CN102457242B - Impedance matching network and design method thereof - Google Patents

Abstract

The invention provides an impedance matching network. By using a value of a passive device in the impedance matching network, the quality factor of the impedance matching network meets the requirement of harmonic suppression performance indexes and the requirement of impedance matching stability indexes during impedance change. Correspondingly, the invention provides a design method of the impedance matching network. In comprehensive consideration of the impedance change and harmonic suppression performance of a piezoelectric ceramic ultrasonic energy converter, an excellent impedance matching effect can be guaranteed under the operating state when the impedance of a load changes.

Description

A kind of impedance matching network and method for designing thereof

Technical field

The present invention relates to impedance match technique field, particularly relate to a kind of impedance matching network when descending impedance to change in working order and method for designing thereof.

Background technology

Impedance matching refers to that load impedance and singal source resistance resist or specific matching relationship between line characteristic impedance.When signal source is given, usually needs to increase an impedance matching network between load and signal source, realize impedance matching.Impedance matching network generally adopts passive device (electric capacity, inductance) load impedance to be matched to singal source resistance to resist or the complex conjugate of line characteristic impedance, thus reduce the power reflection of load end, make load to obtain maximum power, also can play the effect of harmonic inhabitation simultaneously.

Below using piezoelectric ceramic ultrasonic transducer as examples of loads, existing impedance matching methods and existing problems thereof will be described.

Piezoelectric ceramic ultrasonic transducer to be a kind ofly made up of piezoelectric ceramic, realizes with piezoelectric effect the device that electric energy and acoustic energy changes mutually.In recent years, piezoelectric ceramic ultrasonic transducer the underwater sound,

Non-Destructive Testing, radar, geophysics and the application of biologic medical field are very extensive.For high intensity focused ultrasound (High Intensity Focused Ultrasound) treatment technology, ultrasonic power source (namely, signal source) by transmission line by electric power transmission to piezoelectric ceramic ultrasonic transducer, ultrasonic transducer is as electro-acoustic transducing device, change electromagnetic wave into sound wave, and in vitro sound wave is focused on the affected area of inside of human body, thus realize external non-invasive therapy.

Piezoelectric ceramic ultrasonic transducer is made by piezoelectric ceramic plating metal on surface material, and its equivalent-circuit model is more complicated, and electrical impedance is also generally complex impedance.And power source source impedance and line characteristic impedance are generally 50 ohm, as directly piezoelectric ceramic ultrasonic transducer being connected with transmission line, extremely strong power reflection certainly will be produced in line end, make to form standing wave in transmission line, time serious, also may damage power source.Therefore, need to adopt impedance matching network to carry out impedance matching to piezoelectric ceramic ultrasonic transducer and transmission line.

Fig. 1 is the structural representation adopting impedance matching network piezoelectric ceramic ultrasonic transducer and transmission line to be carried out to impedance matching.As shown in Figure 1, the electrical power that power source 100 produces is transmitted by transmission line 101, adopts impedance matching network 102 to carry out impedance matching between ultrasonic transducer 103 and transmission line 101, to reduce power reflection, improves power transmission efficiency.

Impedance matching methods conventional under adopting the single-frequency matching network of Pi type and T-shaped network to become high-power applications occasion owing to being simple and easy to.Fig. 2 a and Fig. 2 b is respectively the circuit topological structure of T-shaped matching network 200 and Pi type matching network 210 in high intensity focused ultrasound application, wherein, 204 represent ultrasonic power source, 205 represent ultrasonic power source internal impedance (abbreviation source impedance) or line characteristic impedance, the load impedance of 206 expression piezoelectric ceramic ultrasonic transducers, 201 and 202 represent the inductance in T-shaped matching network 200,203 represent the electric capacity in T-shaped matching network 200,207 and 209 represent the electric capacity in Pi type matching network 210, and 208 represent the inductance in Pi type matching network 210.

The key of design Pi type matching network 210 and T-shaped matching network 200 is the parameter of the passive device (that is, inductance and electric capacity) determined in circuit network.Due to Pi type matching network 210 and T-shaped matching network 200 dual circuit each other, so here only for T-shaped network 200, introduce existing matching network method for designing.

The method for designing of existing T-shaped matching network is generally based on the basis of quality factor q, namely first determine quality factor q according to harmonics restraint (filtering) performance requirement of matching network, then determine the value of inductance in matching network, electric capacity according to corresponding computing formula.

Below, source impedance or line characteristic impedance 205 are designated as R _s, transducer impedance 206 is designated as Z ₁, inductance 201 is designated as L ₁, inductance 202 is designated as L ₂, electric capacity 203 is designated as C.The task of matching network design determines inductance L exactly ₁, inductance L ₂with the value of electric capacity C.

The first selected good Q of the conventional method for designing based on Q, makes Q>=1/2sqrt (k-1) (k>=1) or Q>=1/2sqrt (1/k-1)) (k≤1), wherein k=R _s/ R ₁, R _lfor the resistance in piezoelectric ceramic transducer impedance 206, following defined parameters Q simultaneously ₁and Q ₂:

$Q_1=\frac{2Q-\sqrt{{4\mathrm{kQ}}^2-{(k-1)}^2}}{1-k}---\left(1\right)$

$Q_2=\frac{2\mathrm{kQ}-\sqrt{{4\mathrm{kQ}}^2-{(k-1)}^2}}{k-1}---\left(2\right)$

T-shaped matching network parameter inductance L ₁, inductance L ₂determine respectively by following formula with electric capacity C:

$L_1=\frac{R_s{Q}_1}{{\mathrm{\ω}}_0}---\left(3\right)$

$L_2=\frac{R_l{Q}_2}{{\mathrm{\ω}}_0}-L_l---\left(4\right)$

$C=\frac{2Q}{{\mathrm{\ω}}_0{R}_s(1+Q_1^2)}=\frac{2Q}{{\mathrm{\ω}}_0{R}_l(1+Q_2^2)}---\left(5\right)$

Wherein, R _land L _lbe respectively the resistance in piezoelectric ceramic transducer impedance 206 and reactance, for representing capacitive load, L here _lcan be negative.

As can be seen from design cycle above, the design key of impedance matching network is the selection of Q.And the choice criteria of Q can only consider the harmonics restraint performance of matching network in existing method for designing.

The frequency response function of T-shaped matching network is:

$\left|H\left(\mathrm{j\ω}\right)\right|=\frac{2(k+1)Q-2p}{{\left\{\begin{array}{c}4{[{(k+1)}^{2}Q-(k+1)p-{(k-1)}^{2}Q{\mathrm{\ω}}_p^2]}^2\\ +{[{(k-1)}^2(3{\mathrm{\ω}}_p-{\mathrm{\ω}}_p^3)+(2(k+1)Q-{8\mathrm{kQ}}^2)({\mathrm{\ω}}_p-{\mathrm{\ω}}_p^3)]}^2\end{array}\right\}}^2}---\left(6\right)$

Wherein, p=4kQ ²-(k-1) ², ω _p=ω/ω ₀, ω ₀for operating frequency.N order harmonics rejection can adopt 20log [| H (jn ω ₀) |/| H (j ω ₀) |] represent.

Can find out from formula (6), different Q can produce different harmonics restraint performances, and therefore Q is directly associated with the harmonics restraint performance of matching network.More particularly, quality factor q is larger, and harmonics restraint performance is better.

For existing matching network method for designing, although for specific ultrasonic transducer 103, matching network has multiple different solution because of the difference of Q, but different Q can only represent different harmonic rejection level, that is impedance matching network can only design for this index of harmonics restraint performance.

And in working order under, the electrical impedance of piezoelectric ceramic ultrasonic transducer 103 very easily changes due to the impact by ambient temperature and acoustic load.If design impedance matching network in the quiescent state, in working order, ultrasonic transducer impedance variation then can cause matching condition to change, and makes coupling lose efficacy (impedance mismatching).

For the piezoelectric ceramic ultrasonic transducer 103 shown in Fig. 1, considerable index when harmonics restraint is no doubt design matching network, but what is more important will ensure the power transmission efficiency under operating state, namely when transducer impedance changes down in working order, matching network still can play the effect of impedance matching, effectively reduces power reflection.Because existing matching network method for designing can only consider this index of harmonics restraint performance, when ultrasonic transducer descends impedance to change in working order, existing method for designing then cannot ensure the impedance matching effect that system still can keep good.

Summary of the invention

In order to overcome the above problems, the invention provides a kind of impedance matching network and method for designing thereof, to consider piezoelectric ceramic ultrasonic transducer impedance variation and harmonic wave rejection, thus still can ensure good impedance matching effect when making to descend load impedance to change in working order.

In order to realize above object, the invention provides a kind of impedance matching network, this impedance matching network is connected between the positive pole of signal source and the tie point of the tie point of load one end and the negative pole of signal source and the load other end, comprise the passive device for realizing impedance matching, it is characterized in that, the requirement of the stability indicator of impedance matching when the value of described passive device makes the quality factor of described impedance matching network meet requirement and the impedance variation of harmonics restraint performance index simultaneously.

Preferably, the value of described passive device is determined according to following steps: determine that singal source resistance resists or the maximum variable quantity of line characteristic impedance, load impedance and load impedance; Select initial quality factor, and repeat following steps, until obtain suitable quality factor: the requirement of the stability indicator of impedance matching when judging whether current quality factor meet requirement and the impedance variation of harmonics restraint performance index simultaneously, if meet the requirement of the stability indicator of impedance matching during requirement and the impedance variation of harmonics restraint performance index simultaneously, then current quality factor are defined as final quality factor, otherwise execution following steps: if harmonics restraint performance index do not meet the demands, then increase quality factor; If stability indicator does not meet the demands, then reduce quality factor; The value of the passive device in impedance matching network is determined according to the final quality factor determined.

Preferably, the stability indicator of impedance matching during described impedance variation is the phase angle of load reflection coefficient.

Preferably, described impedance matching network is T-shaped matching network or Pi type matching network.

Correspondingly, the invention provides a kind of method for designing of impedance matching network, comprising: determine that singal source resistance resists or line characteristic impedance, load impedance and maximum variable quantity thereof; Select initial quality factor, and repeat following steps, until obtain suitable quality factor: the requirement of the stability indicator of impedance matching when judging whether current quality factor meet requirement and the impedance variation of harmonics restraint performance index simultaneously, if meet the requirement of the stability indicator of impedance matching during requirement and the impedance variation of harmonics restraint performance index simultaneously, then current quality factor are defined as final quality factor, otherwise execution following steps: if harmonics restraint performance index do not meet the demands, then increase quality factor; If stability indicator does not meet the demands, then reduce quality factor; The value of the passive device in impedance matching network is determined according to the final quality factor determined.

Preferably, the stability indicator of impedance matching during described impedance variation is the phase angle of load reflection coefficient.

Preferably, described impedance matching network is T-shaped matching network or Pi type matching network.

By above technical scheme, the harmonics restraint performance that the present invention not only can make the matching network designed comparatively be satisfied with, can also ensure the stability of the impedance matching when piezoelectric ceramic ultrasonic transducer impedance variation.

Accompanying drawing explanation

Fig. 1 is the structural representation adopting impedance matching network piezoelectric ceramic ultrasonic transducer and transmission line to be carried out to impedance matching;

Fig. 2 a and Fig. 2 b is respectively the circuit topological structure of T-shaped matching network 200 and Pi type matching network 210 in high intensity focused ultrasound application;

Fig. 3 a, Fig. 3 b and Fig. 3 c are respectively the schematic diagram for illustration of reflection coefficient each in designing impedance matching;

Fig. 4 is the curve chart of relation between the phase angle of reflected load reflection coefficient and quality factor;

Fig. 5 is the flow chart according to design method of impedance matching of the present invention.

Embodiment

Below, exemplarily describe the present invention with the impedance matching of piezoelectric ceramic ultrasonic transducer shown in Fig. 1, easy for describing, piezoelectric ceramic ultrasonic transducer is referred to as transducer.

In order to consider the factor that transducer impedance changes in designing impedance matching, when first Water demand descends transducer impedance to change in working order, affect the factor of the stability of impedance matching.Following by the embodiment of description, the stability of impedance matching when reflection coefficient is changed as transducer impedance consider index, and the quality factor of the requirement of the stability indicator of impedance matching when determining requirement and the impedance variation that simultaneously can meet harmonics restraint performance index by the relation analyzed between quality factor and reflection coefficient.Certainly, should be appreciated that, also can apply other factor affecting impedance matching stability as stability indicator, such as power transit line standing-wave ratio etc.

Fig. 3 a, Fig. 3 b and Fig. 3 c are respectively the schematic diagram for illustration of reflection coefficient each in designing impedance matching, wherein, 301 represent ultrasonic power source, 302 represent source impedance or line characteristic impedance, 303 represent transducer impedance, transducer impedance after changing under 304 expression operating states, 305 and 306 represent the inductance in T-shaped matching network 308 respectively, and 307 represent the electric capacity in T-shaped matching network 308.Below, source impedance or line characteristic impedance 302 are designated as R _s, transducer impedance 303 is designated as Z _l, the transducer impedance 304 after changing under operating state is designated as Z _l', inductance 305 is designated as L ₁, inductance 306 is designated as L ₂, electric capacity 307 is designated as C.Object of the present invention is exactly the value of the passive device determined in T-shaped matching network 308, that is, determine inductance L ₁, inductance L ₂with the value of electric capacity C, make matching network 308 both possess satisfied harmonics restraint performance, can still keep good level of impedance match when transducer impedance 303 changes again, be unlikely to mismatch occurs.

As mentioned above, in order to analyze the impact of transducer impedance change, introducing reflection coefficient in the present embodiment and analyzing.Use Γ _lrepresent the reflection coefficient (being called load reflection coefficient) of transducer end when not carrying out impedance matching in fig. 3 a, use Γ _l' represent transducer impedance in Fig. 3 b change after load reflection coefficient, represent in Fig. 3 c with Γ and carry out down the load reflection coefficient after impedance matching in working order.Meanwhile, Γ is defined _dfor the changing value of load reflection coefficient, i.e. Γ _l'=Γ _l+ Γ _d.

Meanwhile, the changing value defining transducer impedance is Z _d, then have:

Z _l’＝Z _l+Z _d (7)

With reference to Fig. 3 a, the definition according to reflection coefficient in EM theory can obtain:

$Z_l=\frac{1+{\mathrm{\Γ}}_l}{1-{\mathrm{\Γ}}_l}{R}_s---\left(8\right)$

With reference to Fig. 3 b, in like manner can obtain:

${Z_l}^{\′}=\frac{1+{{\mathrm{\Γ}}_l}^{\′}}{1-{{\mathrm{\Γ}}_l}^{\′}}{R}_s=\frac{1+{\mathrm{\Γ}}_l+{\mathrm{\Γ}}_d}{1-{\mathrm{\Γ}}_l-{\mathrm{\Γ}}_d}{R}_s---\left(9\right)$

Formula (8) and formula (9) are substituted in formula (7):

$Z_d={Z_l}^{\′}-Z_l=\frac{2{\mathrm{\Γ}}_d}{{({\mathrm{\Γ}}_1-1)}^2+({\mathrm{\Γ}}_l-1){\mathrm{\Γ}}_d}{R}_s---\left(10\right)$

With reference to Fig. 3 c, the equiva lent impedance after carrying out impedance matching to transducer impedance 304 can be expressed as:

$Z_e=\mathrm{j\ω}{L}_1+\frac{1}{\mathrm{j\ωC}+\frac{1}{\mathrm{j\ω}{L}_2+{Z_l}^{\′}}}$ (11)

$=\mathrm{j\ω}{L}_1+\frac{1}{\mathrm{j\ωC}+\frac{1}{\mathrm{j\ω}{L}_2+R_l+L_l+Z_d}}$

Same with reference to Fig. 3 c, and according to the definition of reflection coefficient in EM theory, can obtain:

$\mathrm{\Γ}=\frac{Z_e-R_s}{Z_e+R_s}---\left(12\right)$

After formula (3)-(5) in existing T-shaped network design method are substituted into formula (11), then by Z _esubstituting into formula (12), can obtain through simplifying:

$\mathrm{\Γ}=-\frac{[{(k-1)}^2+j(4\mathrm{kQ}-p-\mathrm{kp})]k{\mathrm{\Γ}}_d}{[{(k-1)}^2+j(4\mathrm{kQ}-p-\mathrm{kp})][{({\mathrm{\Γ}}_l-1)}^2+(k-1){\mathrm{\Γ}}_d+{\mathrm{\Γ}}_l{\mathrm{\Γ}}_d]}$ (13)

$=-\frac{(A+jB)k{\mathrm{\Γ}}_d}{(A-\mathrm{jB})[{({\mathrm{\Γ}}_l-1)}^2+(k-1){\mathrm{\Γ}}_d+{\mathrm{\Γ}}_l{\mathrm{\Γ}}_d]}$

Wherein, p=sqrt (4kQ ²-(k-1) ²), A=(k-1) ², B=4kQ-p (k+1).

Due to from formula (13), Q only affects the phase angle of load reflection coefficient, and does not affect the amplitude of load reflection coefficient.

Owing to still taking the method for designing based on quality factor q, therefore next step value need analyzing quality factor q is on the impact of matching network stability.From formula (13), although the value of Q does not affect the amplitude of reflection coefficient, theoretical according to reflection of electromagnetic wave, from power delivery angle, the phase angle of reflection coefficient is also wished can be little as much as possible.Phase angle is made to be:

$\mathrm{\θ}=\arg \left(\frac{A+\mathrm{jB}}{A-\mathrm{jB}}\right)---\left(14\right)$

Relation between θ and Q as shown in Figure 4.From the curve Fig. 4, Q value obtains larger, and phase angle theta is larger, and vice versa.Therefore, from the angle of matching network to the stability of transducer impedance variation, wish that Q value obtains the smaller the better.And known according to the formula (6) in existing method for designing, Q value is directly proportional to harmonics restraint, and namely Q value is larger, and the harmonic inhibition capability of matching network is stronger.Therefore from the angle of harmonics restraint performance, but wish that Q value obtains and be the bigger the better.

Analyze known according to above, the quality factor simultaneously meeting the requirement of the stability indicator of impedance matching during requirement and the impedance variation of harmonics restraint performance index necessarily meet the compromise value that this two indices requires simultaneously.Therefore, adopt the mode of circulation checking, this circulation, until obtain a Q value, makes matching network till harmonics restraint performance and stability obtain the compromise value of a satisfaction between the two.

Fig. 5 is the flow chart of the design method of impedance matching according to the embodiment of the present invention.With reference to Fig. 5, the method comprises the following steps:

Step S501, determine the anti-or line characteristic impedance R of singal source resistance _s, transducer impedance Z _lwith the maximum variable quantity Z of transducer impedance _d, wherein, the maximum variable quantity Z of transducer impedance _dby changing temperature environment residing for transducer and acoustics load ring border (being immersed in the liquid of not acoustic impedance) and utilizing electric impedance analyzer to test transducer and obtain, this step belongs to known technology, therefore, omits it and describes in detail; In addition point out, for a lot of application in other field, the variable quantity of load impedance is generally known;

Step S502, selection initial quality factor Q, such as, when k>=1, choose initial Q according to Q>=1/2sqrt (k-1), when k≤1, according to Q>=1/2sqrt (1/k-1)) choose initial Q, wherein k=R _s/ R ₁;

Step S503, the requirement of the stability indicator of impedance matching when judging whether current quality factor meet requirement and the impedance variation of harmonics restraint performance index simultaneously, if met simultaneously, then perform step S507, otherwise perform step S504;

Step S504, judgement are that harmonics restraint performance does not meet the demands or stability indicator does not meet the demands, if harmonics restraint performance does not meet the demands, then perform step S505, if stability indicator does not meet the demands, then perform step S506;

Step S505, increase current quality factor q, and jump to step S503;

Step S506, reduce current quality factor q, and jump to step S503;

Step S507, current quality factor q is defined as final suitable quality factor q;

Step S508, determine the value of the passive device in impedance matching network according to the final quality factor determined.

Here point out, harmonics restraint performance requirement is different for each system (or application scenario), but general for single-frequency matching network, owing to being single-frequency point work, therefore can wish that harmonics restraint is the bigger the better.But excessive harmonics restraint can cause bad stability, therefore harmonics restraint performance index require is that designer oneself is fixed, but general applied field credit union require 2 times, 3 subharmonic suppress at more than 30dB (calculating by formula 6), perhaps, certain each system (or application scenario) has particular/special requirement, as the suppression etc. of nth harmonic.

In addition, as mentioned above, the choosing value of Q can only have influence on the phase angle of reflection coefficient, so stability indicator General Requirements phase angle is here within the scope of 0 to ± pi/2.And when load impedance variable quantity is excessive, the single-frequency impedance matching network related in the present invention is helpless, more complicated dynamic matching network is only taked (to be generally electric-mechanic control system formula, the i.e. parameter dynamic adjustment of the device such as inductance, electric capacity), and judge that the criterion that can single-frequency impedance matching network be suitable for is generally by formula (13), require that the mould of reflection coefficient is no more than 0.5.

Owing to have employed the mode of circulation checking, design cycle of the present invention can be applied to programming very easily, thus realizes the computer automation design of impedance matching.

Below, by with a concrete example, method for designing of the present invention is specifically described.

In this example, the electrical impedance (testing in room temperature, de aerated water environment) of piezoelectric ceramic ultrasonic transducer is Z _l=20+j12, resonance frequency is 8.42MHz.By changing temperature and acoustics load ring border, record the maximum variable quantity Z of electrical impedance of piezoelectric ceramic ultrasonic transducer _dfor 6+j4.Line characteristic impedance R _sbe 50 ohm of (k=R _s/ R _l=2.5).

Adopt the design cycle that the present invention proposes, carry out designing impedance matching to piezoelectric ceramic ultrasonic transducer, design procedure is as follows:

Step a, according to general requirement, system requirements 2 subharmonic suppresses to be not less than 30dB, then can show that Q should be more than or equal to 5.8 by formula (6), get initial value Q=6 here;

Step b, according to formula (13) and (14), during Q=6, phase angle change is about 4/5 π, is about 3 to ensure that phase angle change amount should be reduced in the value of about 1/2 π, Q;

Step c, reduction Q, get Q=3, calculate harmonics restraint according to formula (6), show that 2 subharmonic suppress to be about 25dB;

Steps d, be preferably principle with stability, after reducing harmonics restraint performance, getting Q=3 is final result.

From flow process above, in this example, if do not introduce the formula (13) and (14) that propose in the present invention, and only according to existing method for designing, the value of Q will be taken as more than 6, and the stability of the matching network designed like this when transducer impedance changes is by poor.And according to after step b above, low reactance-resistance ratio falls, between harmonics restraint and stability, obtain compromise, although slightly reduce harmonics restraint performance, ensure that the stability of system.Therefore the present invention can consider the impedance variation of piezoelectric ceramic ultrasonic transducer, adds the constraints of stability in design cycle, thus ensure that the matching network designed is unlikely to lose efficacy because of transducer impedance change.

For the T-shaped matching network being applied to piezoelectric ceramic ultrasonic transducer, the inventive method is illustrated above, and for Pi type matching network, because itself and T-shaped matching network are dual circuits, so for the present invention's application, difference is only that the resistance in Pi type matching network is different with the computing formula of inductance, the present invention can be applied to Pi type matching network substantially similarly, therefore, omits it and describes in detail.

Here point out, after piezoelectric ceramic ultrasonic transducer, the inventive method also similarly can be applicable to the Pi type of any source and impedance and the single-frequency impedance matching of T-shaped network, is especially applicable to load impedance and there is the situation that the change of certain limit or load impedance itself exist test error.

In addition, as mentioned above, except impedance matching when reflection coefficient is changed as transducer impedance stability consider except index, also can apply other factor affecting impedance matching stability as stability indicator, such as power transit line standing-wave ratio.Now, according to the requirement of practical application to power transit line standing-wave ratio, design cycle shown in similar application Fig. 5, can be met the quality factor of the requirement of harmonics restraint performance index and transmission line standing-wave ratio index request simultaneously.Certainly, also can adopt multiple stability indicator, design cycle shown in similar application Fig. 5, between harmonics restraint performance index require and this multiple stability indicator requires, get a quality factor for compromise.Such as, reflection coefficient and power transit line standing-wave ratio are designed as two stability indicators simultaneously.

Below with reference to drawings and Examples to invention has been detailed description; but; should be appreciated that, the present invention is not limited to above disclosed specific embodiment, and the amendment that any those skilled in the art easily expects on this basis and modification all should be included in protection scope of the present invention.

Claims (4)

1. an impedance matching network, is connected between the positive pole of signal source and the tie point of the tie point of load one end and the negative pole of signal source and the load other end, comprising the passive device for realizing impedance matching, it is characterized in that,

The requirement of the stability indicator of impedance matching when the value of described passive device makes the quality factor of described impedance matching network meet requirement and the impedance variation of harmonics restraint performance index simultaneously;

Wherein, the value of described passive device is determined according to following steps:

Determine that singal source resistance resists or the maximum variable quantity of line characteristic impedance, load impedance and load impedance;

Select initial quality factor, and repeat following steps, until obtain suitable quality factor:

The requirement of the stability indicator of impedance matching when judging whether current quality factor meet requirement and the impedance variation of harmonics restraint performance index simultaneously, if meet the requirement of the stability indicator of impedance matching during requirement and the impedance variation of harmonics restraint performance index simultaneously, then current quality factor are defined as final quality factor, otherwise perform following steps:

If harmonics restraint performance index do not meet the demands, then increase quality factor;

If stability indicator does not meet the demands, then reduce quality factor;

The value of the passive device in impedance matching network is determined according to the final quality factor determined;

Wherein, the stability indicator of impedance matching during described impedance variation is the phase angle of load reflection coefficient;

The compromise value of the requirement of the stability indicator of impedance matching when the quality factor of the requirement of the stability indicator of described impedance matching when simultaneously meeting requirement and the impedance variation of harmonics restraint performance index are requirement and the impedance variation simultaneously meeting harmonics restraint performance index.

2. impedance matching network according to claim 1, is characterized in that, described impedance matching network is T-shaped matching network or Pi type matching network.

3. a method for designing for impedance matching network, comprising:

Determine that singal source resistance resists or line characteristic impedance, load impedance and maximum variable quantity thereof;

Select initial quality factor, and repeat following steps, until obtain suitable quality factor:

The requirement of the stability indicator of impedance matching when judging whether current quality factor meet requirement and the impedance variation of harmonics restraint performance index simultaneously, if meet the requirement of the stability indicator of impedance matching during requirement and the impedance variation of harmonics restraint performance index simultaneously, then current quality factor are defined as final quality factor, otherwise perform following steps:

If harmonics restraint performance index do not meet the demands, then increase quality factor;

If stability indicator does not meet the demands, then reduce quality factor;

The value of the passive device in impedance matching network is determined according to the final quality factor determined;

Wherein, the stability indicator of impedance matching during described impedance variation is the phase angle of load reflection coefficient;

The compromise value of the requirement of the stability indicator of impedance matching when the quality factor of the requirement of the stability indicator of described impedance matching when simultaneously meeting requirement and the impedance variation of harmonics restraint performance index are requirement and the impedance variation simultaneously meeting harmonics restraint performance index.

4. method according to claim 3, is characterized in that, described impedance matching network is T-shaped matching network or Pi type matching network.