Circularly polarized wearable antenna loaded with electromagnetic band gap reflecting surface

Abstract

The invention relates to a circularly polarized wearable antenna loaded with an electromagnetic band gap reflecting surface, which comprises two pairs of bent line structure dipoles which are arranged on the upper surface and the lower surface of an upper PDMS flexible substrate and are orthogonally arranged, and coaxial lines with 50 ohm impedance are respectively connected with the orthogonal centers of the two pairs of dipoles, so that antenna center feeding is realized, and a crossed dipole antenna is formed; the phase delay rings are connected to form a 90-degree phase difference, so that the antenna circular polarization characteristic of a required frequency band is realized; the electromagnetic band gap reflecting surface is composed of a PDMS flexible substrate at the lower layer, bent line annular patches printed on the PDMS flexible substrate and arranged in an array and a grounding surface at the bottommost layer, and each bent line annular patch serves as a reflecting surface unit, so that the effective inductance of the electromagnetic band gap reflecting surface is increased, and the working bandwidth of the electromagnetic band gap reflecting surface is widened; and the electromagnetic band gap reflecting surface is placed at a position 1-13mm below the crossed dipole antenna so as to carry out impedance matching. The antenna is less affected by human body coupling, can be stably applied to the wearable field, and has the advantages of flexibility, broadband, high gain, low profile and low specific absorption rate.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave antennas, and in particular to a circularly polarized wearable antenna loaded with an electromagnetic band gap reflector. Background Art

[0002] Wearable devices based on Wireless Body Area Network (WBAN) technology, integrating sensor, computing, and communication functions, are becoming a hot topic in today's society. Recent advances in information and communication technologies have also injected new vitality into the wearable device sector. The development of antenna technology in wireless communications plays a key role in the performance of wearable devices.

[0003] Wearable devices are known for their portability, real-time performance, and personalization. They not only monitor users' physiological parameters and exercise status to provide health monitoring services, but also offer a variety of functions such as communication, entertainment, and navigation. All of these functions require antenna technology to transmit and receive radio signals, enabling information exchange between wearable devices and the outside world. Therefore, the quality of antenna design in wearable devices directly affects the proper functioning of their primary functions.

[0004] In addition, due to the inherent portability of wearable devices, their space and battery capacity are limited to a certain extent, requiring wearable antennas to be designed for miniaturization, flexibility, and bendability. Furthermore, due to changes in the body's posture and movement, communications between wearable antennas and external devices are inevitably affected by multipath effects and polarization mismatch. Circularly polarized waves, however, have an electric field direction that rotates over time and can receive linearly polarized waves from any direction, as well as circularly polarized waves with the same polarization direction as their own. Compared to linearly polarized signals, they can provide a more stable link between the transmitting and receiving antennas. Therefore, flexible, wearable circularly polarized antennas are a good choice for wearable antennas.

[0005] At the same time, wearable devices often operate in complex environments, such as the human body. The human body itself is a complex electromagnetic environment, significantly scattering antenna radiation. When operating near the human body, antennas can experience changes in input impedance, resonant frequency shifts, radiation direction changes, gain reduction, and poor matching, all of which can affect the communication quality of wearable devices. Therefore, the impact of the human body on antenna performance must be fully considered during design. Generally, antennas within wearable devices are required to have multi-band or wideband characteristics and high gain to maintain a certain degree of stability. Furthermore, wearable antennas inherently emit a certain amount of radiation. Besides the electromagnetic waves received by the device, some of the remaining electromagnetic waves are absorbed by the human body. The amount of radiation absorbed is primarily measured by the Specific Absorption Rate (SAR). Therefore, adding a reflective surface to the side of the wearable antenna closest to the human body can not only effectively reduce the SAR while increasing gain, but also mitigate the impact of the human body on antenna performance.

[0006] Furthermore, the addition of a conventional metal reflector results in a larger overall antenna profile. Due to these miniaturization limitations, electromagnetic bandgap (EBG) reflectors, which can achieve a low profile, have become increasingly popular in wearable antenna designs.

[0007] In recent years, researchers from various countries have also conducted extensive research on wearable antennas. The specific research progress is as follows:

[0008] (1) Linearly polarized wearable antenna

[0009] In 2020, Tu Tuan Le and others from Hanyang University in South Korea proposed a dual-band linearly polarized wearable antenna for wireless body area networks (WBAN). The antenna uses a thinner semi-flexible Rogers 5880 material as its dielectric substrate, and designs an I-shaped monopole with an inverted L-shaped slot on its front to excite a high resonant mode at 5.8GHz. Unlike traditional monopole antennas, the back of this antenna abandons the full ground plane and adopts a semi-ground plane, and connects an inverted U-shaped stripline embedded with an inductive meander line to it to excite a low resonant mode at 2.45GHz. Ultimately, the antenna achieves an impedance fractional bandwidth (FBW) of 5.7% and 3.78% near 2.47GHz and 5.83GHz, respectively, with peak gains of 2.1dBi and 3.5dBi, respectively. In summary, the antenna structure has a narrow bandwidth, low gain, is not completely flexible, and because of the incomplete ground plane, it achieves a bidirectional radiation pattern and has a high specific absorption rate (SAR). When loaded with a human body, it is not conducive to human safety.

[0010] In 2023, Xiao Yang and others from Wuhan University of Technology proposed a three-band linearly polarized wearable antenna loaded with an artificial magnetic conductor reflector (AMC) structure. The antenna uses a flexible material polydimethylsiloxane (PDMS) as a substrate and a highly conductive graphene film as a conductive layer. In addition, in order to adapt to its multi-resonance structure while reducing the impact of the antenna on the human body, the authors designed an AMC structure composed of multiple rings. Ultimately, the antenna achieved impedance fractional bandwidths of 8.5%, 4.4%, and 6.3% near 2.36GHz, 3.6GHz, and 5.1GHz, respectively, with peak gains ranging from 5.7dBi to 7.9dBi. Overall, the antenna structure still has problems with narrowband and low gain. As a result, after the antenna is integrated with the human body, the narrowband and low gain of the antenna will deteriorate the stability of the antenna performance due to the influence of the human body on the antenna.

[0011] (2) Circularly polarized wearable antenna

[0012] The wearable antennas described above all radiate linearly. However, linearly polarized antennas are sensitive to polarization mismatch. When the polarization directions of the receiving and transmitting antennas differ, the signal can be significantly attenuated. When a wearable device is integrated into the human body, changes in movement and posture inevitably affect the polarization direction between the wearable antenna and the external receiving / transmitting antennas. Therefore, linearly polarized antennas are not the best choice for wearable antennas. In contrast, circularly polarized antennas, which offer resistance to polarization mismatch and multipath effects, have become popular among wearable antennas.

[0013] In 2019, Ubaid Ullah et al. from Al Ain University in the United Arab Emirates proposed a compact, circularly polarized wearable antenna with unidirectional radiation. Using a thin Rogers RO4003C substrate, the antenna adopts a coplanar waveguide-fed monopole antenna format. Circular polarization is induced by a vertical stub on the right common ground plane and a horizontal edge on the left common ground plane. Furthermore, to minimize the antenna's impact on the human body, the authors placed a conventional metal reflector made of high-dielectric-constant Rogers RO3010 13 mm below the antenna. Ultimately, the antenna achieves an impedance fractional bandwidth and axial ratio fractional bandwidth of 18.3% near 5.16 GHz, with a peak gain of 9.22 dBic. Overall, the antenna has a high profile, making it difficult to bend and integrate with the human body.

[0014] In 2020, Yang Hongcai and others from South China University of Technology proposed a dual-band circularly polarized wearable antenna. This antenna uses a flexible felt material as its base and a flexible conductive nylon fabric as its conductive layer. Furthermore, to achieve dual-band characteristics, the authors introduced two pairs of short-circuited probes on the diagonals of the antenna and cut corners on the opposite corners of the rectangular patch. This produces linearly polarized omnidirectional radiation at 2.38 GHz and circularly polarized unidirectional radiation at 3.5 GHz. Ultimately, the antenna achieves an impedance fractional bandwidth of 4.1% near 2.38 GHz, an impedance fractional bandwidth of 7.0% near 3.5 GHz, and an axial ratio fractional bandwidth of 2.2%, with peak gains of 1.38 dBi and 7.7 dBic, respectively. Overall, this antenna structure still has a narrow bandwidth and low gain. Consequently, once the antenna is integrated with the human body, the narrow bandwidth and low gain can degrade the stability of the antenna's performance due to the human body's influence on the antenna.

[0015] In 2020, Zhu Haoran and others from Wuhan University of Technology proposed a circularly polarized wearable antenna loaded with a polarization-conversion metasurface. This antenna utilizes a highly conductive graphene film as the conductive layer and a PDMS substrate, resulting in excellent flexibility and lightweight. Furthermore, to achieve polarization conversion, the linearly polarized wave radiated by the linearly polarized antenna is converted into a circularly polarized wave. The linearly polarized antenna is first positioned at the center of the metasurface with a Φ = 45° / 135° angle. The reflection phases of the x-polarized and y-polarized incident waves at a certain frequency after passing through the metasurface are designed to be 90° and -90°, respectively, with minimal difference in reflection amplitude. Ultimately, the antenna achieves an impedance fractional bandwidth and axial ratio fractional bandwidth of 1.4% around 5.79 GHz, with a peak gain of 9 dBic. Clearly, the impedance bandwidth and axial ratio bandwidth achieved by this antenna are very narrow. Similarly, once the antenna is integrated with the human body, the narrow bandwidth and low gain of the antenna can degrade the stability of its performance due to the human body's influence on the antenna. Summary of the Invention

[0016] To address the problem of stable performance of wearable antennas, a circularly polarized wearable antenna loaded with an electromagnetic bandgap reflector is proposed. The antenna is less affected by human body coupling and can be stably used in the wearable field. It is also flexible, broadband, high gain, low profile and low specific absorption rate.

[0017] The technical solution of the present invention is: a circularly polarized wearable antenna loaded with an electromagnetic bandgap reflector, comprising two pairs of dipoles with meander-line structures placed orthogonally on the upper and lower surfaces of an upper PDMS flexible substrate, and a 50-ohm impedance coaxial line connected to the orthogonal centers of the two pairs of dipoles to achieve antenna center feeding, thereby forming a cross-dipole antenna;

[0018] The cross-dipole antennas are connected with phase delay rings to form a phase difference of 90°, thereby achieving the circular polarization characteristics of the antenna in the required frequency band;

[0019] The electromagnetic bandgap reflector is composed of a lower PDMS flexible substrate, an array of meander line ring patches printed on the PDMS substrate, and a bottom-layer ground plane. Each meander line ring patch acts as a reflector unit, increasing the effective inductance of the electromagnetic bandgap reflector and widening its operating bandwidth.

[0020] The electromagnetic band gap reflector is placed 1 to 13 mm below the cross dipole antenna to perform impedance matching.

[0021] Preferably, each pair of dipole antennas in the cross-dipole antenna contains two arms, and each arm is composed of two meander line branches of different lengths and an angle interval θ of 45°, and the meander line branches are periodically bent, wherein the long meander line branches are used to control the low frequency band, and the short meander line branches control the high frequency band, and the height difference between the upper and lower meander line segments of each branch is used to extend the current path, increase the effective inductance, and reduce the size of the cross-dipole antenna.

[0022] Preferably, the cross-dipole antenna is connected by a pair of phase delay loops with a length of one quarter wavelength and a width of 0.3 to 0.7 mm to form a phase difference of 90°.

[0023] Preferably, the reflective surface unit is an electromagnetic band gap reflective surface designed by connecting two inner and outer bending line rings using a cross bending line.

[0024] Preferably, in the inner and outer bending line loops and the cross bending line structure in the reflecting surface unit, the length of the bending line loop is used to control the capacitance, thereby affecting the working bandwidth of the electromagnetic band gap reflecting surface and the frequency corresponding to the 0° phase; the width of the bending line loop and the cross bending line is used to control the inductance and capacitance, thereby affecting the frequency corresponding to the 0° phase of the electromagnetic band gap reflecting surface; the height difference between the upper and lower bending line segments is used to increase the effective inductance, thereby reducing the overall size of the electromagnetic band gap reflecting surface.

[0025] Preferably, the ground plane is a wearable contact surface, which reduces the specific absorption rate after the antenna is integrated with the human body.

[0026] The beneficial effects of the present invention are as follows: the present invention is a circularly polarized wearable antenna loaded with an electromagnetic band gap reflector. Compared with existing antenna designs, this antenna design can simultaneously have flexibility, broadband, high gain, low profile, low specific absorption rate and circular polarization characteristics; flexibility: using flexible PDMS material and a meander line design, the antenna performance remains stable when bent with a radius of 100mm, meeting the performance requirements of 5.8GHz wearable devices; broadband: double meander line branch design (each arm of the dipole antenna has two adjacent meander line branches of different lengths); high gain, low profile, low absorption rate: loaded with an electromagnetic band gap reflector design with a meander line structure as the main body; circular polarization characteristics: two pairs of dipoles are placed orthogonally and connected by a pair of quarter-wavelength (the wavelength corresponds to a frequency of 5.8GHz) phase delay rings to form a 90° phase difference. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A top view of a circularly polarized wearable antenna loaded with an electromagnetic bandgap reflector according to the present invention;

[0028] Figure 2 A side view of a circularly polarized wearable antenna loaded with an electromagnetic bandgap reflector according to the present invention;

[0029] Figure 3 Schematic diagram of a reflection unit in the electromagnetic bandgap reflection surface of the antenna of the present invention;

[0030] Figure 4 Schematic diagram of a circularly polarized cross-dipole antenna in the antenna of the present invention;

[0031] Figure 5 Describes the simulation of the antenna in flat and bent states |S 11 |Parameter performance;

[0032] Figure 6 The simulated axial ratio and actual gain performance in the flat and bent states are described;

[0033] Figure 7 Describes the simulation of the proposed antenna with and without human body model loaded|S 11 |Parameter performance comparison;

[0034] Figure 8 The comparison of the simulated axial ratio and actual gain performance of the proposed antenna with and without a human body model is described.

[0035] Figure 9 is the radiation pattern without human body model loaded;

[0036] Figure 10 is the radiation pattern of the loaded human body model. DETAILED DESCRIPTION

[0037] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0038] The overall structure of the antenna includes: two pairs of dipoles with meander line structures; a coaxial feed line with an impedance of 50 ohms; and an electromagnetic bandgap reflector designed by connecting the inner and outer meander line loops using a cross meander line.

[0039] Two pairs of dipoles with meander line structures are placed on the upper and lower surfaces of the PDMS substrate and placed orthogonally. A coaxial line with an impedance of 50 ohms is connected to the orthogonal centers of the two pairs of dipoles to realize center feeding of the antenna, thereby forming a cross-dipole antenna. Among them, the length of the feed circle radius r1 can be 1.1 to 1.7 mm. At the same time, the cross-dipole antenna is connected by a pair of phase delay rings with a length of one-quarter wavelength (the frequency corresponding to the wavelength is 5.8 GHz) and a width Wr of 0.3 to 0.7 mm to form a 90° phase difference, thereby realizing the circular polarization characteristics of the antenna in the 5.8 GHz frequency band. Antennas in other frequency bands can also be connected with phase delay rings of 1 / 4 wavelength and a width of 0.3 to 0.7 mm to form a 90° phase difference.

[0040] By the attached Figure 1 、 2 The circularly polarized wearable antenna is shown in top and side views. The antenna consists of an upper and lower PDMS substrate 2, with two pairs of dipoles 1 printed on the upper and lower surfaces of the upper PDMS substrate. The side length Wa of the upper PDMS substrate can be 52 to 58 mm ( Figure 4 ), the thickness h1 of the upper PDMS substrate can be 1 to 5 mm. Figure 4 As shown, each pair of dipole antennas contains two arms (Arms), and each arm consists of two meander line branches (Branch) of different lengths and an angle interval θ of 45°. These branches are generally periodically bent. Among them, the longer meander line branch W2 is 24 to 28 mm long, which mainly controls the lower frequency band, while the shorter meander line branch W3 is 22 to 26 mm long, which mainly controls the higher frequency band, thereby being used to broaden the overall bandwidth of the antenna. The height difference h6 between the upper and lower meander line segments of each branch is 0.3 to 0.6 mm, which is mainly used to extend the current path, increase the effective inductance, and reduce the size of the cross-dipole antenna. The 50-ohm impedance coaxial feed line 4 connected to the feeding power source 5 passes through the lower PDMS substrate and is respectively connected to the cross dipole 1 on the upper and lower surfaces of the upper PDMS substrate to realize center feeding of the antenna.

[0041] The EBG reflector is composed of a lower PDMS substrate, an array of meander-line annular patches 6 printed on it, and a bottom-layer ground plane 3. Each meander-line annular patch serves as a reflector unit. The lower PDMS substrate has a side length Wt of 60 mm to 70 mm and a thickness h2 of 1 to 5 mm. The distance g1 between adjacent meander-line annular patches is 2 to 6 mm, primarily used to control capacitance and, therefore, the operating bandwidth of the EBG reflector.

[0042] The electromagnetic bandgap reflector has the characteristic of in-phase reflection. Compared with ordinary metal reflectors, it can be placed closer to the antenna radiation unit. This characteristic allows the electromagnetic bandgap reflector to effectively reduce the overall profile while improving the antenna gain, reducing the impact of the human body on the antenna performance after wearable integration, and reducing the overall specific absorption rate of the antenna. In this design, the electromagnetic bandgap reflector can be placed below the cross-dipole antenna at h = 1 to 13 mm for impedance matching. In addition, if Figure 3 As shown, the length W of the outer bending line loop of each reflector unit in the electromagnetic band gap reflector is 8 to 10 mm, which is mainly used to control the capacitance, thereby affecting the working bandwidth of the electromagnetic band gap reflector and the frequency corresponding to the 0° phase; the width g is 0.3 to 0.5 mm, which is mainly used to control the inductance and capacitance, thereby affecting the frequency corresponding to the 0° phase of the electromagnetic band gap reflector; the height difference h3 of the upper and lower bending line segments is 0.6 to 0.8 mm, which is mainly used to increase the effective inductance, thereby reducing the electromagnetic band gap reflector. The overall dimensions of the surface; the length W1 of the inner bending line loop is 4 to 7 mm, and the influencing mechanism is the same as the length W of the outer bending line loop; the width is the same as the width of the outer bending line; the height difference h4 of the upper and lower bending line segments is 0.4 to 0.6 mm, and the influencing mechanism is the same as the outer bending line h3; the width d of the cross bending line is 0.3 to 0.5 mm, which is mainly used to control the inductance and capacitance, thereby affecting the frequency corresponding to the 0° phase of the electromagnetic band gap reflection surface; the height difference h5 of the upper and lower bending line segments is 0.4 to 0.6 mm, and the influencing mechanism is the same as the outer bending line h3.

[0043] The meander line ring patch design primarily increases the effective inductance of the EBG reflector. This increase in effective inductance broadens the EBG reflector's operating bandwidth while reducing its size, thereby reducing the overall size of the antenna. Furthermore, the use of a cross-shaped meander line to connect the inner and outer meander line rings further broadens the EBG reflector's bandwidth. Finally, the use of a ground plane also helps reduce the specific absorption rate (SAR) when the antenna is integrated with the human body.

[0044] In general, this design is based on a meander line structure and uses PDMS flexible material as the substrate. By designing a multi-branch structure for each arm of the cross dipole and a meander line ring structure for the electromagnetic band gap reflector, the antenna bandwidth is effectively improved. The final antenna performance simulation demonstrates flexibility, broadband, high gain, low profile, low specific absorption rate, and circular polarization characteristics.

[0045] Example: Select a PDMS material with a dielectric constant (Dielectric Constant) of 3.2 and a tangent loss (Tangent Loss) of 0.013 as the substrate, and use a material with good conductivity as the radiation unit, such as conductive silver paste or conductive fiber. Print the cross dipole antenna on the upper and lower surfaces of the upper PDMS substrate. The side length Wa of the upper PDMS substrate is selected to be 55mm, and the thickness h1 is selected to be 1mm. The feed circle radius r1 of the cross dipole is selected to be 1.4mm. The width Wr of the phase delay loop used to connect the cross dipoles is selected to be 0.5mm, and the length is still a quarter wavelength (the frequency corresponding to the wavelength is 5.8GHz). In addition, each arm of each pair of dipole antennas has two adjacent bending line branches with different lengths and an angle interval θ of 45°. Among them, the length of the longer bending line branch W2 is selected to be 25.8mm, and the length of the shorter bending line branch W3 is selected to be 23.8mm. The height difference h6 between the upper and lower bending line segments of each branch is selected to be 0.5mm. The side length Wt of the lower PDMS substrate is 62.5mm, and the thickness h2 is 2mm. The height h of the electromagnetic band gap reflector from the cross-dipole antenna is 2mm. Furthermore, the outer bend line loop length W of the reflector unit is 9.9mm, the width g is 0.5mm, and the height difference h3 between the upper and lower bend line segments is 0.7mm. The distance g1 between adjacent bend line ring patches is 2.6mm. The inner bend line loop length W1 is 6.6mm, and the width can be the same as the outer bend line width. The height difference h4 between the upper and lower bend line segments is 0.6mm. The cross bend line width d is 0.4mm, and the height difference h5 between the upper and lower bend line segments is 0.5mm.

[0046] To verify the feasibility of the overall technical solution, this design was simulated using CST Microwave Studio 2019 software. The following is an explanation of the simulation results of the above implementation method:

[0047] This antenna is suitable for wearable devices. Considering that the antenna will bend during integration, its performance in the bent state needs to be considered in the simulation. Figure 5 The simulation of the antenna in flat and bent states is shown. 11 Parameter performance. S 11 The parameter can also be called the reflection coefficient of the antenna, which refers to the ratio of the voltage of the reflected wave on the transmission line to the voltage of the incident wave. The general standard is that the reflection coefficient needs to be less than or equal to -10dB. The smaller the value, the stronger the antenna radiation ability. Figure 5 As can be seen in the figure, in the flat state, the antenna S 11 The continuous bandwidth when ≤-10dB is 5.56GHz to 6.77GHz, and the corresponding fractional bandwidth (FBW) is 19.63%. Therefore, the antenna has good S11 Parameter performance. In addition, it can be seen from the figure that the S 11 The parameters are relatively flat, although there is some frequency shift due to the bending, but the 5.8GHz frequency band is covered. 11 The parameter performance can maintain good stability even when bent, making it suitable for wearable applications.

[0048] At the same time, this antenna is a circularly polarized antenna. Therefore, when simulating, it is also necessary to consider the axial ratio (AR) performance under bending conditions and the actual gain (AR) performance under the corresponding axial ratio frequency band. Figure 6 The simulated AR and Realized Gain performance of the antenna in flat and bent states are shown. The axial ratio parameter is mainly used to judge the quality of the circular polarization performance of the antenna. The general standard is that when the AR is less than or equal to 3dB, the antenna can achieve circular polarization at the frequency corresponding to the AR. The lower the AR, the better the circular polarization performance at the corresponding frequency. The actual gain parameter is used to judge the actual gain that the antenna can generate. The higher the gain, the better the gain performance of the antenna in actual conditions. Figure 6 As can be seen from the figure, in the flat state, the continuous bandwidth of the antenna when AR≤3dB is 5.56GHz to 6.6GHz, and the corresponding fractional bandwidth is 17.1%, which is consistent with S 11 The frequency band coverage of the parameters reaches 85.9%. Furthermore, the maximum actual gain within this frequency band is 12.7dBic, corresponding precisely to 5.8GHz. Furthermore, while the actual gain attenuates when bent, it is generally stable. However, due to the change in the current path, the axial ratio degrades somewhat. When the antenna is bent in the X direction, its axial ratio degrades slightly at lower frequencies, but overall performance is consistent with that in the flat state. However, when the antenna is bent in the Y direction, its axial ratio degrades more significantly than when bent in the X direction. Therefore, bending in the Y direction should be avoided as much as possible. Overall, the actual gain is relatively stable regardless of whether the antenna is bent in the X or Y direction, and its axial ratio in the 5.8GHz band is consistently ≤3dB, meeting the circular polarization requirements for the 5.8GHz band and making it suitable for wearable devices in the 5.8GHz band.

[0049] After integration with the human body, wearable antennas often experience frequency deviation, radiation direction change, gain reduction, etc. due to the influence of human body coupling. Therefore, in order to verify the influence of human body coupling on the proposed antenna and the stability of the proposed antenna, the proposed antenna was placed in the upper arm area of ​​the Gustav human body model in CST Microwave Studio 2019 software, as shown in the attached figure. Figure 7In addition, considering the thickness of the clothing, the proposed antenna is not completely attached to the human body model, but is placed 3mm above it. Figure 7 It can be seen from the figure that after the proposed antenna is loaded with the human body model (On Phatom Arm), its simulation S 11 Parameter performance and simulation of the proposed antenna without human body model (Free Space) 11 The parameter performance is almost the same.

[0050] In addition, from the attached Figure 8 It can also be seen that the simulated axial ratio and actual gain performance of the proposed antenna with and without the human body model show high consistency.

[0051] Attachment Figure 9 、 10 The simulated radiation patterns of the proposed antenna at 5.8 GHz for left-hand circularly polarized (LHCP) and right-hand circularly polarized (RHCP) in the XoZ and YoZ planes with and without a human body model are shown. Figure 9 It can be seen that when the antenna is not loaded with a human body model, its left-handed and right-handed circularly polarized waves have good unidirectionality in the positive z direction (0° direction). In addition, the radiation intensity of the right-handed circularly polarized wave in the positive direction perpendicular to the XoY plane is always more than 15dB stronger than that of the left-handed circularly polarized wave, which shows that the proposed antenna is a right-handed circularly polarized antenna. At the same time, according to the attached Figure 10 It can be seen that the proposed antenna loaded with the human body model exhibits lower backward radiation (Backward Radiation) and higher front to back ratio (FBR) performance compared to the proposed antenna without the human body model.

[0052] In summary, the above simulation results all verify that the proposed antenna is less affected by human body coupling, which also makes the antenna stably applicable in the wearable field.

[0053] This application proposes a flexible, bend-resistant, wearable circularly polarized cross-dipole antenna based on a PDMS flexible material loaded electromagnetic bandgap reflector structure. The antenna adopts a meander line structure as a whole. Simulation results show that even when the antenna is bent with a bending radius of 100mm, its performance remains stable, making it suitable for 5.8GHz wearable applications such as smart monitoring applications installed on the human arm.

[0054] The above-described embodiments merely represent specific implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A circularly polarized wearable antenna loaded with an electromagnetic bandgap reflector, characterized in that: Two pairs of dipoles with meander lines are placed on the upper and lower surfaces of the upper PDMS flexible substrate and are placed orthogonally. A 50-ohm impedance coaxial line is connected to the orthogonal centers of the two pairs of dipoles to achieve antenna center feeding, thus forming a cross-dipole antenna. The cross-dipole antennas are connected with phase delay rings to form a phase difference of 90°, thereby achieving the circular polarization characteristics of the antenna in the required frequency band; The electromagnetic bandgap reflector is composed of a lower PDMS flexible substrate, an array of meander line ring patches printed on the PDMS substrate, and a bottom-layer ground plane. Each meander line ring patch acts as a reflector unit, increasing the effective inductance of the electromagnetic bandgap reflector and widening its operating bandwidth. The electromagnetic band gap reflector is placed 1 to 13 mm below the cross dipole antenna to perform impedance matching.

2. The circularly polarized wearable antenna loaded with an electromagnetic band gap reflector according to claim 1, characterized in that: Each pair of dipole antennas in the cross-dipole antenna contains two arms, and each arm is composed of two meander line branches of different lengths and an angular interval θ of 45°. The meander line branches are periodically bent, wherein the long meander line branches are used to control the low frequency band and the short meander line branches control the high frequency band. The height difference between the upper and lower meander line segments of each branch is used to extend the current path, increase the effective inductance, and reduce the size of the cross-dipole antenna.

3. The circularly polarized wearable antenna loaded with an electromagnetic band gap reflector according to claim 1 or 2, characterized in that: The cross dipole antenna is connected by a pair of phase delay rings with a length of one quarter wavelength and a width of 0.3 to 0.7 mm to form a phase difference of 90 degrees.

4. The circularly polarized wearable antenna loaded with an electromagnetic band gap reflector according to claim 1, characterized in that: The reflective surface unit is an electromagnetic band gap reflective surface designed by connecting two inner and outer bending line rings using a cross bending line.

5. The circularly polarized wearable antenna loaded with an electromagnetic band gap reflector according to claim 4, characterized in that: In the inner and outer meander line loops and the cross meander line structure in the reflector unit, the length of the meander line loop is used to control the capacitance, thereby affecting the operating bandwidth of the electromagnetic band gap reflector and the frequency corresponding to the 0° phase; the width of the meander line loop and the cross meander line is used to control the inductance and capacitance, thereby affecting the frequency corresponding to the 0° phase of the electromagnetic band gap reflector; the height difference between the upper and lower meander line segments is used to increase the effective inductance, thereby reducing the overall size of the electromagnetic band gap reflector.

6. The circularly polarized wearable antenna loaded with an electromagnetic band gap reflector according to claim 1, characterized in that: The ground plane is a wearable contact surface, which reduces the specific absorption rate after the antenna is integrated with the human body.

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