CN102299413A

CN102299413A - UHF (ultra high frequency) RFID (radio frequency identification) reader-writer antenna of smart shelf

Info

Publication number: CN102299413A
Application number: CN2011101481274A
Authority: CN
Inventors: 吴昌英; 任安康; 王婷; 李建周
Original assignee: Northwestern Polytechnical University
Current assignee: Northwestern Polytechnical University
Priority date: 2011-06-02
Filing date: 2011-06-02
Publication date: 2011-12-28

Abstract

The invention discloses a UHF (ultra high frequency) RFID (radio frequency identification) reader-writer antenna of a smart shelf. A PCB (printed circuit board) substrate at the upper layer and a PCB substrate at the lower layer are supported by nylon columns; the upper surface of the PCB substrate at the upper layer is provided with multiple upper surface metal conduction bands, and the lower surface of the PCB substrate at the lower layer is provided with multiple lower surface metal conduction bands and the upper surface of the PCB substrate at the lower layer is coated by copper completely; conductive columns are used for connecting coaxial joints, the upper surface metal conduction bands, the lower surface metal conduction bands with matched loads in series; and the widths of the upper surface metal conduction bands are increased gradually in accordance with the transmission sequence of signals, and the sum of phase shift quantities of each upper surface metal conduction band and each lower surface metal conduction band which are adjacent to each other are the integral multiple of the wavelength. The UHF RFID reader-writer antenna is stronger in the current, and can be designed with the different areas conveniently as well as is even in the magnetic field distribution at the upper part.

Description

Hyper band intelligent commodity shelf rfid interrogator antenna

Technical field

The invention belongs to the antenna structure design field, relate to a kind of rfid interrogator antenna.

Background technology

RFID (Radio Frequency Identification, radio-frequency (RF) identification) technology is a kind of non-contacting automatic identification technology.Reading and writing device antenna plays key effect in rfid system.The frequency of reading and writing device antenna work has low frequency (135kHz is following), high frequency (13.56MHz), hyperfrequency (860-960MHz) and microwave frequency band (more than the 2.4GHz) etc.Reading and writing device antenna is divided according to operating distance, can be divided near field antenna and far field antenna.The near field reading and writing device antenna that works in hyperfrequency is highly suitable for work in narrow space.Because near field antenna is only locating that closely stronger electromagnetic field is just arranged, the intensity of distance electromagnetic fields far away slightly sharply weakens, and the far gain of this antenna is very low, so the large-area metal around the antenna can't exert an influence to the performance of antenna.

Because ultrahigh frequency band near field RFID reader-writer antenna has a lot of premium properties.But after the size of antenna surpassed a wavelength, near the magnetic field it just became inhomogeneous.A lot of companies and individual have done the size that many correlative studys increase antenna, and have product to come out, such as based on the antenna of coupling loop, the loop antenna of amounting to, by the loop antenna of lumped capacitor compensation of phase etc.The size of these antenna is still big inadequately, can't produce the equally distributed electromagnetic field of large tracts of land on large-scale shelf.Document " RFID Smart Shelf with Confined Detection Volume at UHF; Carla R.Mederios; Jorge R.Costa; and Carlos A.Fernandes, IEEE Antennas and Wireless Propagation Letters, 2008; Vol.7; p773-776 " discloses a kind of shelf antenna of realizing with microstrip line, the change length that this antenna can be random, but width can not broaden.Document " Near-Field Antenna for RFID Smart Shelf in UHF; Wonkyu Choi; Jeong-Seok Kim; Ji-Hoon Bae; Gilyoung Choi; and Jong-Suk Chae, Antennas and Propagation Society International Syposiuim, 2009, p1-4 " another kind of shelf antenna is disclosed, be to adopt power splitter that feeder line is divided into the parallel microstrip line of a lot of roots; by a lot of roots slit on the floor electric field energy be coupled away then; this method is owing to there is power splitter, so the electric current on every line can reduce, so weakened the operating distance of antenna.

Summary of the invention

Adopt the deficiency that causes the electric current on the every line to reduce behind the power splitter in order to overcome prior art, the invention provides a kind of hyper band intelligent commodity shelf rfid interrogator antenna, this antenna can produce large-area equally distributed magnetic field.

The technical solution adopted for the present invention to solve the technical problems is: comprise PCB substrate, coaxial fitting and metal conduction band, upper strata PCB substrate and the PCB of lower floor substrate support by several nylon columns and form the air gap; The upper surface of upper strata PCB substrate has upper surface metal conduction band, and the lower surface of the PCB of lower floor substrate has lower surface metal conduction band, and the upper surface of the PCB of lower floor substrate is that integral body is covered copper; This integral body covers copper and the PCB of lower floor substrate, lower surface metal conduction band form microstrip line together, and this integral body covers copper and air gap, upper strata PCB substrate, upper surface metal conduction band form microstrip line together; Upper surface metal conduction band and lower surface metal conduction band all have many, and by alternately the link to each other end of upper surface metal conduction band and lower surface metal conduction band of conductive pole, with described upper surface metal conduction band and the series connection of lower surface metal conduction band, one end of first upper surface metal conduction band links to each other with coaxial fitting, and an end of last root upper surface metal conduction band connects matched load; Signal through upper surface metal conduction band and lower surface metal conduction band alternate transmission, arrives matched load from the coaxial fitting feed-in at last; The width of upper surface metal conduction band increases gradually according to the order of signal transmission, the degree that width increases is constant with the current value of each upper surface metal conduction band of flowing through to be criterion, the characteristic impedance of formed microstrip line reduces to matched load gradually from the coaxial fitting junction, even still can keep the electric current on the upper surface metallic conduction constant under the situation that has radiation loss to exist like this; Upper surface metal conduction band motivates tangential magnetic field, select the length of upper surface metal conduction band and lower surface metal conduction band, the phase-shift phase sum that adjacent single upper surface metal conduction band and single lower surface metal conduction band are produced is the integral multiple of wavelength, the tangential magnetic field that motivates of adjacent upper surface metal conduction band is a homophase like this, be superimposed, form large-area tangential magnetic field and distribute.

The invention has the beneficial effects as follows: do not adopt power splitter, but alternately be connected with lower surface metal conduction band by upper surface metal conduction band, the electric current on the upper surface metal conduction band is stronger like this; Change the length of antenna and the width of change antenna, promptly the radical and the length of upper surface metal conduction band and lower surface metal conduction band are all little to the performance change of antenna, so can design the antenna of different area easily; Because the signal long-distance transmission has decay, and the width of upper surface metal conduction band increases gradually, has reduced the characteristic impedance of microstrip line, has offset the decay of signal, make the CURRENT DISTRIBUTION on upper surface metal conduction band not reduce, so the Distribution of Magnetic Field on antenna top is even.

The present invention is further described below in conjunction with drawings and Examples.

Description of drawings

Fig. 1 is a hyper band intelligent commodity shelf rfid interrogator antenna structure view of the present invention.

Fig. 2 is the top view of Fig. 1.

Fig. 3 is the end view of Fig. 1.

Among the figure, 1, coaxial fitting, 2, upper strata PCB substrate, 3, the PCB of lower floor substrate, 4, upper surface metal conduction band, 5, lower surface metal conduction band, 6, conductive pole, 7, nylon column, 8, the air gap, 9, matched load, 10, integral body covers copper.

Embodiment

With reference to Fig. 1～3, the present invention is covered copper 10 by coaxial fitting 1, upper strata PCB substrate 2, the PCB of lower floor substrate 3, upper surface metal conduction band 4, lower surface metal conduction band 5, conductive pole 6, nylon column 7, air gap 8, matched load 9 and integral body and is formed.

In the present embodiment, the width of upper strata PCB substrate 2 and the PCB of lower floor substrate 3 is 350mm, and length is 700mm, and thickness is 2mm, and material is FR4.Two PCB substrates form air gap 8 by highly being nylon column 6 supports of 10mm on four angles.

Article one the upper surface metal lead 4 the band left sides width be 52mm, the width on the right is 55 millimeters; The width that second upper surface metal is led the 4 band left sides is 55mm, and the width on the right is 58 millimeters; Article three, the width on upper surface metal conduction band 4 left sides is 58mm, and the width on the right is 62 millimeters.The characteristic impedance of covering three microstrip lines that copper 10, air gap 8, upper strata PCB substrate 2 and upper surface metal conduction band 4 formed by integral body carries out the transition to last 44 ohm by 50 ohm through 48 ohm and 46 ohm like this.The impedance of the last matched load 9 that is connected is 44 ohm and microstrip line coupling.

Article one, the width of lower surface metal conduction band 5 is 4.2mm, and characteristic impedance is 48 ohm, connects article one and second upper surface metal conduction band 4 by two conductive poles 6.The width of second lower surface metal conduction band 5 is 4.5mm, and characteristic impedance is 46 ohm, connects second and the 3rd upper surface metal conduction band 4 by two conductive poles 6.

If the width of upper surface metal conduction band 4 and lower surface metal conduction band 5 does not have gradual change, the characteristic impedance of so formed microstrip line all is 50 ohm.The reduction of amplitude through taking place in signal after the long Distance Transmission of microstrip line, this mainly is owing to upper surface metal conduction band 4 and the whole distance radiation loss that produces far away that covers copper 10.Electric current on the upper surface metal conduction band 4 reduces gradually, must cause field weakening on every side, has influenced the distance that reads of antenna.Therefore in the present invention, the width of upper surface metal conduction band 4 increases gradually, and the characteristic impedance of microstrip line reduces gradually, has kept constant along the current amplitude of upper surface metal conduction band 4 like this, and then magnetic field intensity is stable.

In the present embodiment, signal flows into lower surface metal conduction band 5 through upper surface metal conduction band 4 backs by conductive pole 6 to the right, flows into next root upper surface metal conduction band 4 by conductive pole 6 again behind left end.The phase shift that single upper surface metal conduction band 4 and single lower surface metal conduction band 5 common properties are given birth to is six wavelength, so the electric current on the adjacent upper surface metal conduction band 4 all is a homophase.The tangential magnetic field that produces above antenna of upper surface metal conduction band 4 superposes in the same way like this.

Should be understood that the above only is a kind of embodiment of the present invention.For those of ordinary skills, can increase or reduce the radical of upper surface metal conduction band 4 and lower surface metal conduction band 5 easily, to change the width of antenna; Also can increase or reduce the length of antenna, as long as guarantee that the phase-shift phase that single upper surface metal conduction band 4 and single lower surface metal conduction band 5 produce is the integral multiple of wavelength; Also passable upper strata PCB substrate 2 and the PCB of the lower floor substrate 3 of selecting other material for use; Also can choose the height of different nylon column 7, to produce the air gap 8 of different-thickness.

Claims

1. a hyper band intelligent commodity shelf rfid interrogator antenna comprises PCB substrate, coaxial fitting and metal conduction band, it is characterized in that: upper strata PCB substrate and the PCB of lower floor substrate support by several nylon columns and form the air gap; The upper surface of upper strata PCB substrate has upper surface metal conduction band, and the lower surface of the PCB of lower floor substrate has lower surface metal conduction band, and the upper surface of the PCB of lower floor substrate is that integral body is covered copper; Upper surface metal conduction band and lower surface metal conduction band all have many, and by alternately the link to each other end of upper surface metal conduction band and lower surface metal conduction band of conductive pole, with described upper surface metal conduction band and the series connection of lower surface metal conduction band, one end of first upper surface metal conduction band links to each other with coaxial fitting, and an end of last root upper surface metal conduction band connects matched load; The width of upper surface metal conduction band increases gradually according to the order of signal transmission, the degree that increases is constant with the current value of each upper surface metal conduction band of flowing through to be criterion, the length of upper surface metal conduction band and lower surface metal conduction band, the phase-shift phase sum that adjacent single upper surface metal conduction band and single lower surface metal conduction band are produced is the integral multiple of wavelength.