Background
Terahertz (THz) waves generally refer to electromagnetic waves with the frequency range of 0.1 THz-10 THz, are between millimeter waves and infrared light, have the characteristics of microwaves and infrared light, and are characterized by moderate beam width, large system bandwidth, and great contribution to target detection imaging and high-speed high-capacity communication.
The artificial Electromagnetic material (Electromagnetic material) or the composite material (composite material) can break through the limitation of the change freedom of the dielectric constant and the magnetic permeability of the existing material in the nature, and shows great application potential in the aspect of regulating and controlling Electromagnetic waves. The artificial electromagnetic material is an artificial metamaterial which can freely regulate and control the transmission property of electromagnetic waves by designing a certain artificial structural unit in two or more traditional medium materials (such as metal and medium) and combining the artificial structural unit periodically or aperiodically. Metamaterial (Metamaterial) is a hot research field in artificial electromagnetic materials, and required equivalent medium parameters can be designed by changing the size and arrangement mode of a unit structure. Therefore, the metamaterial can realize the electromagnetic characteristics which cannot be realized by natural materials, such as zero-refractive-index phenomenon, negative-refractive-index phenomenon, perfect lens, tunneling effect, negative dielectric constant, highly anisotropic metamaterial and the like.
The academician proposed the concept of encoding metamaterials in 2014, and designed an independently controllable phase shifter resonant structure, with a phase difference of about 180 ° in the frequency band of 8.3-8.9 GHz. The units can be independently controlled, which means that different functions can be realized by controlling the states of different units in the super-surface array, and the super-surface array is subjected to coding operation, so that digital adjustment and real-time adjustment of electromagnetic waves are realized. Later, many scholars have conducted intensive research into the independent control of metamaterials.
However, there is little research on three-dimensional beam steering in the terahertz frequency band. The main difficulty is to achieve independent coded control of the state of each resonant cell. At present, researchers propose that the state of each resonance unit is independently controlled through punching, but the terahertz frequency band is short in frequency and short in wavelength, and the unit size is small. The antenna unit of the terahertz frequency band is difficult to punch, the difficulty of realizing metal conduction after punching is higher, and no report of realizing related process technology exists in the industry at present. Under the background, the switch tube is placed on the lower surface of the unit through the arrangement of the coupling ring, so that the scheme that the state of the unit can be controlled only through the metal through hole is avoided ingeniously, and the independent control of the state of each antenna unit in the array is realized.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides the terahertz independent electric control coding antenna which can be independently controlled, has high efficiency, wide band, stable in-band phase, convenient regulation and control and easy processing.
The technical scheme adopted by the invention for solving the technical problems is that the terahertz independent electrically controlled coding antenna comprises an antenna array formed by square antenna units with the same shape and size in an orthogonal arrangement mode, and is characterized in that the antenna units comprise:
the annular metal coupling ring is arranged on the upper surface of the substrate medium substrate;
the metal coupling sheet layer is arranged on the lower surface of the substrate medium substrate and is provided with an annular channel, a first channel and a second channel, wherein the position and the shape of the annular channel are complementary to those of the metal coupling ring, and the width of the first channel is the same as that of the second channel; the ring-shaped channel, the first channel and the second channel divide the metal coupling sheet into 3 parts: a circular metal patch with the center located at the center of the antenna unit and two semi-arc metal patches with the same shape; two semi-arc-shaped metal patches in the same antenna unit are respectively connected to a source electrode and a drain electrode of a voltage control switch tube, and a grid electrode of the voltage control switch tube is connected with the circular metal patches;
in each row, the semi-arc metal patches on the same side belong to the same integral patch, and the adjacent semi-arc metal patches on both sides of the boundary of the same row belong to the same integral patch.
The substrate dielectric substrate is made of silicon carbide.
The voltage control switch tube is a High Electron Mobility Transistor (HEMT).
The antenna unit is rectangular, and the area of the antenna unit is the sum of the areas occupied by the circular metal patch, the semi-arc metal patch, the annular channel, the first channel and the second channel.
The antenna element is square with a side length of 200 μm,
the thickness of the substrate dielectric substrate is 80 μm,
the radius of the metal coupling ring is 50 μm, the line width is 8 μm,
the first and second trenches are equal in width and are both 7 μm,
the metal coupling ring, the semi-arc metal patch, the circular metal patch and the grid voltage control line are made of metal Au, and the thickness of the metal coupling ring, the semi-arc metal patch, the circular metal patch and the grid voltage control line is 200 nm.
The invention has the following advantages:
1) according to the invention, metal punching in the unit is cancelled, and the switch structure and the complementary structure of the surface coupling ring are combined, so that the structure is simpler, and the regulation and control efficiency is higher;
2) compared with the traditional single-layer reflection resonance structure, the single-layer reflection resonance structure has the advantages that a metal bottom plate is omitted, the metal coupling ring is added, the resonance structure is separated from the switch, the bandwidth is doubled, and meanwhile, the unit independent coding control is realized;
3) the invention adopts the source and drain coplanar design, so that the source and drain feeder line and the coupling structure are combined into a whole, the processing of electrode through holes is greatly reduced, and meanwhile, because the source and drain are separated from the grid, the grid voltage can be independently and directly connected to a PCB control board by ball-planting, thereby greatly reducing the wiring difficulty;
4) the invention improves the coupling effect and the resonance effect among the units by adjusting the key structure parameters and the substrate thickness of the antenna unit, can realize ideal scattering coefficient, scattering phase change, bandwidth widening and improves the in-band flatness;
5) the N multiplied by N array formed by the invention can realize flexible three-dimensional beam control in terahertz wave band. The method has important application value for the development of terahertz three-dimensional beam control.
Detailed Description
The invention is called vacancy interpretation: on a complete planar laminated structure, after removing the structural material of a partial region, the missing part is called a vacancy.
The terahertz independent electrically controlled coding antenna comprises square antenna units which are arranged in an orthogonal array and have the same shape and size, and each antenna unit comprises:
the metal coupling ring 1 is arranged on the upper surface of the substrate medium substrate 2;
the symmetrical semi-arc metal patches 3 are arranged on the lower surface of the substrate medium substrate 2;
the circular metal patch 4 is arranged on the lower surface of the substrate medium substrate 2;
a grid voltage control line 5 arranged on the lower surface of the substrate medium substrate 2;
a voltage control switch tube 6 arranged on the lower surface of the substrate medium substrate 2;
an annular vacant region is arranged between the symmetrical semi-arc metal patch 3 and the circular metal patch 4 on the lower surface of the substrate medium substrate 2, the region surrounded by the annular vacant region is called a central region, and the annular vacant region corresponds to the metal coupling ring 1 on the upper surface of the substrate medium substrate 2 to form a complementary relationship;
a first channel and a second channel are formed between the two symmetrical semi-arc metal patches 3 on the lower surface of the substrate medium substrate 2, wherein the axes of the first channel and the second channel are overlapped, and the axes form the center of a circle through an annular vacant area;
the current input end and the current output end of the switch tube crossing the first channel are respectively and electrically connected with the two symmetrical semi-arc metal patches 3, and the grid voltage control line 5 of the switch tube is electrically connected with the circular metal patch 4;
the voltage of the central area is controlled by the outside, and the voltage is controlled by a PCB control board 9 through a metal planting ball 7;
the axes of the first channel and the second channel of each antenna unit are parallel to the row lines, the first channel and the second channel belong to the connecting channels, and in each antenna unit in the same row, the annular vacant areas of the adjacent antenna units are connected with each other through the connecting channels;
the substrate medium substrate 2 is made of silicon carbide;
the voltage control switch tube 6 is a high electron mobility transistor HEMT, the two symmetrical semi-arc metal patches 3 are respectively connected with a drain electrode and a source electrode of the HEMT, and the grid voltage control line 5 is connected with a grid electrode of the HEMT.
The side length a of the square antenna unit is 200 μm, the thickness d of the substrate dielectric substrate 2 is 80 μm, the radius r of the metal coupling loop 1 is 50 μm, the line width s of the metal coupling loop 1 is 8 μm, and the widths g of the first channel and the second channel are 7 μm; the metal coupling ring 1, the symmetrical semi-arc metal patches 3, the circular metal patches 4 and the grid voltage control line 5 are made of metal Au with the thickness of 200 nm.
The NxN terahertz independent electrically-controlled coding antennas are orthogonally arranged to form an antenna array, and the circular metal patches 4 arranged on the lower surface of each unit substrate medium substrate 2 are connected with the metal patches 8 on the PCB control board 9 in a metal ball-planting mode 7.
Examples
As shown in fig. 1, 2 and 3, the invention comprises a metal coupling ring 1, a substrate dielectric substrate 2, a symmetrical semi-arc metal patch 3, a circular metal patch 4, a gate voltage control line 5 and a voltage control switch tube 6.
The antenna comprises a plurality of antenna units which are arranged in an orthogonal array, wherein each antenna unit comprises a metal coupling ring on the upper surface of a substrate dielectric substrate and a reconfigurable metal structure on the lower surface of the substrate dielectric substrate. The upper surface of the substrate medium substrate 2 is provided with a metal coupling ring 1.
An annular vacant area is arranged between the symmetrical semi-arc metal patches 3 and the circular metal patches 4 on the lower surface of the substrate medium substrate 2, the area surrounded by the annular vacant area is called a central area, and the annular vacant area corresponds to the metal coupling ring 1 on the upper surface of the substrate medium substrate 2; a first channel 101 and a second channel 102 are formed between the two symmetrical semi-arc-shaped metal patches 3, wherein the axes of the first channel 101 and the second channel 102 are coincident, and the axes form the center of a circle through the annular vacant area.
A current input end and a current output end of a voltage control switch tube 6 crossing the first channel are respectively and electrically connected with the two symmetrical semi-arc metal patches 3, and a grid voltage control line 5 of the switch tube is electrically connected with the central area; the voltage in the central area is controlled externally, and the voltage is controlled by a PCB control board 9 through a metal planting ball 7.
The axes of the first channel and the second channel of each antenna unit are parallel to the row line, the first channel and the second channel belong to the connecting channel, and in each antenna unit in the same row, the annular vacant areas of the adjacent antenna units are connected with each other through the connecting channel.
The voltage control switch tube 6 is a high electron mobility transistor HEMT, the two symmetrical semi-arc metal patches 3 are respectively connected with a drain electrode and a source electrode of the HEMT, and the grid voltage control line 5 controls a grid electrode of the HEMT.
The substrate dielectric substrate 2 is made of silicon carbide, and has a dielectric constant of about 9.8, a magnetic permeability of 1, a loss tangent of 0.0003 and a thickness d.
The antenna element is square and has a length and a width. The radius of the open resonant ring is r, and the radius of the grid voltage control metal wire of the HEMT is also r. The width of the metal coupling ring is s, and the widths of the first channel and the second channel are g. The metal coupling ring, the symmetrical semi-arc metal patch, the circular metal patch and the grid voltage control line are made of metal Au with the thickness of h, and the conductivity is 4.561e + 007.
The structural parameters of the multilayer antenna unit shown in fig. 2 are as follows: 108 μm for a, 80 μm for d, 50 μm for r, 8 μm for s, 200nm for h, and 7 μm for g.
The antenna units of the invention can share the same layer structure, for example, the substrate dielectric substrate part of each antenna unit is divided on a whole dielectric substrate, the division is not divided into a plurality of separated substrates, but the positions of the substrates are virtually divided, different position areas are used as the substrate dielectric substrates of the corresponding antenna units, and after the division, the structure is still a complete dielectric substrate.
Fig. 4 and fig. 5 are a schematic diagram of a front structure and a schematic diagram of a back structure of the terahertz independent electrically-controlled coding array provided by the invention, respectively, in the back structure, symmetrical semi-arc metal patches 3 of two units above and below each row are communicated into a whole, and two symmetrical semi-arc metal patches 3 of two units clinging to each other on each row are communicated together. In the back structure, in the same column, when any one of the voltage control switch tubes 6 is turned on, the symmetrical semi-arc metal patches 3 of all the units in the column are communicated, but the turning-on positions of the voltage control switch tubes 6 are different, and the positions where the electromagnetic wave resonance passes are also different, so that the turning-on of the voltage control switch tube 6 in one unit in each column has no influence on other units in the column, and the electromagnetic wave resonance state of each unit in the array is independently controlled.
Fig. 7 is a graph of results of a scattering efficiency coefficient curve and a scattering phase curve for different HEMT control states. The result graphs of the scattering efficiency coefficient curve and the scattering phase curve are obtained by simulating by high-frequency electromagnetic simulation software CST: when the HEMT is switched off, the code is defined as 0, and when the HEMT is switched on, the code is defined as 1; the reflection coefficients of the two encoding states in the bandwidth are both larger than 60%, the phase difference is about 180 degrees at 0.35-0.42THz, and the bandwidth is about 20%; the resonance of "0" occurs at 0.4THz, while the resonance of "1" occurs at 0.345THz and 0.425 THz.
Fig. 8 is a graph simulating the effect of different metal coupling loop sizes on the phase difference result. The influence of different metal coupling ring sizes on the phase difference result is obtained by simulating high-frequency electromagnetic simulation software CST: the mismatch of the coupling loop and the ring-shaped vacant region can cause the phase difference to change, and the mismatch of the coupling loop can cause the attenuation of the resonance field and further can influence the phase difference change between different states.
FIG. 9 is a far field beam scan in one plane under simulation of different column control code states. The simulation is carried out by high-frequency electromagnetic simulation software CST to obtain: by changing different column control coding states, the angle scanning range of the far-field wave beam in the plane, wherein the angle is more than or equal to 16 degrees and more than or equal to theta and less than or equal to 60 degrees, can be realized. Similarly, because each terahertz antenna unit can realize independent electric control coding, the super-surface array is coded in two directions, and three-dimensional scanning in a far-field beam space can be realized.