CN111063968B

CN111063968B - Ultra-wideband band-pass filter based on mirror image open-circuit ladder impedance resonator

Info

Publication number: CN111063968B
Application number: CN201910190928.3A
Authority: CN
Inventors: 刘芬; 姬五胜; 李雅静
Original assignee: Tianjin University of Technology and Education China Vocational Training Instructor Training Center
Current assignee: Tianjin University of Technology and Education China Vocational Training Instructor Training Center
Priority date: 2018-10-17
Filing date: 2019-03-14
Publication date: 2024-06-07
Anticipated expiration: 2039-03-14
Also published as: CN111063968A

Abstract

The invention discloses an ultra-wideband band-pass filter based on an image open-circuit ladder impedance resonator, which is used in the fields of radio frequency and microwave systems. The parallel two-wire coupling structure comprises an input wire, an output wire and a mirror image open-circuit ladder impedance resonator, wherein the input wire is formed by the parallel two-wire coupling structure with the defect ground, and the output wire is formed by the parallel two-wire coupling structure with the defect ground. The input line and the output line are both composed of two parallel coupling microstrip line structures with a defective ground structure, the defective ground structure is composed of two symmetrical rectangular grooves, and the mirror image open-circuit ladder impedance resonator is composed of a common half-wavelength resonator through loading mirror image open-circuit ladder impedance branches. The ultra-wideband band-pass filter adopts a defected ground structure to realize the harmonic suppression effect of a circuit, and the position of a transmission zero point is easy to adjust by loading an image open-circuit ladder impedance resonator through a branch, so that excellent passband selectivity is realized, and poor coupling is avoided.

Description

Ultra-wideband band-pass filter based on mirror image open-circuit ladder impedance resonator

Technical Field

The invention belongs to the field of radio frequency and microwave systems, and particularly relates to a band-pass filter based on an image open-circuit ladder impedance resonator, which has ultra-wide bandwidth and excellent passband selectivity.

Background

The research of the traditional broadband filter is mature, but most of the research is still based on the design theory of the narrowband filter, so that the formula is more complicated, the bandwidth is narrower, and the method is not suitable for the design of the modern broadband filter. At present, the design of a modern broadband filter can be generalized into two aspects, on one hand, the traditional structure of the broadband filter is improved, the traditional design formula is simplified, the design becomes simple and feasible, and the passband bandwidth and the stopband bandwidth of the filter are expanded to a certain extent; on the other hand, new structures and new forms of the broadband filter are continuously proposed so as to radically solve the bandwidth problem and obtain the broadband and ultra-wideband microwave filter with good performance meeting the requirements. For example Zhu l et al in 2005 proposed a three-mode stepped impedance resonator structure for ultra wideband filter design. The design method based on the multimode resonator has the advantages of simple structure and good passband characteristic, so that a great deal of expansibility research is conducted by a great number of students, and a great number of improved resonator structures are proposed to be applied to ultra-wideband filter design. Although these ultra wideband filters can meet the requirements of the Federal Communications Commission (FCC) in the united states for ultra wideband filters in terms of passband characteristics, the attenuation rate at the low frequency sidebands is relatively slow and the high frequency end stopband rejection characteristics are also in need of improvement.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a parallel coupling structure with a defect structure to improve the problem of coupling gaps, and simultaneously, a branch loading mirror image open-circuit ladder impedance resonator is adopted to control transmission zero points at the edges of a lower passband and a higher passband so as to realize excellent passband selectivity.

The technical scheme adopted for solving the technical problems is as follows: the ultra-wideband band-pass filter based on the mirror image open-circuit ladder impedance resonator comprises an input line composed of a parallel two-line coupling structure with a defective ground, an output line composed of a parallel two-line coupling structure with a defective ground and the mirror image open-circuit ladder impedance resonator. The input line and the output line are both composed of two parallel coupling microstrip line structures with a defective ground structure, the defective ground structure is composed of two symmetrical rectangular grooves, and the two symmetrical rectangular grooves are respectively positioned at the substrate grounding end below the parallel coupling structure of the input line/output line. The mirror image open-circuit ladder impedance resonator consists of a common half-wavelength resonator through loading mirror image open-circuit ladder impedance branches, wherein the half-wavelength resonator and the branches have the same symmetry plane in the vertical direction. The input line is positioned at the left side of the mirror image open-circuit ladder impedance resonator, the output line is positioned at the right side of the mirror image open-circuit ladder impedance resonator, two ports are microstrip lines with impedance of 50 ohms, the two ports are respectively positioned at the left side and the right side of the ultra-wideband band-pass filter, the port at the left side is connected with the parallel coupling microstrip line positioned at the bottom of the input line, the port at the right side is connected with the parallel coupling microstrip line positioned at the bottom of the output line, signals are input from the port at the left side and are output from the port at the right side after sequentially passing through the input line, the mirror image open-circuit ladder impedance resonator and the output line.

The gap between the parallel coupling microstrip lines of the input line and the output line can influence the relative bandwidth of the ultra-wideband band-pass filter, the defected ground structure can increase the out-of-band rejection of the filter and improve the impedance characteristic of a circuit, and the mirror image open-circuit stepped impedance resonator determines the frequency of the transmission zero point at the lower and higher passband edges.

The invention has the beneficial effects that the defect ground structure is adopted, so that the distributed inductance and capacitance of the circuit are affected to realize the harmonic suppression effect of the circuit, and the mirror image open-circuit ladder impedance resonator is loaded through the branches, so that the position of the transmission zero point is easy to adjust, thereby realizing excellent passband selectivity and having no bad coupling.

Drawings

Fig. 1 is a schematic diagram of a front structure of an ultra-wideband band-pass filter based on an image open-circuit ladder impedance resonator, and fig. 2 is a schematic diagram of a back structure of an ultra-wideband band-pass filter based on an image open-circuit ladder impedance resonator.

Fig. 3 is a front side of an ultra-wideband filter layout based on a mirror open ladder impedance resonator, and fig. 4 is a back side of an ultra-wideband filter layout based on a mirror open ladder impedance resonator.

Fig. 5 is a simulation diagram of parameter S ₁₁、S₂₁ of an ultra-wideband band-pass filter based on an mirror open-circuit stepped-impedance resonator.

In the figure: 1 and 7 are ports, 2 are input lines, 3 and 8 are defective grounds, 4 are half-wavelength resonators, 5 and 6 are stepped impedance branches, 9 are output lines, 10 and 11 are coupling microstrip lines, and 12 are gaps.

Detailed Description

The invention will be further described with reference to the accompanying drawings.

In fig. 1, port 1 is located at the left end of the filter and port 7 is located at the right end of the filter; the input line 2 consists of two parallel coupling microstrip lines 10, 11; a gap 12 is located between the coupling microstrip line 10 and the coupling microstrip line 11; 9 is an output line, and the input line 2 and the output line 9 are bilaterally symmetrical along a symmetrical plane; the defect ground 3 is positioned at the substrate grounding end below the input line 2; the defect ground 8 is positioned at the ground end of the substrate below the output line 9; 4 is a half wavelength resonator; 5 and 6 are ladder impedance branches; the half-wavelength resonator 4 and the ladder impedance branches 5 and 6 are symmetrically arranged left and right along a symmetry plane; signals are input from the port 1, enter the resonator 4 loaded with the stepped impedance branch through the input line 2, and are output from the port 7 through the output line 9.

In fig. 2, the defective area 3 and the defective area 8 are two rectangular grooves which are symmetrical left and right along the symmetry plane. It should be noted that the defective structure is introduced such that the bandwidth of the filter is changed from 5.6GHz to 6.1GHz, and it is seen that the defective structure has a significant effect on the bandwidth of the filter.

FIG. 3 is a front side of an ultra-wideband band-pass filter layout based on a mirror image open-circuit ladder impedance resonator, and the input port 1 and the output port 7 are both 50 ohm microstrip lines; the input line 2 consists of two parallel coupling microstrip lines 10 and 11, the lengths of the coupling microstrip line 10 and the coupling microstrip line 11 are 4.1mm, the widths are 0.2mm, and a gap 12 between the coupling microstrip line 10 and the coupling microstrip line 11 is 0.1mm; the half wavelength resonator 4 has a length of 8.9mm and a width of 0.2mm; the length of the ladder impedance branch 5 is 6.7mm, and the width is 0.4mm; the length of the ladder impedance branch 6 is 1mm, and the width is 0.9mm; the input line 2 and the output line 9 are bilaterally symmetrical along a symmetry plane; signals are input from the port 1, enter the resonator 4 loaded with the stepped impedance branch through the input line 2, and are output from the port 7 through the output line 9. The dielectric constant of the printed board for manufacturing the band-pass filter is 10.2, the thickness of the board is 0.635mm, and the thickness of the copper foil is 0.035mm.

FIG. 4 is a reverse side of an ultra-wideband band-pass filter layout based on a mirror image open-circuit ladder impedance resonator, with a defective ground 3 at the substrate ground below the input line 2; the defect ground 8 is positioned at the ground end of the substrate below the output line 9; the defect land 3 and the defect land 8 are two rectangular grooves which are symmetrical left and right along a symmetry plane; the defective area 3 and the defective area 8 are each 4.1mm in length and 1mm in width.

Referring to fig. 5, the passband of the bandpass filter is 3.7GHz to 9.8GHz, the center frequency is 6.75GHz, there is excellent out-of-band rejection of more than 35dB around the frequencies 3.57GHz and 10.49GHz corresponding to the two transmission zeroes, and the return loss of the filter is lower than-10 dB.

Claims

1. An ultra-wideband band-pass filter based on an mirror image open-circuit ladder impedance resonator comprises an input line formed by a parallel two-line coupling structure with a defective ground, an output line formed by a parallel two-line coupling structure with a defective ground and a mirror image open-circuit ladder impedance resonator, and is characterized in that the input line is positioned at the left side of the mirror image open-circuit ladder impedance resonator, the output line is positioned at the right side of the mirror image open-circuit ladder impedance resonator, the input line and the output line are symmetrically arranged left and right along the longitudinal symmetry plane of the mirror image open-circuit ladder impedance resonator, two ports are respectively positioned at the left side and the right side of the ultra-wideband band-pass filter, an input signal is input from a left port and sequentially passes through the input line, the mirror image open-circuit ladder impedance resonator and the output line and then is output from a right port; the lengths of the two parallel coupling microstrip lines forming the input line/output line are equal, and the distance between the two parallel coupling microstrip lines of the input line is equal to the distance between the two parallel coupling microstrip lines of the input line; the defect ground structure forming the input line/output line consists of two symmetrical rectangular grooves which are respectively positioned at the grounding end of the substrate below the parallel two-line coupling structure of the input line/output line; the mirror image open-circuit ladder resistance resonator consists of a common half-wavelength resonator through loading mirror image open-circuit ladder resistance branches, wherein the half-wavelength resonator and the branches have the same symmetry plane in the vertical direction.