CN1664594A - Method of testing transmission line characteristic impedance - Google Patents
Method of testing transmission line characteristic impedance Download PDFInfo
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- CN1664594A CN1664594A CN200510059845.9A CN200510059845A CN1664594A CN 1664594 A CN1664594 A CN 1664594A CN 200510059845 A CN200510059845 A CN 200510059845A CN 1664594 A CN1664594 A CN 1664594A
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- transmission line
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Abstract
The invention discloses a method for measuring the characteristic impedance of the transmission line, which comprises the following steps: connecting the end of the transmission line with the matched load ZL, measuring the length of the line, measuring the input impedance Zin in the origin of the line by the nose of the network analyzer, computing the characteristic impedance Z according to the transmission line theory. Another method is: applying the transmission line as two-terminal network, connecting the origin and terminal of the line with the head and reversing port of the network analyzer individually, measuring the S parameter, computing the characteristic impedance according to the theory and S. Through said method, we can get the real and imaginary part of the characteristic impedance and the transfer and depletion characteristic of the transmission line.
Description
The present invention is that application number is 03104554.5, the applying date is on February 18th, 2003, denomination of invention is divided an application for " method of testing of line characteristic impedance " application.
Technical field
The invention belongs to high-frequency electronic communication line field, relate to a kind of line characteristic impedance method of testing, be meant a kind of implementation method that obtains the characteristic impedance of transmission line by the S parameter of measuring transmission line especially.
Background technology
High-frequency circuit must be considered the matching problem of signal transmission.Frequency is high to have the undulatory property of light propagation to electric wave to a certain degree, can have reflection, the refraction of propagating as light in the process of transmission.The reflection of signal transmission, refraction are very big to the work influence of electronic circuit, can cause the distortion of signal in Electronic Circuit of Communication, produce spuious, harmonic wave, reduce communications reception sensitivity, even the operate as normal of destruction device.
The reflection of electric wave transmission is because the uncontinuity of transmission line causes with refraction, and promptly line characteristic impedance and loaded impedance do not match and cause, so the coupling of transmission line and load is extremely important in high-frequency circuit designs.The characteristic impedance of transmission line is to describe the characterisitic parameter that transmission line is propagated electric wave, and in printed circuit board (PCB) (PCB) process, whether the line characteristic impedance of making meets design requirement, and needs through test and validation.
At present, the test of line characteristic impedance adopts the method for Time Domain Reflectometry (TDR) to measure usually, and this method is by square wave of oscillograph emission or step excitation, measures the reflection parameters of transmission line.Because this method adopts the time domain measurement method, therefore usually below frequency is hanged down as 1GHz, be suitable under the loss-free situation of signal transmssion line, under the frequency condition with higher, measuring error is bigger, and can't measure the loss characteristic of transmission line, promptly can only measure the real part of line characteristic impedance, can't measure the imaginary part of line characteristic impedance.
Summary of the invention
The object of the present invention is to provide a kind of method of testing of line characteristic impedance,, measure transmission line real impedance and imaginary impedance to improve the accuracy that line characteristic impedance is measured.
A kind of measuring method of line characteristic impedance, with the transmission line equivalence is two-port, the starting point of transmission line and terminal are connected the forward direction port and the reverse port of network analyzer respectively, measure the S parameter of transmission line, according to transmission line theory and the S parametric solution line characteristic impedance that records.The described line characteristic impedance of finding the solution is according to formula:
S11=j (Z/Z
0-Z
0/ Z) Sin θ/[2Cos θ+j (Z/Z
0+ Z
0/ Z) Sin θ] and
S21=2Z*Z
0/ [2Z*Z
0* Cos θ+j (Z*Z+Z
0* Z
0) Sin θ] find the solution, wherein, Z
0Being the test macro line characteristic impedance, is 50 Europe, and θ is the transmission line electrical length.
Above-mentioned transmission line structure is surperficial microstrip line or covers the welding resistance microstrip line or embed microstrip line or equidistant strip line or not equidistant strip line or coupled microstrip line or co-planar waveguide.
Said method further comprises, increases the technology limit in the circuit board outside, makes transmission line to be measured identical with the actual transmission line structure that uses, certain-length on the technology limit.
The transmission line of making on the described technology limit to be measured and the vertical range of circuit board mesopore are propagated 1/10th of wavelength greater than electric wave in air, the length of transmission line of making on the technology limit to be measured is propagated four/three-wavelength of wavelength in air greater than electric wave, starting point and terminal at transmission line to be measured are reserved test interface, and transmission line to be measured is straight line cabling or miter angle cabling.
Transmission line measuring method provided by the invention, actual measurement is combined with theoretical algorithm, actual measurement is by the S parameter on the direct metering circuit plate of network analyzer, or the S parameter of the transmission line to be measured on the measurement technology limit, carry out single-ended measurement, or carry out double-end measurement, the utilization corresponding calculated obtains line characteristic impedance, thereby obtains the transport property and the loss characteristic of transmission line.Because the present invention is a kind of frequency domain measurement method, therefore can obtain the real impedance and the imaginary impedance of line characteristic impedance, for prior art time domain measurement method, the accuracy height of measurement.The present invention not only is suitable for the radio frequency signal transmission line among the PCB, also is suitable for transmission lines such as concentric cable.
Description of drawings
The schematic diagram that Fig. 1 carries out single-ended measurement for the present invention to transmission line,
Fig. 2 carries out the synoptic diagram of single-ended measurement with the acquisition line characteristic impedance for the present invention to transmission line,
Fig. 3 is that embodiment 1 calculates the line characteristic impedance process flow diagram,
Fig. 4 carries out the schematic diagram of double-end measurement for the present invention to transmission line,
Fig. 5 carries out the synoptic diagram of double-end measurement with the acquisition line characteristic impedance for the present invention to transmission line,
Fig. 6 is that embodiment 2 calculates the line characteristic impedance process flow diagram,
Fig. 7 a～7g is transmission line cross-sectional structure figure,
Fig. 8 is that the position in transmission line and hole concerns synoptic diagram,
Fig. 9 is a transmission line cabling synoptic diagram.
Embodiment
Because signal wavelength and length of transmission line is comparable or more in short-term, voltage, electric current on the transmission line are not only the function of time, but also be function of position, must consider the effect of distribution parameter, line characteristic impedance is a form of expression of transmission line distribution parameter.Its physical significance is the ratio of incident wave voltage and incident wave electric current on the transmission line, or the ratio of reflection wave voltage and reflected current.
When line characteristic impedance and load not simultaneously, can produce the reflection of signal, so communication system defined unified standard, all adopt 50 Europe superscripts punctual at all transmission lines, just can not produce reflection or be reflected in the allowed band.
The present invention measures the transmission line correlation parameter with transmission line theory and combines closely, and the measurement of transmission line correlation parameter comprises transmission line input impedance measurement, transmission line S parameter measurement.Transmission line theory provides the core algorithm of the calculating of line characteristic impedance, describes in detail below in conjunction with embodiment and accompanying drawing.
Embodiment 1
Referring to illustrated in figures 1 and 2, the schematic diagram that Fig. 1 carries out single-ended measurement for the present invention to transmission line, Fig. 2 carries out single-ended measurement to obtain the synoptic diagram of line characteristic impedance for the present invention to transmission line.At first the forward direction port is carried out single-ended calibration, connect 50 Europe matched loads at transmission-wire terminal then, measure input impedance Z with network analyzer
In, voltage standing wave ratio (VSWR) VSWR.If the VSWR of voltage standing wave ratio (VSWR) as a result that measures shows that less than 1.9 the characteristic impedance index of transmission line reaches requirement.Input impedance Z according to reference surface among the known Fig. 1 of transmission line theory
InExpression formula is as follows:
Z
In=Z* (Z
L+ j*Z*tg β L)/(Z+j*Z
L*--------formula 1 tg β L)
Wherein: Z
LBeing terminator, is 50 Europe by standard, is 75 ohm in radio data system,
Z is a line characteristic impedance,
L is a length of transmission line,
β is a phase-shift constant, and β=2 π/λ g, λ g are the transmission wavelength of electric wave on transmission line, and this parameter is relevant with transmission line structure, according to the lamination specific inductive capacity of PCB, and the lamination height, transmission line structure parameters such as live width, using related software can calculate.
From above-mentioned formula 1, Z
InBe measurement result, length of transmission line L can measure, and β can calculate, and unknown parameter only comprises Z, thereby can obtain Z.
The above-mentioned Z that finds the solution can realize that its software flow pattern as shown in Figure 3 by line characteristic impedance software.The input impedance Z of input measurement at first
InAnd length of transmission line, according to transmission line structure and correlation parameter thereof, calculate phase-shift constant β, calculate line characteristic impedance then, and judge whether line characteristic impedance meets the demands.
Embodiment 2
Referring to Fig. 4 and shown in Figure 5, Fig. 4 carries out the schematic diagram of double-end measurement for the present invention to transmission line, and Fig. 5 carries out double-end measurement to obtain the synoptic diagram of line characteristic impedance for the present invention to transmission line.Being that port one and reverse port are that port 2 is calibrated respectively with network analyzer to the forward direction port earlier, is radio frequency network with the transmission line equivalence then, and the S parameter of Measurement Network comprises S11, S21, S12, S22.Wherein, the physical significance of S11 is: when port 2 couplings, and the port one reflection coefficient of network to be measured, port one excitation this moment; The physical significance of S21 is: when port one mated, the port one of network to be measured was to the transmission coefficient of port 2, and this moment, port one encouraged; The physical significance of S22 is: when port one mates, and the reflection coefficient of the network port 2 to be measured, port 2 excitations this moment; The S12 physical significance is: when port 2 couplings, the port 2 of network to be measured is to the transmission coefficient of port one, and port 2 encourages at this moment.Because transmission circuit network is symmetrical reciprocal network, therefore S11=S22 is arranged; S12=S21.Conversion to s-matrix has according to transmission line theory and A matrix:
S11=j (Z/Z
0-Z
0/ Z) Sin θ/[2Cos θ+j (Z/Z
0+ Z
0/ Z) Sin θ]-----Shi 2
S21=2Z*Z
0/ [2Z*Z
0* Cos θ+j (Z*Z+Z
0* Z
0) Sin θ]-------------Shi 3
Formula 2, in the formula 3, Z
0Being the test macro line characteristic impedance, is 50 Europe at this; Z is a line characteristic impedance to be tested.Only there are two unknown quantity: line characteristic impedance Z in last two formulas; θ transmission line electrical length; S11, S21 are measurement result, and through type 2, formula 3 can calculate line characteristic impedance Z, transmission line electrical length θ.Above-mentioned double-end measurement method does not need the transmission line structure parameter, need not measure length of transmission line yet, can draw line characteristic impedance.
Above-mentioned line characteristic impedance Z, finding the solution of transmission line electrical length θ can be calculated by corresponding software, and its process flow diagram is as shown in Figure 6.
Transmission line structure described in the foregoing description 1 and the embodiment 2 can be shown in Fig. 7 a～7g, and Fig. 7 a～7g is transmission line cross-sectional structure figure.Fig. 7 a～7g is respectively surperficial microstrip line, covering welding resistance microstrip line, embedding microstrip line, equidistant strip line, equidistant strip line, coupled microstrip line and co-planar waveguide, and dash area is signal wire and ground wire among the figure, and unblanketed part is a dielectric layer.
Measuring method provided by the invention can directly be measured the characteristic impedance of transmission line on the pcb board, also can increase the technology limit in the pcb board outside, makes the transmission line with the actual transmission line same structure that uses on the technology limit.For guaranteeing that the transmission line of making on the technology limit can reflect the line characteristic impedance of actual use truly, making transmission line on the technology limit should meet the following conditions:
1. the structure of the transmission line on the technology limit and PCB are identical in using, fabrication hole on the technology limit, through hole, via hole should be away from transmission line, as shown in Figure 8, should there be certain distance in transmission line of making on the technology limit and hole, the transmission line of making on the technology limit and the vertical range in hole are propagated 1/10th of wavelength greater than electric wave in air, otherwise will destroy the Electric Field Distribution of transmission line, can't obtain correct test result;
2. transmission line is preferably straight line, and is not crooked, wants translation-angle really, as shown in Figure 9, is designed to the miter angle cabling, otherwise causes transmission line that bigger emission is arranged, and measuring error will occur;
3. because the transmission line of certain-length could truly reflect its characteristic impedance, and transmission line should have certain-length, length of transmission line must be propagated 3/4 wavelength of wavelength greater than electric wave in air;
4. the starting point of transmission line and terminal are reserved test interface on the technology limit, as SMA interface, N type interface or Q type interface or the like, are convenient to the measurement of network analyzer.
Claims (5)
1, a kind of method of testing of line characteristic impedance is characterized in that, is two-port with the transmission line equivalence, and the starting point and the terminal of transmission line is connected the forward direction port and the reverse port of network analyzer respectively, measures the S parameter of transmission line, according to formula:
S11=j (Z/Z
0-Z
0/ Z) Sin θ/[2Cos θ+j (Z/Z
0+ Z
0/ Z) Sin θ] and
S21=2Z*Z
0/ [2Z*Z
0* Cos θ+j (Z*Z+Z
0* Z
0) Sin θ] find the solution line characteristic impedance Z and transmission line electrical length θ, wherein, Z
0Be known test macro line characteristic impedance.
2, method of testing according to claim 1 is characterized in that, described test macro line characteristic impedance Z
0It is 50 ohm.
3, method of testing according to claim 1, it is characterized in that described transmission line structure is surperficial microstrip line or covers the welding resistance microstrip line or embed microstrip line or equidistant strip line or not equidistant strip line or coupled microstrip line or co-planar waveguide.
4, method of testing according to claim 1 is characterized in that, this method further comprises, increases the technology limit in the circuit board outside, makes on the technology limit and the actual identical transmission line to be measured of transmission line structure that uses.
5, method of testing according to claim 4, it is characterized in that, the transmission line of making on the described technology limit to be measured and the vertical range of circuit board mesopore are propagated 1/10th of wavelength greater than electric wave in air, the length of transmission line of making on the technology limit to be measured is propagated four/three-wavelength of wavelength in air greater than electric wave, starting point and terminal are reserved test interface, and transmission line to be measured is straight line cabling or miter angle cabling.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN03104554.5A CN1251468C (en) | 2003-02-18 | 2003-02-18 | Method of testing transmission line characteristic impedance |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN03104554.5A Division CN1251468C (en) | 2003-02-18 | 2003-02-18 | Method of testing transmission line characteristic impedance |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN1664594A true CN1664594A (en) | 2005-09-07 |
| CN100339717C CN100339717C (en) | 2007-09-26 |
Family
ID=34282260
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CNB2005100598459A Expired - Fee Related CN100339717C (en) | 2003-02-18 | 2003-02-18 | Method of testing transmission line characteristic impedance |
| CN03104554.5A Expired - Fee Related CN1251468C (en) | 2003-02-18 | 2003-02-18 | Method of testing transmission line characteristic impedance |
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| Application Number | Title | Priority Date | Filing Date |
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| CN03104554.5A Expired - Fee Related CN1251468C (en) | 2003-02-18 | 2003-02-18 | Method of testing transmission line characteristic impedance |
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| CN2108364U (en) * | 1991-11-23 | 1992-06-24 | 国营第七二○厂 | Coaxial load |
| US5559427A (en) * | 1994-04-04 | 1996-09-24 | Fluke Corporation | Instrument and method for testing local area network cables |
| DE19810587A1 (en) * | 1998-03-11 | 1999-09-16 | Siemens Ag | Ethernet (RTM) network with redundancy characteristics |
-
2003
- 2003-02-18 CN CNB2005100598459A patent/CN100339717C/en not_active Expired - Fee Related
- 2003-02-18 CN CN03104554.5A patent/CN1251468C/en not_active Expired - Fee Related
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Also Published As
| Publication number | Publication date |
|---|---|
| CN1523363A (en) | 2004-08-25 |
| CN1251468C (en) | 2006-04-12 |
| CN100339717C (en) | 2007-09-26 |
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