CN111180894B - OAM antenna dark space reduction method based on frequency selection surface - Google Patents
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
- H01Q15/0006—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices
- H01Q15/0013—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices said selective devices working as frequency-selective reflecting surfaces, e.g. FSS, dichroic plates, surfaces being partly transmissive and reflective
- H01Q15/0046—Theoretical analysis and design methods of such selective devices
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Abstract
The invention discloses an OAM antenna dark space reduction method based on a frequency selection surface, which loads a two-dimensional band-pass frequency selection surface above an OAM antenna to improve the far-field characteristic of the antenna; when electromagnetic waves are incident, the angle stability of the frequency selective surface enables the non-uniform plane wave components of the OAM waves in all directions to be filtered; the method can change the far-field characteristics of the antenna, such as bandwidth, gain and the like, while reshaping the OAM waveform, and the characteristics can be changed by adjusting the geometric structure, the arrangement mode and the physical parameters of the frequency selection surface. The invention designs the adjusting scheme of each parameter by analyzing the influence of each parameter of the frequency selection surface on the characteristics, and finally obtains the high-gain antenna with obviously reduced dark area.
Description
Technical Field
The invention relates to the technical field of wireless communication, in particular to an OAM antenna dark space reduction method based on a frequency selective surface.
Background
With the advent of the high-speed information age, the development of the high-frequency band millimeter wave communication technology can greatly alleviate the shortage of frequency spectrum. At present, technologies such as Code Division Multiplexing (CDM), Time Division Multiplexing (TDM), polarization multiplexing (PDM), Orthogonal Frequency Division Multiplexing (OFDM), and Multiple Input Multiple Output (MIMO) have been applied to solve the problem of spectrum resource shortage, but the application of these technologies still has difficulty in meeting the development trend of higher speed and higher bandwidth for future communication. Therefore, it is becoming a trend to find other multiplexing techniques with new dimensions to improve the spectrum utilization.
Orbital Angular Momentum (OAM) can be used as a new modulation scheme in radio communication systems. The OAM vortex electromagnetic wave carrying information can be transmitted in parallel in the same bandwidth by the OAM multiplexing-based communication technology, and the utilization rate of frequency spectrum can be greatly improved. OAM has been widely used in optics, and by introducing OAM, transmission capability of an optical communication system is greatly improved. The new modulation technique OAM is applied in the microwave band, which presupposes that a high quality OAM beam can be obtained. Therefore, exploring and designing the high-gain OAM antenna with a small dark area has important significance for the practical application of the OAM technology in the microwave radio frequency field.
Since the OAM beam is hollow, the field strength of the middle area, i.e. the dark area, is weak, and as the propagation distance increases, the dark area becomes larger, which makes how to receive the OAM wave a difficult problem. The current methods for receiving the OAM wave include the following methods: the two-point method and the phase gradient method are convenient in single OAM mode receiving detection, but cannot be used in multiple OAM mode receiving; the Partial Angular Aperture Reception (PAAR) method and the Partial Aperture Sampling Reception (PASR) method cannot effectively calculate the OAM mode spectrum utilization; with the variable-scale aperture sampling reception (VSASR) method, orthogonality is slightly impaired, and there are also some other modes of crosstalk OAM.
Disclosure of Invention
The invention aims to provide a frequency selective surface-based OAM antenna dark area reduction method.
The technical solution for realizing the purpose of the invention is as follows: a OAM antenna dark space reduction method based on a frequency selective surface comprises the following steps:
s1, designing a single-layer single-side band-pass frequency selection surface, wherein the overall size of the single-layer single-side band-pass frequency selection surface is equal to the size of an antenna ground plane, and the passband bandwidth of the single-layer single-side band-pass frequency selection surface covers the passband bandwidth of the OAM antenna;
s2, loading the frequency selection surface on the OAM antenna, and setting the distance between the FSS and the OAM antenna according to the Fabry-Perot resonant cavity theory;
s3, changing the dielectric constant of the frequency selective surface substrate, establishing a concave function curve of the frequency selective surface substrate and the OAM antenna non-zero mode dark area, and finding the lowest point of the concave function curve, namely the minimum point of the antenna dark area;
s4, deriving a relation formula y of 0.054+0.046 sin (pi (x +0.74)/3.85) according to the thickness of the dielectric substrate on the frequency selective surface and the frequency deviation curve of the incident angle, where x is the thickness of the dielectric substrate on the frequency selective surface, and y is the deviation difference of the central frequency at the incident angle of 60 ° relative to the central frequency at the incident angle of 0 °, so that the central frequency deviation is minimized at the incident angle of 60 °, i.e. the angle stability is optimized.
Compared with the prior art, the invention has the following remarkable advantages: (1) the fundamental reason for the defects of the traditional receiving method is that the OAM wave with serious wave beam divergence phenomenon can not be completely received, but the method provided by the invention can reduce the divergence angle, namely reduce the area of a dark area, so that the complete receiving of the OAM wave becomes possible; (2) the method for reducing the dark area combines the OAM antenna with the frequency selection surface, and different frequency selection surfaces can be loaded according to the practical application requirement of the OAM antenna, so that the method has the advantages that the characteristics of high gain and small dark area can be kept all the time; (3) the method has strong practicability for receiving the OAM wave and improving the antenna transmission quality.
Drawings
Fig. 1 is a flow chart of the OAM antenna dark space reduction method based on the frequency selective surface of the present invention.
Fig. 2 is a diagram of an antenna structure in the embodiment of the present invention.
FIG. 3 is a graph of the concave function between the dielectric constant and the 0db dark point for an embodiment of the present invention.
FIG. 4 is a data result diagram of unloaded FSS and loaded FSS according to an embodiment of the present invention.
Detailed Description
Aiming at the hollow vortex characteristic of an OAM wave beam, the invention provides a method for reducing the dark area of an OAM antenna based on a frequency selection surface, wherein the frequency selection surface is loaded above the OAM antenna and comprises an antenna main body and the frequency selection surface; the antenna main body is used for transmitting OAM waves, and the frequency selection surface is loaded on the antenna main body and used for carrying out spatial filtering on the OAM antenna.
As shown in fig. 1, the method comprises the steps of:
s1, designing a single-layer single-side band-pass frequency selection surface, wherein the whole size of the single-layer single-side band-pass frequency selection surface is equal to the size of an antenna ground plane, and the passband bandwidth of the single-layer single-side band-pass frequency selection surface covers the passband bandwidth of the OAM antenna;
s2, loading the frequency selection surface on the OAM antenna, and setting the distance between the FSS and the OAM antenna according to the Fabry-Perot resonant cavity theory;
s3, changing the dielectric constant of the frequency selective surface substrate, establishing a concave function curve of the frequency selective surface substrate and the OAM antenna non-zero mode dark area, and finding the lowest point of the concave function curve, namely the minimum point of the antenna dark area;
and S4, deriving a relation formula y of 0.054+0.046 sin (pi (x +0.74)/3.85) according to the thickness of the dielectric substrate on the frequency selection surface and the frequency deviation curve of the incident angle, wherein x is the thickness of the dielectric substrate on the frequency selection surface, and y is the deviation difference of the central frequency at the incident angle of 60 degrees relative to the central frequency at the incident angle of 0 degrees. The central frequency deviation is minimized when the incidence angle is 60 degrees, namely, the angle stability is optimized.
Further, step S1 specifically includes:
designing a unit cell, etching a pattern on a metal surface of the unit cell, and setting a simulation boundary condition as a cell boundary condition;
through mathematical calculation and simulation optimization of the existing mature technology, when plane waves enter the two-dimensional periodic structure which is infinitely and uniformly distributed, the passband bandwidth of the two-dimensional periodic structure covers the passband bandwidth of the OAM antenna;
according to the actual size of the OAM antenna, a single-layer single-face band-pass frequency selection surface with limited-size units periodically arranged along the X axis, the Y axis and the like is finally formed by combining the designed unit units.
Further, step S2 specifically includes:
loading a frequency selection surface above the OAM antenna, so that the frequency selection surface and an antenna ground plate form a Fabry-Perot resonant cavity;
and according to a Fabry-Perot cavity antenna theoretical formula, setting the distance between the FSS and the antenna to ensure that the cavity height meets the resonance condition, and further ensuring that the axial direction of the antenna has the maximum radiation direction.
Further, step S3 specifically includes:
and changing the dielectric constant of the frequency selective surface substrate to establish a concave function curve of the frequency selective surface substrate and the non-zero mode dark region of the OAM antenna.
According to the relationship curve between the two, it can be found that the OAM beam dark area can be significantly changed by changing the dielectric constant, and the dielectric constant corresponding to the lowest point of the curve is found, and the corresponding dark area is the minimum dark area.
Furthermore, OAM waves are emitted through the antenna main body, signals transmitted by the antenna main body are subjected to spatial filtering through the frequency selective surface, and finally the high-gain antenna with the obviously reduced dark area is obtained.
Further, the frequency selective surface includes a metal patch portion and a dielectric substrate: the metal patch part is connected with the dielectric substrate; and by changing various parameters of the dielectric substrate and the metal patch part, especially the dielectric constant, the high-gain antenna with the obviously reduced OAM wave beam dark area can be obtained. At present, no calculation research on the area of a dark area exists at home and abroad, but the reduction of the dark area is directly reflected by the reduction of divergence. The result of the examples below is a reduction in divergence angle to half that when the FSS is not loaded.
Furthermore, the frequency selective surface is a spatial band-pass filter, signals output from the antenna main body are designed and filtered according to the frequency band where the signals are located through the band-pass filter, and the pass band and the stop band of the band-pass filter are set according to the frequency band where the signals output by the antenna main body are located.
In consideration of the oblique incident wave characteristic of the OAM antenna, the dielectric substrate should be thick enough so that the frequency selective surface has good angular stability.
The invention will be further explained and supplemented with reference to the following examples.
Examples
As shown in fig. 2, the present embodiment provides an antenna for realizing dark space reduction of an OAM beam, the antenna including an antenna body, a frequency selective surface; the antenna body is used for transmitting OAM wave beams; the frequency selective surface is loaded above the antenna body and is used for carrying out spatial filtering on OAM waves.
In the embodiment shown in fig. 2, the antenna body includes a dielectric substrate 1, a dielectric substrate 2, a radiating patch 3, and a ground substrate 4. The upper surface of the dielectric substrate 2 is printed with a rectangular radiation patch 3, the lower surface of the dielectric substrate 2 is printed with a square grounding substrate 4, and the dielectric substrate 1 is printed on the lower surface of the grounding substrate 4. The feeding mode adopts coaxial feeding, four feeding ports are arranged below the dielectric substrate 1, the dielectric substrates 1 and 2 and the grounding substrate 4 are provided with through holes, an inner conductor of a coaxial connector penetrates through the through holes to be welded with the radiation patch 3, and an outer conductor is connected with the grounding substrate 4 to form a bottom feeding structure.
In the embodiment shown in fig. 2, the frequency selective surface includes a dielectric substrate 5 and a metal patch part 6, and the surface of the FSS is formed by a plurality of metal patch units 6 arranged periodically. The surface is a band-pass frequency selection surface, and the pass band and the stop band of the surface are designed according to the frequency band of the OAM wave transmitted by the antenna main body, so that the frequency band of the signal output by the output port is consistent with the frequency band of the signal originally output by the output port, and clutter is filtered.
As shown in fig. 1, the dark space reduction method based on the frequency selective surface of the present invention comprises the following steps:
s1, designing a single-layer single-side band-pass frequency selection surface, wherein the size of the single-layer single-side band-pass frequency selection surface is equal to the size of an antenna ground plane, and the passband bandwidth of the single-layer single-side band-pass frequency selection surface covers the passband bandwidth of the OAM antenna, and the method specifically comprises the following steps:
A. designing a unit cell, etching a pattern on the metal surface, and setting the simulation boundary condition as the cell boundary condition.
B. Through mathematical calculation and simulation optimization, the two-dimensional periodic structure which is infinitely and uniformly distributed can reach the purpose that the passband bandwidth covers the passband bandwidth of the OAM antenna when plane waves enter.
C. According to the actual size of the OAM antenna, a single-layer single-face band-pass frequency selection surface with limited-size units periodically arranged along the X axis, the Y axis and the like is finally formed by combining the designed unit units.
In the embodiment, the frequency selective surface loaded by the annular gap is selected, and the distance between the unit and the annular gap of the unit is ensured to be small enough to prevent the premature occurrence of grating lobes. The perimeter of the designed annular slot is approximately equal to the wavelength of the resonant frequency of the antenna.
S2, loading the frequency selection surface on the OAM antenna, and setting the distance between the FSS and the OAM antenna according to the Fabry-Perot resonant cavity theory, which specifically comprises the following steps:
A. and loading a frequency selection surface above the OAM antenna, so that the frequency selection surface and the antenna ground plate form a Fabry-Perot resonant cavity.
B. And according to a Fabry-Perot cavity antenna theoretical formula, setting the distance between the FSS and the antenna to ensure that the cavity height meets the resonance condition, and further ensuring that the axial direction of the antenna has the maximum radiation direction.
In the step B, when the height of the cavity meets the resonance condition, one part of the electromagnetic waves radiated by the OAM antenna is transmitted outwards through the FSS, the other part of the electromagnetic waves is reflected back into the resonant cavity, and the electromagnetic waves after multiple reflections are superposed on the outer surface of the FSS in the same phase to form high-gain radiation, so that the directivity of the antenna is improved, and the beam width is sharpened.
S3, changing the dielectric constant of the frequency selective surface substrate, establishing a concave function curve of the frequency selective surface substrate and the OAM antenna non-zero mode dark area, and finding the lowest point of the concave function curve, namely the minimum point of the dark area.
When the dielectric constant of the frequency selective surface substrate is changed, the beam pointing direction of the main lobe is gradually biased to normal phase while the dark area is reduced. When the dielectric constant increases to the increasing region of the relationship curve, it is found that the main beam pointing direction gradually deviates from the normal phase while the dark region is enlarged.
And changing the dielectric constant of the frequency selective surface substrate to establish a concave function curve of the frequency selective surface substrate and the non-zero mode dark region of the OAM antenna. The graph of this embodiment is shown in fig. 3, and it can be clearly seen that the function graph is a concave function curve, and the 0db angle in the dark region is the minimum when the dielectric constant is 3.5, which is the minimum point in the dark region.
S4, deriving a relation formula y of 0.054+0.046 sin (pi (x +0.74)/3.85) according to the frequency-selective surface dielectric substrate thickness and incident angle frequency deviation curve, so that the central frequency deviation is minimum at an incident angle of 60 °, that is, the angle stability is optimal.
When the thickness of the dielectric substrate of the frequency selective surface is changed, it can be found that the angular stability of the frequency selective surface is significantly improved. Due to the oblique incident wave characteristic of the uniform circular array OAM antenna of the embodiment, the angular stability of the frequency selective surface is very important.
In the embodiment of the dark area reduction method based on the frequency selective surface of the present invention, compared with the result of not loading the frequency selective surface, the angle of the dark area is reduced to half of the original angle at the directional diagram 0db, and the data is summarized as shown in fig. 4. The method provides possibility for receiving most of OAM wave at long distance and even completely receiving OAM wave.
Claims (7)
1. A OAM antenna dark space reduction method based on a frequency selective surface is characterized by comprising the following steps:
s1, designing a single-layer single-side band-pass frequency selection surface, wherein the overall size of the single-layer single-side band-pass frequency selection surface is equal to the size of an antenna ground plane, and the passband bandwidth of the single-layer single-side band-pass frequency selection surface covers the passband bandwidth of the OAM antenna;
s2, loading the frequency selection surface on the OAM antenna, and setting the distance between the FSS and the OAM antenna according to the Fabry-Perot resonant cavity theory;
s3, changing the dielectric constant of the frequency selective surface substrate, establishing a concave function curve of the frequency selective surface substrate and the OAM antenna non-zero mode dark area, and finding the lowest point of the concave function curve, namely the minimum point of the antenna dark area;
s4, deriving a relation formula y of 0.054+0.046 sin (pi (x +0.74)/3.85) according to the thickness of the dielectric substrate on the frequency selective surface and the frequency deviation curve of the incident angle, where x is the thickness of the dielectric substrate on the frequency selective surface, and y is the deviation difference of the central frequency at the incident angle of 60 ° relative to the central frequency at the incident angle of 0 °, so that the central frequency deviation is minimized at the incident angle of 60 °, i.e. the angle stability is optimized.
2. The method of claim 1, wherein the step S1 specifically includes:
designing a unit cell, etching a pattern on a metal surface of the unit cell, and setting a simulation boundary condition as a cell boundary condition;
through mathematical calculation and simulation optimization, when plane waves enter the two-dimensional periodic structure which is infinitely and uniformly distributed, the passband bandwidth of the two-dimensional periodic structure covers the passband bandwidth of the OAM antenna;
according to the actual size of the OAM antenna, a single-layer single-side band-pass frequency selection surface with units of limited size periodically arranged along the X axis, the Y axis and the like is formed by combining the designed unit units.
3. The method of claim 1, wherein the step S2 specifically includes:
loading a frequency selection surface above the OAM antenna, so that the frequency selection surface and an antenna ground plate form a Fabry-Perot resonant cavity;
and according to a Fabry-Perot cavity antenna theoretical formula, setting the distance between the FSS and the antenna to ensure that the cavity height meets the resonance condition and the axial direction of the antenna has the maximum radiation direction.
4. The method of claim 1, wherein the step S3 specifically includes:
changing the dielectric constant of the frequency selective surface substrate, and establishing a concave function curve of the frequency selective surface substrate and the non-zero mode dark region of the OAM antenna;
and finding out the dielectric constant corresponding to the lowest point of the curve according to the relation curve between the two, wherein the corresponding dark area is the minimum dark area.
5. The frequency selective surface based OAM antenna dark space reduction method of claim 1, wherein the OAM waves are transmitted through an antenna body, and signals transmitted by said antenna body are spatially filtered through the frequency selective surface.
6. The frequency selective surface based OAM antenna dark space reduction method of claim 1 or 5, wherein the frequency selective surface comprises a metal patch part and a dielectric substrate, the metal patch part being connected with the dielectric substrate.
7. The method of claim 1 or 5, wherein the frequency selective surface based OAM antenna dark space reduction is a spatial band pass filter.
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