A C-band low-loss phase-independent tunable reflective reconfigurable smart surface unit

Abstract

This invention relates to a C-band low-loss, phase-independently tunable, reflective, reconfigurable smart surface unit. It includes a dielectric substrate. Symmetrical C-shaped metal patches and rectangular metal patches are disposed on the upper surface of the substrate. The rectangular patches are connected to the C-shaped metal patches, and the two rectangular metal patches are connected via varactor diodes and inductors. A feed layer is disposed on the lower surface of the dielectric substrate. The C-shaped metal patches are connected to the feed layer via metal vias for power feeding. A ground plane is disposed below the feed layer, and an air layer exists between the feed layer and the ground plane. This invention achieves both a small initial capacitance value, thereby increasing the phase change range, and minimizes the internal resistance of the circuit, thus reducing losses within the circuit itself. Furthermore, the unit structure is simple, easy to fabricate, assemble, and control.

Description

Technical Field

[0001] This invention relates to the field of antenna technology, and in particular to a C-band low-loss phase-independent tunable reflective reconfigurable smart surface unit. Background Technology

[0002] Reconfigurable Smart Surfaces (RIS) refer to a planar surface composed of numerous near-passive electromagnetic devices such as PIN diodes and varactor diodes. Each electromagnetic device can control the phase and / or amplitude of the incident electromagnetic wave. Utilizing this characteristic, the parameters of the electromagnetic devices can be adjusted specifically according to the incident direction of the electromagnetic wave, thereby forming the desired electromagnetic wave reflection / transmission pattern and achieving the goal of controlling the direction of electromagnetic wave transmission. RIS passively reflects the incoming signal without any complex signal processing operations, avoiding the introduction of thermal noise and significantly reducing system power consumption. Furthermore, its small weight, thinness, and low deployment cost make it easy to install in large quantities on building surfaces such as walls and ceilings, enabling RIS to play a vital role in 6G communications.

[0003] Reflective reconfigurable smart surfaces do not change the amplitude of the incident electromagnetic wave, but only modulate its phase, typically using varactor diodes. However, the optimal operating frequency of varactor diodes is generally below the S-band. When the diode is used at higher frequencies, self-oscillation occurs, degrading the surface performance. The higher the operating frequency of the surface, the smaller the initial value of the variable capacitance of the varactor diode needs to achieve a wide phase change. Due to manufacturing limitations, currently, the smaller the initial value of the variable capacitance of a small varactor diode, the higher its internal resistance. Therefore, how to minimize both the initial value of the variable capacitance and the internal resistance is a problem that needs to be considered.

[0004] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a C-band low-loss phase-independent adjustable reflective reconfigurable smart surface unit, thus solving the problems existing in the prior art.

[0006] The objective of this invention is achieved through the following technical solution: a C-band low-loss phase-independent adjustable reflective reconfigurable smart surface unit, comprising a dielectric substrate, wherein symmetrical C-shaped metal patches and rectangular metal patches are disposed on the upper surface of the dielectric substrate, the rectangular metal patches are connected to the C-shaped metal patches, and the two rectangular metal patches are connected through varactor diodes and inductors.

[0007] A feed layer is provided on the lower surface of the dielectric substrate. A C-type metal patch is connected to the feed layer through a metal via to achieve power feeding. A metal ground is provided below the feed layer, and there is an air layer between the feed layer and the metal ground. Two rectangular metal patches are connected by a varactor diode and an inductor, thereby changing the range of change of internal impedance for the same capacitance change. By selecting an inductor that meets the setting requirements, a smaller capacitance starting value can be achieved, thereby increasing the phase control range.

[0008] The feeding layer includes two metal strips. Each C-type metal patch is connected to the metal strip through a metal via to achieve power feeding. By adjusting the voltage of the two metal strips, the voltage across the varactor diode is controlled, thereby achieving phase modulation of the incident electromagnetic wave.

[0009] The varactor diode and the inductor are connected in parallel, and their two ends are respectively connected to two rectangular metal patches. By connecting an inductor in parallel with the varactor diode, the range of change of internal impedance with the same capacitance variation is changed. By selecting an inductor that meets the setting requirements, a smaller initial capacitance value can be achieved, thereby increasing the phase control range.

[0010] The C-shaped metal patch has a long side length of L1 = 5 mm and a long side width of W1 = 1 mm; a short side length of L2 = 2.5 mm and a short side width of W2 = 1.2 mm; a rectangular metal patch has a length of L3 = 0.4 mm and a width of W3 = 0.8 mm; and both the C-shaped and rectangular metal patches have a thickness of 0.035 mm.

[0011] The dielectric substrate has a thickness of h1 = 2 mm, an air layer thickness of h2 = 1 mm, a metal strip length of L4 = 9 mm, a width of W4 = 0.5 mm, and a thickness of 0.035 mm, a metal ground plane side length of a = 9 mm, and a metal via radius of r = 0.2 mm.

[0012] This invention offers the following advantages: a C-band low-loss, phase-independently tunable, reflective, reconfigurable smart surface cell utilizes a varactor diode with low internal resistance but a large initial capacitance value and a small inductor to achieve a wide variable phase range of approximately 300° around the 6GHz frequency while maintaining low energy loss. This achieves the effect of a small initial capacitance value, thereby increasing the phase change range, while also ensuring that the circuit's internal resistance is minimized, thus reducing losses within the circuit itself. Furthermore, the cell structure is simple, easy to fabricate, assemble, and control. Attached Figure Description

[0013] Figure 1 This is a three-dimensional structural diagram of the present invention;

[0014] Figure 2 This is a top view of the present invention;

[0015] Figure 3This is a front view of the present invention;

[0016] Figure 4 This is a schematic diagram of the equivalent circuit model of a unit with normal incidence.

[0017] Figure 5 The impedance variation curve of SMV1405-079LF is shown.

[0018] Figure 6 The impedance change curve of SMV1405-079LF connected in parallel with a 0.2nH inductor is shown in the figure.

[0019] Figure 7 The impedance variation curve of SMV2019-079LF is shown.

[0020] Figure 8 The phase change curve of the proposed structure is shown.

[0021] Figure 9 The phase change curve is for the control group.

[0022] Figure 10 The graph shows the amplitude variation of the proposed structure.

[0023] Figure 11 The amplitude variation curve is for the control group;

[0024] In the diagram: 1-Dielectric substrate, 2-Metal strip, 3-Metal ground, 4-Air layer, 5-C-type metal patch, 6-Rectangular metal patch, 7-Varactor diode, 8-Inductor, 9-Metal via. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of this application provided below with reference to the accompanying drawings is not intended to limit the scope of protection of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application. The present invention will be further described below with reference to the accompanying drawings.

[0026] like Figures 1-3As shown, the present invention specifically relates to a C-band low-loss phase-independent adjustable reflective reconfigurable smart surface unit with a center frequency of 6 GHz. It includes a dielectric substrate 1, on which symmetrical C-shaped metal patches 5 and rectangular metal patches 6 are disposed on the upper surface of the dielectric substrate 1. The rectangular metal patches 6 are connected to the C-shaped metal patches 5, and the two rectangular metal patches 6 are connected through a varactor diode 7 and an inductor 8.

[0027] A power supply 2 is provided on the lower surface of the dielectric substrate 1. A C-type metal patch 5 is connected to the power supply layer through a metal via 9 to achieve power supply. A square metal ground 3 with the same side length as the dielectric substrate 1 is provided below the power supply layer, and an air layer 4 is provided between the power supply layer and the metal ground 3.

[0028] The feeding layer includes two metal strips 2. Each C-shaped metal patch 5 is connected to the metal strip 2 through a metal via 9 to achieve power feeding. By adjusting the voltage of the two metal strips 2, the voltage across the varactor diode is controlled to achieve phase modulation of the incident electromagnetic wave.

[0029] The varactor diode 7 and the inductor 8 are connected in parallel, and their two ends are respectively connected to two rectangular metal patches 6. By connecting an inductor 8 in parallel with the varactor diode 7, the range of change of internal impedance with the same capacitance change is changed. By selecting an inductor that meets the setting requirements, a smaller starting value of capacitance can be achieved, thereby increasing the phase control range.

[0030] The C-shaped metal patch 5 has a long side length of L1 = 5 mm and a long side width of W1 = 1 mm; a short side length of L2 = 2.5 mm and a short side width of W2 = 1.2 mm; a rectangular metal patch 6 has a length of L3 = 0.4 mm and a width of W3 = 0.8 mm; and both the C-shaped metal patch 5 and the rectangular metal patch 6 have a thickness of 0.035 mm.

[0031] The dielectric substrate 1 has a thickness of h1 = 2 mm, the air layer 4 has a thickness of h2 = 1 mm, the metal strip 2 has a length of L4 = 9 mm, a width of W4 = 0.5 mm, and a thickness of 0.035 mm, the metal ground 3 has a side length of a = 9 mm, and the metal via 9 has a radius of r = 0.2 mm.

[0032] The principle of this invention is as follows: when a varactor diode located on the top layer is reverse biased, the junction capacitance C of the diode changes smoothly according to its relationship with the junction voltage V. This changing characteristic makes the varactor diode a useful element for tuning the resonant frequency of reflected electromagnetic waves or controlling the phase shift of electromagnetic waves at a specific frequency. Two narrow metal strips placed along the lower surface of the dielectric substrate serve as DC bias lines to provide the appropriate DC voltage required by the varactor diode under a given condition.

[0033] like Figure 4As shown, the reconfigurable smart surface can be viewed as the terminal load seen when a planar wave strikes it. For an electromagnetic wave incident on the top metal patch, an induced current is generated on the surface of the metal patch. These currents cause charge accumulation, allowing the metal patch to store electrical energy and behave like a capacitor C. m and inductor L m A varactor diode is equivalent to a series resistor R. v Capacitor C v With inductor L v Surface mount inductor L p The varactor diode appears to be connected in parallel in the equivalent circuit. Based on the unit's response at normal incidence, a general equivalent circuit model of the unit can be established, which can be considered as having C m C v L m L v L p R v Parallel circuit with short-circuited transmission lines.

[0034] The input impedance Z1 seen in the direction of the short-circuited transmission line can be written as:

[0035]

[0036] Where j is the imaginary unit, ε r h and f are the relative permittivity and thickness of the mixed dielectric layer, f is the frequency of the incident electromagnetic wave, and c is the speed of light in a vacuum.

[0037] A varactor diode is equivalent to R in series. v C v With L v Its equivalent impedance can be calculated as follows:

[0038]

[0039] Where the incident electromagnetic wave angular frequency ω = 2πf, then the total input admittance Y in for:

[0040]

[0041] Therefore, the reflection coefficient of the far-field normal incident radiation is:

[0042]

[0043] Where Y0 = 1 / η0, η0 is the free-space characteristic impedance. The above formula demonstrates the theoretical quantitative relationship between the normal incident reflection coefficient, the equivalent impedance of the varactor diode model, and other equivalent circuit elements. Once the structure and dimensions of the unit are determined and manufactured, the various parameters of the equivalent circuit are constants. Only the capacitance C of the varactor diode remains constant.v The impedance can be changed, thus affecting the phase of the reflected wave. According to the impedance calculation formula, connecting an inductor in parallel with a varactor diode can change the range of impedance variation for the same capacitance change. Choosing an appropriate inductor can achieve a smaller initial capacitance value, thereby expanding the phase control range.

[0044] Considering the varactor diode's range and internal resistance, an SC-79 packaged varactor diode (Skyworks-SMV1405-079LF) was selected. When a DC voltage of -30 to 0V is applied, the diode's equivalent capacitance varies between 0.63 and 2.67 pF. Its equivalent resistance is only 0.3 ohms, meaning the unit has high reflectivity, as energy loss primarily originates from the resistance of the equivalent circuit model. The inductor chosen is a 0.2nH surface-mount inductor from Murata Electronics, LQP02HQ0N2W02L.

[0045] Taking 6GHz as an example, calculate the impedance variation range of the SMV1405-079LF transistor itself, and the impedance variation range achieved by connecting the transistor in parallel with an inductor. Figure 5 As shown, the impedance variation range of a varactor diode is relatively narrow. As the capacitance increases, the impedance shifts from the capacitive reactance region to the inductive reactance region. The impedance variation caused by the capacitance in the 0.63pF to 1.2pF range accounts for approximately 2 / 3 of the entire curve, while the influence in the 1.2pF to 2.67pF range is relatively small. Figure 6 As shown, the overall impedance point of the varactor diode connected in parallel with the inductor rotates almost one full circle on the Smith chart as the capacitance changes. Similarly, impedance changes are more sensitive in the small capacitance region. Therefore, connecting the inductor in parallel significantly amplifies the effect of the varactor diode, resulting in a wider range of reflection coefficients and phase changes within the unit cell.

[0046] To demonstrate the EM performance of the proposed structure, this invention uses the commercial software CST Microwave Studio 2020 for full-wave numerical simulation. A frequency domain solver is set up, and an infinite periodic structure is simulated using a Floquet boundary with a normal incident ray polarized wave perpendicular to the unit plane. Simultaneously, a varactor diode in an SC-79 package (Skyworks-SMV2019-079LF) with a smaller initial capacitance (equivalent resistance of 4.8 ohms) is selected for comparison. When a DC voltage of -20 to 0 V is applied, the equivalent capacitance of the diode varies between 0.30 and 2.22 pF, and its impedance variation curve is shown below. Figure 7 As shown.

[0047] like Figure 8 The figure shows the phase change curve of the unit cell using the proposed structure, i.e., using SMV1405-079LF connected in parallel with a 0.2nH inductor; Figure 9The figures show the phase variation curves of the control group, i.e., the unit cell using SMV2019-079LF. As can be seen from the two figures above, the phase variation range of the control group at and around 6 GHz is only 260°, while the proposed structure has an adjustable range of 300° at 6 GHz, and the overall phase variation range is much wider.

[0048] like Figure 10 and Figure 11 The figures show the amplitude variation curves for the two structures. Clearly, the control group has a very low reflection coefficient, meaning most of the energy is not reflected back because the high internal resistance of the varactor diode consumes a significant amount of energy. In contrast, the proposed structure has a reflection coefficient of only about -1.5 dB at 6 GHz, indicating lower energy loss, which is within an acceptable range.

[0049] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A C-band low-loss phase-independent tunable reflective reconfigurable smart surface unit, characterized in that: It includes a dielectric substrate (1), on which symmetrical C-type metal patches (5) and rectangular metal patches (6) are disposed on the upper surface of the dielectric substrate (1). The rectangular metal patches (6) are connected to the C-type metal patches (5), and the two rectangular metal patches (6) are connected through a varactor diode (7) and an inductor (8). A power feeding layer is provided on the lower surface of the dielectric substrate (1). A C-type metal patch (5) is connected to the power feeding layer through a metal via (9) to achieve power feeding. A metal ground (3) is provided below the power feeding layer and an air layer (4) is provided between the power feeding layer and the metal ground (3). The varactor diode (7) and the inductor (8) are connected in parallel, and the two ends of the parallel connection are respectively connected to two rectangular metal patches (6). By connecting an inductor (8) in parallel with the varactor diode (7), the range of change of the internal impedance of the same capacitance change is changed. By selecting an inductor that meets the setting requirements, a smaller capacitance starting value is achieved, thereby increasing the phase control range.

2. The C-band low-loss phase-independent tunable reflective reconfigurable smart surface unit according to claim 1, characterized in that: The feeding layer includes two metal strips (2). Each C-type metal patch (5) is connected to the metal strip (2) through a metal via (9) to achieve power feeding. By adjusting the voltage of the two metal strips (2), the voltage across the varactor diode is controlled to achieve phase modulation of the incident electromagnetic wave.

3. The C-band low-loss phase-independent tunable reflective reconfigurable smart surface unit according to claim 1, characterized in that: The C-shaped metal patch (5) has a long side length of L1=5mm and a long side width of W1=1mm; a short side length of L2=2.5mm and a short side width of W2=1.2mm; a rectangular metal patch (6) has a length of L3=0.4mm and a width of W3=0.8mm; and both the C-shaped metal patch (5) and the rectangular metal patch (6) have a thickness of 0.035mm.

4. The C-band low-loss phase-independent tunable reflective reconfigurable smart surface unit according to claim 2, characterized in that: The thickness of the dielectric substrate (1) is h1=2mm, the thickness of the air layer (4) is h2=1mm; the length of the metal strip (2) is L4=9mm, the width is W4=0.5mm, and the thickness is 0.035mm; the side length of the metal ground (3) is a=9mm; and the radius of the metal via (9) is r=0.2mm.

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