CN106785298A - A kind of microstrip filter method for designing - Google Patents

Abstract

The present invention provides a kind of method for designing of microstrip filter.It is characterized in that following key step：The first step, sets up the lumped parameter equivalent network of microstrip filter, derives the equivalent relation formula between the electric parameter and the element of lumped parameter equivalent network of microstrip filter.Second step, according to the technical indicator of microstrip filter, each component value of lumped parameter equivalent network is determined using lumped wave filter method for designing；3rd step, according to equivalent relation formula, each electric parameter of microstrip filter is calculated by each component value of lumped parameter equivalent network, and then determine corresponding values of the structural parameters；4th step, is modeled using the values of the structural parameters of the microstrip filter being calculated, and carries out Electromagnetic Simulation optimization, the performance of line filter is finally met the requirement of technical indicator.The method for designing that the present invention is provided can disclose the physical mechanism of microstrip filter, shorten its lead time.

Description

A kind of microstrip filter method for designing

Technical field

The invention belongs to communication technical field, and in particular to a kind of method for designing of microstrip filter.

Background technology

Wave filter is one of Primary Component in radar, communication and measuring system, and its function is to allow that certain part frequency The signal of rate smoothly passes through, and allows the signal of another part frequency to be suppressed by larger, and its performance is for whole system Performance has important influence.The technical indicator of wave filter includes pass band width, insertion loss, passband fluctuation, return loss, resistance With degree of suppression, with interior phase linearity and group delay etc..Divided according to the type of frequency response, oval filtering can be divided into Device, Butterworth filter, Gaussian filter, general Chebyshev filters and inverse general Chebyshev filters etc..For For analog filter, it is divided into lumped parameter analog filter and distributed constant analog filter.In RF/Microwave/optical frequency etc. In higher frequency band, various transmission knots such as microstrip line, strip line, the line of rabbet joint, fin line, co-planar waveguide, coaxial line, waveguide are mainly used Structure.These transmission lines have distributed constant effect, and its electrical characteristic is closely related with physical dimension.In these frequency ranges, generally Use the line filters such as waveguide filter, coaxial line filter, strip line filter and microstripline filter.

The content of the invention

Up to the present, people have worked out diversified line filter structure.However, line filter With distributed constant effect, its design is much more complex more than the design of lumped wave filter.Each line filter There may be different physical mechanisms, it is necessary to specifically be analyzed.Only understand the physical mechanism of line filter in depth, Be possible to the more preferable frequency response that must be used them to required for realizing.Invention describes a kind of design of microstrip filter Method.The structure of microstrip line is as shown in figure 1, mainly include three layers.Tier I is metal overlying strata, and tier ii is dielectric substrate, the III layers is coating under metal.The microstrip filter structure that the present invention is studied is as shown in Figure 2.The etching in metal overlying strata (I) Following metal pattern：Incoming feeder (1), the first parallel coupled line section (2), transmission line section (3), the second parallel coupled line section (4) With output feeder (5).It is characterized in that：The right-hand member of incoming feeder (1) is connected to the left end of the first parallel coupled line section (2), the The right-hand member of one parallel coupled line section (2) is connected to the left end of transmission line section (3), and it is flat that the right-hand member of transmission line section (3) is connected to second The left end of row coupling line section (4), the right-hand member of the second parallel coupled line section (4) is connected to the left end of output feeder (5).Wave filter knot Structure is symmetrical on central plane.If the characteristic impedance of incoming feeder (1) and output feeder (5) is all R_S.First parallel coupling The even mode impedance of line section (2) and the second parallel coupled line section (4) is all Z_1e, odd mode impedance is all Z_1o, electrical length is all θ₁.Transmission The characteristic impedance of line section (3) is Z₂, electrical length is θ₂。

In actual use, it is necessary to the technical indicator be given according to user designs this wave filter.In other words, as How each structural parameters of wave filter must quick and precisely be determined.The thing of this wave filter can be described by means of transmission line theory Reason mechanism, for example, can derive its corresponding collision matrix, admittance matrix, impedance matrix or concatenation matrix.But these squares Generally all include some special functions such as trigonometric function in battle array, make wave filter that there is distributed constant effect, so as to allow design to become Obtain extremely difficult.The present invention proposes a kind of new design method for this wave filter.The first of method for designing of the present invention Step, sets up the lumped parameter equivalent network of microstrip filter, derives the electric parameter and lumped parameter equivalent network of microstrip filter Equivalent relation formula between the element of network.Microstrip filter shown in Fig. 2 can be regarded as several basic transmission line structures It is formed by connecting.As long as deriving the lumped parameter equivalent network of these basic transmission line structures, it becomes possible to filtered in micro-strip according to them Annexation in ripple device, and then set up the lumped parameter equivalent network of microstrip filter.Finally, the micro-strip filtering shown in Fig. 2 The lumped parameter equivalent network of device is as shown in Figure 3.Wherein, L is inductance, and jX is reactance, K₁₂And K₂₃It is impedance inverter, R_SIt is source And load impedance, V_SIt is driving source.Between the element of the electric parameter of microstrip filter and its lumped parameter equivalent network etc. Imitating relational expression is：

K₂₃=Z₂/sinθ₂ (3)

In addition, ω₀=-X/L is resonant frequency.

The second step of method for designing, according to the technical indicator of microstrip filter, using lumped wave filter method for designing Determine each component value of lumped parameter equivalent network；3rd step of method for designing, according to derived equivalent relation in the first step Formula, each electric parameter of microstrip filter is calculated by each component value of lumped parameter equivalent network, and then determine phase The values of the structural parameters answered；4th step of method for designing, is modeled using the values of the structural parameters of the microstrip filter being calculated, and is carried out Electromagnetic Simulation optimizes, and the performance of line filter is finally met the requirement of technical indicator.

The beneficial effect of method for designing of the present invention is：It can disclose the physical mechanism of the microstrip filter, so that Can be with its performance of better control；It quickly can obtain one group of values of the structural parameters by calculating, and can shorten the lead time.

Brief description of the drawings

Fig. 1：Microstrip line construction schematic diagram；

Fig. 2：Microstrip bandpass filter schematic diagram；

Fig. 3：The lumped parameter equivalent network schematic diagram of microstrip bandpass filter；

Fig. 4：Preferable fourth-order band-pass frequency response chart；

Fig. 5：Using computation structure parameter value emulate the frequency response chart for obtaining；

Fig. 6：Improve microstrip bandpass filter structural representation；

Fig. 7:Improve the optimization Simulation result and actual test result figure of microstrip bandpass filter.

Specific embodiment

The present invention is described further with specific embodiment below in conjunction with the accompanying drawings, but embodiments of the present invention are not limited In this.Lumped parameter equivalent network shown in Fig. 3 discloses the physical mechanism of the microstrip filter in Fig. 2.As seen from Figure 3, should Line filter has four resonant frequencies, therefore can realize a bandpass response for quadravalence.Illustratively, do not lose Generality, a fourth-order band-pass frequency response is realized with this microstrip filter, and technical indicator is：Centre frequency in 2.0GHz, Passband is located at [1.5,2.5] GHz, and return loss is less than -20dB, and four transmission zeros are located at infinite point.Preferable quadravalence band Logical frequency response is as shown in Figure 4.According to this technical indicator, Fig. 3 institutes can be determined by the method for designing of lumped wave filter Show each component value in lumped parameter equivalent network.For example, using the design of generalized chebyshev type lumped wave filter Method determines these component values, as follows：

L=1.485210^-8H, X=-186.6360 Ω, K₁₂=42.4858 Ω, K₂₃=32.6491 Ω and R_S=50 Ω

Before recycling between the element of the electric parameter of derived microstrip filter and its lumped parameter equivalent network Equivalent relation formula (1)-(3), the electric parameter that can obtain microstrip filter is：

Z_1e=161.3018 Ω, Z_1o=76.3302 Ω, θ₁=pi/2, Z₂=16.3245 Ω and θ₂=π/6.

Illustratively, without loss of generality, from 4350 substrates of Rogers, its dielectric constant is 3.66, and substrate thickness is 0.508mm.The values of the structural parameters that microstrip filter can be then calculated is

w₁=0.15mm, s₁=0.17mm, l₁=23.30mm, w₂=5.00mm and l₂=6.93mm.

Based on the values of the structural parameters modeling being the previously calculated, and Electromagnetic Simulation is carried out, simulation result is as shown in Figure 5.Can See, simulation result is generally adjacent to preferable fourth-order band-pass frequency response as shown in Figure 4.Due to the collection Headquarters of the General Staff of microstrip filter Number equivalent network only considered topmost physical mechanism, not including all of discontinuity effect.Frequency shown in Fig. 4 Response is not met by technical requirement.It is flat first in order to further improve the return loss of microstrip filter shown in Fig. 2 The left end difference cut away portion transmission line section of the right-hand member of row coupling line section (2) and the second parallel coupled line section (4), as shown in Figure 6. Based on the values of the structural parameters modeling being the previously calculated, the performance of microstrip filter is optimized by means of Electromagnetic Simulation, carefully Micro-adjustment these valuess of the structural parameters, it is final determine microstrip filter structural parameters be：

w₁=0.20mm, s₁=0.13mm, l₁=26.70mm, w₂=3.80mm, l₂=5.43mm and l₃=2.76mm

The performance of the microstrip filter after optimization disclosure satisfy that technical indicator, as shown in Figure 7.After these optimizations Values of the structural parameters, processing test has been carried out to this microstrip filter, and test result is as shown in Figure 7.It can be seen that, test result with emulation Result is quite coincide, and meets technical requirement.

Embodiment enumerated above has absolutely proved that method for designing of the present invention deep enough can must disclose micro-strip filter The physical mechanism of ripple device, shortens its lead time.One of ordinary skill in the art will be appreciated that, embodiment described here It is to aid in reader and understands principle of the invention, it should be understood that protection scope of the present invention is not limited to such special Statement and embodiment.One of ordinary skill in the art can make according to these technical inspirations disclosed by the invention and various not take off From other various specific deformations and combination of essence of the invention, these deformations and combination are still within the scope of the present invention.

Claims (5)

1. a kind of method for designing of microstrip filter, it is characterised in that implementation step is as follows：Step one, sets up microstrip filter Lumped parameter equivalent network, derive microstrip filter electric parameter and the element of lumped parameter equivalent network between it is equivalent Relational expression.Step 2, according to the technical indicator of microstrip filter, lumped parameter is determined using lumped wave filter method for designing Each component value of equivalent network；Step 3, the equivalent relation formula according to derived from step one, by each of lumped parameter equivalent network Individual component value is calculated each electric parameter of microstrip filter, and then determines corresponding values of the structural parameters；Step 4, uses The values of the structural parameters modeling of the microstrip filter being calculated, carries out Electromagnetic Simulation optimization, makes the performance of line filter most The requirement of technical indicator is met eventually.

2., according to the method for designing described in claim 1, lumped parameter equivalent network is made up of inductance and reactance.

3. a kind of microstrip filter is characterised by：The right-hand member of incoming feeder (1) is connected to a left side for the first parallel coupled line section (2) End, the right-hand member of the first parallel coupled line section (2) is connected to the left end of transmission line section (3), and the right-hand member of transmission line section (3) is connected to the The left end of two parallel coupled line sections (4), the right-hand member of the second parallel coupled line section (4) is connected to the left end of output feeder (5).

4., according to the method for designing described in claim 1, lumped parameter equivalent network is set up to the microstrip filter in claim 3 Network.If the characteristic impedance of the incoming feeder (1) and output feeder (5) of microstrip filter is all R_S.First parallel coupled line section (2) Even mode impedance with the second parallel coupled line section (4) is all Z_1e, odd mode impedance is all Z_1o, electrical length is all θ₁.Transmission line section (3) Characteristic impedance be Z₂, electrical length is θ₂.The lumped parameter equivalent network of microstrip filter is as shown in Figure 3.Wherein, L is inductance, JX is reactance, K₁₂And K₂₃It is impedance inverter, R_SIt is source and load impedance, V_SIt is driving source.The electric parameter of microstrip filter And the equivalent relation formula between the element of its lumped parameter equivalent network is：

$K_{12}=\frac{Z_{1e}-Z_{1o}}{2{\mathrm{sin\θ}}_1}$

$L=\frac{\mathrm{\π}}{2}\frac{1}{{\mathrm{\ω}}_0}\left(\frac{Z_{1e}+Z_{1o}}{2}\right)$

K₂₃=Z₂/sinθ₂

In addition, ω₀=-X/L is resonant frequency.

5. understand that the microstrip filter can be real according to the lumped parameter equivalent network of the microstrip filter described in claim 4 An existing fourth-order band-pass frequency response.