Ultrahigh frequency RFID identification system

Abstract

The invention discloses an ultrahigh frequency RFID identification system, which comprises a planar antenna array, a power division phase shift network and an ultrahigh frequency reader-writer module, and is characterized in that the planar antenna array comprises a plurality of ultrahigh frequency antenna groups, and the plurality of ultrahigh frequency antenna groups are placed in a coplanar manner; and the power division phase shift network is respectively connected with the ultrahigh frequency antenna group and the ultrahigh frequency reader-writer module. The ultrahigh frequency antenna group comprises a plurality of linearly arranged antenna array elements and an independent feed structure, and the feed power ratio is 1: 1-8: 1. The planar antenna array is adopted to replace a traditional single-antenna system or a multi-antenna system, accurate control over the radiation boundary of the ultrahigh-frequency RFID recognition system and beam scanning in the specific direction are achieved through distribution of the feed amplitude and phase of the planar antenna array, and therefore the probability of serial reading and missed reading is reduced, and robustness in the RFID recognition process is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of radio frequency identification, and in particular relates to an ultra-high frequency RFID identification system. Background Art

[0002] According to the working frequency of the electromagnetic waves for data exchange between the RFID system reader and the tag, the working frequency band of the RFID system can be divided into four frequency bands: low frequency (LF, 30-300KHz, typical frequencies are 125KHz and 134.2KHz), high frequency (HF, 3-30MHz, typical frequency is 1.56MHz), ultra-high frequency (UHF, 300-968MHz, typical frequencies are 869.5MHz and 915.3MHz), and microwave (MW, 2.45-5.8GHz, typical frequency is 2.45GHz). According to different working frequency bands, in the passive case, the technical characteristics and application specifications are different. Due to the advantages of the UHF band, such as long reading and writing distance, fast multi-tag recognition speed, strong anti-interference ability, small tag size and large capacity, the UHF band RFID technology and its related standard protocols have become the focus of the global RFID industry and research departments.

[0003] There is no doubt that with the rise of the Internet of Things, RFID, as an automatic identification technology, has broad development space and bright prospects. However, due to the characteristics of RFID communication itself, it is subject to the influence of the working environment, the movement of the identification target, the directional sensitivity of the antenna, etc., which easily causes the RFID tag to be missed and read in series, which greatly reduces the performance of the RFID system in practical applications. In order to alleviate the influence of the above factors, an RFID system with a specific spatial beam scanning capability is an excellent solution.

[0004] Therefore, it is necessary to provide an ultra-high frequency RFID identification system to improve the robustness of RFID identification by controlling the direction and coverage of the antenna beam. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide an ultra-high frequency RFID identification system, which improves the robustness of RFID identification by controlling the direction and coverage of the antenna beam.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: the UHF RFID identification system includes a planar antenna array, a power division and phase shifting network and an UHF reader / writer module, the planar antenna array includes multiple UHF antenna groups, and the multiple UHF antenna groups are placed in the same plane; the power division and phase shifting network are respectively connected to the UHF antenna groups and the UHF reader / writer modules.

[0007] By adopting the above technical scheme, a plurality of UHF antenna groups are designed to be coplanarly placed to form a planar antenna array, wherein the UHF antenna group is used for radiating the UHF signal in a specific space; the power division phase shift network is used for changing the amplitude and phase of the UHF antenna group signal to realize automatic scanning of the antenna beam in a specific space; the UHF reader / writer module is used for modulation and transmission of the UHF signal, demodulation and reception, and phase control of the power division phase shift network; a planar antenna array is used to replace the traditional single antenna system or multi-antenna system, and by allocating the feeding amplitude and phase of the planar antenna array, the radiation boundary of the UHF RFID identification system is precisely controlled and the beam scanning in a specific direction is scanned, thereby reducing the probability of cross-reading and missed reading, and improving the robustness of the RFID identification process.

[0008] Preferably, the UHF antenna group includes a plurality of linearly arranged antenna array elements and an independent feeding structure, and the feeding power ratio is 1:1 to 8:1.

[0009] Preferably, the power division and phase shifting network comprises a power division network and a phase shifting network, the power division network is connected to the phase shifting network and the ultra-high frequency antenna group respectively; the phase shifting network is connected to the ultra-high frequency antenna group.

[0010] Preferably, the planar antenna array includes three UHF antenna groups, namely a first UHF antenna group, a second UHF antenna group and a third UHF antenna group, and the power division and phase shifting network are respectively connected to the first UHF antenna group, the second UHF antenna group and the third UHF antenna group.

[0011] Preferably, the first UHF antenna group, the second UHF antenna group and the third UHF antenna group are placed in the same plane to form a 3×3 9-element planar antenna array. By forming the first UHF antenna group, the second UHF antenna group and the third UHF antenna into 9 array elements with different feeding powers, the side lobes of the antenna array can be reduced while the spatial gain outside the main radiation area decreases rapidly, reducing the probability of cross-reading. At the same time, the 9-element planar antenna array composed of the first UHF antenna group, the second UHF antenna group and the third UHF antenna group compresses the beam widths in two orthogonal directions in the horizontal plane, improves the gain in the main radiation direction of the antenna and the effective aperture of the antenna, and thus enhances the recognition ability of the system.

[0012] Preferably, the power division network includes a power division input branch and multiple power division output branches, the power division input branch is respectively connected to the multiple power division output branches, and the power division output branches are respectively connected to the ultra-high frequency antenna group and the phase shift network; the phase shift network includes a phase shift branch and a control port, and the control port is connected to the phase shift branch; the ultra-high frequency reader module is connected to the power division input branch and the control port.

[0013] Preferably, the UHF reader / writer module inputs the UHF RFID signal through the power division input branch of the power division phase shifting network, and the input RFID signal is equally divided into three outputs through the output branch of the power division network; correspondingly, the output branch includes a first power division output branch, a second power division output branch and a third power division output branch, and the power distribution ratio of the first power division output branch, the second power division output branch and the third power division output branch is 1:1:1.

[0014] Preferably, the phase-shifting branch includes a first phase-shifting branch and a second phase-shifting branch. The second power-dividing output branch is connected to the second UHF antenna group after being phase-shifted by the first phase-shifting branch, and its signal phase lags / advances an integral multiple of a reference phase of 22.5°; the third power-dividing output branch is connected to the third UHF antenna group after being phase-shifted by the second phase-shifting branch, and its signal phase lags / advances an integral multiple of a reference phase of 45°; the first power-dividing output branch is connected to the first UHF antenna group, and its output signal phase is a reference phase. The UHF reader-writer module inputs an UHF RFID signal through the power-dividing input branch of the power-dividing phase-shifting network. The input RFID signal is equally divided into three outputs through the power-dividing network. The first power-dividing output branch is connected to the first UHF antenna group, the second power-dividing output branch is connected to the second UHF antenna group after being phase-shifted by the first phase-shifting branch, and the third power-dividing output branch is connected to the third UHF antenna group after being phase-shifted by the second phase-shifting branch. By setting the phase lag or advance angle of the first phase-shift branch and the second phase-shift branch of the power division phase-shift network, the antenna array can automatically scan the beam in a specific direction, thereby improving the ability of the UHF RFID system to identify moving targets and reducing the occurrence of missed reads.

[0015] Preferably, the feeding power ratios of the first UHF antenna group and the third UHF antenna group are both 1:1:1, and the feeding power ratio of the second UHF antenna group is 1:8:1.

[0016] Preferably, the first phase-shift branch and the second phase-shift branch are both composed of 4 high- and low-pass PIN diode phase-shift units to form a 4-bit digital phase-shift network with a phase-shift resolution of 22.5°, wherein the high- and low-pass PIN diode phase-shift network refers to an electrical network containing a high-pass filter branch and a low-pass filter branch of a PIN diode, the high-pass filter branch has a phase-frequency characteristic of phase lead, and the low-pass filter branch has a phase-frequency characteristic of phase lag, and by controlling the on and off of the PIN diode, the signal selects the high-pass branch or the low-pass branch to achieve the desired phase lag or lead. 4-bit digital refers to a circuit with 4 high- and low-pass filter units, which are controlled by 4-bit digital signals respectively, so the phase-shift resolution of the phase-shift network is 3600 / 24, i.e., 22.5°, and the phase-shift range is -180° to 180°, a negative phase-shift angle indicates a phase lag, and a positive phase-shift angle indicates a phase lead.

[0017] Compared with the prior art, the present invention has the following beneficial effects: a planar antenna array is used to replace a traditional single antenna system or a multi-antenna system, and by allocating the feeding amplitude and phase of the planar antenna array, precise control of the radiation boundary of the ultra-high frequency RFID identification system and beam scanning in a specific direction are achieved, thereby reducing the probability of cross-reading and missed reading and improving the robustness of the RFID identification process. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is an overall block diagram of the ceiling UHF RFID system of the UHF RFID identification system of the present invention;

[0019] Figure 2 It is a block diagram of the first UHF antenna group of the UHF RFID identification system of the present invention;

[0020] Figure 3 It is a topological schematic diagram of the planar array antenna elements of the ultra-high frequency RFID identification system of the present invention;

[0021] Figure 4 It is a block diagram of the power division and phase shifting network of the ultra-high frequency RFID identification system of the present invention;

[0022] Figure 5 It is a block diagram of the phase shift branch composition of the UHF RFID identification system of the present invention;

[0023] Figure 6 It is a principle diagram of a phase-shift branch unit of an ultra-high frequency RFID identification system of the present invention;

[0024] Figure 7 It is a schematic diagram of beam scanning of an ultra-high frequency RFID identification system of the ultra-high frequency RFID identification system of the present invention;

[0025] Wherein: 1-planar antenna array, 101-first UHF antenna group, 1011-first UHF antenna group array element 1, 1012-first UHF antenna group array element 2, 1013-first UHF antenna group array element 3, 1014-first UHF antenna group feeding structure, 102-second UHF antenna group, 103-third UHF antenna group, 2-power division phase shift network, 201-power division network, 2011-power division input branch, 2012-first power division output branch, 2013-second power division output branch, 2014-third power division output branch, 202-phase shift network, 2021-first phase shift branch, 20211-first phase shift branch high-low pass PIN phase shift unit 1, 2022-second phase shift branch, 2023-control port, 3-UHF reader / writer module. DETAILED DESCRIPTION

[0026] The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the protection scope of the present invention.

[0027] Embodiment: The UHF RFID identification system comprises a planar antenna array 1, a power division phase shift network 2 and an UHF reader / writer module 3, wherein the planar antenna array 1 comprises a plurality of UHF antenna groups, and the plurality of UHF antenna groups are coplanarly placed; the power division phase shift network 2 is respectively connected to the UHF antenna group and the UHF reader / writer module 3; the plurality of UHF antenna groups are coplanarly placed to form a planar antenna array, wherein the UHF antenna group is used for radiating the UHF signal in a specific space; the power division phase shift network 2 is used to change the UHF antenna group. The amplitude and phase of the high-frequency antenna group signal realize automatic scanning of the antenna beam in a specific space; the UHF reader module 3 is used for modulation and transmission of UHF signals, demodulation and reception, and phase control of the power division and phase shifting network; the UHF antenna group includes a plurality of linearly arranged antenna array elements and an independent feeding structure, and the feeding power ratio is 1:1 to 8:1; the power division and phase shifting network 2 includes a power division network 201 and a phase shifting network 202, and the power division network 201 is connected to the phase shifting network 202 and the UHF antenna group respectively; the phase shifting network 202 is connected to The UHF antenna groups are connected; the planar antenna array 1 includes three UHF antenna groups, namely the first UHF antenna group 101, the second UHF antenna group 102 and the third UHF antenna group 103, and the power division phase shift network 2 is respectively connected to the first UHF antenna group 101, the second UHF antenna group 102 and the third UHF antenna group 103; the first UHF antenna group 101, the second UHF antenna group 102 and the third UHF antenna group 103 are placed in the same plane to form a 3×3 9-element planar antenna array 1; by The high frequency antenna group 101, the second ultra-high frequency antenna group 102 and the third ultra-high frequency antenna 13 form 9 array elements with different feeding powers, which can reduce the side lobes of the antenna array while rapidly reducing the spatial gain outside the main radiation area, thereby reducing the probability of cross-reading; at the same time, the 9-element planar antenna array 1 composed of the first ultra-high frequency antenna group 101, the second ultra-high frequency antenna group 102 and the third ultra-high frequency antenna 13 compresses the beam width in two orthogonal directions in the horizontal plane, improves the gain in the main radiation direction of the antenna and the effective aperture of the antenna, thereby enhancing the recognition ability of the system. The feeding power ratios of the first ultra-high frequency antenna group 101 and the third ultra-high frequency antenna group 103 are both 1:1:1, and the feeding power ratio of the second ultra-high frequency antenna group 102 is 1:8:1;

[0028] The power division network 201 includes a power division input branch 2011 and multiple power division output branches, the power division input branch 2011 is respectively connected to multiple power division output branches, and the power division output branches are respectively connected to the UHF antenna group and the phase shift network 202; the phase shift network 202 includes a phase shift branch and a control port 2023, and the control port 2023 is connected to the phase shift branch; the UHF reader module 3 is connected to the power division input branch 2011 and the control port 2023; the UHF reader module 3 inputs the UHF RFID signal through the power division input branch 2011 of the power division phase shift network 2, and the input RFID signal is equally divided into 3 outputs through the output branch of the power division network 2; correspondingly, the output branch includes a first power division output branch 2012, a second power division output branch 2013 and a The third power division output branch 2014, the power distribution ratio of the first power division output branch 2012, the second power division output branch 2013 and the third power division output branch 2014 is 1:1:1; the phase shift branch includes a first phase shift branch 2021 and a second phase shift branch 2022, the second power division output branch 2013 is connected to the second ultra-high frequency antenna group 102 after being phase shifted by the first phase shift branch 2021, and its signal phase lags / leads the reference phase by an integer multiple of 22.5°; the third power division output branch 2014 is connected to the third ultra-high frequency antenna group 103 after being phase shifted by the second phase shift branch 2022, and its signal phase lags / leads the reference phase by an integer multiple of 45°; the first power division output branch 2012 is connected to the first ultra-high frequency antenna group 101, and its output signal phase is the reference phase.

[0029] The UHF reader / writer module 3 inputs the UHF RFID signal through the power division input branch 2011 of the power division phase shift network 2. The input RFID signal is equally divided into three outputs through the power division network 201. The first power division output branch 2012 is connected to the first UHF antenna group 101, the second power division output branch 2013 is connected to the second UHF antenna group 102 after phase shifting through the first phase shift branch 2021, and the third power division output branch 2014 is connected to the third UHF antenna group 103 after phase shifting through the second phase shift branch. The first phase-shift branch 2021 and the second phase-shift branch 2022 are both composed of 4 high- and low-pass PIN diode phase-shift units to form a 4-bit digital phase-shift network with a phase-shift resolution of 22.5°. The high- and low-pass PIN diode phase-shift network refers to an electrical network containing a high-pass filter branch and a low-pass filter branch of a PIN diode. The high-pass filter branch has a phase-frequency characteristic of phase advance, while the low-pass filter branch has a phase-frequency characteristic of phase lag. By controlling the on and off of the PIN diode, the signal selects the high-pass branch or the low-pass branch to achieve the desired phase lag or advance. The 4-bit digital refers to a circuit with 4 high- and low-pass filter units, which are controlled by 4-bit digital signals respectively. Therefore, the phase-shift resolution of the phase-shift network 202 is 3600 / 24, that is, 22.5°, and the phase-shift range is -180° to 180°. A negative phase-shift angle indicates a phase lag, and a positive phase-shift angle indicates a phase advance.

[0030] Specifically, Figure 1 As shown, the ceiling UHF RFID inventory antenna of this embodiment includes a planar antenna array 1, a power division phase shift network 2, and an UHF reader / writer module 3; the planar antenna array 1 includes a first UHF antenna group 101, a second UHF antenna group 102 and a third UHF antenna group 103, which are used for radiating UHF signals in a specific space; the power division phase shift network 2 is respectively connected to the first UHF antenna group 101, the second UHF antenna group 102 and the third UHF antenna group 103, and is used to change the signal amplitude and phase of the UHF antenna group 12 and the UHF antenna group 13, so as to realize automatic scanning of the antenna beam in a specific space; the UHF reader / writer module 3 is connected to the input end 2011 and the control end of the power division phase shift network 2, and is used for modulation and transmission of UHF signals, demodulation and reception, and phase control of the power division phase shift network.

[0031] like Figure 2 As shown, the first UHF antenna group 101 includes three linearly arranged first UHF antenna group array elements 1 1011, first UHF antenna group array element 2 1012, first UHF antenna group array element 3 1013 and an independent feeding structure 1014; the second UHF antenna group 102, the third UHF antenna group 103 and the first UHF antenna group 101 have the same topological arrangement form; as shown Figure 3As shown, the first UHF antenna group 101, the second UHF antenna group 102 and the third UHF antenna group 103 are placed in the same plane to form a 3×3 9-element planar array; the 9 array elements of the planar array adopt a non-uniform feeding method, and the feeding power ratio of the first UHF antenna group element 1 1011, the first UHF antenna group element 2 1012, and the first UHF antenna group element 3 1013 of the first UHF antenna group 1 is 1:1:1, and the feeding power ratio of the second UHF antenna group element 1, the second UHF antenna group element 2 and the second UHF antenna group element 3 in the second UHF antenna group 102 is 1:8:1, and the feeding power ratio of the third UHF antenna group element 1, the third UHF antenna group element 2 and the third UHF antenna group element 3 of the third UHF antenna group 103 is 1:1:1, that is, the feeding amplitude matrix of the planar array 1 is:

[0032]

[0033] like Figure 4 As shown, the power division and phase shifting network 2 includes a power division network 201 and a phase shifting network 202. The power division network 201 consists of an input branch 2011, a first power division output branch 2012, a second power division output branch 2013, and a third power division output branch 2014. The power distribution ratio of the first power division output branch 2012, the second power division output branch 2013, and the third power division output branch 2014 is 1:1:1. The phase shifting network 202 consists of a first phase shifting branch 2021, a second phase shifting branch 2022, and a control port 2013. The UHF reader / writer module 3 inputs the UHF RFID signal through the power division input branch 2011 of the power division phase shift network 2. The input RFID signal is equally divided into three outputs through the power division network 201. The first power division output branch 2012 is connected to the first UHF antenna group 101. The second power division output branch 2013 is connected to the second UHF antenna group 102 after phase shifting through the first phase shift branch 2021. The third power division output branch 2014 is connected to the third UHF antenna group 103 after phase shifting through the second phase shift branch. Specifically, in this embodiment, the phase of the output signal of the first power division output branch 2012 is the reference phase, the phase of the output signal of the first phase shift branch 2021 is an integer multiple of 22.5° behind or ahead of the first power division output branch 2012, and the phase of the output signal of the second phase shift branch 2022 is an integer multiple of 45° behind or ahead of the first power division output branch 2012.

[0034] In this embodiment, the first phase-shifting branch 2021 and the second phase-shifting branch 2021 have the same structure and parameters. Figure 5As shown, the first phase shift branch 2021 is composed of a first phase shift branch high-low pass PIN phase shift unit 20221, a first phase shift branch high-low pass PIN phase shift unit, a first phase shift branch high-low pass PIN phase shift unit, and a first phase shift branch high-low pass PIN phase shift unit to form a 4-bit digital phase shift network, as shown in FIG. Figure 6 As shown. Specifically, the parallel inductor Lp and the series capacitor Cs form a π-type high-pass branch, PIN diodes PIN1 and PIN2 control the conduction or shutdown of the high-pass branch, the series inductor Ls and the parallel capacitor Cp form a π-shaped low-pass branch, and PIN diodes PIN3 and PIN4 control the conduction or shutdown of the low-pass branch. The series capacitors C1 and C2 are AC coupling capacitors between different phase shifting units. R1 and R2 are current limiting resistors of the control loop, RFC is an RF choke inductor to prevent ultra-high frequency signals from entering the control loop, BIT0 is the control signal, when BIT0 is positive polarity, the high-pass branch is turned on and the low-pass branch is turned off, when BIT0 is negative polarity, the low-pass branch is turned on and the high-pass branch is turned off. The four high- and low-pass PIN phase shifting units have the same circuit structure, and the circuit element parameters are determined by the following formula:

[0035]

[0036] Among them, B n is the admittance of the parallel elements in the high-pass branch and the low-pass branch, X n is the reactance of the parallel elements in the high-pass branch and the low-pass branch, and Δφ is the desired phase shift. Specifically, in this embodiment, the phase shift of the high-low pass PIN phase shift unit 1 20211 of the first phase-shifting branch is 22.5°, the phase shift of the high-low pass PIN phase shift unit 2 of the first phase-shifting branch is 45°, the phase shift of the high-low pass PIN phase shift unit 3 of the first phase-shifting branch is 90°, and the phase shift of the high-low pass PIN phase shift unit 4 of the first phase-shifting branch is 180°; wherein, the structures of the high-low pass PIN phase shift unit 2 of the first phase-shifting branch, the high-low pass PIN phase shift unit 3 of the first phase-shifting branch, and the high-low pass PIN phase shift unit 4 of the first phase-shifting branch are the same as those of the high-low pass PIN phase shift unit 1 of the first phase-shifting branch. Therefore, the phase shift resolution of the 4-bit digital phase shifter is 22.5°, and the phase shift range is -180° to 180°. By controlling the phase shift of the second UHF antenna group 102 and the third UHF antenna group 103, the UHF RFID identification system can achieve beam scanning in a certain range in a specific direction, such as Figure 7 shown.

[0037] For ordinary technicians in this field, the specific embodiments are only illustrative descriptions of the present invention. It is obvious that the specific implementation of the present invention is not limited to the above-mentioned methods. As long as various non-substantial improvements are made using the method concepts and technical solutions of the present invention, or the concepts and technical solutions of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. An ultra-high frequency RFID identification system, characterized in that: It includes a planar antenna array, a power division phase shift network and an ultra-high frequency reader / writer module. The planar antenna array includes multiple ultra-high frequency antenna groups, and the multiple ultra-high frequency antenna groups are placed in the same plane; the power division phase shift network is respectively connected to the ultra-high frequency antenna groups and the ultra-high frequency reader / writer module.

2. The UHF RFID identification system according to claim 1, characterized in that: The ultra-high frequency antenna group includes a plurality of linearly arranged antenna array elements and an independent feeding structure, and the feeding power ratio is 1:1 to 8:

1.

3. The UHF RFID identification system according to claim 2, characterized in that: The power division and phase shifting network comprises a power division network and a phase shifting network. The power division network is connected to the phase shifting network and the ultra-high frequency antenna group respectively; the phase shifting network is connected to the ultra-high frequency antenna group.

4. The UHF RFID identification system according to claim 3, characterized in that: The planar antenna array includes three UHF antenna groups, namely a first UHF antenna group, a second UHF antenna group and a third UHF antenna group. The power division and phase shifting network are respectively connected to the first UHF antenna group, the second UHF antenna group and the third UHF antenna group.

5. The UHF RFID identification system according to claim 2, characterized in that: The first UHF antenna group, the second UHF antenna group and the third UHF antenna group are placed in the same plane to form a 3×3 9-element planar antenna array.

6. The UHF RFID identification system according to claim 4, characterized in that: The power division network includes a power division input branch and multiple power division output branches, the power division input branch is respectively connected to the multiple power division output branches, and the power division output branches are respectively connected to the ultra-high frequency antenna group and the phase shift network; the phase shift network includes a phase shift branch and a control port, and the control port is connected to the phase shift branch; the ultra-high frequency reader module is connected to the power division input branch and the control port.

7. The UHF RFID identification system according to claim 6, characterized in that: The UHF reader / writer module inputs an UHF RFID signal through the power division input branch of the power division phase shifting network, and the input RFID signal is equally divided into three outputs through the output branch of the power division network; correspondingly, the output branch includes a first power division output branch, a second power division output branch and a third power division output branch, and the power distribution ratio of the first power division output branch, the second power division output branch and the third power division output branch is 1:1:

1.

8. The UHF RFID identification system according to claim 7, characterized in that: The phase shift branch includes a first phase shift branch and a second phase shift branch, the second power division output branch is connected to the second UHF antenna group after being phase shifted by the first phase shift branch, and its signal phase lags / leads the reference phase by an integer multiple of 22.5°; The third power division output branch is connected to the third UHF antenna group after being phase-shifted by the second phase-shifting branch, and its signal phase lags / leads the reference phase by an integer multiple of 45°; The first power division output branch is connected to the first ultra-high frequency antenna group, and the output signal phase thereof is a reference phase.

9. The UHF RFID identification system according to claim 5, characterized in that: The feeding power ratios of the first UHF antenna group and the third UHF antenna group are both 1:1:1, and the feeding power ratio of the second UHF antenna group is 1:8:

1.

10. The UHF RFID identification system according to claim 8, characterized in that: The first phase-shift branch and the second phase-shift branch are both composed of four high-low pass PIN diode phase-shift units to form a 4-bit digital phase-shift network with a phase-shift resolution of 22.5°.

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