CN112018479B - Passive intermodulation suppression method for circulator for communication - Google Patents
Passive intermodulation suppression method for circulator for communication Download PDFInfo
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- CN112018479B CN112018479B CN202010895080.7A CN202010895080A CN112018479B CN 112018479 B CN112018479 B CN 112018479B CN 202010895080 A CN202010895080 A CN 202010895080A CN 112018479 B CN112018479 B CN 112018479B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
- H01P1/00—Auxiliary devices
- H01P1/32—Non-reciprocal transmission devices
- H01P1/38—Circulators
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- H—ELECTRICITY
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- H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
- H01P11/00—Apparatus or processes specially adapted for manufacturing waveguides or resonators, lines, or other devices of the waveguide type
Abstract
The invention discloses a passive intermodulation suppression method of a circulator for communication, which comprises the following steps of (1) determining a circulator frequency band to be processed, a power index and an expected PIM value expected to be reached under the power index; (2) establishing a simulation model of the circulator in HFSS simulation software, and obtaining the value in (2) under the power indexf 1‑f 2）、（2f 2‑f 1) A, B; (3) calculating a PIM value for the simulation model from A, B, labeled as a simulated PIM value; (4) and comparing the simulation PIM value with the expected PIM value, and adjusting the structure of the simulation model in HFSS simulation software according to the comparison result until the condition is met. The invention determines a determinant factor causing circulator passive intermodulation, provides a method for quantitatively analyzing circulator passive intermodulation indexes by using the determinant factor, and is also suitable for other microwave passive devices with the requirement of three-order passive intermodulation suppression based on gyromagnetic ferrite materials.
Description
Technical Field
The invention relates to a passive intermodulation suppression method, in particular to a passive intermodulation suppression method of a circulator for communication.
Background
It is well known that active devices produce nonlinear effects in the system. Various techniques have been developed to improve the performance of such devices during the design and operational stages. To be easily ignored, passive devices may also introduce nonlinear effects; these non-linear effects, if not corrected for, can severely impact system performance. In 5G cellular communication systems, passive intermodulation can cause interference, reduce receiver sensitivity, and even completely block communication, which interference can affect the cell in which it originates and other receivers nearby, is a significant problem and difficult to resolve in the cellular communication industry.
The ferrite circulator isolator is a passive device widely applied in a 4G \5G communication system, due to the nonlinear effect of ferrite materials, the device is easy to generate intermodulation signals at intermodulation frequency points when multiple paths of high-power signals are input, particularly three-order intermodulation frequency points such as 2f1-f2 and 2f2-f1, and the frequency of the three-order intermodulation frequency points is very close to the central frequency point and is difficult to eliminate by a method of adding a filter, so that adverse effects are often generated on communication quality and a system scheme. The traditional passive intermodulation suppression method is generally characterized in that qualitative analysis is carried out on a device, and according to experience and experimental verification, multi-version iteration of device design is generally carried out, so that time and labor are wasted.
PIM, known as Passive inter-Modulation, is a phenomenon of IM intermodulation products generated by various Passive devices in a transmitting system under the excitation of specific power, usually high-power radio frequency signals. PIM is usually caused by metal-to-metal contact, most commonly and problematic.
Disclosure of Invention
The present invention is directed to a method for suppressing passive intermodulation of a circulator for communication, which can solve the above problems, determine a determining factor causing the passive intermodulation of the circulator, and assist the quantitative design of the passive intermodulation suppression of the circulator by analysis.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows: a method for suppressing passive intermodulation of a circulator for communication comprises the following steps:
(1) determining the frequency band and power index of the circulator to be processed, and the expected PIM value expected to be achieved under the power index, and randomly selecting two frequencies f within the working frequency band of the circulator1And f2The input signal of (1);
(2) establishing a simulation model of the circulator in HFSS simulation software, and obtaining the frequency 1 of the intermodulation signal as (2 f) under the power index1-f2) Has a maximum field strength A and an intermodulation signal frequency 2 of (2 f)2-f1) The maximum field strength B;
(3) calculating a PIM value for the simulation model from A, B, labeled as a simulated PIM value;
(4) comparing the simulated PIM value with the expected PIM value;
presetting an experience margin, if the simulation PIM value is less than or equal to the expected PIM value and the experience margin, adjusting the structure of the simulation model in HFSS simulation software, and repeating the steps (2) and (3) until the simulation PIM value is greater than the expected PIM value and the experience margin, thereby completing the simulation design.
Preferably, the method comprises the following steps: and (2) establishing a simulation model of the circulator in HFSS simulation software, wherein index parameters of the circulator are required to be input, and the index parameters comprise a working frequency band, gyromagnetic ferrite material parameters, central conductor parameters, substrate parameters, overall dimensions, ports and boundary conditions.
Preferably, the method comprises the following steps: the step (3) is specifically calculated by the following formula:
(31) calculating intermediate values a, b according to the following formula;
the expression for each intermediate value is:
b1＝μeff2K1(3×0.1078+0.1588)/(f1×μ1)+(μeff1K2/μ2-μeff2K1/μ1)×(3×0.1078+0.1588)/(f1-f2)；
fm＝γ×MS；
f0＝γ×(H0-MS)；
H0＝1700+iii；
μ1＝1+f0×fm/(f0 2-f1 2)；
μ2＝1+f0×fm/(f0 2-f2 2)；
K1＝f1×fm/(f0 2-f1 2)；
K2＝f2×fm/(f0 2-f1 2)；
in the formula, MSFerrite saturation magnetization, gamma is the gyromagnetic ratio, iii is the external bias field, mu0Is a vacuum permeability, K1Propagation constant, K, for intermodulation signal frequency 12Is the propagation constant, mu, of the intermodulation signal frequency 2eff1、μeff2Effective magnetic conductivity of an intermodulation signal frequency 1 and an intermodulation signal frequency 2 in the ferrite is shown, and eps is a ferrite dielectric constant;
(32) calculate PIM value, PIM 10 log10 ((a)2+b2)/(A2))。
Preferably, the method comprises the following steps: in the step (4), the structure of the simulation model is adjusted, specifically: optionally one or more of the following means (a), (b) and (c);
(a) silver plating is carried out on the center conductor of the circulator, glue solution is added at the contact position of the center conductor and the ferrite, and the maximum field intensity value of the circulator when power is loaded is reduced;
(b) processing the inner wall of the cavity to make the surface smooth;
(c) and (3) adding conductive adhesive before assembly through the cavity connecting part screwed by the screw, and curing after debugging.
In the invention, through detailed analysis of the mechanism of generation of the intermodulation signals and related factors, the determining factor causing the passive intermodulation of the circulator is determined to be the maximum field intensity of the intermodulation frequency point; then, a method for calculating PIM value through field intensity is provided, which is used for assisting the circulator passive intermodulation suppression quantitative design. In the calculation process, the parameters needed to be used comprise the gyromagnetic ratio gamma of the ferrite, the saturation magnetization Ms, the ferrite dielectric constant eps and the frequency 1 f1Input signal of frequency 2f2Input signal, device design upper limit frequency fupVacuum magnetic permeability mu0The external bias field, the input power, etc. are known parameters, and the unknown parameter A, B can be obtained by HFSS simulation calculation through electromagnetic simulation software.
So after the value of A, B is obtained by simulation, we can calculate the PIM value under the current simulation condition according to the formula. And then the calculated value of the passive intermodulation of the circulator meets the index provided by a user by means of adjusting the internal structure of the circulator and the like, so that the inhibition condition of the passive intermodulation, which can be achieved by the circulator, can be verified by calculation instead of experiments.
Compared with the prior art, the invention has the advantages that: a decision factor causing the passive intermodulation of the circulator is determined, a method for quantitatively analyzing the passive intermodulation index of the circulator by using the decision factor is provided, and a solution scheme when the index is not met is provided. The passive intermodulation suppression method provided by the invention is also suitable for other microwave passive devices with three-order passive intermodulation suppression requirements based on gyromagnetic ferrite materials.
Drawings
FIG. 1 is a schematic diagram of a circulator;
FIG. 2 is a flow chart of the present invention.
FIG. 3 is an electrical property simulation curve of example 2;
FIG. 4 is an insertion loss test curve of the product obtained by the method of example 2;
FIG. 5 is a graph of the isolation test of the product obtained by the method of example 2;
fig. 6 is a measured curve of the third order intermodulation versus input power of example 2.
In the figure: 1. a center conductor; 2. an upper cavity; 3. a lower cavity; 4. a gyromagnetic ferrite substrate; 5. a permanent magnet; 6. a compensation plate; 7. a matching medium; 8. and (5) shielding the magnetic circuit.
Detailed Description
The invention will be further explained with reference to the drawings.
Example 1: referring to fig. 1 to 2, the circulator for communication includes a cavity formed by an upper cavity and a lower cavity, and a central conductor, a gyromagnetic ferrite substrate, a permanent magnet, a compensation plate, a matching medium, and a magnetic circuit shield are arranged in the cavity. The embodiment provides a method for suppressing passive intermodulation of a circulator for communication, which comprises the following steps:
(1) determining the frequency band and power index of the circulator to be processed, and the expected PIM value expected to be achieved under the power index, and randomly selecting two frequencies f within the working frequency band of the circulator1And f2The input signal of (1);
(2) establishing a simulation model of the circulator in HFSS simulation software, and obtaining the frequency 1 of the intermodulation signal as (2 f) under the power index1-f2) Has a maximum field strength A and an intermodulation signal frequency 2 of (2 f)2-f1) The maximum field strength B;
(3) calculating a PIM value for the simulation model from A, B, labeled as a simulated PIM value;
(4) comparing the simulated PIM value with the expected PIM value;
presetting an experience margin, if the simulation PIM value is less than or equal to the expected PIM value and the experience margin, adjusting the structure of the simulation model in HFSS simulation software, and repeating the steps (2) and (3) until the simulation PIM value is greater than the expected PIM value and the experience margin, thereby completing the simulation design.
In this embodiment, in step (2), a simulation model of the circulator is established in HFSS simulation software, and index parameters of the circulator need to be input, where the index parameters include a working frequency band, gyromagnetic ferrite material parameters, center conductor parameters, substrate parameters, external dimensions, ports, and boundary conditions.
The step (3) is specifically calculated by the following formula:
(31) calculating intermediate values a, b according to the following formula;
the expression for each intermediate value is:
b1＝μeff2K1(3×0.1078+0.1588)/(f1×μ1)+(μeff1K2/μ2-μeff2K1/μ1)×(3×0.1078+0.1588)/(f1-f2)；
fm＝γ×MS；
f0＝γ×(H0-MS)；
H0＝1700+iii；
μ1＝1+f0×fm/(f0 2-f1 2)；
μ2＝1+f0×fm/(f0 2-f2 2)；
K1＝f1×fm/(f0 2-f1 2)；
K2＝f2×fm/(f0 2-f1 2)；
in the formula, MSIs ferrite saturation magnetization, gamma is gyromagnetic ratio, is external bias magnetic field, mu0Is a vacuum permeability, K1Propagation constant, K, for intermodulation signal frequency 12Is the propagation constant, mu, of the intermodulation signal frequency 2eff1、μeff2Effective magnetic conductivity of an intermodulation signal frequency 1 and an intermodulation signal frequency 2 in the ferrite is shown, and eps is a ferrite dielectric constant;
(32) calculate PIM value, PIM 10 log10 ((a)2+b2)/(A2))。
In the step (4), the structure of the simulation model is adjusted, specifically: optionally one or more of the following means (a), (b) and (c);
(a) silver plating is carried out on the center conductor of the circulator, glue solution is added at the contact position of the center conductor and the ferrite, and the maximum field intensity value of the circulator when power is loaded is reduced;
(b) processing the inner wall of the cavity to make the surface smooth;
(c) and (3) adding conductive adhesive before assembly through the cavity connecting part screwed by the screw, and curing after debugging.
Example 2: referring to fig. 1 to 6, we further exemplify the present invention on the basis of example 1 and give detailed numerical values for better illustration of the present invention.
A method for suppressing passive intermodulation of a circulator for communication comprises the following steps:
(1) determining the frequency band and power index of the circulator to be processed, and the expected PIM value expected to be achieved under the power index, and randomly selecting two frequencies f within the working frequency band of the circulator1And f2The input signal of (1);
in this embodiment, we should design a circulator for communication, which has a structure of a circulator with a line, a device operating frequency of 925 to 960MHz, and power indexes of the circulator: loaded with power ofTwo-way 40dBm, the expected PIM value expected to be reached under the power index is-80 dBc @2 x 40dBm, and the input signal f1Is 935M, f2Is 950M. In practice, the frequency f1And f2Can be randomly selected, and can also generally adopt two end values of working frequency as f1And f2。
(2) Establishing a simulation model of the circulator in HFSS simulation software, and inputting index parameters of the circulator, wherein the index parameters comprise
Working frequency band: 925-960 MHz;
gyromagnetic ferrite material parameters: the saturation magnetization is 1830Gs, and the dielectric constant is 14;
center conductor parameters: the central conductor is of a double-Y disc knot structure, and the thickness of the central conductor is 0.2 mm;
the external dimension is as follows: the external dimension of the circulator is about 20x20x6 (mm);
port and boundary conditions: three ports of the circulator are of a strip line transmission line structure, and the impedance of the ports is 50 ohm; the circulator external magnetic field factor takes 2.
And obtaining the signal frequency 1 (2 f) of the intermodulation signal under the power index1-f2) Maximum field strength A and intermodulation signal frequency 2, i.e., (2 f)2-f1) The maximum field strength B;
in this embodiment, a is 41000V/M, and B is 41000V/M, which are calculated by HFSS simulation software.
(3) Calculating a PIM value of the simulation model according to A, B, marking as a simulation PIM value, substituting the value in the step (2) in the embodiment, and calculating the simulation PIM according to the steps (31) and (32);
(4) comparing the simulated PIM value with the expected PIM value;
presetting an experience allowance to be 5dBc, if the simulation PIM value is less than or equal to 85dBc because the expected PIM value is 80dBc, adjusting the structure of the simulation model in HFSS simulation software, and repeating the steps (2) and (3) until the simulation PIM value is greater than 85dBc, thereby completing the simulation design.
When (1) - (3) are performed for the first time, we find that the simulation PIM is 77dBc, and then adjust the structure of the simulation model, specifically: one or more of the means (a), (b), and (c) in (4) in example 1 is optionally employed.
After adjustment, repeating the steps (2) and (3) again, and obtaining a simulated PIM value of-86 dBc, namely 86dBc after repeating for a plurality of times; by contrast, 86dBc is greater than 80dBc +5dBc, so that the requirements of people are met, and the simulation design is completed.
Based on the simulation result of this embodiment, we produce the circulator to obtain the actual circulator product, and test the product to obtain the insertion loss test curve and the isolation test curve shown in fig. 4 and 5, and the third-order intermodulation and input power relation actual measurement curve shown in fig. 6.
From fig. 4 and 5, it can be seen that the actual electrical performance index of the circulator is matched with the simulation index, the electrical performance index of the circulator meeting the user requirement is satisfied, and a certain margin is provided, and the maximum field strength under the circulator intermodulation signal obtained by using the electrical performance model as the basis of the third-order intermodulation calculation of the circulator can accurately reflect the actual use condition of the circulator.
In fig. 6, when the loading power is two-way 40dBm, the PIM test value is-86 dBc, and when the design is performed, and the external magnetic factor is selected to be 2, a margin of 5dBc is reserved with the predetermined index of 80dBc, and the deviation between the actual measurement value and the calculated value is not large in consideration of the influences of various aspects such as process manufacturing, performance deviation, and test dynamic range; meanwhile, in the test condition that the loading power is from 42dBm to 46dBm, the loading power and PIM increase are more consistent with the theoretical analysis result.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (3)
1. A method for suppressing passive intermodulation of a circulator for communication is characterized in that: the method comprises the following steps:
(1) determining the frequency band and power index of the circulator to be processed, and the expected PIM value expected to be achieved under the power index, and randomly selecting two frequencies f within the working frequency band of the circulator1And f2The input signal of (1);
(2) establishing a simulation model of the circulator, and obtaining the frequency 1 of the intermodulation signal as (2 f) under the power index1-f2) Has a maximum field strength A and an intermodulation signal frequency 2 of (2 f)2-f1) The maximum field strength B;
(3) calculating a PIM value for the simulation model from A, B, labeled as a simulated PIM value;
(4) comparing the simulated PIM value with the expected PIM value;
presetting an experience margin, if the simulation PIM value is less than or equal to the expected PIM value and the experience margin, adjusting the structure of the simulation model in HFSS simulation software, and repeating the steps (2) and (3) until the simulation PIM value is greater than the expected PIM value and the experience margin, thereby completing simulation design;
the step (3) is specifically calculated by the following formula:
(31) calculating intermediate values a, b according to the following formula;
the expression for each intermediate value is:
fm＝γ×MS；
f0＝γ×(H0-MS)；
H0＝1700+iii；
μ1＝1+f0×fm/(f0 2-f1 2)；
μ2＝1+f0×fm/(f0 2-f2 2)；
K1＝f1×fm/(f0 2-f1 2)；
K2＝f2×fm/(f0 2-f1 2)；
in the formula, MSFerrite saturation magnetization, gamma is the gyromagnetic ratio, iii is the external bias field, mu0Is a vacuum permeability, K1Propagation constant, K, for intermodulation signal frequency 12Is the propagation constant, mu, of the intermodulation signal frequency 2eff1、μeff2Effective magnetic conductivity of an intermodulation signal frequency 1 and an intermodulation signal frequency 2 in the ferrite is shown, and eps is a ferrite dielectric constant;
(32) calculate PIM value, PIM 10 log10 ((a)2+b2)/(A2))。
2. The method for suppressing the passive intermodulation of a circulator for communication according to claim 1, wherein: and (2) establishing a simulation model of the circulator in HFSS simulation software, wherein index parameters of the circulator are required to be input, and the index parameters comprise a working frequency band, gyromagnetic ferrite material parameters, central conductor parameters, substrate parameters, overall dimensions, ports and boundary conditions.
3. The method for suppressing the passive intermodulation of a circulator for communication according to claim 1, wherein: in the step (4), the structure of the simulation model is adjusted, specifically:
and silver plating the center conductor of the circulator, and adding glue solution at the contact part of the center conductor and the ferrite to reduce the maximum field intensity value of the circulator when power is loaded.
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