CN104332693A - High-performance miniaturized narrowband band-stop filter design method - Google Patents

Abstract

The invention relates to a high-performance miniaturized narrowband band-stop filter design method. The design method comprises the following steps:1) calculating normalization susceptance slope parameter Xi/Y0 of each resonance unit; 2) using screw-type defect micro-strip structure units as equivalent resonance units and calculating 3dB bandwidth [delta]f3dBi required by each screw-type defect micro-strip structure unit; and 3) obtaining dimension and space between units of each screw-type defect micro-strip structure unit. The high-performance miniaturized narrowband band-stop filter design method is simple in design process and convenient in engineering application; the design method uses the screw-type defect micro-strip structure units as the equivalent resonance units, so that a realized narrowband band-stop filter only utilizes the space in a micro-strip conduction band without occupying other areas; and meanwhile, the method has the advantages of high stop band suppression degree and improved spurious response and the like.

Description

A kind of method for designing of high performance mini narrow-band band-elimination filter

Technical field

The invention belongs to radio frequency and technical field of micro communication, relate to a kind of high performance mini narrow-band band-elimination filter design method, the band stop filter utilizing the method to realize can be used for the narrow-band interference signal suppressing to exist in wireless communication system, is specially adapted to device size and the higher occasion of performance requirement.

Background technology

Band stop filter is as the significant components in wireless communication system, its effect is the interference component in filtering useful signal, when there is very strong interference signal in system or need high decay on certain Frequency point, adopt the effect of band stop filter will be better than band pass filter far away, can be used for the parasitic passband etc. that the spuious output of curb transmitter, nonlinear power amplifier or band pass filter produce.In general, the working frequency range of band stop filter is narrower, and be suitable for interference signal and useful signal at a distance of very near situation in frequency spectrum, thus the present invention is also for narrow-band band-elimination filter.

Traditional narrow-band band-elimination filter is mainly realized by 1/2 wavelength open circuit resonators in parallel or 1/4 wavelength short-circuit resonant device, this method is simple and easy to use, but exist in the design process of reality design parameter limited, in the frequency range of resonance frequency integral multiple, there is the problems such as spurious response, in addition, the stopband effect of single resonator is not generally clearly, often need just can reach required belt resistance inhibitor system by the multiple resonator of cascade, cause the increase of filter size.

Defected microstrip structure etches even or non-homogeneous slit on micro-band conduction band, there is significant stopband and Slow-wave effect, and than defect ground structure, there is less electromagnetic interference surface noise, but current developed defected microstrip structure size and Q value remain to be further improved, when being operated in radio frequency band, miniaturization issues seems especially outstanding, what is more important, and the design how utilizing defected microstrip structure to carry out narrow-band band-elimination filter is badly in need of solving.

Summary of the invention

In order to solve above-mentioned technical problem, the object of the present invention is to provide a kind of method for designing of high performance mini narrow-band band-elimination filter, the narrow-band band-elimination filter utilizing the method to design is specially adapted to device size and the higher occasion of performance requirement, be highly susceptible to other planar circuit integrated, and be easy to processing, cost is low.

In order to realize above-mentioned object, the present invention is achieved by the following technical programs:

A method for designing for high performance mini narrow-band band-elimination filter, the method comprises the following steps:

1) the normalized susceptance Slope Parameters X of each resonant element is calculated _i/ Y ₀

Assuming that the 3dB of the stopband left and right sides decays, frequency is respectively f ₁, f ₂, stopband center frequency f ₀can be expressed as with 3dB relative bandwidth FBW:

$f_0=\sqrt{f_1{f}_2},\mathrm{FBW}=\frac{f_2-f_1}{f_0}---\left(1\right)$

By network synthesis and the frequency translation of lowpass prototype filter, solve the Characteristic mobility Y obtaining converter between resonant element _uwith the normalized susceptance Slope Parameters X of each resonant element _i/ Y ₀,

${\left(\frac{Y_U}{Y_0}\right)}^2=\frac{1}{g_0{g}_{n+1}}$

(2)

$\frac{X_i}{Y_0}={\left(\frac{Y_U}{Y_0}\right)}^2\frac{g_0}{g_i\mathrm{FBW}}$

Wherein, i=1,2 ..., n, n are the exponent number of filter, g ₀..., g _n+1for the normalization component value of lowpass prototype filter, Y ₀it is the Characteristic mobility of input/output port;

2) use spiral type defected microstrip structure unit as the resonant element of equivalence, calculate the three dB bandwidth Δ f needed for each spiral type defected microstrip structure unit _3dBi

Spiral type defect sturcture unit is that the gap etching spiral type shape on micro-band conduction band forms, (i.e. (f under narrowband condition ₂-f ₁)/f ₀<<1), the three dB bandwidth Δ f needed for each spiral type defected microstrip structure unit _3dBiby normalized susceptance Slope Parameters X _i/ Y ₀calculate, be specially:

$\mathrm{\&Delta;}{f}_{3\mathrm{dBi}}=\frac{f_0}{2}{\left(\frac{X_i}{Y_0}\right)}^{-1}---\left(3\right)$

3) size and the unit interval of each spiral type defected microstrip structure unit is obtained

Each spiral type defected microstrip structure unit is all operated in center frequency point f ₀, in spiral type defected microstrip structure unit, the total length L s in gap is estimated by following formula:

$\mathrm{Ls}\&ap;\frac{c}{2f_0\sqrt{{\mathrm{\&epsiv;}}_{\mathrm{slot}}}}---\left(4\right)$

Wherein, c is the propagation velocity of electromagnetic wave at free space, ε _slotthe relative efficiency dielectric constant of gap at center frequency point f0 place.

As preferably, after estimating total length L s, the width of choice structure unit, relend the length that helps full-wave simulation instrument adjust structure unit until meet required Δ f3dBi, spacing between spiral-shaped structure unit is about λ g/4, λ g is the guide wavelength at center frequency point f0 place, and final size is obtained by the optimization of full-wave simulation instrument.

As preferably, the exponent number n of filter is less than 5 usually to ensure the miniaturization of device.

High performance mini narrow-band band-elimination filter design method of the present invention, design process is simple, engineer applied is convenient, this method for designing employs the resonant element of spiral type defected microstrip structure unit as equivalence, the narrow-band band-elimination filter realized only make use of the space on micro-band conduction band, do not need the area occupying other, there is the advantages such as belt resistance inhibitor system is high, spurious response improves simultaneously.

Accompanying drawing explanation

Fig. 1 is the second order bandstop filter general illustration utilizing the inventive method to realize, and 1 is microstrip line, and 2 is spiral type defected microstrip structure unit; 3 is ground plate.

Fig. 2 is the second order bandstop filter front schematic view utilizing the inventive method to realize.

Fig. 3 is the second order bandstop filter simulation result utilizing the inventive method to realize.

Fig. 4 is the three rank band stop filter front schematic view utilizing the inventive method to realize.

Fig. 5 is the three rank band stop filter simulation results utilizing the inventive method to realize.

Embodiment

Below in conjunction with accompanying drawing, high performance mini narrow-band band-elimination filter design method of the present invention is further described.

A kind of high performance mini narrow-band band-elimination filter design method of the present invention, as shown in Figure 1, what this embodiment realized is second order bandstop filter to an embodiment layout, and concrete steps are:

1) the normalized susceptance Slope Parameters X of each resonant element is calculated _i/ Y ₀

Assuming that the second order bandstop filter 3dB of design decays, frequency is respectively 3.4GHz and 3.7GHz, then stopband center frequency f ₀equal 3.55GHz, 3dB relative bandwidth FBW is 8.46%, and adopt second order Butterworth (Butterworth) lowpass prototype filter, normalized component value is: g ₀=g ₃=1, g ₁=g ₂=1.4142, calculate: Y _u=Y ₀, X ₁/ Y ₀=X ₂/ Y ₀=8.3583.

2) the three dB bandwidth Δ f needed for each spiral type defected microstrip structure unit 2 is calculated _3dBi

Because the normalization Slope Parameters of two resonant elements is equal, the three dB bandwidth needed for each spiral type defected microstrip structure unit 2 is also identical, can be calculated Δ f _3dB1=Δ f _3dB2=0.21GHz.

3) size and the unit interval of each spiral type defected microstrip structure unit 2 is obtained

The medium substrate relative dielectric constant selected is 2.55, the width of microstrip line is 4.5mm, the characteristic impedance of input/output port is 50 Ω, the gap total length utilizing formula (4) estimation to obtain is about 35.3mm, in order to the convenience designed, width and the spacing be connected between parallel slit in gap keep equal, relation between the width of spiral type defected microstrip structure unit 2 and three dB bandwidth can be calculated by full-wave simulation instrument, in this embodiment, two spiral type defected microstrip structure unit 2 measure-alike, the width in gap is 0.3mm, the width of spiral-shaped structure unit is 2.7mm, length is 6.7mm, unit interval after optimization is 14.5mm.

Fig. 2 gives the front schematic view of second order bandstop filter, Fig. 3 is the simulation result of this second order bandstop filter, as can be seen from the figure two 3dB decay frequencies lay respectively at 3.39GHz and 3.68GHz, the degree of suppression of stopband center position is greater than 30dB, meet the requirement of design objective, and there are two zero points (close to 2.5GHz and 4.0GHz place) in reflection coefficient curve, further improve the performance of filter.

A kind of high performance mini narrow-band band-elimination filter design method of the present invention, as shown in Figure 4, what this embodiment realized is three rank band stop filters to another embodiment layout, and concrete steps are:

1) the normalized susceptance Slope Parameters X of each resonant element is calculated _i/ Y ₀

Assuming that the second order bandstop filter 3dB of design decays, frequency is respectively 3.85GHz and 4.15GHz, then stopband center frequency f ₀equal 3.98GHz, 3dB relative bandwidth FBW is 7.51%, and adopt three rank Butterworth (Butterworth) lowpass prototype filters, normalized component value is: g ₀=g ₄=1, g ₁=g ₃=1.0, g ₂=2.0, calculate: Y _u=Y ₀, X ₁/ Y ₀=X ₃/ Y ₀=21.1627, X ₂/ Y ₀=13.7232.

2) the three dB bandwidth Δ f needed for each spiral type defected microstrip structure unit 2 is calculated _3dBi

Because the normalization Slope Parameters of the first resonant element and the 3rd resonant element is equal, the first spiral type defected microstrip structure unit 2 is also identical with the three dB bandwidth needed for triple helical type defected microstrip structure unit 2, can be calculated Δ f _3dB1=Δ f _3dB3=0.15GHz, the three dB bandwidth Δ f needed for the second spiral type defected microstrip structure unit 2 _3dB2=0.30GHz.

3) size and the unit interval of each spiral type defected microstrip structure unit 2 is obtained

The medium substrate relative dielectric constant selected is 2.55, the width of microstrip line is 4.5mm, the characteristic impedance of input/output port is 50 Ω, the gap total length utilizing formula (4) estimation to obtain is about 35.8mm, first spiral type defected microstrip structure unit 2 and triple helical type defected microstrip structure unit 2 measure-alike, the width in gap is 0.25mm, the width of unit is 2.25mm, length is 6mm, the width in the second spiral type defected microstrip structure unit 2 gap is 0.35mm, the width of this unit is 3.15mm, length is 5.4mm, obtaining unit interval after optimization is 12.5mm.

Fig. 5 is the simulation result of three rank band stop filters, as can be seen from the figure two 3dB decay frequencies lay respectively at 3.85GHz and 4.14GHz, the degree of suppression of stopband center position is greater than 50dB, meet the requirement of design objective, there is multiple zero point in reflection coefficient curve, lay respectively at 2.33GHz, 3.68GHz, 4.19GHz and 5.06GHz position.

Claims (3)

1. a method for designing for high performance mini narrow-band band-elimination filter, is characterized in that the method comprises the following steps:

1) the normalized susceptance Slope Parameters X of each resonant element is calculated _i/ Y ₀

Assuming that the 3dB of the stopband left and right sides decays, frequency is respectively f ₁, f ₂, stopband center frequency f ₀can be expressed as with 3dB relative bandwidth FBW:

$f_0=\sqrt{f_1{f}_2},\mathrm{FBW}=\frac{f_2-f_1}{f_0}---\left(1\right)$

By network synthesis and the frequency translation of lowpass prototype filter, solve the Characteristic mobility Y obtaining converter between resonant element _uwith the normalized susceptance Slope Parameters X of each resonant element _i/ Y ₀,

$\begin{array}{c}{\left(\frac{Y_U}{Y_0}\right)}^2=\frac{1}{g_0{g}_{n+1}}\\ \frac{X_i}{Y_0}={\left(\frac{Y_U}{Y_0}\right)}^2\frac{g_0}{g_i\mathrm{FBW}}\end{array}---\left(2\right)$

Wherein, i=1,2 ..., n, n are the exponent number of filter, g ₀..., g _n+1for the normalization component value of lowpass prototype filter, Y ₀it is the Characteristic mobility of input/output port;

2) use spiral type defected microstrip structure unit as the resonant element of equivalence, calculate the three dB bandwidth Δ f needed for each spiral type defected microstrip structure unit _3dBi

Spiral type defect sturcture unit is that the gap etching spiral type shape on micro-band conduction band forms, (i.e. (f under narrowband condition ₂-f ₁)/f ₀<<1), the three dB bandwidth Δ f needed for each spiral type defected microstrip structure unit _3dBiby normalized susceptance Slope Parameters X _i/ Y ₀calculate, be specially:

$\mathrm{\&Delta;}{f}_{3\mathrm{dBi}}=\frac{f_0}{2}{\left(\frac{X_i}{Y_0}\right)}^{-1}---\left(3\right)$

3) size and the unit interval of each spiral type defected microstrip structure unit is obtained

Each spiral type defected microstrip structure unit is all operated in center frequency point f ₀, in spiral type defected microstrip structure unit, the total length L s in gap is estimated by following formula:

$\mathrm{Ls}\&ap;\frac{c}{2f_0\sqrt{{\mathrm{\&epsiv;}}_{\mathrm{slot}}}}---\left(4\right)$

Wherein, c is the propagation velocity of electromagnetic wave at free space, ε _slotthat gap is at center frequency point f ₀the relative efficiency dielectric constant at place.

2. the method for designing of a kind of high performance mini narrow-band band-elimination filter according to claim 1, it is characterized in that: after estimating total length L s, the width of choice structure unit, relend the length that helps full-wave simulation instrument adjust structure unit until meet required Δ f3dBi, spacing between spiral-shaped structure unit is about λ g/4, λ g is the guide wavelength at center frequency point f0 place, and final size is obtained by the optimization of full-wave simulation instrument.

3. the method for designing of a kind of high performance mini narrow-band band-elimination filter according to claim 1, is characterized in that: the exponent number n of filter is less than 5 usually to ensure the miniaturization of device.