RU2432643C1 - Bandpass microwave filter - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: device comprises a dielectric substrate, at one side of which there is a grounding screen, and at the other side - a microstrip structure, which realises filter elements with link chains. At the same time the microstrip structure includes four resonators, two capacitors for connection of a signal source and a load, three capacitors to provide an electric connection between neighbouring resonators, and also a transformer on joined transmission lines, which is connected by two arms between non-neighbouring resonators, and two its other arms are closed to the grounding screen. At the same time connection between the neighbouring first, second, third and fourth resonators are of capacitance type, and connection between the non-neighbouring first and fourth resonators is of inductance type. Each resonator may be arranged in the form of a section of a short-circuited strip line or in the form of a coaxial pin. The transformer may be arranged with the possibility to change the distance between joined transmission lines.

EFFECT: invention makes it possible to smoothly tune selectivity of a frequency characteristic, reduction of losses and increased selectivity near a working strip of the bandpass microwave filter without distortion of characteristics in the working strip.

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Description

The invention relates to techniques for microwave frequencies and can be used in frequency-selective circuits of microwave transceivers.

A microwave filter is known from the prior art (US patent No. 6529750, publication date 03/04/2003) containing a dielectric substrate, on one side of which there is a conductive screen, and on the other a microstrip structure that implements filter elements with communication circuits between two non-adjacent resonators to increase selectivity near the filter working band.

The disadvantages of this device are the inability to adjust the filter for selectivity and increased accuracy of equipment for the manufacture of microstrip structures.

Known microwave microstrip filter ("Compact microstrip filters with increased selectivity", Nikolaev M., Modern Electronics, No. 1 2008, p. 28-30) containing a dielectric substrate, on one side of which is a conductive screen, and on the other side is a system coupled strip conductors. The required form of the frequency response of the filter, and therefore the selectivity, is provided by the choice of links between adjacent and non-adjacent resonators. The connection between non-adjacent resonators is established by means of an open at the ends of the strip line. The presence of inductive spatial coupling between non-adjacent filter cavities gives attenuation poles in the obstacle band at the given frequencies, which provides an increase in filter selectivity.

The disadvantages of this device are the inability to smoothly adjust the filter for selectivity, since the selectivity of this filter depends on the magnitude of the connection between non-adjacent resonators, which is fixed by the topology of the open strip line, as well as the size of the gaps between it and non-adjacent resonators associated with it (tuning is possible only discrete, usually carried out by removing discrete sections of the strip line open at the ends); the impossibility of reversibly adjusting the filter for selectivity (adjustment is only possible irreversible, since it is carried out by removing discrete sections of the strip line open at the ends).

Known microstrip microwave filter (patent for invention RU No. 1683099, published on 10/07/1991, IPC: Н01Р 1/205), selected as a prototype. The microwave microstrip filter contains a dielectric substrate, on one side of which there is a conductive screen, and on the other side is a system of coupled resonators of strip V-shaped conductors. The required form of the frequency response of the filter, and therefore the selectivity, is ensured by an appropriate choice of links between adjacent and non-adjacent resonators. The connection between non-adjacent resonators is established by means of a shortened strip line. The presence of a certain connection between non-adjacent filter resonators gives attenuation poles in the obstacle band at given frequencies, which ensures an increase in filter selectivity.

The disadvantages of this device are: the lack of the ability to adjust the filter for selectivity, since the selectivity of this filter depends on the magnitude of the connection between non-adjacent resonators, which is fixed by the topology of the shortened strip line, and the gaps between it and the non-adjacent resonators associated with it; increased accuracy of equipment for the manufacture of a microstrip structure, necessary to realize the required coupling coefficient between the shorted strip line at the ends and the non-adjacent resonators associated with it.

The technical result of the proposed technical solution is to provide the possibility of smoothly adjusting the selectivity of the frequency response, reducing losses and increasing selectivity near the working band of the microwave pass-band filter, without distorting the characteristics in the working band.

The technical result is achieved due to the fact that the microwave pass-band filter contains a dielectric substrate, on one side of which there is a grounding screen, and on the other side, a microstrip structure that implements filter elements with communication circuits. At the same time, it differs from the prototype in that the microstrip structure includes the first, second, third and fourth resonators, some of whose conclusions are closed to the grounding screen, while others are interconnected by means of the first, second and third capacitors. In this case, the first and fourth resonators are connected to the fourth and fifth capacitors, respectively, as well as to the two arms of the transformer on the connected transmission lines, the other two arms of which are closed to the grounding screen, forming a capacitive coupling between the adjacent first, second, third, and fourth resonators , and between the non-adjacent first and fourth resonators there is an inductive type coupling. Moreover, each resonator of the microwave pass-band filter can be made in the form of a segment of a short-circuited strip line, or in the form of a corresponding coaxial pin. The microwave bandpass filter transformer is configured to vary the distance between the associated transmission lines.

The technical essence of the invention is illustrated by drawings, where:

Figure 1 - design of a bandpass microwave filter;

Figure 2 - the design of the transformer on the connected transmission lines;

Figure 3 - frequency response of the selectivity of the microwave pass-band filter.

The microwave bandpass filter is made in the form of a dielectric substrate 1, on one side of which there is a grounding shield 2. On the other side of the dielectric substrate, the microwave bandpass filter contains a microstrip structure, including the first 3, second 4, third 5 and fourth 6 resonators, one the conclusions of which are closed to the grounding screen 2, and the others are interconnected by means of the first 7, second 8 and third 9 capacitors. In this case, the first 3 and fourth 6 resonators are connected to the input and output of the filter by means of the fourth 10 and fifth 11 capacitors, respectively, as well as by microstrip communication lines 17 and 18, they are connected to two arms 12 of the transformer 13 on the connected transmission lines 14 and 15, two the other arms 16 of which are closed to the grounding shield 2, forming a capacitive coupling between adjacent first 3, second 4, third 5 and fourth 6 cavities, and an inductive coupling between non-adjacent first 3 and fourth 6 cavities. Moreover, each resonator 3, 4, 5, 6 of the microwave pass-band filter can be made in the form of a segment of a short-circuited strip line, or in the form of a corresponding coaxial pin. The transformer 13 on the connected transmission lines of the microwave bandpass filter is configured to change the distance between the connected transmission lines 14, 15.

In the proposed design of the microwave pass-band filter, the coupling between adjacent resonators 3, 4, 5, 6 is of a capacitive type, and between non-adjacent resonators 3, 6 of an inductive type. In accordance with the general theory of coupled resonators (Hong J.-Sh., Lancaster MJ Microstrip Filters for RF / Microwave Applications. John Wiley & Sons, Inc, 2001), this combination of coupling types in the four resonators gives a pair of attenuation poles on either side of the band transmission, increasing the selectivity of the microwave pass-band filter.

All capacitors 7, 8, 9, 10, 11 of the microwave pass-band filter can be elements with distributed or concentrated parameters.

The operation of the microwave pass-band filter is as follows. The input microwave signal is fed to the input of the microwave pass-band filter and is filtered by a frequency-selective structure formed of capacitors 10 and 11, resonators 3, 4, 5, 6 and communication elements between the resonators (capacitors 7, 8, 9 and transformer 13) . By changing the distance between the connected transmission lines 14, 15 of the transformer 13, the coupling coefficient between the non-adjacent first resonator 3 and the fourth resonator 6 is changed, which leads to a change in the position of the attenuation poles on both sides of the passband, changing the selectivity of the microwave pass-band filter. The selectivity of the microwave pass-band filter in this invention is carried out mechanically, by bending the wire jumpers used as elements of the connected transmission lines 14, 15 of the transformer 13, without the use of special tools and a microscope, which helps to reduce the complexity and ensure manufacturability.

For an example of a specific implementation (FIG. 2), one embodiment of a transformer 13 is shown on connected lines 14, 15 included in a microwave pass-band filter. The connected lines 14, 15 of the transformer 13 are made in the form of U-shaped wire jumpers 16, which are connected on one side to the grounding screen of the microstrip structure and, on the other hand, are connected to microstrip connected lines 17, 18, which communicate with two non-adjacent first resonators 3 and the fourth resonator 6. When bending the jumpers 16 of the transformer 13 in the transverse direction, the distance W changes, and therefore the coupling coefficient between the connected lines 14, 15, which leads to a change in the position of the attenuation poles along baa side of the bandwidth by changing the selectivity bandpass microwave filter.

Figure 3 shows the experimental characteristic of the selectivity of the frequency response of the microwave pass-band filter, depending on the distance W between the jumpers 16 of the transformer 13. From the comparison of the curves it is seen that with decreasing distance W between the jumpers 16, the selectivity near the working band of the microwave pass-filter increases .

In the proposed microwave pass-band filter, the possibility of smoothly adjusting the frequency response according to selectivity by introducing a change in the coupling coefficient between the connected lines of the transformer 13 connected between the non-adjacent first resonator 3 and the fourth resonator 6 is introduced.

The proposed design of a microwave pass-band filter allows for the possibility of reversibly adjusting its frequency response according to selectivity (the ability to change its coupling coefficient between the connected lines 14, 15 of the transformer 13 to its original value).

In the proposed microwave pass-band filter, the requirements for precision manufacturing of a microstrip structure are reduced. The ability to smoothly adjust the frequency response of the microwave pass-band filter for selectivity allows to reduce the sensitivity of its parameters to the accuracy of manufacturing a microstrip structure, which significantly reduces the cost of the device.

Claims (4)

1. A microwave bandpass filter containing a dielectric substrate, on one side of which a grounding shield is placed, and on the other side is a microstrip structure realizing filter elements with communication circuits, characterized in that the microstrip structure includes first, second, third and fourth resonators some conclusions of which are closed to the grounding screen, while others are interconnected by means of the first, second and third capacitors, while the first and fourth resonators are connected to the fourth and fifth capacitors respectively, as well as with two arms of the transformer on connected transmission lines, the other two arms of which are closed to the grounding screen, forming a capacitive coupling between adjacent first, second, third and fourth resonators, and an inductive coupling between the adjacent first and fourth resonators type. 2. The microwave pass-band filter according to claim 1, characterized in that each resonator is made in the form of a segment of a short-circuited strip line. 3. The microwave pass-band filter according to claim 1, characterized in that each resonator is made in the form of a coaxial pin. 4. The microwave pass-band filter according to claim 1, characterized in that the transformer is configured to change the distance between the connected transmission lines.

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