CN109301405B - Three-dimensional absorption type frequency selection structure with suction - Google Patents
Three-dimensional absorption type frequency selection structure with suction Download PDFInfo
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- CN109301405B CN109301405B CN201810906596.XA CN201810906596A CN109301405B CN 109301405 B CN109301405 B CN 109301405B CN 201810906596 A CN201810906596 A CN 201810906596A CN 109301405 B CN109301405 B CN 109301405B
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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
Abstract
The invention discloses a three-dimensional absorption type frequency selective structure. The invention is a periodic distribution structure, the structural unit adopts a mode of stacking two layers of stepped impedance parallel plate waveguides, and the loading of lumped capacitance resistance is combined, so that the wave-transmitting performance in a low-frequency band and the wave-absorbing performance in a high-frequency band are realized. The structure unit consists of an upper layer parallel plate waveguide, a front end loading part, a rear end loading part, a lower layer parallel plate waveguide and a rear end loading part. The invention can be used for the stealth antenna housing of the low-frequency band antenna in the military field. The three-dimensional band absorption type frequency selective structure can transmit electromagnetic waves at a low frequency without loss, and realizes a wave absorption function in a frequency band with a very wide high frequency, so that the reflection of the electromagnetic waves outside a passband is reduced, and a good stealth characteristic is realized.
Description
Technical Field
The invention belongs to the technical field of microwaves, and relates to a three-dimensional absorption type frequency selection structure based on a stepped impedance parallel plate waveguide.
Background
Frequency Selective Surface (FSS) is a spatial filter composed of periodically arranged structural units, which can effectively control the transmission and reflection characteristics of electromagnetic waves with different frequencies. In the military field, it can be used for a stealth radome, and the reflected wave of the counterpart Radar is deviated from the incident direction by the change of the shape, thereby reducing the Radar scattering Section (RCS) of the antenna. However, only a single station RCS is so reduced.
An Absorption Frequency Selective Surface (AFSS) can be regarded as a combination of a traditional Frequency selective surface and a wave absorber, and has both spatial filtering and wave absorbing characteristics. Usually, it is formed by cascading a lossy layer in a Salisbury/Jaumann/Circuit Analog absorber with a conventional frequency selective surface through a quarter-wave transformer. When applied to a radome, the absorptive frequency selective surface can absorb the incident wave of the counterpart radar with little reflection. A radome constructed from absorbing frequency selective surfaces is thus equally effective for the reduction of two-station to multi-station RCS.
Conventional AFSS is a laminated two-dimensional structure, which has the disadvantages that: 1) the unit size is large, so that the frequency response characteristic of the unit is unstable along with the change of the incident angle of the electromagnetic wave; 2) the filtering characteristics are poor, and it is difficult to realize high-frequency selection characteristics. To solve these problems, a three-dimensional absorption frequency selective structure (3D AFSS) has been developed. The dimension of the electromagnetic wave propagation direction is fully utilized to construct a transmission line (parallel plate waveguide, microstrip line and the like) resonator, so that the resonance frequency is independent of the size of a periodic unit. The three-dimensional absorption type frequency selective structure has very high frequency selective characteristics and angular stability to incident waves.
The AFSS is classified into a belt-through type and a belt-suction type.
The bandpass type AFSS is characterized in that: 1) a pass-band, whose bandwidth is typically not very wide (within 50%); 2) two wave-absorbing bands are positioned at two sides of the pass band. When the antenna is used for the stealth antenna cover, the suitable antenna working frequency band is positioned in the passband. The main application of the band-pass type AFSS is in the high frequency radar, such as the radar operating in C, X frequency band, where the designed AFSS has a smaller unit size or a thinner thickness. The defect is also obvious, when the working frequency band of the antenna is in a low frequency, such as UHF and VHF frequency bands, the unit size of the designed AFSS becomes very large or the thickness thereof is very thick, which is not beneficial to practical application.
The suction type AFSS is characterized in that: 1) an absorption band designed in the common radar frequency band, such as C, X frequency band; 2) the frequency band lower than the absorption band is wave-transparent. Its performance can be summarized as "low pass high absorption". The area inhales type AFSS is mainly oriented to the demand of many stealth antenna covers working in systems of communication, spectrum monitoring and the like of UHF and VHF frequency bands. These systems are currently installed in large numbers on large combat platforms, but the aforementioned band-pass type AFSS is clearly not applicable to their radomes. These low-band antenna operating bands often cover several octaves and are lower than the usual radar bands. Therefore, the stealth antenna covers of the antenna have the requirements of absorbing waves in a common radar wave band (such as a C wave band, an X wave band and the like) and transmitting waves below a wave-absorbing frequency band. In the existing band absorption type AFSS structure, one is to replace a reflection back plate of a traditional wave absorber with a band elimination type FSS, but the bandwidth of a wave absorbing band of the scheme is limited. To increase the bandwidth, a broadband three-dimensional bandstop FSS can be used, but this results in a significant increase in the thickness of the structure. The other three-dimensional band absorption type AFSS is formed by laminating a three-dimensional band elimination FSS and a three-dimensional wave absorber. Electromagnetic waves incident in a high-frequency band enter the wave absorber to be absorbed, the wave absorber is almost in short circuit in a low-frequency band, and the incident waves enter the band elimination FSS to realize transmission. The structure has the defects that the structure is complex, two layers of printed circuit boards and two layers of air exist in one unit, and the processing difficulty is high. According to the invention, by constructing the mixed wave absorbing/wave transmitting channel, one channel simultaneously realizes the functions of high-frequency wave absorbing and low-frequency wave transmitting, the structural complexity is greatly reduced, the processing and the assembly are simplified, and the cost is reduced.
Disclosure of Invention
The invention aims to provide a novel three-dimensional belt suction type AFSS aiming at the defects of the prior art.
The invention is a periodic distribution structure, and each structural unit is seamlessly distributed along x and y axes. Each periodic structure unit is formed by stacking an upper layer of parallel plate waveguides and a lower layer of parallel plate waveguides. Wherein the thickness (electromagnetic wave propagation direction) of the unit structure is about one sixth wavelength of the lowest frequency of the wave-absorbing band; the ratio of the width (negative z-axis) to the height (positive y-axis) of the cell structure is about 0.7.
The upper layer parallel plate waveguide consists of a first metal surface, a second metal surface, a first air cavity and a second air cavity between the first metal surface and the second metal surface; the second metal surface is of a stepped structure; the first air cavity and the second air cavity are sequentially arranged from the front end to the rear end of the upper-layer parallel plate waveguide. The front end of the upper layer parallel plate waveguide of the first metal surface is connected with the front end of the upper layer parallel plate waveguide of the second metal surface through a first metal wire, wherein the first metal wire is loaded with a first capacitor and a first resistor. The rear end of the upper layer parallel plate waveguide of the first metal surface is connected with the rear end of the upper layer parallel plate waveguide of the second metal surface through a second metal wire, wherein the second metal wire is loaded with a second capacitor.
A gap is formed in the second metal surface close to the rear end of the upper layer parallel plate waveguide along the x-axis direction, and two ends of the gap are open; and a second resistor is arranged between the gaps and is used for connecting the disconnected second metal surface. The gap corresponds to the second air cavity.
The height (positive y-axis direction) of the first air cavity is greater than the height (positive y-axis direction) of the second air cavity so that the impedance of the front half is greater than that of the rear half, thereby constituting a stepped impedance from high to low.
The lower layer parallel plate waveguide consists of a second metal surface, a third medium cavity and a fourth medium cavity between the second metal surface and the third metal surface; the third dielectric cavity and the fourth dielectric cavity are sequentially arranged from the front end to the rear end of the lower-layer parallel plate waveguide. The rear end of the lower parallel plate waveguide of the second metal surface is connected with the rear end of the lower parallel plate waveguide of the third metal surface through a third metal wire, wherein the third metal wire is loaded with a third capacitor.
The height (y-axis positive direction) of the third medium cavity is smaller than the height (y-axis positive direction) of the fourth medium cavity, so that the impedance of the first half part is smaller than that of the second half part, and therefore step impedance from low to high is formed.
The media of the third and fourth media cavities are the same, and the preferred media is air.
The second metal surface and the second resistor are shared by the upper and lower layers of parallel plate waveguides.
The position of the absorption band is mainly determined by the thickness (z direction) of the parallel plate waveguide and is also influenced by the step impedance in the parallel plate waveguide, i.e., the ratio of the heights of the air cavities at both ends (e.g., the ratio of the first and second air cavities). The wave absorbing performance of the wave absorbing band depends on the impedance of the unit structure, and the affected parameters are more, such as the aspect ratio of the unit structure, the resistance values of the first resistor and the second resistor, and the capacitance values of the first capacitor, the second capacitor and the third capacitor.
The front end and the rear end of the parallel plate waveguide are that electromagnetic waves are transmitted towards the negative direction of the z axis, and the section of the structure where the electromagnetic waves arrive first is called the front end, and the section where the electromagnetic waves arrive last is called the rear end.
The working principle is as follows:
the structure of the invention adopts a mode of stacking two layers of stepped impedance parallel plate waveguides, and combines lumped capacitance resistance to design a mixed wave absorbing/wave transmitting channel. The invention utilizes the principle that parallel plate waveguide is completely transparent to the linearly polarized incident wave vertical to the polarization, adopts two technical means of back-end capacitance loading and step impedance, and ingeniously constructs two working modes: the low-frequency band wave-transparent is equivalent to a parallel plate waveguide; high-frequency wave absorption is equivalent to a wave absorber with a short circuit at the rear end. The principle that the parallel plate waveguide generates a short circuit effect at the rear end of a high frequency band is as follows: the inductance and capacitance of the metal wire form an LC series circuit. By properly designing the values of L and C, the wave-absorbing material can resonate in a high-frequency wave-absorbing band, and the impedance of the wave-absorbing material is 0 at the moment, which is equivalent to short-circuiting an upper metal plate and a lower metal plate at the rear end of the parallel plate waveguide.
The working process is as follows: after electromagnetic waves with different frequencies enter the structure, different responses can be generated. When the incident wave frequency is in the wave absorption band, the structure is equivalent to a wave absorber, and the incident wave is absorbed by the first resistor and the second resistor. When the incident wave is lower than the absorption wave band, the structure is equivalent to a parallel plate waveguide, the first resistor and the second resistor have little effect, and the incident wave passes through the parallel plate waveguide almost without loss.
The three-dimensional band-absorption AFSS based on the stepped impedance parallel plate waveguide has the following advantages:
(1) the three-dimensional band absorption type frequency selective structure can transmit electromagnetic waves at a low frequency without loss, and realizes a wave absorption function in a frequency band with a very wide high frequency, so that the reflection of the electromagnetic waves outside the pass band is reduced, and a good stealth characteristic is realized.
(2) The three-dimensional band-absorption type frequency selection structure adopts a three-dimensional structure, and can reduce the unit size of the x-y plane periodic arrangement to be very small under the condition that a design process can be realized, so that very stable frequency response characteristics are realized.
Drawings
FIG. 1 is a schematic diagram of a three-dimensional periodic building block of the present invention;
FIG. 2 is an elevation view of a three-dimensional periodic building unit of the invention and its labeling;
FIG. 3 is a side view of a three-dimensional periodic building block of the invention and its labeling;
FIG. 4 is the transmission and reflection coefficients (| S) of the present invention21I and I S11|) simulation result graph;
FIG. 5 is a wave absorption rate simulation result diagram of the present invention.
In the figure: the capacitor comprises a first metal surface 1, a first metal wire 2, a first capacitor 3, a first resistor 4, a second resistor 5, a second metal surface 6, a second metal wire 7, a second capacitor 8, a third metal wire 9, a third capacitor 10 and a third metal surface 11.
Detailed Description
The present invention is further analyzed with reference to the following specific examples.
The upper layer parallel plate waveguide only consists of a first metal surface and a second metal surface, and no medium is filled between the two metal surfaces. Preferably, the second metal surface is folded and stepped, so that the front half of the upper layer parallel plate waveguide has a larger height than the rear half, thereby having the effect that the impedance of the front half is larger than that of the rear half, and thus constituting a stepped impedance from high to low. The front end of the parallel plate waveguide is provided with a first capacitor and a first resistor which are connected with the first metal surface and the second metal surface through a first metal wire. The back end of the parallel plate is provided with a second capacitor which is connected with the first metal surface and the second metal surface through a second metal wire. And a second resistor is arranged at a certain distance from the rear end of the second metal surface.
The lower layer parallel plate waveguide is only composed of a second metal surface and a third metal surface, and no medium is filled in front of the two metal surfaces. Generally, due to the step distribution of the second metal surface, the front half part and the rear half part of the lower-layer parallel plate waveguide also form step impedance, but the impedance of the front half part is smaller than that of the rear half part. And the rear end of the layer of parallel plate waveguide is provided with a third capacitor which is connected with the second metal surface and the third metal surface through a third metal wire. And a second resistor is arranged at a certain distance from the rear end of the second metal surface. It can be seen that the second metal plane and the second resistor are shared by the upper and lower parallel plate waveguides.
The front end and the rear end are clearly defined, that is, electromagnetic waves are transmitted towards the negative direction of the z axis, and the section of the structure where the electromagnetic waves arrive first is called the front end, and the section where the electromagnetic waves arrive last is called the rear end.
Example (b):
according to the invention, a three-dimensional band absorption type AFSS is built in a way of stacking two layers of parallel plate waveguides, so that the low-pass characteristic can be realized, and an extremely wide wave absorption band is generated at a position close to high frequency.
As shown in fig. 1 and 2, the three-dimensional band-absorption-type AFSS based on the stepped impedance parallel plate waveguide is a periodic structure, and each periodic structure unit comprises an upper layer of parallel plate waveguide and a lower layer of parallel plate waveguide.
The upper-layer parallel plate waveguide comprises a first metal surface 1, a second metal surface 6, a first metal wire 2, a second metal wire 7, a first capacitor 3, a second capacitor 8, a first resistor 4 and a second resistor 5; the first capacitor 3 and the first resistor 4 are connected with the first metal surface 1 and the second metal surface 6 through the first metal wire 2; the second capacitor 8 is connected with the first metal surface 1 and the second metal surface 6 through a second metal wire 7; the second resistor 5 is welded to the second metal surface 6.
The lower-layer parallel plate waveguide comprises a second metal surface 6, a third metal surface 11, a second resistor 5, a third metal wire 9 and a third capacitor 10; the third capacitor 10 is connected to the second metal plane and the third metal plane via a third metal line 9.
The specific structural geometric parameters are as follows:
wherein b and H are the period lengths of the unit structure in the x-axis direction and the y-axis direction respectively; l is the length of the unit structure in the z-axis direction; h is2The height of the front section of the upper layer parallel plate waveguide formed by the first metal surface 1 and the second metal surface 2 is L-LaThe height of the rear section is H-H3The length of the posterior segment is la；h1Height h of front section of lower parallel plate waveguide formed for second metal surface 6 and third metal surface 113Is the height of the rear section; d is the distance between the second resistor 5 and the rear end of the structure; w is a1、w2、w3The widths of the first metal line, the second metal line and the third metal line are respectively.
| b(mm) | 13 | H(mm) | 18 |
| L(mm) | 12.5 | h1(mm) | 2 |
| h2(mm) | 16 | h3(mm) | 6 |
| la(mm) | 6.5 | d(mm) | 1.5 |
| w1(mm) | 0.3 | w2(mm) | 1.5 |
| w3(mm) | 1 | R1(Ω) | 180 |
| R2(Ω) | 50 | C1(pF) | 0.17 |
| C2(pF) | 0.3 | C3(pF) | 0.3 |
The scheme provided by the embodiment can also regulate and control the performance by changing corresponding parameters. For example, the frequency band position of the high frequency absorption band can be adjusted mainly by changing the length L of the cell structure in the z-axis direction, assisted by adjusting other parameters. Typically, L is about λ/6, where λ is the wavelength in vacuum corresponding to the lowest frequency of the absorbing band.
Fig. 4 and 5 are simulation results of the S parameter and the wave absorption rate of the three-dimensional absorption-type AFSS, respectively. Simulation results show that the structure has a very wide absorption band (reflection and transmission coefficients are lower than-10 dB) in a high frequency band, the frequency band is 3.8GHz to 7.21GHz, and the relative bandwidth is 61.9%. At low frequencies, the structure exhibits low-pass performance, with transmission coefficients greater than-1 dB (i.e., insertion loss less than 1dB) at frequencies below 900 MHz.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be construed as the protection scope of the present invention.
Claims (3)
1. The three-dimensional absorption type frequency selective structure comprises a plurality of periodically distributed unit structures which are arranged along x and y axes in a seamless mode, and is characterized in that each unit structure is formed by stacking an upper layer of parallel plate waveguide and a lower layer of parallel plate waveguide; the upper and lower layers of parallel plate waveguides are parallel to the xoz surface in the xyz coordinate system;
the upper layer parallel plate waveguide is composed of a first metal surface, a second metal surface, a first air cavity and a second air cavity between the first metal surface and the second metal surface; the second metal surface is of a stepped structure; the first air cavity and the second air cavity are sequentially arranged from the front end to the rear end of the upper layer parallel plate waveguide; the front end of the upper layer parallel plate waveguide of the first metal surface is connected with the front end of the upper layer parallel plate waveguide of the second metal surface through a first metal wire, wherein the first metal wire is loaded with a first capacitor and a first resistor; the rear end of the upper layer parallel plate waveguide of the first metal surface is connected with the rear end of the upper layer parallel plate waveguide of the second metal surface through a second metal wire, wherein the second metal wire is loaded with a second capacitor;
a gap is formed in the second metal surface close to the rear end of the upper layer parallel plate waveguide along the x-axis direction, and two ends of the gap are open; a second resistor is arranged between the gaps and is used for connecting the disconnected second metal surface; the gap corresponds to a second air cavity;
the height of the first air cavity is larger than that of the second air cavity, so that the impedance of the front half part of the upper-layer parallel plate waveguide is larger than that of the rear half part of the upper-layer parallel plate waveguide, and step impedance from high to low is formed;
the lower layer parallel plate waveguide is composed of a second metal surface, a third medium cavity and a fourth medium cavity between the second metal surface and the third metal surface; the third dielectric cavity and the fourth dielectric cavity are sequentially arranged from the front end to the rear end of the lower-layer parallel plate waveguide; the rear end of the lower parallel plate waveguide of the second metal surface is connected with the rear end of the lower parallel plate waveguide of the third metal surface through a third metal wire, wherein the third metal wire is loaded with a third capacitor;
the height of the third dielectric cavity is smaller than that of the fourth dielectric cavity, so that the impedance of the front half part of the lower-layer parallel plate waveguide is smaller than that of the rear half part of the lower-layer parallel plate waveguide, and stepped impedance from low to high is formed;
the dielectric constants of the media in the third and fourth dielectric cavities are the same.
2. The three-dimensional band-absorption-type absorption frequency selective structure according to claim 1, wherein the thickness of the unit structure in the propagation direction of the electromagnetic wave is one sixth wavelength of the lowest frequency of the absorption band.
3. The three-dimensional band-absorption-type absorption frequency selective structure as claimed in claim 1, wherein the medium in the third and fourth dielectric cavities is air.
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| CN109818153B (en) * | 2019-02-28 | 2021-05-07 | 杭州电子科技大学 | Novel single-polarization three-dimensional ultra-wideband wave absorber |
| CN111641046B (en) * | 2020-05-07 | 2021-07-06 | 宁波大学 | Microwave band broadband circular dichroism chirality wave absorber |
| CN111817010B (en) * | 2020-06-02 | 2022-02-11 | 杭州电子科技大学 | Reflecting band switchable three-dimensional broadband absorption type frequency selection structure |
| CN112086757B (en) * | 2020-09-14 | 2021-09-14 | 中国空气动力研究与发展中心高速空气动力研究所 | Microwave irradiation absorbing device based on microstrip line resonant cavity array |
| CN113381201B (en) * | 2021-05-21 | 2022-07-15 | 宁波大学 | Broadband wave-absorbing structure with frequency selectivity transmission function |
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| CN105024174A (en) * | 2014-04-15 | 2015-11-04 | 波音公司 | Configurable antenna assembly |
| CN106099269A (en) * | 2016-08-12 | 2016-11-09 | 华南理工大学 | A kind of dielectric cavity frequency-selective surfaces structure |
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| US9559426B1 (en) * | 2013-04-23 | 2017-01-31 | Imaging Systems Technology, Inc. | Frequency selective surfaces |
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| CN105024174A (en) * | 2014-04-15 | 2015-11-04 | 波音公司 | Configurable antenna assembly |
| CN106099269A (en) * | 2016-08-12 | 2016-11-09 | 华南理工大学 | A kind of dielectric cavity frequency-selective surfaces structure |
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