RU2766057C1 - Device for increasing amplitude frequency response of microwave filter unit - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to radio engineering and microwave engineering. Device for filtering microwave signals consists of a band-pass filter with internal connections between links, a rejection filter, the links of which are tuned so that the zeros of the rejection filters are located as close as possible to the pass band. Links of the notch filter have different characteristics of amplitude-frequency response in depth and band of rejection, a delay line, which is a line of connection between filters in the device and an element of control of amplitude-frequency response of the device. Band-pass filter is connected to the first controlled delay line, the first controlled delay line is connected to the first notch filter, first notch filter is connected to the second adjustable delay line, the second adjustable delay line is connected to the second notch filter, the bandpass filter consists of eight links, seven links between links and three links between mirror links, rejection filter consists of four rejection links connected to a single communication line, which is a strip line from the inlet to the outlet of the rejection filter, wherein the filter is configured to obtain a steepness of the amplitude-frequency response characteristic, which is greater than a similar characteristic, which is achieved by bandpass and rejection filters without using a delay line.

EFFECT: increase in the slope of the amplitude-frequency characteristic.

12 cl, 3 dwg

Description

The invention relates to radio engineering and microwave technology (hereinafter referred to as microwave), namely to multichannel microwave filters, consisting of bandpass and rejection filters, and connected by coaxial cables, which act as phase delays. The invention is intended for selection of signals in communication devices, radar, radio navigation and measuring equipment.

An urgent task is to increase the steepness of the fronts of various microwave filters, especially in cases where the difference between the cutoff frequency of the passband and the cutoff frequency of the stopband is less than 0.5% of the frequency.

Known bandpass filters (hereinafter - BPF) with additional screens according to patent RU 2688826 C1 ["MICROSTRIP BANDPASS FILTER", FGAOUVO "Siberian Federal University", 06/18/2018]. The presence of screens makes it possible to introduce additional losses in parasitic passbands and in the BPF blocking band.

The disadvantages include the impossibility of the influence of screens on the steepness of the slopes of the PPF itself. There is no description of the mutual influence of this type of filters on other filters when they are connected in a single device.

Known BPF with increased steepness due to the presence of connections according to the patent US6236292B1 ["BANDPASS FILTER", Delaware Capital Formation Inc., Jun. 30, 1999]. The proposed filter construction option has advantages over classical filters, due to obtaining filter frequency response zeros through the use of additional capacitive or inductive couplings.

The disadvantages include the impossibility of the influence of zeros on the steepness of the slopes of the BPF at frequencies close to the passband. There is no description of the mutual influence of this type of filters on other filters when they are connected in a single device.

Filters with links between PPF elements are known according to patent EP2741364A2 [“RADIO FREQUENCY FILTER EMPLOYING NOTCH STRUCTURE”, KMW Inc., 08/05/2011]. The proposed filter design option has advantages over classical filters, due to obtaining filter frequency response zeros through the use of additional capacitive and inductive couplings. The use of several connections at once allows you to form a larger number of zeros of the frequency response.

Taken as a prototype.

The disadvantages of the prototype include:

- the impossibility of the influence of zeros on the steepness of the slopes of the BPF at frequencies close to the passband;

- there is no description of the mutual influence of this type of filters on other filters when they are connected in a single device.

The invention does not have these disadvantages.

Detailed description of the invention:

The aim of the invention was to obtain a method for joint tuning of several microwave filters, taking into account delay lines, in order to increase the slope of the frequency response of the BPF, which is not obvious from the characteristics of the units included in the microwave filter and to create a microwave filter unit that provides a slope of less than 0.2% the difference between the cutoff frequency of the passband and the cutoff frequency of the stopband.

The principle of operation of the filters included in the microwave filter unit does not differ from the well-known ones. The main difference between the microwave filter unit (device) with delay lines, which are made in the form of fifty-ohm coaxial lines, between individual filters is the increase in the steepness of the characteristic due to the mutual phasing of two or more slopes of different filter sections (including taking into account the communication loops between the links BPF, while the number of links between links can be from one to N-2, where N is the number of BPF links), which are part of this device. In PPF, connections between links can be both capacitive and inductive. BPF and notch filters included in the device can be made both on microstrip technology and on cavity resonators, and have both air and dielectric filling.

The inventive level is achieved by forming the frequency response of the BPF using notch filters, while each of the notch filters used can have different frequency responses in depth and rejection band, through adjustable (selectable) delay lines, while the selection or adjustment can be carried out both mechanically and and electrically. Together, such a device provides an increase in the steepness of the slope of the frequency response characteristic greater than is provided by the sum of the individual characteristics of the filters that make up the microwave filter unit, while an increase in the slope can be achieved both from the upper frequencies and from the lower ones.

The novelty is ensured due to the small number of PPF units that provide the same characteristics as well-known analogues, including taking into account the use of additional rejection filters.

Obtaining the effect of increasing the steepness is possible both when using one additional notch filter, and when using several notch filters connected by the same delay line.

The essence of the invention is illustrated by drawings:

1 shows a block diagram of a microwave filter bank.

Figure 2 shows the equivalent electrical circuit of the microwave filter unit and its constituents: BPF of the 8th order, two notch filters of the 3rd order and two delay lines.

Figure 3 shows a comparison of the frequency response of the traditional design of the filter unit and the microwave filter unit. Both compared designs consist of: 8th order BPF, two 3rd order notch filters and two delay lines.

Advantages of the above design:

The microwave filter unit with delay lines between the individual filters makes it possible to obtain a steepness of the slope of the frequency response characteristic greater than the sum of the individual characteristics of the filters that make up the device.

Disclosure and implementation of the invention:

The first essential feature sufficient to achieve the above technical result is the use of delay lines between microwave filters in the microwave filter unit.

The second essential feature is the use of a sequence of connecting BPF and notch filters. When changing the connection sequence, as well as when changing the settings of each of the filters, the delay lines must be reselected, as well as reconfiguring the filters.

The third significant feature is the use of communication loops in the BPF, which provides additional adjustment elements and enhances the influence of the delay lines and increases the steepness of the BPF slopes.

The operation of the microwave filter unit:

The microwave filter unit 4 consists of a flat pass filter (PPF) 1, two delay lines 2-1 and 2-2, two notch filters 3-1 and 3-2, the input connector 5 is located on the BPF 1, and the output connector 6 is on the extreme notch filter 3-2. Delay lines 2-1 and 2-2 carry out the time delay of the signal and its phase shift. The length of the delay lines is selected or adjusted when setting up the microwave filter unit 4 in such a way as to match the zeros of the notch filters 3-1 and 3-2 and the zeros of the communication loops 8, 9, 10 of the BPF 1.

PPF 1 consists of eight links 7-1, 7-2, 7-3, 7-4, 7-5, 7-6, 7-7, 7-8, seven links between links 11-1, 11-2, 11-3, 11-4, 11-5, 11-6, 11-7 and three links 8, 9, 10 between mirror links 7-1 and 7-8, 7-2 and 7-7, 7-3 and 7-6. Link 9 is switched on in antiphase to links 8 and 10.

Notch filter 3-1 consists of four notch sections 12-1, 12-2, 12-3, 12-4, connected to a single communication line, which is a strip line from the input to the output of the notch filter 3-1. The cutter 3-2 with links 12-5, 12-6, 12-7 and 12-8 is arranged in a similar way.

Delay lines 2-1 and 2-2 are selected based on the frequency response and characteristics of the connected BPF 1 and notch filters 3-1 and 3-2. The criterion for evaluating the correctness of the choice of the length of the delay lines 2-1 and 2-2 (taking into account the phase shift in the line) is the characteristic obtained during the connection. BPF 1 and notch filters 3-1 and 3-2 are individually tuned to frequencies close to the required ones (zeros of BPF 1 and notch filters 3-1 and 3-2 should be located as close to the passband as possible). Then BPF 1 and notch filters 3-1 and 3-2 are connected by delay lines 2-1 and 2-2. Delay lines 2-1 and 2-2 are selectable or adjustable. When choosing the length of delay lines 2-1 and 2-2, pay attention to the final frequency response. With optimally selected delay lines, a deep and wide total zero should form in the blocking band, which was not the case with other options for delay lines. When selecting delay lines, BPF 1 and notch filters 3-1 and 3-2 are not adjusted.

After selecting the optimal lengths of the delay lines 2-1 and 2-2, it is necessary to rebuild the notch filters 3-1 and 3-2 and links 8, 9, 10 in BPF 1, since with the optimal delay lines 2-1 and 2-2 it becomes possible additionally move the zeros of links 8, 9, 10 and notch filters 3-1 and 3-2 to the passband, but without the effect of reducing the depth of zeros, which is observed with other lengths of delay lines 2-1 and 2-2.

Claims (12)

1. A device for filtering microwave signals, consisting of a band pass filter with internal connections between the links, at least one notch filter, the links of which are configured so that the zeros of the notch filters are located as close as possible to the passband, the links of the notch filter have different frequency response characteristics in depth and a notch band, and at least one delay line, which is a communication line between the filters in the device and the frequency response control element of the device, characterized in that the bandpass filter is connected to the first adjustable delay line, the first adjustable delay line is connected to the first notch filter, the first notch the filter is connected to the second adjustable delay line, the second adjustable delay line is connected to the second notch filter, the band pass filter consists of eight links, seven links between the links and three links between the mirror links, the notch filter consists of four notch links, connect connected to a single communication line, which is a strip line from the input to the output of the notch filter, while the filter is configured to obtain a slope of the frequency response characteristic that exceeds the same characteristic achievable by bandpass and notch filters without using a delay line. 2. The device according to claim 1, characterized in that the delay line is made in the form of a coaxial fifty-ohm line. 3. The device according to claim 1, characterized in that the notch filter sections are configured in such a way that they have different frequency response characteristics in terms of depth and notch band. 4. The device according to claim 1, characterized in that it provides an increase in the steepness of the frequency response from both the upper and lower frequencies or from one of them. 5. The device according to claim 1, characterized in that the delay line is selectable or adjustable, and the length is selected or adjusted to ensure alignment of the zeros of the notch filters and the zeros of the communication loops of the band pass filters, while the delay lines are selected in such a way as to form a deep and wide total zero in the blocking band. 6. Device according to claim 5, characterized in that the adjustable delay line is mechanically or electrically adjustable. 7. The device according to claim 1, characterized in that the connections between the links of the bandpass filter are used both capacitive and inductive. 8. The device according to claim 7, characterized in that the number of connections between the links of the bandpass filter is from one to N-2, where N is the number of links of the bandpass filter. 9. The device according to claim 1, characterized in that the bandpass and rejection filters are made using stripline technology. 10. The device according to claim 9, characterized in that the bandpass and rejection filters are made using microstrip technology. 11. The device according to claim 1, characterized in that the bandpass and rejection filters are made in the form of cavity resonators. 12. The device according to claim 11, characterized in that the bandpass and rejection filters are made in the form of cavity resonators with both air and dielectric filling.

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