CN115224496A - Diffraction phased array antenna based on space feed - Google Patents
Diffraction phased array antenna based on space feed Download PDFInfo
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Abstract
The invention discloses a diffraction phased array antenna based on spatial feed. The diffraction phased-array antenna comprises a space feed source and a radiation panel, wherein the space feed source and the radiation panel are arranged in parallel at intervals, the geometric centers of the space feed source and the radiation panel are at the same height, and the space feed source and the radiation panel are arranged at a close distance; the radiation panel is a plane caliber formed by periodically uniformly or non-uniformly arranging a plurality of reconfigurable artificial surface units; electromagnetic waves radiated by the space feed source are transmitted to the radiation panel through free space, and the plurality of reconfigurable artificial surface units perform independent phase compensation on the electromagnetic waves transmitted to the reconfigurable artificial surface units in the incident field to obtain the target diffraction phased array. The invention adopts the space feed source, the aspheric wave field is incident to the radiation panel, and the phase compensation is carried out on the incident electromagnetic wave by virtue of the phase reconfigurability of the artificial surface, so that the aperture efficiency is improved, the fluctuation of the gain of different directional wave beams is reduced, and the larger angle scanning range is realized.
Description
Technical Field
The invention belongs to a diffractive phased array antenna in the field of non-traditional phased array antennas, and particularly relates to a diffractive phased array antenna based on space feed.
Background
The traditional phased array takes a patch array as a radiation panel, and a huge power division network, a radio frequency amplifier, a phase shifter, an attenuator and other devices are connected behind the patch array. The system has large loss in the millimeter wave frequency band, high cost and technical bottleneck of difficult heat dissipation. Therefore, a space feed phased array using a large number of radio frequency devices is avoided to become a preferred scheme of the phased array in the millimeter wave frequency band. A space feed phased array, such as a transmission array and a fresnel zone plate, generally uses a single horn antenna as a space feed source, and is approximately regarded as an ideal point source radiation spherical wave incident on a radiation panel. According to the Huygens principle, each point on the radiation panel is used as a secondary emission source, the incident field is radiated again after phase compensation, and a beam scanning diagram is obtained by coherent superposition in the far-field beam pointing direction. However, conventional spatially fed phased arrays have several problems: 1. the feed source is a single spherical wave feed source, the placement distance is long, the section of the phased array is high, and the application of millimeter waves and even terahertz wave bands is limited by the height of the section. 2. As the beam scan angle increases, the beam gain exhibits a rapidly decreasing trend, and thus the spatial scan range is typically less than 60 degrees. 3. The large angle gain attenuation is large and the main lobe of the wave beam is wide, which is not favorable for accurate communication. The conventional solution is to increase the transmit power and to scale up the array to improve beam performance. However, in millimeter wave band and even higher frequency band, the transmission power and the array size are limited by the low efficiency and compact space of the rf device, and cannot meet the expansion requirement.
Disclosure of Invention
In order to solve the problems in the background art, the invention provides a large-angle scanning diffraction phased array antenna based on space feed. The antenna array is used as a space feed source, and the limitation of a single spherical wave feed source is broken. Spherical waves radiated by each array element of the feed antenna array are propagated through a free space, and the spherical waves are superposed on the radiation panel to form an incident total field with randomly fluctuated amplitude and phase. According to the required beam direction, the phase of the original incident total field is compensated by means of the phase reconfigurability of the artificial surface, and the aperture efficiency of the phased array is improved. Under the condition of not increasing the transmitting power and expanding the aperture of the radiation panel, the wide-angle scanning diffraction phased array with the beam scanning angle up to 70 degrees and the gain fluctuation not exceeding 4dB is realized.
The technical scheme adopted by the invention is as follows:
the space feed source feed antenna array and the radiation panel are arranged in parallel at intervals, the geometric centers of the space feed source feed antenna array and the radiation panel are on the same height, and the space feed source feed antenna array and the radiation panel are arranged in a close range; the radiation panel is a plane caliber formed by periodically uniformly or non-uniformly arranging a plurality of reconfigurable artificial surface units;
electromagnetic waves radiated by the space feed source feed antenna array are transmitted to the radiation panel through free space, an incident field with non-uniform distribution of amplitude and phase is formed on the back of the radiation panel, and a plurality of reconfigurable artificial surface units of the radiation panel perform independent phase compensation on the electromagnetic waves incident to the electromagnetic waves in the incident field to obtain the target diffraction phased array.
The spatial feed antenna array includes but is not limited to a patch array, a slot array, and a dipole array.
The space feed source feed antenna array is a feed antenna array consisting of a plurality of array units; the number N of array elements and the spacing d between two adjacent array elements and the distance F between the feed antenna array and the radiating panel are determined by using methods including, but not limited to, simulation, analytical calculation and experimental measurement, which take the maximum aperture efficiency of the target diffraction phased array and the lowest gain drop when the beam is scanned to the maximum angle as optimization targets.
The close distance between the space feed source feed antenna array and the radiation panel is set, specifically, the ratio of the distance F between the space feed source feed antenna array and the radiation panel to the side length L of the radiation panel is not more than 0.5.
The reconfigurable artificial surface unit comprises but is not limited to a multilayer dielectric structure welded with a PIN tube or a varactor, and the multilayer dielectric structure performs phase compensation on electromagnetic waves incident to the multilayer dielectric structure according to beam pointing requirements.
The phase compensation is specifically 1-bit or multi-bit discrete phase compensation, or 180-degree or 360-degree continuous phase compensation. The form of the feed antenna array adopted by the invention is not limited, such as a patch array, a slot array or a dipole array. Each array element can be equivalent to an ideal spherical wave point source. The total field of incidence on the radiation panel is a vector superposition of the spherical wave field of each ideal point source radiation on the radiation panel. A traditional single spherical wave feed source forms electric field distribution on a radiation panel, wherein the amplitude of the electric field distribution is monotonically decreased from the center to the outside, and the phase of the electric field distribution is monotonically increased from the center to the outside. The amplitude and phase of the total incident field under the action of the feed antenna array feed source depend on the parameters such as the number N of the array elements, the spacing d of the array elements, the distance F between the feed antenna array and the radiation panel and the like, so that the amplitude and phase of the total incident field are changed along with the parameters and have no fixed distribution rule.
According to the phased array principle and the Wheatstone-Fresnel diffraction principle, the maximum aperture efficiency of the phased array and the gain reduction degree of the beam scanning to the maximum angle are used as optimization objective functions, and the number N of array elements of the feed antenna array, the distance d between adjacent array elements and the distance F between the feed antenna array and the radiation panel are subjected to parameter scanning by a simulation, analytical calculation or experimental measurement method to obtain respective optimal solutions as design guidance.
And subsequently, according to a phase compensation scheme of a Reconfigurable Artificial Surface (RAS) adopted on the radiation panel, phase compensation is carried out on the incident total field, so that electromagnetic waves are coherently superposed in a radiation far field after passing through each RAS unit, and energy is converged in the required beam pointing direction, thereby realizing beam scanning.
The invention has the following beneficial effects:
under the condition of the same input total power, compared with a single spherical wave space feed source, the short-distance feed by taking the antenna array as the space feed source effectively reduces the section height of the phased array, shortens the transmission path of the electromagnetic wave in the free space, reduces the corresponding transmission loss, improves the power utilization rate, and has important significance for the application of millimeter wave and terahertz frequency bands.
Compared with the traditional space feed phased array, the standard horn antenna is required to be a feed source, the requirement on the feed source is relaxed, the form of incident electromagnetic waves is not limited, any feed antenna array can be used as the feed source of the radiation panel, and the design of the phased array is more flexible and changeable.
In the whole space beam scanning process, the beam gain keeps small fluctuation, and the gain fluctuation is not more than 4dB when the beam scanning angle is up to 70 degrees, so that the technical problem that the scanning angle is limited due to the fact that the large-angle gain in the traditional phased array is quickly attenuated is effectively solved.
Drawings
FIG. 1 is a block diagram of a diffraction phased array structure based on array spatial feeding;
FIG. 2 is a block diagram of a conventional spatial feed phased array;
FIG. 3 is a schematic diagram of an example patch array structure;
FIG. 4 is a schematic structural diagram of an example slot antenna array;
FIG. 5 is a schematic diagram of an example structure of a half-wave oscillator array;
FIG. 6 is a graph of amplitude and phase distribution of the total field incident on the array feed;
FIG. 7 is a comparison graph of aperture efficiency for different phase compensation modes;
FIG. 8 is a block diagram of an example feed for a Ka-band 1x2 patch array;
fig. 9 is a graph of the results of s11 for the feed antenna array of fig. 8;
fig. 10 is a phase difference distribution corresponding to beam scanning based on 1x2 patch array spatial feeding;
fig. 11 is a beam scanning normalized beam gain diagram based on 1x2 patch array spatial feeding.
Wherein: 1. the antenna comprises a space feed source feed antenna array, 2 a radiation panel, 3 array units, 4 non-uniform field distribution based on array feed, 5 horn antenna, 6 spherical wave, 7 spherical wave field distribution, 8 dielectric substrate of patch array, 9 patch units, 10 dielectric substrate of slot array, 11 slot units, 12 half-wave oscillator units, 13 metal reflecting plates, 14.1x2 patch units of patch array, 15.1x2 upper dielectric substrate of patch array, 16.1x2 feed metal holes of patch units, 17.1x2 lower dielectric substrate of patch array, 18.50 ohm microstrip lines and 19.100 ohm microstrip lines.
Detailed Description
The invention will be further described and illustrated with reference to the following figures and examples: the present embodiment is based on the technical solution of the present invention, and the protection scope of the present invention includes, but is not limited to, the following embodiments.
As shown in fig. 1, the antenna comprises a spatial feed antenna array 1 and a radiation panel 2, wherein the spatial feed antenna array 1 and the radiation panel 2 are arranged in parallel and at intervals, the geometric centers of the spatial feed antenna array 1 and the radiation panel 2 are at the same height, and the spatial feed antenna array 1 and the radiation panel 2 are arranged in a close distance; thereby reducing the profile height of the diffractive phased array antenna. The sectional height of the diffractive phased array antenna refers to a vertical distance from the back surface of the feed antenna array to the surface of the radiation panel where the electromagnetic wave is radiated.
The spatial feed antenna array 1 is an unlimited form of feed antenna array, and includes a plurality of array elements 3 that can be equivalent to ideal point sources. Generally, the number of the array elements is not less than 2 and the array elements are uniformly distributed.
The radiation panel 2 is a planar aperture formed by a periodic uniform or non-uniform arrangement of a plurality of reconfigurable artificial surface (RAS, such as frequency selective surface) elements;
electromagnetic waves radiated by the feed antenna array are transmitted to the radiation panel 2 through free space, an incident field 4 with non-uniform distribution of amplitude and phase is formed on the back of the radiation panel 2, a plurality of reconfigurable artificial surface units of the radiation panel 2 perform independent phase compensation on the electromagnetic waves incident to the reconfigurable artificial surface units in the incident field 4, so that the electromagnetic waves emitted from the radiation surface of the radiation panel (2) are converged along a specified beam direction, even if transmitted waves are deflected to a specified scanning direction, the fluctuation of beam gains pointing to different directions is reduced while a larger scanning angle is realized, and a target diffraction phased array is obtained.
As shown in fig. 2, a conventional phased array feeds an antenna array with a single antenna, typically a horn antenna 5, as a spatial feed. After the spherical wave 6 radiated by the radiation panel is propagated through a free space, an incident field 7 which is concentrically and annularly distributed in amplitude and phase and regular in shape is formed on the radiation panel. Unlike the conventional single spherical wave feed represented by a horn antenna shown in fig. 2, the feed antenna array of the present invention includes, but is not limited to, a patch array, a slot array, and a dipole array.
The number N of the array units 3 of the spatial feed antenna array 1, the distance d between two adjacent array units 3 and the distance F between the spatial feed antenna array 1 and the radiation panel 2 are determined by using the maximum aperture efficiency of the target diffraction phased array and the minimum gain drop when the beam is scanned to the maximum angle as optimization targets, and the method includes but is not limited to simulation, analytic calculation and experimental measurement. Here, the pitch d between two adjacent array units 3 refers to a distance between geometric centers of two adjacent array units 3. The distance F between the feed antenna array and the radiation panel 2 is a distance perpendicular to the plane direction of the radiation panel and the feed antenna array.
The close distance setting between the space feed source feed antenna array 1 and the radiation panel 2 is specifically that the ratio F/L of the distance F between the space feed source feed antenna array and the radiation panel 2 and the side length L of the radiation panel 2 is not more than 0.5.
The electromagnetic wave incident on the radiation panel in the present invention is not limited to the spherical wave because the electromagnetic wave is the field superposition on the radiation panel of the spherical wave simultaneously radiated by a plurality of array elements (i.e. array elements 3) of the feed antenna array which approximate to the ideal point source. And thus an arbitrary field with arbitrary amplitude and phase fluctuations as shown in fig. 6.
The reconfigurable artificial surface unit comprises but is not limited to a multilayer dielectric structure welded with a PIN tube or a varactor, the multilayer dielectric structure performs phase compensation on electromagnetic waves incident to the multilayer dielectric structure according to the beam pointing requirement, and the phase compensation is specifically 1-bit or multi-bit discrete phase compensation or 180-degree or 360-degree continuous phase compensation.
A Cartesian coordinate system is established by using the plane of the radiation panel, the geometric center of the radiation panel is used as a coordinate origin O (0, 0), and the geometric center is used as a phase reference point. The current electric field phase value of the rest points on the radiation panel and the equal phase difference line distribution of the ideal phase required by beam scanning are used as phase compensation basis, and the non-central point on the aperture surface is marked as P (x, y). The direction perpendicular to the radiation panel is the direction of the z axis of the outgoing direction of the electromagnetic wave, the geometric center of the feed antenna array and the geometric center of the radiation panel are positioned on the z axis and are arranged in parallel, and the distance between the geometric centers is represented by a parameter F. The side length of the radiation panel is set to be L, and the focal length ratio F/L of the phased array based on the array feed is not more than 0.5. Electromagnetic waves radiated by the feed antenna array are transmitted through free space and enter the radiation panel to form non-uniform field distribution 4 with random fluctuation of amplitude and phase based on array feed, and the phase difference distribution can be random state distribution without fixed rules in the shape of a plurality of ellipses, irregular polygons or other arbitrary closed-loop contour line gradient forms. Each RAS unit on the radiation panel performs independent phase compensation on incident electromagnetic waves, so that transmission wave energy is converged to a specified beam direction, and a diffraction phased array with small gain fluctuation during large-angle scanning is realized.
As shown in fig. 2, the conventional phased array uses a single feedhorn 5 as the spatial feed feedantenna array. To achieve large angular scanning, it is typically placed at a distance from the radiation panel corresponding to a focal length ratio F/L of 0.6 to 0.8, where F/L is 1 in individual designs. The horn antenna is equivalent to an ideal point source, and spherical wave field distribution 7 with the amplitude and the phase distributed concentrically and annularly is formed by the spherical wave 6 radiated by the horn antenna and propagating on a radiation panel through free space. Whereas the incident field formed in fig. 1 based on the co-feeding of a plurality of ideal point sources is in an irregular shape as a whole.
The invention does not require the excitation mode of each array element in the feed antenna array, because each array element is similar to an ideal power supply and radiates spherical waves no matter which excitation mode is adopted. Only the influence of the number N of elements and the spacing d of the elements on the side of the feed antenna array facing the radiating panel on the total field incident on the radiating panel is considered. In addition, the number N of array elements and the distance d between the array elements of the feed antenna array, and the distance F between the feed antenna array and the radiation panel are determined in an actual engineering design by using a method in which the maximum aperture efficiency of the phased array and the gain reduction degree when the beam is scanned to the maximum angle are used as an optimization objective function, wherein the method includes but is not limited to simulation, analytical calculation and experimental measurement. The feed antenna array structure diagrams described below are therefore only shown schematically as an example of the form and distribution of the array elements, and the number, spacing and size of the array elements are not set as parameters for specific examples.
Fig. 3 shows a schematic diagram of a uniform patch array, one form of feed antenna array. And etching the patch units 9 on the dielectric substrate 8 of the patch array, and uniformly placing the patch units at equal intervals d along the directions of the x axis and the y axis. The shape and size of the patch unit are designed according to the working frequency of RAS in the phased array and the electromagnetic wave polarization mode. The patch array in fig. 3 has a total of 4 rectangular patches, with a horizontal polarization along the narrow sides of the patch elements, and a pitch d of 2 wavelengths. Each patch unit is used as a spherical wave source and emits spherical waves with equal amplitude and same phase to the radiation panel.
Fig. 4 shows a composed 2x3 array of 6 rectangular slots (i.e., slot cells 11) uniformly distributed. The slot units 11 are symmetrically distributed about the x and y axes of the dielectric substrate 10 of the slot array, and adjacent slots are spaced by 3 wavelengths. By the babinet reciprocity theorem, the slot cell can be regarded as a dipole cell, the in-phase excitation radiation electromagnetic wave is incident to the radiation panel, and the electric field polarization is vertical polarization along the narrow side of the slot.
Fig. 5 shows that 3 half-wave oscillator units 12 with half wavelength length are arranged at equal intervals along the horizontal direction to form a dipole linear array. Because the dipoles uniformly radiate in all directions on a plane perpendicular to the oscillator arms, and the feed antenna array in the phased array only needs to radiate towards the direction with the radiating panel in the front direction, a metal reflecting plate 13 with the same magnitude as the feed antenna array is arranged at the backward quarter wavelength away from the half-wave oscillator array, backward radiation electromagnetic waves of the feed antenna array are subjected to reverse radiation, and backward radiation energy is radiated towards the direction of the radiating panel again.
Based on the design principle of the feed antenna array in the present invention, fig. 3, fig. 4 and fig. 5 show schematic diagrams of three different feed antenna array structures, that is, no matter what excitation method is adopted, each array element can be approximately regarded as an ideal point source to radiate spherical waves outwards, and an incident total field with randomly distributed amplitude and phase is formed on a radiation panel by superposition. As shown in fig. 6 (a) and (b), the amplitude and phase distribution of the incident electric field on a radiation panel with a square aperture is shown. The maximum amplitude on the panel is used for normalization, the amplitude attenuation of other points is between 0 and-20 dB, and the attenuation of each point is irregular, so that the method is different from the traditional method that the amplitude is monotonically attenuated from the center to the outer direction when a single spherical wave is used as a feed source. The phase distribution is also any fluctuation distribution between 0 degree and 360 degrees, and is different from the traditional method that the phase is monotonously increased from the center to the outer radial direction when a single spherical wave is used as a feed source.
The operating principle of a phased array based on array feeding is explained next. As shown in FIG. 1, the aperture area is L x ×L y The geometric center point of the radiation panel is used as the origin of coordinates to establish a Cartesian rectangular coordinate system. The origin of coordinates O (0, 0) is set as a phase reference point, and the point P with coordinates (x, y) represents any other point on the radiation panel except the origin of coordinates. An array feed comprising N elements is placed at a distance F directly behind the radiating panel. Suppose the array feed is located at (x) n ,y n And F) the excitation current of the nth array element of the coordinate point is
Wherein I n Representing the amplitude, alpha, of the exciting current of the nth array element n Representing the phase of the excitation current of the nth array element, j representing the imaginary identification of the imaginary number, N =1,2,3 \ 8230n, N, the total field of incidence E at any point P (x, y) on the radiating panel tot (x, y) may be expressed as:
wherein,
and (4) radiating a Green function expression of spherical waves for the nth array element.
Is the straight line distance between the nth array element and the P (x, y) point on the radiation panel. k is the free space wavenumber. E (x, y) represents an arbitrary point on the radiation panelTotal field of incidence E at P (x, y) tot The magnitude of (x, y).
According to the phased array principle, for a given beam deflection direction
Ideal phase Ψ for P (x, y) point P (x, y) may be expressed as:
wherein, theta 0 Representing the angle between the main lobe direction of the phased array beam and the z-axis.
And the included angle between the projection of the main lobe direction of the phased array beam on the xoy plane and the x axis is shown.
The phase difference Δ Φ (x, y) between the P (x, y) point on the radiation panel and the phase reference point O (0, 0) is calculated by:
ΔΦ(x,y)＝Ψ P (x,y)-(Φ(x,y)-Φ(0,0)) (3)
where Φ (x, y) and Φ (0, 0) are the incident total field E of the P-point and O-point tot Phase values of (x, y). Based on equations (2) and (3), the phase difference Δ Φ (x, y) can be expressed as:
due to the periodicity of 2 pi. The phase difference Δ Φ (x, y) will be divided into four quadrants as shown in equation (5):
wherein m is a cycle number, and is an integer, quadrant I represents a first Quadrant, quadrant II represents a second Quadrant, quadrant III represents a third Quadrant, and Quadrant IV represents a fourth Quadrant. For those points where the phase difference belongs to a quadrant, the electromagnetic waves emitted from the radiation surface of the radiation panel 2 are coherently and constructively superimposed in the far field, especially at the point where the phase difference is zero, the emitted electromagnetic waves are superimposed in the far field in the same phase, and the electric field can be maximally enhanced. The phase difference belongs to a point of two quadrants and three quadrants, and the emergent electromagnetic waves are incoherently superposed in a far field, so that the total field is offset and weakened. Therefore, the phase compensation capability of each unit of the RAS on the radiation panel is usually utilized to provide an additional phase for the outgoing waves of each point, so as to compensate the phase difference, so that as many outgoing electromagnetic waves as possible are coherently superposed in the far field, and the radiation far field is maximized.
There are generally a phase 1 bit type, a 2 bit type, and a continuous 180 degree multi-bit type, etc., according to the RAS compensation capability and manner. If the RAS is designed based on a PIN switch tube, the phase switching of transmitting electromagnetic waves of 0/180 degrees of the RAS unit can be realized by controlling the on-off of the PIN tube, and the method is applied to a typical phase 1 bit 0 degree/180 degree compensation mode. Specifically, 180-degree extra phase is provided for each point in the non-coherent region, that is, 180 degrees are uniformly compensated for the non-coherent region, so that the non-coherent region becomes the coherent region. And providing a 0-degree compensation value for each point originally positioned in the coherent region, namely, not changing the phase of the electromagnetic wave of the originally coherent region. Thus, all the regions are changed into coherent regions, and the transmittance of energy is improved. The phase compensation value Δ Ψ (x, y) for a specific P (x, y) point can be calculated by the following equation:
another phase compensation approach is based on the RAS embedded varactor. The bias dc voltage of the varactor on the RAS is typically controlled to vary continuously and the phase of the transmitted electromagnetic wave on the RAS cell will vary continuously, such as by 180 or 360 degrees. Based on the continuous 180-degree phase compensation method, the phase compensation value Δ Ψ (x, y) at the P (x, y) point on the radiation panel can be calculated as follows:
as can be seen from equation (7), the continuous 180-degree phase compensation method specifically operates to completely compensate for the area where the phase difference is in the first and second quadrants, i.e., to change the original phase difference to 0. And the area with the phase difference in the third quadrant is uniformly compensated for 180 degrees, and the area with the phase difference in the fourth quadrant is uniformly not compensated.
After compensation, the total radiation field of each point on the radiation panel needs to be added with a phase compensation value on the basis of the original total incident field, which can be expressed as:
wherein, E' tot (x, y) represents the total field of radiation at any point P (x, y) on the radiation panel,
indicating a defining symbol, i.e. E immediately before tot (x,y)e jΔΨ(x,y) Is defined as E (x, y) E jΦ′(x,y) The method of (4).
The corresponding phase difference after compensation becomes:
ΔΦ′(x,y)＝Ψ P (x,y)-(Φ′(x,y)-Φ′(0,0)) (9)
where Φ '(x, y) and Φ' (0, 0) are the phase values of the compensated total field of radiation for point P and point O, respectively. Based on equation (9), the phased array aperture efficiency η is calculated as follows:
η＝|∫∫E t ′ ot (x,y)dS| 2 /S∫∫E′ tot (x,y)| 2 dS (10)
wherein S = L x ×L y Is the area of the radiating panel, ds represents the integral over the area of the radiating panel, | survival 2 Representing a mathematical operation of modular re-squaring complex numbers within a symbol.
The aperture efficiency, which is one of the most important performance indexes of the phased array, is used as a measurement standard, and the results of comparing the advantages and disadvantages of the phase 1 bit type and the continuous 180-degree compensation mode under different focal length ratios are shown in fig. 7. From the analysis in the figure, when F/L is more than 0.3, the aperture efficiencies of the two modes tend to be saturated. The overall aperture efficiency of the continuous 180-degree compensation mode is about 40% higher than that of the 1-bit type, and the superiority of the continuous 180-degree compensation mode in the diffraction phased array is illustrated.
According to the huygens-fresnel principle, the electric field of the phased array in the far radiation region can be expressed as:
the corresponding directivity factor can be expressed as:
wherein, θ and
respectively represents the pitch angle and the azimuth angle of the space direction under the spherical coordinate, namely theta represents the included angle between the space vector and the z axis,
and the included angle between the projection of the space vector on the xoy plane and the x axis is represented.
Representing phased array beams in space
The directivity factor in the direction of the direction,
representing phased array beams in space
The strength of the electric field in the direction.
Representing phased array wavesMain valve of bundle
The strength of the electric field in the direction.
So far, with the help of a monte-larlo optimization algorithm, under the condition of giving the aperture area S of the radiation panel, the aperture efficiency of the phased array and the directivity coefficient of each beam, namely the ideal gain, are respectively calculated according to formulas (10) and (12), the number N of feed antenna arrays, the array element spacing d and the focal length F are optimized, and the optimal values of the parameters N, d and F under the maximum aperture efficiency and the minimum gain fluctuation are obtained and used for actual engineering design.
Take an example of a diffractive phased array operating in the 5G millimeter wave 28GHz band. The radiating panel in the example is a rectangular aperture of 6 x3 lambda. The most common microstrip patch array is a spatial feed antenna array. The number of the patch array elements obtained by optimization is 2, the distance d is 30mm, and the focal length F is 20mm. Fig. 8 (a) and (b) are top patch layer and bottom microstrip power-layering structure diagrams of a 1x2 patch array, respectively. Two standard patch units 14 are placed in parallel at a distance of 30mm on an upper dielectric substrate 15 of a 1x2 patch array, and the lower surface layer of the upper dielectric substrate 15 of the 1x2 patch array is an integral metal ground, namely a lower dielectric substrate 17 of the 1x2 patch array. A micro-strip power dividing network is arranged on a lower-layer dielectric substrate 17 of the 1x2 patch array, a 50-ohm micro-strip line 18 is used as a total input port of the feed antenna array, and a left 100-ohm micro-strip line 19 and a right 100-ohm micro-strip line 19 are divided on a central axis of the dielectric plate. And a feed metal hole 16 of a 1x2 patch unit represented by a black dot of each patch is used as a feed through hole, and the patches and the 100 ohm microstrip line are connected with metal for realizing impedance matching for radiation excitation. The upper dielectric substrate 15 and the lower dielectric substrate 17 both adopt Rogers 4350B plates with the thickness of 0.254 mm. Fig. 9 shows the s11 curve of the patch array, and the s11 of the feed antenna array is lower than-10 dB in the frequency band of 26GHz-28.6GHz, and the good broadband matching characteristic is shown.
A 1x2 array of patches was placed 20mm directly behind the radiating panel as a feed. The RAS is designed to be a multi-layer dielectric laminated structure embedded with a varactor and has continuous 180-degree phase compensation capacity. Assuming that the beam is scanned in the horizontal direction, i.e.
θ 0 The phase difference distribution after phase compensation is calculated according to equation (9) by scanning from 0 ° to 70 ° at an interval of 10 °. As shown in fig. 10, each of the small graphs represents a distribution of diffraction phase differences corresponding to the beam orientations. It can be seen from the figure that the area ratio of the region with the phase difference of 0 is the largest when the beam is directed (20 ° and 0 °), which represents the beam direction, the ratio of the electromagnetic wave emitted from the radiation panel in the far-field superposition type in-phase superposition is the largest, and it corresponds to the peak gain of the beam occurring in the 20 ° direction during the beam scanning process. Finally, the beam gain result calculated according to the formula (12) is shown in fig. 11, the gain and the phase difference distribution mapping result are completely matched, and the peak gain occurs in the 0 ° direction. The whole scanning range can reach 70 degrees, and the gain of the beam scanning to 70 degrees is reduced by only 3.94dB. The overall profile height of the diffractive phased array in this example is 22mm, which is a 60% reduction over the conventional profile height using a feedhorn.
In summary, the main innovation point of the present invention is to provide a feeding antenna array for spatially close feeding a radiation panel with reconfigurable phase. Under the condition that the input total power is the same, compared with a single spherical wave feed source, the feed antenna array feeds in a close distance mode, the section height of the phased array is effectively reduced, the transmission path of electromagnetic waves in a free space is shortened, the corresponding transmission loss is reduced, the power utilization rate is improved, and the feed antenna array has important significance for application of millimeter waves and terahertz frequency bands.
In the whole space beam scanning process, the beam gain keeps small fluctuation, and the gain fluctuation is not more than 4dB when the beam scanning angle is up to 70 degrees, so that the technical problem that the scanning angle is limited due to the fact that the large-angle gain in the traditional phased array is quickly attenuated is effectively solved. Diffractive phased array antennas may be used in the radio frequency, microwave, millimeter wave, and terahertz wave fields.
The above examples are merely preferred examples of the diffraction phased array of the present invention for a fixed aperture area at a specific frequency band of 28GHz, and are not intended to limit the invention in any way, and any person skilled in the art may modify or modify the equivalent examples using the above disclosure. However, any simple modification, equivalent change and modification made to the above examples according to the technical essence of the present invention are still within the protection scope of the present invention, unless the technical essence of the present invention departs from the technical solution content of the present invention.
Claims (6)
1. The diffraction phased array antenna based on space feed is characterized by comprising a space feed antenna array (1) and a radiation panel (2), wherein the space feed antenna array (1) and the radiation panel (2) are arranged in parallel at intervals, the geometric centers of the space feed antenna array (1) and the radiation panel (2) are at the same height, and the space feed antenna array (1) and the radiation panel (2) are arranged in a close range; the radiation panel (2) is a plane caliber formed by periodically uniformly or non-uniformly arranging a plurality of reconfigurable artificial surface units;
electromagnetic waves radiated by the space feed source feed antenna array (1) are transmitted to the radiation panel (2) through free space, an incident field (4) with non-uniform distribution of amplitude and phase is formed on the back surface of the radiation panel (2), and a plurality of reconfigurable artificial surface units of the radiation panel (2) perform independent phase compensation on the electromagnetic waves incident to the electromagnetic waves in the incident field (4) to obtain the target diffraction phased array.
2. A spatial feed based diffractive phased array antenna according to claim 1, characterized in that the spatial feed antenna array (1) comprises but is not limited to patch array, slot array, dipole array.
3. A spatial feed based diffractive phased array antenna as claimed in claim 1, characterized in that said spatial feed antenna array (1) is a feed antenna array consisting of a plurality of array elements (3); the number N of the array units (3), the spacing d between two adjacent array units (3) and the distance F between the feed antenna array and the radiation panel (2) are determined by adopting a method which takes the maximum aperture efficiency of a target diffraction phased array and the lowest gain reduction when a beam is scanned to the maximum angle as optimization targets, wherein the method comprises but is not limited to simulation, analytic calculation and experimental measurement.
4. The spatial feed based diffractive phased array antenna according to claim 1, characterized in that a close distance is set between the spatial feed antenna array (1) and the radiation panel (2), specifically, the ratio of the distance F between the spatial feed antenna array (1) and the radiation panel (2) to the side length L of the radiation panel (2) is not more than 0.5.
5. The spatial feed based diffractive phased array antenna according to claim 1, wherein the reconfigurable artificial surface unit comprises but is not limited to a multilayer dielectric structure welded with PIN tubes or varactors, and the multilayer dielectric structure performs phase compensation on electromagnetic waves incident to the reconfigurable artificial surface unit according to beam pointing requirements.
6. A spatial feed based diffractive phased array antenna as claimed in claim 1 or 5, characterized in that said phase compensation is in particular a discrete phase compensation of 1 or more bits or a continuous phase compensation of 180 or 360 degrees.
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