Apparatus and method for implementing a janus antenna array with unidirectional near-field coupling

Abstract

This invention discloses an apparatus and method for realizing unidirectional near-field coupling of a Janus antenna array, achieving more flexible near-field directional excitation of light. The apparatus for realizing unidirectional near-field coupling of a Janus antenna array includes a feed network structure and an external coupler. The external coupler includes two parallel dielectric waveguides, spaced apart to form an assembly space. The feed network structure includes a feed network and multiple Janus antennas based on Janus dipoles connected to the feed network. The multiple Janus antenna arrays are arranged in the assembly space. Each Janus antenna has an electric dipole and a magnetic dipole that are perpendicular to each other and have a phase difference. The magnetic dipole corresponds to the width direction of the assembly space, and the electric dipole corresponds to the length direction of the assembly space to excite quasi-TM waves in the dielectric waveguides.

Description

Technical Field

[0001] This invention relates to the field of microwave technology, and more particularly to a device and method for realizing unidirectional near-field coupling of a Janus antenna array. Background Technology

[0002] Due to their unique near-field directivity, Janus dipoles have significant application value in fields such as novel on-chip light sources and optical MIMO systems. When using Janus dipoles to achieve near-field directional excitation of light, there are coupled and uncoupled surfaces. When the waveguide is aligned with the coupled surface, the guided wave can be effectively excited; however, when the waveguide is aligned with the uncoupled surface, the guided wave cannot be effectively excited. Recent research has focused on the relationship between the polarization state of guided waves excited by Janus dipoles and the coupled surface. The polarization state of guided waves can be divided into transverse magnetic (TM or p-polarized) waves and transverse electric (TE or s-polarized) waves. The former, during propagation, has only an electric field component along the propagation direction, with all magnetic field components lying in a transverse plane perpendicular to the propagation direction; the latter, during propagation, has only a magnetic field component along the propagation direction, with all electric field components lying in a transverse plane perpendicular to the propagation direction. For example, for transverse magnetic (TM or p-polarized) surface waves, the coupling plane direction is always opposite to that of transverse electric (TE or s-polarized) surface waves. It has been proposed that the direction of near-field coupling can be controlled by polarization. Other studies have shown that perfect excitation of transverse electric and transverse magnetic surface waves can be achieved by designing Janus dipoles and waveguides, exciting only p-polarized waves in one waveguide and only s-polarized waves in another waveguide.

[0003] The aforementioned studies primarily focus on the properties of the guided waves excited on the coupling surface, without considering the direction of the guided waves on the coupling surface. Typically, for a long rectangular waveguide, when it is aligned with the coupling surface of a Janus dipole, the excited guided waves propagate in both directions of the waveguide. Therefore, is it possible to design a device that allows the guided waves to propagate in only one direction on the coupling surface, while preventing the effective excitation of guided waves on other coupling surfaces and in other directions, thereby achieving more flexible near-field directional excitation of light? Summary of the Invention

[0004] To solve the above-mentioned technical problems, the present invention provides a device and method for realizing unidirectional near-field coupling of a Janus antenna array. By designing the Janus antenna array, the excited guided wave propagates only along one direction of the coupling surface, while guided waves in other coupling surfaces and other directions cannot be effectively excited, thereby achieving more flexible near-field directional excitation of light.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A device for realizing unidirectional near-field coupling of a Janus antenna array includes a feed network structure and an external coupler. The external coupler includes two parallel dielectric waveguides spaced apart to form an assembly space. The feed network structure includes a feed network and multiple Janus antennas based on Janus dipoles connected to the feed network. The multiple Janus antenna arrays are arranged in the assembly space, and the Janus antennas are mutually perpendicular and have... Electric and magnetic dipoles with phase difference, the magnetic dipoles corresponding to the width direction of the assembly space and the electric dipoles corresponding to the length direction of the assembly space, are used to excite quasi-TM waves in the dielectric waveguide.

[0006] Preferably, the dielectric waveguide is a strip waveguide, and the strip waveguide is surrounded by air.

[0007] Preferably, the feed network includes a substrate and microstrip lines etched on the substrate, with one end of each microstrip line interconnected as a signal input and the other end serving as a signal output and connected to a Janus antenna.

[0008] Preferably, both the signal input and signal output terminals are equipped with SMA connectors. A coaxial cable is provided between the SMA connector of the signal output terminal and the Janus antenna, and the SMA connector of the signal input terminal is connected to the feed PCB.

[0009] The design steps for the above-mentioned power supply network structure are as follows: A1: Determine the operating frequency of the dielectric waveguide and calculate the corresponding dispersion curve; A2: Based on the dispersion curve characteristics of the dielectric waveguide, determine the phase difference of the Janus antenna and the spacing between adjacent Janus antennas. A3: Design the length of the microstrip line based on the determined phase difference and spacing.

[0010] Based on the aforementioned apparatus for realizing unidirectional near-field coupling of a Janus antenna array, this invention also provides a method for realizing unidirectional near-field coupling of a Janus antenna array, comprising the following steps: B1: Establish a spatial rectangular coordinate system and place the Janus antenna in the yz plane of the coordinate system, and place the dielectric waveguide and the feed PCB in the xy plane of the coordinate system; B2: The electromagnetic waves radiated by the Janus antenna array are coupled into the dielectric waveguide to generate quasi-TM guided waves; B3: The electromagnetic fields of the two dielectric waveguide surfaces are measured using a probe of a detection device to obtain the corresponding electromagnetic field distribution maps. The detection device is a 3672B vector network analyzer. Port 1 of the 3672B vector network analyzer outputs a signal, and port 2 measures the vertical electric field intensity distribution on the dielectric waveguide surface through connection with the probe. The bottom of the probe has an SMA connector, which connects to port 2 of the vector network analyzer via a coaxial cable. The exposed metal wire portion at the top is perpendicular to the dielectric waveguide surface, thus allowing for the measurement of the vertical electric field intensity distribution on the dielectric waveguide surface. B4: Analyze the near-field coupling characteristics of quasi-TM waves excited by multiple Janus antennas in the waveguide based on measurement data.

[0011] Compared with the prior art, the present invention has the following beneficial effects: This invention designs a Janus antenna array so that the excited guided wave propagates only along one direction of the coupling surface, while guided waves in other directions and outside the coupling surface cannot be effectively excited, thus achieving more flexible near-field directional excitation of light. Attached Figure Description

[0012] Figure 1 A structural diagram for achieving unidirectional near-field coupling at the coupling surface of a Janus antenna array; Figure 2 The spatial frequency spectrum of a single Janus dipole; Figure 3 The spatial frequency spectrum of the Janus antenna array; Figure 4 Simulation results for guided waves excited by a single Janus antenna; Figure 5 Simulation results for guided waves excited by a Janus antenna array; Figure 6 It is the upper metal layer structure of a single Janus antenna; Figure 7 This is the upper metal layer structure of the feed network for the Janus antenna array.

[0013] Figure labels: 1. Feed network structure, 2. External coupler, 21. Dielectric waveguide, 22. Assembly space, 11. Feed network, 12. Janus antenna, 13. SMA connector, 14. Coaxial cable, 111. Substrate, 112. Microstrip line. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0015] Example 1 like Figure 1-4The apparatus shown is for realizing unidirectional near-field coupling of a Janus antenna array, comprising a feed network structure 1 and an external coupler 2. The external coupler 2 includes two parallel dielectric waveguides 21, which are spaced apart to form an assembly space 22. The feed network structure 1 includes a feed network 11 and a plurality of Janus antennas 12 based on Janus dipoles connected to the feed network 11. The plurality of Janus antennas 12 are arranged in an array in the assembly space 22, and the Janus antennas 12 are mutually perpendicular and have... Electric and magnetic dipoles with phase difference, the magnetic dipoles corresponding to the width direction of the assembly space 22 and the electric dipoles corresponding to the length direction of the assembly space 22, are used to excite quasi-TM waves in the dielectric waveguide 21.

[0016] The aforementioned dielectric waveguide 21 is a strip waveguide, surrounded by air. Specifically, if the dielectric waveguide 21 were a planar waveguide, the guided wave would propagate outwards like ripples on water after a stone is thrown in; if it were a strip waveguide, the guided wave would only propagate along the long side of the waveguide. Furthermore, p-polarized (TM) waves exist in planar waveguides, while only quasi-TM waves exist in strip waveguides. Electromagnetic waves of the same frequency propagate with different wave vectors in different waveguides, i.e. different.

[0017] like Figure 1 As shown, after arranging multiple Janus antennas 12 in an array, the guided waves in the +y direction of the two dielectric waveguides 21 cannot be effectively excited due to the phase difference and spacing between the individual Janus antennas 12. The upper waveguide is aligned with the uncoupled surface of the Janus dipole antenna 12, and its guided waves in the -y direction cannot be effectively excited (e.g., Figure 4 As shown). Therefore, the Janus antenna array only generates guided waves in the -y direction of the lower waveguide (as shown). Figure 5 (As shown). The upper waveguide mentioned above refers to the strip waveguide located above the Janus antenna 12, and the lower waveguide refers to the strip waveguide located below the Janus antenna 12.

[0018] As a preferred embodiment of the above, the power supply network 11 includes a substrate 111 and microstrip lines 112 etched on the substrate 111. One end of each of the multiple microstrip lines 112 is connected to each other as a signal input terminal, and the other end serves as a signal output terminal and is connected to the Janus antenna 12.

[0019] As a preferred embodiment of the above, both the signal input terminal and the signal output terminal are provided with SMA connectors 13. A coaxial cable 14 is provided between the SMA connector 13 of the signal output terminal and the Janus antenna 12, and the SMA connector 13 of the signal input terminal is connected to the feed PCB. The function of the coaxial cable 14 is to transmit the radio frequency signal from the output terminal of the feed network 11 to the Janus antenna 12, so that the radio frequency signal is radiated through the antenna and coupled into the waveguide.

[0020] The design steps for the above-mentioned feeder network structure 1 are as follows: A1: Determine the operating frequency of the dielectric waveguide 21 and calculate the corresponding dispersion curve (after determining the operating frequency, the dispersion curve of the dielectric waveguide 21 can be obtained based on its relative permittivity and thickness). Specifically, the dielectric waveguide 21 used in this application is a dielectric strip waveguide surrounded by air. In this case, the dispersion curve of the strip waveguide refers to the curve of the effective refractive index changing with frequency. This curve cannot be accurately obtained through mathematical calculation, nor can it be expressed by a mathematical formula. In practical applications, the dispersion curve is obtained by numerical simulation using FDTD software, such as Ansys Lumerical, after modeling the material and dimensions of the strip waveguide.

[0021] A2: The phase difference of the Janus antenna 12 and the spacing between adjacent Janus antennas 12 are determined based on the dispersion curve characteristics of the dielectric waveguide 21. Specifically, the phase difference of the Janus antenna (12) and the spacing between two adjacent Janus antennas (12) are expressed by the following formulas. For waveguide mid-line and For waves propagating in different directions, the corresponding fields are as follows:

[0022]

[0023] in, For the longitudinal wave vector of the quasi-TM wave designed at the target frequency propagating in the waveguide, Equation (5) is the wave propagating in the +y direction in the waveguide, and Equation (6) is the wave propagating in the -y direction in the waveguide.

[0024] Let the formula (5) In formula (6) When both conditions are met, the phase difference can be obtained. ,spacing .

[0025] A3: Design the length of the microstrip line 112 based on the determined phase difference and spacing. After determining the phase difference of the Janus antenna 12 and the spacing between two adjacent Janus antennas 12, design the microstrip line 112 structure using the Advanced Design System (ADS) software, calculate the required length of the microstrip line 112 to achieve the corresponding phase difference, and control the spacing of each signal output terminal to be equal to the spacing between two adjacent Janus antennas 12. Specifically: First, when a signal propagates on microstrip line 112, the longer the microstrip line 112, the more advanced its phase. Therefore, to achieve a phase difference, the signal needs to be propagated through microstrip lines 112 of varying lengths. For example... Figure 7 As shown, the signal is input from the lower end, and 2* more signals are transmitted to port 2 than to port 1. The distance is such that, correspondingly, the signal transmitted to port 3 is 2* more than that to port 2, and the signal transmitted to port 4 is 2* more than that to port 3. The distance.

[0026] Secondly, the calculations mentioned here are not derived from mathematical formulas, but are obtained through the calculation tools built into the ADS software. The steps are as follows: When calculating the length of microstrip line 112, we already knew how much phase difference was required. In ADS software, the LineCalc tool is used to calculate the width W and length L of microstrip line 112.

[0027] Example 2 Based on the above-described apparatus for realizing unidirectional near-field coupling of a Janus antenna array, this embodiment discloses a method for realizing unidirectional near-field coupling of a Janus antenna array, comprising the following steps: B1: Establish a spatial rectangular coordinate system and place the Janus antenna 12 in the yz plane of the coordinate system, and place the dielectric waveguide 21 and the feed PCB in the xy plane of the coordinate system; B2: The electromagnetic waves radiated by the Janus antenna array are coupled into the dielectric waveguide 21 to generate quasi-TM guided waves; specifically, the dielectric waveguide is a slow-wave structure in which electromagnetic waves propagate slower than in air, which means that the waveguide mode has a specific propagation constant. This means the wave vector in the waveguide is greater than the wave vector in free space. If the antenna is very far away (far field), it can only provide a wavenumber of 1. plane waves, due to The two are mismatched; electromagnetic waves in free space cannot couple into the waveguide. However, in the near-field region of the antenna, the composition of the electromagnetic field is extremely complex. According to Fourier optics or electromagnetic field theory, the near-field of the antenna contains a broad spatial spectrum, which includes not only radiating electromagnetic waves but also electromagnetic waves that can be emitted from the waveguide. The composition also includes a large number of high-k components, which manifest as evanescent waves (exponentially decaying, non-radiative) in air, but the "momentum" they carry just covers the amount required by the waveguide. Value. At this point, these fleeting field components, which originally could not be transmitted over long distances in the air, must necessarily have a portion of their wavenumbers. It is exactly equal to (or very close to) the propagation constant of a quasi-TM wave in a dielectric waveguide. The phase velocity of these electromagnetic fields along the waveguide length is the same as the phase velocity of the quasi-TM wave. At this time, the near-field electromagnetic wave couples into the waveguide, exciting the quasi-TM wave. B3: The electromagnetic fields on the surfaces of the two dielectric waveguides 21 are measured using the probes of the detection device to obtain the corresponding electromagnetic field distribution maps. The detection device is a 3672B vector network analyzer. Port 1 of the 3672B vector network analyzer outputs a signal, and port 2 measures the vertical electric field intensity distribution on the dielectric waveguide surface through connection with the probe. The bottom of the probe has an SMA connector, which is connected to port 2 of the vector network analyzer via a coaxial cable. The exposed metal wire portion at the top is perpendicular to the dielectric waveguide surface, thus allowing the measurement of the vertical electric field intensity distribution on the dielectric waveguide surface. B4: Based on measurement data, the near-field coupling characteristics of quasi-TM waves excited by multiple Janus antennas 12 in the waveguide are analyzed. The specific analysis process is as follows: 1. Considering the two-dimensional case, the guided wave travels only along... Directional propagation.

[0028] For a single Janus dipole (the dipole of a single Janus antenna 12), choose the electric field strength To describe the quasi-TM wave it generates, through plane wave expansion, the P-polarized wave can be represented as:

[0029]

[0030]

[0031] The origin is taken at the position of the Janus dipole. , It is the speed of light in a vacuum. Explanation: The origin refers to the origin of the rectangular coordinate system, which coincides with the first Janus dipole; the Janus dipole is a physical concept, and the Janus antenna is a device to realize this physical concept. The Janus dipole can be understood as a point where an electric dipole and a magnetic dipole exist simultaneously, and the two are 90 degrees out of phase, that is, the Janus dipole is a combination of an electric dipole and a magnetic dipole.

[0032] The "+" in formula (3) applies to "-" is applicable . For evanescent waves on the waveguide surface, It is a purely imaginary number. This refers to the electric field in Components in direction, For position vectors, Let be the wave vector of the electromagnetic wave propagating along the y-axis. , The wave vector of an electromagnetic wave in free space. , The frequency of electromagnetic waves, The angular frequency of the electromagnetic wave. It is the speed of light. The vacuum permittivity, The imaginary unit, Let be the magnetic dipole moment of the magnetic dipole in the x-direction. Let be the electric dipole moment of the electric dipole in the y-direction. Let be the wave vector of an evanescent wave propagating along the z-axis.

[0033] According to formula (3), the graph can be drawn from... and The spatial spectrum diagram of the Janus dipole is as follows: Figure 2 As shown, the Janus dipole constructed in this way will effectively excite p-polarized guided waves in the lower waveguide, while in the upper waveguide, interference cancellation will occur, and the guided waves cannot be effectively excited. Furthermore, if the magnetic dipole is replaced with... In the upper waveguide, there will be no guided wave at all, and the Janus dipole can only excite p-polarized guided waves in the lower waveguide.

[0034] See Figure 1 , Figure 1 This is a structural diagram of a Janus antenna array achieving unidirectional near-field coupling at the coupling surface. The external coupler 2 consists of two parallel dielectric waveguides 21, and the relative permittivity of the dielectric waveguides 21 is... ,thickness , The wavelength of the electromagnetic wave in free space at the operating frequency.

[0035] The distance between the upper (lower) waveguide and the upper (lower) edge of the Janus antenna is The electric dipole moment of a Janus dipole Magnetic dipole moment , This is the serial number of the Janus dipole. The phase difference between adjacent Janus dipoles is represented by the fact that each Janus dipole is placed at equal intervals along the [path]. There is a decreasing phase shift in the direction.

[0036] For Janus dipole arrays, the difference lies in the generation It needs to be multiplied by an array factor, which can be expressed as

[0037] The origin is taken at the position of the first Janus dipole. The phase difference between adjacent Janus dipoles. The distance between adjacent Janus dipoles. This represents the number of Janus dipoles. Its spatial spectrum is shown below. Figure 3 As shown.

[0038] For waveguide mid-line and For waves propagating in a certain direction, the corresponding fields are respectively

[0039] in, The longitudinal wave vector of the quasi-TM wave designed at the target frequency propagating in the waveguide; Equation (5) is the wave propagating in the +y direction in the waveguide; Equation (6) is the wave propagating in the -y direction in the waveguide; Let the wave vector in Equation (5) be the longitudinal wave vector of the quasi-TM wave propagating in the waveguide. In formula (6) When both conditions are met, the phase difference of Janus antenna 12 can be obtained. and the spacing between two adjacent Janus antennas 12 .

[0040] The phase difference and spacing are designed to make , Substituting these equations into equations (5) and (6), we have:

[0041]

[0042] Equation (7) shows that when the following conditions are met... When the evanescent waves excited by the Janus dipole array on the waveguide surface undergo destructive interference, equation (8) shows that when the following conditions are met... When, the "+" in the formula corresponds to the lower waveguide Evanescent waves in a certain direction will undergo constructive interference, where "-" corresponds to the upper waveguide. The evanescent waves in the direction still undergo destructive interference due to the properties of the Janus dipole.

[0043] After constructing the dipole array, along the two waveguides The guided waves in the directional direction cannot be effectively excited due to the array effect. The upper waveguide is aligned with the uncoupled surface of the Janus dipole, and its... The guided wave in the direction cannot be effectively excited before the array is constructed, such as... Figure 4 As shown. Therefore, the Janus dipole array is only used in the lower waveguide. Direction generates guided waves, such as Figure 5 As shown.

[0044] In specific structural simulations, the operating frequency wave vector of guided wave , The number of Janus antennas is the wave vector in free space. Phase difference between adjacent dipoles Dipole spacing . Figure 6 This is the front structure of the Janus antenna. The dielectric substrate for the Janus antenna is Rogers 5880, with a relative permittivity of [missing information]. Loss tangent The thickness is 0.508mm, and the metal layer thickness is 0.035mm. Figure 7 This is the front structure of the antenna array feed network. The dielectric substrate and metal layer parameters of the feed network are the same as those of the Janus antenna, and its back side is a metal ground layer. From Figure 5 In conclusion, we can confidently conclude that to achieve effective excitation of unidirectional guided waves on the coupling surface, it is necessary to design both the external coupler (such as a dielectric waveguide) and the dipole array.

[0045] In short, the directionality of the Janus dipole itself is used to realize the coupling effect in the upper waveguide (uncoupled surface). Destructive interference of directional guide waves, and then using array factors to design phase difference and spacing to achieve phase difference between two waveguides. The destructive interference of directional guide waves can ultimately achieve effective excitation only of the lower waveguide (coupling surface). Directional guided waves.

[0046] The mechanism of waveguide formation is total internal reflection and light interference, as detailed below: Total internal reflection: The waveguide structure of this patent is a strip waveguide with a refractive index of n1=2.1 and a refractive index of n2=1 in the surrounding air.

[0047] According to Snell's law, when light travels from an optically denser medium (high refractive index) to an optically less dense medium (low refractive index), if the angle of incidence... greater than a certain critical angle The light will not refract out of the interface, but will be reflected back into the core layer, meaning the light is confined to propagate within the waveguide.

[0048] Light interference: Only when the total phase change produced by the light wave's one-way reflection within the waveguide is an integer multiple of 2π can the wavefronts overlap and superimpose, forming a stable propagation.

[0049] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

Claims

1. A device for realizing unidirectional near-field coupling of a Janus antenna array, characterized in that, The assembly includes a feed network structure (1) and an external coupler (2). The external coupler (2) includes two parallel dielectric waveguides (21) spaced apart to form an assembly space (22). The feed network structure (1) includes a feed network (11) and multiple Janus antennas (12) based on Janus dipoles connected to the feed network (11). The multiple Janus antennas (12) are arranged in an array in the assembly space (22). The Janus antennas (12) are perpendicular to each other and have... Electric and magnetic dipoles with phase difference, the magnetic dipoles corresponding to the width direction of the assembly space (22) and the electric dipoles corresponding to the length direction of the assembly space (22) to excite quasi-TM waves in the dielectric waveguide (21); The dielectric waveguide (21) is a strip waveguide surrounded by air; the feed network (11) includes a substrate (111) and microstrip lines (112) etched on the substrate (111). One end of each of the multiple microstrip lines (112) is connected to each other as a signal input terminal, and the other end is used as a signal output terminal and connected to the Janus antenna (12); both the signal input terminal and the signal output terminal are provided with SMA connectors (13). A coaxial cable (14) is provided between the SMA connector (13) of the signal output terminal and the Janus antenna (12). The SMA connector (13) of the signal input terminal is connected to the feed PCB. The design steps of the power supply network structure (1) are as follows: A1: Determine the operating frequency of the dielectric waveguide (21) and calculate the corresponding dispersion curve; A2: The phase difference of the Janus antenna (12) and the spacing between adjacent Janus antennas (12) are determined based on the dispersion curve characteristics of the dielectric waveguide (21). A3: Design the length of the microstrip line (112) based on the determined phase difference and spacing.

2. A method for realizing unidirectional near-field coupling of a Janus antenna array, characterized in that, The apparatus for realizing unidirectional near-field coupling of a Janus antenna array based on claim 1 includes the following steps: B1: Establish a spatial rectangular coordinate system and place the Janus antenna (12) in the yz plane of the coordinate system, and place the dielectric waveguide (21) and the feed PCB in the xy plane of the coordinate system; B2: The electromagnetic waves radiated by the Janus antenna array are coupled into the dielectric waveguide (21) to generate quasi-TM guided waves; B3: The electromagnetic fields on the surfaces of the two dielectric waveguides (21) are measured using the probe of the detection device to obtain the corresponding electromagnetic field distribution map. The detection device is a 3672B vector network analyzer. B4: Based on the measurement data, analyze the near-field coupling characteristics of the quasi-TM waves excited by multiple Janus antennas (12) in the waveguide.

3. The method for realizing unidirectional near-field coupling of a Janus antenna array according to claim 2, characterized in that, The 3672B vector network analyzer outputs a signal at port 1, and measures the vertical electric field intensity distribution on the surface of the dielectric waveguide through a connection with a probe at port 2. The bottom of the probe has an SMA connector and is connected to port 2 of the vector network analyzer via a coaxial cable. The exposed metal wire at the top is perpendicular to the surface of the dielectric waveguide, thus allowing the measurement of the vertical electric field intensity distribution on the surface of the dielectric waveguide.

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