A three-band wearable antenna

Abstract

The present invention relates to the field of electronic technology, and provides a three-band wearable antenna. The main purpose is to achieve antenna miniaturization and impedance matching performance under multi-bands when reducing the number of antennas and adopting multi-band integration, and optimize the antenna radiation performance. The main scheme includes a first dielectric substrate, a metal radiating plate, a metal ground, a second dielectric substrate, a metamaterial EBG structure printed on the top surface of the second dielectric substrate, and an EBG structure metal ground arranged on the bottom surface of the second dielectric substrate, wherein the metal radiating plate and the metal ground of the antenna are both located on the top surface of the first dielectric substrate, the metal radiating plate is divided into two branches, the first branch is a U-shaped strip arranged at the top end of a coplanar waveguide feeding radiation strip, the second branch is a lateral branch connected to the top end of the coplanar waveguide feeding radiation strip, and an L branch is arranged on the metal ground on the right side of the coplanar waveguide feeding radiation strip.

Description

Technical Field

[0001] The present invention relates to the field of electronic technology, in particular to wearable devices and antenna technology for wireless medical systems, and provides a three-band wearable antenna. Background Art

[0002] In modern healthcare, people use wearable medical devices to monitor their health status in real time, such as body temperature, heart rate, blood pressure, sleep quality, etc. Wearable devices have become a cross-border device that realizes data interaction and cloud interaction through mobile Internet. Its emergence has brought great changes to people's lives. Wearable antennas are important components in wearable devices to ensure the quality of communication with external devices. The communication of wearable antennas is usually divided into three categories: in-body, on-body, and off-body.

[0003] There are many types of wearable antennas, such as planar inverted F antenna, monopole antenna, slot antenna, microstrip antenna, fractal antenna, etc. Wearable antennas face a series of challenges, such as low profile, bandwidth, polarization, and safety to the human body.

[0004] Existing technology:

[0005] A miniaturized dual-band antenna for LoRa wearable devices discloses that the antenna's -10dB impedance bandwidth can cover most of the LoRa device's operating frequency bands of 470-510MHz and 863-868MHz. The antenna has a simple structure, wide coverage frequency, small size, and good radiation performance within the operating frequency band.

[0006] This solution has the following defects:

[0007] 1) The original structure is a dual-band antenna, which is not as good as the tri-band antenna in terms of frequency band application and functions;

[0008] 2) The antenna proposed in the prior art is a bracket antenna, which has a lower profile than the printed antenna.

[0009] 3) The original technology is mainly for LoRa devices, and its operating frequency bands are 470-510MHz and 863-868MHz. Its operating frequency bands are not used by most current wearable devices, so its application scope is narrow;

[0010] 4) The design of the antenna does not take human safety into consideration. Summary of the invention

[0011] The purpose of the present invention is to realize a three-band antenna by using a coplanar waveguide (CPW) fed monopole antenna, so that the frequency bands of multiple single-band antennas or dual-band antennas are integrated into one antenna, which can reduce the number of antennas and make the wearable device more compact, thereby facilitating the miniaturization of the device. When multi-band integration is adopted, it is necessary to solve the problem of how to achieve antenna miniaturization and impedance matching performance under multi-bands and antenna radiation performance optimization.

[0012] In order to achieve the above purpose, the present invention adopts the following technical means:

[0013] The present invention provides a three-band wearable antenna, comprising a first dielectric substrate, a metal radiating plate, a metal ground, a second dielectric substrate, a metamaterial EBG structure printed on the top surface of the second dielectric substrate, and an EBG structure metal ground arranged on the bottom surface of the second dielectric substrate, wherein the metal radiating plate and the metal ground of the antenna are both located on the top surface of the first dielectric substrate, the metal radiating plate is divided into two branches, the first branch is a U-shaped band arranged at the top end of a coplanar waveguide feeding radiation band, generating a 2.45 GHz frequency band, the second branch is a lateral branch connected to the top end of the coplanar waveguide feeding radiation band, generating a 5.8 GHz frequency band, and an L branch is arranged on the metal ground on the right side of the coplanar waveguide feeding radiation band to generate a 3.5 GHz frequency band.

[0014] In the above technical solution, the metamaterial EBG structure includes an EBG unit, and the EBG unit includes a first rectangular ring, a second rectangular ring arranged in the first rectangular ring, and a circular ring arranged in the second rectangular ring. The in-phase reflection characteristics of the metamaterial EBG structure are utilized to form a three-band consistent with the antenna frequency band.

[0015] In the above technical solution, the metal ground includes a left metal ground and a right metal ground, and the left metal ground and the right metal ground are arranged on both sides of the coplanar waveguide feeding radiation strip.

[0016] In the above technical solution, a rectangular groove is opened at the upper left corner of the left metal ground, and a rectangular groove is opened at the upper right corner of the right metal ground, so as to comprehensively adjust the impedance matching performance of each frequency band.

[0017] In the above technical solution, the EBG units are distributed in a 3×3 array horizontally and vertically.

[0018] In the above technical solution, the distance between the bottom surface of the first dielectric substrate and the metal surface on the second dielectric substrate is 3 mm, and the distance can be adjusted according to the comprehensive performance of the integrated antenna.

[0019] In the above technical solution, the material of the first dielectric substrate (2) is Rogers 4350, with a dielectric constant of 3.48 and a thickness of 1.5 mm. Generally, a distance greater than the thickness of the substrate but much less than a quarter wavelength is selected, and the middle is an air layer, which can be replaced by plastic foam or the like during actual production. If a metal plate is placed under the antenna to improve the antenna pattern, a quarter wavelength is theoretically required. Therefore, the use of metamaterials requires a smaller distance than that required by the metal plate, and the side height of the antenna can be reduced.

[0020] Because the present invention adopts the above technical solution, it has the following beneficial effects:

[0021] 1. The antenna uses a multi-branch monopole antenna fed by a coplanar waveguide and ground branch technology, which enables the antenna to work in three frequency bands at the same time. The meander technology is used to miniaturize the size of the antenna.

[0022] 2. The antenna is a tri-band antenna that can cover the industrial, scientific and medical frequency bands (ISM, 2.4-2.48GHz, 5.725-5.875GHz), and the WiMax frequency band (3.4-3.6GHz).

[0023] 3. The antenna uses a metamaterial structure, which is composed of multiple tri-band metamaterial units. The metamaterial structure can be used to improve the antenna's front-to-back ratio, gain and other radiation performance. The metamaterial structure can change the antenna from omnidirectional to directional radiation, improve the antenna's radiation performance to the outside world, thereby increasing the antenna's gain and improving the antenna's communication capabilities.

[0024] 4. This antenna is a wearable antenna and is suitable for a variety of wearable devices in wireless body area networks.

[0025] 5. This patent directly leads out a radiation strip through the coplanar waveguide feeder and bends it into an asymmetric U-shaped structure. The other grounded radiation branch is also bent into an L-shape, thereby greatly reducing the size of the antenna. The antenna size of this patent is 26mm long and 25mm wide. With the same working frequency band, it is much smaller than the original invention patent. It meets the requirements of miniaturization of wearable antennas.

[0026] 6. The invention cuts a rectangular groove on both sides of the coplanar waveguide, thereby increasing the freedom of impedance control and being more conducive to achieving good impedance matching performance of the antenna. The S11 of the three frequency bands of the invention is about -20dB. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Top and side views of the wearable antenna structure.

[0028] Figure 2 Top view and side view of the EBG structure of the wearable antenna.

[0029] Figure 3 is the return loss of the wearable antenna.

[0030] Figure 4 is the two-dimensional far-field pattern of the wearable antenna at a frequency of 2.45 GHz;

[0031] Figure 5 is the two-dimensional far-field pattern of the wearable antenna at 3.5 GHz;

[0032] Figure 6 is the two-dimensional far-field pattern of the wearable antenna at 5.8 GHz;

[0033] Figure 7 It is a triple-band integrated antenna structure;

[0034] Figure 8 It is an EBG unit structure;

[0035] Fig. 9 is the reflection phase of the triple-band EBG unit.

[0036] Description of Reference Numerals

[0037] 1-metal radiation plate, 2-first dielectric substrate, 3-metal ground, 4-metal surface, 5-second dielectric substrate, 6-EBG structure metal ground, 11-coplanar waveguide feeding radiation strip, 12-U-shaped strip, 13-lateral branch, 31-left metal ground, 32-right metal ground, 41-first rectangular ring, 42-second rectangular ring, 43-circular ring. DETAILED DESCRIPTION

[0038] The following is a detailed description of the embodiments of the present invention. Although the present invention will be described and illustrated in conjunction with some specific embodiments, it should be noted that the present invention is not limited to these embodiments. On the contrary, modifications or equivalent substitutions made to the present invention should all be included in the scope of the claims of the present invention.

[0039] In addition, in order to better illustrate the present invention, numerous specific details are given in the following specific embodiments. It will be understood by those skilled in the art that the present invention can also be implemented without these specific details.

[0040] In recent years, metamaterial structures have been proven to effectively reduce the SAR value of antennas and reduce the radiation of antennas to the human body, including artificial magnetic conductors (AMCs), electromagnetic band gap (EBG) structures, metasurface structures, etc. Most of the current research focuses on the design of single-band or dual-band wearable antennas, and there are few multi-band antennas with three bands or more. Existing multi-band antennas do not use corresponding multi-band metamaterial structures to improve their performance. This patent invents a new three-band wearable integrated antenna, which is formed by integrating a three-band EBG structure with a coplanar waveguide-fed three-band monopole antenna. To realize a multi-band antenna with three bands or more while maintaining the same or reduced overall size, it is necessary to comprehensively utilize antenna theory, reasonably design the antenna structure, and meet the impedance matching performance of the antenna in each band, the antenna radiation performance, etc. Generally, the more bands there are, the greater the design difficulty.

[0041] This patent provides a three-band wearable antenna based on EBG metamaterial structure. The working frequency bands include industrial, scientific and medical bands (ISM, 2.4-2.48GHz, 5.725-5.875GHz), and WIMAX bands (3.4-3.6GHz). It is mainly based on multi-band antenna technology, multi-band metamaterial technology, monopole antenna technology, and coplanar waveguide technology, and is suitable for application in wearable devices.

[0042] The antenna is composed of a metal radiating plate, a dielectric substrate, a coplanar metal ground, an EBG structure, etc., wherein the metal radiating plate and the ground of the antenna are both located on the top surface of the dielectric substrate, and there is no metal on the bottom surface of the dielectric substrate; the EBG unit is produced by a double rectangular ring and a circular ring, and a finite periodic structure is formed by using 3×3 EBG units, which is placed a certain distance below the antenna and serves as a magnetic conductor to improve the front-to-back ratio radiation performance of the antenna.

[0043] (1) The antenna as a whole is composed of a multi-branch monopole fed by a coplanar waveguide and a ground branch. The main radiation band of the antenna is composed of a 50-ohm coplanar waveguide fed radiation band connected to an asymmetric U-shaped band, and this current path can generate a 2.45 GHz frequency band. The other radiation band of the antenna is composed of a 50-ohm coplanar waveguide fed radiation band connected to a lateral branch, and this current path can generate a 5.8 GHz frequency band. The 3.5 GHz frequency band of the antenna is generated by an L branch introduced to the ground on the right side of the coplanar waveguide. The U-shaped band and the L branch use meander technology, which is conducive to reducing the size of the antenna.

[0044] (2) Using tri-band antenna technology and utilizing multiple branches to generate tri-band signals is beneficial to reducing the number of antennas in wearable devices, saving internal space, and facilitating the miniaturization of wearable devices.

[0045] (3) The EBG unit is composed of two rectangular rings and one circular ring, and the in-phase reflection characteristics of the EBG structure are used to form a three-band frequency band consistent with the antenna frequency band.

[0046] (4) Multi-band EBG is conducive to targeted improvement of antenna performance in each frequency band.

[0047] (5) Using coplanar waveguide technology, the metal layers of the antenna are located in the same plane, making it easy to connect the antenna in parallel or series with other devices, thereby increasing the flexibility of circuit design.

[0048] The operating frequency of the antenna can be further adjusted by changing the branch size and ground branch size of the monopole antenna. The impedance matching of the antenna can be adjusted by changing the height of the antenna coplanar waveguide and the size of the rectangular slots on both sides of the coplanar waveguide. In addition, the effect of the EBG structure can be adjusted by changing the number of EBG units and the distance between the EBG periodic structure and the antenna.

[0049] Theoretically, a metamaterial with a reflection phase of 0° can be regarded as a perfect magnetic conductor (PMC). In simulation, the frequency range of the reflection phase between -90° and 90° is usually used as the working frequency band of the metamaterial. Figure 2 is the reflection phase diagram of the EBG structure, and its operating frequencies cover the 2.45GHz, 3.5GHz and 5.8GHz bands, corresponding to the antenna operating frequency band. In practical applications, multiple EBG units form a finite array and are integrated into the antenna to improve the radiation performance of the antenna. This patent uses Figure 3 The 3×3 EBG array structure shown in FIG. 1 is integrated into the antenna to obtain the following Figure 4 The integrated antenna shown in the figure. This patent uses a 3×3EBG structure to improve the front-to-back ratio of the antenna's radiation pattern, and transforms the omnidirectional pattern originally radiated independently by the monopole antenna into directional radiation, such as Figure 4-6 As shown, the radiation to the human body is reduced, so that the safety of the human body is guaranteed. Secondly, the gain of radiation to the outside of the body is increased, and the communication quality of the antenna is improved.

[0050] Of course, according to the compromise between size and performance, metamaterial structures of sizes such as 2×2EBG and 4×4EBG can also be constructed to improve antenna performance. Generally, the more EBG units there are, the better the effect will be, but the size will also be larger.

[0051] See also Figure 1 The antenna is composed of a metal radiation plate 1, a first dielectric substrate 2, and a metal ground 3. Figure 2 The metamaterial structure is composed of 3×3 EBG units, each of which includes a double metal rectangular ring, namely a first rectangular ring 41 , a second rectangular ring 42 , a circular ring 43 of metal material, a second dielectric substrate 5 and an EBG structure metal ground 6 .

[0052] Example

[0053] The antenna part of the wearable antenna structure is as follows Figure 1 As shown, the antenna is composed of a top metal radiation plate 1, a first dielectric substrate 2, and a top metal ground 3. The material of the first dielectric substrate 2 is Rogers 4350, with a dielectric constant of 3.48 and a thickness of 1.5 mm. The top metal radiation plate of the antenna is divided into two branches. The first branch is composed of a coplanar waveguide feeding radiation strip 11 and a U-shaped strip 12, which produces a frequency band of 2.45 GHz; the second branch is composed of a coplanar waveguide feeding radiation strip 11 and a lateral branch 13, which produces a frequency band of 5.8 GHz. The top metal ground 3 is composed of a left metal ground 31 and a right metal ground 32, and a rectangular groove is opened in the upper left and upper right of the ground to comprehensively adjust the impedance of each frequency band. In addition, an L-shaped branch 33 is added above the right metal ground 32 to produce a 3.5 GHz frequency band.

[0054] Metamaterial EBG structures for wearable antenna structures such as Figure 2 As shown, the metamaterial is composed of 3×3 EBG units. The top metal of each EBG unit is composed of a double rectangular ring, namely a first rectangular ring 41, a second rectangular ring 42 and a circular ring 43. The bottom of the second dielectric substrate 5 that constitutes the EBG structure is fully covered with an EBG structure metal ground 6. The metamaterial is located below the antenna, and the distance between the metal surface 4 on its second dielectric substrate 5 (i.e., the metal surface of the double rectangular ring and the circular ring) and the metal radiation plate 1 of the antenna is about 3 mm. This distance can be adjusted according to the comprehensive performance of the integrated antenna. In addition, in order to simulate the performance of the antenna on the human body, we constructed a 3-layer human tissue consisting of skin, fat and muscle. Considering the thickness of the clothing, the human tissue is about 10 mm away from the antenna.

[0055] According to the antenna's directional pattern in different frequency bands ( Figure 4 , 5, 6), the EBG structure can simultaneously improve the radiation performance of the antenna in three frequency bands, so that the antenna mainly radiates in a direction away from the human body. Therefore, the EBG structure can improve the communication quality of the antenna while meeting the safety of the human body.

[0056] At the same time, compared with the existing patent "low-profile three-band adjustable antenna", the existing patent is a three-band antenna realized by reconfigurable technology, which realizes three frequency bands through PIN switches. It can only produce one frequency band in a certain PIN switch combination state. It is essentially a single-band antenna and cannot meet the requirements of three frequency bands at the same time. In addition, the EBG structure designed is a single-band structure, which can have an effect on two adjacent frequency bands, but not on all three frequency bands. The antenna of this patent works in three frequency bands at the same time, and the designed EBG structure can also have an effect on the three frequency bands of the antenna at the same time.

Claims

1. A three-band wearable antenna, comprising a first dielectric substrate (2), a metal radiation sheet (1), a metal ground (3), a second dielectric substrate (5), a metamaterial EBG structure (4) printed on the top surface of the second dielectric substrate (5), and an EBG structure metal ground (6) arranged on the bottom surface of the second dielectric substrate (5). It is characterized in that The metal radiation sheet (1) and the metal ground (3) are both located on the top surface of the first dielectric substrate (2); the metal radiation sheet (1) is divided into two branches, the first branch is a U-shaped strip (12) arranged at the top of the coplanar waveguide feeding radiation strip (11); the second branch is a transverse branch (13) connected to the top of the coplanar waveguide feeding radiation strip (11); and an L branch is arranged on the metal ground (3) on the right side of the coplanar waveguide feeding radiation strip; The metamaterial EBG structure comprises an EBG unit, the EBG unit comprising a first rectangular ring (41), a second rectangular ring (42) arranged in the first rectangular ring (41), and a circular ring (43) arranged in the second rectangular ring (42), and utilizing the in-phase reflection characteristics of the metamaterial EBG structure to form a triple frequency band consistent with the antenna frequency band; The EBG units are arranged in a 3×3 array horizontally and vertically; The material of the first dielectric substrate (2) is Rogers 4350, with a dielectric constant of 3.48 and a thickness of 1.5 mm.

2. A tri-band wearable antenna according to claim 1, It is characterized in that The metal ground (3) comprises a left metal ground (31) and a right metal ground (32), and the left metal ground (31) and the right metal ground (32) are arranged on both sides of the coplanar waveguide feeding radiation strip (11).

3. The tri-band wearable antenna according to claim 1, It is characterized in that A rectangular groove is provided at the upper left corner of the left metal ground (31), and a rectangular groove is provided at the upper right corner of the right metal ground (32).

4. The tri-band wearable antenna according to claim 1, It is characterized in that The distance between the bottom surface of the first dielectric substrate (2) and the metal surface (4) on the second dielectric substrate (5) is 3 mm.

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