阅读说明：本技术 应用于智能电信机柜的超高频rfid读写器阵列天线 (Ultrahigh frequency RFID reader-writer array antenna applied to intelligent telecommunication cabinet ) 是由 文舸一 顾晓忠 于 2019-08-29 设计创作，主要内容包括：本发明公开了一种应用于智能电信机柜的超高频RFID读写器阵列天线,以功率传输效率最优化理论为基础,采用四单元线极化微带阵列天线的形式,天线工作在922.5MHz,其中四单元阵列工作频段仿真结果为900-930MHz,覆盖了我国RFID超高频段(920-925MHz),实现了RFID读写器天线在金属电信机柜环境下均匀的近场分布,并对RFID标签具有良好的读取。(The invention discloses an ultrahigh frequency RFID reader-writer array antenna applied to an intelligent telecommunication cabinet, which is based on the power transmission efficiency optimization theory and adopts the form of a four-unit linearly polarized microstrip array antenna, wherein the antenna works at 922.5MHz, the simulation result of the working frequency band of the four-unit array is 900 plus 930MHz, the ultrahigh frequency band (920 plus 925MHz) of the RFID in China is covered, the uniform near field distribution of the RFID reader-writer antenna in the environment of a metal telecommunication cabinet is realized, and the RFID tag is well read.)

1. An ultrahigh frequency RFID reader-writer array antenna applied to an intelligent telecommunication cabinet is characterized by comprising

The microstrip antenna units can be arranged at the side wall of the cabinet close to the cabinet door, and at least two microstrip antenna units are arranged in the cabinet in order to meet the requirement of the cabinet monitoring coverage range; the vertical reading range of the microstrip antenna unit is not less than 700 mm;

the receiving antenna units are arranged at the electric field scanning lines in the cabinet, the number of the receiving antenna units is the same as that of the microstrip antenna units, the receiving antenna units are arranged at equal intervals, and the receiving antenna units and the microstrip antenna units form a near-field transmission system;

the feed network is arranged together with the microstrip antenna unit and is communicated with the microstrip antenna unit in a welding mode of a coaxial feed line, and the feed network adopts a power transmission optimization theory to obtain optimized excitation.

2. The uhf RFID reader/writer array antenna applied to an intelligent telecommunications rack of claim 1, wherein the microstrip antenna unit is a square linearly polarized microstrip antenna, the feeding mode thereof adopts coaxial feeding, the substrate thereof adopts FR4 material with dielectric constant of 4.4, loss tangent angle of 0.02 and thickness of 3mm, and the size parameter L of the antenna unit is 75.7mm, and D is 15 mm.

3. The UHF RFID reader/writer array antenna applied to the intelligent telecommunication cabinet as claimed in claim 1, wherein the microstrip antenna unit is pre-arranged on a substrate with a length, width and thickness of 650mm x 120mm x 3mm, and the substrate still adopts FR4 material; the distance between the microstrip antenna units is 160 mm.

4. The UHF RFID reader-writer array antenna applied to the intelligent telecommunication cabinet as claimed in claim 1, wherein the substrate of the feed network is made of FR4 material, the length and the width of the substrate are 650mm x 120mm x 1.6mm, the substrate of the feed network is attached to the substrate with the pre-arranged microstrip antenna unit, and a metal ground is arranged between the substrate and the substrate.

5. The UHF RFID reader-writer array antenna applied to an intelligent telecommunication cabinet as claimed in claim 1, wherein the optimized excitation of the feeding network is obtained as follows:

assuming a near-field transmission system composed of an N-port transmitting antenna array and an M-port receiving antenna array, the whole near-field beamforming system can be regarded as an M + N-port network, and can be represented by an (N + M) × (N + M) scattering matrix as formula (1):

the normalized incident wave and reflected wave of the transmitting antenna array and the receiving antenna array can be respectively expressed as:

the letter subscript 'T' represents a transmitting antenna, and the subscript 'r' represents a receiving antenna, wherein the maximum power transmission efficiency T of the near field forming transmission system is defined as_arrayDescribed as the ratio of the received power of the receive antenna array load to the total input power of the transmit antenna array:

assuming each of the receiving antennasIf the units are perfectly matched, [ a ] can be obtained_r]0, which can be obtained by substituting it into formula (1) and formula (2):

in equation (3) above, (-) is expressed as the inner product of two vector vectors, [ A ] and [ B ] represent two arrays, respectively:

receiving the incident wave normalized by the antenna array when the receiving and transmitting system is completely matched_r]Can be expressed as:

[b_r]＝[S_rt][a_t] (4)

to obtain a uniform electric field distribution, the power transfer efficiency must be maximized under the following constraints:

therefore, the near-field shaped array optimization problem can be expressed as a quadratic constraint problem:

wherein x represents [ a ]_t]The superscript H denotes the hermitian operation;

we introduce n_rA correction matrix y of x 1 dimension instead of solving equation (6) directly; thus, equation (6) can be expressed as:

wherein the matrix S represents [ S ]_rt]，

We can solve equation (7) with the lagrange multiplier method, whose solution is:

x^*＝A^-1S^H(SA^-1S^H)^-1y (8)

the maximum transmission efficiency between the receiving antenna and the transmitting antenna array can be obtained by solving the formula (8), and the optimal excitation amplitude and phase of the transmitting antenna array are obtained at the same time, and the method is realized by designing a feed network.

Technical Field

The invention relates to the field of electronic antennas, in particular to an ultrahigh frequency RFID reader-writer array antenna applied to an intelligent telecommunication cabinet.

Background

In recent years, the research on near field RFID reader antennas has been receiving more and more attention. For the reader-writer antenna of the low frequency band and the high frequency band, the working range is in a near field area, the influence of the environment is small, but the transmission data rate is low. The ultra-high frequency band RFID reader antenna receives attention from researchers due to its high information transmission exchange rate and its reliable tag identification capability as low frequency band and high frequency band. In order to avoid misreading or missing reading of the RFID tag, the near field RFID reader antenna must have uniform near field distribution and strong ability to resist complex electromagnetic environments in the target identification area. For the RFID reader antenna applied to the telecommunication cabinet, the current research does not fully consider the influence of the metal cabinet, which often causes the missed reading or misreading of the RFID tag.

The invention is based on the power transmission optimization theory, adopts the form of a four-unit microstrip antenna array, avoids the problem that a target identification area cannot be effectively covered by a single antenna, and realizes the uniform near field distribution of the RFID reader-writer antenna in the environment of the metal telecommunication cabinet through the feed network designed according to the excitation distribution obtained by optimization.

Disclosure of Invention

The purpose of the invention is as follows: the invention aims to provide an ultrahigh frequency RFID reader-writer array antenna applied to an intelligent telecommunication cabinet, which is based on the theory of power transmission efficiency optimization and adopts a four-unit linearly polarized microstrip array antenna mode, wherein the antenna works at 922.5MHz (the invention is not limited to specific frequency, and the design method is similar when the frequency is changed). The simulation result of the working frequency band of the four-unit array is 900 plus 930MHz, the RFID ultrahigh frequency band (920 plus 925MHz) in China is covered, uniform near field distribution of the RFID reader antenna in the metal telecommunication cabinet environment is realized, and the RFID tag can be well read.

The technical scheme is as follows: the invention relates to an ultrahigh frequency RFID reader-writer array antenna applied to an intelligent telecommunication cabinet, which comprises:

the microstrip antenna units can be arranged at the side wall of the cabinet close to the cabinet door, and at least two microstrip antenna units are arranged in the cabinet in order to meet the requirement of the cabinet monitoring coverage range; the vertical reading range of the microstrip antenna unit is not less than 700 mm;

the receiving antenna units are arranged at the electric field scanning lines in the cabinet, the number of the receiving antenna units is the same as that of the microstrip antenna units, the receiving antenna units are arranged at equal intervals, and the receiving antenna units and the microstrip antenna units form a near-field transmission system;

the feed network is arranged together with the microstrip antenna unit and is communicated with the microstrip antenna unit in a welding mode of a coaxial feed line, and the feed network adopts a power transmission optimization theory to obtain optimized excitation.

Furthermore, the microstrip antenna unit is a square linearly polarized microstrip antenna, the feeding mode adopts coaxial feeding, the substrate adopts FR4 material with dielectric constant of 4.4, loss tangent angle of 0.02 and thickness of 3mm, the size parameter L of the antenna unit is 75.7mm, and D is 15 mm.

Furthermore, the microstrip antenna unit is arranged on a substrate with the length, width and thickness of 650mm multiplied by 120mm multiplied by 3mm in advance, and the substrate still adopts FR4 material; the distance between the microstrip antenna units is 160 mm.

Furthermore, the substrate of the feed network is made of FR4 material, the length and the width of the substrate are 650mm multiplied by 120mm multiplied by 1.6mm, the substrate of the feed network and the substrate provided with the microstrip antenna unit in advance are attached, and a metal ground is arranged between the substrate of the feed network and the substrate.

Further, the optimized excitation of the feed network is obtained as follows:

assuming a near-field transmission system composed of an N-port transmitting antenna array and an M-port receiving antenna array, the whole near-field beamforming system can be regarded as an M + N-port network, and can be represented by an (N + M) × (N + M) scattering matrix as formula (1):

the normalized incident wave and reflected wave of the transmitting antenna array and the receiving antenna array can be respectively expressed as:

the letter subscript't' represents a transmit antenna and the subscript 'r' represents a receive antenna. The maximum power transmission efficiency T of the near field forming transmission system is defined as_arrayDescribed as the ratio of the received power of the receive antenna array load to the total input power of the transmit antenna array:

assuming that the elements of the receive antenna are perfectly matched, [ a ] can be obtained_r]0, which can be obtained by substituting it into formula (1) and formula (2):

in equation (3) above, (-) is expressed as the inner product of two vector vectors, [ A ] and [ B ] represent two arrays, respectively:

receiving the incident wave normalized by the antenna array when the receiving and transmitting system is completely matched_r]Can be expressed as:

[b_r]＝[S_rt][a_t] (4)

to obtain a uniform electric field distribution, the power transfer efficiency must be maximized under the following constraints:

therefore, the near-field shaped array optimization problem can be expressed as a quadratic constraint problem:

wherein x represents [ a ]_t]The superscript H denotes the hermitian operation.

However, the solution of equation (6) is difficult. We introduce n_rX 1-dimensional correction matrix y instead of solving equation (6) directly. Thus, equation (6) can be expressed as:

wherein the matrix S represents [ S ]_rt]。

We can solve equation (7) with the lagrange multiplier method, whose solution is:

x^*＝A^-1S^H(SA^-1S^H)^-1y (8)

the maximum transmission efficiency between the receiving antenna and the transmitting antenna array can be obtained by solving the formula (8), the optimal excitation amplitude and phase of the transmitting antenna array are obtained at the same time, and the design of the feed network is used for realizing

Has the advantages that: compared with the prior art, the invention has the following technical advantages:

because the metal cabinet environment has a large influence on the near field distribution, the near field distribution of the antenna of the traditional RFID reader-writer is often uneven, and therefore the tag is missed to read or is misread. Different from the traditional ultrahigh frequency near field RFID reader-writer antenna, the four-unit array antenna designed by the invention considers the influence of the metal cabinet on the near field distribution of the antenna, considers the metal cabinet in the design process and simultaneously realizes the uniform near field electric field distribution of the antenna.

Drawings

Fig. 1 is a schematic structural view of a telecommunications cabinet of the present invention.

FIG. 2 is a schematic diagram of the structure of the array unit according to the present invention.

Fig. 3 is a simulated reflection coefficient of an array cell of the present invention.

Fig. 4 is a schematic diagram of a 4-element array antenna according to the present invention.

Fig. 5 is a schematic structural diagram of a near field forming transmission system according to the present invention.

Fig. 6 is a schematic diagram of the feed network of the present invention.

Fig. 7 is a schematic diagram of the feed network and array antenna side connection of the present invention.

FIG. 8 shows measured and simulated reflection coefficients for a 4-element array antenna according to the present invention.

FIG. 9 shows the results of the normalized near field electric field simulation and measurement of the 4-element array antenna of the present invention.

FIG. 10 is an RFID read-write test system of the present invention.

Detailed Description

The near field RFID reader-writer array antenna designed by the invention is applicable to telecommunication cabinets with the length, width and height of 600mm multiplied by 900 mm. Wherein five surfaces of the cabinet except the front surface are provided as perfect conductors to simply simulate a real cabinet environment. The tags were placed at the edge of the communication server, vertically aligned along the scan line, 200mm from the antenna array, and 140mm from the front of the cabinet, as shown in fig. 1. The reader antenna is placed along the left side edge of the cabinet to reduce the space occupied by the antenna. In consideration of heat dissipation, moisture resistance and the like, the RFID reader antenna, namely the microstrip antenna unit, is required to have a vertical reading range of not less than 700mm in a telecommunication cabinet. To avoid missed or misread of the tag, the electric field distribution within the target identification area (i.e., at the scan lines) must be as uniform as possible.

Because the microstrip antenna has the advantages of simple processing, lower cost and convenient design and adjustment, the square linearly polarized microstrip antenna unit is selected as the array antenna unit, the feeding mode adopts coaxial feeding, and the substrate adopts FR4 material with the dielectric constant of 4.4, the loss tangent angle of 0.02 and the thickness of 3 mm. The size parameter L of the antenna unit is 75.7mm, d is 15mm, the specific structure is as shown in fig. 2, the unit matching is good, and the simulated reflection coefficient is as shown in fig. 3. In order to meet the requirement of the cabinet monitoring coverage range, three identical microstrip antenna units are added on the basis of one antenna unit, and the effect of uniform electric field at the scanning line is achieved by adopting a four-unit array antenna structure. The substrate on which the microstrip antenna elements are placed is still made of FR4 material, and has dimensions of 650mm × 120mm × 3mm, and the spacing between the microstrip antenna elements is 160mm, as shown in fig. 4. In order to make the electric field distribution in the target identification area as uniform as possible, four receiving antennas (test antennas) arranged at equal intervals are introduced at the electric field scanning line, and the unit interval is 170mm, so that the near field transmission system shown in fig. 5 is formed, the performance of the transmission system can be described by scattering parameters, and all the scattering parameters are obtained by using electromagnetic simulation software HFSS 15.0. The maximum transmission efficiency and the excitation distribution with uniform near-field distribution can be obtained by using a power transmission optimization method, and the corresponding excitation distribution can be realized by designing a feed network. The feed network substrate is made of FR4 material, and the size of the feed network substrate is 650mm multiplied by 120mm multiplied by 1.6mm, as shown in figure 6. The 4-unit microstrip array antenna and the feed network are manufactured and welded with the coaxial feed line, and the array antenna and the feed network share one metal ground, as shown in fig. 7.

The optimized excitation (amplitude and phase) of the feed network is obtained by adopting a power transmission optimization theory, and the method comprises the following steps:

assuming a near-field transmission system composed of an N-port transmitting antenna array and an M-port receiving antenna array, the whole near-field beamforming system can be regarded as an M + N-port network, and can be represented by an (N + M) × (N + M) scattering matrix as formula (1):

the normalized incident wave and reflected wave of the transmitting antenna array and the receiving antenna array can be respectively expressed as:

the letter subscript't' represents a transmit antenna and the subscript 'r' represents a receive antenna. The maximum power transmission efficiency T of the near field forming transmission system is defined as_arrayDescribed as the ratio of the received power of the receive antenna array load to the total input power of the transmit antenna array:

assuming that the elements of the receive antenna are perfectly matched, [ a ] can be obtained_r]0, which can be obtained by substituting it into formula (1) and formula (2):

in equation (3) above, (-) is expressed as the inner product of two vector vectors, [ A ] and [ B ] represent two arrays, respectively:

receiving the incident wave normalized by the antenna array when the receiving and transmitting system is completely matched_r]Can be expressed as:

[b_r]＝[S_rt][a_t] (4)

to obtain a uniform electric field distribution, the power transfer efficiency must be maximized under the following constraints:

therefore, the near-field shaped array optimization problem can be expressed as a quadratic constraint problem:

wherein x represents [ a ]_t]The superscript H denotes the hermitian operation.

However, the solution of equation (6) is difficult. We introduce n_rX 1-dimensional correction matrix y instead of solving equation (6) directly. Thus, equation (6) can be expressed as:

wherein the matrix S represents [ S ]_rt]。

We can solve equation (7) with the lagrange multiplier method, whose solution is:

x^*＝A^-1S^H(SA^-1S^H)^-1y (8)

the maximum transmission efficiency between the receiving antenna and the transmitting antenna array can be obtained by solving the formula (8), and the optimal excitation amplitude and phase of the transmitting antenna array are obtained at the same time, and the method is realized by designing a feed network. Fig. 8 shows simulation and actual measurement results of S parameters of the antenna, which show that the antenna is well matched, and the return loss bandwidth of the antenna below-10 dB is from 900MHz to 930 MHz.

In order to verify the effect of near-field shaping in a metal cabinet, a vector network analyzer with two ports is used for carrying out experimental test on a four-unit near-field electric field shaping array antenna. The antenna array and monopole (test antenna, whip antenna operating at 922 MHz) were connected to ports 1 and 2 of the vector network analyzer. Here, S is taken₂₁I to represent the normalized electric field strength. The normalized electric field strength is measured in a real metal cabinet environment in consideration of the influence of the metal cabinet on the near field distribution of the array antenna. Test antenna moving along scan lineThe transmission coefficient can be directly obtained through the vector network analyzer, the transmission coefficient obtained through measurement is calculated, the level value of each test point can be obtained, normalization is carried out on the level value, and finally the electric field distribution curve at the scanning line position is obtained. Fig. 9 is a result of measurement and simulation of normalized electric field distribution of the four-unit near-field shaped antenna array along the scan line, and the result shows that the coincidence is good. To show the effect of the optimization method, simulation results of the electric field distribution at the scanning line when the array antenna is excited with equal amplitude in the same direction are also shown in the figure. It is clear that the four-element array antenna excited using the optimization method has the best performance, the electric field intensity variation at the scan line is less than 1.5dB, and the normalized field measured at 1.5dB has a width of 710mm, while the length of the antenna is only 650mm at this time.

In order to verify the read-write effect of the RFID reader-writer array antenna in the application of the telecommunication cabinet, the RFID reader-writer array antenna, the reader-writer and the computer are connected to form an RFID read-write system. The tested RFID tags are placed in the target identification area, maintained in alignment with the polarization of the transmitting antenna, and arranged vertically along the scan line, as shown in fig. 10. When tagged communication servers are placed in the target identification area of the cabinet, they are both identifiable by the designed near field RFID antenna.

The invention designs a 4-unit near-field electric field shaped array antenna with the working frequency of 922.5MHz applied to an intelligent telecommunication cabinet. Based on the power transmission optimization theory, the optimal excitation distribution of the transmitting antenna array is calculated by introducing the receiving antenna in the target identification area, so that a relatively uniform near-field electric field distribution is formed at the target identification area, the electric field intensity variation is less than 1.5dB, the width of a normalized field measured at 1.5dB is 710mm, and the length of the antenna is only 650mm at the moment. The optimization method can be applied to antenna units in any form, fully considers the influence of the metal cabinet on near-field distribution, and brings the metal cabinet into the design process for integrated design. Due to the adoption of the form of the array antenna, the invention can adapt to cabinets with different sizes.