Equivalent circuit and reflection-transmission coefficient modeling method of smart omnidirectional surface

Abstract

The application discloses an equivalent circuit and a reflection and transmission coefficient modeling method of an intelligent omnidirectional surface. The equivalent circuit comprises top layer metal pattern equivalent circuits, top layer feeder equivalent circuits, bottom layer feeder equivalent circuits and bottom layer metal pattern equivalent circuits connected in parallel, and coupling admittance between layers; one port of the top layer metal pattern equivalent circuit is connected with a first transmission line; one port of the bottom layer metal pattern equivalent circuit is connected with a second transmission line; the top layer metal pattern equivalent circuit, the top layer feeder equivalent circuit, the bottom layer feeder equivalent circuit and the bottom layer metal pattern equivalent circuit are all two-port microwave networks connected in parallel with an RLC circuit; when an incident wave is input to the top layer metal pattern equivalent circuit through the first transmission line, the first transmission line outputs corresponding reflected waves, and the second transmission line outputs corresponding refracted waves. The intelligent omnidirectional surface structure parameters and the channel assisted by the intelligent omnidirectional surface which affect the reflection coefficient and the transmission coefficient are not reciprocal.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electronics, in particular to an equivalent circuit of an intelligent omnidirectional surface and a reflection and transmission coefficient modeling method. BACKGROUND

[0002] As one of the key technologies for future wireless networks, intelligent omnidirectional surface (IOS) can change the wireless propagation environment and thus improve the communication performance of users on both sides. However, in the existing literature on IOS, the reflection-transmission model adopted is too simplified, which has caused some limitations on the case studies that can be analyzed and the conclusions that can be drawn therefrom. Specifically, in the existing research work, the relationship between the physical implementation of IOS and the reflection and transmission coefficients is not explicitly given. Therefore, it is uncertain which structure parameters in IOS can be optimized to obtain ideal reflection and transmission characteristics. In addition, the existing model does not reflect the influence of the incident angle on the reflection and transmission coefficients. Therefore, it is still unknown whether the IOS-assisted channel is reciprocal, which may cause design challenges, such as implementing channel estimation in a time division duplex scheme. SUMMARY

[0003] To solve the above technical problems, the present application proposes an equivalent circuit of an intelligent omnidirectional surface and a reflection and transmission coefficient modeling method.

[0004] An equivalent circuit of an intelligent omnidirectional surface includes a top layer metal pattern equivalent circuit, a top layer feed line equivalent circuit, a bottom layer feed line equivalent circuit and a bottom layer metal pattern equivalent circuit connected in parallel, and a coupling admittance between layers.

[0005] One port of the top layer metal pattern equivalent circuit is connected with a first transmission line, and the first transmission line is equivalent to a vacuum on one side of an intelligent omnidirectional surface unit.

[0006] One port of the bottom layer metal pattern equivalent circuit is connected with a second transmission line, and the second transmission line is equivalent to a vacuum on the other side of the intelligent omnidirectional surface unit.

[0007] The top layer metal pattern equivalent circuit, the top layer feed line equivalent circuit, the bottom layer feed line equivalent circuit and the bottom layer metal pattern equivalent circuit are each a two-port microwave network connected in parallel with an RLC circuit, and the structure and values of the RLC circuit are related to the parameters of the intelligent omnidirectional surface.

[0008] When an incident wave is input to the top layer metal pattern equivalent circuit through the first transmission line, the first transmission line outputs a corresponding reflection wave, and the second transmission line outputs a corresponding transmission wave.

[0009] Further, the RLC circuit in the top layer metal pattern equivalent circuit is composed of the following: the resistance R1 is connected in parallel with one end of the resistance R2, the other end of the resistance R1 is connected to one end of the inductor L1, the other end of the inductor L1 is connected to one end of the capacitor C2, the other end of the capacitor C2 is connected to one end of the diode group and one end of the capacitor C1 respectively, the other end of the diode group, the other end of the capacitor C1 and one end of the inductor L2 are connected in parallel, and the other end of the inductor L2 is connected to the other end of the resistance R2.

[0010] Further, the resistance R1 represents the resistance generated by the center metal sheet; the inductance L1 represents the inductance generated by the center metal sheet; the resistance R2 represents the resistance generated by the ground; the inductance L2 represents the inductance generated by the ground; and the capacitances C1 and C2 represent two capacitances generated between the center metal sheet and the ground, the values of which are positively correlated with the width of the smart omnidirectional surface unit and the width of the metal patch, and are negatively correlated with the gap between the metal sheet and the ground.

[0011] Further, the RLC circuit in the top layer metal pattern equivalent circuit is composed of the following: the resistance R1 is connected in parallel with one end of the resistance R2, the other end of the resistance R1 is connected to one end of the inductor L1, the other end of the inductor L1 is connected to one end of the capacitor C2, the other end of the capacitor C2 is connected to one end of the diode group and one end of the capacitor C1 respectively, the other end of the diode group, the other end of the capacitor C1 and one end of the inductor L2 are connected in parallel, and the other end of the inductor L2 is connected to the other end of the resistance R2.

[0012] Further, the resistance R2 represents the resistance generated by the top layer feed line; the inductance L3 represents the inductance generated by the top layer feed line; the capacitance C3 represents the capacitance generated by the feed line of the smart omnidirectional surface unit and the feed line of the adjacent unit; and the inductance L3 is positively correlated with the width w of the feed line. F

[0013] A modeling method of the reflection and transmission coefficients of a smart omnidirectional surface, the steps of which include:

[0014] Obtaining the characteristic impedance and propagation parameters of the first transmission line and the second transmission line;

[0015] Combining the propagation parameters, constructing the ABCD transmission matrix of the equivalent circuit obtained by any of the above methods;

[0016] Based on the characteristic impedance and the ABCD transmission matrix, modeling the reflection coefficient and the transmission coefficient respectively to obtain the reflection and transmission model.

[0017] Further, the ABCD transmission matrix is constructed by the following steps:

[0018] 1) Calculating the interlayer coupling admittance between the top layer metal pattern and the top layer feed line the interlayer coupling admittance between the top layer feed line and the bottom layer feed line and the interlayer coupling admittance between the bottom layer feed line and the bottom layer metal pattern ​

[0019] 2) Calculate the parallel admittance corresponding to the top layer metal pattern, top layer feed line, bottom layer feed line and bottom layer metal pattern respectively Parallel admittance Parallel admittance Parallel admittance

[0020] 3) Based on the interlayer admittance Interlayer admittance Interlayer admittance Parallel admittance Parallel admittance Parallel admittance Parallel admittance Construct the ABCD transmission matrix.

[0021] Further, based on the reflection coefficient calculation model and the refraction coefficient calculation model, the intelligent omnidirectional surface structure parameters which will affect the reflection coefficient and the transmission coefficient are obtained; the intelligent omnidirectional surface structure parameters include: the width and length of the intelligent omnidirectional surface unit, the width and length of the metal patch, the width of the feed line and the gap between the center metal sheet and the ground.

[0022] A storage medium, the storage medium has a computer program stored therein, wherein the computer program is configured to execute the method described above when running.

[0023] An electronic device, characterized by comprising a memory and a processor, the memory has a computer program stored therein, and the processor is configured to execute the computer program to execute any of the methods described above.

[0024] Compared with the prior art, the present application has at least the following advantages:

[0025] Based on the model, the present application can deduce that by optimizing the structure parameters of which IOS can obtain ideal reflection coefficient and transmission coefficient; at the same time, based on the model, it can also be deduced that the IOS assisted channel is not reciprocal, so as to facilitate the design of channel estimation scheme. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 Intelligent omnidirectional metasurface unit schematic diagram.

[0027] Figure 2 Equivalent circuit diagram of IOS unit.

[0028] Figure 3 Flow chart of reflection coefficient and transmission coefficient modeling method.

[0029] Figure 4 Diode equivalent circuit.

[0030] Figure 5When two PIN diodes are in the (OFF, OFF) state, the unit reflection / transmission amplitudes of the present invention and a prior art at different frequencies are shown.

[0031] Figure 6 Two PIN diodes are in the (ON, ON) state, and the unit reflection / transmission amplitudes of the present invention and a prior art at different frequencies.

[0032] Figure 7 When two PIN diodes are in the (OFF, OFF) state, the unit reflection / transmission phases of the present invention and a prior art at different frequencies are shown.

[0033] Figure 8 Two PIN diodes are in the (ON, ON) state, and the unit reflection / transmission phases of the present invention and a prior art at different frequencies. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only specific embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0035] An IOS is a two-dimensional array of electrically controllable scattering elements of equal size. Figure 1 As shown, each reconfigurable unit consists of two symmetrical layers, each layer has a dielectric material substrate, on which there is a metal patch and N PIN diodes evenly distributed. The metal patch is connected to the ground through the PIN diode. According to the predetermined bias voltage, the PIN diode can be switched between ON and OFF states, and the state of each IOS unit is determined by the state of the PIN diode on the unit. At the bottom of each layer, there is a feed line that is connected to the metal patch through a via. The feed line is used to provide the required bias voltage to the PIN diode

[0036] When an electromagnetic wave is incident on an IOS cell, it excites a time-varying current within the cell, which in turn re-radiates the reflected and refracted electromagnetic waves. When the IOS cell is configured in different states, the surface impedance of the cell changes accordingly, which in turn affects the excitation current and the re-radiated electromagnetic waves. Therefore, the reflection and refraction characteristics of the IOS cell depend on the state of the cell, that is, the configuration of the PIN diode. Among all the possible states of the IOS cell, select N s states to control electromagnetic waves. The set of selected states is denoted by S. In order to fully characterize the reflection and refraction properties of an IOS, a reflection and transmission coefficient model is required.

[0037] To model the reflection and transmission properties of an IOS unit, the present invention introduces an equivalent circuit, as shown in Figure 2 The equivalent circuit has the following features: the vacuum on both sides of the IOS is modeled by two semi-infinite transmission lines, and the IOS unit is modeled by a two-port microwave network. Since the IOS unit contains four metal layers, namely the metal pattern on the top layer, the feed line on the top layer, the feed line on the bottom layer, and the metal pattern on the bottom layer, the equivalent two-port network model consists of the four metal layers and three coupling admittances between these layers. In the following, the present invention elaborates on these metal layers and coupling admittances.

[0038] Each metal layer of the IOS unit is modeled using an equivalent parallel admittance, which is represented by an RLC circuit. The RLC equivalent circuit of the metal patterns on the top and bottom layers consists of two capacitances, two inductances, one resistance, and several PIN diodes. Specifically, C1 and C2 describe the capacitances formed by the metal patch and the ground. Both C1 and C2 are positively correlated with the width w E of the metal patch and negatively correlated with the gap g P between the metal patch and the ground. The parameters L1 and R1 represent the inductance and resistance of the central metal patch, respectively, where the inductance L1 increases with the length l P of the patch. In addition, L2 and R2 model the inductance and resistance generated by the ground, respectively, where L2 is positively correlated with the length l E of the ground. Each PIN diode can also be modeled by an equivalent RLC circuit, the structure of which depends on the state of the PIN diode. The RLC equivalent circuit of the feed line consists of a resistance R3, an inductance L3, and a capacitance C3 in series, where R3 and L3 are generated by the feed line, and the capacitance C3 is generated by the feed line of the IOS unit and the feed line of the adjacent unit. Specifically, the capacitance C3 increases with the length w E of the feed line and decreases with the length l E of the unit. In addition, the larger the width w F of the feed line, the larger the inductance L3.

[0039] Based on the above equivalent circuit, the present invention further discloses a method for modeling the reflection and transmission coefficients of an intelligent omnidirectional surface, as shown in Figure 3 The method comprises the following steps:

[0040] Step 1: Obtain the characteristic impedance and propagation parameters of the first transmission line and the second transmission line.

[0041] In an example, the first transmission line and the second transmission line are set to have the same properties. In this example, the characteristic impedance Z0 of the transmission line is set to be the impedance of free space, and the propagation constant is set to be the wave number in vacuum, where λ is the wavelength of the electromagnetic wave in vacuum.

[0042] Step 2: Based on the propagation parameters, the ABCD transmission matrix of the equivalent circuit is constructed.

[0043] The ABCD transmission matrix of the equivalent circuit can be expressed as:

[0044]

[0045] is the interlayer coupling admittance between the top layer metal pattern and the top layer feed line, is the interlayer coupling admittance between the top layer feed line and the bottom layer feed line, is the interlayer coupling admittance between the bottom layer feed line and the bottom layer metal pattern, and Y

[0046] The parallel admittance can be expressed as:

[0047]

[0048]

[0049]

[0050] where ω is the angular frequency, represents the admittance of the i-th PIN diode, which is determined by the state of the PIN diode, and U and L represent the set of PIN diodes located on the top layer metal layer and the bottom layer metal layer of the IOS unit, respectively.

[0051] Step 3: Based on the characteristic impedance and the ABCD transmission matrix, a reflection coefficient calculation model and a refraction coefficient calculation model are established respectively.

[0052] Based on the above ABCD transmission matrix, the reflection and transmission model (reflection coefficient Γ r and transmission coefficient Γ t ) of the IOS unit can be expressed as:

[0053]

[0054]

[0055] where d1 and d2 represent the distance between the reference plane and the surface of the IOS unit. exp(-j2βd1) and exp(-jβ(d1+d2)) in the above formula describe the influence of the distance relative to the IOS on the reflection and transmission coefficients when measuring the reflection and transmission coefficients, for example, by means of full-wave electromagnetic simulation analysis of the IOS unit. Therefore, in the present application, d1 and d2 are fixed and cannot be designed to optimize the reflection and transmission coefficients. ​

[0056] Based on the above reflection transmission model, the intelligent omnidirectional surface structure parameters that affect the reflection coefficient and the transmission coefficient can be obtained; the intelligent omnidirectional surface structure parameters include: the width and length of the intelligent omnidirectional surface unit, the width and length of the metal patch, the width of the feed line, and the gap between the center metal sheet and the ground.

[0057] Experimental data:

[0058] In order to verify the equivalent circuit proposed, and the reflection coefficient Γ r and the transmission coefficient Γ t , the present application considers a special case of IOS unit, and compares the reflection coefficient Γ r and the transmission coefficient Γ t obtained using a full-wave simulator, that is, not dependent on the circuit-based model, but numerically solving Maxwell's equations. Specifically, consider an IOS unit operating at 3:6GHz, and assume that the tunability is ensured by a PIN diode located on the upper metal plate and a PIN diode located on the lower metal plate. The size of the IOS unit is 2.87x1.42x0.71cm 3 , which means that the maximum side of the IOS unit is about one third of the wavelength of 3.6GHz. The distance between the two layers constituting the IOS unit is 0.3cm. There is a rectangular copper patch on each layer, with a size of 1.6x1.0cm 2 (That is, the size of the patch is about λ / 5.21xλ / 8.33, λ≈8.33cm is the wavelength corresponding to 3.6GHz) printed on a dielectric woven glass PTFE substrate with a dielectric constant of 2.2 and a loss tangent of 0.0019@3:6GHz. The copper feed line on the other side of the substrate has a width of 0.04cm, and the thickness of the patch and the feed line is 3.9x10-3cm. There is a ground with a width of 0.02cm on the boundary of each layer. The ground is connected to the patch through a BAR 65-02L PIN diode. The equivalent circuit model of the PIN diode is as shown in Figure 4 , it can be found that the state of the PIN diode has an effect on the structure of its equivalent circuit model. In the example considered, it is assumed that each IOS unit can be reconfigured according to two states: both PIN diodes are set to the ON state, i.e., state (ON, ON), and both diodes are set to the OFF state, i.e., state (OFF, OFF).

[0059] The full-wave simulation is performed using the transient simulation package in Microwave Studio and CST software. The IOS cell with unit cell boundary is assumed to be under normal incidence of plane wave in the simulation. In addition, the equivalent circuit model of PIN diode is incorporated into the simulation software. The reflection and transmission responses obtained from the full-wave simulation are incorporated into the reflection and transmission coefficient model, and the equations are solved to obtain the equivalent circuit parameters, as shown in Table 1. Figures 5-8 The comparison of the unit cell reflection and transmission amplitude and phase obtained from the full-wave simulation and the present model for the PIN diode in the ON, ON or OFF, OFF states is recorded, which shows that the present model provides good accuracy for the considered case study.

[0060] Parameters [R1(Ω)] [R2(Ω)] [R3(Ω)] [L1(nH)] [L2(nH)] [L3(nH)] [C1(pF)] [C2(pF)] [C3(pF)] Values 10 -3.18 ]] 10 -3.78 ]] 10 -7.07 ]] 10 -3.17 ]] 0.40 10 -2.04 ]] 8.03 962.24 209.45

[0061] Table 1. Equivalent circuit parameters of the IOS cell under normal incidence

[0062] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An equivalent circuit of an intelligent omnidirectional surface, comprising a top layer metal pattern equivalent circuit, a top layer feed line equivalent circuit, a bottom layer feed line equivalent circuit, a bottom layer metal pattern equivalent circuit, and a coupling admittance between layers in parallel; one port of the top layer metal pattern equivalent circuit is connected to a first transmission line, which is equivalent to one side of the intelligent omnidirectional surface unit in vacuum; one port of the bottom layer metal pattern equivalent circuit is connected to a second transmission line, which is equivalent to the other side of the intelligent omnidirectional surface unit in vacuum; the width and length of the intelligent omnidirectional surface unit, the width and length of the metal patch, the width of the feed line, and the gap between the center metal patch and the ground; wherein, when an incident wave is input to the top layer metal pattern equivalent circuit through the first transmission line, the first transmission line outputs a corresponding reflected wave, and the second transmission line outputs a corresponding refracted wave. In the top layer metal pattern equivalent circuit, an RLC circuit is composed as follows: one end of a resistor R1 is connected in parallel to one end of a resistor R2, the other end of the resistor R1 is connected to one end of an inductor L1, the other end of the inductor L1 is connected to one end of a capacitor C2, the other end of the capacitor C2 is connected to one end of a diode group and one end of a capacitor C1 respectively, the other end of the diode group, the other end of the capacitor C1 and one end of an inductor L2 are connected in parallel, and the other end of the inductor L2 is connected to the other end of the resistor R2. The resistor R1 represents the resistance generated by the center metal patch; the inductor L1 represents the inductance generated by the center metal patch; the resistor R2 represents the resistance generated by the ground; the inductor L2 represents the inductance generated by the ground; and the capacitor C1 and the capacitor C2 represent two capacitances generated between the center metal patch and the ground, the values of which are positively correlated with the width of the intelligent omnidirectional surface unit and the width of the metal patch, and are negatively correlated with the gap between the metal patch and the ground. The top layer metal pattern equivalent circuit, the top layer feed line equivalent circuit, the bottom layer feed line equivalent circuit and the bottom layer metal pattern equivalent circuit are all two-port microwave networks in parallel with an RLC circuit, and the structure and value of the RLC circuit are related to the smart omnidirectional surface parameters; the smart omnidirectional surface parameters include: In the top layer feed line equivalent circuit, an RLC circuit is composed as follows: one end of a resistor R3 is connected to one end of an inductor L3, and the other end of the inductor L3 is connected to one end of a capacitor C3, thereby forming an RLC series circuit. 6.A modeling method of a reflection and transmission coefficient of an intelligent omnidirectional surface, comprising the following steps:

2. The equivalent circuit of claim 1, wherein, obtaining characteristic impedances and propagation parameters of the first transmission line and the second transmission line; 3. The equivalent circuit of claim 2, wherein, combining the propagation parameters to construct an ABCD transmission matrix of the equivalent circuit obtained by any of the methods of claims 1-5; 4. The equivalent circuit of claim 1, wherein, based on the characteristic impedances and the ABCD transmission matrix, modeling the reflection coefficient and the transmission coefficient respectively to obtain a reflection and transmission model; 5. The equivalent circuit of claim 4, wherein, The resistance R3 represents the resistance generated by the top layer feed line; the inductance L3 represents the inductance generated by the top layer feed line; the capacitance C3 represents the capacitance generated by the feed line of the smart omnidirectional surface unit and the feed line of the adjacent unit; the inductance L3 and the width w of the feed line F are positively correlated. based on the reflection coefficient calculation model and the refraction coefficient calculation model, obtaining intelligent omnidirectional surface structure parameters that affect the reflection coefficient and the transmission coefficient; the intelligent omnidirectional surface structure parameters include the width and length of the intelligent omnidirectional surface unit, the width and length of the metal patch, the width of the feed line, and the gap between the center metal patch and the ground. The ABCD transmission matrix is constructed by the following steps: The computer program is configured to execute the method of any of claims 6-7 when running. ​ ​ 7. The method of claim 6, wherein, ​ 1) Calculate the interlayer coupling admittance between the top metal pattern and the top feed line, respectively the interlayer coupling admittance between the top feed line and the bottom feed line and the interlayer coupling admittance between the bottom feed line and the bottom metal pattern 2) Calculate the parallel admittance corresponding to the top metal pattern, top feed line, bottom feed line and bottom metal pattern, respectively Parallel admittance Parallel admittance Parallel admittance 3) based on interlayer admittance interlayer admittance interlayer admittance parallel admittance parallel admittance parallel admittance and parallel admittance constructing the ABCD transfer matrix.

8. A storage medium having stored therein a computer program, wherein, ​ 9. An electronic device, comprising: A computer program product comprising a memory having stored therein a computer program and a processor arranged to execute the computer program to perform the method of any of claims 6-7.

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