CN115939706B

CN115939706B - A Stopband Enhanced Low-Pass Coaxial Filter

Info

Publication number: CN115939706B
Application number: CN202211480849.4A
Authority: CN
Inventors: 吴杰; 李少恩; 董培松; 韩国栋; 齐宏业; 吴旭
Original assignee: CETC 54 Research Institute
Current assignee: CETC 54 Research Institute
Priority date: 2022-11-24
Filing date: 2022-11-24
Publication date: 2025-01-24
Anticipated expiration: 2042-11-24
Also published as: CN115939706A

Abstract

The present invention discloses a stopband enhanced low-pass coaxial filter. It consists of a coaxial input, a filtering structure and a coaxial output part. The filtering structure consists of a high-low impedance low-pass filter and an embedded coupling short column. A zero-pit effect (stopband enhancement) is formed by introducing a coupling short-circuit column in the cavity of the high-resistance part, thereby achieving the effect of suppressing high-order harmonics and out-of-band spurious. And the position of the zero-pit frequency can be controlled by adjusting the position of the short-circuit column and the gap height between the short-circuit column and the cavity of the high-resistance part. The designed stopband enhanced low-pass coaxial filter has a simple structure and can be directly integrated with an antenna radiator or a T/R component. It has the characteristics of low insertion loss and high power capacity. It can also be used as a double-female, double-male or male-female conversion connector with filtering characteristics.

Description

Stop band enhancement type low-pass coaxial filter

Technical Field

The invention relates to the field of design and manufacture of microwave and millimeter wave passive circuits, in particular to a low-pass coaxial filter.

Background

Filters are common constituent modules in antennas and radio frequency front ends. For phased array antennas, a band-pass filter is often required to be connected between the array element and the T/R component to suppress out-of-band interference or reduce spurious signals, however, the band-pass filter may generate a parasitic passband on a far band to affect suppression of higher harmonics, so that notch suppression or stop band enhancement treatment is required at some special frequency bands outside the passband. Zhang Juan et al, in a dual-pass bandwidth stop-band filter based on a defective ground structure (patent application number: CN 202210574121) propose to achieve a stop-band effect within a specific frequency band by introducing a defective ground structure. The low-pass filter can play an important role in the aspect of high-order harmonic suppression, and the parasitic passband problem encountered in the design of the band-pass filter can be overcome through the combined use of low-pass and band-pass. Low pass filters with band reject or notch characteristics can further reject out-of-band interference and spurious emissions and therefore have strong application requirements. For example, patent "Low pass rectangular waveguide with band stop characteristics for interpolating SSPP Material" (patent application number: CN 202210579240) proposes interpolating SSPP material in rectangular waveguide to form a low pass filter with band stop characteristics. However, such low-pass filters have complex structural forms, high insertion loss, and may require additional transition structures when connected to the T/R assembly, which is disadvantageous for miniaturized integrated designs.

Disclosure of Invention

The invention aims to provide a low-pass coaxial filter which can be directly interconnected with a T/R component, can realize enhanced suppression on a stop band, meets the requirement of suppression of higher harmonics, and can be directly interconnected with a standard 50 ohm coaxial connector.

In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:

The stop band enhanced low-pass coaxial filter comprises a coaxial input structure 1, a filter structure 2 and a coaxial output structure 3 which are sequentially connected, wherein the coaxial input structure 1 and the coaxial output structure 3 are composed of a coaxial inner conductor, a coaxial outer conductor and an insulating medium positioned between the coaxial inner conductor and the coaxial outer conductor, and the stop band enhanced low-pass coaxial filter is characterized in that the filter structure 2 comprises a common inner conductor 21 and a common outer conductor 25, a middle air cavity 23 is arranged in the center of the common outer conductor 25, an upper medium insulating layer 22 is arranged between the common inner conductor 21 and the common outer conductor 25 at the upper part of the middle air cavity 23, and a lower medium insulating layer 24 is arranged between the common inner conductor 21 and the common outer conductor 25 at the lower part of the middle air cavity 23.

Further, the device also comprises a coupling short-circuit column 26, wherein the coupling short-circuit column 26 is offset from the outer circumference of the public inner conductor 21 by a certain distance, the bottom of the coupling short-circuit column 26 is directly connected with the lower surface of the middle air cavity 23 to form a short-circuit surface, and the top of the coupling short-circuit column 26 is spaced from the upper surface of the middle air cavity 23 by a certain distance to form an equivalent capacitor.

Further, the bottom of the coupling short-circuit column 26 is provided with external threads, a corresponding position on the common external conductor 25 at the bottom of the middle air cavity 23 is provided with a threaded hole, and the coupling short-circuit column 26 is used for adjusting the distance between the top of the coupling short-circuit column 26 and the upper surface of the middle air cavity 23 through threaded rotation.

Further, the characteristic impedance of the coaxial input structure 1 and the characteristic impedance of the coaxial output structure 3 are both 50 ohms, the characteristic impedance of the common inner conductor 21, the upper dielectric insulating layer 22 and the common outer conductor 25 form a low-impedance resonator, the characteristic impedance of the low-impedance resonator is smaller than 50 ohms, the characteristic impedance of the common inner conductor 21, the middle air cavity 23 and the common outer conductor 25 form a high-impedance resonator, the characteristic impedance of the high-impedance resonator is larger than 50 ohms, and the characteristic impedance of the low-impedance resonator is smaller than 50 ohms.

Further, two ends of the common inner conductor 21 of the filtering structure 2 are connected with the coaxial inner conductor of the coaxial input structure 1 and the coaxial inner conductor of the coaxial output structure 3 in a one-to-one correspondence manner, and two ends of the common outer conductor 25 of the filtering structure 2 are connected with the coaxial outer conductor of the coaxial input structure 1 and the coaxial outer conductor of the coaxial output structure 3 in a one-to-one correspondence manner.

Further, the axial length of each of the upper dielectric insulating layer, the middle air cavity and the lower dielectric insulating layer is smaller than the waveguide wavelength of the center frequency of the eighth passband.

The invention has the beneficial effects that:

The invention provides a miniaturized and easy-to-realize filter design method, which is characterized in that a coupling short-circuit column null effect (stop band enhancement) is introduced into a cavity of a high-resistance part of a high-low impedance filter, so that the effects of restraining higher harmonic waves and out-of-band spurious are achieved, the adjusting range of the null frequency is large, and the adjusting means is simple. The stop band enhanced low-pass coaxial filter is of a standard 50 ohm coaxial input and output structure, can be directly integrated with an antenna radiator or a T/R assembly, and has the characteristics of small insertion loss and high power capacity. In addition, it can also be used as a connector for double-negative, double-positive or double-positive conversion with filtering characteristics.

Drawings

FIG. 1 is a schematic three-dimensional structure of a stop band enhanced low-pass coaxial filter according to the present invention;

FIG. 2 is a diagram showing the filter structure of a stop band enhancement type low-pass coaxial filter according to the present invention;

fig. 3 is a simulation effect diagram of a stop band enhancement type low-pass coaxial filter according to the present invention.

The figure indicates:

1. The coaxial input structure 2, the filter structure 21, the common inner conductor 22, the upper medium insulating layer 23, the middle air cavity 24, the lower medium insulating layer 25, the common outer conductor 26, the coupling short-circuit column 26,3 and the coaxial output structure.

Detailed Description

The invention is described in further detail below with reference to figures 1-3 and examples.

In the embodiment, the stop band enhancement type low-pass coaxial filter comprises a coaxial input structure 1, a filtering structure 2 and a coaxial output structure 3 which are sequentially connected, wherein the coaxial input structure 1 and the coaxial output structure 3 are composed of a coaxial inner conductor, a coaxial outer conductor and an insulating medium positioned between the coaxial inner conductor and the coaxial outer conductor, the filtering structure 2 comprises a common inner conductor 21 and a common outer conductor 25, a middle air cavity 23 is arranged in the center of the common outer conductor 25, an upper medium insulating layer 22 is arranged between the common inner conductor 21 and the common outer conductor 25 at the upper part of the middle air cavity 23, and a lower medium insulating layer 24 is arranged between the common inner conductor 21 and the common outer conductor 25 at the lower part of the middle air cavity 23. The middle air cavity 23 is also provided with a coupling short-circuit column 26, the coupling short-circuit column 26 deviates from the outer circumference of the public inner conductor 21 by a certain distance, the bottom of the coupling short-circuit column 26 is directly connected with the lower surface of the middle air cavity 23 to form a short-circuit surface, and the top of the coupling short-circuit column 26 is separated from the upper surface of the middle air cavity 23 by a certain distance to form an equivalent capacitor.

The two ends of the common inner conductor 21 of the filter structure 2 are connected with the coaxial inner conductor of the coaxial input structure 1 and the coaxial inner conductor of the coaxial output structure 3 in a one-to-one correspondence manner, and the two ends of the common outer conductor 25 of the filter structure 2 are connected with the coaxial outer conductor of the coaxial input structure 1 and the coaxial outer conductor of the coaxial output structure 3 in a one-to-one correspondence manner.

As shown in fig. 2, the common inner conductor 21, the upper dielectric insulating layer 22, the middle air cavity 23, the lower dielectric insulating layer 24 and the outer conductor 25 together form a third-order low-pass filter.

The characteristic impedance of the coaxial input structure 1 and the characteristic impedance of the coaxial output structure 3 are both 50 ohms, the common inner conductor 21, the upper medium insulating layer 22 and the common outer conductor 25 form a low-impedance resonator, the characteristic impedance of the low-impedance resonator is smaller than 50 ohms, the common inner conductor 21, the middle air cavity 23 and the common outer conductor 25 form a high-impedance resonator, the characteristic impedance of the high-impedance resonator is larger than 50 ohms, and the common inner conductor 21, the lower medium insulating layer 24 and the common outer conductor 25 form a low-impedance resonator, and the characteristic impedance of the low-impedance resonator is smaller than 50 ohms. The axial length of each of the upper dielectric insulating layer, the middle air cavity and the lower dielectric insulating layer is smaller than the waveguide wavelength of the center frequency of the eighth passband.

As shown in fig. 2, the coupling shorting post 26 is located inside the middle air chamber 23 and is offset from the center by a certain distance, and the offset direction can be arbitrary due to circular symmetry. The bottom of the coupling short-circuit column 26 is directly connected with the lower surface of the middle air cavity 23 to form a short-circuit surface, and the top of the coupling short-circuit column 26 is spaced from the upper surface of the middle air cavity 23 by a certain distance to form an equivalent capacitor.

In the invention, due to the introduction of the coupling short-circuit column 26, a null is formed on the stop band of the low-pass filter, so that the effect of enhancing the stop band is achieved. The position of the null frequency can be controlled by adjusting the distance between the top of the coupling shorting post 26 and the upper surface of the middle air chamber 23. In addition, adjusting the relative position of the coupling shorting stub 26 and the common inner conductor 21 also has an effect on the location of the nulling frequency. It is worth mentioning that the introduction of the coupling shorting stub 26 has little effect on the passband characteristics of the low pass filtering.

In the embodiment, the bottom of the coupling short-circuit column 26 is provided with an external thread, and a corresponding position on the common external conductor 25 at the bottom of the middle air cavity 23 is provided with a threaded hole, and the coupling short-circuit column 26 is used for adjusting the distance between the top of the coupling short-circuit column 26 and the upper surface of the middle air cavity 23 by rotating the threads.

In the invention, the filter structure 2 is not limited to a three-order high-low impedance low-pass filter, and can be further expanded to a 2N+1-order low-pass filter, wherein the filter structure comprises a public inner conductor, a first dielectric insulating layer, a first air cavity, a second dielectric insulating layer and a second air cavity. The corresponding coupling short-circuit columns can be loaded with N at most, and are respectively positioned in N air cavities for realizing stop band enhancement of the low-pass filter.

The specific design of the stop band enhanced low-pass coaxial filter is completed aiming at the scheme. In the stop band enhanced low-pass coaxial filter in the embodiment, the center frequency of a pass band is 4GHz, and broadband suppression is required to be carried out at 8 GHz-18 GHz.

As shown in FIG. 3, the full-wave simulation of electromagnetic simulation software Ansys Electronics Desktop shows that the passband loss of the low-pass coaxial filter designed on the surface is smaller than 0.2dB, the stopband frequency is 8 GHz-18 GHz, and the stopband enhancement suppression on the required frequency can be carried out in the 8 GHz-18 GHz frequency band by adjusting the height of h ₄.

Claims

1. A stopband enhanced low-pass coaxial filter, comprising a coaxial input structure (1), a filtering structure (2) and a coaxial output structure (3) connected in sequence; the coaxial input structure (1) and the coaxial output structure (3) are both composed of a coaxial inner conductor, a coaxial outer conductor and an insulating medium located between the coaxial inner conductor and the coaxial outer conductor; the filter structure (2) comprises a common inner conductor (21) and a common outer conductor (25); a middle air cavity (23) is arranged at the center of the common outer conductor (25); an upper dielectric insulating layer (22) is arranged between the common inner conductor (21) and the common outer conductor (25) at the upper part of the middle air cavity (23); and a dielectric insulating layer (22) is arranged between the common inner conductor (21) and the common outer conductor (25) at the lower part of the middle air cavity (23). A lower dielectric insulating layer (24) is arranged between the common outer conductor (25); and a coupling short-circuit column (26) is also included; the coupling short-circuit column (26) is deviated from the outer circumference of the common inner conductor (21) by a certain distance, and the bottom of the coupling short-circuit column (26) is directly connected to the lower surface of the middle air cavity (23) to form a short-circuit surface; the top of the coupling short-circuit column (26) is spaced a certain distance from the upper surface of the middle air cavity (23) to form an equivalent capacitor; the bottom of the coupling short-circuit column (26) is provided with an external thread, and a threaded hole is provided at a corresponding position on the common outer conductor (25) at the bottom of the middle air cavity (23); the coupling short-circuit column (26) is used to adjust the distance between the top of the coupling short-circuit column (26) and the upper surface of the middle air cavity (23) by rotating the thread.

2. A stopband enhanced low-pass coaxial filter according to claim 1, characterized in that: the characteristic impedance of the coaxial input structure (1) and the coaxial output structure (3) are both 50 ohms; the common inner conductor (21), the upper dielectric insulating layer (22) and the common outer conductor (25) constitute a low-impedance resonator, whose characteristic impedance is less than 50 ohms; the common inner conductor (21), the middle air cavity (23) and the common outer conductor (25) constitute a high-impedance resonator, whose characteristic impedance is greater than 50 ohms; the common inner conductor (21), the lower dielectric insulating layer (24) and the common outer conductor (25) constitute a low-impedance resonator, whose characteristic impedance is less than 50 ohms.

3. A stopband enhanced low-pass coaxial filter according to claim 1, characterized in that: the two ends of the common inner conductor (21) of the filtering structure (2) are connected to the coaxial inner conductor of the coaxial input structure (1) and the coaxial inner conductor of the coaxial output structure (3) in a one-to-one correspondence, and the two ends of the common outer conductor (25) of the filtering structure (2) are connected to the coaxial outer conductor of the coaxial input structure (1) and the coaxial outer conductor of the coaxial output structure (3) in a one-to-one correspondence.

4. A stopband enhanced low-pass coaxial filter according to claim 1, characterized in that the axial lengths of the upper dielectric insulating layer (22), the middle air cavity (23) and the lower dielectric insulating layer (24) are each less than one eighth of the waveguide wavelength of the passband center frequency.