Miniaturized Four-Arm Helical Antenna for Portable UHF RFID Devices

Abstract

A miniaturized four-arm spiral antenna for a portable UHF RFID device, comprising a dielectric cylinder, four groups of spiral arms and a one-to-four feed network. The four groups of spiral arms are wound around the outer surface of the dielectric cylinder along the axis. The one-to-four feed network has two layers of dielectric substrates. A one-to-two feed network is respectively arranged on the upper surface of the upper dielectric substrate and the lower surface of the lower dielectric substrate. A grounding line is arranged between the two layers of dielectric substrates. The spiral arm includes an L-shaped radiation branch and a short-circuit branch. The L-shaped radiation branches of two groups of spiral arms are connected to the upper one-to-two feed network, and the L-shaped radiation branches of the other two groups of spiral arms are connected to the lower one-to-two feed network. The short-circuit branch is connected to the grounding line. The one-to-four feed network sequentially provides phase differences of 0, -90, -180 and -270 degrees for the four groups of spiral arms, so as to form circular polarization. The miniaturized four-arm spiral antenna has the advantages of miniaturization, high gain and wide beamwidth.

Description

Technical Field

[0001] The present invention relates to the technical field of antennas, and particularly to a miniaturized quadrifilar helix antenna for portable UHF RFID devices. Background Art

[0002] In recent years, due to the rapid development of the Internet of Things, Radio Frequency Identification (RFID) technology has attracted more and more attention. An RFID system generally includes two parts, an RFID reader and a tag, and the RFID reader antenna has a great influence on the performance of the RFID system. Usually in the UHF band (860 - 960 MHz), the RFID system has a larger transmission range and a faster transmission rate. The quadrifilar helix antenna is suitable for use in UHF RFID systems due to its advantages such as circular polarization, heart-shaped pattern, and excellent front-to-back ratio. At present, with the rise of handheld RFID reading and writing devices, there is an urgent need to provide antennas with the characteristics of miniaturization, high gain, and wide beamwidth.

[0003] It should be noted that the information disclosed in the above background art section is only for understanding the background of the present application, and thus may include information that does not constitute the prior art known to those of ordinary skill in the art. Summary of the Invention

[0004] The main object of the present invention is to provide a quadrifilar helix antenna for portable UHF RFID devices, overcoming the deficiencies of traditional antennas in terms of combining miniaturization, high gain, and wide beamwidth.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A miniaturized quadrifilar helix antenna for portable UHF RFID devices includes a dielectric cylinder, four groups of helical arms, and a one-to-four power feeding network. The four groups of helical arms are wound around the outer surface of the dielectric cylinder along the axis. The one-to-four power feeding network has two layers of dielectric substrates. A one-to-two power feeding network is respectively arranged on the upper surface of the upper dielectric substrate and the lower surface of the lower dielectric substrate among the two layers of dielectric substrates. A grounding line is arranged between the two layers of dielectric substrates. Each helical arm includes an L-shaped radiation branch and a short-circuit branch. The L-shaped radiation branches of two groups of helical arms are connected to the upper one-to-two power feeding network, and the L-shaped radiation branches of the other two groups of helical arms are connected to the lower one-to-two power feeding network. The short-circuit branches are connected to the grounding line. The one-to-four power feeding network provides phase differences of 0, -90, -180, and -270 degrees for the four groups of helical arms in sequence, thereby forming circular polarization.

[0007] Furthermore:

[0008] The material of the dielectric cylinder is alumina ceramic.

[0009] The shorting stubs of the four groups of spiral arms are connected to the metal floor through shorting probes. Among them, the L-shaped radiating stubs of 2 groups of spiral arms are directly connected to the upper one-to-two power feeding network, and the L-shaped radiating stubs of the other 2 groups of spiral arms are connected to the lower one-to-two power feeding network through shorting probes.

[0010] The one-to-four power feeding network is fed through a coaxial cable. The inner core of the coaxial cable is connected to the upper one-to-two power feeding network, and the outer conductor of the coaxial cable is connected to the lower one-to-two power feeding network.

[0011] The one-to-two power feeding network includes three sections of microstrip lines and a patch type bridge. The patch type bridge has 6 pins, among which 3 pins are respectively connected to the three sections of microstrip lines, 2 pins are connected to the grounding line through shorting probes. Among them, one section of the microstrip line of the upper one-to-two power feeding network is also connected to the inner core of the coaxial cable, and one section of the microstrip line of the lower one-to-two power feeding network is also connected to the outer conductor of the coaxial cable.

[0012] The three sections of microstrip lines are three sections of 50-ohm microstrip lines.

[0013] The patch type bridge is a patch type 3dB bridge.

[0014] The dielectric substrate is an FR4 dielectric substrate.

[0015] The grounding line is a metal floor.

[0016] The dielectric cylinder is a dielectric cylinder.

[0017] The present invention has the following beneficial effects:

[0018] The present invention provides a miniaturized four-arm spiral antenna, which has the advantages of miniaturization, high gain, and wide beamwidth. While effectively meeting the miniaturization requirements, the four-arm spiral antenna also has a relatively high gain, which can enable the RFID system to maintain a relatively long reading distance. Moreover, it also has a relatively wide beamwidth, which can enable the RFID system to accurately read within a relatively large angular range. The above advantages make the four-arm spiral antenna particularly suitable for use in portable UHF RFID devices. Description of the Drawings

[0019] Figure 1 It is a side view of the four-arm spiral antenna provided by the embodiment of the present invention;

[0020] Figure 2 It is a planar unfolded view of the four-arm spiral antenna provided by the embodiment of the present invention;

[0021] Figure 3 It is a top view of the one-to-four power feeding network provided by the embodiment of the present invention;

[0022] Figure 4 The echo loss curve graph of the four-arm spiral antenna provided by the embodiment of the present invention;

[0023] Figure 5 The axial ratio and gain curve graphs of the four-arm spiral antenna provided by the embodiment of the present invention;

[0024] Figure 6 The axial ratio and gain curve graphs of the four-arm spiral antenna at 915 MHz provided by the embodiment of the present invention;

[0025] Figure 7 The gain radiation pattern of the four-arm spiral antenna at 915 MHz provided by the embodiment of the present invention;

[0026] Explanation of reference numerals: 1, dielectric cylinder; 2, four groups of spiral arms; 2A, radiation branch; 2B, short-circuit branch; 3, one-to-four power feeding network; 4, dielectric substrate; 5, upper one-to-two power feeding network; 6, lower one-to-two power feeding network; 7, metal floor; 8, short-circuit probe; 9, coaxial cable; 10, patch type bridge; 11, plastic screw; 12, three-section microstrip line. Detailed implementation manners

[0027] The following makes a detailed description of the implementation manners of the present invention. It should be emphasized that the following description is merely exemplary and not intended to limit the scope of the present invention and its applications.

[0028] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element. In addition, the connection can be for a fixing function or for a coupling or communication function.

[0029] It should be understood that the orientation or positional relationship indicated by the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the embodiments of the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation to the present invention.

[0030] In addition, the terms "first" and "second" are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the embodiments of the present invention, "a plurality of" means two or more unless otherwise specifically defined.

[0031] Referring to Figures 1 to 3 , an embodiment of the present invention provides a miniaturized quadrifilar helix antenna for a portable UHF RFID device, including a dielectric cylinder 1, four groups of helical arms 2, and a one-to-four power feeding network 3. The dielectric cylinder 1 is preferably a dielectric cylinder. The four groups of helical arms 2 are wound around the outer surface of the dielectric cylinder 1 along the axis. The one-to-four power feeding network 3 has two layers of dielectric substrates 4. One-to-two power feeding networks are respectively disposed on the upper surface of the upper dielectric substrate 4 and the lower surface of the lower dielectric substrate 4 among the two layers of dielectric substrates 4. A grounding line (such as a metal floor 7) is disposed between the two layers of dielectric substrates 4. The helical arm 2 includes an L-shaped radiation branch 2A and a short-circuit branch 2B. The L-shaped radiation branches 2A of two groups of helical arms 2 are connected to the upper one-to-two power feeding network 5, and the L-shaped radiation branches 2A of the other two groups of helical arms 2 are connected to the lower one-to-two power feeding network 6. The short-circuit branch 2B is connected to the grounding line. The one-to-four power feeding network 3 provides phase differences of 0, -90, -180, and -270 degrees for the four groups of helical arms 2 in sequence, thereby forming circular polarization.

[0032] The quadrifilar helix antenna of the embodiment of the present invention has the advantages of miniaturization, high gain, and wide beam. While effectively meeting the miniaturization requirements, as Figures 4 to 7 shown in the test data, it also has a relatively high gain, which can enable the RFID system to maintain a relatively long reading distance, and also has a relatively wide beam width, which can enable the RFID system to accurately read within a relatively large angular range. The above advantages make the quadrifilar helix antenna particularly suitable for use in portable UHF RFID devices.

[0033] In a preferred embodiment, the dielectric cylinder 1 is made of alumina ceramic, which is beneficial to realizing the miniaturization of the antenna.

[0034] Referring to Figures 1 to 2 , in a preferred embodiment, the short-circuit branches 2B of the four groups of helical arms 2 are connected to the metal floor through short-circuit probes 8. The L-shaped radiation branches 2A of two groups of helical arms 2 are directly connected to the upper one-to-two power feeding network 5, and the L-shaped radiation branches 2A of the other two groups of helical arms 2 are connected to the lower one-to-two power feeding network 6 through short-circuit probes 8.

[0035] Referring to Figures 1 to 2, in a preferred embodiment, the one-to-four feed network 3 is fed through a coaxial cable 9. The inner core of the coaxial cable 9 is connected to the upper one-to-two feed network 5, and the outer conductor of the coaxial cable 9 is connected to the lower one-to-two feed network 6.

[0036] Refer to Figure 3 , in a preferred embodiment, the one-to-two feed network includes three microstrip lines 12 and a patch type bridge 10. The patch type bridge 10 has 6 pins, and 3 of the pins are respectively connected to the three microstrip lines 12. Two pins are connected to the grounding line through shorting probes 8. One microstrip line of the upper one-to-two feed network 5 is also connected to the inner core of the coaxial cable 9, and one microstrip line of the lower one-to-two feed network 6 is also connected to the outer conductor of the coaxial cable 9.

[0037] In some embodiments, the three microstrip lines 12 are preferably three 50-ohm microstrip lines. The patch type bridge 10 is preferably a patch type 3dB bridge and serves as a patch type 3dB power divider.

[0038] In some embodiments, the dielectric substrate 4 can be an FR4 dielectric substrate.

[0039] In a preferred embodiment, the grounding line can adopt a metal floor 7.

[0040] The specific embodiments of the present invention are further described below.

[0041] As Figures 1 to 3 shown, a specific embodiment provides a miniaturized four-arm spiral antenna applied to a portable UHF RFID device, including a dielectric cylinder 1 made of alumina ceramic material, four groups of spiral arms 2, and a one-to-four feed network 3 below the dielectric cylinder 1. Among them, the four groups of spiral arms 2 are wound around the outer surface of the dielectric cylinder 1 made of alumina ceramic material around the axis. Each group of spiral arms 2 includes an L-shaped radiation branch 2A and a shorting branch 2B; the one-to-four feed network has two layers of dielectric substrates 4, preferably using FR4 dielectric substrates, and one-to-two feed networks 5, 6 are printed on the upper and lower surfaces of the two layers of dielectric substrates 4, and a metal floor 7 is printed on the intermediate layer; among them, the one-to-two feed networks 5, 6 include three microstrip lines 12 and a patch type bridge 10, preferably using three 50-ohm microstrip lines and a patch type 3dB bridge; in addition, the shorting branch 2B is connected to the metal floor 7 through a shorting probe 8, and two groups of L-shaped radiation branches 2A are connected to the lower one-to-two feed network 6 through shorting probes 8; the one-to-four feed network 3 provides phase differences of 0, -90, -180, and -270 degrees for the four groups of spiral arms in sequence, so as to form circular polarization.

[0042] In this embodiment, the dielectric cylinder 1 is made of alumina ceramic with a high dielectric constant, which is beneficial to miniaturization. The spiral arm 2 includes a radiating L-shaped stub 2A and a shorting stub 2B. The purpose of bending the radiating stub into an L shape is to reduce the axial length, and the function of adding the shorting stub is to improve impedance matching. The one-to-two power divider network 5 or 6 includes a patch-type 3 dB hybrid and three sections of 50-ohm microstrip lines 12. The pins at both ends of the patch-type hybrid 10 are connected to the three sections of microstrip lines 12, and the middle pin is connected to the metal floor 7. The one-to-four power divider network 3 is fed by a coaxial cable 9. The inner core of the coaxial cable 9 is connected to the upper one-to-two power divider network 5, and the outer conductor of the coaxial cable 9 is connected to the lower one-to-two power divider network 6. The function of the one-to-four power divider network 3 is to achieve a 90-degree phase difference and equal-amplitude power at the four output ports, thereby realizing circular polarization. In addition, the output ports A and B of the upper one-to-two power divider network 5 are directly connected to two groups of spiral arms 2, and the output ports C and D of the lower one-to-two power divider network 6 are connected to the other two groups of spiral arms 2 through shorting probes. Finally, the one-to-four power divider network is fixed by plastic screws 11. Refer to Figures 4 to 7 , the four-arm spiral antenna of the embodiment has the advantages of high gain, small size, wide beamwidth, heart-shaped radiation pattern, and excellent front-to-back ratio.

[0043] As Figure 4 shown, the return loss of the antenna is less than -10 dB in the frequency band of 0.8 - 1 GHz; as Figure 5 shown, the average gain of the antenna is 4.5 dB in the UHF RFID frequency band, and the axial ratio is less than 0.08; as Figure 6 shown, the 3 dB gain beamwidth of the antenna is 120 degrees and the 3 dB axial ratio beamwidth is 184 degrees at 915 MHz; as Figure 7 shown, the radiation pattern of the antenna has a front-to-back ratio of 22 dB and a heart-shaped radiation pattern at 915 MHz.

[0044] The background section of the present invention may include background information about the problems or environment of the present invention, rather than necessarily describing the prior art. Therefore, the content included in the background art section is not an admission by the applicant of the prior art.

[0045] The above content is a further detailed description of the present invention in combination with specific / preferred embodiments, and it cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, they can also make several substitutions or modifications to these described embodiments, and these substitution or modification methods should all be regarded as belonging to the protection scope of the present invention. In the description of this specification, the description with reference to terms such as "an embodiment", "some embodiments", "preferred embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. Without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the scope of protection of the patent application.

Claims

1. A miniaturized quadrifilar helix antenna for a portable UHF RFID device, characterized in that, It includes a dielectric cylinder, four groups of spiral arms, and a one-to-four power feeding network. The four groups of spiral arms are wound around the outer surface of the dielectric cylinder along the axis. The one-to-four power feeding network has two layers of dielectric substrates, and the dielectric substrates are FR4 dielectric substrates. The upper surface of the upper dielectric substrate and the lower surface of the lower dielectric substrate in the two layers of dielectric substrates are respectively provided with a one-to-two power feeding network. A grounding line is arranged between the two layers of dielectric substrates, and the grounding line is a metal floor. The spiral arm includes an L-shaped radiation branch and a short-circuit branch. The L-shaped radiation branches of two groups of spiral arms are connected to the upper one-to-two power feeding network, and the L-shaped radiation branches of the other two groups of spiral arms are connected to the lower one-to-two power feeding network. The short-circuit branch is connected to the grounding line. The one-to-four power feeding network provides phase differences of 0, -90, -180, and -270 degrees for the four groups of spiral arms in sequence, so as to form circular polarization.

2. The miniaturized four-arm helical antenna according to claim 1, wherein The material of the dielectric cylinder is alumina ceramic.

3. The miniaturized four-arm spiral antenna according to claim 1, wherein The short-circuit branches of the four groups of spiral arms are connected to the metal floor through short-circuit probes. The L-shaped radiation branches of two groups of spiral arms are directly connected to the upper one-to-two power feeding network, and the L-shaped radiation branches of the other two groups of spiral arms are connected to the lower one-to-two power feeding network through short-circuit probes.

4. The miniaturized four-arm spiral antenna according to claim 1, wherein, The one-to-four power feeding network is fed through a coaxial cable. The inner core of the coaxial cable is connected to the upper one-to-two power feeding network, and the outer conductor of the coaxial cable is connected to the lower one-to-two power feeding network.

5. The miniaturized four-arm spiral antenna according to claim 4, characterized in that, The one-to-two power feeding network includes three sections of microstrip lines and a patch type bridge. The patch type bridge has 6 pins, and 3 of the pins are respectively connected to the three sections of microstrip lines. 2 pins are connected to the grounding line through short-circuit probes. One section of the microstrip line of the upper one-to-two power feeding network is also connected to the inner core of the coaxial cable, and one section of the microstrip line of the lower one-to-two power feeding network is also connected to the outer conductor of the coaxial cable.

6. The miniaturized four-arm spiral antenna according to claim 5, characterized in that, The three sections of microstrip lines are three sections of 50-ohm microstrip lines.

7. The miniaturized four-arm spiral antenna according to claim 5, wherein, The patch type bridge is a patch type 3dB bridge.

8. The miniaturized four-arm spiral antenna according to any one of claims 1 to 7, characterized in that, The dielectric cylinder is a dielectric cylinder.

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