CN101154762A - Dual Elliptical Helical Antenna - Google Patents

Abstract

The invention provides a double-ellipse helical antenna, which comprises a main ellipse helical coil, a dielectric substrate, a matching circuit and a coaxial SMA joint, wherein the double-ellipse helical antenna further comprises a parasitic ellipse helical coil, and the parasitic ellipse helical coil is coupled and connected with the main ellipse helical coil. The double-ellipse helical antenna has higher gain, simple feed structure and small volume, and is suitable for being applied to handheld mobile communication equipment.

Description

Dual Elliptical Helical Antenna

technical field

The present invention relates to helical antennas, and more particularly to dual elliptical helical antennas. The invention is suitable for handheld mobile communication equipment.

Background technique

The axial mode helical antenna, as shown in Figure 1, is a circularly polarized antenna invented by Kraus in 1946. It has very unique advantages in receiving echo signals containing various possible polarization forms, and can greatly The receiving strength of the signal can be greatly improved, and the relative frequency bandwidth of the axial-mode helical antenna is about 30%, and its sensitivity to multipath propagation effects is low. In addition, the helical antenna has a simple structure and is easy to process, and is especially suitable for Mobile communication and satellite communication systems, and have been widely used in satellite communication base stations and other fields. There are a large number of reference materials at home and abroad for specific applications, such as "Wave Propagation on Helical Antennas", IEEE Trans.on Antennas Propagat. , Vol.20, No.5, September 1972, pp556-560: "Broadband Quasi-Taper Helical Antennas", IEEE Trans. on Antennas Propagat., Vol.27, No.1, January1979, pp72-78; "Axial Mode Helical Antennas", IEEE Trans. on Antennas Propagat., Vol.34, No.9, September 1986, pp1143-1148; "Design and Realization of an L-band Helical Antenna", Proceedings of MTT-S, USA, 2003, pp143-145 . In terms of improving the directivity of the helical antenna, studies have shown that the gain of the helical antenna depends on the number of turns of the helix. The gain can be improved by increasing the number of turns of the helical antenna, and it is also possible to use two, three or Four helical coils for increased gain.

However, the existing helical antennas also have various defects:

First, although the gain of the helical antenna can be increased by increasing the number of helical turns, the size of the helical antenna will increase with the increase of the number of turns. Currently, handheld mobile communication devices are developing towards a compact and highly integrated trend. Too many turns will reduce the Affect the application of antennas in the field of handheld mobile communication equipment;

Second, as shown in Figure 2 and Figure 3, although the method of using multiple helical coils on a helical antenna to increase the gain can increase the gain, the feed structure is quite complicated;

Thirdly, since the conventional helical coil is usually circular, the volume occupied by the antenna is relatively large, especially when it is applied to a handheld device, it is difficult for the circular antenna to match the flat structure of most handheld mobile communication devices.

Contents of the invention

In view of the above-mentioned defects, the purpose of the present invention is to propose a double elliptical helical antenna, which has a greater improvement in gain performance than the helical antenna of the prior art, and has a simple single-feed structure. The size of the helical antenna is greatly reduced, so it is expected to be widely used in handheld mobile communication devices.

For the purpose of the invention of the present invention, the present invention provides a dual elliptical helical antenna, comprising a main elliptical helical coil, a dielectric substrate, a matching circuit and a coaxial SMA connector, wherein the dual elliptical helical antenna further comprises a parasitic elliptical helical coil, wherein, The parasitic elliptical spiral coil is coupled and connected to the main elliptical spiral coil.

The dual elliptical helical antenna according to a preferred technical concept of the present invention, wherein the matching circuit includes a 50 ohm microstrip line connected to the coaxial SMA connector, and a dual elliptical helical antenna connected to the lower end of the main elliptical helical coil The input port, and the middle matching section between the 50 ohm microstrip line and the input port of the dual elliptical helical antenna.

According to a preferred technical concept of the dual elliptical helical antenna of the present invention, the ratio of the major axis to the minor axis of the main elliptical helical coil and the parasitic elliptical helical coil is 1.3.

According to a preferred technical conception of the dual elliptical helical antenna of the present invention, the upper end of the parasitic elliptical helical coil is flush with the upper end of the main elliptical helical coil.

According to a preferred technical concept of the dual elliptical helical antenna of the present invention, the lower end of the parasitic elliptical helical coil is coupled and connected to the minimum value of the traveling wave current of the main elliptic helical coil.

According to a preferred technical conception of the dual elliptical helical antenna of the present invention, the major and minor axes of the main elliptical helical coil and the parasitic elliptical helical coil respectively coincide.

According to a preferred technical conception of the dual elliptical helical antenna of the present invention, the signal source provides single feed to the elliptical helical coil through a coaxial SMA connector and a matching circuit.

According to a preferred technical concept of the dual elliptical helical antenna of the present invention, when the central frequency of the coil is 2.5 GHz, the lower end of the parasitic elliptical helical coil is coupled and connected to 2 to 4 turns of the main elliptical helical coil from the lower end upwards.

According to a preferred technical concept of the dual elliptical helical antenna of the present invention, when the center frequency of the coil is 2.5 GHz, the parasitic elliptical helical coil is coupled and connected to 2.5 turns of the main elliptical helical coil from the lower end upwards.

The invention has the advantages that the double elliptical helical antenna has high gain, simple feeding structure and small size, and is suitable for handheld mobile communication equipment.

Description of drawings

Fig. 1 is a structural schematic diagram of a single-coil helical antenna according to the prior art,

Fig. 2 is a structural schematic diagram of a dual-coil helical antenna according to the prior art,

Fig. 3 is a structural schematic diagram of a four-coil helical antenna according to the prior art,

Fig. 4 is a schematic structural view of a single-feed dual elliptical helical circularly polarized antenna according to the present invention,

Fig. 5 is a structural top view of a single-feed dual elliptical helical circularly polarized antenna according to the present invention,

FIG. 6 is a structural schematic diagram of a matching circuit of a single-feed dual elliptical helical circularly polarized antenna according to the present invention.

Fig. 7 is the 10dB input impedance bandwidth figure of single-feed dual elliptical helical circularly polarized antenna according to the present invention,

Fig. 8 is the 3dB axial ratio bandwidth figure of single-feed dual elliptical helical circularly polarized antenna according to the present invention,

Fig. 9 is the gain diagram when the operating frequency of the single-feed dual elliptical helical circularly polarized antenna according to the present invention is 2.5GHz,

Fig. 10 is a radiation pattern diagram of the single-feed dual elliptical helical circularly polarized antenna according to the present invention when the working frequency is 2.4 GHz.

Detailed ways

According to the purpose of the present invention, the present invention uses two elliptical helical coils with different numbers of turns to form an antenna capable of radiating circularly polarized waves, and adopts a simple single-feed structure.

For the purpose of this invention, the present invention selects the geometric structure of the helical coil and the relative position of the main helical coil and the parasitic helical coil through theoretical analysis, so that the circular polarization 3dB axial ratio bandwidth is close to 40%. In addition, because the helical structure can be determined through theoretical analysis Therefore, the impedance conversion from the 50 ohm coaxial connector to the antenna input port can be realized with a simple matching structure, and the 10dB input impedance bandwidth can reach about 30%. The design idea of the present invention is introduced in detail below:

(1) Select the spiral radius and the spacing between adjacent spiral coils according to the working frequency;

(2) In order to conform to the future fourth-generation mobile communication mobile phone in order to obtain better practical applications, according to theoretical analysis, the ratio of the major and minor axes of the helical coil is changed from 1 to about 1.3, that is, an elliptical coil is used instead of a circle Shaped spiral coil;

(3) In order to improve the radiation gain of the helical coil, two elliptical helical coils with the same shape but different numbers of turns are used, and the long and short axes of the two are coincident;

(4) According to theoretical analysis, the second elliptical helical coil (parasitic helical coil) is coupled and connected to the minimum value of the traveling wave current of the first helical coil (main helical coil), and a new wave is excited in the parasitic helical coil The current distribution, therefore, the sum of the currents on these two coils is greater than a single coil, and the gain of the helical antenna is increased. At the same time, because the selected position of the parasitic helical coil ensures that the currents on the two coils are in phase in the surface wave region, the radiated electromagnetic waves are superimposed in the far region to form circularly polarized electromagnetic waves;

(5) The input impedance of the double elliptical helical coil structure is obtained by theoretical analysis;

(6) Using simple impedance transformation, the impedance transformation from a 50-ohm coaxial joint to a double elliptical helical coil structure can be realized;

(7) The impedance transformation adopted in the present invention is designed on the surface of the dielectric substrate, and the main elliptical helical coil can be directly welded thereon, which simplifies the requirements of engineering manufacture. At the same time, the backside of the substrate (ie, the ground plane) is also used as the radiation plane of the elliptical helical antenna.

The invention is proposed for the future fourth-generation mobile communication, and the elliptical structure is very consistent with the flat shape of the mobile phone. At the same time, the hollow structure in the middle can be used to put the mobile phone core into it, so there is no need for an additional dielectric support structure, which can greatly simplify the design and reduce the production cost.

A preferred specific embodiment of the present invention can be obtained according to the design idea above, and the specific embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

This specific embodiment is a double elliptical helical antenna, as shown in Figure 4 and Figure 5, its main structure includes a main elliptical helical coil 1, a parasitic elliptical helical coil 2, a dielectric substrate 3, a matching circuit 4 and a coaxial SMA connector 5, Wherein the matching circuit 4 is located on the dielectric substrate 3, the coaxial SMA connector 5 passes through the dielectric substrate 3 and connects with one end of the matching circuit 4, the lower end of the main elliptical spiral coil 1 is connected with the other end of the matching circuit 4, and the parasitic elliptical spiral coil 2 The coupling is connected to the main elliptical spiral coil 1 .

The specific structure of the matching circuit 4 is shown in Figure 6, the matching circuit 4 includes a 50 ohm microstrip line 6 connected to the coaxial SMA connector 5, a dual elliptical helical antenna input port 8 connected to the main elliptical helical coil 1, And the middle matching section 7 between the 50 ohm microstrip line 6 and the input port 8 of the dual elliptical helical antenna.

The specific structure of the coil part is shown in Figure 4. The upper end of the parasitic elliptical helical coil 2 is flush with the upper end of the main elliptical helical coil 1, and the lower end of the parasitic elliptical helical coil 2 is coupled and connected to the main elliptic helical coil 1 counting from the lower end to 2 to 1. 4 laps. The top view structure of the dual elliptical helical antenna is shown in FIG. 5 , the axes of the major axis and the minor axis of the main elliptical helical coil 1 and the parasitic elliptic helical coil 2 coincide respectively.

When the central operating frequency of the coil is 2.5 GHz, the parasitic elliptical helical coil 2 is coupled and connected to the 2.5 turns of the main elliptical helical coil 1 from the lower end to the top. This setting can make the antenna gain the highest.

The underside of the dielectric substrate 3, ie, the ground plane of the impedance matching structure, also serves as the radiation plane of the elliptical helical antenna.

The details and working conditions of the specific device proposed according to the present invention will be described in detail below in conjunction with FIG. 4 .

The wire radius of the main elliptical spiral coil 1 is a _l = 0.5mm, the semi-major axis of the coil is b = 19mm, and the semi-minor axis is a = 15mm, then the ratio of the major and minor axes is about 1.3, the number of turns is 5, and the distance between each turn is 23mm; the wire radius a _l of the parasitic elliptical helical coil 2 =0.5mm, the semi-major axis of the coil is b=19mm, the semi-minor axis is a=15mm, the parasitic helical coil and the main helical coil completely overlap, so the ratio of its major and minor axes is also the same as The main helical coil is the same, the number of turns is 2.5 turns, starting from the bottom to the top 2.5 turns of the main coil, and the distance between each turn is also 23mm. The thickness of the dielectric substrate 3 is 1.5 mm, and the dielectric constant ε _r =2.65.

As shown in FIG. 6 , the matching circuit 4 is designed on the substrate and is a simple quarter-wavelength matching structure. The outer conductor of the 50 ohm coaxial SMA connector 5 is connected to the back of the substrate (ie, the ground plate), and the inner conductor is connected to the input end of the matching circuit designed on the surface of the substrate. The corresponding width of the 50-ohm input port 6 on the matching circuit shown in FIG. 3 is 4.102mm; the width of the intermediate conversion section 7 is 1.34mm, and the length is 21.85mm; the microstrip width of the antenna input port 8 is 0.116mm. The connector of the helical antenna is soldered directly to the output end of the matching circuit.

When the lower end of the parasitic coil is coupled and connected to the position of 2 turns of the main coil, the performance parameters of the antenna are as follows: 3dB axial ratio bandwidth is 30%, and the gain at 2.5GHz is 10.6dB; when the lower end of the parasitic coil is coupled and connected to the position of 4 turns of the main coil , the parameters of the antenna are as follows: the 3dB axial ratio bandwidth is 45%, and the gain at 2.5GHz is 10.0dB. Therefore, according to the experimental data of the present invention, an ideal gain can be obtained when the lower end of the parasitic coil is coupled and connected within the range of the second to fourth turns of the main coil.

To detect various parameters of the antenna in this specific embodiment, first, the input matching characteristics of the antenna are measured by means of a vector network analyzer, and the 10 dB input impedance bandwidth is about 30%, as shown in FIG. 7 . Then, using the automatic far-field test equipment, various performance indicators of the antenna can be measured, including the axial ratio of the antenna, radiation pattern, cross-polarization, gain, etc.

The results show that the 3dB axial ratio bandwidth of the dual elliptical helical antenna is close to 40%, as shown in Figure 8; when the dual elliptical helical antenna works at the design frequency (2.5GHz), its gain can reach 11dB, as shown in Figure 9 It shows that compared with the situation without parasitic helical coil, its gain is significantly improved; as shown in Figure 10, when the dual elliptical helical antenna works at the design frequency (2.4GHz), its 3dB beamwidth is about 60 degrees, Therefore, the dual elliptical helical antenna can radiate signals in a wide range.

Claims (8)

1. double-ellipse helical antenna, comprise main ellipse spiral coil, medium substrate, match circuit and coaxial sub-miniature A connector, it is characterized in that, this double-ellipse helical antenna further comprises parasitic ellipse spiral coil, wherein, this parasitism ellipse spiral coil is of coupled connections on this main ellipse spiral coil.

2. double-ellipse helical antenna as claimed in claim 1, the axial ratio that it is characterized in that main ellipse spiral coil and parasitic ellipse spiral coil is 1.3.

3. double-ellipse helical antenna as claimed in claim 1 is characterized in that the upper end of parasitic ellipse spiral coil is concordant with the upper end of main ellipse spiral coil.

4. double-ellipse helical antenna as claimed in claim 1 is characterized in that the lower end of parasitic ellipse spiral coil is of coupled connections in the travelling wave current minimum value place of main ellipse spiral coil.

5. double-ellipse helical antenna as claimed in claim 1 is characterized in that the axis of main ellipse spiral coil and parasitic ellipse spiral coil major axis and minor axis overlaps respectively.

6. double-ellipse helical antenna as claimed in claim 1 is characterized in that signal source carries out SF single feed by coaxial sub-miniature A connector and match circuit to the ellipse spiral coil.

7. double-ellipse helical antenna as claimed in claim 1 is characterized in that when the hub of a spool frequency is 2.5GHz, and the lower end of parasitic ellipse spiral coil is of coupled connections and upwards 2 to 4 of number encloses from the lower end in main ellipse spiral coil.

8. double-ellipse helical antenna as claimed in claim 1 is characterized in that when the hub of a spool frequency is 2.5GHz, and parasitic ellipse spiral coil is of coupled connections and upwards 2.5 of number encloses from the lower end in main ellipse spiral coil.

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