout>}}_2}$$

.

и ReY₂ с изменением частоты от нуля до бесконечности уменьшаются от величины, равной $$\frac{1}{R_2}$$

до нуля. На частотах, когда $$\frac{\omega L_2}{R_2}<1$$

, сопротивление этой цепи приближается к R₂ а затем по мере увеличения частоты возрастает.Quantities $$|\; |\; |{\mathrm{<figure-callout\; id="2"\; label="Y"\; filenames="00000014.png,00000016.png"\; state="\{\{state\}\}">Y</figure-callout>}}_2|\; |\; |$$

and ReY ₂ with a change in frequency from zero to infinity decrease from a value equal to $$\frac{\mathrm{one}}{{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="00000014.png,00000016.png"\; state="\{\{state\}\}">R</figure-callout>}}_2}$$

to zero. At frequencies when $$\frac{\omega L_2}{R_2}<\mathrm{one}$$

, the resistance of this circuit approaches R ₂ and then increases with increasing frequency.

Thus, the combined influence of these two circuits with an appropriate choice of their parameters (for example, when R ₁ = R ₂ = R _n and Q ₁ = Q ₂ ≈0.5 ÷ 1.0 at the average filter frequency) leads to equalization of the input filter resistance in detention bands. The input filter resistance can be approximated at these frequencies to the resistance of the signal source, the energy of the source is released on the resistors 9 and 10. This allows a relatively simple way to improve the standing wave coefficient.

Figure 3 shows the frequency response of a band-pass filter at a frequency of 40 MHz with a bandwidth of 15 MHz, a diagram of which with the inclusion of corrective circuits is shown in figure 4. The standing wave coefficient (SWR) in the passband of the filter is 1.5 ÷ 1.6, in the delay bands it is 1.8 ÷ 1.9. At the edges of the passband, the SWR is 3.1. Insertion attenuation in a passband of 2.9 dB at a quality factor of inductors of 100 units

The source of information

N.E. Pleshkov, A.M. Zingerenko, B.C. Lavrish, V.F. Klimovich, B.K. Isakson. Telecommunication technology. -L.: VKAS, 1951, p. 220, Fig. 181.

Claims (1)

A band-pass LC filter with compensation for reflections in the delay band, which contains several cascade-connected, identical in structure links, each of which has a first inductance coil, the first output of which is the input of the link, its second output is connected to the first capacitor, the second output of which is connected to the second and a third capacitor, wherein the second terminal of the second capacitor is connected to a common bus, the second terminal of the third capacitor is connected to a second inductor, the second terminal of which is the output this link, characterized in that the fourth capacitor and the third inductor are connected to the first output of the first inductance coil of the first link, the second output of the fourth capacitor connected to the common bus through the first resistor and the second output of the third inductance connected to the common bus through the second resistor.

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