CN102569956A - Electrically tunable filter of varactor - Google Patents

Abstract

The invention discloses an electrically tunable filter of a varactor, comprising an input micro-strip line, a first micro-strip resonator, a second micro-strip resonator and an output micro-strip line, wherein the first micro-strip resonator and the second micro-strip resonator open outwards and are arranged side by side in a mirror image manner, the adjacent parts of the first micro-strip resonator and the second micro-strip resonator form direct coupling; the input micro-strip line and the output micro-strip line are respectively arranged below the first micro-strip resonator and the second micro-strip resonator and are arranged side by side in a mirror image manner, the tail ends of the input micro-strip line and the output micro-strip line both deflect for 90 degrees along the direction away from the first micro-strip resonator and the second micro-strip resonator and two deflected parts are mutually parallel to form cross coupling and the symbol of the cross coupling is opposite to the symbol of the direct coupling. The transfer function of the electrically tunable filter of the varactor generates a transmission zero point and has the like elliptic function feature, and therefore the filter has good rectangle coefficient, and the filtering performance is improved.

Description

A kind of varactor electricity tunable filter

Technical field

The present invention relates to electron trade signal processing technology field, but relate in particular to a kind of varactor electricity tone category filter.

Background technology

The electricity tunable filter is used for the occasion of frequency change, particularly in the radar detection field, is used for signal is carried out filtering, thereby obtains purer frequency spectrum, improves the antijamming capability of system.The electricity tunable filter is divided into electric tunable filter of yttrium iron garnet (Yttrium Iron Garnet, be called for short YIG) and two types of the electric tunable filters of varactor usually.YIG electricity tunable filter has very high quality factor, but owing to receive the influence of hysteresis effect, its tuned speed is slow, can not be applicable to the frequency agility occasion.Varactor electrically tunable filter tuned speed is fast, can satisfy the needs of frequency agility, selects for use the varactor of high quality factor can obtain higher quality factor.

Because the difficulty brought in coupling and design, the varactor electrically tunable filter all is the comb filter structure usually, and this structure can't type of realization elliptic function filter characteristic, can't suppress nearby pass lower.And type elliptic function filter be owing to can produce transmission zero near passband, thereby its filtering performance is greatly improved, but its coupled mode to filter has specific requirement.

In realizing process of the present invention; The applicant recognizes that there is following technological deficiency in prior art: existing varactor electrically tunable filter adopts Butterworth comprehensive or Chebyshev is comprehensive usually; These Filter Design scheme squareness factors are bad, specifically, do not have precipitous edge; Thereby be bad, thereby suppress demanding occasion at sideband and can not satisfy the demands the filter effect of sideband.

Summary of the invention

The technical problem that (one) will solve

For solving the above problems, the invention provides a kind of varactor electricity tunable filter, the micro-strip resonantor design class elliptic function filter that utilizes two joint varactors to load, sideband has formed a pair of transmission zero, reaches good sideband and suppresses effect; Be applied to the bias voltage on the varactor through adjusting simultaneously, the centre frequency that makes this varactor electrically tunable filter is along with applied voltage changes, to satisfy the needs of frequency agility.

(2) technical scheme

According to an aspect of the present invention, a kind of varactor electricity tunable filter is provided.This varactor electricity tunable filter comprises: input microstrip line, first micro-strip resonantor, second micro-strip resonantor and output microstrip line; Wherein, first micro-strip resonantor and the second micro-strip resonantor opening are outside, mirror image setting side by side, and both form direct coupling in position adjacent to one another; Input microstrip line and output microstrip line lay respectively at the below of first micro-strip resonantor and second micro-strip resonantor; Mirror image setting side by side; Both is terminal all along direction deviation 90 degree away from first micro-strip resonantor and second micro-strip resonantor; Form cross-couplings, this cross-couplings and this direct-coupled opposite in sign.

(3) beneficial effect

Can find out that from technique scheme varactor electricity tunable filter of the present invention has following beneficial effect:

(1) first micro-strip resonantor and second micro-strip resonantor position adjacent to one another form direct coupling; The input microstrip line forms cross-couplings with the end of output microstrip line; Directly coupling and this cross-couplings opposite in sign make the transfer function of filter produce transmission zero, type of having elliptic function characteristic; Thereby make filter have good squareness factor, improved filtering performance;

(2) owing to adopted the varactor electricity to transfer structure, change the centre frequency of filtering through the VT that changes on the varactor, and keep the shape invariance of filter curve, the centre frequency of filter has very fast tuned speed, satisfies the demand of frequency agility;

(3) owing to adopted input microstrip line and output microstrip line; Utilize this input microstrip line and the cross-couplings of output microstrip line for filter; Make varactor electricity tunable filter of the present invention still less, and traditional class elliptic function filter needs at least one pair of resonator to construct cross-couplings than traditional needed resonator number of class elliptic function filter.

Description of drawings

Fig. 1 is the structural representation of embodiment of the invention varactor electricity tunable filter;

Fig. 2 is the structural representation of resonator in the embodiment of the invention varactor electricity tunable filter;

Fig. 3 is the emulation of embodiment of the invention varactor electricity tunable filter and the response curve under the actual measurement.

Embodiment

For making the object of the invention, technical scheme and advantage clearer, below in conjunction with specific embodiment, and with reference to accompanying drawing, to further explain of the present invention.Though this paper can provide the demonstration of the parameter that comprises particular value, should be appreciated that parameter need not definitely to equal corresponding value, but can in acceptable error margin or design constraint, be similar to corresponding value.

In Theory of Electromagnetic Field, electromagnetic wave with the form transmission of sine wave, can demonstrate voltage wave peak dot and nodal point at ad-hoc location on transmission line, and at the voltage wave peak dot, voltage reaches maximum, and this moment, electric current was 0, showed as the form of electric field; At the voltage wave node, voltage reaches minimum value, and electric current reaches maximum, shows as the form in magnetic field.The coupling that relies on electric field to carry out electromagnetic energy is called electric coupling, and the coupling that relies on magnetic field to carry out is called the magnetic coupling, when being coupled by electric field and magnetic field acting in conjunction, is called hybrid coupled.

For any one transmission line structure, because its open end electric current can't pass through, this moment, electric current was 0, and electromagnetic wave always demonstrates the voltage wave peak dot, shows as the electric field form, the electromagnetic energy that carries out herein be coupled as electric coupling.At the earth point of transmission line, voltage reaches minimum value, and can think does not have voltage difference between itself and the ground, and this moment, electromagnetic electric current reached maximum, showed as the form in magnetic field, and that carries out herein is coupled as the magnetic coupling.To a half-wave open-loop resonator, its two ends open circuit, electromagnetic wave reaches voltage max at the resonator two ends, shows as electric field, can only carry out electric coupling; In the centre of open-loop resonator, because electromagnetic periodic law can only be the voltage wave node, show as magnetic field, can only carry out the magnetic coupling here; In other position then is hybrid coupled.

Fig. 1 is the structural representation of varactor electricity tunable filter of the present invention.In Fig. 1, for clarity sake, do not provide the bias circuit of varactor, this bias circuit will be elaborated in Fig. 2.As shown in Figure 1, this filter includes input microstrip line, first micro-strip resonantor, second micro-strip resonantor and output microstrip line.Wherein, first micro-strip resonantor and the second micro-strip resonantor opening are outside, mirror image setting side by side, and both form direct coupling in position adjacent to one another, the coupling between the promptly adjacent sequence number transmission unit; Input microstrip line and output microstrip line lay respectively at the below of first micro-strip resonantor and second micro-strip resonantor; Mirror image setting side by side, both is terminal all along direction deviation 90 degree away from first micro-strip resonantor and second micro-strip resonantor, forms cross-couplings; It is the coupling between the non-adjacent sequence number transmission unit; Should directly be coupled and this cross-couplings opposite in sign, i.e. magnetic coupling is just got, and electric coupling is got negative.Model, the specification of first micro-strip resonantor and second micro-strip resonantor are identical.

According to the approximate collective model of Levy, want to make the transfer function of cross-couplings filter to obtain transmission zero, the direct coupling and the cross-couplings that constitute between the cross-linked transmission unit must have opposite symbol.For present embodiment, constitute a cross-couplings transmission unit by input microstrip line, first micro-strip resonantor, second micro-strip resonantor and output microstrip line and constitute cross-linked transmission unit.Coupling between first micro-strip resonantor, second micro-strip resonantor constitutes directly coupling.

Adopted the magnetic CGCM between first micro-strip resonantor shown in Figure 1 and second micro-strip resonantor, thereby the input microstrip line must adopt the electric coupling pattern with the output microstrip line.In addition, if first micro-strip resonantor and second micro-strip resonantor have adopted the electric coupling pattern, then import between microstrip line and the output microstrip line and should adopt the magnetic CGCM.

In the present embodiment, parallel first micro-strip resonantor that is coupled to of input microstrip line is the hybrid coupled pattern between the two, i.e. electric coupling and magnetic coupling acting in conjunction.Be the magnetic CGCM between first micro-strip resonantor and second micro-strip resonantor.Parallel second micro-strip resonantor that is coupled to of output microstrip line is the hybrid coupled pattern between the two.Be the magnetic CGCM between first micro-strip resonantor and second micro-strip resonantor.Thereby the transfer function of whole varactor tunable filter produces a pair of transmission zero at the passband edge, has improved the signal suppressing ability to neighboring trace.

Below respectively each part of varactor electricity tunable filter is elaborated.

1, resonator.Resonator is the elementary cell of filter, and filter of the present invention has adopted the half-wave resonator structure, is made up of micro-band resonance line and varactor.The positive pole of varactor is received an end of micro-band resonance line open circuit, receives the other end of micro-band resonance line open circuit behind the negative pole series connection partiting dc capacitor, and VT Vt is added to the varactor negative pole through bias resistance R1; Be used for regulating the centre frequency of filter, the micro-band resonance line is through bias resistance R2 ground connection, the i.e. ground connection in the centre position of resonator; It is the signal voltage nodal point here; The parasitic parameter of introducing is minimum, forms the bias voltage path of varactor, resonator structure promptly as shown in Figure 2.

A, micro-band resonance line

The micro-band resonance line adopts 50 ohm characteristic impedance transmission lines, calculates the length d of micro-band resonance line according to formula 1.

Varactor is loaded half-wave resonator, and the length gauge formula of micro-band resonance line is:

$d=\frac{2}{\mathrm{\β}}\mathrm{arctg}\left(\frac{1}{\mathrm{\π}{f}_0{Z}_{0}C}\right)---\left(1\right)$

F wherein ₀Be the centre frequency of filter, Z ₀Be line characteristic impedance, C is the middle capacitance value of varactor, and β is the Propagation of guided waves constant, and it is by the dielectric constant and the thickness decision of transmission medium.

B, varactor

For reducing to insert loss, select high Q varactor for use as far as possible, the capacitance size is got little under the situation that satisfies frequency transfer scope as far as possible, and promptly the Q value and the capacitance of varactor are inversely proportional to, and preferably adopting model is the varactor of SMV1233.Under the situation of given microstrip line length, suppose that the centre frequency transfer area requirement of filter is f ₁～f ₂, the capacitance variation scope that then requires varactor is C ₁～C ₂The electric capacity of varactor is transferred the scope demand and is calculated by formula 2:

$\left.\begin{array}{c}{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="HDA0000139069840000011.png"\; state="\{\{state\}\}">C</figure-callout>}}_1=\frac{1}{\mathrm{\&pi;}{f}_1{Z}_0\mathrm{tg}(\mathrm{\&beta;d}/2)}\\ {\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="HDA0000139069840000011.png"\; state="\{\{state\}\}">C</figure-callout>}}_2=\frac{1}{\mathrm{\&pi;}{f}_2{Z}_0\mathrm{tg}(\mathrm{\&beta;d}/2)}\end{array}\right\}---\left(2\right)$

Wherein, β is the Propagation of guided waves constant, and d is the length of micro-band resonance line, f ₁, f ₂Be respectively the top/bottom latitude of the centre frequency transfer of filter, Z ₀Be line characteristic impedance.

2, input microstrip line and output microstrip line

Input, output microstrip line adopt 50 ohm characteristic impedance microstrip transmission lines, with thinking that filter provides the pair of cross coupling, forms a pair of transmission zero.The electric coupling that is utilized in the terminal structure of the open circuit pair of parallel of input, output microstrip line among Fig. 1 forms cross-couplings-electric coupling.The length of input microstrip line and output microstrip line, shape changes with coupling coefficient.

Coupling coefficient M between input, the output microstrip line _IoBig I calculate according to formula 3.Its coupling size has determined the distance of the position of transmission zero apart from passband.If this coupling is excessive, then transmission zero is very near apart from passband, and the band outside inhibitory can will descend to some extent; If this coupling is too small, then transmission zero is far away excessively apart from getting around regulations band, and the squareness factor of filtering is with variation.

$M_{\mathrm{io}}=-k*\frac{f_0}{f_2-f_1}*\frac{M_{12}}{Q_e}---\left(3\right)$

M wherein ₁₂Be the size of the coupling coefficient between first resonator and second resonator, Q _eBe outside loaded quality factor (annexation between its expression input-output line resonator), f ₀Be centre frequency, f ₁And f ₂Be respectively the frequency of two transmission zeros that desire establishes, k is a coupling factor, and comprehensively going out the k value is 1.597, and it also can go other values by length and spacing decision of input and output microstrip line, changes position that k value will make transmission zero and produces and squint.

Distributed constant Filter Design formula is commonly referred to aggregative formula, does not have rigorous mathematic(al) representation, and various collective model is arranged, and can carry out the Design of Filter of ad hoc structure according to collective model, and various models are not general.For the filter of labyrinth, do not have ready-made collective model to use, but can adopt the method that extracts coupling coefficient and external sort factor to design, it has universality, a filter according to experience optimization earlier that is:; And then the filter that optimization is accomplished extracts its coupling coefficient and external sort factor; Designer afterwards just can design according to it.For the varactor electricity tunable filter of present embodiment, the process of its design is roughly following:

One, design parameter: centre frequency transfer scope is 1.4GHz～1.85GHz, and relative bandwidth FBW is 0.04.The relevant parameter that covers the little band plate of copper that adopts is: dielectric constant: 3.2, and dielectric thickness: 1mm;

Two, by above-mentioned design parameter and peripheral parameter; If the length d that the loading capacitance of resonator is 1.2pF obtains the micro-band resonance line is 32mm; Calculate the capacitance variations scope by formula 3 and be at least 1pF to 1.5pF; The capacitance of considering gained is to be connected with the 3pF partiting dc capacitor by varactor in the present embodiment; The appearance value excursion of corresponding varactor should be at least the result according to aforementioned calculation of 1.5pF to 3pF varactor, and (its corresponding capacitance is 1.1pF6V, 3pF1V) can to select the varactor of model SMV1233 for use;

Three, the parameters such as bending length of the spacing of adjustment first resonator and second resonator, input microstrip line and output microstrip line obtain best filter curve; Then this filter of adjusting is extracted its coupling coefficient and external sort factor, the filter of later same type can normalize to the centre frequency that needs according to good coupling coefficient of this optimization and external sort factor and design.The coupling coefficient of this filter and external sort factor are respectively:

$\left.\begin{array}{c}{M}_{12}=0.078\\ M_{\mathrm{io}}=-0.0044\\ Q_e=14.89\end{array}\right\}---\left(4\right)$

And the concrete structural parameters of this filter are (dielectric constant of medium is 3.3, dielectric thickness 1mm): the coupling length of input and output microstrip line is 3mm, and spacing is 1mm; Coupling length between first resonator and second resonator is 5mm, spacing 0.7mm, and the spacing 12mm of the input and output microstrip line and first resonator and second resonator, spacing 0.2mm, the total length of little band section is 32mm in the resonator.

Fig. 3 is S parameter S 21 response curves of this filter, and wherein solid line is an actual measurement profile, and dotted line is a simulation curve, and simulation curve and actual measurement profile are coincide good.When the applied voltage of varactor was regulated by 1V～5V, the centre frequency of filter moved on to 1.85GHZ by 1.4GHz, and S21 has remained a pair of transmission zero simultaneously.

Receive the influence of varactor Q value; The varactor electrically tunable filter is bigger in the insertion loss of frequency end, and when its reason was that biased electrical is forced down, the Q value of varactor was less relatively; Less in the high-end insertion loss of frequency; Can after filtering, amplify compensation in the practical application, or only get the high-end adjustable frequency of frequency, and in the present embodiment centre frequency when 1.6GHz～1.85GHz, to insert loss less; The varactor of the length of resonator microstrip line and use can be according to formula to make corresponding change, as long as can satisfy the frequency transfer scope of filter in the present embodiment.After particularly adopting the varactor of higher Q value, like MA4ST250, the insertion loss of its low frequency end can obtain improvement to a certain degree.

Above-described specific embodiment; The object of the invention, technical scheme and beneficial effect have been carried out further explain, and institute it should be understood that the above is merely specific embodiment of the present invention; Be not limited to the present invention; All within spirit of the present invention and principle, any modification of being made, be equal to replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (10)

1. a varactor electricity tunable filter comprises: input microstrip line, first micro-strip resonantor, second micro-strip resonantor and output microstrip line; Wherein,

First micro-strip resonantor and the second micro-strip resonantor opening are outside, mirror image setting side by side, and both form direct coupling in position adjacent to one another;

Input microstrip line and output microstrip line lay respectively at the below of first micro-strip resonantor and second micro-strip resonantor; Mirror image setting side by side; Both is terminal all along direction deviation 90 degree away from first micro-strip resonantor and second micro-strip resonantor; Two deviations partly are parallel to each other, and form cross-couplings, this cross-couplings and this direct-coupled opposite in sign.

2. varactor electricity tunable filter according to claim 1, wherein, the said magnetic that directly is coupled as is coupled, and said cross-couplings is electric coupling.

3. varactor electricity tunable filter according to claim 2, wherein, the said input microstrip line and first micro-strip resonantor form hybrid coupled; The output microstrip line and second micro-strip resonantor form hybrid coupled.

4. varactor electricity tunable filter according to claim 2, wherein, said first micro-strip resonantor and second micro-strip resonantor are half-wave resonator, and this half-wave resonator comprises:

The micro-band resonance line, it is through the second bias resistance ground connection; And

Varactor, its positive pole are connected to an end of micro-band resonance line open circuit, receive the other end of micro-band resonance line open circuit behind its negative pole series connection partiting dc capacitor, and VT is added to the varactor negative pole through first bias resistance.

5. varactor electricity tunable filter according to claim 4, wherein, the micro-band resonance line is 50 ohm characteristic impedance transmission lines, and its length is d, and wherein d satisfies:

$d=\frac{2}{\mathrm{\&beta;}}\mathrm{arctg}\left(\frac{1}{\mathrm{\&pi;}{f}_0{Z}_{0}C}\right)$

Wherein, f ₀Be the centre frequency of filter, Z ₀Be line characteristic impedance, C is the middle capacitance value of varactor, and β is the Propagation of guided waves constant.

6. varactor electricity tunable filter according to claim 5, wherein, the capacitance variation scope of varactor is at least C ₁～C ₂, C wherein ₁, C ₂Satisfy:

$\left.\begin{array}{c}{C}_1=\frac{1}{\mathrm{\&pi;}{f}_1{Z}_0\mathrm{tg}(\mathrm{\&beta;d}/2)}\\ C_2=\frac{1}{\mathrm{\&pi;}{f}_2{Z}_0\mathrm{tg}(\mathrm{\&beta;d}/2)}\end{array}\right\}.$

7. varactor electricity tunable filter according to claim 6, wherein, coupling coefficient is M between input, the output microstrip line _Io, the coupling coefficient between first resonator and second resonator is M ₁₂, M then _IoAnd M ₁₂Satisfy:

$M_{\mathrm{io}}=-k*\frac{f_0}{f_2-f_1}*\frac{M_{12}}{Q_e}$

Wherein, Q _eBe the outside loaded quality factor of the annexation between the expression input-output line resonator, f ₀Be centre frequency, f ₁And f ₂Be respectively the frequency of two transmission zeros that desire establishes, k=1.597 is a coupling factor.

8. varactor electricity tunable filter according to claim 7, its centre frequency transfer scope is 1.4GHz～1.85GHz, relative bandwidth is 0.04;

Coupling coefficient M _Io, coupling coefficient M ₁₂Satisfy with the external sort factor:

$\left.\begin{array}{c}{M}_{12}=0.078\\ M_{\mathrm{io}}=-0.0044\\ Q_e=14.89\end{array}\right\}.$

9. varactor electricity tunable filter according to claim 7, its centre frequency transfer scope is 1.4GHz～1.85GHz, relative bandwidth is 0.04;

The dielectric constant of used little band plate medium is 3.2, and thickness is 1mm;

The capacitance variations scope of the middle capacitance value C of varactor is C1～C2:C ₁=1.1pF, C ₂=3pF;

The coupling length of input and output microstrip line is 3mm, and spacing is 1mm;

Coupling length between first resonator and second resonator is 5mm, spacing 0.7mm;

The spacing 12mm of the input and output microstrip line and first resonator and second resonator, spacing 0.2mm, the total length of micro-band resonance line is 32mm in first resonator and second resonator.

10. according to each described varactor electricity tunable filter in the claim 1 to 9, its type of being elliptic function filter.

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