CN109273864B

CN109273864B - Device for generating millimeter wave Bessel wave beam by using double-fed source

Info

Publication number: CN109273864B
Application number: CN201811036786.7A
Authority: CN
Inventors: 刘喆; 张德海
Original assignee: National Space Science Center of CAS
Current assignee: National Space Science Center of CAS
Priority date: 2018-09-06
Filing date: 2018-09-06
Publication date: 2020-12-11
Anticipated expiration: 2038-09-06
Also published as: CN109273864A

Abstract

The invention discloses a device for generating Bessel beams by utilizing a double-fed source, which comprises: two identical feed sources and a lens on a plane; the distances between the geometric centers of the emergent surfaces of the two feed sources and the focal point of the lens are equal, the two feed sources are dielectric rod antennas and are used for enabling the two generated Gaussian beams to be incident on the lens, and the lens is used for outputting Bessel beams. The device of the invention utilizes two same feed sources, solves the problem of beam splitting in the traditional method, directly utilizes two coherent beams to modulate to obtain Bessel beams, and has simple and practical whole device and 20 percent shorter length compared with the prior device.

Description

Device for generating millimeter wave Bessel wave beam by using double-fed source

Technical Field

The invention belongs to the technical field of millimeter wave application, and particularly relates to a device for generating Bessel beams by utilizing a double-fed source.

Background

In the visible light and infrared field, the gaussian beam is usually utilized to perform operations such as collimation and cutting, and the gaussian beam is expected to have the characteristics of small diffraction angle and small beam radius, but in practical application, the beam divergence angle and the diffraction angle present an inverse correlation relationship, so people are always searching for a mode which can enable the laser beam not to be diffracted or not to be diffracted within a certain transmission distance, in 1987, american scientists introduce the concept of 'no-diffracted beam' for the first time and are verified in theory and experiments, theoretically, the fact that the no-diffracted beam cannot exist in the absolute sense is proved, but in the relative sense, the beam with limited energy can still realize the no-diffracted transmission in the limited distance, so the research work of predecessors is concentrated on how to simply and effectively generate the bessel beam, and how the bessel beam can realize no-diffraction in a longer distance, whether the conversion efficiency of the bessel beam can be improved.

In a millimeter wave band, a method for generating Bessel beams is similar to visible light and infrared bands, but the difficulty is different, beam collimation of the millimeter wave band is not as easy as infrared and visible light, and many methods cannot be adopted, such as an inverted telescope method. Therefore, in the millimeter wave band, the generated Bessel beam requires that the size of a light spot is as small as possible, the device is as simple as possible, and the obtained transmission distance is as long as possible.

The Bessel beam generation is a hotspot of current research, particularly the frequency is as low as a millimeter wave band, the Bessel beam generation mode is certainly different from an optical band and an infrared band, the Bessel beam generation method generally utilizes two Gaussian beams to generate a result of interference, therefore, no matter a hologram, an axicon or a slit method is adopted, a beam emitted by the same emission feed source is utilized to split the beam, the beam direction is deflected, a traditional spherical wave is converted into a conical beam, and the interference of the two conical beams is utilized to form the Bessel beam.

Disclosure of Invention

The invention aims to overcome the defects of the conventional Bessel beam generating device, adopts a device with a double-feed structure, does not need a prism with higher processing precision requirement, and has the advantage of high conversion efficiency.

In order to achieve the above object, the present invention provides an apparatus for generating a millimeter wave bessel beam using a dual feed, the apparatus comprising: two identical feed sources and a lens on a plane; the distances between the geometric centers of the emergent surfaces of the two feed sources and the focal point of the lens are equal, the two feed sources are dielectric rod antennas and are used for enabling the two generated Gaussian beams to be incident on the lens, and the lens is used for outputting Bessel beams.

As an improvement of the device, the distance between the geometric center of the emergent surface of the feed source and the focal point of the lens is 5 mm.

As an improvement of the above device, the vertical distance between the feed source and the lens is more than 100 mm; the vertical distance between the feed source and the lens is the distance S from the center point of the Gaussian beam to the aperture surface of the feed source and the distance S from the center point of the Gaussian beam to the lens₁The sum of (1); the calculation process of the distance S from the center point of the Gaussian beam to the aperture plane of the feed source is as follows: using far field direction of desired feedObtaining the 3dB azimuth angle theta of the feed source, and meeting the Gaussian beam waist radius omega emitted by the feed source₀₁And (3) under the condition that the lambda is more than or equal to 0.9 lambda, the lambda is the wavelength under the frequency, and the distance S from the center point of the Gaussian beam to the aperture plane of the feed source is calculated:

as an improvement of the device, the caliber D of the lens satisfies the following conditions: d is more than or equal to 3 omega, wherein omega is the radius of the Gaussian beam waist of the incident surface of the lens:

as an improvement of the above device, the thickness T of the lens is:

wherein R (S)₁) Radius of curvature for gaussian beam incident on the lens aperture:

as an improvement of the above apparatus, the maximum transmission distance of the bessel beam generated by the apparatus is greater than 200 mm.

The invention has the advantages that:

the device of the invention utilizes two same feed source antennas, solves the problem of beam splitting in the traditional method, directly utilizes two coherent beams to modulate to obtain Bessel beams, and has simple and practical whole device and length of only 20 percent of that of the traditional device.

Drawings

FIG. 1 is a flow chart of a method of designing an apparatus for generating millimeter wave Bessel beams using a dual feed according to the present invention;

FIG. 2 is a schematic structural diagram of an apparatus for generating millimeter wave Bessel beams using a double feed source according to the present invention;

FIG. 3 is a graph of Bessel beam axial near field gain produced by the apparatus of the present invention;

FIG. 4 is a plane gain diagram of Bessel beams obtained by the apparatus of the present invention, with ordinate 300mm to 800mm and abscissa-50 mm to 50 mm.

Detailed Description

The invention is described in detail below with reference to the figures and specific embodiments.

As shown in fig. 1, the present invention provides a method for designing an apparatus for generating a millimeter wave bessel beam by using a dual feed source, the bessel beam being obtained by using the dual feed source and a lens antenna, the method comprising:

step 1) obtaining a 3dB azimuth angle theta of a feed source antenna by utilizing a far field directional diagram of a required feed source, and obtaining a Gaussian beam waist radius omega output by the feed source₀₁Satisfy omega₀₁The distance S from the center point of the Gaussian beam to the aperture plane of the feed source is larger than or equal to 0.9 lambda;

λ is the wavelength at this frequency, ω₀₁The distance S between the center point of the Gaussian beam and the aperture plane of the feed source is expressed by the following formula, wherein the distance S is 1.18 times of the beam radius of 3dB of the far field gain of an antenna directional diagram:

step 2) Using omega₀₁And the distance S from the center point of the set Gaussian beam to the lens₁Using omega₀₁And the distance S from the center point of the Gaussian beam to the lens₁Obtaining the radius omega of the beam waist of the Gaussian beam at the incident position of the front surface of the lens:

in order to ensure that the capture rate of Gaussian beam energy reaches more than 98 percent as much as possible, the aperture D of the lens needs to meet the condition that D is more than or equal to 3 omega;

step 3) solving the curvature radius of the Gaussian beam incident to the lens mouth surface:

wherein:

step 4) utilizing the curvature radius R (S) obtained in step 3)₁) The thickness T of the lens is determined:

step 5) arranging the two feed sources into a line, and respectively keeping the distance from the positive feed point by 5 mm;

and 6) feeding the two feed sources respectively on the basis of the step 5), observing the formed beam shape and the maximum transmission distance, finishing the design if the transmission distance reaches more than 200mm, and redesigning the feed source antenna and the lens antenna according to the process if the transmission distance does not meet the requirement.

As shown in fig. 2, the present invention provides an apparatus for generating millimeter wave bessel beams by using a double-fed source, the apparatus comprising: two identical feed sources and a lens on a plane; the geometric centers of the emergent surfaces of the two feed sources are equal to the distance between the focal points of the lenses: the feed source is a dielectric rod antenna and is used for enabling the generated Gaussian beam to be incident on a lens, and the lens is used for outputting a Bessel beam.

The vertical distance between each feed source and the lens is more than 100 mm; the vertical distance between the feed source and the lens is the distance S from the center point of the Gaussian beam to the aperture surface of the feed source and the distance S from the center point of the Gaussian beam to the lens₁The sum of (1); wherein the calculation process of S is as follows: obtaining the 3dB azimuth angle theta of the feed source by using the far field directional diagram of the required feed source, and meeting the requirement of the Gaussian beam waist radius omega emitted by the feed source₀₁And (3) under the condition that the lambda is more than or equal to 0.9 lambda, the lambda is the wavelength under the frequency, and the distance S from the center point of the Gaussian beam to the aperture plane of the feed source is calculated:

preferably, the aperture D of the lens needs to satisfy the condition D ≧ 3 ω, ω being the Gaussian beam waist radius of the lens incidence plane:

thickness T of lens:

wherein,

as shown in fig. 3 and 4, the bessel beams generated by the device of the present invention reach the design requirement that the transmission distance reaches more than 200 mm.

Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and are not limited. Although the present invention has been described in detail with reference to the embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. An apparatus for generating bessel beams using dual feeds, the apparatus comprising: two identical feed sources and a lens on a plane; the distance between the geometric centers of the emergent surfaces of the two feed sources and the focal point of the lens is equal, the two feed sources are dielectric rod antennas and are used for enabling the two generated Gaussian beams to be incident on the lens, and the lens is used for outputting Bessel beams;

the distance between the geometric center of the emergent surface of the feed source and the focal point of the lens is 5 mm;

the vertical distance between the feed source and the lens is more than 100 mm; the vertical distance between the feed source and the lens is the distance S from the center point of the Gaussian beam to the aperture surface of the feed source and the distance S from the center point of the Gaussian beam to the lens₁The sum of (1); the calculation process of the distance S from the center point of the Gaussian beam to the aperture plane of the feed source is as follows: obtaining the 3dB azimuth angle theta of the feed source by using the far field directional diagram of the required feed source, and meeting the requirement of the Gaussian beam waist radius omega emitted by the feed source₀₁And (3) under the condition that the lambda is more than or equal to 0.9 lambda, the lambda is the wavelength under the frequency, and the distance S from the center point of the Gaussian beam to the aperture plane of the feed source is calculated:

ω₀₁the maximum transmission distance of the Bessel beam generated by the device is more than 200mm, which is 1.18 times of the beam radius of 3dB of the far field gain of an antenna directional diagram;

the aperture D of the lens satisfies: d is more than or equal to 3 omega, wherein omega is the radius of the Gaussian beam waist of the incident surface of the lens:

the thickness T of the lens is as follows: