CN113224535A

CN113224535A - Low-profile dual-circular-polarization microstrip antenna

Info

Publication number: CN113224535A
Application number: CN202110486474.1A
Authority: CN
Inventors: 何佳桅; 崔杰; 马晓峰; 张仁李; 盛卫星; 韩玉兵; 郭山红; 张书瑞
Original assignee: Nanjing University of Science and Technology
Current assignee: Nanjing University of Science and Technology
Priority date: 2021-04-30
Filing date: 2021-04-30
Publication date: 2021-08-06

Abstract

The invention provides a low-profile dual-circular-polarization microstrip antenna which is of a step-shaped structure and sequentially comprises a circular patch, a dielectric layer, a directional coupler and a bottom floor from top to bottom, wherein the directional coupler adopts a small three-branch directional coupler, the middle branch of the directional coupler is a gradient line, a metal through hole is formed in the dielectric layer and used for connecting the directional coupler and the circular patch, and an isolation ring belonging to a through hole bottom hole plate is arranged on the bottom floor and used for ensuring the isolation of a signal layer and the floor. The invention has the advantages of low profile and easy conformal; the dual-circular polarized wave with low axial ratio and high isolation can be emitted in the working frequency band.

Description

Low-profile dual-circular-polarization microstrip antenna

Technical Field

The invention relates to a microwave emitter technology, in particular to a novel low-profile dual-circular-polarization microstrip patch antenna.

Background

The antenna is a key device at the front end of a wireless communication system and is responsible for conversion of guided electromagnetic waves and space electromagnetic waves. The microstrip antenna has the advantages of light weight, small volume, low section, flexible feed mode, low processing cost, diversified functions and the like. The circularly polarized antenna is little affected by rain and snow weather, has strong anti-interference capability and is not easy to generate polarization distortion in an ionized layer. And, the polarization angle between the circularly polarized transmit-receive antennas has arbitrariness, can finish more stable signal transmit-receive. In addition, circularly polarized waves have rotation orthogonality. When a circularly polarized wave is incident on a symmetric target, the reflected wave becomes a circularly polarized wave of an opposite rotation direction. The double circularly polarized antennas replace two circularly polarized antennas with one antenna, so that the double circularly polarized antennas are advantageous in miniaturization, the processing cost is reduced, and a new development way is opened up for some established circularly polarized communication systems. In recent years, the research on the dual circularly polarized antenna attracts the attention of the researchers, and the dual circularly polarized antenna with excellent performance is emerging. At present, the development of the application field of electronic devices gradually changes the antenna to a broadband and high integration direction, the technology of the linear polarization antenna is mature in this respect, and the dual circular polarization antenna has a great design difficulty and relatively lags in development, so that a plurality of problems to be solved still exist.

Disclosure of Invention

The invention aims to provide a novel low-profile dual-circular-polarization microstrip patch antenna.

The technical solution for realizing the purpose of the invention is as follows: the utility model provides a two circular polarization microstrip antenna of low section, antenna are notch cuttype structure, and top-down is circular paster, dielectric layer, directional coupler, underfloor in proper order, and wherein directional coupler adopts small-size three-branch directional coupler, and its middle minor matters is the gradual change line, set up the metal through-hole on the dielectric layer for connect directional coupler and circular paster, set up the isolating ring that belongs to through-hole bottom hole dish on the underfloor, be used for guaranteeing the isolation on signal layer and floor.

Further, the dielectric layer is formed by pressing RO4350B with the thickness of 1.542mm and a prepreg RO4450F with the thickness of 0.204 mm.

Further, the directional coupler is printed on RO4350B with a thickness of 0.508 mm.

Furthermore, each layer of the double circularly polarized microstrip antenna is in mirror symmetry.

Furthermore, the directional coupler comprises two feeding ports and two output ports, the coupler switches the feeding ports, and the rotation direction of the circularly polarized wave is changed accordingly.

Furthermore, the s parameter, the standing-wave ratio and the axial ratio are adjusted by changing the radius of the bonding pad of the directional coupler, the side length of the directional coupler, the position between the position of the metallized hole and the edge of the circular patch.

Compared with the prior art, the invention has the following remarkable advantages: 1) the thickness of the antenna is 2.236mm, the thickness of the antenna is about 0.07 lambda (lambda is the free space wavelength of a central frequency point), and the antenna has the advantages of low profile and easiness in conformation; 2) the dual-circular polarized wave with low axial ratio and high isolation can be emitted in the working frequency band.

Drawings

Fig. 1 is a schematic diagram of a conventional three-branch directional coupler.

Fig. 2 is a schematic diagram of a miniaturized three-branch directional coupler.

Fig. 3 is a schematic diagram of simulated S-parameters and output port phase differences for a miniaturized three-branch directional coupler, where (a) is the simulated S-parameters and (b) is the output port phase differences.

Fig. 4 is a schematic diagram of a low-profile dual circularly polarized microstrip antenna of the present invention.

Fig. 5 is a top view of a low-profile dual circularly polarized microstrip antenna of the present invention.

FIG. 6 is a graph of voltage transmission coefficient S12, axial ratio, with R2 increasing from 0.5mm to 1.3 mm. Wherein (a) is the variation graph of S12 parameter with frequency, and (b) is the variation graph of AR curve with frequency.

FIG. 7 is a graph of standing wave ratio, voltage transmission coefficient S12, and AR for d varying from 0.2mm to 0.8 mm. Wherein (a) is a standing wave ratio variation graph with frequency, (b) is a S12 parameter variation graph with frequency, and (c) is an AR curve variation graph with frequency.

FIG. 8 is a graph of the standing wave ratio of L3 as it changes from 5.9mm to 6.5 mm.

Fig. 9 is a diagram showing simulation and test results of the standing wave ratio of the antenna.

Fig. 10 is a graph of simulation and test of isolation.

FIG. 11 is a graph of simulation and test results of right and left hand circular polarization axial ratios. Wherein the graph (a) is a simulation and test comparison graph of the right-hand circularly polarized axial ratio, and the graph (b) is a simulation and test comparison graph of the left-hand circularly polarized axial ratio.

FIG. 12 is a graph of right and left hand circular polarization gain as a function of frequency. Wherein the graph (a) is a simulation and test comparison graph of right-hand circularly polarized gain, and the graph (b) is a simulation and test comparison graph of left-hand circularly polarized gain.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

The distance between the input port and the output port of the traditional three-branch directional coupler is about one half of the waveguide wavelength, and the requirement of a small-size antenna cannot be met. Low-impedance branches are connected in parallel on a transverse quarter-wavelength line of the traditional three-branch directional coupler, and the size of the three-branch directional coupler is reduced by adopting a T-shaped equivalent method. The four-branch-shaped structure is characterized in that two open-circuit low-impedance branches are connected in parallel on a quarter-wavelength line, so that the four T-shaped structures are symmetrical. The improved three-branch directional coupler is called a miniaturized three-branch directional coupler. A conventional three-branch directional coupler as shown in fig. 1 and a miniaturized three-branch directional coupler as shown in fig. 2. Compared with a high-impedance line, the low-impedance open-circuit branch can obtain good coupler performance more easily, and the more the number of the parallel open-circuit branches is, the wider the bandwidth of the coupler is. Fig. 3(a) (b) show the simulated S-parameters and output port phase difference, respectively, of the miniaturized three-branch directional coupler. As can be seen from the observation of FIG. 3, the amplitude difference is less than 0.32dB and the phase difference is 90 degrees +/-0.34 degrees within 9-11 GHz. The miniaturized three-branch directional coupler has excellent performance, and lays a good foundation for realizing a circularly polarized antenna with excellent performance.

As shown in FIG. 4, the ladder-type structure is composed of a top circular patch, 1.542mm RO4350B, 0.204mm RO4450F, a directional coupler, 0.508mm RO4350B and a floor from top to bottom.

The top view is shown in fig. 5. In order to reduce the signal reflection at the connection, the invention uses the gradual change line to construct the middle branch of the small three-branch directional coupler. The directional coupler is provided with two feeding ports, the feeding ports are switched, and the rotation direction of the circularly polarized wave is changed accordingly. Port 1 of the unit feeds power, and port 2 radiates right-hand circularly polarized wave when connected with matched load; the port 2 feeds power, and the port 1 radiates left-hand circularly polarized wave when connected with a matched load.

Metal vias are the key structure for connecting the directional coupler and the circular patch. In actual processing, the isolation ring of the hole disc at the bottom layer of the metal through hole is etched on the floor, so that the isolation between the signal layer and the floor is ensured. The location of the metal vias, the aperture, the size of the directional coupler pads, and the size of the floor isolation ring all affect the impedance matching between the circular patch and the directional coupler, and these variables need to be considered together to obtain the best performance.

Taking the directional coupler pad radius R2 as an example, R2 has a greater effect on the voltage transmission coefficient S12, the axial ratio, than the standing wave ratio. Increasing R2 from 0.5mm to 1.3mm gives the S12, axial ratio curve in FIG. 6. As can be seen from the observation of FIG. 6, when R2 is increased to 1.3mm, the impedance matching at the center connection of the pad is poor, and S12 is increased to about-7 dB within 9.7-10.7 GHz. As R2 changes, the two modes of the directional coupler output change. When the R2 is increased to 1.3mm, the amplitude difference of the left-hand mode and the right-hand mode is increased, the phase difference deviates 90 degrees, and the axial ratio AR of a low frequency band is obviously increased.

The distance between the position of the metal through hole and the edge of the circular patch is recorded as d. FIG. 7 shows the standing wave ratio, S12 and AR curves when d is changed from 0.2mm to 0.8 mm. And the distances between the metal through holes and the edges of the circular patch are different, so that the impedance values at the circle center connection part of the bonding pad are different. The energy reflected back to the coupler changes, affecting the standing wave ratio and S12. From fig. 7, when d is 0.8mm, the standing-wave ratio of the 9.2-10.5GHz band becomes significantly large, and the isolation bandwidth is narrowest. The impedance matching at the connection is poor, resulting in more energy being reflected back to both ports, causing a deterioration in standing wave ratio and isolation. In addition, variations in the location of the metal vias can also alter the current distribution of the antenna patch. The key to ensuring good circular polarization performance is to form two equal-amplitude, orthogonal modes, so the metal via position is related to the axial ratio bandwidth, and fig. 7c) verifies the effect of the metal via position d on the circular polarization performance.

Keeping other parameters constant, the radius of the circular patch determines the operating frequency of the antenna. The radius increases, the resonant wavelength of the antenna increases, equivalent to a decrease in frequency. In addition, the side lengths L1 and L3 of the directional coupler determine the frequency of the output signal of the coupler, thereby affecting the operating frequency band of the antenna. FIG. 8 plots the standing wave ratio for L3 as it changes from 5.9mm to 6.5 mm. As can be seen from fig. 8, as L3 increases, the frequency band with the standing wave ratio of the antenna less than 2 moves to a low frequency, and the effect of L3 on the operating frequency of the antenna is verified.

All parameters can be classified into three categories: circular patch parameters, directional coupler parameters, and metal via parameters. In order to obtain excellent performance of the dual circularly polarized antenna, the sizes of the circular patch and the directional coupler are adjusted, and matching at the connection position is optimized. By analyzing important parameters of the antenna and comprehensively considering the gap between the axial ratio, the standing-wave ratio and the S12 simulated value and the design target, the parameters are optimized purposefully to obtain excellent antenna performance.

For example, to achieve the following criteria: (1) the working frequency is as follows: 9-10 GHz; (2) standing-wave ratio: VSWR is less than or equal to 2; (3) degree of isolation: greater than 10 dB; (4) polarization form: double circular polarization; (5) axial ratio: AR is less than or equal to 4 dB; (6) beam width: greater than 60 degrees; (7) gain: the normal gain is larger than 4dBi, and parameter optimization is performed on the basis of the structure shown in FIG. 5, so that the optimal values of some important parameters are shown in Table 1.

TABLE 1 parameter value-taking table

R1 is the radius of a circular patch, R2 is the radius of a small three-branch directional coupler pad, R3 is the radius of a feed port, L1 and L3 are the length of a coupler side, L4 and L5 are the length of an antenna unit side, L2 is the length of a low-impedance open stub, W1, W2 and W5 are the widths of the coupler branches, W3 is the width of the low-impedance open stub, W4 is the shortest extension width of a tapered stub, W6 is the width of the widest part of the tapered stub, and d is the diameter of a metalized through hole.

Fig. 9 shows simulation and test results of the standing wave ratio of the antenna. According to the graph of FIG. 9, the simulation result of the standing-wave ratio of two ports in 9.2-9.8GHz is less than 1.78, and the test result is less than 1.9. Compared with a simulation curve, although the in-band standing wave ratio obtained by the test is slightly deteriorated, the in-band standing wave ratio is still remarkably superior to a project index. The test curve shows that the impedance matching performance of the real object antenna is good, and the energy reflected back to the input port is little.

Fig. 10 shows simulation and test curves for isolation. Simulation results show that S12 and S21 are less than-20.3 dB within 9.2-9.8GHz, and S12 and S21 within a band obtained by testing are less than-19.3 dB. The standing-wave ratio of the object antenna is less than 2, and the frequency bands of S12 and S21 which are less than-10 dB are 9.2-9.55 GHz.

Fig. 11 shows simulation and test results of right-hand and left-hand circularly polarized axial ratios. As shown in fig. 11, the simulation and test values of the right-hand circular polarization axial ratio within 9.2-9.8GHz are less than 3.5dB, the simulation and test values of the left-hand circular polarization axial ratio are less than 3.3dB, and the axial ratio of the real object antenna meets the design index.

Fig. 12 shows the right and left hand circularly polarized gain curves as a function of frequency. According to FIG. 12, the range of right-hand circularly polarized gain variation in 9.2-9.8GHz is 4.77dB-5.49dB and the range of left-hand circularly polarized gain variation in 4.57dB-5.39 dB.

In the target frequency band, the difference between the test value of the dual circularly polarized microstrip antenna and the simulation value is small. Within 9.2-9.8GHz, the standing wave ratio of the antenna is less than 1.9, the isolation is higher than 19.3dB, the axial ratio is lower than 3.5dB, the lowest gain value is 4.57dBi, and all performances meet the design requirements. The feasibility of the antenna design scheme and the processing accuracy are verified by a better test result. The reasons for incomplete consistency of antenna test and simulation results include processing errors, excessive soldering tin for welding the SMA connector, abrasion of a connecting SMA joint during testing and the like. In a far-field test, the single antenna has small gain and light weight, and the jitter of the cable in the test makes the connection condition between the antenna and the cable unstable.

In conclusion, the dual circularly polarized microstrip antenna provided by the invention has the advantages of low standing-wave ratio, high isolation, low axial ratio, high gain and the like in a target frequency band, and meanwhile, the structure is simpler, so that the dual circularly polarized microstrip antenna is suitable for being widely applied to various communication networks.

The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. The utility model provides a two circular polarization microstrip antenna of low section, its characterized in that, the antenna is the notch cuttype structure, and top-down is circular paster, dielectric layer, directional coupler, underfloor in proper order, and wherein directional coupler adopts small-size three-branch directional coupler, and its middle branch festival is the gradual change line, set up the metal through-hole on the dielectric layer for connect directional coupler and circular paster, set up the isolating ring who belongs to through-hole bottom hole dish on the underfloor for guarantee the isolation on signal layer and floor.

2. The low profile dual circularly polarized microstrip antenna of claim 1 wherein the circular patch is a copper sheet.

3. The low-profile dual circularly polarized microstrip antenna of claim 1 wherein the dielectric layer is laminated with RO4350B of 1.542mm thickness and 0.204mm prepreg RO 4450F.

4. The low-profile dual circularly polarized microstrip antenna of claim 1 wherein the directional coupler is printed on RO4350B with a thickness of 0.508mm using a copper clad process.

5. The low-profile dual circularly polarized microstrip antenna of claim 1 wherein each layer of the dual circularly polarized microstrip antenna is mirror symmetric.

6. The low-profile dual circularly polarized microstrip antenna of claim 1 wherein the directional coupler comprises two feed ports and two output ports, the coupler switching the feed ports and the handedness of the circularly polarized wave is changed.

7. The low profile dual circularly polarized microstrip antenna of claim 1 wherein the s-parameter, standing wave ratio and axial ratio are adjusted by changing the directional coupler pad radius, the directional coupler side length, the location of the metallized hole and the edge of the circular patch.