SU1758721A1 - Bandpass filter - Google Patents

Abstract

This invention relates to frequency selective miniature microwave devices. The goal is to eliminate spurious bandwidths. The band-pass filter contains a segment 1 of the transmission line, to which loops 2, 3 are connected in parallel at equal distances from one another. The execution of loops 2 closed with a given law of wave impedance change, and loops 3 open, eliminates parasitic passbands by combining the frequencies of poles and zeros introduced by loops 2, 3 at all frequencies except for workers. 2 yl

Description

The invention relates to a microwave technique and can be used in the construction of frequency selective devices.

A band-pass filter is known with direct connections to the half-wave resonators through the end capacitances.

The disadvantage of such a filter is the difficulty of practical implementation of small gaps between half-wave resonators and the criticality of the frequency response of the filter to the width of these gaps.

Closest to the proposed technical solution is a band-pass filter containing a segment of the transmission line, to which the loops are connected in parallel at equal distances from one another.

A disadvantage of the known bandpass filter is the presence of spurious bandwidths.

The purpose of the invention is to eliminate spurious bandwidths.

The goal is achieved by the fact that in a band-pass filter containing a segment of a transmission line, to which loops are connected in parallel at equal distances from one another, some loops are made short-circuited and with a wave resistance varying according to a certain law. .

1 shows the construction of a band pass filter.

The band pass filter contains a segment of transmission line 1, to which, at equal distances from each other, loops 2 and 3 are connected in parallel, and loops 2 are made short-circuited and with a wave resistance varying according to a certain law, and loops 3 are open.

The band pass filter works as follows.

The microwave signal in the passband passes through a section of transmission line 1, in

with C

x |

el oe

x |

hO

The barrier is reflected due to the presence of loops 2 and 3.

The effect of eliminating parasitic passbands in a band-pass filter is achieved by the fact that the frequencies of the successive a) 0 (-1,2, ...) and parallel Wpi resonances of the two types of loops are mutually opposite and compensate each other, m. e. the frequencies o) oi of one loop coincide with the frequencies Wpi of another loop and vice versa. Moreover, mutual compensation takes place for all resonant frequencies, except for one frequency of the series resonance Won of a short-circuited loop with a variable impedance, which does not coincide with the frequency of the parallel resonance Wpn of the open loop, a) Op-co pp. In the vicinity of these mismatched frequencies, the only passband of the filter is located. The wave impedance function of the short-circuited loop W (t), t is the current coordinate, measured from the connection point of the loop to the transmission line segment, is described by

W (t) W0 x

L

1 + Jon tg w pn rtg won r

(one

w

pn

+ lpn tg m pn rtgwon t Won

where W0 is the characteristic impedance of the short-circuited cable at the point of its connection to the transmission line segment.

In the above expression, the sequence number n of the eigenfrequencies Won, Wpn can be chosen at its own discretion, which allows the single bandwidth of the filter to be shifted to a region of lower or higher frequencies. The value of n 1 corresponds to the bandwidth on oscillations of the AO / 2 type, and the value of n 2 corresponds to the bandwidth on oscillations x 2 To / 2, etc.

FIG. Figure 2 shows the frequency distributions of the serial and parallel resonances of the loops.

FIG. 2a shows the eigenfrequencies of an open loop, the frequency axis is normalized with respect to the value of a) 01: o) 0) in FIG. 26-frequency, wpi squirrel loop; Fig. 2b shows the eigenfrequencies of a short-circuited loop with a variable impedance impedance, whose frequency Sho 1 differs from w P1 of the open loop (in this case the filter passband corresponds to the oscillations Lo / 2); in fig. 2d is the frequencies of parallel and series resonances of a short-circuited irregular loop, whose value w 02 differs from w P2 of the open loop. The bandwidth of the filter with such loops corresponds to oscillations of the type 2 Le / 2.

Claims (1)

Claims of the invention A band-pass filter containing a segment of the transmission line to which the loops are connected in parallel at equal distances from one another, about tl and h. so that, in order to eliminate spurious bandwidths, some of the loops are made korogkozaklyutymi and with impedance, changing according to the law W (t) W0 x 1 + pn Ttg Won g a) pn 1 + tgw pn rtg won r where Wo is the characteristic impedance of the short-circuited loop at the point of its connection to the transmission line segment; Won is the frequency of the series resonance of the short-circuited loop; Wpn is the frequency of the parallel resonance of the open loop; p 1,2 „..; t is the current coordinate of the short-circuited loop, starting from the point of its connection to the segment of the transmission line; and other loops are open. 1 XX SGH- 0 WO / -about- ; topi -k- yrg # - Could rg Мoz Mrz ob Mpb h) Xo about “W -j 02 TW / 7J ctf nope 0lt #  l N0} -6 - Hf g. 2 W / 7J ctf nope 0lt 0) . 4t  l -Ha) about; five and)