CN105789784A - Micro-strip tunable radio-frequency filter - Google Patents

Micro-strip tunable radio-frequency filter Download PDF

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Publication number
CN105789784A
CN105789784A CN201610152783.4A CN201610152783A CN105789784A CN 105789784 A CN105789784 A CN 105789784A CN 201610152783 A CN201610152783 A CN 201610152783A CN 105789784 A CN105789784 A CN 105789784A
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micro
strip
tunable
microstrip line
magnetic coupling
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CN105789784B (en
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向乾尹
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Southwest Jiaotong University
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P1/00—Auxiliary devices
    • H01P1/20—Frequency-selective devices, e.g. filters
    • H01P1/201—Filters for transverse electromagnetic waves
    • H01P1/203—Strip line filters

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Abstract

The invention discloses a micro-strip tunable radio-frequency filter and relates to the field of tunable radio-frequency band-pass filters. The micro-strip tunable radio-frequency filter comprises a substrate with a grounded metal backboard on the lower surface and a micro-strip structure positioned on the upper surface of the substrate, wherein the micro-strip structure comprises two sections of magnetic coupling feeder lines (2) arranged in parallel; eudipleural half-wavelength tunable resonators are arranged between the two sections of the magnetic coupling feeder lines (2); the two half-wavelength tunable resonators are coupled to each other through two sections of third micro-strip lines (7); first micro-strip lines (5) of the two half-wavelength tunable resonators are coupled to the magnetic coupling feeder lines (2) close to the first micro-strip lines; and one ends of the two magnetic coupling feeder lines (2) are grounded through via hole grounding points (3) while the other ends of the two magnetic coupling feeder lines (2) are connected with input or output micro-strip lines (1). The invention provides the micro-strip tunable radio-frequency filter which is based on electric coupling, has a coupling coefficient increased along with resonant frequency reduction and can realize stable bandwidth. The device structure lays a foundation for developing and constructing complicated tunable filters such as a high-performance cross-coupling filter and the like in the future.

Description

A kind of micro-strip tunable radio frequency wave filter
Technical field
The present invention relates to tunable radio frequency band filter, in particular, a kind of micro-strip tunable radio frequency filter circuit with constant absolute bandwidth.
Background technology
In today that information technology develops rapidly, microwave communication frequency resource becomes growing tension, and the application indexes of microwave filter is had higher requirement.Therefore develop high performance wave filter in the short term and become the requirement of key technology.This certainly will require to enter microwave filter deeper into research.
Tunable radio frequency wave filter is the core devices of multifrequency, frequency hopping, restructural radio-frequency front-end, and one of its key performance is the stablizing of pass-band performance in tuning process.Tunable radio frequency wave filter is generally faced with defect: be especially embodied in Modern Communication System, the absolute bandwidth of many wireless channels is invariable, therefore, when tunable optic filter is applied in this occasion, it is necessary to when tuning mid frequency, the absolute bandwidth of passband and waveform keep invariable.But, in prior art, along with the change of mid frequency, absolute bandwidth is acute variation often.
Theoretical according to tradition (fixed frequency responses) filter synthesis, the normalized frequency response characteristic of wave filter can be determined by its normalizated unit transformation matrix (Metzler matrix), and Metzler matrix can be determined by the coupling matrix (k matrix) between resonators at different levels:
M i , j = k i , j f 0 A B W , ( i , j = 1 , 2 , ... ) - - - ( 1 )
Wherein, ABW is passband absolute bandwidth, f0It it is passband central frequency；ki,j(i, j=1,2 ...) represent as viewed from the coefficient of coup between source i-stage and j level resonator.To obtain ABW stable in tuning process, then need stable ki,j, f0.Need for this to realize coefficient of coup ki,jWith passband central frequency f0Decline and increase.
For basic LC coupled resonance loop, its coupling channel unity-coefficient-of-coupling k can be written as:
| k |=| MC-EC | (2)
Wherein, MC=Lm/ L is magnetic coupling coefficient (LmRepresent that between resonator, equivalent coupled inductance, L are resonator equivalent tank inductance), EC=Cm/ C is electric coupling coefficient (CmRepresent that between resonator, equivalent binding capacitance, C are resonator equivalent tank electric capacity).The resonant frequency of LC resonant tank can be similar to and be written as:
f 0 = 1 2 π L C - - - ( 3 )
So, it is possible to realize tuning by L, C, again through LmAnd CmRealize coefficient of coup regulation and control further.But the high-performance that RF microelectronic technique is supported at present, the electricity being easily integrated adjust device main or semiconductor variable container piece.And couple electric capacity CmLess, it is difficult to direct regulation and control.Therefore existing major part tunable filter mainly adopts magnetic coupling to be that main, thermocouple is combined into auxiliary hybrid coupled mode.
By formula (2) and (3) it can be seen that along with the increase of C, its resonant frequency declines, and be auxiliary owing to magnetic is main, electricity, therefore its coefficient of coup will rise, and regulate and control slope by coupling the ratio of electric capacity and resonant capacitance, thus the ABW stablized in tuning process.Correlation technique is found in the many scientific papers delivered, as: " Sang-JunePark；Rebeiz,G.M.,Low-LossTwo-PoleTunableFiltersWithThreeDifferentPredefinedBandwidthCharacteristics,inMicrowaveTheoryandTechniques,IEEETransactionson,vol.56,no.5,pp.1137-1148,May2008”、“ChuanGe；Xiao-WeiZhu, Highly-SelectiveTunableBandpassFilterWithTwo-PathMixedCo upling, inMicrowaveandWirelessComponentsLetters, IEEE, vol.24, no.7, pp.451-453, July2014 " etc..
But, magnetic coupling is that main, thermocouple is combined into auxiliary hybrid coupled mode be combined into main, magnetic coupling with thermocouple be compared with auxiliary hybrid coupled mode, limit the design of the tunable filter topologys such as cross-couplings, for this reason, it is necessary to build thermocouple, to be combined into main, magnetic coupling be auxiliary tunable filter bandwidth antihunt means.
Summary of the invention
In view of the drawback of prior art, it is an object of the invention to, it is provided that a kind of thermocouple is combined into main, to realize stablizing bandwidth micro-strip tunable radio frequency wave filter.
Technical scheme is as follows:
A kind of micro-strip tunable radio frequency wave filter, including the substrate that: lower surface is grounded metal backboard and the microstrip structure being positioned at substrate top surface, it is characterized in that, described microstrip structure includes arranged in parallel two section magnetic coupling feeder line 2, is provided with symmetrical two sections of U-shaped micro-strip folding lines between two sections of magnetic coupling feeder lines 2；Described U-shaped micro-strip folding line by first microstrip line the 5, second microstrip line 6 and the 3rd microstrip line 7 be linked in sequence and formed, the 3rd microstrip line 7 away from the second microstrip line 6 one end for open circuit；The second of first microstrip line 5 of described U-shaped micro-strip folding line away from microstrip line 6 one end by after a tunable capacitor 4 through hole earth point 3 ground connection so that U-shaped micro-strip folding line and tunable capacitor 4 constitute a half-wavelength tunable resonator；Being intercoupled by two section of the 3rd microstrip line 7 between two half-wavelength tunable resonators, the magnetic coupling feeder line 2 that the first microstrip line 5 of two sections of U-shaped micro-strip folding lines is adjacent to respectively intercouples；The magnetic coupling feeder line 2 that first microstrip line 5 of two half-wavelength tunable resonators is adjacent to respectively intercouples, and one end of two sections of magnetic coupling feeder lines 2 is through via earth point 3 ground connection, and the other end connects input or output microstrip line 1 respectively.
Coupling length between said two half-wavelength tunable resonator is within operating frequency place quarter-wave scope；
Described tunable capacitor 4 can be the suitable tunable capacitors such as variable displacement type diode, mechanical type tunable capacitor, quasiconductor numeral tunable capacitor；When wherein tunable capacitor is varactor, the anode of varactor passes through via earth point 3 ground connection, and its negative electrode carries out voltage bias by microstrip line 6 outer meeting resistance R；
The characteristic impedance of the port microstrip line 1 of described input and outfan is 50 ohm；
Described substrate can be the one in any suitable flat structural panels such as low-loss politef, ferrite, glass.
According to transmission line theory and in conjunction with shown in accompanying drawing 1, in half-wavelength tunable resonator, the 3rd microstrip line 7 is away from the open end that one end is tunable resonator of the second microstrip line 6, and the electric field at open end is the strongest, magnetic field is the most weak.Simultaneously with open end for the quarter-wave of starting point, leave inside tunable resonator terminal more remote time, its electric field weakens gradually, magnetic field strengthens gradually.So, when the length of the 3rd microstrip line 7 meets within the scope of quarter-wave, it is ensured that its internal electric field is distributed more than Distribution of Magnetic Field.
Characterize electric field, magnetic field with the open end of the 3rd microstrip line 7 to second microstrip line the 6, first microstrip line 5, the voltage of tunable capacitor 4, CURRENT DISTRIBUTION, then voltage and current is successively in half-wave cosine distribution and half-wave Sine distribution.Simultaneously along with the increase of tunable capacitor 4, the operation wavelength increase and operating frequency that cause tunable resonator are reduced, its internal electric field and Distribution of Magnetic Field will stretch, thus the electric field caused in structure 0 in two half-wavelength tunable resonator coupled structures increases, magnetic field reduces, unity-coefficient-of-coupling declines with operating frequency and increases.
Compared to prior art, the invention have the advantages that
Input and output direct feed of the present invention, is that wave filter Insertion Loss is only small；Strong adaptability, applied range, it is possible to improve according to the actual requirements, flexible design is simple, it is possible to regulate resonant operational frequency range by changing tunable capacitor kind, model or resonator parameter etc.；The present invention can realize thermocouple and be combined into main, unity-coefficient-of-coupling and decline with operating frequency and increase thus realizing in relatively wide mid frequency tuning range, and bandwidth still can keep relative stability.
Accompanying drawing explanation
Fig. 1 is micro-strip tunable radio frequency band filter microstrip circuit structure chart of the present invention.
Fig. 2 is resonator normalized voltage, CURRENT DISTRIBUTION schematic diagram after the different capacitance electric capacity of loading.
Fig. 3 is the microstrip circuit of an embodiment of micro-strip tunable radio frequency band filter electric coupling of the present invention.
Fig. 4 is the simulation waveform of embodiment of the present invention circuit.
Fig. 5 is the bandwidth characteristic statistics of embodiment of the present invention circuit.
Fig. 6 is invention electromechanical coupling characteristic checking circuit.
Fig. 7 is electromechanical coupling characteristic of the present invention checking waveform.
Detailed description of the invention
Accompanying drawing is coordinated to explain detailedly with specific embodiment below, in order to be easier to understand the know-why of the present invention.
The technical scheme of micro-strip tunable radio frequency wave filter of the present invention is as it is shown in figure 1, in substrate top surface, microstrip structure includes the electric coupling structure 0 of two ports, two symmetrical half-wavelength tunable resonator formation；Said two port respectively input port and output port, two-port is connected with magnetic coupling feeder line 2 by 50 ohm characteristic impedance microstrip lines 1；The magnetic coupling feeder line 2 at two ends is by tunable capacitor earth point 3 ground connection, and forms magnetic coupling feed, tunable resonator energy feed-in two coupled respectively with the first microstrip line 5 in two tunable resonators, it is achieved stablizing of tuning process median filter bandwidth.
Single half-wavelength tunable resonator micro-strip part includes first microstrip line the 5, second microstrip line the 6, the 3rd microstrip line 7, definition micro-strip part total length is d, the length of microstrip line 7 is s, so it is the coupled structure of s that the tunable resonator of coupling forms coupling length from respective open end.In conjunction with resonator normalized voltage, CURRENT DISTRIBUTION schematic diagram after the loading difference capacitance electric capacity of Fig. 2, according to transmission line theory, from the open end of the 3rd microstrip line 7 to the distribution of the voltage and current of tunable capacitor 4 such as Fig. 2 from left to right in half-wave cosine and Sine distribution.When the capacitance of tunable capacitor 4 is more big, its equivalent length is more big (is designated as Δ d1, operating frequency is more low, and corresponding voltage and current is distributed as V1And I1.When the capacitance of tunable capacitor 4, more hour its equivalent length is more little (is designated as Δ d2), operating frequency is more high, and corresponding voltage and current is distributed as V2And I2。
Increase along with tunable capacitor, the operation wavelength increase and operating frequency that cause tunable resonator are reduced, its internal electric field and Distribution of Magnetic Field will stretch, thus cause the electric field in microstrip line 7 to increase, magnetic field reduces, in structure type 0, unity-coefficient-of-coupling between tunable resonator declines with operating frequency and increases.
As it is clear from fig. 2 that two half-wavelength tunable radio-frequency filters are in the coupled structure part that length is s, its voltage's distribiuting is more than CURRENT DISTRIBUTION, so being be combined into main coupling type with thermocouple.
Simultaneously, reduction along with frequency, the i.e. increase of resonator equivalent length, voltage's distribiuting at coupling unit increases, CURRENT DISTRIBUTION reduces, increase thus realizing overall electric coupling coefficient along with the reduction of resonant frequency, meet the requirement of formula (1), it is achieved the absolute bandwidth of tunable optic filter stablizing in tuning process.
It is further elaborated below in conjunction with example:
Embodiment 1:
A kind of scheme adopting varactor SMV1405-SC70 to be tunable capacitor, major parameter is as it is shown on figure 3, D in figure1And D2Being SMV1405-SC70, include two diodes inside each encapsulation, being connected by the two of SMV1405-SC70 anodes uses.D1And D2Anode by via earth point 3 ground connection of each resonator, negative electrode by the microstrip line 6 of each resonator by 51k Ω resistance R1And R2Carry out voltage Vc biasing.When Vc changes at 0～30V, the capacitance of internal two diodes in parallels of SMV1405-SC70 can about change between 1.26pF～5.34pF.The politef microwave backing material that substrate adopts relative dielectric constant to be 2.65, loss tangent angle is 0.001, thickness is 0.8mm.
By setting specific microstrip structure parameter, the response characteristic of different frequency range, bandwidth can be obtained.Transmission characteristic shown in Fig. 4 be set microstrip line 5, the simulation result of microstrip line 6, microstrip line 7 passive structures when being constituted width 2.6mm, long 18mm, corresponding statistical property is as shown in Figure 5, this embodiment is as case, it is achieved that passband is tunable between 1.95GHz～2.90GHz.Its absolute bandwidth changes between 182MHz～194MHz, fluctuates less, highly stable.Simultaneously its relative bandwidth increases along with the reduction of tuned frequency, the requirement of coincidence formula (1), it was demonstrated that the effectiveness that the coefficient of coup is regulated and controled by the embodiment of the present invention.
Embodiment 2:
Adopt varactor SMV1405-SC70 for introducing coupling electric capacity C based on tunable capacitor by embodiment 1, this embodiment can verify that the present invention is electric coupling structure, major parameter as shown in Figure 6, when C=-0.05pF, 0 ,+0.05pF time, its simulated properties is as shown in Figure 7.Visible, filter bandwidht increases along with the increase of C, by formula (1), (2) it can be seen that its coupling is combined into master with thermocouple.
Above in association with accompanying drawing, embodiments of the invention are set forth; but the invention is not limited in above-mentioned detailed description of the invention; above-mentioned detailed description of the invention is merely schematic; rather than it is restrictive; those of ordinary skill in the art is under the enlightenment of the present invention; without departing under present inventive concept and scope of the claimed protection situation, it may also be made that a lot of form, these belong within the protection of the present invention.

Claims (4)

1. a micro-strip tunable radio frequency wave filter, including the substrate that: lower surface is grounded metal backboard and the microstrip structure being positioned at substrate top surface, it is characterized in that, described microstrip structure includes arranged in parallel two section magnetic coupling feeder line (2), is provided with symmetrical two sections of U-shaped micro-strip folding lines between two sections of magnetic coupling feeder lines (2)；Described U-shaped micro-strip folding line is linked in sequence by the first microstrip line (5), the second microstrip line (6) and the 3rd microstrip line (7) and forms, and the 3rd microstrip line (7) is open circuit away from one end of the second microstrip line (6)；The open end of first microstrip line (5) of described U-shaped micro-strip folding line passes through a tunable capacitor (4) by hole earth point (3) ground connection so that U-shaped micro-strip folding line and tunable capacitor (4) constitute a half-wavelength tunable resonator；Being intercoupled by two section of the 3rd microstrip line (7) between two half-wavelength tunable resonators, the magnetic coupling feeder line (2) that first microstrip line (5) of two half-wavelength tunable resonators is adjacent to respectively intercouples；One end of two sections of magnetic coupling feeder lines (2) is through via earth point (3) ground connection, and the other end connects input or output microstrip line (1) respectively.
2. micro-strip tunable radio frequency wave filter according to claim 1, it is characterised in that the coupling length between described two section of the 3rd microstrip line (7) is within operating frequency place quarter-wave scope.
3. micro-strip tunable radio frequency wave filter according to claim 2, it is characterised in that the characteristic impedance of described input or output microstrip line (1) is 50 ohm.
4. the micro-strip tunable radio frequency wave filter according to claim 1,2 or 3, it is characterized in that, described tunable capacitor (4) is varactor, and the anode of varactor is by via earth point (3) ground connection, its negative electrode carries out voltage bias by the second microstrip line (6) outer meeting resistance R.
CN201610152783.4A 2016-03-17 2016-03-17 A kind of micro-strip tunable radio frequency filter Active CN105789784B (en)

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106972227A (en) * 2017-03-23 2017-07-21 西南交通大学 A kind of high-order variable band-pass filter based on cross coupling structure
CN109599650A (en) * 2018-11-06 2019-04-09 杨涛 Restructural balun filter based on mini strip line resonator
CN111781586A (en) * 2020-07-10 2020-10-16 成都镭迪昇科技有限公司 Microwave sensor based on electromagnetic hybrid coupling filter structure
CN114824699A (en) * 2022-04-22 2022-07-29 成都威频科技有限公司 Capacitor and inductor loading hybrid resonant thin-film filter

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101894995A (en) * 2010-05-19 2010-11-24 华南理工大学 Radio frequency electrically adjusted band-pass filter with constant absolute bandwidth
CN102324599A (en) * 2011-05-27 2012-01-18 华南理工大学 Balanced type radio frequency voltage tunable bandpass filter with constant absolute bandwidth

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101894995A (en) * 2010-05-19 2010-11-24 华南理工大学 Radio frequency electrically adjusted band-pass filter with constant absolute bandwidth
CN102324599A (en) * 2011-05-27 2012-01-18 华南理工大学 Balanced type radio frequency voltage tunable bandpass filter with constant absolute bandwidth

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* Cited by examiner, † Cited by third party
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QIANYIN XIANG: "Electrical Tunable Microstrip LC Bandpass Filters With Constant Bandwidth", 《IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES》 *
SANG-JUNE PARK: "Low-Loss Two-Pole Tunable Filters With Three Different Predefined Bandwidth Characteristics", 《IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES》 *
向乾尹: "平面小型化可调射频滤波器研究", 《中国博士学位论文全文数据库》 *

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106972227A (en) * 2017-03-23 2017-07-21 西南交通大学 A kind of high-order variable band-pass filter based on cross coupling structure
CN106972227B (en) * 2017-03-23 2019-02-26 西南交通大学 A kind of high-order variable band-pass filter based on cross coupling structure
CN109599650A (en) * 2018-11-06 2019-04-09 杨涛 Restructural balun filter based on mini strip line resonator
CN111781586A (en) * 2020-07-10 2020-10-16 成都镭迪昇科技有限公司 Microwave sensor based on electromagnetic hybrid coupling filter structure
CN114824699A (en) * 2022-04-22 2022-07-29 成都威频科技有限公司 Capacitor and inductor loading hybrid resonant thin-film filter

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