The microwave filter of the wide suppression of high selectivity and method for designing thereof
Technical field
The invention belongs to communication equipment, radar equipment, the technical fields such as measuring instrument, be specifically related to microwave filter and the method for designing thereof of the wide suppression of high selectivity.
Background technology
Along with the fast development of wireless communication technology, microwave device receives increasing concern.The wireless communication system application of continuous appearance it is also proposed higher requirement to Wireless Telecom Equipment, and high-performance, high reliability, miniaturization, low cost have become the basic demand of novel wireless communication electronic equipment.Microwave filter is one of critical elements in Modern Communication System, and it plays the important function selecting signal, and the quality of its performance is directly connected to the quality of whole communication system.Along with the development of wireless communication system, frequency spectrum resource growing tension, the interval between frequency is more and more less, it is also proposed higher requirement to filter.High selectivity, miniaturized one of the study hotspot and difficult point having become microwave filter, the interference simultaneously how curbing other wireless signal in wider band band limits is also a difficult point.
The normal cavity body filter used is comparatively large due to size on the market at present, is suitable only for higher microwave frequency band; The size of substrate integral wave guide filter is for the low side of microwave frequency band, and its size is larger, is still only suitable for higher frequency band application; And LTCC filter also has, and Insertion Loss in complex manufacturing, passband is large, throwing sheet high in cost of production shortcoming.
Summary of the invention
For above-mentioned deficiency of the prior art, the microwave filter of the wide suppression of high selectivity provided by the invention and method for designing thereof solve tradition and realize the problem that highly selective filter needs more exponent number to cause filter area to increase.
In order to reach foregoing invention object, the technical solution used in the present invention is:
First aspect, provides the microwave filter of the wide suppression of a kind of high selectivity, it comprise by conduct electricity gluing with together with pcb board and metal support plate; Pcb board comprises medium substrate, and the upper and lower surface of medium substrate all has copper coating; The copper coating of medium substrate upper surface comprises the incoming feeder and output feeder that are arranged on medium substrate two ends, incoming feeder and the first parallel coupling anatomical connectivity, output feeder and the second parallel coupling anatomical connectivity;
First parallel coupling structure and the second parallel coupling structure all has a defect sturcture; First parallel coupling structure and the second parallel coupling structure are linked together by two the filter feeder lines arranged; Every bar filter feeder line is at least connected with a SIR resonator; Article two, filter feeder line is provided with the metallic vias with the conducting of medium substrate lower surface copper coating.
Second aspect, provide the method for designing of the microwave filter of the wide suppression of a kind of high selectivity, it comprises the following steps:
Obtain the centre frequency of microwave filter, the relative dielectric constant of the medium substrate of pcb board and the thickness of medium substrate;
According to relative dielectric constant and the thickness of medium substrate, calculate the width of incoming feeder and output feeder:
Wherein, Z
cfor the characteristic impedance of feeder line, ε
rfor the relative dielectric constant of medium substrate, h is the thickness of medium substrate, ε
refor effective dielectric constant; η is free space wave impedance, and W is the width of incoming feeder or output feeder;
The size of SIR resonator is calculated according to the centre frequency of microwave filter:
Wherein, l
rfor SIR resonator dimensions, f
0for the centre frequency of microwave filter, c is the light velocity in vacuum, ε
rfor the relative dielectric constant of medium substrate;
According to impedance and the impedance ratio of the high low-impedance line of SIR resonator, calculate high resistant line electrical length:
θ
2=arctan[Z
1/(Z
2tanθ
1)]
Wherein, θ
1for low-resistance line electrical length, θ
2for high resistant line electrical length, Z
1and Z
2for the characteristic impedance of the high low-impedance line of SIR resonator;
By Chebyshev filter low pass prototype, calculate the coupling amount between each SIR resonator;
Wherein, m
i, i-1be the amount of coupling between i-th SIR resonator with the i-th+1 SIR resonator, FBW is the relative bandwidth of microwave filter, g
ifor low-pass prototype parameter, n is the number of SIR resonator, 1≤i≤n-1;
Microwave filter adds defect sturcture, and the size of parasitic passband design defect structure according to microwave filter;
The size of 3 D electromagnetic emulation to the coupling amount between the size of calculated value incoming feeder width, output feeder width, resonator, high resistant line electrical length, each resonator and defect sturcture is adopted to be optimized;
When the frequency response of all calculated values equals set point, export the size of coupling amount between the incoming feeder width after optimizing, output feeder width, the size of resonator, high resistant line electrical length, each resonator and defect sturcture.
Compared with realizing highly selective filter with tradition, beneficial effect of the present invention is:
1, the microwave filter of this programme is owing to have employed two parallel coupling structures as design cell, recruitment 4 zero points (two internal layer zero points and two outer zero points when fixed filters exponent number, in microwave filter passband left and right each two), solve the problem that the technology such as conventional microstrip, co-planar waveguide causes selectivity poor at microwave frequency band because Q value is lower.
2, owing to have employed defect sturcture, additionally notch band is introduced at stopband, inhibit the generation of the parasitic passband of filter, thus greatly widened this filter band outside inhibitory energy, (20dB Out-of-band rejection scope is about four times in centre frequency 4f to make this microwave filter have wider Out-of-band rejection scope
0).
3, this microwave filter structure is simply compact, take circuit size area less (for tradition has 2/3 of four zero filter areas), two parallel coupling structures that the present invention adopts, while introducing transmission zero, do not increase extra circuit area, be very beneficial for Miniaturization Design.
4, because this microwave filter adopts planar structure, be easy to integrated with other planar circuits, it also has, and structure is simple, processing cost is low, fabrication cycle is short, easy to process, Standard PC B processing technology thus can be adopted to process.
Accompanying drawing explanation
Fig. 1 is the stereogram of the pcb board of the microwave filter of the wide suppression of high selectivity.
Fig. 2 is the vertical view of pcb board.
Fig. 3 is the upward view of pcb board.
Fig. 4 is broadband response (S parameter) figure;
Fig. 5 is narrowband response (S parameter) figure.
Wherein, 1, medium substrate; 2, incoming feeder; 3, the first parallel coupling structure; 4, defect sturcture; 5, filter feeder line; 6, SIR resonator; 7, metallic vias; 8, the second parallel coupling structure; 9, output feeder 9; 10, internal layer 0. 10; 11, outer 0. 11.
Embodiment
Below the specific embodiment of the present invention is described; so that those skilled in the art understand the present invention; but should be clear; the invention is not restricted to the scope of embodiment; to those skilled in the art; as long as various change to limit and in the spirit and scope of the present invention determined, these changes are apparent, and all innovation and creation utilizing the present invention to conceive are all at the row of protection in appended claim.
The microwave filter of the wide suppression of this high selectivity comprise by conduct electricity gluing with together with pcb board and metal support plate; Pcb board and metal support plate by conduction gluing and together with shout, put into oven for baking and takes out after 2 hours, baking temperature is 150 DEG C, this temperature both guarantees abundant glue and while can not destroy metal support plate.
The size of metal support plate and the size of microwave filter are consistent, its Thickness Design is 2mm, and adopt the copper material that conductivity is good, simultaneously gold-plated process has been carried out to keep good conductivity to provide good earthing effect in its surface, and the thickness of Gold plated Layer is 1um.During use, metal support plate can as public stratum for filter reference planes are provided while provide physical support for filter, instant microwave filter fixing with measure.
As shown in Figure 1, Figure 2 and Figure 3, pcb board comprises medium substrate 1, and the upper and lower surface of medium substrate 1 all has copper coating; During design, preferable medium substrate 1 adopts low-loss Rogers5880, and its dielectric constant is 2.2, and loss angle tangent is 0.001, and dielectric-slab thickness is 0.254mm; The thickness of the copper coating of the upper and lower surface of medium substrate 1 is set to 0.035mm, wherein, the copper coating of medium substrate 1 upper surface to the major part of overwrite media substrate 1 upper surface, the whole surface of the copper coating overwrite media substrate 1 of medium substrate 1 lower surface.
Refer again to Fig. 1, the copper coating of medium substrate 1 upper surface comprises the incoming feeder 2 and output feeder 9 that are arranged on medium substrate 1 two ends, incoming feeder 2 is identical with the size of output feeder 9, wherein, incoming feeder 2 and output feeder 9 all adopt 50 ohm microstrip, and incoming feeder 2 and output feeder 9 adopt the main purpose of 50 ohm microstrip to be convenient for measuring to be connected with other circuit with being easy to.
Incoming feeder 2 is connected with the first parallel coupling structure 3, and output feeder 9 is connected with the second parallel coupling structure 8; Preferably the first parallel coupling structure 3 is parallel with the second parallel coupling structure 8.First parallel coupling structure 3 and the second parallel coupling structure 8 all has a defect sturcture 4; First parallel coupling structure 3 and the second parallel coupling structure 8 are linked together by two the filter feeder lines 5 arranged; Every bar filter feeder line 5 is at least connected with a SIR resonator 6; Article two, filter feeder line 5 is provided with the metallic vias 7 with the conducting of medium substrate 1 lower surface copper coating.
This programme preferably arranges two SIR resonators 6 on every bar filter feeder line 5, and adopt edge to be coupled between each SIR resonator 6 and realize, between two SIR resonators 6, the size of coupling amount is controlled by Edge Distance.During design, centre frequency needed for microwave filter and relative bandwidth, calculated the size of coupling amount between each SIR resonator 6 by Chebyshev filter low pass prototype, and determine the size of coupling distance according to the relation of coupling amount size and edge coupling distance; In addition, the connection on four SIR resonators 6 and floor, by plated-through hole, is connected by incoming feeder 2 and output feeder 9 with the connection of input and output.
As shown in Figure 5, two outer 0. 11 in four zero points (two internal layers 0. 10 and two outer 0. 11) by cross coupling structure, (cross coupling structure is the structure that non-conterminous two filters are formed, cross-couplings is the coupling between non-adjacent two filters) realize, the position at four zero points is determined by the coupling amount size of cross coupling structure, and two internal layers 0. 10 are determined by the first parallel coupling structure 3 and the second parallel coupling structure 8.
In addition, defect sturcture 4 is made up of half-wavelength slots line structure, and the feature utilizing its band to fall into frequency response makes to produce zero point on a specific frequency, thus forms parasitic band suppression, finally obtains the frequency response of wide Out-of-band rejection, specifically as shown in Figure 5.
During design, preferred SIR resonator 6 is quarter-wave resonance device; After arranging like this, notch band is introduced at the parasitic passband place of passband upper sideband, thus inhibit the generation of the parasitic passband of filter, thus greatly widened this filter band outside inhibitory energy, (20dB Out-of-band rejection scope is about four times in centre frequency 4f to make this microwave filter have wider Out-of-band rejection scope
0).
So far, to complete the detailed description of the microwave filter to the wide suppression of high selectivity, then the method for designing of the microwave filter of the wide suppression of high selectivity is described in detail below:
The method for designing of the microwave filter of the wide suppression of high selectivity comprises the following steps:
Obtain the centre frequency of microwave filter, the relative dielectric constant of the medium substrate 1 of pcb board and the thickness of medium substrate 1; The parameters such as the relative dielectric constant of the medium substrate 1 of microwave filter centre frequency, pcb board and the thickness of medium substrate 1 selected as required before design microwave filter.
According to relative dielectric constant and the thickness of medium substrate 1, calculate the width of incoming feeder 2 and output feeder 9:
Wherein, Z
cfor the characteristic impedance of feeder line, ε
rfor the relative dielectric constant of medium substrate 1, h is the thickness of medium substrate 1, ε
refor effective dielectric constant; η is free space wave impedance, and W is the width of incoming feeder 2 or output feeder 9; Because incoming feeder 2 and output feeder 9 size are duplicate, herein, only need to calculate one of them.
The size of SIR resonator 6 is calculated according to the centre frequency of microwave filter:
Wherein, l
rfor SIR resonator 6 size, f
0for the centre frequency of microwave filter, c is the light velocity in vacuum, ε
rfor the relative dielectric constant of medium substrate 1;
According to high low-impedance line characteristic impedance and the impedance ratio of any resonator 6, calculate high resistant line electrical length:
θ
2=arctan[Z
1/(Z
2tanθ
1)]
Wherein, θ
1for low-resistance line electrical length, θ
2for high resistant line electrical length, Z
1and Z
2for the characteristic impedance of the high low-impedance line of SIR resonator 6;
By Chebyshev filter low pass prototype, calculate the coupling amount between each SIR resonator 6;
Wherein, m
i, i-1be the amount of coupling between i-th SIR resonator 6 with the i-th+1 SIR resonator 6, FBW is the relative bandwidth of microwave filter, g
ifor low-pass prototype parameter, n is the number of SIR resonator 6,1≤i≤n-1;
Microwave filter adds defect sturcture 4, and the size of parasitic passband design defect structure 4 according to microwave filter; The size of defect sturcture 4 herein can obtain according to the parasitic passband of microwave filter, and its width is 0.2mm, and length is 1/2nd wavelength of the parasitic passband of microwave filter.
The size of 3 D electromagnetic emulation to the coupling amount between the size of calculated value incoming feeder 2 width, output feeder 9 width, resonator, high resistant line electrical length, each resonator and defect sturcture 4 is adopted to be optimized.
When the frequency response of all calculated values equals set point (set point is herein 20dB), export the size of coupling amount between incoming feeder 2 width after optimizing, output feeder 9 width, the size of resonator, high resistant line electrical length, each resonator and defect sturcture 4.
During design, preferred η is 377, θ
1for π/4; When the number of SIR resonator 6 is four, low-pass prototype parameter g
0=1, g
1=1.1088, g
2=1.3062, g
3=1.7704, g
4=0.8181, g
5=1.3554.
In sum, this programme adopts on double-sided copper-clad pcb board and etches quarter-wave resonance device pattern to form SIR resonator 6, ensure that the planar structure of microwave filter on the one hand, it is easy to integrated with other planar circuit, Standard PC B board machining process is adopted on the other hand due to it, process-cycle is short, is conducive to application to engineering practice.
Adopt the mode of two parallel coupling structures, while maintaining microwave filter miniaturization, also introduce the frequency selectivity that extra transmission zero improves microwave filter on microwave filter passband both sides.Adopt defect sturcture 4 to introduce trap wave point mode, while maintaining microwave filter high selectivity, obtain wider Out-of-band rejection scope.