Coplanar waveguide feed broadband circularly polarized antenna

Abstract

The invention discloses a broadband circularly polarized antenna with coplanar waveguide feed. The broadband circularly polarized antenna comprises a rectangular dielectric substrate, a rectangular plate is arranged on the upper surface of the rectangular dielectric substrate, a circular gap is etched in the middle of the upper surface of the rectangular plate, a second Z-shaped branch knot and a first Z-shaped branch knot are arranged on the left side and the right side of the interior of the circular gap respectively, and an L-shaped feed band is arranged at the lower end of the circular gap. The middle part of the lower surface of the rectangular plate is provided with a first rectangular gap for the antenna of the L-shaped feed band to pass through. Triangular gaps are etched in the left upper end and the right lower end of the rectangular plate; arc-shaped long gaps are etched in the right upper end and the left lower end of the rectangular plate; according to the coplanar waveguide feed broadband circularly polarized antenna, the axial ratio frequency band is broadened through optimization design, a plurality of wireless communication frequency bands are covered, and the requirements of a modern communication system for high bandwidth and multi-frequency-band work are met.

Description

Technical Field

[0001] The invention relates to the technical field of communications, in particular to a broadband circularly polarized antenna fed by a coplanar waveguide. Background Art

[0002] With the advancement of communication systems, scholars have been conducting more and more in-depth research on circularly polarized antennas in recent decades. It is precisely because circularly polarized antennas are orthogonal in polarization direction that they are often used in combination with other antennas. Circularly polarized antenna elements are usually used in satellite applications, whether as low-gain unit antennas, high-gain array antennas, or reflector antenna feeds. The main advantages of circularly polarized radiation technology are: 1. Reduce polarization loss: Even if the corresponding terminal of the communication only uses a linearly polarized antenna, it can ensure the reception of electromagnetic waves, thereby improving the stability of the communication link; 2. Avoid Faraday rotation: During satellite communication, due to the influence of the strong magnetic field of the earth's ionosphere, the linearly polarized signal wave will produce a rotation of the polarization plane, the so-called Faraday rotation, and the two orthogonal polarization components of the circularly polarized wave are simultaneously affected by the Faraday rotation effect, thereby eliminating the influence caused by the rotation effect. Circularly polarized antennas are often used in satellite communication systems. Satellite signal transmission is often interfered by the atmosphere and ground objects. Compared with traditional single-polarization antennas, circularly polarized antennas can more effectively suppress multipath fading and reduce the loss caused by polarization mismatch, providing more stable signal transmission and reception quality.

[0003] Due to the growing demand for communication services, many researchers are currently committed to expanding the communication capacity. According to Shannon's theorem, to expand the channel capacity, it is necessary to increase the communication channel bandwidth or improve the signal-to-noise ratio. Bands with higher frequencies than K-band, Ka-band, etc. have larger bandwidths, and the application of various multiple access multiplexing technologies can greatly improve the channel capacity, which is especially suitable for high-speed transmission services. This is undoubtedly of great research value today when frequency resources are scarce. In addition to expanding bandwidth, multi-frequency sharing technology of antennas is also the main development direction of satellite communications. A set of antenna systems can work in multiple frequency bands, which can not only reduce the number of satellite earth stations built and thus control operating costs, but also increase communication capacity to provide better communication services.

[0004] At present, UHF band antennas are often used in RFID readers, military communications, radio and television, and medical equipment due to their strong signal penetration, strong terminal practicality, global coverage, broadcast networking, and guaranteed access. Antennas in the UHF band are often designed for circularly polarized radiation, and many slot antennas with CP radiation have been proposed for use in UHF band RFID readers. However, just like RFID reader antennas, 840-960MHz in the UHF band is the most common application band, and the 485-503MHz band is not used much. Antennas working in this ultra-high frequency band are also mainly three-dimensional antennas, but this type of antenna is not conducive to integration and miniaturization design. In addition, the current broadband circularly polarized antennas cannot meet the needs of modern communication systems for high bandwidth and multi-band operation. Summary of the invention

[0005] The purpose of the present invention is to provide a coplanar waveguide-fed broadband circularly polarized antenna. The coplanar waveguide-fed broadband circularly polarized antenna widens the axial ratio band through optimized design, covers multiple wireless communication frequency bands, meets the requirements of modern communication systems for high bandwidth and multi-band operation, and can effectively solve the problems in the background technology.

[0006] To achieve the above object, the present invention provides the following technical solution: a coplanar waveguide-fed broadband circularly polarized antenna, comprising a rectangular dielectric base; a rectangular plate is provided on the upper surface of the rectangular dielectric base, a circular slot with a radius of R1 is etched in the middle of the upper surface of the rectangular plate, a Z-shaped branch second and a Z-shaped branch first are respectively provided on the left and right sides of the circular slot, and an L-shaped feeding belt is provided at the lower end of the circular slot;

[0007] A rectangular gap 1 is provided in the middle of the lower surface of the rectangular plate for the antenna of the L-shaped feeding strip to pass through;

[0008] The upper left end and the lower right end of the rectangular plate are both etched with triangular gaps;

[0009] The upper right end and the lower left end of the rectangular plate are both etched with long arc-shaped gaps;

[0010] The triangular gap and the long arc gap are both connected to the circular gap through the rectangular gap 2;

[0011] The lower end of the L-shaped feeding strip extends to the lower edge of the upper surface of the dielectric substrate to form a feeding end;

[0012] A coupling branch is provided at the lower left end of the inner part of the circular gap.

[0013] Compared with the prior art, the broadband circularly polarized antenna fed by the coplanar waveguide has the following significant advantages:

[0014] (1) Miniaturization design: By adding Z-shaped branches and long gaps to the circular gaps, the current distribution and flow direction are adjusted to achieve a lower frequency point and circular polarization radiation characteristics. This design enables the antenna to reduce the operating frequency without increasing the size, thus achieving a miniaturization design;

[0015] (2) Multi-band performance: By changing the position and shape of the radiating branches on the dielectric substrate and using multi-slot technology, the magnitude and direction of the current flowing through the branches can be adjusted to stimulate different resonant frequencies. This method facilitates the realization of multi-band performance of the antenna.

[0016] (3) Wideband characteristics: The interaction between the L-shaped feed strip and the patch produces inductive reactance and capacitive reactance, and the interaction between the two produces resonance. Therefore, the operating frequency and bandwidth of the antenna can be flexibly controlled by adjusting the size and size of the L-shaped feed strip, which facilitates design and optimization.

[0017] (4) Good circular polarization performance: By loading two centrally symmetrical Z-shaped branches in the circular gap, the electric field and current direction in the circular gap are disturbed, so that the circular polarization radiation performance is further improved. In addition, by selecting the appropriate size of W4 and L8, a wider axial ratio bandwidth can be achieved.

[0018] (5) Easy to process and integrate: The coplanar waveguide-fed antenna has a simple structure, a wide operating bandwidth, and is easy to process and manufacture. This makes it more suitable for application scenarios that require miniaturization and integration.

[0019] (6) Wide range of applications: Due to its miniaturization, multi-band, wide bandwidth and good circular polarization performance, the coplanar waveguide-fed broadband circularly polarized antenna is suitable for a variety of communication systems, such as UHF band RFID readers, military communications, radio and television, medical equipment and maritime communications.

[0020] (7) Cost-effectiveness: Due to the use of coplanar waveguide feeding technology, the antenna reduces costs and improves economic benefits while maintaining high performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the structure of this application.

[0022] Figure 2 This is a schematic diagram of the dimensions of the present application when the epitaxial branch 1, the epitaxial branch 2 and the triangular short segment are removed.

[0023] Figure 3 This is the curve of return loss changing with L3 for this application.

[0024] Figure 4 This is the curve of return loss changing with L5 for this application.

[0025] Figure 5 This is the curve of return loss changing with q for this application.

[0026] Figure 6 This is the curve of axis ratio changing with W4.

[0027] Figure 7 This is the curve of axis ratio changing with L8.

[0028] Figure 8 Simulation results of return loss curve and axial ratio curve.

[0029] Fig. 9 These are the E-plane and H-plane gain diagrams of the antenna of this application.

[0030] Fig.10 The surface current distribution diagrams are at four phases with a difference of 90°.

[0031] In the figure: 1-triangular gap, 2-arc-shaped long gap, 3-Z-shaped branch node 1, 4-L-shaped feeding strip, 5-coupling branch node, 6-rectangular plate, 7-Z-shaped branch node 2, 8-epitaxial branch node 1, 9-epitaxial branch node 2, 10-triangular short segment. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0033] In the description of this application, if the orientation description is involved, for example, the orientation or position relationship indicated by "upper", "lower", "front", "back", "left", "right", etc. is based on the attached Figure 1 The orientation or position relationship shown is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as a limitation of the present application. When a feature is referred to as being "set", "fixed", or "connected" to another feature, it can be directly set, fixed, or connected to the other feature, or it can be indirectly set, fixed, or connected to the other feature.

[0034] Combination Figure 1 , Figure 2The present invention proposes a coplanar waveguide-fed broadband circularly polarized antenna, comprising a rectangular dielectric base; a rectangular plate 6 is provided on the upper surface of the rectangular dielectric base, a circular slot with a radius of R1 is etched in the middle of the upper surface of the rectangular plate 6, a Z-shaped branch 2 7 and a Z-shaped branch 1 3 are respectively provided on the left and right sides of the circular slot, and an L-shaped feeding belt 4 is provided at the lower end of the circular slot.

[0035] A rectangular gap 1 is provided in the middle of the lower surface of the rectangular plate 6 for the antenna of the L-shaped feeding strip 4 to pass through.

[0036] A triangular gap 1 is etched on the upper left end and the lower right end of the rectangular plate 6 .

[0037] The upper right end and the lower left end of the rectangular plate 6 are both etched with long arc-shaped gaps 2 .

[0038] The triangular gap 1 and the arc-shaped long gap 2 are both connected to the circular gap through the rectangular gap 2;

[0039] The lower end of the L-shaped feeding strip 4 extends to the lower edge of the upper surface of the dielectric substrate to form a feeding end.

[0040] A coupling branch 5 is provided at the lower left end of the inner part of the circular gap.

[0041] Specifically, the present application adjusts the distribution and flow direction of the current by adding Z-shaped branches on the left and right sides of the middle feed strip of the circular gap and opening long gaps around the circular gap, thereby achieving a lower frequency and circularly polarized radiation characteristics.

[0042] More specifically, four asymmetric slots are etched on the outer sides of the circular slot to increase the magnetic current path, thereby reducing the operating frequency of the antenna without increasing the size of the antenna.

[0043] Furthermore, the Z-shaped branch node 1 3 , the L-shaped feeding strip 4 , the coupling branch node 5 , the rectangular plate 6 , and the Z-shaped branch node 2 7 are all copper-clad plates.

[0044] Specifically, the thickness of the copper clad laminate is preferably 1.2 mm.

[0045] Furthermore, the working mode of the coplanar waveguide-fed broadband circularly polarized antenna is UHF band circular polarization.

[0046] The dual-band operating frequency band of the antenna is: 485MHz-503MHz.

[0047] The standing wave ratio of the antenna is less than 2.

[0048] The characteristic impedance of the antenna is: 50Ω.

[0049] The polarization mode of the antenna is left-hand circular polarization.

[0050] The gain of the antenna is greater than 0dBi±50°.

[0051] The axial ratio of the antenna is less than 6dB±50°.

[0052] Furthermore, the Z-shaped branch 1 3 is provided with an extension branch 1 8 .

[0053] Furthermore, an extension branch 2 9 is provided at the end of the coupling branch 5 .

[0054] Furthermore, a triangular short section 10 is provided at the lower end of the L-shaped feeding strip 4 near the coupling branch 5 .

[0055] Specifically, the first extension branch 8 and the second extension branch 9 are combined with the triangular short segment 10 arranged at the lower end of the L-shaped feeding strip to enable a smooth transition between the two frequency bands.

[0056] For details, please refer to the attached manual. Figure 2 As shown, the specific structural size parameters of this application are as follows:

[0057]

[0058]

[0059] Figure 1 The following is a schematic diagram of the antenna structure. The antenna is etched on a FR-4 dielectric substrate with a thickness of 1.2 mm, a dielectric constant of 4.4, and a loss tangent of 0.02. A circular gap with a radius of 52.8 mm is etched in the center of the antenna. A rectangular gap of 4.2 mm × 18.7 mm is left at the bottom of the circular gap to place the antenna feeder. Four asymmetric gaps are etched in the middle and outside of the circular gap to increase the magnetic flow path, thereby reducing the operating frequency of the antenna without increasing the size of the antenna. The original intention of using an asymmetric layout is to give the antenna specific functions by adjusting the formation and the radiation element. Based on the observation of the current distribution, the areas with weak or symmetrical current distribution are removed, so as to reduce the size of the antenna while minimizing the negative impact on the radiation characteristics. The size of the antenna is calculated using the following formula:

[0060]

[0061] where ε ris the dielectric constant, c is the speed of light in free space, and f is the resonant frequency. According to this formula, the size of the antenna working at 485MHz-503MHz is about 180mm. However, in order to reduce the overall size of the antenna and facilitate processing and integration, it is necessary to open long gaps around the circular gap to increase the magnetic flow path and reduce the operating frequency while reducing the size of the antenna. The final size of the antenna is 136.5mm×146.5mm, and the side length is approximately equal to 0.5λ g . g is the wavelength of the designed center frequency at 500MHz, which can be calculated as follows:

[0062]

[0063] Where c0 is 3×10 8 m / s, ε eff is the dielectric constant of the FR-4 dielectric material.

[0064] In the antenna structure of the present application, an L-shaped feeding strip 4 with intermediate feeding is used. The L-shaped feeding strip 4 generates resonance through interaction with the patch, which can broaden the working bandwidth of the antenna and make it present multi-band or wide-band characteristics. When the resonant frequency needs to be adjusted, an inductive reactance is generated between the vertical part of the L-shaped feeding strip 4 and the patch, and a capacitive reactance is generated between the horizontal part and the patch. The two interact to generate resonance. Therefore, this design can flexibly control the working frequency and bandwidth of the antenna by adjusting the size and size of the L-shaped feeding strip 4, which is convenient for design and optimization.

[0065] Specifically, the resonant frequency and bandwidth under different L3 and L5 conditions are as follows: Figure 3 and Figure 4 As shown, from Figure 3 and Figure 4 It can be seen that when L3 is widened from 19mm to 21mm, the return loss at the lower frequency in the antenna working band decreases, but the larger L3 is, the smaller the bandwidth of the antenna is. Although reducing L3 can increase the bandwidth while maintaining a good return loss, the reduction of L3 will also affect the size of the axial ratio bandwidth. Therefore, a moderate value is selected after comprehensive consideration, and the final value of L3 is 23.4mm. In comparison, the change in L5 causes a smaller change in the return loss amplitude. As L5 increases from 7mm to 9mm, the return loss increases and the bandwidth gradually narrows. Therefore, without affecting the axial ratio, the value of L5 should be selected as a lower value. After comprehensive consideration, the final value of L5 is 7.2mm.

[0066] The main function of the gaps around the circular gap is to increase the magnetic flow path, thereby reducing the working frequency of the antenna, which is very important for the miniaturization design of the antenna. Therefore, the length of the gap has a greater impact on the working frequency of the antenna. Figure 5It can be seen that when q decreases from 15° to 5°, the slot line becomes longer, the magnetic current path on the antenna surface increases, the antenna operating frequency is significantly reduced, but the return loss also increases. When q becomes larger, the frequency point of the antenna shifts significantly to the right. Therefore, while using a long slot to reduce the operating frequency, the return loss performance of the antenna must also be considered. After comprehensive consideration, the q value of 13° is selected.

[0067] Two centrally symmetrical Z-shaped branches are set in the circular gap. The function of these two branches is to disturb the electric field and current direction in the circular gap, so that the circular polarization radiation performance is further improved. The influence of the two Z-shaped branches on the axial ratio will be analyzed based on specific simulation data.

[0068] Figure 6 and Figure 7 The curve of the antenna's axial ratio bandwidth changing with W4 and L8. When W4 increases from 9mm to 14mm, the operating frequency band gradually shifts to the left, and the axial ratio bandwidth gradually narrows. Therefore, when selecting the size of W4, the operating frequency band and the axial ratio width should be considered at the same time to select the appropriate W4 size. At the same time, it can be observed in this figure that when L8 increases from 32mm to 38mm, the operating frequency band also gradually shifts to the left, but the axial ratio bandwidth first widens and then narrows. If you need to design the widest axial ratio bandwidth possible, you need to choose a moderate L8 size. It can be seen that the Z-shaped branches on the left and right sides have a greater impact on the axial ratio performance.

[0069] The final simulation result of the coplanar waveguide-fed circularly polarized antenna is shown in the figure. Figure 8 It can be seen that the bandwidth of the antenna is from 489MHz to 520MHz, and the axial ratio bandwidth is lower than 4dB in the working frequency band, which has good circular polarization performance. However, the axial ratio bandwidth does not meet the requirement of lower than 3dB in the working frequency band. This is because the axial ratio performance of the antenna is affected by opening long slits around the circular slot in order to reduce the working frequency band of the antenna, and part of the axial ratio performance is also sacrificed in order to meet the lower return loss of the antenna at ultra-high frequency.

[0070] Fig. 9 It is the gain performance of the E-plane and H-plane at the two ends of the working frequency band of the antenna. As can be seen from the figure, the maximum gain of the E-plane and H-plane of the antenna is equal at 485MHz, reaching 2.7dBic. At 503MHz, the maximum gain of the E-plane and H-plane is also equal, reaching 2.9dBic, and both frequencies radiate obvious left-hand circular polarization, which meets the antenna design requirements.

[0071] To explain the mechanism of circularly polarized radiation, Fig.10The surface current distribution of the proposed antenna with four phase angles of 0°, 90°, 180° and 270° at 495MHz is shown in FIG. As shown in the figure, it is observed that the surface current distributions at the phase angles of 180° and 270° are opposite to those at the phase angles of 0° and 90°, respectively. When the phase angle increases by 90°, the surface current rotates clockwise. Therefore, the proposed antenna excites left-hand circularly polarized (LHCP) radiation in the +Z direction and right-hand circularly polarized (RHCP) radiation in the -Z direction, and has dual circular polarization characteristics. By mirror-flipping the directions of the Z-shaped branches and the L-shaped grounding plate on both sides, the RHCP radiation can be excited in the +Z direction.

[0072] Although the embodiments of the present application have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present application, and that the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A broadband circularly polarized antenna fed by a coplanar waveguide, characterized in that: It comprises a rectangular dielectric substrate; a rectangular plate (6) is provided on the upper surface of the rectangular dielectric substrate; a circular slot with a radius of R1 is etched in the middle of the upper surface of the rectangular plate (6); a Z-shaped branch node 2 (7) and a Z-shaped branch node 1 (3) are respectively provided on the left and right sides of the circular slot; and an L-shaped feeding strip (4) is provided at the lower end of the circular slot; A rectangular slit 1 is provided in the middle of the lower surface of the rectangular plate (6) for the antenna of the L-shaped feeding strip (4) to pass through; The upper left end and the lower right end of the rectangular plate (6) are both etched with triangular gaps (1); The upper right end and the lower left end of the rectangular plate (6) are both etched with long arc-shaped gaps (2); The triangular gap (1) and the arc-shaped long gap (2) are both connected to the circular gap through the rectangular gap 2; The lower end of the L-shaped feeding strip (4) extends to the lower edge of the upper surface of the dielectric substrate to form a feeding end; A coupling branch (5) is provided at the lower left end of the inner part of the circular gap.

2. A coplanar waveguide-fed broadband circularly polarized antenna according to claim 1, characterized in that: The Z-shaped branch node 1 (3), the L-shaped feeding strip (4), the coupling branch node (5), the rectangular plate (6), and the Z-shaped branch node 2 (7) are all copper-clad plates.

3. The coplanar waveguide-fed broadband circularly polarized antenna according to claim 1, characterized in that: The working mode of the coplanar waveguide-fed broadband circularly polarized antenna is UHF band circular polarization; the dual-frequency working frequency band is 485MHz-503MHz.

4. A coplanar waveguide-fed broadband circularly polarized antenna according to claim 3, characterized in that: The standing wave ratio of the antenna is less than 2, the characteristic impedance is 50Ω, and the polarization mode is left-hand circular polarization.

5. The coplanar waveguide-fed broadband circularly polarized antenna according to claim 1, characterized in that: The Z-shaped branch node 1 (3) is provided with an extension branch node 1 (8).

6. The coplanar waveguide-fed broadband circularly polarized antenna according to claim 1, characterized in that: The end of the coupling branch (5) is provided with an extension branch 2 (9).

7. The coplanar waveguide-fed broadband circularly polarized antenna according to claim 1, characterized in that: A triangular short section (10) is provided at the lower end of the L-shaped feeding strip (4) near the coupling branch (5).

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