CN112332053A

CN112332053A - Wide-stopband filtering power divider

Info

Publication number: CN112332053A
Application number: CN202011013247.9A
Authority: CN
Inventors: 肖飞; 黄丹; 陈邦超; 曹煜; 吴超超
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2020-09-24
Filing date: 2020-09-24
Publication date: 2021-02-05
Anticipated expiration: 2040-09-24
Also published as: CN112332053B

Abstract

The invention provides a microstrip filtering power divider which is based on a multimode resonator and simultaneously realizes the functions of filtering and power division, thereby effectively reducing the size of elements. The filter power divider realizes a third-order band-pass frequency response, and because the T-shaped open-circuit branch is loaded, a transmission zero point is respectively arranged at the limited frequency position of each side of a pass band, so that the frequency selectivity of two sides of the pass band can be improved; the high-frequency impedance band has a plurality of transmission zeros, and has excellent out-of-band rejection; in addition, a high degree of isolation can be obtained between the output ports in a wide frequency range. The filtering power divider has the advantages of superior performance, simple design process and the like.

Description

Wide-stopband filtering power divider

Technical Field

The invention belongs to the technical field of communication, and particularly relates to a microstrip filtering power divider with a wide stop band and a broadband isolation characteristic.

Background

In higher frequency bands such as radio frequency/microwave/optical frequency and the like, the microstrip line has the advantages of small volume, light weight, wide use frequency band, high reliability, low manufacturing cost and the like, and is a transmission line with wide application. The microstrip line has a distributed parameter effect, and the electrical characteristics of the microstrip line are closely related to the structural size. The power divider is called a power divider, and is an important device in a communication or radar system. The device divides one path of input signal energy into two paths or multiple paths of input signal energy which are output with equal or unequal energy, and can also synthesize the multiple paths of signal energy into one path of output in turn, and at the moment, the device can also be called a combiner. Since the power divider can be used in reverse as a combiner, the following discussion takes the power divider as an example. Certain isolation degree should be guaranteed between output ports of one power divider. In addition, the filter is another microwave device, and functions to allow signals of a certain frequency to pass through smoothly, and allow signals of another frequency to be greatly suppressed. Conventional filters and power splitters are two separate components that assume different functions.

Disclosure of Invention

In order to overcome the defect that the size is larger because the traditional power divider and the traditional filter belong to two elements, the invention provides a novel micro-strip power divider which simultaneously realizes the functions of band-pass filtering and power division; good isolation is achieved between the two output ports in a wide frequency range; in addition, the method has the advantages of good frequency selectivity, small size, easy design and the like. Hereinafter referred to as filter power divider.

The structure of a typical microstrip is shown in fig. 1 and mainly comprises three layers. The first layer is a metal upper cladding layer, the second layer is a dielectric substrate, and the third layer is a metal lower cladding layer. As shown in fig. 2, the filter power divider of the present invention is disposed in the metal upper cladding (I), and is characterized in that: the first Port (Port #1) is connected to the middle of the coupling three-wire structure (1), the other end of the middle of the coupling three-wire structure (1) is connected with the T-shaped open circuit wire section (2), the left side of the coupling three-wire structure (1) is connected to the right end of the first transmission wire section (21), the left end of the first transmission wire section (21) is connected with the right ends of the first open circuit branch section (22) and the second transmission wire section (23), the left end of the second transmission wire section (23) is connected with the right ends of the second open circuit branch section (24) and the third transmission wire section (25), the left end of the third transmission wire section (25) is connected with the third open circuit branch section (26) and the right end of the first two-wire coupling structure (27), and the left end of the first coupling two-wire structure (27) is connected with the second Port # 2); the right side in the coupled three-wire structure (1) is connected to the left end of a fourth transmission line section (31), the right end of the fourth transmission line section (31) is connected with the left ends of a fourth branch section (32) and a fifth transmission line section (33), the right end of the fifth transmission line section (33) is connected with the left ends of a fifth open-circuit branch section (34) and a sixth transmission line section (35), the left end of the sixth transmission line section (35) is connected with the left ends of a sixth open-circuit branch section (36) and a second coupled two-wire structure (37), and the right end of the second coupled two-wire structure (37) is connected with a third Port (Port # 3); a first resistor (R1) and a second resistor (R2) are connected across the coupled three-wire structure (1).

In the filter power divider, two multimode resonators are included, as shown in fig. 3. Fig. 4 is an equivalent circuit diagram thereof. Since the multimode resonator is a symmetrical structure, the equivalent circuit of fig. 4 can be analyzed using an odd-even mode analysis method. The odd and even mode equivalent circuits are shown in FIGS. 5 and 6, where θ_i(i-1, …,6) is the electrical length, Y_i(i ═ 1, …,6) is the characteristic admittance. According to the odd-mode equivalent circuit of FIG. 5, the odd-mode input admittance Y is seen from the node in the figure_in,oddIs composed of

From the even-mode equivalent circuit of FIG. 6, the even-mode input admittance Y looking into the node in the figure_in,evenIs composed of

Wherein the content of the first and second substances,

θ_A＝θ₅+θ₆。

order odd mode input admittance Y_in,oddEqual to zero, the equation for the odd mode resonance condition can be found as

(Y₄ cotθ₄-Y₃ tanθ₃)(Y₂cotθ₁-Y₁ tanθ₂)-Y₂(Y₁+Y₂cotθ₁tanθ₂) 0 (3) order even mode input admittance Y_in，evenResonance equal to zero, even modeThe conditional equation is

Furthermore, the filtering power divider can realize a third-order band-pass frequency response, and each side of the pass band is provided with a transmission zero, so that the frequency selectivity of two sides of the pass band can be improved.

The filter power divider has the beneficial effects that: one path of input signals can be divided into two paths to be output, and on the contrary, the two paths of input signals can be combined into one path to be output; the power divider has band-pass frequency response, and each side of the pass band is provided with a transmission zero respectively, so that the frequency selectivity is greatly improved; the stopband has excellent inhibition capability; the isolation between the output ports is high; the size is less, the design process is simple, and the debugging is easy.

Drawings

FIG. 1: a schematic structural diagram of a microstrip line;

FIG. 2: a schematic diagram of a filtering power divider;

FIG. 3: a schematic diagram of a multimode resonator;

FIG. 4: a multimode resonator equivalent circuit diagram;

FIG. 5: an odd-mode equivalent circuit diagram of the multimode resonator;

FIG. 6: an even mode equivalent circuit diagram of a multimode resonator;

FIG. 7: marking a schematic diagram of structural parameters of the filtering power divider;

FIG. 8: t-type open-end section (2) for | S of example₂₁The influence effect graph of | is shown;

FIG. 9: example | S₂₁I and I S₁₁I, a simulation test result graph;

FIG. 10: example | S₃₂And | simulating a test result graph.

Detailed Description

In order to embody the inventive and novel aspects of the present invention, the following description is made with reference to the accompanying drawings and specific examples, but the embodiments of the present invention are not limited thereto. Without loss of generality, the embodiment selects a common microstrip substrate with a relative dielectric constant of 3.66 and a substrate thickness of 0.508 mm.

First embodiment is to verify the characteristics of the multimode resonator as shown in fig. 3. The electrical length and characteristic admittance with a center frequency of 2GHz are chosen as follows: y is₁＝0.00075S，Y₂＝0.01528S，Y₃＝0.03607S，Y₄＝0.01633S，Y₅＝0.02295S，Y₆＝0.00079rad，θ₁＝0.3468rad，θ₂＝0.1617rad，θ₃＝0.29882rad，θ₄＝0.0222rad，θ₅＝0.15047rad，θ₆0.0009 rad. Solving an odd-mode resonance condition equation (3) according to the selected electrical length and the characteristic admittance calculation tool to obtain two odd-mode resonance frequencies: f. of_o1＝1.64GHz，f_o22.66 GHz. Solving the dual-mode resonance condition equation (4) to obtain a resonance frequency as follows: f. of_e2.11 GHz. To further verify the correctness of the resonance frequency, the structural parameters (unit: mm) of fig. 3 were obtained according to the selected electrical length and characteristic admittance at 2 GHz: w is a₁＝0.12，w₂＝0.7，w₃＝2.6，w₄＝0.79，w₅＝1.38，w₆＝0.14，l₁＝16.3，l₂＝7.3，l₃＝12.77，l₄＝1，l₅＝6.61，l₆0.42. The results of the simulation of the resonance frequency were obtained by full-wave simulation using these parameters and compared with the results of the calculation, as shown in table 1. It can be seen that the theoretical calculations of the three resonant frequencies of a multimode resonator are very close to the electromagnetic simulation values. Therefore, it can be seen from the above analysis that, by an appropriate feeding manner, three resonant modes of the resonator can be excited for use in the design of the third-order filter power divider.

TABLE 1 comparison of the resonant frequency calculation and simulation results for multimode resonators

Resonant frequency	Odd model f_o1	Even mode f_e	Odd model f_o2
				Theoretical calculation value	1.64GHz	2.11GHz	2.63GHz
Electromagnetic simulation value	1.73GHz	2.25GHz	2.66GHz

The second embodiment is a filtering power divider, and the structural parameters of the second embodiment are labeled as shown in fig. 7, and the specific values are (unit: mm): w is a₁＝0.12，w₂＝0.7，w₃＝2.6，w₄＝0.79，w₅＝1.38，w₆＝0.14，w₇＝0.31，w₈＝0.14，w₉＝3.6，w₃₃＝0.78，l₁＝16.3，l₂＝7.3，l₃＝12.77，l₄＝1，l₅＝6.61，l₆＝0.42，l₇＝20.7，l₈＝39.2，l₉＝0.58，l₃₃＝16.3，R₁＝860Ω，R₂8700 Ω. The dimensions occupied by the embodiment are about 0.49 λ g × 0.69 λ g, λ g being the waveguide wavelength at the center frequency.

As shown in fig. 7, the T-shaped open-circuit link (2) introduces a transmission zero on each side of the pass band, thereby effectively improving the frequency selectivity. Input impedance Z as seen from the position shown in FIG. 7_inIs composed of

Wherein Z is₈Is a line width of w₈Sum line length is l₈Characteristic impedance of microstrip line of (1), Z₉Is a line width of w₈Sum line length is l₈The input impedance of the microstrip line viewed from the middle. When the input impedance Z_inA transmission zero occurs at the frequency point corresponding to 0. As a result of the simulation, as shown in FIG. 8, the T-shaped open-circuit wire segment (2) connected to the coupled three-wire structure (1) can provide a transmission zero point f for each side of the pass band_z1And transmission zero point f_z2The two zero points are generated, so that the selectivity of the filtering power divider is greatly improved.

The test result of the embodiment is shown in fig. 9, the center frequency is at 2.22GHz, the insertion loss is 3.86dB, the return loss is better than 21.6dB, the 3dB relative bandwidth is 45.9%, and the transmission zero point at 0.79GHz and 3.14GHz is extremely high, so that the selectivity of the filter power divider is improved. Meanwhile, the suppression degree from direct current to low frequency of 0.75GHz is measured to be better than 40dB, and the zero point f is transmitted from the outside of the passband_z23.14GHz to 14GHz (about 6.3 f)₀) The high-frequency stop band rejection capability of the filter is better than 20 dB.

The isolation between the output ports was tested and compared as shown in FIG. 10 from DC to 14GHz (6.3 f)₀) Better than 17.1dB isolation is achieved over a wide frequency band. In addition, table 2 compares the comparative examples with similar power dividers in other publications. As can be seen from the table, the embodiment has excellent out-of-band rejection capability, and has small insertion loss and return loss, thereby having remarkable technical progress.

Table 2 example compares similar power dividers in other publications

f₀: a center frequency; 3dB FBW: 3 decibels relative bandwidth; IL: inserting loss; RL: return loss; iso.: isolating; STB (stopband)>20 dB): rejection of stop band bandwidths of more than 20 dB.

Reference to the literature

[1]M.Chen，C.Tang.Design of the filtering power divider with a wide passband and stopband[J].IEEE Microwave and Wireless Components Letters，2018，28(7):570-572

[2]Y.Deng，J.Wang，et al.Filtering power divider with good isolation performance and harmonic suppression[J].IEEE Microwave and Wireless Components Letters，2016，26(12):984-986.

[3]Y.C.Li，Q.Chen，D.Wu，et al.Filtering power divider with high selectivity using modified coupled-line bandpass filter.IEEE MTT-S International Wireless Symposium(IWS),Chengdu,2018,pp.1-3.

[4]Y.Wang,F.Xiao,Y.Cao,et al.Novel wideband microstrip filtering power divider using multiple resistors for port isolation[J].IEEE Access，2019,(99):1-1.

The above-mentioned embodiments fully illustrate that the filtering power divider of the present invention has the advantages of good frequency response, small size, simple design process, etc., and has significant technical progress. It will be appreciated by those of ordinary skill in the art that the embodiments described herein are intended to assist the reader in understanding the principles of the invention and are to be construed as being without limitation to such specifically recited embodiments and examples. Those skilled in the art can make various other specific changes and combinations based on the teachings of the present invention without departing from the spirit of the invention, and these changes and combinations are within the scope of the invention.

Claims

1. A microstrip filter power divider is characterized in that: the first Port (Port #1) is connected to the middle of the coupling three-wire structure (1), the other end of the middle of the coupling three-wire structure (1) is connected with the T-shaped open circuit wire section (2), the left side of the coupling three-wire structure (1) is connected to the right end of the first transmission wire section (21), the left end of the first transmission wire section (21) is connected with the right ends of the first open circuit branch section (22) and the second transmission wire section (23), the left end of the second transmission wire section (23) is connected with the right ends of the second open circuit branch section (24) and the third transmission wire section (25), the left end of the third transmission wire section (25) is connected with the third open circuit branch section (26) and the right end of the first two-wire coupling structure (27), and the left end of the first coupling two-wire structure (27) is connected with the second Port # 2); the right side in the coupled three-wire structure (1) is connected to the left end of a fourth transmission line section (31), the right end of the fourth transmission line section (31) is connected with the left ends of a fourth branch section (32) and a fifth transmission line section (33), the right end of the fifth transmission line section (33) is connected with the left ends of a fifth open-circuit branch section (34) and a sixth transmission line section (35), the left end of the sixth transmission line section (35) is connected with the left ends of a sixth open-circuit branch section (36) and a second coupled two-wire structure (37), and the right end of the second coupled two-wire structure (37) is connected with a third Port (Port # 3); a first resistor (R1) and a second resistor (R2) are connected across the coupled three-wire structure (1).

2. The microstrip filter power divider according to claim 1, comprising a multimode resonator having an odd-mode resonance condition equation of

(Y₄cotθ₄-Y₃tanθ₃)(Y₂cotθ₁-Y₁tanθ₂)-Y₂(Y₁+Y₂cotθ₁tanθ₂)＝0

The resonance condition equation of the even mode is

3. The microstrip filter power divider according to claim 1, implementing a third order bandpass frequency response, with a transmission zero at each limited frequency on each side of the passband; a plurality of transmission zeros are arranged in the high-frequency stop band; the output ports can obtain higher isolation in a wider frequency range.

4. The microstrip filter power divider according to claim 1, wherein the T-shaped open-circuit line section (2) introduces a transmission zero point on each side of the pass band, thereby effectively improving the frequency selectivity; input impedance Z_inIs shown as

Wherein Z is₈Is a line width of w₈Sum line length is l₈Characteristic impedance of microstrip line of (1), Z₉Is a line width of w₈Sum line length is l₈The input impedance of the microstrip line viewed from the middle; when the input impedance Z_inA transmission zero occurs at the frequency point corresponding to 0.

5. The microstrip filter power divider according to claim 1, based on a microstrip substrate, having a relative dielectric constant of 3.66 and a substrate thickness of 0.508 mm; the specific values of the structural parameters are (unit: mm): w is a₁＝0.12，w₂＝0.7，w₃＝2.6，w₄＝0.79，w₅＝1.38，w₆＝0.14，w₇＝0.31，w₈＝0.14，w₉＝3.6，w₃₃＝0.78，l₁＝16.3，l₂＝7.3，l₃＝12.77，l₄＝1，l₅＝6.61，l₆＝0.42，l₇＝20.7，l₈＝39.2，l₉＝0.58，l₃₃＝16.3，R₁＝860Ω，R₂8700 Ω; the center frequency is 2.22GHz, the insertion loss is 3.86dB, the return loss is better than 21.6dB, the 3dB relative bandwidth is 45.9%, and transmission zeros are respectively arranged at 0.79GHz and 3.14 GHz.