CN111079881B - Microstrip antenna, anti-metal electronic tag and manufacturing method thereof - Google Patents

Abstract

A microstrip antenna comprising: a radiation sheet; a ground plate parallel to the radiating fin; a shorting tab conductively connecting the radiating tab and the ground plate; and a feed tab between the radiating tab and the ground plate; the radiation sheet is provided with a slit so that the radiation sheet is generally formed into a U shape, and the U shape comprises two sub-sheets forming two arms of the U shape and a connecting part forming the bottom edge of the U shape; wherein, a feed source is arranged in the slit, one of the anode and the cathode of the feed source is electrically connected with the connecting part, and the other of the anode and the cathode of the feed source is electrically connected with the feed sheet through a feed line; wherein the bottom side of the feed tab is disposed proximate to the ground plane and spaced therefrom by an insulating film having a thickness substantially less than 1/4 wavelength corresponding to a resonant frequency of the microstrip antenna. The microstrip antenna of the invention is easy to realize mass production and maintain consistent performance, has good metal resistance, is easy to adjust, and can be adapted to different frequency band requirements of different countries and regions in a simple way.

Description

Microstrip antenna, anti-metal electronic tag and manufacturing method thereof

Technical Field

The invention relates to the technical field of wireless communication, in particular to a microstrip antenna, an electronic tag with an anti-metal function and a manufacturing method of the electronic tag.

Background

Nowadays, more and more commodities are incorporated into an internet of things system, and the use of electronic tags is more and more extensive. At present, the electronic tag with the lowest price is an Ultra High Frequency (UHF) electronic tag working at UHF (Ultra High Frequency), wherein the UHF RFID Frequency band suitable for europe is an ETSI Frequency band (865-868 MHz), the UHF RFID Frequency band suitable for the usa is an FCC Frequency band (902-928 MHz), and the main Frequency in china is 915MHz. Different from the first two generations of 125KHz and 13.56MHz magnetic induction coupling data transmission, the ultrahigh frequency RFID adopts a mode of directly transmitting electromagnetic waves similar to the active RFID, and the read-write distance of the ultrahigh frequency RFID is farthest in a passive tag. The data communication rate is also high, the maximum data communication rate can reach 640kbit/s, and hundreds of labels can be read at one time. In addition, the cost is lower, so the method becomes an application hotspot in the field of the Internet of things.

However, in the field of metal goods management, the performance of a common ultrahigh frequency electronic tag can be rapidly deteriorated. Because metal objects also reflect electromagnetic waves, they interfere with the normal reception and scattering of electromagnetic waves by the tag. After metal boundary conditions are increased, the indexes of the working frequency, the input impedance and the gain of the tag antenna also deviate from normal values seriously, so that the reading and writing distance is reduced, and even reading and writing cannot be carried out.

Although some electronic tags with anti-metal function are also introduced in the market, for example, chinese patent CN102955969A discloses an ultra-thin, flexible, anti-metal ultrahigh frequency electronic tag, CN203644063U discloses a flexible UHF-band RFID tag, CN203616775U discloses a novel ultra-thin flexible RFID anti-metal tag, CN106845604A discloses a flexible UHF RFID anti-metal tag, CN206209826U discloses an ultra-thin flexible anti-metal electronic tag, and CN106981722A discloses a flexible anti-metal RFID tag.

However, most of these products are printed circuit board structures and cannot be bent and attached to metal objects with spherical surfaces such as steel bottles, beer barrels and chemicals. A few products adopt a structure of ferrite wave-absorbing materials and a common antenna, and can be made to be very soft and thin as a non-metal-resistant label and have a metal-resistant function. But also has the problems of high cost, short read-write distance and the like, and can not meet the group read-group write requirement frequently required by UHF frequency. Therefore, it is a research interest in the art to design suitable antennas for RFID tags and, accordingly, to design electronic tags to overcome the above-mentioned technical problems.

US patent US8477079B2 discloses an antenna for use in an RFID tag, which is designed, as shown in fig. 1, with a resonant structure 650 comprising three conductive sheets arranged in parallel and spaced apart from each other, namely conductive sheets 610-1, 610-2 and a floating element 670, the conductive sheets 610-1, 610-2 being connected at their adjacent sides by an electrical connection 620, the floating element 670 being spaced apart from the conductive sheet 610-1 via a dielectric structure 610-1, and a load element 630 being connected between the conductive sheet 610-2 and the floating element 670 by two connection points 640-1 and 640-2. Wherein the conductive sheet 610-2 and the floating element 670 have a distance 660 therebetween, the distance 660 being no less than half the pitch of the conductive sheets 610-1, 610-2.

Although the antenna disclosed in the above-mentioned US patent US8477079B2 can be used in an RFID tag, its high sensitivity of performance (e.g., resonant frequency) to structural dimensions requires strict control of relevant parameters (e.g., distance 660, conductive sheet 610-1, 610-2 spacing, etc.) during its manufacture, thereby limiting its mass production and maintaining consistent performance, and requiring high production costs.

In addition, the antenna structure disclosed in the prior art needs to be customized complicatedly to adapt to the uhf electronic tag frequency bands in different countries and regions, such as the united states, europe, and china.

Therefore, there is a need in the field of RFID tags, in particular, for a suitable antenna structure which is easy to mass produce and maintains consistent performance, has good metal resistance, is easy to adjust, and can be adapted to different frequency band requirements in different countries and regions in a simple manner.

Disclosure of Invention

In view of the above problems in the prior art, the present invention provides a microstrip antenna and an electronic tag, which can solve the data read-write problem of the spherical surface metal goods electronic management in the prior art.

To achieve the above object, in one aspect, the present invention provides a microstrip antenna comprising: a radiation sheet; a ground plate parallel to the radiating patch; a shorting tab conductively connecting the radiating tab and the ground plate; and a feed tab positioned between the radiating tab and the ground plane; the radiation piece is provided with a slit so that the radiation piece is generally formed into a U shape, and the U shape comprises two sub-pieces forming two arms of the U shape and a connecting part forming the bottom edge of the U shape; a feed source is arranged in the slit, one of the positive pole and the negative pole of the feed source is electrically connected with the connecting part, and the other of the positive pole and the negative pole of the feed source is electrically connected with the feed sheet through a feed line; wherein the bottom side of the feed tab is disposed in close proximity to the ground plane and spaced apart from the ground plane by an insulating film having a thickness substantially less than 1/4 wavelength corresponding to a resonant frequency of the microstrip antenna.

In one embodiment of the present invention, the thickness of the insulating film is equal to or less than 0.2% of 1/4 wavelength, preferably equal to or less than 0.15% of 1/4 wavelength, and preferably equal to or less than 0.1% of 1/4 wavelength.

Preferably, the thickness of the insulating film is 0.1mm or less.

Optionally, the feed tab is located within a range of a projection of the periphery of the radiating tab in a direction perpendicular to the radiating tab.

In one embodiment of the present invention, the microstrip antenna further comprises an elastic medium disposed between the radiating patch and the ground plate, wherein the feeding patch is disposed below the medium.

Optionally, the radiating patch, shorting patch, and ground plane are disposed proximate to the dielectric, and the feed line is folded around or through the dielectric.

Preferably, the medium is silicone rubber.

Preferably, the radiation patch, the shorting patch, the ground plate, the feed source, the feed line, and the feed patch are coupled to one side of the insulating film.

Further preferably, the radiation patch, the shorting patch, the ground plate, the feed source, the feed line, and the feed patch form an inlay structure with the insulating film.

Preferably, the radiating patch, shorting patch and ground plane are integrally formed from a conductive material, and the feed line and feed patch are integrally formed from a conductive material.

Preferably, the two sub-radiator elements are arranged symmetrically with respect to a longitudinal central axis of the radiator element.

Optionally, the ground plate and/or the radiating patch is provided with one or more linear grooves near the shorting patch.

Preferably, the length of the linear groove is not more than 1/2 of the width of the radiation sheet, the distance between the linear groove and the short-circuit sheet is not more than 1/2 of the length of the radiation sheet, and the width of the linear groove is not more than 0.1mm.

Optionally, a protruding portion is disposed on the connecting portion, and one of the positive electrode and the negative electrode of the feed source is electrically connected to the protruding portion.

Preferably, the feed source is an RFID UHF label chip.

In another aspect of the present invention, there is provided an electronic tag including: a first generally U-shaped sheet of electrically conductive material, wherein a bottom edge of the U-shape has an elongated longitudinal length; a second generally T-shaped sheet of electrically conductive material, wherein a top edge of the T-shape has an elongated longitudinal length; and a feed source; wherein the first sheet, the second sheet and the feed are bonded to one side of the insulating film to form a strip assembly which is folded into a closed loop to form the microstrip antenna described above, wherein the radiating patch, the shorting patch and the ground plane are integrally formed from the first sheet, and the feed line and the feed patch are integrally formed from the second sheet.

Optionally, the electronic tag has a PC plastic housing or an ABS plastic housing.

A method of making an electronic label comprising the steps of: forming a first generally U-shaped sheet of electrically conductive material, wherein a bottom edge of the U-shape has an elongated longitudinal length; a second generally T-shaped sheet of electrically conductive material, wherein a top edge of the T-shape has an elongated longitudinal length; bonding the first sheet, the second sheet, and the feed to one side of the insulating film to form a tape assembly; the microstrip antenna described above is formed by folding the strip assembly into a closed loop, wherein the radiating patch, shorting patch and ground plane are integrally formed from a first sheet and the feed line and feed patch are integrally formed from a second sheet.

Preferably, the step of bonding the first sheet, the second sheet and the feed to one side of the insulating film to form the strip assembly comprises forming the radiating patch, the shorting patch, the ground plate, the feed line and the feed patch with the insulating film by etching to form an inlay structure.

Optionally, the method further comprises the steps of: one or more straight grooves are formed in the grounding plate and/or the radiating sheet at the position close to the short circuit sheet; the antenna is mounted into a PC plastic housing or an ABS plastic housing.

The microstrip antenna of the invention forms the separation of the radiation circuit and the feed circuit by the slit, the two sub-pieces of the radiation piece and the feed piece, so that the resonant frequency is easy to adjust, and the following design purposes are achieved:

1. separating the radiating circuit and the feeding circuit. The two sub-pieces of the radiation piece respectively form two radiation circuits, the feed piece forms a feed circuit, the feed piece is close to the grounding plate, and the smaller the distance between the feed piece and the grounding plate is, the better the coupling effect is. The structure can utilize the power of incident electromagnetic waves to the maximum efficiency, thereby reducing the size of the microstrip antenna and improving the reading distance of the label.

2. The radiating patch, the slit and the feed patch form a resonant frequency tuning scheme. The resonant frequency is adjusted by changing the length and the width of the radiation sheet and the slit, and the resonant frequency point is finely adjusted by adjusting the area of the feed sheet, so that the microstrip antenna can achieve the maximum power energy radiation at a specific frequency point. The invention provides a scheme which is easy to realize and adjust, so that the resonant frequency of the tag can be adapted to requirements of different market environments.

3. Aiming at different label packaging shells, the straight-line grooves are formed at different positions away from the radiating patch and/or the grounding plate of the microstrip antenna, so that the impedance introduced by different shell materials can be matched.

4. A method of manufacturing a microstrip antenna by wrapping a dielectric of a flexible material with a strip assembly formed of a ground plate, a radiation plate, a feed plate, an insulating film, and the like, which is easy to realize in industrial production, low in cost, and capable of maintaining a high degree of uniformity, and suitable for mass production. And, because the medium adopts flexible material, therefore the label can relatively easily carry out the adjustment of shape according to the application implementation scene.

5. The resonant frequency design formula of the microstrip antenna is as follows:

the invention comprehensively adjusts the inductance value L and the capacitance value C of the microstrip antenna by changing the size of the radiating sheet, the slotting position of the straight slot and the size of the feed sheet so as to adjust the designed resonant frequency of the antenna.

6. The design of the radiating patch, which includes two sub-patches, can produce a greater inductive reactance to match the impedance of the feed. The feeder line and the feed sheet form a J-shaped or L-shaped structure as a whole, coupling feed is realized, and the read-write capability when the metal goods are used is enhanced through the improvement of impedance and a feed mode.

In addition, in particular, compared with the chinese patent application CN102955969A, the present invention can be adapted to different label housings so as to be applied to various application scenarios with special requirements on strength, corrosivity, housing digital code printing, etc. Chinese patent application CN102955969A must be directly attached to a metal surface to obtain metal resistant properties, and cannot be packed and placed into a formed label housing.

Compared with the Chinese utility model patent CN203644063U, the invention adopts flexible silica gel as a medium layer, does not need adhesive, has good flexibility and is easy to install, and can be assembled in label shells with different shapes so as to adapt to different application scenes. The CN203644063U dielectric layer is made of acrylic, although the acrylic can be bent, the elasticity and the hardness of the acrylic are higher than those of flexible silica gel, and an acrylic adhesive is used for bonding, so that the processing technology is complex and the production cost is high.

Compared with the Chinese utility model CN203616775U, the invention has simple structure, only one layer of flexible printed circuit board is needed, and the design of the anti-metal high-performance label can be completed. CN203644063U needs 3-layer structure design, the ground plate of the metal conducting layer is separated from the antenna, the installation process is complex, and the requirement for the processing precision is high. The invention has simple installation process and easy realization of high consistency in production, thereby reducing the cost.

Compared with the Chinese patent application CN106845604A, the invention adopts flexible silica gel as a dielectric layer, achieves smaller label volume and larger signal reflection surface by folding the aluminum foil, and is easy to be installed in label shells with different shapes. CN106845604A uses foam sponge as the flexible medium, and the label volume is great, and the scene of using is limited. The invention has small volume and is easy to process to match with metal surfaces of different shapes, so the application scene is wider.

Compared with the Chinese utility model patent CN206209826U, the invention has simple structure, and can complete the design of the anti-metal high-performance label only by one layer of flexible printed circuit board. CN206209826U is laminated for 6 layers of structures, and processing technology is complicated, and uses PVC plastics as flexible dielectric layer, can influence the crookedness under the condition of increase thickness to make application scene limited. The invention has small volume and is easy to process to match with metal surfaces of different shapes, so the application scene is wider.

Compared with the Chinese patent application CN106981722A, the invention has simple structure and small design, uses silica gel as a flexible medium, is easy to process into various label shells and is easy to adapt to surfaces with various curvatures. CN106981722A is bigger in size, uses PVC and PET as flexible medium, and the crookedness is comparatively limited, is difficult to adapt to the label shell of different shapes. The invention has small volume and is easy to process to match with metal surfaces of different shapes, so the application scene is wider.

Compared with the US patent US8477079B2, the invention is easy to realize mass production and maintain consistent performance, reduces the production cost, has good metal resistance, is easy to adjust, and can be simply adapted to different frequency band requirements of different countries and regions to realize mass production and maintain consistent performance.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below, and it should be understood that the drawings in the following description are only schematic examples of some embodiments of the present invention, and do not limit the scope of the present invention. In the drawings:

FIG. 1 is a schematic diagram of a prior art antenna that may be used in an RFID tag;

fig. 2 is a schematic diagram of a longitudinal cross section of a structure of a microstrip antenna provided in a preferred embodiment of the present invention;

FIG. 3 is a perspective view of the microstrip antenna shown in FIG. 2;

fig. 4 is a perspective view of the microstrip antenna shown in fig. 3;

fig. 5 is a schematic view illustrating a connection relationship of a radiation patch, a feed line, a feed source, and a feed patch of the microstrip antenna shown in fig. 3;

fig. 6 is a schematic longitudinal cross-section of a structure of a microstrip antenna provided in a second preferred embodiment of the present invention;

fig. 7 is a perspective view of the microstrip antenna shown in fig. 6;

FIG. 8 is a schematic diagram showing the standing wave distribution of a dipole antenna with two arms of unequal length;

fig. 9 is a schematic view of the standing wave distribution of the new antenna obtained by translating and folding the two arms of the dipole antenna shown in fig. 8;

FIG. 10 is a schematic view of the current distribution of the microstrip antenna provided in the second preferred embodiment of the present invention with the antenna shown in FIG. 9 fully folded and flattened;

fig. 11 is a diagram showing a simulation result of vector current distribution on a radiating patch of a microstrip antenna according to a second preferred embodiment of the present invention;

fig. 12 is a graph of a simulation result of the distribution of the vector current on the ground plane of the microstrip antenna depicted in fig. 11;

fig. 13 is a graph of a simulation result of the distribution of the vector current on the ground plane after the feed tab of the microstrip antenna depicted in fig. 11 is configured to be directly coupled;

FIG. 14 shows a schematic view of an electronic tag provided in an embodiment of the present invention mounted on a cylinder;

fig. 15 shows the widths of the feed patch and the slot of the microstrip antenna in the electronic tag shown in fig. 14.

Fig. 16 is a schematic diagram of S11 parameters of the electronic tag shown in fig. 14 simulated in a metal environment with a spherical metal surface.

Fig. 17 is a simulation result of radiation leakage of the microstrip antenna in the electronic tag shown in fig. 14.

Fig. 18 depicts the radiation direction of the microstrip antenna shown in fig. 17.

Fig. 19 is a schematic view showing a connection relationship of the first sheet/second sheet and the feed for producing the electronic tag of the present invention according to one embodiment of the present invention.

Fig. 20 is a perspective view showing an intermediate step of folding a strip assembly around a medium to form a microstrip antenna of the present invention, according to the present invention.

Fig. 21 shows a top view of a microstrip antenna formed by folding.

Detailed Description

To further illustrate the technical means and effects of the present invention adopted to achieve the predetermined objects, the following detailed description will be given to specific embodiments, structures, features and effects of the microstrip antenna, the electronic tag and the method for manufacturing the electronic tag according to the present invention with reference to the accompanying drawings and preferred embodiments.

As shown in fig. 2 to 5, in the first preferred embodiment of the present invention, the microstrip antenna of the present invention comprises aground plane 20, a radiation patch including a sub-patch 211 and a sub-patch 212, a dielectric 26, afeed 22, afeed line 23, a short-circuit patch 27, afeed patch 24, and an insulating film. The medium 26 is of generally flat rectangular parallelepiped configuration and is formed of an elastomeric material, such as silicone rubber, in this embodiment. In the XYZ coordinate system shown in FIG. 3, the length or longitudinal direction of the medium 26 is along the X-axis direction, the width or transverse direction is along the Y-axis direction, and the thickness or up-down direction is along the Z-axis direction. And the length, width and/or thickness of other structures for microstrip antennas are described in this specification in a similar manner by the coordinate system, if not explicitly stated.

A radiation patch on the upper surface of the dielectric 26, aground plate 20 on the lower surface of the dielectric 26, and a shortingpatch 27 on one side surface of the dielectric 28, the shortingpatch 27 connecting the radiation patch and theground plate 20 together; the radiation sheet further comprises a connecting portion connected to the first ends of the twosub-sheets 211, 222, and the twosub-sheets 211, 222 are identical in shape, arranged side by side and spaced apart from each other by the slit. The slits extend longitudinally (i.e., in the lengthwise direction of the medium 20, in the X-axis direction shown in the figure) from the connection portion of the radiation piece up to the side of the radiation piece opposite the connection portion.

Thefeed 22 is disposed in a slot at the upper surface of the medium 26, near the connection to the radiating patch. Which is a dedicated chip, such as an RFID UHF tag chip, the positive electrode of which is electrically connected to the connection portion of the radiation patch, and the negative electrode of which is electrically connected to thefeed patch 24 via thefeed line 23. It is understood that the connections of the positive and negative electrodes may be interchanged without departing from the scope of the invention.

In this embodiment, thefeed line 23 extends from thefeed 22, between the twosub-patches 211, 222, at the upper surface of the dielectric 20, and extends beyond the slot to one side surface of the dielectric 26, and then bends downward, extending at that side surface to the lower surface of the dielectric 20, where the end of thefeed line 23 is connected to thefeed patch 24 disposed between the lower surface of the dielectric 26 and theground plate 20; thefeed tab 24 is substantially parallel to theground plate 20 and is attached to and electrically insulated from theground plate 20 by an insulating film covering its surface. In the present embodiment, the radiation patch, thefeed line 23, thefeed patch 24, theground plate 20, and the shortingpatch 27 are all formed of a metal thin film (e.g., aluminum foil).

In addition, two in-line slots 25 may be formed in the radiating patch near the shortingpatch 27, for example, within a distance from the shortingpatch 27 less than half the length of the radiating patch, for altering the phase of the antenna surface current to achieve matching with thefeed 22. They are in-line slots that extend from one side edge of the radiation patch to the middle of the radiation patch, generally in the width direction of the media 26 (i.e., the Y-axis direction). Preferably, the slot width (its span in the X-axis) of the in-line slot 25 is not more than 1mm, and its length (its extension in the Y-axis) is not more than half of the width of the radiation patch (i.e., the extension of the connection in the Y-axis) and does not penetrate the slot between the twosub-patches 211, 212.

As a non-limiting example, in the present embodiment, the shortingtab 27, the connection portion of the radiating tab, and theground plate 20 have the same width, preferably the width is not greater than 30mm, that is, the width of the microstrip antenna formed last is not greater than 30mm. It will be appreciated that the shortingtab 27, the connection portion of the radiating tab, and theground plate 20 may also have different widths. In addition, in one embodiment, the thickness of the dielectric film is not greater than 0.1mm, and the sum of the thicknesses of the radiating patch, the dielectric 26, thefeed patch 24, the dielectric film, and theground plane 20 is not greater than 3.5mm, i.e., the thickness of the resulting microstrip antenna is not greater than 3.5mm. Further, it is preferable that the maximum length of theground plate 20 is not more than 57mm. Preferably, the width offeed tab 24 is greater than the width of the slot, e.g., 0.5-2.5mm greater than the slot width. Preferably, the radiating patch, thefeed line 23, thefeed tab 24, the shortingtab 27, and theground plane 20 are all structures that are symmetrical about an axis passing through the slot.

Preferably, the radiation patch, thefeed line 23, thefeed tab 24, the shortingtab 27, the in-line slot 25 and theground plane 20 in this embodiment may be integrally formed by using an aluminum foil material. More preferably, the microstrip antenna of the present embodiment may be formed by integrally and simultaneously forming the radiation patch, thefeed line 23, thefeed patch 24, the short-circuit patch 27, the insulating film, and theground plane 20 using an inlay (inlay) material, which is, for example, a double-layered composite film of aluminum foil and an insulating film, or a double-layered composite film of a film of other conductive material and an insulating film, applying an etching process, and then by appropriately wrapping the formed film over the dielectric 26.

For example, referring to fig. 19 to 21, the microstrip antenna of the present invention may be fabricated by the following steps: afirst sheet 281 of electrically conductive material, generally U-shaped with the bottom of the U having an elongated longitudinal length; a second generally T-shapedsheet 282 of electrically conductive material, wherein the top edge of the T has an elongated longitudinal length; bonding thefirst sheet 281, thesecond sheet 282 and thefeed 22 to one side of the insulating film 29 to form atape assembly 32; the microstrip antenna of the present invention is formed by folding thestrip assembly 32 into a closed loop shape, in which the radiating patch including the sub-patches 211, 212, the shortingpatch 27, and theground plane 10 are integrally formed from thefirst sheet 281, and thefeed line 23 and thefeed patch 24 are integrally formed from thesecond sheet 282. Alternatively,strip assembly 32 may be folded aroundmedium 26 to form the microstrip antenna of the present invention in a simple manner. It should be understood that, herein, the "first sheet" and the "second sheet" may be separate sheet materials, or may be a conductive material layer etched to be formed in an inlay (inlay), or a conductive material plating layer formed by plating or the like, or a conductive material layer printed on an insulating film. Preferably, the radiation patch, the shorting patch, the ground plate, the feed, the feeder, and the feed patch form an inlay structure with the insulating film.

When the radiation patch, thefeed line 23, thefeed patch 24, the shortingpatch 27, the in-line slot 25, and theground plane 20 are formed through the above steps, these structures may be designed according to actual needs (e.g., according to a desired resonant frequency), especially where the size parameters of thefeed patch 24 and the in-line slot 25. In addition, the dimensional parameters of the medium 26, especially the thickness thereof, can be designed according to actual needs (for example, according to a desired resonant frequency), so as to realize the production of a microstrip antenna meeting the requirements.

It should be noted that, since thefeed patch 24, the insulating film and theground plate 20 are formed of thin films and have thicknesses that are very small and are negligible with respect to the dimensional parameters of the microstrip antenna (e.g., the thickness of the dielectric 26), for the sake of simplicity and clarity, although the microstrip antenna in the present embodiment is drawn in the form of fig. 2 in a cross section perpendicular to the Y-axis direction, it will be understood by those skilled in the art that the distance between thefeed patch 24 and the ground plate 20 (i.e., the thickness of the insulating film) is much smaller than 1/4 wavelength corresponding to the resonance frequency of the microstrip antenna. In one embodiment, the thickness of the insulating film is 0.2% or less of 1/4 wavelength. In a preferred embodiment, the thickness of the insulating film is 0.15% or less of 1/4 wavelength. In a further preferred embodiment, the thickness of the insulating film is equal to or less than 0.1% of 1/4 wavelength. Alternatively, the thickness of the insulating film is 0.1mm or less.

It will be understood by those skilled in the art that the 1/4 wavelength corresponding to the resonant frequency of the microstrip antenna depends on the resonant frequency of the microstrip antenna. By way of non-limiting example, the numerical value of 1/4 wavelength is shown in the following table:

it is to be understood that the invention is not limited to the specific wavelength values listed herein. One skilled in the art, after reading this disclosure, will be able to apply the principles of the present invention to other resonant frequencies specified in other countries and/or regions.

Fig. 6 and 7 show the structure of the microstrip antenna of the present invention in a second preferred embodiment of the present invention. Unlike the previous embodiment, in this embodiment, thefeed line 23 in the microstrip antenna extends from thefeed 22 along the length of the medium 26, not beyond the slot, but bends and extends downward near one side surface of the medium 26 until near the lower surface of the medium 20, where the end of thefeed line 23 is connected to thefeed tab 24 provided in the medium 26 and adjacent to the lower surface thereof. In the present embodiment, it is not necessary to use an insulating film to ensure electrical insulation between thefeed tab 24 and theground plate 20. The distance between thefeed tab 24 and theground plane 20 is the same as in the previous embodiment, which corresponds to the thickness of the dielectric film, e.g. the layer of dielectric film in the inlay material, i.e. not more than 1mm.

In addition, two in-line grooves 25 in the present embodiment are formed on theground plate 20. Similarly to the previous embodiment, the two in-line slots 25 have a slot width of not more than 1mm, a length of not more than half the width of theground plate 20, and a distance from the shortingtab 27 of not more than 1/2 of the length of the radiating tab.

It should be noted that the microstrip antenna in this embodiment may also be designed to take the form of the straight-line slot 25 as shown in the previous embodiment, i.e., the straight-line slot 25 is formed on the radiating patch. The former embodiment may also be designed to take the form of the in-line slot 25 as shown in the present embodiment, i.e., the in-line slot 25 is formed on theground plate 20. It will be appreciated by those skilled in the art, upon reading the present disclosure, that the in-line slot may take a different form than that specifically shown in the embodiments to fine-tune the resonant frequency of the microstrip antenna.

The characteristics of the microstrip antenna shown in the second embodiment will be described by means of theory, simulation, and the like, taking the microstrip antenna as an example.

In order to facilitate the analysis by using a transmission line and a standing wave theory, the microstrip antenna is considered as a product after a dipole antenna with two unequal arm lengths is folded: one arm is about 1/2 wavelength long and the other arm is about 1/4 wavelength long. Under the excitation of the left positive and right negative differential ports, the currents on both arms conform to the standing wave distribution, as shown in fig. 8, the left side presents a current sinusoidal distribution, and the right side presents a current sinusoidal distribution- (shown by the dotted line in fig. 8). The left 1/2 wavelength arm is shifted to the right by 1/4 wavelength relative to the feed source, and the middle point of the arm is connected with the anode port. While allowing the right 1/4 wavelength arm end to fold into a "J" configuration. The folded arms still conform to this standing wave distribution as shown in fig. 9. And then turning the left half part of the 1/2 wavelength arm around the feed source by about 270 degrees in a counterclockwise manner to obtain a side view structure shown in figure 10, namely the side view structure is equivalent to the microstrip antenna designed in the scheme, and the flow direction and amplitude distribution of the surface current of the microstrip antenna are estimated to be still basically consistent with the structure, namely the current is weaker when the microstrip antenna is closer to the open end, and the current is stronger when the microstrip antenna is closer to the short-circuit piece 27. The structure in fig. 10 was simulated (using HFSS simulation software from ANSYS corporation), and the vector current distribution on the radiation plate was as shown in fig. 11, and the vector current distribution on theground plate 20 was as shown in fig. 12. And the feedingsheet 24 is set to be directly coupled and then simulation is performed, it can be seen that the vector current distribution on theground plate 20 is as shown in fig. 13. Comparing the simulation structures of the two designs, the direct-coupledground plate 20 at the right end thereof generates a stronger star-shaped current distribution, and the direction of the current generated by the coupled feed is substantially the same as that of the direct-coupled ground plate, which indicates that the coupling in the embodiment can achieve the effect similar to that of the direct-coupled ground plate. Different from the common L-shaped probe coupling applied to the microstrip antenna, the capacitive reactance is generated between the two horizontal coupling units in the L-shaped probe coupling, and in the design, because the amplitude difference of the currents at the open circuit end of thefeed sheet 24 and theground plate 20 is not large, the sine distribution phases of the currents are relatively close regardless of the flow direction, the L-shaped probe coupling is beneficial to generating larger inductive reactance, and can be better matched with the impedance of a feed chip. In addition, in the simulation debugging, it is found that the closer the distance between thefeed tab 24 and theground plate 20 is, the better the coupling effect is, and the closer the total gain is to the total gain of the direct coupling.

Since the microstrip antennas in the two embodiments have similar electrical structures, the analysis and simulation results described above are also applicable to the microstrip antenna in the first embodiment.

In the following, an electronic tag with a metal-resistant function, in particular a flexible electronic tag, is implemented by a microstrip antenna in a second embodiment.

In the present embodiment, the housing used is PC plastic, and the microstrip antenna of the structure shown in fig. 7 is placed therein to form theelectronic tag 31 shown in fig. 14. Specifically, after the shapedelectronic tag 31 is attached to the soft filler, it is bent and inserted into the hard shell of the PC plastic, and a complete anti-metal tag is assembled. In this embodiment, the electronic tag finally provided with the outer shell has an arc length of 65mm, a width of 35-40mm, and a thickness of 6mm.

Wherein, the silicon rubber is selected as the material of the medium 26, the dielectric constant of the silicon rubber is 3.2, and the tangent loss is between 0.002 and 0.003. Due to the selection of flexible materials such as silicone rubber to form the dielectric 26 of the microstrip antenna of the present invention, the resultingelectronic tag 31 can be attached to a metal object having a spherical surface shape, such as thesteel cylinder 30 shown in fig. 14.

In this embodiment, the specific structural parameters of the microstrip antenna are selected as follows: the twosub-patches 211, 212 and the radiating patch have a length of 47-53mm, theground plane 20 has a length of 52-57mm, the slot has a width L1 (see fig. 15) of 5mm, and thefeed patch 24 has a width L2 that is 2.5-2.5mm greater than L1. Further, for a resonance frequency of 915MHz, the structural parameters of the microstrip antenna in this embodiment are further defined as: the feed piece is 12 by 8.4mm, the radiation piece is 10.4 by 51.2mm, and the length of thestraight groove 25 is 10.2mm.

Note that, since the case of PC plastic is used in this embodiment, the microstrip antenna having the structure shown in fig. 7 is selected. If other materials are used, such as an ABS material, the position of theslot 25 in the microstrip antenna shown in fig. 7 can be adjusted, for example, by opening one or bothslots 25 to the radiating patch, as shown in fig. 3.

In addition, thefeed 22 on the microstrip antenna used is selected to be an RFID UHF tag chip, such as the chip Monza 4. Generally, the RFID UHF tag chip has two sets of differential ports, and one of the two sets is used here. For a general dual-port antenna, if one end of the dual-port antenna is connected to the radiating patch, the corresponding opposite-polarity end is connected to theground plate 20, and it is not necessary to distinguish the specific positive and negative polarities.

In order to predict the metal resistance of theelectronic tag 31 of the present invention, theelectronic tag 31 was simulated in a metal environment. Specifically, using HFSS (simulation software HFSS from ANSYS corporation), a 120 × 90mm metal plate was added below theelectronic tag 31 to simulate the outer shell of thesteel cylinder 30, and finally, the radiation gain and the S11 parameter were simulated as shown in fig. 13. As can be seen from the results shown in the figure, the electronic tag of the present embodiment has excellent metal resistance.

Fig. 15 is a simulation result of the radiation performance of the microstrip antenna of theelectronic tag 31 in the present embodiment, which uses simulation software HFSS of ANSYS corporation, and it is clear from the figure that sufficiently strong electromagnetic leakage occurs at thefeed tab 24.

Fig. 16 schematically shows the radiation direction of the microstrip antenna shown in fig. 15. It should be noted that, for clearly illustrating the radiation direction, the distance between the feeding tab and the ground plate is illustrated as being larger and not drawn to actual scale, but those skilled in the art can understand from the above description that the distance between the feeding tab and the ground plate is very small, which is equivalent to the thickness of the insulating film in the inlay material.

The excellent metal resistance and radiation resistance of the electronic tag of the invention can also be derived from the following analysis: the internal impedance of an RFID UHF label chip, such as a chip Monza 4, is 11-145j ohms, and the absolute value of the internal impedance part is large and can be regarded as a capacitor. According to the requirement of impedance matching, the impedance of the tag antenna must be designed to be 11+145j ohm, and a large inductance is needed. As described in the foregoing analysis of the performance of the microstrip antenna of the present invention, thefeed line 23 and thefeed tab 24 in the microstrip antenna of the present invention form a "J" shaped structure, which causes the current passing through thefeed line 23 to flow to the feed tab 2 and to theground plate 20 in a radiation leakage manner, so that thefeed tab 24 and the shortingtab 27 become a two-wire transmission line, thereby changing the impedance of the microstrip antenna. This is a transformer effect that changes part of the capacitive reactance into inductive reactance, thereby forming the whole microstrip antenna resonance.

When the electronic tag of the present invention is in operation, the feeding plate is used as the end of the conductor, which is located at the open end of the current path, and is adjacent to the ground plate, and the distance between the feeding plate and the ground plate is much less than 1/4 wavelength (see the previous description about fig. 8-10), so that a strong fringe magnetic field is generated between the feeding plate and the ground plate, and the radiation mechanism of the fringe magnetic field is actually high-frequency electromagnetic leakage. When the whole microstrip antenna works in a resonance state, surface current passes through the microstrip antenna, radiation is obviously enhanced, and radiation efficiency is greatly improved; and the higher the resonant frequency, the stronger the radiation leakage and the higher the radiation efficiency.

Therefore, the matching with the feed source can be achieved by changing the current phase on the surface of the antenna in the modes of finely adjusting the length of the antenna and the position of the feed source (chip), adjusting the length and the width of a slit between two sub-pieces, increasing a transverse straight-line groove and the like. Wherein, the longer the feeder line, the more obvious the change, and the length is less than 1/2 wavelength. In addition, if the spacing between the radiating patch and the ground plane of the microstrip antenna and the height of the dielectric 26 are increased, the microstrip antenna gain is also increased.

In addition, the material of the housing also affects the radiation characteristics and impedance matching of the microstrip antenna, so that the impedance matching debugging of the electronic tag of the present invention must be performed synchronously in combination with the housing.

In practical use, after theelectronic tag 31 of the present invention is adhered to the corresponding position of thesteel cylinder 30, the test is performed by using a handset with the transmitting power of 26-30dBm, the farthest read-write distance of the front surface can reach about 6m, and if a fixed reader-writer is used, the read-write distance is farther. To increase the difficulty of reading and writing, 16 cylinders were packed into a 4 x 4 packing cell. Meanwhile, a gate with the width of 8m and the height of 5m is built, 4 flat antennas are arranged on the top beam of the gate, two antennas are arranged on the stand columns on the two sides respectively, and the radiation directions of all the antennas face the inner side of the gate. A total of 8 antennas are connected with an impinj 420 reader-writer, and work in turn at the maximum output power of 30 dbm. And a 4-4 packing grid is selected, eachsteel bottle 30 is provided with a label, the labels are allowed to face randomly but must be arranged at the bottle neck, and the packing grid is carried through a gate by a common tent truck. The 5 passes were repeated and 100% of all tags were read each time. The performance of the label meets the common group reading and writing requirements of thesteel cylinder 30 circulation link, and a new solution is provided for the Internet of things management of metal objects with spherical surface shapes such as thesteel cylinder 30.

Although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (22)

1. A microstrip antenna, comprising:

a radiation sheet;

a ground plate parallel to the radiating patch;

a shorting tab conductively connecting the radiating tab and the ground plate; and

a feed tab positioned between the radiating tab and the ground plate;

the radiation piece is provided with a slit so that the radiation piece is generally formed into a U shape, and the U shape comprises two sub pieces forming two arms of the U shape and a connecting part forming the bottom edge of the U shape;

a feed source is arranged in the slit, one of the positive pole and the negative pole of the feed source is electrically connected with the connecting part, and the other of the positive pole and the negative pole of the feed source is electrically connected with the feed sheet through a feed line;

wherein the bottom side of the feed tab is disposed proximate to the ground plane and spaced apart from the ground plane by an insulating film having a thickness less than 1/4 wavelength corresponding to a resonant frequency of the microstrip antenna.

2. The antenna according to claim 1, wherein the thickness of the insulating film is 0.2% or less of 1/4 wavelength.

3. The antenna according to claim 1, wherein the thickness of the insulating film is 0.15% or less of 1/4 wavelength.

4. The antenna according to claim 1, wherein the thickness of the insulating film is 0.1% or less of 1/4 wavelength.

5. The antenna according to claim 1, wherein a thickness of the insulating film is 0.1mm or less.

6. The antenna of claim 1, wherein the feed tab is located within a range of a projection of the periphery of the radiating tab in a direction perpendicular to the radiating tab.

7. The antenna of claim 1, further comprising a resilient dielectric disposed between the radiating patch and the ground plane, wherein the feed patch is disposed below the dielectric.

8. The antenna of claim 7, wherein the radiating patch, shorting patch, ground plane are disposed proximate to the dielectric, and wherein the feed line is folded around or through the dielectric.

9. The antenna of claim 7, wherein the dielectric is silicone rubber.

10. The antenna of claim 1, wherein the radiating patch, shorting patch, ground plane, feed line, and feed patch are bonded to one side of the insulating film.

11. The antenna of claim 10, wherein the radiating patch, shorting patch, ground plane, feed line, and feed patch form an inlay structure with the insulative film.

12. The antenna of claim 1, wherein the radiating patch, shorting patch, and ground plane are integrally formed from a conductive material, and wherein the feed line and feed patch are integrally formed from a conductive material.

13. The antenna of claim 1, wherein the two sub-patches are symmetrically arranged with respect to a longitudinal central axis of the radiating patch.

14. The antenna of claim 1, wherein the ground plane and/or the radiating patch is formed with one or more in-line slots adjacent to the shorting patch.

15. The antenna of claim 14, wherein the length of the linear slot is no more than 1/2 of the width of the radiating patch, the distance from the linear slot to the shorting patch is no more than 1/2 of the length of the radiating patch, and the width of the linear slot is no more than 0.1mm.

16. The antenna of claim 1, wherein the connection portion is provided with a protrusion, and one of the positive electrode and the negative electrode of the feed source is electrically connected to the protrusion.

17. The antenna of claim 1, wherein the feed is an RFID UHF tag chip.

18. An electronic tag, comprising:

a first generally U-shaped sheet of electrically conductive material, wherein a bottom edge of the U-shape has an elongated longitudinal length;

a second generally T-shaped sheet of electrically conductive material, wherein a top edge of the T-shape has an elongated longitudinal length; and

a feed source;

wherein a first sheet, a second sheet and a feed are bonded to one side of an insulating film to form a strip assembly which is folded into a closed loop to form a microstrip antenna according to any one of claims 1 to 17, wherein the radiating patch, shorting patch and ground plane are integrally formed from the first sheet and the feed and feed patches are integrally formed from the second sheet.

19. The electronic tag according to claim 18, characterized in that the electronic tag has a PC plastic housing or an ABS plastic housing.

20. A method of making an electronic tag, comprising the steps of:

forming a first generally U-shaped sheet of electrically conductive material, wherein a bottom edge of the U-shape has an elongated longitudinal length;

a second generally T-shaped sheet of electrically conductive material, wherein a top edge of the T-shape has an elongated longitudinal length;

bonding the first sheet, the second sheet, and the feed to one side of the insulating film to form a tape assembly;

folding the strip assembly into a closed loop to form a microstrip antenna according to any of claims 1 to 17, wherein the radiating patch, shorting patch and ground plane are integrally formed from a first sheet and the feed and feed patches are integrally formed from a second sheet.

21. The method of claim 20, wherein the step of bonding the first sheet, the second sheet, and the feed to one side of the insulating film to form the strip assembly comprises forming the radiating patch, the shorting patch, the ground plate, the feed line, and the feed patch with the insulating film by etching to form an inlay structure.

22. The method of claim 20, further comprising the steps of:

one or more straight grooves are formed in the grounding plate and/or the radiation sheet at the position close to the short-circuit sheet;

the antenna is mounted into a PC plastic housing or an ABS plastic housing.

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