CN115458932B

CN115458932B - Miniaturized flexible wearable antenna capable of improving high-order mode radiation characteristics

Info

Publication number: CN115458932B
Application number: CN202211401778.4A
Authority: CN
Inventors: 赵晨; 李文冉; 潘成胜
Original assignee: Nanjing University of Information Science and Technology
Current assignee: Nanjing University of Information Science and Technology
Priority date: 2022-11-10
Filing date: 2022-11-10
Publication date: 2023-04-18
Anticipated expiration: 2042-11-10
Also published as: CN115458932A

Abstract

The invention discloses a miniaturized flexible wearable antenna for improving the radiation characteristic of a high-order mode in the field of wireless mobile communication, which comprises three layers of felt substrates and four layers of polyimide film circuits, wherein a metal structure is printed on the polyimide film, the metal structure comprises four layers, and the four layers of metal layers sequentially comprise a micro-strip line layer, a gap coupling layer, a uniform super-surface layer and a non-uniform stacked patch layer from bottom to top. The antenna effectively inhibits the distortion of a high-order mode directional diagram, keeps good broadside radiation characteristic in a high-frequency band, also has very wide matching bandwidth, and has stable antenna gain, wherein the gain bandwidth of 3dB exceeds 49 percent; the whole flexible material that is processed, the size is less, be fit for wearing, has stronger robustness, and the performance receives the influence of flexible substrate deformation less, and the antenna receives human tissue influence moreover for a short time, and the electromagnetic radiation absorption rate is in safe range.

Description

Miniaturized flexible wearable antenna capable of improving high-order mode radiation characteristics

Technical Field

The invention belongs to the field of wireless mobile communication, and particularly relates to a miniaturized flexible wearable antenna for improving the radiation characteristic of a high-order mode.

Background

Under the background of continuous development of Wireless communication technology, wireless Body Area Networks (WBANs) are increasingly researched, and by flexibly receiving and processing human Body signals from wearable devices and sensors, the Wireless Body Area networks can be widely applied to monitoring medical treatment, sports training and military application, and considering the particularity of a working scene, wearable antennas need to meet more requirements than traditional antennas.

Firstly, in order not to affect the wearing comfort, the antenna should be made of flexible materials, and the performance is less affected by deformation, secondly, the miniaturized and broadband wearable antenna will contribute to the compact design of the system, and can effectively resist the frequency deviation phenomenon caused by human tissue loading, and maintain stable and good performance in the dynamically changing human environment, and furthermore, the wearable antenna needs to have lower coupling with the human tissue, which not only can improve the radiation efficiency and gain of the antenna, reduce the node power consumption, but also help to reduce the Specific Absorption Rate (SAR), so that the human body is prevented from being damaged by electromagnetic radiation.

Although the super-surface antenna has the advantages of low profile, wide frequency band and high gain, and perfectly conforms to the requirements of the wearable antenna, when the frequency is high, the radiation pattern of the super-surface antenna can be distorted due to the excitation of high-order modes, and in addition, the super-surface antenna usually has a large volume, so that the application prospect of the super-surface antenna in the wearable antenna is influenced.

Disclosure of Invention

In view of the shortcomings in the prior art, the present invention is directed to a miniaturized flexible wearable antenna with improved high-order mode radiation characteristics, so as to solve the problems mentioned in the background art.

The purpose of the invention can be realized by the following technical scheme:

the utility model provides an improve flexible wearable antenna of miniaturization of higher mode radiation characteristic, the antenna includes three-layer felt base plate and four-layer polyimide film circuit, and metal structure is printed on the polyimide film, and metal structure has four layers, and four layers of metal level from the bottom up is microstrip line layer, gap coupling layer, even super superficial layer and inhomogeneous paster layer that piles up in proper order.

Preferably, the felt substrate has a dielectric constant of 1.26, a loss tangent of 0.02, a thickness of the polyimide film of 0.07mm, a dielectric constant of 3.4, and a loss tangent of 0.008.

Preferably, the three layers of the felt base plate have thicknesses of 1mm, 3mm and 1mm from bottom to top in sequence.

Preferably, the microstrip line layer is a Y-shaped microstrip line structure, and includes a section of 50 Ω microstrip transmission line with a length Lf1 and two sections of microstrip arms with a length Lf3, and the distance between the two arms is Lf2;

the gap coupling layer is formed by etching a rectangular groove with the length Lss and the width Wss in the middle of the metal layer;

the super surface layer is composed of a group of 4 multiplied by 4 patch arrays, the unit side length is L1, and the unit gap is g;

the stacked patch layers are formed by placing patches with different sizes right above transverse gaps formed among units of the square metal layer, the patches are divided into two groups according to the sizes, the two rows of units in the middle are L2 multiplied by W2, the two units in the middle are in short circuit with the lower layer through two copper wires with the diameter of d, and the two rows of the edges are L3 multiplied by W3.

Preferably, the specific parameters of the antenna are as follows: ws =50mm, w1=7mm, w2=7mm, w3=7mm, wf1=4.6mm, wf2=1.4mm, wss =1.5mm, l1=7mm, l2=6.8mm, l3=7.5mm, lf1=21mm, lf2=11.4mm, lf3=10.3mm, lss =17.5mm, d =1.2mm, dsp =1mm, g =1mm.

Preferably, the antenna inhibits the distortion of the high-order radiation mode pattern of the super-surface antenna by loading the short-circuit column.

The invention has the beneficial effects that:

1. the antenna effectively inhibits the distortion of a high-order mode directional diagram, keeps good broadside radiation characteristic in a high-frequency section, also has very wide matching bandwidth, and has stable antenna gain, wherein the gain bandwidth of 3dB exceeds 49%;

2. the antenna is integrally made of flexible materials, has small size, is suitable for wearing, has strong robustness, and has small influence of the deformation of the flexible substrate on the performance, and the antenna is slightly influenced by human tissues, and the electromagnetic radiation absorption rate is in a safe range.

Drawings

In order to more clearly illustrate the embodiments or technical solutions in the prior art of the present invention, the drawings used in the description of the embodiments or prior art will be briefly described below, and it is obvious for those skilled in the art that other drawings can be obtained based on these drawings without creative efforts.

FIG. 1 is a schematic diagram of a layered structure of a miniaturized flexible wearable antenna of the present invention;

FIG. 2 is a structure view of a microstrip line layer according to the present invention;

FIG. 3 is a view showing the structure of the super surface layer in the present invention;

fig. 4 is a diagram of a stacked patch layer structure in the present invention;

FIG. 5 is a current distribution diagram of a higher order mode in eigenmode analysis according to the present invention;

wherein, (a) there is no short-circuiting pillar, (b) there is short-circuiting pillar;

FIG. 6 is a graph comparing radiation characteristics with and without short-circuiting pillars in the characteristic mode analysis of the present invention;

FIG. 7 is a graph of the effect of human body structure on antenna reflection coefficient and gain in the present invention;

FIG. 8 is a graph of the effect of distortion on antenna reflection and gain in accordance with the present invention;

FIG. 9 is a directional diagram of the antenna of the present invention in free space;

wherein, (a) 5 GHz, (b) 6GHz, (c) 7 GHz;

FIG. 10 is a graph showing a comparison of radiation characteristics of high-order modes in the presence/absence of a short-circuited column in full-wave simulation according to the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Referring to fig. 1 to 10, in the design scheme of the miniaturized flexible wearable antenna for improving the radiation characteristic of the high-order mode, the impedance bandwidth of 4.42 to 7.66GHz (53.6%) is realized through slot coupling feeding, the peak gain is 9.6 dBi, the in-band gain is stable, the 3dB gain bandwidth is 4.55 to 7.54ghz (49.5%), and the size of the patch is only 0.62 × 0.62 λ 0 ² (λ 0 is the wavelength corresponding to the center frequency).

The antenna provided by the invention comprises a three-layer felt substrate and a four-layer polyimide film circuit, wherein the dielectric constant of the felt is 1.26, the loss tangent of the felt is 0.02, the thickness of the polyimide film is 0.07mm, the dielectric constant of the polyimide film is 3.4, and the loss tangent of the polyimide film is 0.008. The metal structure is a microstrip line layer, a gap coupling layer, an even super surface layer and an uneven stacking patch layer from bottom to top in sequence. The microstrip line layer comprises a 50 omega microstrip transmission line and two microstrip arms, the slot coupling layer is formed by etching a rectangular groove at the middle position of a metal layer covering the whole thin film, the super surface layer is composed of a group of 4 multiplied by 4 patch arrays, and the stacked patch layer at the uppermost layer is positioned right above a transverse slot formed between units of the super surface layer, so that the equivalent capacitance between super surface structures can be increased, and the size of the antenna is reduced. In addition, the two units positioned at the center are in short circuit with the lower layer through the copper wires, so that the radiation characteristic of the high-order mode of the super-surface can be optimized, and the antenna still keeps good broadside radiation characteristic at high frequency.

Fig. 1 is a layered structure diagram of an antenna, the antenna comprises three layers of felt substrates and four layers of polyimide films, the three layers of felt substrates are 1mm, 3mm and 1mm in thickness from bottom to top in sequence, a metal structure is printed on the polyimide film, and the four layers of metal layers are a microstrip line layer, a slot coupling layer, a uniform super surface layer and a non-uniform stacked patch layer from bottom to top in sequence.

Fig. 2-4 show structure diagrams of each layer, where the microstrip line layer is a Y-shaped microstrip line structure, and includes a 50 Ω microstrip transmission line with a length Lf1 and two microstrip arms with a length Lf3, the distance between the two arms is Lf2, the slot coupling layer is formed by etching a rectangular slot with a length Lss and a width Wss at the middle position of the metal layer on the whole film, the super surface layer is composed of a group of 4 × 4 patch arrays, the unit side length is L1, the unit gap is g, the top stacked patch layer is formed by placing patches with different sizes right above the transverse slot formed between the units of the square metal layer, and the stacked patch layer can be divided into two groups according to the sizes, where the two rows in the middle are L2 × W2, and the two units in the middle are shorted with the lower layer by two copper wires with a diameter d, and the two rows at the edge are L3 × W3. The specific parameters of the antenna are as follows: ws =50mm, w1=7mm, W2=7mm, w3=7mm, wf1=4.6mm, wf2=1.4mm, wss =1.5mm, l1=7mm, l2=6.8mm, l3=7.5mm, lf1=21mm, lf2=11.4mm, lf3=10.3mm, lss =17.5mm, d =1.2mm, dsp =1mm, g =1mm. The size parameter is an optimization result aiming at the reflection coefficient, and finally, the impedance bandwidth of 4.42 to 7.66GHz (53.6%) is realized, the peak gain is 9.6 dBi, and the 3dB gain bandwidth is 4.55 to 7.54GHz (49.5%).

Fig. 5 and 6 respectively show the current distribution and radiation characteristics of the high-order mode when the short-circuit column is loaded or not in the characteristic mode analysis, and the current on the two rows of super-surface structures in the middle and the stacked patches is reduced by loading the short-circuit column so as to achieve the purpose of improving the directional diagram. And after the short-circuit column is loaded, the directivity coefficient and the main lobe beam width are obviously improved, and more importantly, the side lobe level is obviously reduced from-1.8 dB to-10 dB.

Fig. 7 shows the reflection coefficient and gain of the antenna 5mm above the human tissue in free space, the human tissue causes slight frequency offset of the reflection coefficient of the antenna, and the overall gain of the antenna is reduced due to the absorption of electromagnetic waves by the human body, but still maintains a high level, so that the antenna is suitable for working around the human body. Fig. 8 shows the performance of the antenna after being bent along the cylinders with different radii, and it can be seen that the overall performance of the antenna is slightly deteriorated due to the influence of the shape bending, but a very wide operating bandwidth can still be ensured, so that the antenna has strong robustness.

Fig. 9 shows the directional diagram of the antenna in free space, and at 5 GHz, 6GHz and 7 GHz, the antenna radiates in the normal direction and has very low cross polarization, which can satisfy the external communication well.

In fig. 10, the radiation characteristics at the higher-order resonant frequency point when a short-circuit column exists or not under full-wave simulation are compared, the result is similar to the characteristic mode analysis result, when no short-circuit column is loaded, due to the interference of a higher-order mode, the radiation pattern side lobe is higher, the antenna gain is reduced, after the short-circuit column is added, the higher-order radiation mode is better inhibited, and the radiation characteristics are obviously improved.

Finally, establishing a three-layer human tissue model of skin, fat and muscle in CST simulation software, simulating the influence of an antenna on a human body, setting the input power of the antenna to be 0.1W, and when the distance is 5mm away from the human tissue, obtaining SAR values through simulation as shown in Table 1, wherein the SAR values of the antenna at 5 GHz, 6GHz and 7 GHz are respectively 1.59W/kg, 1.38W/kg and 1.07W/kg under the 1g standard; under the 10g standard, the SAR values are 0.60W/kg, 0.42W/kg and 0.38W/kg respectively at 5 GHz, 6GHz and 7 GHz, and the SAR values of the antenna in the working frequency band all meet the standards of the United states and the European Union.

Table 1: simulation result of SAR value of antenna at different frequencies

Frequency of	1 g SAR	10 g SAR
			5GHz	1.59 W/kg	0.60 W/kg
6GHz	1.38 W/kg	0.42W/kg
			7GHz	1.07 W/kg	0.38 W/kg

In the description of the present invention, it is to be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and thus, are not to be construed as limiting the present invention.

In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; they may be directly connected or indirectly connected through intervening media, or they may be interconnected within two elements or in a relationship where two elements interact with each other unless otherwise specifically limited. The specific meanings of the above terms in the present invention can be understood according to specific situations by those of ordinary skill in the art.

In the present invention, unless otherwise expressly stated or limited, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through an intermediate. Also, a first feature "on," "above," and "over" a second feature may mean that the first feature is directly above or obliquely above the second feature, or that only the first feature is at a higher level than the second feature. A first feature "under," "beneath," and "under" a second feature may be directly under or obliquely under the second feature, or may simply mean that the first feature is at a lesser elevation than the second feature.

In the description herein, references to the description of "one embodiment," "an example," "a specific example" or the like are intended to mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

The foregoing shows and describes the general principles, principal features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are given by way of illustration of the principles of the present invention, but that various changes and modifications may be made without departing from the spirit and scope of the invention, and such changes and modifications are within the scope of the invention as claimed.

Claims

1. A miniaturized flexible wearable antenna for improving the radiation characteristic of a high-order mode is characterized by comprising three layers of felt substrates and four layers of polyimide film circuits, wherein a metal structure is printed on the polyimide film and comprises four layers, and the four metal layers are a microstrip line layer, a gap coupling layer, a uniform super-surface layer and a non-uniform stacked patch layer from bottom to top in sequence;

the microstrip line layer is of a Y-shaped microstrip line structure and comprises a section of 50 omega microstrip transmission line with the length of Lf1 and two sections of microstrip arms with the length of Lf3, wherein the distance between the two sections of microstrip transmission line is Lf2;

the stacked patch layers are formed by placing patches with different sizes right above transverse gaps formed among units of the square metal layer, the patches are divided into two groups according to the sizes, wherein two rows of units in the middle are L2 multiplied by W2, the two units in the middle are in short circuit with the lower layer through two copper wires with the diameter of d, and the two rows at the edge are L3 multiplied by W3;

the antenna inhibits the distortion of a high-order radiation mode directional diagram of the super-surface antenna by loading the short-circuit columns on the middle two units.

2. The miniaturized flexible wearable antenna for improving the radiation characteristics of the high-order mode as claimed in claim 1, wherein the felt substrate has a dielectric constant of 1.26 and a loss tangent of 0.02, the polyimide film has a thickness of 0.07mm, the dielectric constant of 3.4 and the loss tangent of 0.008.

3. The miniaturized flexible wearable antenna for improving the radiation characteristic of the high-order mode as claimed in claim 1, wherein the three layers of the felt substrate have thicknesses of 1mm, 3mm and 1mm from bottom to top.

4. The miniaturized flexible wearable antenna for improving the radiation characteristic of the high-order mode as claimed in claim 1, wherein the specific parameters of the antenna are as follows: ws =50mm, w1=7mm, w2=7mm, w3=7mm, wf1=4.6mm, wf2=1.4mm, wss =1.5mm, l1=7mm, l2=6.8mm, l3=7.5mm, lf1=21mm, lf2=11.4mm, lf3=10.3mm, lss =17.5mm, d =1.2mm, dsp =1mm, g =1mm.