A reader antenna

Abstract

The application provides a reader antenna. The reader antenna comprises a radio frequency channel, a switch circuit, a switch signal generator, a quadrature coupler and an antenna radiation unit. The radio frequency channel is electrically connected to the switch circuit and the switch signal generator. The switch circuit is electrically connected to the quadrature coupler. The quadrature coupler is electrically connected to the antenna radiation unit. The radio frequency channel transmits RF signals to the switch circuit and distributes part of the signals to the switch signal generator. The switch signal generator generates a control signal based on the received signals and transmits the control signal to the switch circuit. The switch circuit selects a corresponding switch channel using the received control signal and inputs the signal into the quadrature coupler connected to the switch channel. The quadrature coupler matches different input signals and changes the phase of two output signals, thereby changing the polarization mode of the antenna radiation unit. The automatic switching of left-handed circular polarization and right-handed circular polarization in the UHF frequency band is realized.

Description

Technical Field

[0001] This application relates to the field of wireless communication, and more specifically, to a reconfigurable reader antenna capable of automatically switching between left and right circular polarization. Background Technology

[0002] Currently, in recent years, RFID technology has been widely used in traffic management systems, access control, item identification and tracking, attracting widespread attention. The main components of an RFID system are RFID readers, reader antennas, and tags. The widespread use of this technology requires tags to be small and inexpensive, and the reader is a key factor determining the overall system performance. Typically, readers have high gain, wide bandwidth, and polarization suitable for matching the reader's orientation and ensuring proper communication. However, problems such as polarization mismatch and multipath interference exist in RFID systems. To address these issues, numerous studies and solutions have been proposed.Some studies have focused on innovative CP antenna designs [such as J. Guo, J. Ouyang, Y. Yan, S. Zhang and Z. Lu, "Compact Circular Polarization Antenna Based on Slot Structure for UHF RFID Handheld Reader," 2018 IEEE International Symposium on Antennas and Propagation & USNC / URSI National Radio Science Meeting, 2018, pp. 331-332, doi:10.1109 / APUSNCURSINRSM.2018.8608323, and P. Janpangngern and C. Phongcharoenpanich, "Circularly polarized single-fed wide-slot antenna for UHF RFID reader," 2017 International Symposium on Antennas and Propagation (ISAP), 2017, pp. 1-2, doi: 10.1109 / ISANP.2017.8228870, while other studies utilize the concept of reconfigurability to flexibly switch between online and circular polarization states [e.g., D. Duraj, K. Nyka and M. Rzymowski, "Dual polarization antennas for UHF RFID readers," 2014 20th International Conference on Microwaves, Radar and Wireless Communications (MIKON), 2014, pp. 1-4, doi: 10.1109 / MIKON.2014.6899830 and P. Parthiban, B.-C. Seetand XJLi, "Low-cost low-profile UHF RFID reader antenna with reconfigurable beams and polarizations," 2017 IEEE International Conference on...]. [Revealed in RFID (RFID), 2017, pp. 81-87, doi:10.1109 / RFID.2017.7945591].However, even when both solutions are applied simultaneously, the inefficiency caused by polarization matching still exists. Therefore, a scheme was proposed that allows the polarization to be switched between left-handed circular polarization (LHCP) and right-handed circular polarization (RHCP) [as revealed in the literature W. Lin and H. Wong, "Wideband Circular Polarization Reconfigurable Antenna," in IEEE Transactions on Antennas and Propagation, vol. 63, no. 12, pp. 5938-5944, Dec. 2015, doi: 10.1109 / TAP. 2015. 2489210 and X. Yi, L. Huitema and H. Wong, "Polarization and Pattern Reconfigurable Cuboid Quadrifilar Helical Antenna," in IEEE Transactions on Antennas and Propagation, vol. 66, no. 6, pp. 2707-2715, June 2018, doi: 10.1109 / TAP. 2018. 2816785].

[0003] However, these solutions fall into two categories: one category achieves reconfigurable antenna polarization by manually controlling the DC voltage, which is not suitable for high-speed detection scenarios; the other category requires programming control, which necessitates additional programming devices and increases the complexity of the design. Summary of the Invention

[0004] To overcome the aforementioned shortcomings, the purpose of this application is to propose a reconfigurable reader antenna that can automatically switch between left and right circular polarization, addressing the polarization reconfiguration method of polarization-reconfigurable antennas. This antenna automatically switches polarization modes, allowing the reading of electronic marks of any polarization within the antenna's radiation lobe. This achieves wide polarization coverage within the antenna's power irradiation range.

[0005] To achieve the above objectives, this application adopts the following technical solution:

[0006] A reader antenna, comprising:

[0007] RF path, switching circuit, switching signal generator, quadrature coupler, and antenna radiating element.

[0008] The radio frequency path is electrically connected to the switching circuit and the switching signal generator, respectively.

[0009] The switching circuit is electrically connected to the quadrature coupler.

[0010] The orthogonal coupler is electrically connected to the antenna radiating element.

[0011] The RF signal is transmitted to the switching circuit through the radio frequency path, and a portion of the signal is distributed to the switching signal generator. The switching signal generator generates a control signal based on the received signal and transmits it to the switching circuit. The switching circuit uses the received control signal to select the corresponding switching path and inputs the signal to the cross-coupler connected to it. The quadrature coupler matches different input signals, and the phase of the two output signals changes, thereby changing the polarization of the antenna radiating element.

[0012] Preferably, the antenna radiating element includes: a first radiating plate, a copper pillar, and a second radiating plate.

[0013] The first radiating plate includes two orthogonal coupling branches, a first substrate, and a bottom radiating plate. The two orthogonal coupling branches are disposed on one side of the first substrate, and the bottom radiating plate is located on the side of the first substrate opposite to the coupling branches.

[0014] The second radiating plate includes a second substrate, on one side of which a feeding network is disposed, and on the side opposite the feeding network a metal ground plane is disposed.

[0015] One side of the copper pillar is electrically connected to the coupling stub, and the other end is connected to the feed network.

[0016] Preferably, the coupling stub is provided with a feed point, which is electrically connected to the copper pillar.

[0017] Preferably, the feed point is used to generate an excitation current on the coupling stub, and couple the energy to the bottom radiating substrate through the capacitance effect of the first substrate, and emit radio frequency energy on the bottom radiating substrate.

[0018] Preferably, there is a gap between the first radiating plate and the second radiating plate.

[0019] Preferably, the switching circuit is a radio frequency absorption type single-pole double-throw switch.

[0020] Preferably, the radio frequency path includes an RF and DC combining module, which is used to extract the DC signal from the received RF and DC mixed signal.

[0021] Preferably, the combining module uses a quarter-wavelength line.

[0022] Preferably, the switching circuit includes:

[0023] A directional coupler with a coupling degree of 26dB is provided. The coupling output terminal of the directional coupler is electrically connected to a rectifier circuit, which converts the acquired modulation signal into a rectangular pulse signal.

[0024] A voltage amplifier, connected to the output of a rectifier circuit, is used to amplify the input rectangular pulse.

[0025] The SR trigger receives amplified pulses and outputs a rectangular wave to a switch to achieve automatic switching between left-hand circular polarization and right-hand circular polarization in the UHF band.

[0026] Preferably, the rectangular wave output by the SR trigger distinguishes adjacent periods of the reader antenna, and its output level remains unchanged within each period.

[0027] Beneficial effects

[0028] Compared to existing technologies, the reader antenna proposed in this application achieves automatic switching between left-hand and right-hand circular polarization within the UHF band. It covers all electronic tags with different polarizations within the effective radiation lobe of the reader antenna, further improving the tag reading success rate. The antenna's radiating element employs a capacitively coupled feeding method, reducing the antenna's size and profile height, thus facilitating cost reduction and installation in practical applications. Attached Figure Description

[0029] Figure 1 This is a block diagram illustrating the principle of an RFID antenna with automatic left-right circular polarization switching for a reader antenna according to an embodiment of this application.

[0030] Figure 2 This is a schematic diagram illustrating the radio frequency path and switching signal generator functions according to an embodiment of this application.

[0031] Figure 3 This is an internal block diagram of an absorption-type single-pole double-throw radio frequency switch according to an embodiment of this application.

[0032] Figure 4 This is a schematic diagram of the orthogonal coupler structure according to an embodiment of this application.

[0033] Figure 5 This is a schematic diagram of the antenna radiating element according to an embodiment of this application.

[0034] Figure 6 This is a schematic diagram showing the antenna gain and axial ratio of the reader antenna according to an embodiment of this application.

[0035] Figure 7 This is the radiation pattern of a left-hand circularly polarized antenna for a reader antenna according to an embodiment of this application.

[0036] Figure 8 This is a right-hand circularly polarized antenna radiation pattern of the reader antenna according to an embodiment of this application. Detailed Implementation

[0037] The above-described solution will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application. The implementation conditions used in the embodiments may be further adjusted according to the conditions of specific manufacturers, and the implementation conditions not specified are generally those in routine experiments.

[0038] The reader antenna of this application will now be described with reference to the accompanying drawings.

[0039] like Figure 1 The diagram shown is a functional block diagram of the automatic switching of left and right circular polarization of the reader antenna (also known as an ultra-high frequency RFID reader antenna).

[0040] The reader antenna includes: an RF path, a switching circuit, a switching signal generator, an orthogonal coupler, and an antenna radiating element.

[0041] The radio frequency path is electrically connected to the switching circuit and the switching signal generator, respectively.

[0042] The majority of the RF signal is transmitted to the electrically connected switching circuit via the radio frequency path, while a small portion of the signal is allocated to the switching signal generator.

[0043] The switching signal generator generates a control signal based on the received signal and transmits it to the switching circuit. The switching circuit uses the received control signal to select the corresponding switching path and inputs the signal to the cocoupler connected to it.

[0044] This orthogonal coupler matches different input signals, and the phase of the two output signals changes, thereby altering the polarization of the subsequent antenna. In this embodiment, the antenna radiating element is a dual-input orthogonal antenna. Thus, it achieves left or right polarization of the antenna by varying the phase of the input signals, and can automatically switch between left and right circular polarization, enabling operation at medium to long distances.

[0045] The functional block diagram of the reader antenna is as follows: Figure 2 As shown,

[0046] The RF path includes a directional coupler and a DC block unit. The directional coupler includes a switch, the first end of which is electrically connected to a switch signal generator (DC extraction unit of the switch signal generator), the third end of which is electrically connected to the RF rectification module of the switch signal generator, the second end of which is electrically connected to one end of the DC block unit, and the other end of the DC block unit is electrically connected to a switching circuit. The switching circuit has a first output terminal RHCP (e.g., right-hand circular polarization) and a second output terminal LHCP (e.g., left-hand circular polarization). The output terminal of the RF rectification module is electrically connected to a signal amplification unit (envelope signal amplification), the output of which is electrically connected to a periodic signal extraction unit, and the periodic signal extraction unit is electrically connected to the switching circuit. In this embodiment, the DC extraction unit uses a quarter-wavelength line to convert a far-end RF short circuit into a near-end RF open circuit, while simultaneously allowing DC to pass through. The directional coupler has a coupling degree of 26dB, and its coupled output terminal is electrically connected to the rectifier circuit to convert the acquired modulated signal into a rectangular pulse signal. The signal amplification unit, also known as a voltage amplifier, is connected to the output of the RF rectifier circuit. It amplifies the input rectangular pulse (pulse amplitude is increased). The amplified pulse is then input to the envelope signal amplification unit (sometimes an SR trigger). The rectangular wave output by the SR trigger is fed to the switch, and this output distinguishes adjacent cycles of the RFID reader. Furthermore, its output level remains constant within each cycle. This achieves automatic switching between left-hand and right-hand circular polarization in the UHF band. The combination of the RF rectifier module and the DC extraction unit is also called an RF and DC combining module.

[0047] The switching circuit uses a radio frequency absorption type single-pole double-throw switch, and its internal circuit block diagram is as follows: Figure 3 As shown, ports J1 and J2 are output terminals, which are grounded through an internal 50Ω impedance when not connected to the common input terminal RFC. A two-digit control signal V1 and V2 are used to switch between them. The truth table of the control signals is shown in Table 1. In this embodiment, the single-pole double-throw switch is model SKY13348-374LF.

[0048] Table 1

[0049]

[0050] The orthogonal coupler adopts a traditional branch-line coupler structure, and its structure and parameters are as follows: Figure 4 As shown.

[0051] When the input port 41 of the coupler changes, the phase difference between its two output ports 42 changes by 180 degrees. That is, a 90-degree phase difference will become -90 degrees.

[0052] like Figure 5 The diagram shows the structure of an antenna radiating element.

[0053] The antenna radiating element includes a first radiating plate 10, a copper pillar 20, and a second radiating plate 30, wherein the first radiating plate and the second radiating plate are connected by the copper pillar.

[0054] The first radiant panel is located on the upper side of the metal floor.

[0055] The radiating plate includes two orthogonally coupled branches 11, a first substrate 12, and a bottom radiating base plate 13.

[0056] Two orthogonally coupled stubs 11 are disposed on one side (top side) of a first substrate, the side of the first substrate opposite to the coupled stubs having a bottom radiating plate (this side is close to the metal ground plane).

[0057] The second radiating plate includes a second substrate 32, on one side of which a power supply network 31 is disposed, and on the side opposite the power supply network a metal ground 33 (also referred to as a ground plane of finite size) is disposed.

[0058] One side of the copper pillar 20 is electrically connected to the corresponding coupling stub 11, and the other end is connected to the feed network 31. In this embodiment, the first substrate 12 and the second substrate 32 are respectively made of FR4 substrate with a relative permittivity of ε. r =4.4, loss tangent is σ=0.001. There is a gap between the first and second radiating plates, that is, the first and second radiating plates are separated by air. There is a feed point on each of the two coupling branches, which is used to electrically connect and fix to the metal ground plane with copper pillars. In this embodiment, unlike the direct feeding of traditional microstrip flat panel antennas, the significance of using capacitive coupling feeding is to reduce the antenna size and profile height. Specifically, excitation current is generated on the coupling branches on the radiating plates through the two feed points, and the energy is coupled to the radiating element through the substrate capacitance effect, and the radio frequency energy is emitted from the radiating element. The reader antenna automatically switches between left-hand circular polarization and right-hand circular polarization in the UHF band. All electronic tags with different polarizations are covered within the effective radiation lobe of the reader antenna, further improving the tag reading success rate. The reader antenna can be left-hand and right-hand polarized in the 840MHz-928MHz range.

[0059] In this embodiment, the parameters of the reader antenna are as follows:

[0060] T xy =135mm, P xy =130mm, H1=1.6mm, G xy =160mm, H1=1.6mm, H2=1.6mm, H3=13mm,

[0061] L = 23.6 mm, W = 6 mm, R = 1.2 mm. The two coupling stubs on the top layer of the radiating plate each have a length of L = 23.6 mm and a width of W = 6 mm. Let the coordinates of the feed points of the two stubs be (x1, y1) and (x2, y2) respectively. After optimization, while ensuring 50 ohms antenna impedance matching, the optimal position of the coupling stubs is...

[0062] x1=y2=d x =1 / 2T xy =67.5mm, x2=y1=d y =1 / 3T xy = 45mm. The dimensions of the metal floor are: side length G xy A square with a diameter of 160mm and a thickness of H2 = 1.6mm, also made of FR4 board.

[0063] Figure 6 Antenna gain (describing the degree to which an antenna concentrates input power for radiation) and axial ratio (representing the purity of circular polarization, an important indicator of the difference in signal gain for different directions) are given. This antenna achieves good 50-ohm impedance matching in the UHF band, with return loss |S 11 The impedance bandwidth of <10dB is 29.5% (0.78-1.05GHz), and the axial ratio bandwidth of 3dB is 20% (0.81-0.99GHz). The gain in both left-hand and right-hand circular polarization can reach 5dBic. The E-plane, H-plane, and overall gain diagrams for different circular polarization directions are shown below. Figure 7 , 8 As shown.

[0064] The above embodiments are only for illustrating the technical concept and features of this application, and are intended to enable those skilled in the art to understand the content of this application and implement it accordingly. They should not be used to limit the scope of protection of this application. All equivalent changes or modifications made in accordance with the spirit and essence of this application should be included within the scope of protection of this application.

Claims

1. A reader antenna, comprising: The application relates to a reader antenna, comprising: a radio frequency channel, a switch circuit, a switch signal generator, a quadrature coupler and an antenna radiation unit, wherein the radio frequency channel is electrically connected to the switch circuit and the switch signal generator, and the radio frequency channel comprises a directional coupler; the switch circuit is electrically connected to the quadrature coupler, and the switch circuit has a first output end RHCP and a second output end LHCP; the switch circuit comprises: a directional coupler with a coupling degree of 26 dB, a coupling output end of the directional coupler is electrically connected to a rectifier circuit, the rectifier circuit converts an acquired modulated signal into a rectangular pulse signal, a voltage amplifier is connected to an output end of the rectifier circuit and is used for amplifying an input rectangular pulse, an SR trigger receives the amplified pulse and outputs a rectangular wave to the switch to realize automatic switching of left-handed circular polarization and right-handed circular polarization in a UHF frequency band; the quadrature coupler is electrically connected to the antenna radiation unit; RF signals are transmitted to the switch circuit through the radio frequency channel, and part of the signals are distributed to the switch signal generator; the switch signal generator generates a control signal based on the received signals and transmits the control signal to the switch circuit; the switch circuit selects a corresponding switch channel by using the received control signal and inputs the signals into the quadrature coupler connected to the switch channel; the quadrature coupler matches different input signals, and the phase of two output signals of the quadrature coupler changes; and the antenna radiation unit is a double-input quadrature antenna, so that the polarization mode of the antenna radiation unit is changed.

2. The reader antenna of claim 1, wherein the antenna radiation unit comprises a first radiation plate, a copper column and a second radiation plate, the first radiation plate comprises two orthogonal coupling branches, a first substrate and a bottom layer radiation bottom plate, the two orthogonal coupling branches are arranged on one side of the first substrate, the first substrate has the bottom layer radiation bottom plate on the side opposite to the coupling branches, the second radiation plate comprises a second substrate, one side of the second substrate is provided with a feed network, and the side opposite to the feed network is provided with a metal ground, and one side of the copper column is electrically connected to the coupling branches, and the other end of the copper column is connected to the feed network.

3. The reader antenna of claim 2, wherein a feed point is arranged on the coupling branches, and the feed point is electrically connected to the copper column.

4. The reader antenna of claim 3, wherein the feed point is used for generating an excitation current on the coupling branches, coupling energy to the bottom layer radiation bottom plate through the capacitive effect of the first substrate, and emitting radio frequency energy on the bottom layer radiation bottom plate.

5. The reader antenna of claim 2, wherein the first radiation plate and the second radiation plate have a gap therebetween.

6. The reader antenna of claim 1, wherein the switch circuit is a radio frequency absorption type single-pole double-throw switch.

7. The reader antenna of claim 1, wherein the radio frequency channel comprises an RF and DC combining module, which is used for extracting DC from a received mixed signal of RF and DC. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 8. A reader antenna as defined in Claim 7, wherein: the combining module employs a quarter wave line.

9. A reader antenna as defined in Claim 7, wherein: the square wave output of the SR flip-flop distinguishes adjacent cycles of the reader antenna and the output level remains constant for each cycle.

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