A Stopband Enhanced Low-Pass Coaxial Filter

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-pitching 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-pitching 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

Technical Field

[0001] The invention relates to the field of microwave and millimeter wave passive circuit design and manufacturing, and in particular to a low-pass coaxial filter. Background Art

[0002] Filters are common components in antennas and RF front-ends. For phased array antennas, bandpass filters are often required between array elements and T / R components to suppress out-of-band interference or reduce spurious signals. However, bandpass filters may produce parasitic passbands in the far band, affecting the suppression of higher-order harmonics. Therefore, it is necessary to perform notch suppression or stopband enhancement processing on certain special frequency bands outside the passband. Zhang Juan et al. proposed in "Dual-pass bandwidth stopband filter based on defective ground structure" (invention patent, application number: CN202210574121) to achieve the stopband effect in a special frequency band by introducing a defective ground structure. Low-pass filters can play an important role in suppressing higher-order harmonics. By combining low-pass and bandpass, the parasitic passband problem encountered in the design of bandpass filters can be overcome. Low-pass filters with band-stop or notch characteristics can further suppress out-of-band interference and spurious signals, so they have strong application needs. For example, the patent "A low-pass rectangular waveguide with band-stop characteristics with inserted SSPP material" (invention patent, application number: CN202210579240) proposes inserting SSPP material in a rectangular waveguide to form a low-pass filter with band-stop characteristics. However, this type of low-pass filter has a complex structure, large insertion loss, and may require an additional transition structure when connected to the T / R component, which is not conducive to miniaturized integrated design. Summary of the invention

[0003] The purpose of the present invention is to provide a low-pass coaxial filter that can be directly interconnected with a T / R component, can achieve suppression enhancement in the stop band, meet the suppression requirements of high-order harmonics, and can be directly interconnected with a standard 50-ohm coaxial connector.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is:

[0005] A stopband enhanced low-pass coaxial filter comprises a coaxial input structure 1, a filtering structure 2 and a coaxial output structure 3 which are 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 lower dielectric 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.

[0006] Furthermore, it also includes a coupling short-circuit column 26; the coupling short-circuit column 26 deviates 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.

[0007] Furthermore, an external thread is provided at the bottom of the coupling short-circuit column 26, 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.

[0008] Furthermore, the characteristic impedances 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.

[0009] Furthermore, the two ends of the common inner conductor 21 of the filtering structure 2 are connected one-to-one to the coaxial inner conductor of the coaxial input structure 1 and the coaxial inner conductor of the coaxial output structure 3, and the two ends of the common outer conductor 25 of the filtering structure 2 are connected one-to-one to the coaxial outer conductor of the coaxial input structure 1 and the coaxial outer conductor of the coaxial output structure 3.

[0010] Furthermore, the axial lengths of the upper dielectric insulating layer, the middle air cavity and the lower dielectric insulating layer are all less than one eighth of the waveguide wavelength of the passband center frequency.

[0011] Beneficial effects of the present invention:

[0012] The stopband enhanced low-pass coaxial filter described in the present invention proposes a miniaturized and easy-to-implement filter design method, which forms a zero-notch effect (stopband enhancement) by introducing a coupled short-circuit column in the cavity of the high-impedance part of the high-low impedance filter, thereby achieving the effect of suppressing high-order harmonics and out-of-band spurious, and the zero-notch frequency adjustment range is large and the adjustment means are simple. The invented stopband enhanced low-pass coaxial filter is a standard 50 ohm coaxial input and output structure, which can be directly integrated with an antenna radiator or a T / R component, and has the characteristics of low insertion loss and high power capacity. In addition, it can also be used as a dual-female, dual-male or yin-yang conversion connector with filtering characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1It is a three-dimensional structural schematic diagram of a stopband enhanced low-pass coaxial filter of the present invention;

[0014] Figure 2 It is a filter structure composition diagram of a stopband enhanced low-pass coaxial filter of the present invention;

[0015] Figure 3 It is a simulation effect diagram of a stopband enhanced low-pass coaxial filter of the present invention.

[0016] Description of the markings in the figure:

[0017] 1. Coaxial input structure, 2. Filtering structure, 21. Common inner conductor, 22. Upper dielectric insulating layer, 23. Middle air cavity, 24. Lower dielectric insulating layer, 25. Common outer conductor, 26. Coupling short-circuit column 26, 3. Coaxial output structure. DETAILED DESCRIPTION

[0018] The following is combined with Figure 1-3 The present invention is further described in detail with reference to the accompanying drawings and embodiments.

[0019] In an embodiment, a stopband enhanced low-pass coaxial filter comprises 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 filtering 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 lower dielectric 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. A coupling short-circuit column 26 is also provided in the middle air cavity 23; the coupling short-circuit column 26 deviates 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.

[0020] 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 manner, 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 manner.

[0021] like Figure 2 As shown, 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.

[0022] 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. The axial lengths of the upper dielectric insulating layer, the middle air cavity and the lower dielectric insulating layer are all less than one eighth of the waveguide wavelength of the passband center frequency.

[0023] like Figure 2 As shown, the coupling short-circuit column 26 is located inside the middle air cavity 23 and deviates from the center by a certain distance. Due to the circular symmetry, the deviation direction can be arbitrary. 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.

[0024] In the present invention, the introduction of the coupling short-circuit column 26 will form a zero-depression on the stop band of the above-mentioned low-pass filter, which plays a role in stop band enhancement. The position of the zero-depression frequency can be controlled by adjusting the spacing between the top of the coupling short-circuit column 26 and the upper surface of the middle air cavity 23. In addition, adjusting the relative position of the coupling short-circuit column 26 and the common inner conductor 21 will also affect the position of the zero-depression frequency. It is worth mentioning that the introduction of the coupling short-circuit column 26 has almost no effect on the passband characteristics of the low-pass filter.

[0025] In the embodiment, an external thread is provided at the bottom of the coupling short-circuit column 26, 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.

[0026] In the present invention, the filter structure 2 is not limited to a third-order high-low impedance low-pass filter, but can also be extended to a 2N+1 order low-pass filter, which is composed of: a common inner conductor, a first dielectric insulating layer, a first air cavity, a second dielectric insulating layer, a second air cavity... a 2N+1 dielectric insulating layer, an outer conductor. A maximum of N corresponding coupling short-circuit posts can be loaded simultaneously, respectively located in N air cavities, to achieve low-pass filter stopband enhancement.

[0027] A specific design of a stopband enhanced low-pass coaxial filter is completed for this solution. The stopband enhanced low-pass coaxial filter in this embodiment has a passband center frequency of 4 GHz and needs to perform broadband suppression in the range of 8 GHz to 18 GHz.

[0028] The full-wave simulation of electromagnetic simulation software Ansys Electronics Desktop is as follows Figure 3 As shown in the results, the designed stopband enhanced low-pass coaxial filter has a passband loss of less than 0.2dB and a stopband frequency of 8GHz to 18GHz, and the stopband enhanced suppression at the required frequency in the 8GHz to 18GHz band can be performed by adjusting the height of h4.

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; characterized in that: The filtering structure (2) comprises a common inner conductor (21) and a common outer conductor (25); a central 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 central air cavity (23); and a lower dielectric insulating layer (24) is arranged between the common inner conductor (21) and the common outer conductor (25) at the lower part of the central air cavity (23); and further comprises a coupling short-circuit column (26); the coupling short-circuit column (26) is offset from the common inner conductor. (21) a certain distance from the outer circumference, 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), and 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. The 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) form 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) form 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) form a low-impedance resonator, whose characteristic impedance is less than 50 ohms.

3. The stopband enhanced low-pass coaxial filter according to claim 1, characterized in that: Two ends of the common inner conductor (21) of the filter 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 two ends of the common outer conductor (25) of the filter 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. The 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 all less than one eighth of the waveguide wavelength of the passband center frequency.

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