CN112993498A

CN112993498A - Suspension strip line ultra-wideband adjustable zero-point band-pass filter

Info

Publication number: CN112993498A
Application number: CN202110183869.4A
Authority: CN
Inventors: 徐照旭; 钟鸣海; 蔡喆
Original assignee: Southwest Electronic Technology Institute No 10 Institute of Cetc
Current assignee: Southwest Electronic Technology Institute No 10 Institute of Cetc
Priority date: 2021-02-10
Filing date: 2021-02-10
Publication date: 2021-06-18
Anticipated expiration: 2041-02-10
Also published as: CN112993498B

Abstract

The suspension strip line ultra-wideband zero-point-adjustable band-pass filter disclosed by the invention is small in area, high in integration level and excellent in standing wave performance. The invention is realized by the following technical scheme: at least two resonators and a double-layer metallized coupling via hole which are arranged between double rows of metallized coupling via holes are distributed on the front and back surfaces of the dielectric substrate, each resonator is composed of a main resonator positioned on one side and a resonator loading capacitor positioned on the other side, and the resonator loading capacitors of all the resonators are connected with the two sides of the dielectric substrate in a metal mode; the transmission lines at the two ends are connected with the upper layer and the lower layer through a metallized through hole, and each resonator can adjust the self-resonant frequency of the resonator by adjusting the size of a loading capacitor of the resonator on the back of the dielectric substrate. Increasing the size of the capacitive loading part will shift the self-resonant frequency of the resonator towards the lower end of the frequency, decreasing the capacitive loading size on the back of the resonator, and shift the self-resonant frequency of the resonator towards the higher end of the frequency.

Description

Suspension strip line ultra-wideband adjustable zero-point band-pass filter

Technical Field

The invention relates to a radio frequency microwave filter, in particular to a band-pass filter which can be widely applied to the front end of a radio frequency communication system.

Background

A filter is one of indispensable devices in a wireless communication system. With the development of new technologies in the rf/microwave field, filters are also developed toward high performance, miniaturization, high power capacity, light weight, and low cost. In a communication system, signals are subject to interference from ambient noise signals outside the system, as well as harmonic effects within the system due to system nonlinearities, which can significantly degrade the communication quality of the communication system. In order to suppress the interference signals outside the system and the harmonic signals generated by the nonlinearity in the system, a filter is required to be added to the system to ensure that the useful signals can pass through with small loss, and the useless signals can be greatly suppressed. Band pass filters have found wide application in Microwave Integrated Circuits (MICs) and Radio Frequency Integrated Circuits (RFICs) because of their advantages of light weight, small size, low cost, ease of integration, and the like. With the development of communication technology, the spectrum resources are increasingly strained, and in modern communication systems, a high-performance narrow-band-pass filter with low insertion loss in a pass band and high rejection outside the pass band is required. There are generally two approaches to improving out-of-band rejection: firstly, increasing the stage number of the filter; secondly, a transmission zero point is added out of the band. Increasing the number of stages of the filter results in an increase in the overall size of the device, which is not conducive to integration, and increases in-band insertion loss. By adding the transmission zero outside the band, out-of-band rejection can be improved, a compact structure is convenient to design, and the size problem is solved to a certain extent. However, the electric coupling and the magnetic coupling are simultaneously introduced between the resonators, which increases the difficulty of the filter design and complicates the filter design. Although it is convenient to generate transmission zero by using parallel coupled lines, since a one-cavity single-mode structure is used, at least two resonators are required to adjust the bandwidth, so that the overall size of the filter is not compact.

The ultra-wideband technology has the characteristics of simple system structure, low cost, low power consumption, high safety, difficult interference generation, high data transmission rate and the like, and has high performance and high integration level. With the development trend of broadband and miniaturization of communication systems, higher and higher requirements are put on filters. In order to enhance the out-of-band rejection characteristic of the filter, it is required to add transmission zeros to one or both sides of the stop band of the filter to improve the sideband rejection characteristic of the filter.

The suspension strip line is a superior transmission line system, can be used for realizing various types of filters, has smaller current density on a metal layer and smaller electric field intensity on a medium layer compared with a microstrip line and a coplanar waveguide, and thus effectively reduces loss. The suspended strip line structure can provide a high Q value, reduces the insertion loss of the filter and has excellent selectivity. The suspended strip line has the advantages of low loss, excellent temperature performance, high-precision controllable process, good batch consistency and the like, so that the suspended strip line is very suitable for designing broadband microwave components, and a filter designed and manufactured by utilizing the suspended strip line has a multi-octave ultra-wideband, low loss and very high rectangularity. The suspension strip line is a general transmission medium of microwave frequency, and besides lower loss relative to the microstrip line, the suspension strip line can be selectively manufactured into a double-sided circuit. The suspended strip line structure is composed of a medium substrate suspended in the middle of the metal box body and metal conduction bands on the upper side and the lower side or on one side of the medium substrate. The suspension microstrip line mostly adopts side surface grounding, and the peripheral cavity is used as a ground reference plane, so that higher requirements are provided for the processing precision of the outer cavity and the mounting precision of a system. Suspended microstrip lines also have certain limitations. Due to the cavity structure, the volume and the weight are increased to a certain degree. The microstrip-line-mounted structure is typically grounded through a side-wall metal surface, while the suspended microstrip-line substrate is typically partially sandwiched in a peripheral cavity for securing the suspended microstrip-line substrate. When the size of the outer cavity is close to the width of the suspended microstrip line, the impedance is obviously influenced by the size of the cavity. The characteristic impedance and the wavelength of the suspended microstrip line are obviously influenced, and the application of the suspended microstrip line filter is limited to a certain extent.

The existing ultra-wideband filter mainly adopts a high-low pass filter cascade, a micro-strip multi-mode resonance technology, a low temperature co-fired ceramic (LTCC) technology and a Liquid Crystal Polymer (LCP) technology. The mode of cascading high-low pass filters is adopted, which is equivalent to the function of realizing one band-pass filter by two filters, and the size is too large; the microstrip multimode resonance technology is one of the mainstream technologies for realizing the ultra-wideband filter, but because the microstrip multimode resonance technology only has one resonator, the transmission zero point is difficult to be introduced outside the passband in the structural form; the low-temperature co-fired ceramic technology and the liquid crystal polymer technology have complex processing and high cost, and are difficult to introduce transmission zero. After simulation, the filter response is found to be poor, and the standing-wave ratio is larger.

Disclosure of Invention

The invention aims to overcome the defects of the existing ultra-wideband filter and provides the suspended stripline ultra-wideband adjustable zero band-pass filter which is simple and compact in structure, small in area, easy to process, high in integration level, good in expandable characteristic, large in out-of-band rejection and excellent in standing wave performance. The method has universality and good accuracy.

The above object of the present invention can be achieved by the following technical solutions, and a suspended stripline ultra-wideband zero-point-tunable bandpass filter includes: cavity 2 under the metal with pin hole sets up the dielectric substrate 3 between cavity 1, the cavity 2 under the metal on the metal to and adopt the suspension stripline as the wave filter of transmission line on the dielectric substrate 3, its characterized in that: metallized coupling through holes 11 arranged according to linear arrays, at least five resonators distributed between double rows of metallized through holes and a double-layer metallized coupling through hole 10 are arranged on two sides of the length direction of the front and back surfaces of a dielectric substrate (3), wherein a first resonator 5 and a second resonator 6 are fixed on the front surface of the dielectric substrate 3, a third resonator 7, a fourth resonator 8 and a fifth resonator 9 are fixed on the back surface of the dielectric substrate 3, each resonator is connected to a metal ground on one side through a vertical suspension strip line 6-2 to form a capacitance loading type SIR resonator, and a resonator loading capacitor 13 connected to the metal ground on the same side is arranged on the side of a high-impedance end of each resonator; the double-layer metalized coupling via hole 10 on the front surface of the dielectric substrate 3 is connected with the input end 50 ohm transmission line 14 plane microstrip through a section of high impedance line, the double-layer metalized coupling via hole 10 on the back surface of the dielectric substrate 3 is connected with the high impedance section of the third resonator 7, the front surface 50 ohm transmission line and the back surface third resonator are connected in an upper layer and a lower layer through the metalized via hole, each resonator on the back surface of the dielectric substrate 3 is different from each resonator on the front surface of the dielectric substrate 3, the self-resonance frequency of the resonator can be adjusted by adjusting the size of the resonator loading capacitor 13, the self-resonance frequency of the resonator is shifted to the low end or the high end of the frequency, and a source is generated by the double-layer metalized coupling via hole 10 to be in cross coupling with the third resonator 7, so that an adjustable transmission zero point is generated at the.

The invention has the following beneficial effects:

the structure is simple and compact, the area is small, and the processing is easy. The invention adopts the dielectric substrate 3 arranged between the metal upper cavity 1 and the metal lower cavity 2 and the dielectric substrate 3, adopts the suspended strip line as the filter of the transmission line, and the two sides of the dielectric substrate 3 in the length direction are provided with double-layer metallized through holes arranged according to the linear array, and five resonators are distributed between the double-layer metallized through holes, thus the invention has compact structure, small area, low cost and low requirement on processing precision. The size of the resonator is effectively reduced by utilizing the capacitance loading effect, the structure is more compact, the size is smaller, the miniaturization of the ultra-wideband filter is realized, and the ultra-wideband filter is convenient to integrate with a peripheral circuit in the application of a suspended stripline filter.

The integration level is high. The invention fixes a first resonator 5 and a second resonator 6 on the front surface of a dielectric substrate 3, fixes a third resonator 7, a fourth resonator 8 and a fifth resonator 9 on the back surface of the dielectric substrate 3, and each resonator is composed of a main resonator on one side and a resonator loading capacitor 13 on the other side, and the resonator loading capacitors 13 of all the resonators are connected with both sides of the dielectric substrate 3 in a metal manner, so that the integration level is high.

According to the method, a generalized Chebyshev filter comprehensive method is adopted to obtain prototype coupling matrix parameters of the filter, the coupling matrix parameters are mapped to a specific physical structure, the problems that the filter is not flexible enough and cannot generate transmission zero points at any position in the traditional mapping method are solved, the development and development period is shortened, and the research and development efficiency is improved.

Good scalability and high out-of-band rejection. Each resonator adopted by the invention is divided into three parts, namely a low-impedance line part, a high-impedance line part and a resonator loading capacitor 13 positioned on the back of a low-impedance line dielectric slab, all the resonators and the resonator loading capacitors are connected with the two sides of a dielectric substrate 3 in a metal manner, and each high-impedance transmission line realizes the connection of an upper layer and a lower layer through metalized through holes at the two ends of the dielectric substrate 3; has good scalability. According to the actual index requirement, the out-of-band rejection is large by increasing the order of the filter, and the out-of-band rejection characteristic is obviously improved. Compared with the common microstrip band-pass filter, the tunable microstrip band-pass filter has good adjustability. A controllable transmission zero is generated in a low-frequency band outside a passband of the ultra-wideband filter through the double-layer metalized coupling via hole coupling structure. By adjusting the length Ld of the high impedance line segment in the dual-layer metalized coupling via 10, the transmission zero can be moved outside the passband. The direct coupling of the source and the third resonator can be effectively adjusted by adjusting the length of the high-impedance line, so that the out-of-band transmission zero point generates controllable offset, and a powerful means is provided for flexibly realizing the out-of-band rejection characteristic of the filter. The band-pass filter with the adjustable transmission zero position has a continuously adjustable transmission zero at a stop band, and the adjustment range of the zero is from 600MHz to 1200 MH.

The standing wave performance is excellent. The invention adopts the structure that each resonator can adjust the self-resonance frequency of the resonator by adjusting the size of the loading capacitor part of the resonator on the back of the dielectric substrate 3. The self-resonance frequency of the resonator is shifted towards the low-end direction of the frequency, the loading size of the capacitor on the back of the resonator is increased, the self-resonance frequency of the resonator is shifted towards the high-end direction of the frequency, and the loading size of the capacitor on the back of the resonator is reduced. Because the loading capacitor part of the resonator does not exceed the area of the low-impedance section of the resonator, compared with the traditional resonator, the resonator can obviously reduce the resonance frequency of the resonator under the condition of not increasing the size of the filter, thereby realizing good miniaturization performance, and flexibly adjusting the resonance frequency of the resonator to generate good standing wave characteristic in a pass band range during design. All transmission zeros of the traditional band-pass filter are positioned at infinity of a frequency axis, and the generalized Chebyshev function response filter introduces cross coupling between non-adjacent resonant cavities of the filter, so that part or all of the transmission zeros are positioned at the infinity of the frequency axis, and the out-of-band attenuation characteristic of the filter is improved.

According to the filter, by utilizing the comprehensive theory of the filter, the cross coupling of a source and a third resonator is generated through the double-layer metalized coupling through hole 10 designed by the invention, and a transmission zero point can be generated at the low end of the frequency. By adjusting the length Ld of the high impedance line in the double-layer via hole coupling structure, the coupling amount between the source and the third resonator can be adjusted, so that the transmission zero point is shifted. And adjustable transmission zero is formed outside the band, so that the frequency selection characteristic of the microstrip filter is improved.

The invention is suitable for radio frequency microwave communication systems.

Drawings

FIG. 1 is a schematic diagram of a suspended stripline ultra-wideband tunable zero band-pass filter in the invention;

FIG. 2 is a schematic front view of the dielectric plate of FIG. 1;

FIG. 3 is a schematic view of the reverse side of the dielectric sheet of FIG. 2;

FIG. 4 is a graph of a frequency response of an ultra-wideband suspended stripline bandpass filter of an embodiment of the invention;

figure 5 is a graph of the movement of the out-of-band zero of the ultra-wideband suspended stripline band-pass filter with the change of parameters.

In the figure: the resonator comprises a metal upper cavity 1, a metal lower cavity 2, a dielectric substrate 3, a pin 4, a first resonator 5, a second resonator 6, a third resonator 7, a fourth resonator 8, a fifth resonator 9, a double-layer metalized coupling via hole broadband 10, a metalized through hole 11, a metal ground 12, a resonator loading capacitor 13, a 50-ohm transmission line at an input end 14 and a 50-ohm transmission line at an output end 15. (explain: the double-layer metalized coupling via only has one hole physically, so as to realize the connection of the upper and lower patterns, so that the double-layer metalized coupling via is called, and the via plays a role of coupling, so that the coupling via is called).

The present invention will be further described with reference to the following drawings and examples, which should be understood that the examples described herein are intended to illustrate and explain the present invention, and are not intended to limit the present invention.

Detailed Description

See fig. 1-3. In a preferred embodiment described below, a suspended stripline ultra-wideband tunable zero bandpass filter comprises: through the metal upper and lower cavity of butt joint about pin 4, set up on cavity 1, the metal under the dielectric substrate 3 and the dielectric substrate 3 between cavity 2, adopt the filter of suspension stripline as the transmission line, its characterized in that: metallized coupling through holes arranged according to linear arrays are arranged on two sides of the length direction of the dielectric substrate 3, at least five resonators and a double-layer metallized coupling through hole 10 which are arranged between double rows of metallized coupling through holes are distributed on the front surface and the back surface of the dielectric substrate 3, wherein a first resonator 5 and a second resonator 6 are fixed on the front surface of the dielectric substrate 3, a third resonator 7, a fourth resonator 8 and a fifth resonator 9 are fixed on the back surface of the dielectric substrate 3, each resonator is composed of a main resonator positioned on one side and a resonator loading capacitor 13 positioned on the other side, and the resonator loading capacitors 13 of all the resonators are connected with two sides of the dielectric substrate 3 in a metal mode; two ends of the double-layer metalized coupling via hole 10 are provided with a high-impedance line and a metalized via hole, one section of the high-impedance line is positioned on the front surface of the dielectric substrate 3 and connected with the input section 50 ohm transmission line 14, the high-impedance line on the other end is positioned on the back surface of the dielectric substrate 3 and connected with the high-impedance line section of the third resonator 7, the transmission lines at the two ends are connected with the upper layer and the lower layer through a metalized via hole 11, each resonator can adjust the self-resonant frequency of the resonator by adjusting the size of the resonator loading capacitor 13 on the back surface of the dielectric substrate 3, the self-resonant frequency of the resonator is shifted to the low-end direction of the frequency, the back-surface capacitor loading size of the resonator is increased, the self-resonant frequency of the resonator is shifted.

The butt joint surfaces of the upper metal cavity 1 and the lower metal cavity 2 are provided with rectangular through grooves for waveguides, and the dielectric substrate 3 is fixed on the butt joint end planes of the upper metal cavity 1 and the lower metal cavity 2 through pins 4 to form a waveguide cavity together.

The main transmission link path of the signal is that the signal is output from the third resonator 7 to the first resonator 5, the fourth resonator 8, the second resonator 6 and the fifth resonator 9 in sequence through the input end 50 ohm transmission line 14 and finally through the output end 50 ohm transmission line 15; the adjustable zero band-pass filter generates a controllable transmission zero at a low frequency band outside a passband of the ultra-wideband filter through the double-layer metalized coupling via hole 10. By adjusting the length Ld of the high impedance line segment connected by the double-layer metalized coupling via 10, the coupling amount of the source and the third resonator can be changed, so that the out-of-band transmission zero point is controllably offset. According to the comprehensive theory of the filter, the coupling matrix of the filter can be obtained by a generalized Chebyshev comprehensive method according to the design requirement, and the parameters of the coupling matrix are mapped to the HFSS physical model, so that the design is rapidly completed.

The two sides of the dielectric substrate 3 are metal grounds 12, and the resonator loading capacitors 13 of all the resonators are connected with the metal grounds 12 on the two sides of the dielectric substrate 3. The metal ground 12 is provided with a metalized through hole 11 which ensures good metal ground connection on the front side and the back side of the dielectric plate.

In this embodiment, each resonator is composed of three parts, i.e., a high impedance line, a low impedance line and a resonator loading capacitor 13. By adjusting the length of the high impedance line of the resonator loading capacitor 13, the adjusted self-resonant frequency of the first resonator 5 can be obtained.

In this embodiment, the high impedance section of each resonator may be equivalent to an inductor, the low impedance section may be equivalent to a capacitor, and the resonator loading capacitor 13 may be equivalent to a series capacitor. The larger the size of the resonator loading capacitor 13, the larger the equivalent series capacitance value. According to the basic principle of a resonant circuit, the resonant frequency is inversely proportional to the equivalent capacitance. I.e. the larger the resonator loading capacitance 13, the lower the resonator's self-resonator frequency.

In this embodiment, the dielectric constant of the dielectric plate is 3.55-3.6, and the thickness of the dielectric plate is 0.254mm-0.300 mm. The filter has an overall area size of 10mm 22mm-15mm 25mm, and has good miniaturization performance.

See fig. 4. Simulation and test results of an ultra-wideband suspended stripline band-pass filter with an adjustable zero point, wherein S11 represents a return loss parameter of the filter in the embodiment, and S21 represents an insertion loss parameter of the filter in the embodiment. In the embodiment, the center frequency of the passband of the filter is 2GHz, the bandwidth is 850MHz, the relative bandwidth is more than 40%, the out-of-band rejection is more than 60dBc, the spurious frequency appears at 7.7GHz and is 3.85 times of the center frequency, and the filter shows good out-of-band rejection characteristic and spurious rejection characteristic.

Having thus described the embodiments of the present invention in detail, those skilled in the art will appreciate that various modifications and adaptations of the embodiments can be made without departing from the spirit and scope of the present invention. The present patent claims encompass such modifications and variations.

Claims

1. A suspended stripline ultra-wideband tunable zero bandpass filter comprising: cavity (2) under the metal with cotter hole sets up dielectric substrate (3) between cavity (2) under cavity (1), the metal on the metal to and adopt suspension strip line as the wave filter of transmission line on dielectric substrate (3), its characterized in that: metallized coupling through holes (11) arranged according to a linear array, five resonators distributed between double rows of metallized through holes and a double-layer metallized coupling through hole (10) are arranged on two sides of the length direction of the front and back surfaces of a dielectric substrate (3), wherein a first resonator (5) and a second resonator (6) are fixed on the front surface of the dielectric substrate (3), a third resonator (7), a fourth resonator (8) and a fifth resonator (9) are fixed on the back surface of the dielectric substrate (3), each resonator is connected to a metal ground on one side through a vertical suspension strip line (6-2) to form a capacitance loading type SIR resonator, and a resonator loading capacitor (13) connected to the metal ground on the same side is arranged beside a high impedance end of each resonator; the double-layer metalized coupling via hole (10) on the front surface of the dielectric substrate (3) is connected with a planar microstrip of an input end 50 ohm transmission line (14) through a section of high-impedance line, the double-layer metalized coupling via hole (10) on the back surface of the dielectric substrate (3) is connected with a high-impedance section of a third resonator (7), the upper layer and the lower layer of the front surface 50 ohm transmission line and the back surface third resonator are connected through the metalized via hole, the self-resonance frequency of the resonator can be adjusted by adjusting the size of a resonator loading capacitor (13) on different sides of each resonator on the back surface of the dielectric substrate (3) and each resonator on the front surface of the dielectric substrate (3), and the self-resonance frequency of the resonator is shifted towards the low end or the high end of the frequency, cross-coupling of a source to the third resonator (7) is effected through a double-layer metallised coupling via (10) to produce an adjustable transmission zero at the low end of the frequency.

2. The suspended stripline ultra-wideband tunable zero bandpass filter of claim 1, wherein: rectangular through grooves are formed in butt joint surfaces of the metal upper cavity (1) and the metal lower cavity (2), and the medium substrate (3) is fixed to butt joint end planes of the metal upper cavity (1) and the metal lower cavity (2) through pins (4) to form a waveguide cavity together.

3. The suspended stripline ultra-wideband tunable zero bandpass filter of claim 1, wherein: the dielectric constant of the dielectric plate is 3.55-3.6, the thickness of the dielectric plate is 0.254mm-0.300mm, the whole area size of the filter is 10mm 22mm-15mm 25mm, and the miniaturization performance is good.

4. The suspended stripline ultra-wideband tunable zero bandpass filter of claim 1, wherein: the signal main transmission link path is that signals are transmitted to the third resonator (7) from the input end ohmic transmission line (14) main transmission link through the input end ohmic transmission line (14), the third resonator (7) sequentially transmits to the first resonator (5), the fourth resonator (8), the second resonator (6) and the fifth resonator (9), and the transmission zero point is finally output through the output end 50 ohm transmission line (15) plane microstrip.

5. The suspended stripline ultra-wideband tunable zero bandpass filter of claim 1, wherein: the adjustable zero band-pass filter generates a controllable transmission zero at a low frequency band outside the passband of the ultra-wideband filter through the double-layer metalized coupling through holes (10), and changes the coupling amount of a source and a third resonator (7) by adjusting the length Ld of a high-impedance line segment connected with the double-layer metalized coupling through holes (10), so that the out-of-band transmission zero is subjected to controllable offset.

6. The suspended stripline ultra-wideband tunable zero bandpass filter of claim 1, wherein: a transmission zero is introduced at a limited frequency by a direct comprehensive method of the generalized Chebyshev filter, so that a normalized equivalent circuit coupling matrix of the ideal band-pass filter is obtained, a coupling coefficient and a self-resonance frequency parameter in the coupling matrix are denormalized and mapped into an HFSS physical model based on electromagnetic field theoretical simulation, and the design of the ultra-wideband adjustable zero band-pass filter is rapidly completed.

7. The suspended stripline ultra-wideband tunable zero bandpass filter of claim 1, wherein: the resonator loading capacitors (13) of all the resonators are connected with metal grounds (12) on both sides of the dielectric substrate (3).

8. The suspended stripline ultra-wideband tunable zero bandpass filter of claim 1, wherein: the metal ground (12) is provided with a metalized coupling through hole (11) which ensures good metal ground connection of the front side and the back side of the dielectric plate and is a through hole.

9. The suspended stripline ultra-wideband tunable zero bandpass filter of claim 1, wherein: each resonator is composed of a high-impedance line segment, a low-impedance line segment and a resonator loading capacitor (13), and the length size of the high-impedance line segment of the resonator loading capacitor (13) is adjusted to obtain the self-resonant frequency adjusted by the first resonator (5).

10. The suspended stripline ultra-wideband tunable zero bandpass filter of claim 1, wherein: the high-impedance section of each resonator is equivalent to a section of coupled inductor circuit model, the low-impedance section is equivalent to a section of capacitor circuit model, and the resonator loading capacitor (13) is equivalent to a section of series capacitor circuit model.