A dielectric coaxial low-pass filter with transmission zero point

Abstract

The present invention proposes a dielectric coaxial low-pass filter with a transmission zero point based on a dielectric resonator with a metallized surface, which includes an input port and an output port, a metal rod connecting the input port and the output port, a plurality of dielectric resonators with a metallized surface fixed on the metal rod, and a metal shell. Compared with the traditional metal coaxial low-pass filter, the unique structure of the dielectric resonator with a metallized surface produces a transmission zero point at the filter sideband, thereby greatly improving the sideband roll-off coefficient, and at the same time improving the stopband suppression in the entire stopband range. Taking the first design example of the present invention as an example, the roll-off coefficient of the traditional metal coaxial low-pass filter is about 48dB / GHz, which is the same as the fifth-order low-pass filter and the same size, while the sideband roll-off coefficient of the present invention is about 364dB / GHz, which is about 7.5 times higher; the stopband suppression of the present invention is at least 5dB higher than that of the traditional metal coaxial low-pass filter.

Description

Technical Field

[0001] The invention relates to a dielectric coaxial low-pass filter with a transmission zero point, belonging to the technical field of radio frequency communication filtering. Background Art

[0002] Due to its advantages of low loss, wide stopband, large power capacity, simple structure and design method, traditional metal coaxial low-pass filters are widely used in the RF front end of mobile communication system base stations to suppress out-of-band interference, crosstalk between systems, etc. Traditional metal coaxial low-pass filters are composed of high and low impedance lines, where the high impedance line is equivalent to a series inductor and the low impedance line is equivalent to a parallel capacitor to achieve a low-pass response. However, the traditional metal coaxial structure can only design a low-pass filter with a Chebyshev response, and its sideband roll-off coefficient and stopband suppression are limited and need to be further improved. Summary of the invention

[0003] The present invention aims to solve the above-mentioned defects and provides a dielectric coaxial low-pass filter with a transmission zero point, which has a reasonable structure and improves the roll-off coefficient and stop-band suppression of the designed low-pass filter.

[0004] To this end, the technical solution adopted by the present invention is: a dielectric coaxial low-pass filter with a transmission zero point, the filter includes an input port and an output port, and a plurality of high-impedance structures arranged in series are arranged on the filter, low-impedance structures and capacitor structures are arranged between adjacent high-impedance structures, and corresponding low-impedance structures and capacitor structures are arranged in parallel.

[0005] Furthermore, a metal rod in contact with the input port and the output port is provided between the input port and the output port;

[0006] A plurality of dielectric resonators are arranged on the metal rod along the axial direction of the metal rod, and a metal layer is arranged on the dielectric resonator;

[0007] The above arrangement forms the following structural form: the metal rods between the input port and the dielectric resonator, the metal rods between adjacent dielectric resonators, and the metal rods between the dielectric resonator and the output port form a high impedance structure, the dielectric resonators form a low impedance structure, and the metal layers on the dielectric resonators form a capacitor structure.

[0008] Furthermore, an upper metal layer is disposed on the upper side surface and upper end surface of each dielectric resonator, and a lower metal layer is disposed on the lower side surface and lower end surface of each dielectric resonator, and the upper metal layer and the lower metal layer form a capacitor structure.

[0009] Furthermore, the upper metal layer and the lower metal layer form a symmetrical structure.

[0010] Furthermore, an upper metal layer is disposed on the surface of the upper end surface of each dielectric resonator, and a lower metal layer is disposed on the surface of the lower end surface of each dielectric resonator, and the upper metal layer and the lower metal layer form a capacitor structure.

[0011] Furthermore, the metal layer is silver.

[0012] Furthermore, each of the dielectric resonators is fixed on the metal rod.

[0013] The advantages of the present invention are as follows: the present invention replaces the low impedance line of the traditional metal coaxial low-pass filter with a dielectric resonator whose surface is partially metallized, and introduces a transmission zero point by utilizing the series capacitance effect between the metals on the surface of the dielectric resonator, thereby improving the roll-off coefficient and stopband suppression of the designed low-pass filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 FIG. 1 is a schematic diagram of the structure of the filter of the first embodiment.

[0015] Figure 2 It is an equivalent circuit diagram of embodiment 1.

[0016] Figure 3 It is a comparison chart of simulation results of Example 1 and a traditional metal coaxial low-pass filter.

[0017] Figure 4 FIG. 4 is a schematic diagram of the structure of the filter of the second embodiment.

[0018] Figure 5 This is a simulation result diagram of Example 2.

[0019] Figure 6 FIG. 4 is a schematic diagram of the structure of the filter of Example 3.

[0020] Figure 7 This is a simulation result diagram of Example 3. DETAILED DESCRIPTION

[0021] A dielectric coaxial low-pass filter with a transmission zero point, the filter comprising an input port and an output port, the filter being provided with a plurality of high-impedance structures arranged in series, low-impedance structures and capacitance structures being arranged between adjacent high-impedance structures, and corresponding low-impedance structures and capacitance structures being arranged in parallel.

[0022] Furthermore, a metal rod in contact with the input port and the output port is provided between the input port and the output port;

[0023] A plurality of dielectric resonators are arranged on the metal rod along the axial direction of the metal rod, and a metal layer is arranged on the dielectric resonator;

[0024] The above arrangement forms the following structural form: the metal rods between the input port and the dielectric resonator, the metal rods between adjacent dielectric resonators, and the metal rods between the dielectric resonator and the output port form a high impedance structure, the dielectric resonators form a low impedance structure, and the metal layers on the dielectric resonators form a capacitor structure.

[0025] Furthermore, an upper metal layer is disposed on the upper side surface and upper end surface of each dielectric resonator, and a lower metal layer is disposed on the lower side surface and lower end surface of each dielectric resonator, and the upper metal layer and the lower metal layer form a capacitor structure.

[0026] Furthermore, the upper metal layer and the lower metal layer form a symmetrical structure.

[0027] Furthermore, an upper metal layer is disposed on the surface of the upper end surface of each dielectric resonator, and a lower metal layer is disposed on the surface of the lower end surface of each dielectric resonator, and the upper metal layer and the lower metal layer form a capacitor structure.

[0028] Furthermore, the metal layer is silver.

[0029] Furthermore, each of the dielectric resonators is fixed on the metal rod.

[0030] Three groups of embodiments are listed below to provide a more detailed understanding of the present invention.

[0031] Embodiment 1:

[0032] See Figure 1 :

[0033] Figure 1 The fifth-order low-pass filter structure shown in the figure is used to analyze the working principle of the present invention. It includes an input wide port P1, an output port P2, a first dielectric resonator C1 with silver coating on the surface, a second dielectric resonator C2 with silver coating on the surface, the first dielectric resonator C1 with silver coating on the surface includes two parts: a first silver coating part S1 and a second silver coating part S2, the second dielectric resonator C2 with silver coating on the surface includes two parts: a third silver coating part S3 and a fourth silver coating part S4, a metal shell K1, and a metal rod connecting the input and output ports, the metal rod is divided into five parts: a first section of the metal rod L1 from port 1 to the first dielectric resonator C1, a second section of the metal rod F1 fixing the first dielectric resonator C1, a third section of the metal rod L2 from the first dielectric resonator C1 to the second dielectric resonator C2, a fourth section of the metal rod F2 fixing the second dielectric resonator C2, and a fifth section of the metal rod L3 from the second dielectric resonator C2 to the output port P2.

[0034] The equivalent circuit of Example 1 of the present invention is as follows: Figure 2 shown. Figure 1The first metal rod L1, the third metal rod L2, and the fifth metal rod L3 respectively form high impedance line 1, high impedance line 2, and high impedance line 3, the first dielectric resonator C1 and the second dielectric resonator C2 respectively form low impedance line 1 and low impedance line 2, a capacitor 1 is formed between the first silver-coated portion S1 and the second silver-coated portion S2 on the surface of the first dielectric resonator C1, and a capacitor 2 is also formed between the third silver-coated portion S3 and the fourth silver-coated portion S4 on the surface of the second dielectric resonator C2. The introduction of capacitor 1 and capacitor 2 generates a transmission zero at the sideband of the low-pass response, thereby improving the roll-off coefficient and stopband suppression of the filtering performance.

[0035] The first design example was simulated and verified by the full-wave simulation software HFSS. The simulation results are as follows Figure 3 The solid curve in the figure shows the simulation results of the conventional metal coaxial low-pass filter with the same size as the first design example is shown in the hollow curve in Figure 3. The cutoff frequency of both is 0.55 GHz, and the return loss in the passband is 20 dB. R f Calculate according to the following formula:

[0036] . (1)

[0037] in, f 3dB Represents the frequency corresponding to 3dB attenuation, f 30dB represents the frequency corresponding to 30 dB attenuation. According to formula (1), the roll-off factor of the conventional metal coaxial low-pass filter is about 48 dB / GHz, while the roll-off factor of the first design example is about 364 dB / GHz, which is about 7.5 times higher. In addition, compared with the conventional metal coaxial low-pass filter, the stopband suppression of the first embodiment is improved by at least 5 dB.

[0038] Embodiment 2:

[0039] Figure 4 The second design example of the dielectric coaxial low-pass filter of the present invention is given. This example designs a seventh-order low-pass filter using three dielectric resonators with metal surfaces. The simulation results are shown in Figure 2. Figure 5 Its roll-off factor is 1038dB / GHz, which is about 2.8 times that of the first design example.

[0040] Embodiment three:

[0041] In the previous two embodiments, the metallized portion of the dielectric resonator surface covers the bottom surface and part of the side surface of the dielectric resonator. In the third embodiment, the metallized portion of the dielectric resonator surface only covers part of the bottom surface of the dielectric resonator. Figure 6This design example is a fifth-order filter, and its simulation results are shown in Figure 7 The cut-off frequency is 1 GHz, the passband return loss is about 20 dB, and the roll-off factor is about 375 dB / GHz, which is equivalent to the result of the first embodiment.

Claims

1. A dielectric coaxial low-pass filter with a transmission zero point, characterized in that: The filter comprises an input port and an output port, and is provided with a plurality of high-impedance structures arranged in series, and low-impedance structures and capacitor structures are arranged between adjacent high-impedance structures, and corresponding low-impedance structures and capacitor structures are arranged in parallel; A metal rod in contact with the input port and the output port is provided between the input port and the output port; A plurality of dielectric resonators are arranged on the metal rod along the axial direction of the metal rod, and a metal layer is arranged on the dielectric resonator; The above arrangement forms the following structural form: the metal rods between the input port and the dielectric resonator, the metal rods between adjacent dielectric resonators, and the metal rods between the dielectric resonator and the output port form a high impedance structure, each dielectric resonator forms a low impedance structure, and the metal layer on each dielectric resonator forms a capacitor structure; Each of the dielectric resonators is fixed on the metal rod; Also has any of the following structural forms: One is: the upper side surface and the upper end surface of each dielectric resonator are provided with an upper metal layer, and the lower side surface and the lower end surface are provided with a lower metal layer, and the upper metal layer and the lower metal layer form a capacitor structure; The second is that an upper metal layer is arranged on the surface of the upper end surface of each dielectric resonator, and a lower metal layer is arranged on the surface of the lower end surface, and the upper metal layer and the lower metal layer form a capacitor structure.

2. A dielectric coaxial low-pass filter with a transmission zero point according to claim 1, characterized in that: The upper metal layer and the lower metal layer form a symmetrical structure.

3. The dielectric coaxial low-pass filter with a transmission zero point according to claim 1, characterized in that: The metal layer is silver.

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