CN103107390A - Balance type radio frequency electronically-controlled band-pass filter with bandwidth control - Google Patents
Balance type radio frequency electronically-controlled band-pass filter with bandwidth control Download PDFInfo
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- CN103107390A CN103107390A CN2013100239145A CN201310023914A CN103107390A CN 103107390 A CN103107390 A CN 103107390A CN 2013100239145 A CN2013100239145 A CN 2013100239145A CN 201310023914 A CN201310023914 A CN 201310023914A CN 103107390 A CN103107390 A CN 103107390A
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Abstract
The invention relates to a balance type radio frequency electronically-controlled band-pass filter with bandwidth control. The balance type radio frequency electronically-controlled band-pass filter with bandwidth control is composed of an upper layer micro-strip structure, an intermediate layer dielectric substrate and a lower layer grounded metal. Two input ports in the upper layer micro-strip structure are respectively connected with two input feed networks, and two output ports are respectively connected with two output feed networks. Two input feed networks are coupled with a first half-wavelength phrase step impedance resonator, a first half-wavelength phrase step impedance resonator is coupled with a second half-wavelength phrase step impedance resonator, finally the second half-wavelength phrase step impedance resonator is coupled with two output feed networks, and the whole filter structure is in a structure of longitudinal mirror symmetry. The balance type radio frequency electronically-controlled band-pass filter with bandwidth control achieves flexible bandwidth control, has the advantages of being high in common-mode rejection ration and wide in stop band and can be used for a reconfigurable radio frequency front end of the wireless communication or a radar system.
Description
Technical field
The present invention relates to a kind of novel tuning band pass filter of balanced type radio frequency electrical based on variable capacitance diode, particularly a kind of balanced type radio frequency electrically adjusted band-pass filter that bandwidth is controlled that has that can be applicable in multiband, broadband and restructural radio-frequency front-end system.
Background technology
Electrically tunable filter is one of key technology of the aspects such as frequency hopping spread spectrum (FHSS) communication technology, unjammable radar, dynamic frequency allocation technology, multi function receiver, spurious emissions measurement.Since World War II, electrically tunable filter always is one of focus of various countries' research.Aspect this, some research reports have been arranged at present, multiple different tuning device also is used, such as semiconductor variable capacitance diode, radio-frequency micro electromechanical system (RF MEMS) capacitance tube and ferroelectric thin-flim materials varactor etc.Wherein semiconductor variable capacitance diode fast because of its tuned speed, control voltage and the advantages such as power consumption is low, technical maturity are widely used in the design of reconfigurable system.
Modern ULTRA-WIDEBAND RADAR and radio communication require to adopt high performance restructural radio-frequency front-end.For example in the cognitive radio system, in order to take full advantage of and to merge various wireless channel and standard, radio-frequency front-end need to be operated on different frequencies, and this just needs the tunable restructural radio-frequency front-end of centre frequency.Along with the fast development of radar and the communication technology in recent years, frequency spectrum resource is day by day crowded, and these systems often have again strict bandwidth requirement and antijamming capability simultaneously.According to actual application environment, mainly also there is following problem in the radio frequency electrically adjusted filter of the balanced type of current design:
(1) for most of tuned filters, when tuning passband central frequency, the absolute bandwidth of passband or relative bandwidth often present random variation, and in a lot of practical applications, bandwidth are had certain requirement.Therefore we need to can control the tuned filter of the variation of pass band width in the time of tuning centre frequency.
(2) along with development and the extensive use of wireless system, the interference of ambient noise is not more allowed to ignore.The existence of ambient noise causes the hydraulic performance decline of filter, and then has influence on the noise factor of radio-frequency front-end.Therefore must take some to suppress the method for ambient noise.
(3) stopband expansion.Along with frequency spectrum resource is day by day crowded, may there be the microwave signal of multiple different frequency to coexist in a space.Therefore the band of band pass filter is outer must guarantee the noise signal of wider stopband to suppress to enter.
Carry out the problem that bandwidth is controlled when tuning for centre frequency, proposed at present certain methods.At present relatively commonly used have two kinds: the analysis that provides according to " S.J.Park and G.M.Rebeiz; Low-loss two-pole tunable filters with three different predefined band width characteristics; IEEE Trans.Microw.Theory Tech.; vol.56; no.5, pp.1137-1148, May2008. " as can be known, adopt independently electric coupling and magnetic coupling mechanism to control the variation of coupling coefficient, can realize bandwidth control; The analysis that provides according to " M.A.ElTanani and G.M.Rebeiz; High performance1.5-2.5GHz RF-MEMS tunable filters for wireless applications; IEEE Trans.Microw.Theory Tech.; vol.58; no.6; pp.1629-1637, Jun.2010. " adopts electromagnetism hybrid coupled mechanism can control bandwidth equally as can be known.Yet the above-mentioned method that proposes is all the single port circuit, there is no remarkable result for the inhibition of ambient noise.
The balanced structure circuit has inhibition preferably to ambient noise, and therefore balancing circuitry is used widely in Modern Communication System.The research of most concentrates on the aspects such as stopband expansion, common mode inhibition, broad passband.The analysis that provides according to " J.Shi; and Quan Xue; Balanced Bandpass Filters Using Center-Loaded Half-Wavelength Resonators; IEEE Trans.Microw.Theory Tech.; vol.59, no.10, pp.2452-2460; Oct.2011. " as can be known, the mode of middle loading capacitance can absorb common-mode signal.Yet the design of most of balanced type filters is all nonadjustable, only have at present in " Y.C.Li and Quan Xue; Tunable balanced bandpass filter with constant bandwidth and high commonmode suppression; IEEE Trans.Microw.Theory Tech.; vol.59; no.10, pp.2452-2460, Oct.2011. " literary composition and proposed a kind of balanced type tunable filter.Yet only realized in literary composition that constant absolute bandwidth is controlled and constant relative bandwidth is controlled, and the bandwidth of unrealized other modes is controlled.
For the problem of widening stopband, according to " M.Sagawa; M.Makimoto; and S.Yamashita; Geometrical structures and fundamental characteristics ofmicrowave stepped impedance resonators; IEEE Trans.Microw.Theory Tech.; vol.45, no.7, pp.1078-1085, July1997. " analysis that provides in the situation that fundamental frequency is constant, can be controlled the frequency of second harmonic as can be known by the impedance ratio that changes the Stepped Impedance resonator.The design that present application Stepped Impedance resonator is widened bandwidth is all nonadjustable, does not also have research report that the application of Stepped Impedance resonator in radio frequency electrically adjusted filter was discussed.
In a word, control bandwidth when present technology also need solve tuning centre frequency, suppress simultaneously the problem of ambient noise and stopband expansion, but there is no associated description.
Summary of the invention
The object of the present invention is to provide a kind of balanced type radio frequency electrically adjusted band-pass filter that bandwidth is controlled that has, this type balanced type band pass filter can be controlled its bandwidth changing pattern flexibly when design, have simultaneously wider rejection band and common-mode signal is had good inhibitory action.
The technical scheme that realizes the object of the invention is: a kind of balanced type radio frequency electrically adjusted band-pass filter with bandwidth control, the microstrip structure that comprises the upper strata, the grounded metal of interlayer substrate and lower floor, the microstrip structure on upper strata is attached to interlayer plate upper surface, and interlayer plate lower surface is grounded metal.
The microstrip structure on described upper strata comprises two half-wavelength Stepped Impedance resonators, two input feeding networks, two outputs feeding network, two input ports and two output ports; Wherein each half-wavelength Stepped Impedance resonator includes one section microstrip line and two variable capacitance diodes, described two variable capacitance diodes are connected to the two ends of microstrip line, wherein the interlude impedance of microstrip line is different with both sides, consist of one section about in the microstrip line of point-symmetric Stepped Impedance; The centre of one of them half-wavelength Stepped Impedance resonator is loaded with for the electric capacity that absorbs common-mode signal; Two input feeding networks with are connected an output feeding network and include 50 ohm microstrip, capacitance and the coupled microstrip line that connects successively, the other end of coupled microstrip line has the ground connection via hole; Two input ports are connected with 50 ohm microstrip of two input feeding networks respectively, two output ports also are connected with 50 ohm microstrip of two output feeding networks respectively, and the characteristic impedance of above-mentioned two input ports and two output ports is 50 ohm; Input feeding network and the coupling of the first half-wavelength Stepped Impedance resonator for two, the first half-wavelength Stepped Impedance resonator and the coupling of the second half-wavelength Stepped Impedance resonator, the second last half-wavelength Stepped Impedance resonator is coupled with two output feeding networks respectively, and whole filter construction is all symmetrical up and down.
In the above-mentioned balanced type radio frequency electrically adjusted band-pass filter with bandwidth control, described the first half-wavelength Stepped Impedance resonator comprises successively the first variable capacitance diode, the first rectangular microstrip line, the second rectangular microstrip line, the 3rd rectangular microstrip line, the 4th rectangular microstrip line, the 5th rectangular microstrip line, the 6th rectangular microstrip line, the 7th rectangular microstrip line, the 8th rectangular microstrip line, the 9th rectangular microstrip line, the second variable capacitance diode that connects, and the anode of the first variable capacitance diode and the second variable capacitance diode all passes the intermediate medium substrate and is connected with the lower floor grounded metal; The second half-wavelength Stepped Impedance resonator is identical with the first half-wavelength Stepped Impedance resonator structure, is loaded with in the middle of it for the electric capacity that absorbs common-mode signal, and the other end of electric capacity passes the interlayer substrate and is connected with the lower floor grounded metal; Above-mentioned two half-wavelength Stepped Impedance resonators are arranged into left and right, equal symmetrical structure up and down together.
in the above-mentioned balanced type radio frequency electrically adjusted band-pass filter with bandwidth control, the first input feeding network in described two input feeding networks is by 50 ohm of rectangular microstrip lines, capacitance, the tenth rectangular microstrip line, the 11 rectangular microstrip line connects and composes in turn, wherein the tenth rectangular microstrip line and the 11 rectangular microstrip line and the first half-wavelength Stepped Impedance resonator consist of the parallel coupling structure in order to feed, the 11 rectangular microstrip line end passes the interlayer substrate by the ground connection via hole and is connected with the lower floor grounded metal, the structure of the second input feeding network is identical with the first input feeding network, two output feeding networks are identical with two input feeding network structures, two input feeding networks, two outputs feeding networks, two input ports, two output ports and above-mentioned two half-wavelength Stepped Impedance resonators are arranged into left and right, equal symmetrical structure up and down together.
In the above-mentioned balanced type radio frequency electrically adjusted band-pass filter with bandwidth control, in the first rectangular microstrip line of described the first half-wavelength Stepped Impedance resonator, the 5th rectangular microstrip line and the 9th rectangular microstrip line respectively with the second half-wavelength Stepped Impedance resonator, corresponding the 12 rectangular microstrip line, the 13 rectangular microstrip line, the 14 rectangular microstrip line parallel placed and consisted of three sections interstage coupling structures.
In the above-mentioned balanced type radio frequency electrically adjusted band-pass filter with bandwidth control, the second rectangular microstrip line of described the first half-wavelength Stepped Impedance resonator, the 3rd rectangular microstrip line, the 4th rectangular microstrip line, the 5th rectangular microstrip line, the 6th rectangular microstrip line, the 7th rectangular microstrip line, the 8th rectangular microstrip line have identical resistance value, the first rectangular microstrip line and the 9th rectangular microstrip line have identical resistance value, above-mentioned two resistance value differences, the structure of formation Stepped Impedance.
Described balanced type radio frequency electrically adjusted band-pass filter with bandwidth control, when first input end mouth and the second input port input difference mode signal, whole filter forms an electric divider wall on the linear position of the mid point place of the first half-wavelength Stepped Impedance resonator and the second half-wavelength Stepped Impedance resonator.In the case, the second half-wavelength Stepped Impedance resonator centre position does not have electric current, and the described electric capacity that is carried in this position can be ignored.So under the difference mode signal excitation, the first half-wavelength Stepped Impedance resonator and the second half-wavelength Stepped Impedance resonator equivalence are the quarter-wave resonance device of two couplings, wherein magnetic coupling is main coupling path, also has simultaneously the electric coupling path as the negative feedback minor matters.When first input end mouth and the second input port input common-mode signal, whole filter forms a magnetic divider wall on the linear position of the mid point place of the first half-wavelength Stepped Impedance resonator and the second half-wavelength Stepped Impedance resonator.In the case, the second half-wavelength Stepped Impedance resonator interposition is equipped with electric current to be passed through, and being carried on the described electric capacity of this position has current flowing.When not considering this electric capacity, the first half-wavelength Stepped Impedance resonator and the second half-wavelength Stepped Impedance resonator equivalence are 1/2nd wave resonator of two couplings, and resonance frequency is the twice of difference mode signal when excitation resonance frequency.When considering the middle described electric capacity that loads of the second half-wavelength Stepped Impedance resonator, the resonance frequency of two 1/2nd wave resonator of equivalence is different, makes common-mode signal not pass through, and reaches the effect of inhibition.
in order further to realize purpose of the present invention, described the second rectangular microstrip line with first half-wavelength Stepped Impedance resonator of the balanced type radio frequency electrically adjusted band-pass filter that bandwidth controls, the 3rd rectangular microstrip line, the 4th rectangular microstrip line, the 5th rectangular microstrip line, the 6th rectangular microstrip line, the 7th rectangular microstrip line, the 8th rectangular microstrip live width 0.2～2mm, the first rectangular microstrip line and the 9th rectangular microstrip live width 0.2～2mm, first rectangular microstrip line length 2～10mm, second rectangular microstrip line length 3～10mm, the 3rd rectangular microstrip line length 5～20mm, the 4th rectangular microstrip line length 3～10mm, the 5th rectangular microstrip line length 4～20mm, the appearance value of all capacitances is the same and all more than 6pF, in the middle of the second half-wavelength Stepped Impedance resonator, the capacitance of loading capacitance is 6～100pF, distance between the first rectangular microstrip line and the 12 rectangular microstrip line is 0.1～1mm, distance between the 9th rectangular microstrip line and the 14 rectangular microstrip line is also 0.1～1mm, distance between the 5th rectangular microstrip line and the 13 rectangular microstrip line is 0.1～0.5mm.
The DIELECTRIC CONSTANT ε of described medium substrate
rBeing 2～10, is highly 0.2～2mm.
The present invention compared with prior art, its remarkable advantage is: 1) due to the balance structural design, this band pass filter can work for difference mode signal, for common-mode signal, inhibitory action is preferably arranged, therefore disturbs for this class of ambient noise to have immunologic function.The common mode inhibition level of surveying in embodiment all surpasses-20dB; 2) the present invention is provided with one group of stronger magnetic coupling as main coupling path between two half-wave resonator, again by introducing symmetrical parallel coupling line that terminal connects variable capacitance diode as the pair minor matters that are coupled, strengthen or offset stronger magnetic coupling, realizing that the bandwidth when centre frequency is tuning is controlled; Do not need to change topological structure, only need regulate the spacing between the parallel coupled line of the secondary coupling in both sides minor matters, can realize bandwidth with the various variation patterns of frequency, to satisfy different application demands; 3) by introducing the Stepped Impedance resonator, widened stopband.More than the stopband of actual measurement may extend to 3GHz in an embodiment.
The present invention is further detailed explanation below in conjunction with accompanying drawing.
Description of drawings
Fig. 1 is the schematic diagram with balanced type radio frequency electrically adjusted band-pass filter structure of bandwidth control.
Fig. 2 is the schematic diagram of half-wavelength Stepped Impedance resonator.
Fig. 3 is that the half-wavelength Stepped Impedance resonator in Fig. 2 is got in the situation of different impedance ratio Rz, and second harmonic is to the normalized value of the fundamental frequency situation with the capacitance variation of transfiguration diode.
When Fig. 4 a is constant absolute bandwidth, emulation and the measured curve of the differential mode transmission characteristic under different DC biased.
When Fig. 4 b is constant absolute bandwidth, emulation and the measured curve of the differential mode return loss under different DC biased.
When Fig. 4 c is constant absolute bandwidth, the measured curve of the common mode transmission characteristic under different DC biased.
When Fig. 5 a is Constant relative bandwidth, emulation and the measured curve of the differential mode transmission characteristic under different DC biased.
When Fig. 5 b is Constant relative bandwidth, emulation and the measured curve of the differential mode return loss under different DC biased.
When Fig. 5 c is Constant relative bandwidth, the measured curve of the common mode transmission characteristic under different DC biased.
Embodiment
A kind of balanced type radio frequency electrically adjusted band-pass filter with bandwidth control, the microstrip structure that comprises the upper strata, the grounded metal of interlayer substrate and lower floor, the microstrip structure on upper strata are attached to interlayer plate upper surface, and interlayer plate lower surface is grounded metal.
The microstrip structure on described upper strata comprises two half-wavelength Stepped Impedance resonators, two input feeding networks, two outputs feeding network, two input ports and two output ports; Wherein each half-wavelength Stepped Impedance resonator includes one section microstrip line and two variable capacitance diodes, described two variable capacitance diodes are connected to the two ends of microstrip line, wherein the interlude impedance of microstrip line is different with both sides, consist of one section about in the microstrip line of point-symmetric Stepped Impedance; The centre of one of them half-wavelength Stepped Impedance resonator is loaded with for the electric capacity that absorbs common-mode signal; Two input feeding networks with are connected an output feeding network and include 50 ohm microstrip, capacitance and the coupled microstrip line that connects successively, the other end of coupled microstrip line has the ground connection via hole; Two input ports are connected with 50 ohm microstrip of two input feeding networks respectively, two output ports also are connected with 50 ohm microstrip of two output feeding networks respectively, and the characteristic impedance of above-mentioned two input ports and two output ports is 50 ohm; Input feeding network and the coupling of the first half-wavelength Stepped Impedance resonator for two, the first half-wavelength Stepped Impedance resonator and the coupling of the second half-wavelength Stepped Impedance resonator, the second last half-wavelength Stepped Impedance resonator is coupled with two output feeding networks respectively, and whole filter construction is all symmetrical up and down.
in the above-mentioned balanced type radio frequency electrically adjusted band-pass filter with bandwidth control, described the first half-wavelength Stepped Impedance resonator comprises the first variable capacitance diode 14 that connects successively, the first rectangular microstrip line 5, the second rectangular microstrip line 6, the 3rd rectangular microstrip line 7, the 4th rectangular microstrip line 8, the 5th rectangular microstrip line 9, the 6th rectangular microstrip line 10, the 7th rectangular microstrip line 11, the 8th rectangular microstrip line 12, the 9th rectangular microstrip line 13, the second variable capacitance diode 15, the anode of the first variable capacitance diode 14 and the second variable capacitance diode 15 all passes the intermediate medium substrate and is connected with the lower floor grounded metal, the second half-wavelength Stepped Impedance resonator is identical with the first half-wavelength Stepped Impedance resonator structure, is loaded with in the middle of it for the electric capacity 20 that absorbs common-mode signal, and the other end of electric capacity 20 passes the interlayer substrate and is connected with the lower floor grounded metal, above-mentioned two half-wavelength Stepped Impedance resonators are arranged into left and right, equal symmetrical structure up and down together.
in the above-mentioned balanced type radio frequency electrically adjusted band-pass filter with bandwidth control, the first input feeding network of described two input feeding networks is by 50 ohm of rectangular microstrip lines 1, capacitance 2, the tenth rectangular microstrip line 3, the 11 rectangular microstrip line 4 connects and composes in turn, wherein the tenth rectangular microstrip line 3 and the 11 rectangular microstrip line 4 and the first half-wavelength Stepped Impedance resonator consist of the parallel coupling structure in order to feed, the 11 rectangular microstrip line 4 ends pass the interlayer substrate by ground connection via hole 21 and are connected with the lower floor grounded metal, the structure of the second input feeding network is identical with the first input feeding network, two output feeding networks are identical with two input feeding network structures, two input feeding networks, two outputs feeding networks, two input ports, two output ports and above-mentioned two half-wavelength Stepped Impedance resonators are arranged into left and right, equal symmetrical structure up and down together.
Described balanced type radio frequency electrically adjusted band-pass filter with bandwidth control, the 12 rectangular microstrip line 17, the 13 rectangular microstrip line 19, the 14 parallel placement of rectangular microstrip line 18 corresponding in the first rectangular microstrip line 5 of the first half-wavelength Stepped Impedance resonator, the 5th rectangular microstrip line 9 and the 9th rectangular microstrip line 13 respectively with the second half-wavelength Stepped Impedance resonators consist of three sections interstage coupling structures.
Described balanced type radio frequency electrically adjusted band-pass filter with bandwidth control, the second rectangular microstrip line 6 of the first half-wavelength Stepped Impedance resonator, the 3rd rectangular microstrip line 7, the 4th rectangular microstrip line 8, the 5th rectangular microstrip line 9, the 6th rectangular microstrip line 10, the 7th rectangular microstrip line 11, the 8th rectangular microstrip line 12 have identical resistance value, the first rectangular microstrip line 5 and the 9th rectangular microstrip line 13 have identical resistance value, above-mentioned two resistance value differences, the structure of formation Stepped Impedance.
described balanced type radio frequency electrically adjusted band-pass filter with bandwidth control, the second rectangular microstrip line 6 of the first half-wavelength Stepped Impedance resonator, the 3rd rectangular microstrip line 7, the 4th rectangular microstrip line 8, the 5th rectangular microstrip line 9, the 6th rectangular microstrip line 10, the 7th rectangular microstrip line 11, the 8th wide 0.2～2mm of rectangular microstrip line 12, the first rectangular microstrip line 5 and the 9th wide 0.2～2mm of rectangular microstrip line 13, the first long 2～10mm of rectangular microstrip line 5, the second long 3～10mm of rectangular microstrip line 6, the 3rd long 5～20mm of rectangular microstrip line 7, the 4th long 3～10mm of rectangular microstrip line 8, the 5th long 4～20mm of rectangular microstrip line 9, the appearance value of all capacitances is the same and all more than 6pF, in the middle of the second half-wavelength Stepped Impedance resonator, the capacitance of loading capacitance is 6～100pF, distance between the first rectangular microstrip line 5 and the 12 rectangular microstrip line 17 is 0.1～1mm, distance between the 9th rectangular microstrip line 13 and the 14 rectangular microstrip line 18 is also 0.1～1mm, distance between the 5th rectangular microstrip line 9 and the 13 rectangular microstrip line 19 is 0.1～0.5mm.
The DIELECTRIC CONSTANT ε of described medium substrate
rBeing 2～10, is highly 0.2～2mm.
Adjust the parameters of filter, make filter reach balance on total.What Fig. 2 showed is the tunable half-wavelength Stepped Impedance resonator that proposes.When first input end mouth IN and the second input port IN' input difference mode signal, whole filter forms an electric divider wall on the linear position of the mid point place of the first half-wavelength Stepped Impedance resonator and the second half-wavelength Stepped Impedance resonator.In the case, the second half-wavelength Stepped Impedance resonator centre position does not have electric current, and the electric capacity 20 that is carried in this position can be ignored.So under the difference mode signal excitation, the first half-wavelength Stepped Impedance resonator and the second half-wavelength Stepped Impedance resonator equivalence are the quarter-wave resonance device of two couplings.When quarter-wave resonance device resonance, its first-harmonic resonance frequency and harmonic resonance frequency can be solved by following condition of resonance:
ω=2 π f wherein, resonance frequency centered by f, C is the capacitance of variable capacitance diode under different voltages, Y
1The characteristic admittance of this half-wavelength Stepped Impedance resonator mid portion microstrip line, Y
2The characteristic admittance of these half-wavelength Stepped Impedance resonator both sides part microstrip lines (the first rectangular microstrip line 5, the 9th rectangular microstrip line 13), θ
1, θ
2The electrical length of corresponding microstrip line, definition impedance ratio R
zFor:
Compare with the uniform impedance resonator, the Stepped Impedance resonator is at R
zThe advantage that increases the second order resonance frequency 1 o'clock arranged.Fig. 3 has showed different impedance ratios to the impact of second harmonic, and wherein abscissa is the capacitance of the variable capacitance diode that connects of resonator two ends, and ordinate is the numerical value of second harmonic frequency after to fundamental frequency normalization.
When first input end mouth IN and the second input port IN' input common-mode signal, whole filter forms a magnetic divider wall on the linear position of the mid point place of the first half-wavelength Stepped Impedance resonator and the second half-wavelength Stepped Impedance resonator.In the case, the second half-wavelength Stepped Impedance resonator interposition is equipped with electric current to be passed through, and being carried on the described electric capacity 20 of this position has current flowing.The condition of resonance that look over from the center reference planes this moment can be expressed as:
ω=2 π f wherein, resonance frequency centered by f, C
LBe the capacitance of described loading capacitance 20, C is the capacitance of variable capacitance diode under different voltages, Y
1The characteristic admittance of this half-wavelength Stepped Impedance resonator mid portion microstrip line, Y
2The characteristic admittance of these half-wavelength Stepped Impedance resonator both sides part microstrip lines (the first rectangular microstrip line 5, the 9th rectangular microstrip line 13), θ
1, θ
2It is the electrical length of corresponding microstrip line.
Work as C
LWhen equaling 0pF, following formula can be write:
The common mode resonance condition of 1/2nd wavelength Stepped Impedance resonators during loading capacitance not namely.If the resonator of a center loaded electric capacity and center not resonator of loading capacitance are coupled, as long as both distances are enough large, the coupling coefficient between them can be thought zero.Therefore, can be in the situation that do not affect the differential mode resonance frequency, effective common-mode noise that suppresses in the Whole frequency band scope.
As shown in fig. 1, exist three coupling paths in the middle of two half-wavelength Stepped Impedance resonators, the magnetic coupling intensity that wherein is comprised of middle the 5th rectangular microstrip line 9 and the 13 rectangular microstrip line 19 parallel couplings is higher, is main coupling path, mainly is responsible for the transmission of energy.And on the resonator both sides, formed respectively secondary coupling path by the first rectangular microstrip line 5, the 9th rectangular microstrip line 13 and the 12 rectangular microstrip line 17, the 14 rectangular microstrip line 18, take electric coupling as main, can offset the excessive magnetic coupling of a part in secondary coupling path.By controlling the spacing between secondary coupling path coupling line, can control flexibly the power of electric coupling, and then control the mode that bandwidth changes.Wherein concrete principle can be with reference to the analysis in " S.J.Park and G. M.Rebeiz; Low-loss two-pole tunable filters with three different predefined band width characteristics; IEEE Trans.Microw.Theory Tech.; vol.56; no.5; pp.1137-1148, May2008. ".
The radio frequency electrically adjusted band-pass filter with bandwidth control that relates in the present invention can realize that absolute bandwidth or relative bandwidth diminish, become large or constant with centre frequency.For the ease of showing, chosen below the mode of operation of constant absolute bandwidth and the mode of operation of constant relative bandwidth in embodiment, but be not confined to this two kinds of bandwidth control forms.Below in embodiment 1 and embodiment 2, realize respectively the balanced type electrically tunable filter that has the constant absolute bandwidth of 95MHz and have 9.8% constant relative bandwidth, be produced on dielectric constant and be 2.2, thickness is on the medium substrate of 0.8mm.Variable capacitance diode is selected the silicon variable capacitance diode JSV2S71E of Toshiba.
Embodiment 1: the radio frequency electrically adjusted filter of balanced type of realizing having the constant absolute bandwidth of 95MHz
The radio frequency electrically adjusted filter construction of balanced type that operating frequency has a constant absolute bandwidth of 95MHz at 733MHz-1603MHz as shown in Figure 1.Design parameter is: the first long 4.3mm of rectangular microstrip line 5, wide 1.2mm; The second long 3mm of rectangular microstrip line 6, wide 1mm; The 3rd long 11mm of rectangular microstrip line 7, wide 1mm; The 5th long 8mm of rectangular microstrip line 9, wide 1mm; Ground connection via hole 21 centers that are connected with the 11 rectangular microstrip line 4 and the distance of the 5th rectangular microstrip line 9 are 0.8mm; The appearance value of all capacitances is 10pF; The appearance value of the electric capacity 20 that loads in the middle of the second half-wavelength Stepped Impedance resonator is 10pF; The first rectangular microstrip line 5(the 5th rectangular microstrip line 13) and the 12 rectangular microstrip line 17(the 13 rectangular microstrip line 18) between distance be 0.2mm; Distance between the 9th rectangular microstrip line 9 and the 14 rectangular microstrip line 19 is 0.15mm; Distance between the tenth rectangular microstrip line 3 and the 3rd rectangular microstrip line 7 is 0.12mm, and the distance between the 11 rectangular microstrip line 4 and the 14 rectangular microstrip line 8 is also 0.12mm.Fig. 4 has provided the result that the filter that utilizes above-mentioned parameter design carries out emulation and actual measurement, and wherein emulation and actual measurement are respectively to complete with the business electromagnetism ADS of simulation software and the N5230C PNA-L network analyzer of Agilent company.Fig. 4 a is under this filter differential mode working condition, the emulation when six different bias voltages and test transmission characteristic, and transverse axis represents frequency, the longitudinal axis represents the differential mode transmission characteristic | S
Dd21|.Fig. 4 b is depicted as reflection characteristic corresponding under this filter differential mode working condition, and transverse axis represents frequency, and the longitudinal axis represents return loss | S
Dd11|.By Fig. 4 a and Fig. 4 b as seen, during constant absolute bandwidth, the band connection frequency of filter can be transferred to 1603MHz from 733MHz, has 74.5% relative adjustment scope.To all tuning states, between 2.5dB, all lower than-10dB, three dB bandwidth is 95 ± 10MHz to return loss to the in-band insertion loss of measurement, substantially keeps constant at 5.7dB.To all tuning states, its second harmonic frequency has realized all higher than 3GHz the purpose that stopband is widened preferably.Fig. 4 c has shown under the common mode working condition inhibition to common-mode noise, and as seen common mode inhibition is all lower than-20dB in whole frequency range, and the common mode inhibition in passband can reach-40dB, far away higher than desired in communication system-20dB common mode inhibition level.
Embodiment 2: the radio frequency electrically adjusted filter of balanced type that realization has 9.8% constant relative bandwidth
The radio frequency electrically adjusted filter construction of balanced type that 726MHz-1625MHz has 9.8% a constant relative bandwidth as shown in Figure 1.Design parameter is: the first long 4.3mm of rectangular microstrip line 5, wide 1.3mm; The second long 3mm of rectangular microstrip line 6, wide 1mm; The 3rd long 11mm of rectangular microstrip line 7, wide 1mm; The 5th long 8mm of rectangular microstrip line 9, wide 1mm; Ground connection via hole 21 centers that are connected with the 11 rectangular microstrip line 4 and the distance of the 5th rectangular microstrip line 9 are 0.8mm; The appearance value of all capacitances is 10pF; The appearance value of the electric capacity 20 that loads in the middle of the second half-wavelength Stepped Impedance resonator is 10pF; The first rectangular microstrip line 5(the 5th rectangular microstrip line 13) and the 12 rectangular microstrip line 17(the 13 rectangular microstrip line 18) between distance be 0.4mm; Distance between the 9th rectangular microstrip line 9 and the 14 rectangular microstrip line 19 is 0.15mm; Distance between the tenth rectangular microstrip line 3 and the 3rd rectangular microstrip line 7 is 0.12mm, and the distance between the 11 rectangular microstrip line 4 and the 14 rectangular microstrip line 8 is also 0.12mm.Fig. 5 has provided the result that the filter that utilizes above-mentioned parameter design carries out emulation and actual measurement, and wherein emulation and actual measurement are respectively to complete with the business electromagnetism ADS of simulation software and the N5230C PNA-L network analyzer of Agilent company.Fig. 5 a is under this filter differential mode working condition, the emulation when six different bias voltages and test transmission characteristic, and transverse axis represents frequency, the longitudinal axis represents the differential mode transmission characteristic | S
Dd21|.Fig. 5 b is depicted as reflection characteristic corresponding under this filter differential mode working condition, and transverse axis represents frequency, and the longitudinal axis represents return loss | S
Dd11|.By Fig. 5 a and Fig. 5 b as seen, during Constant relative bandwidth, the band connection frequency of filter can be transferred to 1625MHz from 726MHz, has 76.5% relative adjustment scope.To all tuning states, between 1.7dB, return loss is all lower than-12dB at 6.0dB for the in-band insertion loss of measurement.The 3dB relative bandwidth is 9.8% ± 1.2%, substantially constant.To all tuning states, its second harmonic frequency has realized all higher than 3GHz the purpose that stopband is widened preferably.Fig. 5 c has shown under the common mode working condition inhibition to common-mode noise, and as seen common mode inhibition is all lower than-20dB in whole frequency range, and the common mode inhibition in passband can reach-40dB, far away higher than desired in communication system-20dB common mode inhibition level.
By finding out in above two embodiment, have described a balanced type radio frequency electrically adjusted band-pass filter that bandwidth controls, only need change the coupling space (distances that the first rectangular microstrip line 5 and the 12 rectangular microstrip line are 17) in secondary coupling, can control bandwidth with the variation of frequency.
The present invention is based on the balanced structure of mirror image symmetry, equivalence is band pass filter under difference mode signal, and inhibited for the common mode disturbances in broad frequency band.By introducing many coupling paths, realized that the bandwidth when centre frequency is tuning is controlled.Need not change structure, only need regulate several structural parameters and just can realize that multi-form bandwidth controls, satisfied different application demands.Stopband has been widened in the introducing of Stepped Impedance resonator, has avoided the interference of high frequency clutter to system.By the parameter of adjusted design, this structure can realize the balanced type electrically adjusted band-pass filter that various frequencies, bandwidth and bandwidth are controlled.
The above is only preferred embodiments of the present invention, and is in order to limit the present invention, within the spirit and principles in the present invention not all, any modification of doing, is equal to replacement, improvement etc., within all should being included in protection scope of the present invention.
Claims (8)
1. one kind has the balanced type radio frequency electrically adjusted band-pass filter that bandwidth is controlled, it is characterized in that, comprise the microstrip structure on upper strata, the grounded metal of interlayer substrate and lower floor, the microstrip structure on upper strata is attached to interlayer plate upper surface, and interlayer plate lower surface is grounded metal;
The microstrip structure on described upper strata comprises two half-wavelength Stepped Impedance resonators, two input feeding networks, two outputs feeding network, two input ports and two output ports; Wherein each half-wavelength Stepped Impedance resonator includes one section microstrip line and two variable capacitance diodes, described two variable capacitance diodes are connected to the two ends of microstrip line, wherein the interlude impedance of microstrip line is different with both sides, consist of one section about in the microstrip line of point-symmetric Stepped Impedance; The centre of one of them half-wavelength Stepped Impedance resonator is loaded with for the electric capacity that absorbs common-mode signal; Two input feeding networks with are connected an output feeding network and include 50 ohm microstrip, capacitance and the coupled microstrip line that connects successively, the other end of coupled microstrip line has the ground connection via hole; Two input ports are connected with 50 ohm microstrip of two input feeding networks respectively, two output ports also are connected with 50 ohm microstrip of two output feeding networks respectively, and the characteristic impedance of above-mentioned two input ports and two output ports is 50 ohm; Input feeding network and the coupling of the first half-wavelength Stepped Impedance resonator for two, the first half-wavelength Stepped Impedance resonator and the coupling of the second half-wavelength Stepped Impedance resonator, the second last half-wavelength Stepped Impedance resonator is coupled with two output feeding networks respectively, and whole filter construction is all symmetrical up and down.
2. according to claim 1 have a balanced type radio frequency electrically adjusted band-pass filter that bandwidth is controlled, it is characterized in that, the first half-wavelength Stepped Impedance resonator comprises the first variable capacitance diode [14] that connects successively, the first rectangular microstrip line [5], the second rectangular microstrip line [6], the 3rd rectangular microstrip line [7], the 4th rectangular microstrip line [8], the 5th rectangular microstrip line [9], the 6th rectangular microstrip line [10], the 7th rectangular microstrip line [11], the 8th rectangular microstrip line [12], the 9th rectangular microstrip line [13], the second variable capacitance diode [15], the anode of the first variable capacitance diode [14] and the second variable capacitance diode [15] all passes the intermediate medium substrate and is connected with the lower floor grounded metal, the second half-wavelength Stepped Impedance resonator is identical with the first half-wavelength Stepped Impedance resonator structure, is loaded with in the middle of it for the electric capacity [20] that absorbs common-mode signal, and the other end of electric capacity [20] passes the interlayer substrate and is connected with the lower floor grounded metal, above-mentioned two half-wavelength Stepped Impedance resonators are arranged into left and right, equal symmetrical structure up and down together.
3. according to claim 1 have a balanced type radio frequency electrically adjusted band-pass filter that bandwidth is controlled, it is characterized in that, input first in feeding network for two and input feeding network by 50 ohm of rectangular microstrip lines [1], capacitance [2], the tenth rectangular microstrip line [3], the 11 rectangular microstrip line [4] connects and composes in turn, wherein the tenth rectangular microstrip line [3] and the 11 rectangular microstrip line [4] consist of the parallel coupling structure in order to feed with the first half-wavelength Stepped Impedance resonator, the 11 rectangular microstrip line [4] end passes the interlayer substrate by ground connection via hole [21] and is connected with the lower floor grounded metal, the structure of the second input feeding network is identical with the first input feeding network, two output feeding networks are identical with two input feeding network structures, two input feeding networks, two outputs feeding networks, two input ports, two output ports and above-mentioned two half-wavelength Stepped Impedance resonators are arranged into left and right, equal symmetrical structure up and down together.
4. according to claim 1 have a balanced type radio frequency electrically adjusted band-pass filter that bandwidth is controlled, it is characterized in that, the 12 rectangular microstrip line [17], the 13 rectangular microstrip line [19], the 14 parallel placement of rectangular microstrip line [18] corresponding in the first rectangular microstrip line [5] of the first half-wavelength Stepped Impedance resonator, the 5th rectangular microstrip line [9] and the 9th rectangular microstrip line [13] respectively with the second half-wavelength Stepped Impedance resonator consist of three sections interstage coupling structures.
5. according to claim 1 have a balanced type radio frequency electrically adjusted band-pass filter that bandwidth is controlled, it is characterized in that, the second rectangular microstrip line [6] of the first half-wavelength Stepped Impedance resonator, the 3rd rectangular microstrip line [7], the 4th rectangular microstrip line [8], the 5th rectangular microstrip line [9], the 6th rectangular microstrip line [10], the 7th rectangular microstrip line [11], the 8th rectangular microstrip line [12] have identical resistance value, the first rectangular microstrip line [5] and the 9th rectangular microstrip line [13] have identical resistance value, above-mentioned two resistance value differences, the structure of formation Stepped Impedance.
6. according to claim 1～5 any one are described has a balanced type radio frequency electrically adjusted band-pass filter that bandwidth is controlled, it is characterized in that, the second rectangular microstrip line [6] of the first half-wavelength Stepped Impedance resonator, the 3rd rectangular microstrip line [7], the 4th rectangular microstrip line [8], the 5th rectangular microstrip line [9], the 6th rectangular microstrip line [10], the 7th rectangular microstrip line [11], the 8th wide 0.2～2mm of rectangular microstrip line [12], the first rectangular microstrip line [5] and the 9th wide 0.2～2mm of rectangular microstrip line [13], long 2～the 10mm of the first rectangular microstrip line [5], long 3～the 10mm of the second rectangular microstrip line [6], long 5～the 20mm of the 3rd rectangular microstrip line [7], long 3～the 10mm of the 4th rectangular microstrip line [8], long 4～the 20mm of the 5th rectangular microstrip line [9], the appearance value of all capacitances is the same and all more than 6pF, in the middle of the second half-wavelength Stepped Impedance resonator, the capacitance of loading capacitance is 6～100 pF, distance between the first rectangular microstrip line 5 and the 12 rectangular microstrip line [17] is 0.1～1mm, distance between the 9th rectangular microstrip line [13] and the 14 rectangular microstrip line [18] is also 0.1～1mm, distance between the 5th rectangular microstrip line [9] and the 13 rectangular microstrip line [19] is 0.1～0.5mm.
7. the described balanced type radio frequency electrically adjusted band-pass filter with bandwidth control of according to claim 1～5 any one, is characterized in that the dielectric constant of medium substrate
ε rBeing 2～10, is highly 0.2～2mm.
8. the balanced type radio frequency electrically adjusted band-pass filter with bandwidth control according to claim 6, is characterized in that the dielectric constant of medium substrate
ε rBeing 2～10, is highly 0.2～2mm.
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