CN104241824B - A kind of universal combined reader antenna - Google Patents

Abstract

The invention discloses a combined general-purpose reader antenna, which includes a circularly polarized antenna and a linearly polarized antenna. The circularly polarized antenna provides a four-feed structure introduced by an annular microstrip feeder line. A thicker air dielectric layer is used between the main radiation patch and the first main radiation patch and the first parasitic patch, and the linearly polarized antenna is built into the square slot of the first parasitic patch in the middle of the circularly polarized antenna , the first parasitic patch and the ring-shaped conductor strip of the circularly polarized antenna act as the reflector of the linearly polarized antenna, making full use of the space and reducing the overall volume of the antenna.

Description

A Combined Universal Reader Antenna

technical field

The invention relates to the field of radio frequency identification, in particular to a combined universal reader antenna.

Background technique

With the development of society, radio frequency identification (RFID) technology is playing an increasingly important role in people's lives. Radio frequency identification technology can identify any object with an electronic tag through the medium of electromagnetic waves. The design of the reader antenna plays an important role in the continuing development of this technology. In view of the advantages of long recognition distance, fast reading and writing speed and high transmission rate, UHF band RFID systems are widely used in real life, such as animal identification, supply chain management, and electronic payment. However, RFID licensed UHF bands are different in different countries or regions, for example, 840.5-844.5MHz and 920.5-924MHz in China, 866-869MHz in Europe, 920-926MHz in Australia, 902-928MHz in North America, and 952MHz in Japan -955MHz. Therefore, if the RFID system can cover the entire UHF frequency band of 840-955MHz, then the installation and adjustment of the system can be effectively simplified, the construction cost can be reduced, and global use can be achieved.

Since readers covering the general UHF RFID application frequency band and the microwave frequency band 2.45/5.8GHz may be required at the same time in the same scenario, dual-frequency or multi-frequency readers have practical significance and can be further simplified. system, reducing construction costs.

An RFID system generally consists of two parts: a reader and a tag, and the tag usually carries a linearly polarized antenna. Considering the uncertainty of tag orientation, circularly polarized antennas are widely used in RFID readers in order to avoid severe polarization mismatch between the reader and the tag and improve the reliability of information transmission. In some scenarios where the placement of tags is relatively certain, RFID readers with linearly polarized antennas also have corresponding application prospects.

Contents of the invention

In order to overcome the shortcomings and deficiencies of the prior art, the present invention provides a combined universal reader antenna.

The present invention is a combination antenna organically combined with a circularly polarized antenna and a linearly polarized antenna, wherein the circularly polarized antenna is a general-purpose ultra-high frequency with high gain, excellent impedance matching and axial ratio performance, and can cover the 840MHz-960MHz frequency band Circularly polarized reader antenna, linearly polarized antenna is a linearly polarized reader antenna covering the 2.45GHz microwave frequency band.

The present invention adopts following technical scheme:

A combined universal reader antenna, including a circularly polarized antenna and a linearly polarized antenna;

The circularly polarized antenna adopts a stacked structure, including a first parasitic patch, a first main radiation patch, a first feed network, and a first floor from top to bottom, and the first feed network includes a ring microstrip Conductive wire and four metal probes, the four metal probes are placed on the annular microstrip conductive line evenly at intervals of 1/4λ ₀ along the current direction of the annular microstrip conductive line, wherein λ ₀ is determined by the central frequency of 900MHz Corresponding to the wavelength of free space, the first main radiation patch and the first parasitic patch are connected through four metal probes, and a square groove is opened at the center of the first parasitic patch and the first main radiation patch, It also includes a ring-shaped conductor strip structure, and the ring-shaped conductor strip structure is sleeved on the edge of the first parasitic patch;

The linearly polarized antenna is installed above the square slot of the first parasitic patch, adopts a stacked structure, and includes a second parasitic patch, a second main radiation patch, and a second feed network in sequence from top to bottom, and the first parasitic patch The two main radiating patches and the second parasitic patch are both square structures, the second main radiating patch is composed of two U-shaped microstrip lines with unequal arms symmetrical to the center, and the second feeding network is composed of equal arm The U-shaped microstrip line conduction line is coupled to the second floor with a gap in the middle, and the upper, left, and right corners of the second floor are cut with rectangular cutouts of the same size.

The upper left corner and the lower right corner of the second parasitic patch are respectively cut with an isosceles right triangle, and the waist length of the isosceles right triangle is 0.049λ ₁ , where λ ₁ corresponds to the center frequency of the microwave frequency band 2.45GHz The wavelength of free space.

The second main radiation patch is composed of two centrally symmetrical U-shaped microstrip lines with unequal arms. Both sides of the bottom end of the U-shaped microstrip lines with unequal arms are provided with isosceles right-angled triangle cut corners, etc. The waist length of the waist right triangle is half of the width of the U-shaped microstrip line with unequal arms. The overall length of the two centrally symmetrical U-shaped microstrip lines with unequal arms is 0.552λ ₁ , and the width is about 0.083λ ₁ , where λ ₁ is the wavelength of free space corresponding to the central frequency of microwave frequency band 2.45GHz.

The arm length of the equal-arm U-shaped microstrip line is 0.155λ ₁ , the bottom width is 0.06λ ₁ , the arm width is 0.016λ ₁ , and the second floor is 0.22λ ₁ and 0.189λ ₁ in length and width respectively. Rectangular, and the center line of the second floor has a gap with a length of 0.22λ ₁ and a width of 0.024λ ₁ , which divides the floor into two parts. The rectangular cutout of the second floor is 0.045λ ₁ in length and 0.02, where λ ₁ is the wavelength of free space corresponding to the center frequency of microwave frequency band 2.45GHz.

Both the first main radiation patch and the first parasitic patch are bronze coin structures with an outer circle and an inner square. arc-shaped notches, the radiation angles of the two arc-shaped notches are both 20 degrees, and are symmetrical about the diagonal, the radius of the first main radiation patch is 0.27λ ₀ , and the radius of the first parasitic patch is 0.23λ ₀ , which means that the height of the ring-shaped conductor strip structure is 0.012λ ₀ , where λ ₀ is the wavelength of free space corresponding to the center frequency of 900MHz in the ultra-frequency band.

Both the first main radiation patch and the central part of the first parasitic patch have a square groove, the side length of the square groove of the first main radiation patch is 0.09λ ₀ , and the side length of the square groove of the first parasitic patch is 0.072λ ₀ , the length of the arc-shaped notch is 0.031λ ₀ , where λ ₀ is the wavelength of free space corresponding to the central frequency of 900 MHz in the UHF band.

The linearly polarized antenna is on the same level as the upper edge of the ring-shaped conductor strip structure, and the distance between the second main radiation patch and the square groove of the first parasitic patch is 4 mm.

The upper and lower edges of the initial segment of the annular microstrip conduction line have a rectangular notch, the rectangular notch on the edge of the beginning end of the annular microstrip conduction line has a length of 0.045λ ₀ and a width of 0.006λ ₀ , where λ ₀ is the free zone corresponding to the center frequency of 900MHz. the wavelength of space.

Beneficial effects of the present invention:

(1) The circularly polarized antenna can be realized by exciting two equal-amplitude degenerate modes that are orthogonal in space and have a phase difference of 90°. The feeding network of the circularly polarized antenna of the present invention is composed of a ring-shaped microstrip conductive line and four metal probes, and the positions of the four probes are orthogonal in space, which can excite and separate mutually orthogonal degenerate mode, forming a 90° phase difference, thus meeting the two conditions for generating circularly polarized waves.

(2) The circularly polarized antenna adopts a four-feed structure guided by a ring-shaped microstrip conductive line, which has the characteristics of structural symmetry, can achieve wider frequency band coverage, and form a symmetrical hemispherical radiation pattern.

(3) A thicker air dielectric layer is used between the main radiation patch and the parasitic patch of the circularly polarized antenna, which can effectively improve the bandwidth and gain.

(4) Both the circularly polarized main radiation patch and the parasitic patch adopt an ancient copper coin-shaped structure with an outer circle and an inner square. The notches in the center of the main radiation patch and the parasitic patch can be used to install other electronic devices, such as placing A small antenna in a higher frequency band, so as to realize a dual-band or multi-band combined antenna.

(5) The ring-shaped conductor strip inlaid on the edge of the parasitic patch of the circularly polarized antenna forms a circular current, which is equivalent to a magnetic dipole, which can effectively improve the impedance matching and improve the 3-dB axial ratio performance.

(6) The linearly polarized antenna is built into the notch in the center of the circularly polarized antenna. The parasitic patch and ring-shaped conductor strip structure of antenna 1 are used as the reflector of the linearly polarized antenna. The combined structure of the two antennas can effectively improve space utilization rate, and the antenna 2 in the microwave frequency band also has excellent impedance matching and high gain.

(7) There is a high degree of isolation between the circularly polarized antenna and the linearly polarized antenna.

Description of drawings

Fig. 1 (a)～Fig. 1 (b) is the structure top view and side view structural schematic diagram of a kind of combined universal reader antenna of the present invention;

Fig. 2 is a schematic structural diagram of the linearly polarized antenna in Fig. 1;

Fig. 3(a) is a schematic structural diagram of the second parasitic patch in Fig. 2, and Fig. 3(b) is a schematic structural diagram of the second main radiation patch in Fig. 2;

Fig. 4(a) is a simulation diagram of reflection coefficient of a combined reader antenna, Fig. 4(b) is a simulation diagram of axial ratio of a combined reader antenna, and Fig. 4(c) is a simulation diagram of gain of the present invention.

detailed description

The present invention will be described in further detail below in conjunction with the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

Example

As shown in Figure 1(a) to Figure 1(b), a combined universal reader antenna includes a circularly polarized antenna and a linearly polarized antenna,

The circularly polarized antenna adopts a stacked structure, including a first parasitic patch 2, a first main radiation patch 1, a first feed network and a first floor 11 from top to bottom, and the first feed network includes Ring-shaped microstrip conduction line 4 and four metal probes 9A-9D, the four metal probes are placed on the ring-shaped microstrip conduction line evenly at intervals of 1/ _4λ0 successively along the ring-shaped microstrip conduction line 4 current direction, Wherein λ ₀ is the wavelength of the free space corresponding to the center frequency 900MHz, the first main radiation patch 1 is connected to the first parasitic patch 2 through four metal probes 9A-9D, and the first parasitic patch 2 is connected to the first parasitic patch 2. The center of the first main radiation patch 1 has a square groove, and also includes a ring-shaped conductor strip structure 3, and the ring-shaped conductor strip structure 3 is vertically sleeved on the edge of the first parasitic patch 2;

The linearly polarized antenna is installed above the square slot 6 of the first parasitic patch, adopts a stacked structure, and specifically includes a second parasitic patch 14, a second main radiation patch 13 and a second feed network, the second Both the main radiation patch 13 and the second parasitic patch 14 are of square structure, the second main radiation patch 13 is composed of two U-shaped microstrip lines with symmetrical arms, and the second feed network consists of The equal-arm U-shaped microstrip conductive line 16 is coupled to the second floor 17 with a slit 18 in the middle, and the second floor 17 has rectangular cutouts 19A-19B of the same size on the upper, left, and right corners.

In circularly polarized antennas:

The ring-shaped microstrip conduction line 4 is connected to the first main radiation patch 1 through four metal probes with a phase interval of 90°, and then the coaxial line 10 is directly connected to the ring-shaped microstrip conduction line 4 by the first floor 11 The RF signal input end constitutes the entire feed network.

Both the first main radiation patch 1 and the first parasitic patch 2 are bronze coin structures with an outer circle and an inner square. There are arc-shaped notches 7A-7B, the radiation angles of the two arc-shaped notches 7A-7B are both 20 degrees, and they are symmetrical about the diagonal, and the radius of the first main radiation patch 1 is 0.27λ ₀ , the radius of the first parasitic patch 2 is 0.23λ ₀ , and the height of the ring-shaped conductor strip structure 3 is 0.012λ ₀ , where λ ₀ is the wavelength of free space corresponding to the center frequency of 900 MHz in the superfrequency band.

Both the central part of the first main radiation patch 1 and the first parasitic patch 2 have a square groove, the side length of the square groove 5 of the first main radiation patch is 0.09λ ₀ , and the side length of the square groove 6 of the first parasitic patch is 0.072λ ₀ , the edge of the oblique 45° diagonal of the first main radiation patch has an arc-shaped notch with a radiation angle of 20° and a length Phi of 0.031λ ₀ , where λ ₀ is the UHF band The wavelength of free space corresponding to the center frequency of 900MHz.

The upper and lower edges of the initial segment of the ring-shaped microstrip conduction line 4 have rectangular notches 8A-8B. The length of the notch on the edge of the start end of the ring-shaped microstrip conduction line is theoretically 0.045λ ₀ , the width is 0.006λ ₀ in theory, and its inner diameter is about Rs_in0.108λ ₀ , outer diameter Rs_out 0.186λ ₀ , where λ ₀ is the wavelength of free space corresponding to the center frequency 900MHz.

The distance between the first floor 11 and the ring-shaped microstrip conducting line 4 is 5 mm, the distance between the ring-shaped microstrip conducting line 4 and the first main radiation patch 1 is 20 mm, the first main radiation patch 1 and the first parasitic The distance between the patches 2 is 10mm, and the height of the ring conductor strip line structure is 4mm.

The square slots of the first main radiating patch and the first parasitic body sheet can enhance the coupling between the two radiating patches, and have a significant impact on impedance matching and 3-dB axial ratio performance.

The design of the circularly polarized antenna's multi-layer stack structure broadens the impedance matching bandwidth and the axial ratio bandwidth, and improves the antenna gain. The -25dB return loss bandwidth of the circularly polarized antenna can reach 17.4% (807-961MHz), the 3-dB axial ratio bandwidth can reach 14.4% (833-962MHz), and the 2-dB axial ratio bandwidth can reach 12.9% (842-958MHz) . In the working frequency band, the gain can reach more than 9.1dBic, and the peak gain can reach 9.8dBic.

The linearly polarized antenna uses a broadband balun feed to expand the broadband of the microwave frequency band. The linearly polarized antenna is perpendicular to the feed network of the circularly polarized antenna, and the first main radiation patch and the first parasitic patch of the circularly polarized antenna It has an isolation effect on linearly polarized antennas, thereby achieving a high degree of isolation between linearly polarized and circularly polarized.

In a linearly polarized antenna:

As shown in Figure 2, the dielectric substrates etched by the second main radiation patch 13 and the second parasitic patch 14 are both square, with a size of about 0.345λ ₁ , as shown in Figure 3(b), the first The second main radiation patch is composed of two center-symmetric U-shaped microstrip lines with unequal arms. The overall length is about 0.552λ ₁ , and the width W1 is about 0.083λ ₁ . Each U-shaped microstrip line with unequal arms has two cut corners, and the cut corners 22A-22D of the U-shaped microstrip lines with unequal arms There are four in total, and the cut angle is an isosceles direct triangle, located on the upper and lower sides of the bottom of the unequal U-shaped microstrip line (as seen in the figure), and the waist length Lc1 is the U-shaped microstrip with unequal arms half of the width W1.

As shown in Figure 3 (a), the upper left corner and the lower right corner of the second parasitic patch 14 are provided with isosceles right-angled triangle cut corners, and there are two cut corners 23A-23B of the second parasitic patch. is about 0.049λ ₁ , the shape of the second parasitic patch is square, and its side length is about 0.278λ ₁ , the height of the interval between the second main radiation patch and the second parasitic patch is 2.4mm, where λ ₁ It is the wavelength of free space corresponding to the center frequency of microwave frequency band 2.45GHz.

The arm length FL of the equal-arm U-shaped microstrip conductive line 16 is about 0.155λ ₁ , the bottom width FW is about 0.06λ ₁ , the microstrip width W2 is about 0.016λ ₁ , and the length Lg and width Wg of the second floor 17 are respectively 0.22λ ₁ and 0.189λ ₁ rectangular patches, and on the center line of the second floor 17, there is a gap with a length Lg of 0.22λ ₁ and a width Ws of 0.024λ ₁ , which divides the second floor into two part, the left and right corners of the upper side of the second floor 17 are respectively cut with rectangular incisions 19A-19B, the length of the rectangular incision L1 is 0.045λ ₁ , and the width hs3 is 0.02λ ₁ , where λ ₁ is determined by the central frequency of the microwave frequency band of 2.45GHz corresponds to the wavelength in free space.

The dielectric substrate of the linearly polarized antenna is a high-frequency board RO4003 with a thickness of 0.8mm, a relative permittivity of 3.55, and a loss tangent of 0.0027. The parasitic patch and the main radiation patch are etched in a square with a side length of 42.2mm.

The coaxial line adopts RG316-SMSM, the diameter is 2.5mm, and the characteristic impedance is 50Ω.

As shown in Figure 4(a)-Figure 4(c), the -15dB return loss of the linearly polarized antenna achieves coverage of 2.395-2.668GHz, and the gain can reach more than 9.0dBi in the working frequency band. At 2.45GHz, the cross-polarization ratio of antenna 2 can reach 19.5dB, and the isolation between the two antenna ports in the UHF band (840-960MHz) can reach below -19.5dB. The isolation can reach below -27dB.

The circularly polarized antenna of the present invention provides a four-feed structure introduced by an annular microstrip feeder, and a thicker air dielectric layer is used between the annular microstrip feeder and the main radiation patch, and between the main radiation patch and the parasitic patch. The linearly polarized antenna is built into the square slot in the middle of the circularly polarized antenna. The parasitic patch and ring-shaped conductor strip of the circularly polarized antenna act as the reflector of the linearly polarized antenna, which makes full use of the space and reduces the overall volume of the antenna.

Utilizing the structural features of the invention, it is also possible to design a multi-band combined reader antenna. This combined reader antenna can not only cover the general UHF RFID application frequency band of 840-960MHz, but also cover the microwave application frequency bands of 2.45GHz and 5.8GHz at the same time, further meeting different application requirements in different occasions.

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the embodiment, and any other changes, modifications, substitutions and combinations made without departing from the spirit and principle of the present invention , simplification, all should be equivalent replacement methods, and are all included in the protection scope of the present invention.

Claims (7)

1. a kind of universal combined reader antenna, it is characterised in that including circular polarized antenna and linear polarized antenna；

The circular polarized antenna adopts stacked structure, include successively from top to bottom the first parasitic patch, the first primary radiation paster, the One feeding network and the first floor, first feeding network include annular micro-strip call wire and four metal probes, described four Root metal probe is spaced 1/4 λ successively along the annular micro-strip call wire sense of current₀Uniformly it is placed on annular micro-strip call wire, Wherein λ₀Centered on free space corresponding to frequency 900MHz wavelength, the first primary radiation paster and annular micro-strip call wire Connected by four metal probes, first parasitic patch is provided with square groove with the first primary radiation paster center, also wraps Finger ring-shaped conductor band structure is included, the finger ring-shaped conductor band structure is enclosed within the edge of the first parasitic patch；

The linear polarized antenna is arranged on above the square groove of the first parasitic patch, using stacked structure, is wrapped successively from top to bottom Include the second parasitic patch, the second primary radiation paster and the second feeding network, the second primary radiation paster and the second parasitic patch It is square structure, the second primary radiation paster is made up of the U-shaped microstrip line of two centrosymmetric unequal arms, second feedback Electric network is opened apertured second floor by the U-shaped microstrip line call wire coupling middle part of equiarm and is constituted, the left and right on second floor Two jiaos of top cuts with the rectangular cutout of formed objects；

The bottom both sides of the U-shaped microstrip line of the unequal arm are provided with isosceles right triangle corner cut, the waist of isosceles right triangle The half of the U-shaped micro belt line width of a length of unequal arm, the entire length of the U-shaped microstrip line of two centrosymmetric unequal arms is 0.552λ₁, a width of 0.083 λ₁, wherein λ₁The wavelength of free space corresponding to the mid frequency 2.45GHz of microwave frequency band.

2. reader antenna according to claim 1, it is characterised in that the upper left corner and bottom right of second parasitic patch Angle has isosceles right triangle corner cut, a length of 0.049 λ of waist of the isosceles right triangle₁, wherein λ₁For Microwave Frequency The wavelength of free space corresponding to the mid frequency 2.45GHz of section.

3. reader antenna according to claim 1, it is characterised in that the brachium of the U-shaped microstrip line call wire of the equiarm For 0.155 λ₁, bottom width is 0.06 λ₁, a width of 0.016 λ of arm₁, the second floor is that length and width is respectively 0.22 λ₁With 0.189 λ₁It is rectangular A length of 0.22 λ is provided with shape, and the centrage on the second floor₁, a width of 0.024 λ₁Gap, floor is divided into into two parts, institute State a length of 0.045 λ of rectangular cutout on the second floor₁, a width of 0.02 λ₁, wherein λ₁For microwave frequency band mid frequency 2.45GHz institutes The wavelength of correspondence free space.

4. reader antenna according to claim 1, it is characterised in that the first primary radiation paster and the first parasitic patch Piece is round outside but spuare inside GUTONGBI structure, the first primary radiation paster and horizontal plane positive direction into 45 degree cornerwise two End has arc-shaped slot, and the radiation angle of two arc-shaped slots is 20 degree, and symmetrical with regard to the diagonal, first master The radius of radiation patch is 0.27 λ₀, the radius of the first parasitic patch is 0.23 λ₀, refer to that the height of ring-shaped conductor band structure is 0.012λ₀, wherein λ₀The wavelength of free space corresponding to the mid frequency 900MHz of overclocking wave band.

5. reader antenna according to claim 4, it is characterised in that in the first primary radiation paster and the first parasitic patch Center portion point is provided with square groove, and the square groove length of side of the first primary radiation paster is 0.09 λ₀, the square trough rim of the first parasitic patch A length of 0.072 λ₀, the arc-shaped slot length is 0.031 λ₀, wherein λ₀Corresponding to the mid frequency 900MHz of shf band The wavelength of free space.

6. reader antenna according to claim 1, it is characterised in that the linear polarized antenna with refer to ring-shaped conductor band knot In same level, the square groove distance of the first parasitic patch of the second primary radiation paster distance is 4mm for the upper edge of structure.

7. reader antenna according to claim 1, it is characterised in that the initial segment of the annular micro-strip call wire is upper and lower Edge is provided with rectangular v notch v, a length of 0.045 λ of rectangular v notch v of the initial end edge of annular micro-strip call wire₀, a width of 0.006 λ₀, wherein λ₀Centered on free space corresponding to frequency 900MHz wavelength.