CN108172992B - A Novel Archimedes Spiral Antenna for Stepped Frequency Ground Penetrating Radar - Google Patents

Abstract

The invention belongs to the field of design of a stepping frequency ground penetrating radar, and particularly relates to an Archimedes spiral antenna device for the stepping frequency ground penetrating radar; the antenna arm is a square double-arm spiral antenna sheet with four corners all having cutting angles, the cutting angles are isosceles right triangle-shaped, the angles of the cutting angles are gradually decreased from the center to the outside by 0.5-5 degrees per turn, the initial angle is not more than 45 degrees, and the square double-arm spiral antenna sheet with the four corners all having the cutting angles is loaded with terminal resistors at the position of the quarter wavelength of the minimum working frequency between the double arms and the tail end. The invention realizes a miniaturized, broadband and high-directivity Archimedes spiral antenna for a step frequency ground penetrating radar, the working frequency of the antenna is 250 MHz-1600 MHz, the size of the antenna is not more than 300mm multiplied by 300mm, the axial ratio is less than 3dB, the directional diagram is good, the gain is not less than 3dB, and the return loss S11 is less than-10 dB.

Description

A Novel Archimedes Spiral Antenna for Stepped Frequency Ground Penetrating Radar

technical field

The invention belongs to the design field of stepped frequency ground penetrating radar, in particular to an Archimedes helical antenna device used for stepped frequency ground penetrating radar.

Background technique

Ground penetrating radar is an efficient geophysical method that uses high-frequency electromagnetic waves with frequencies between 100MHz and 4000MHz to determine the distribution of underground media. At present, there are two main working methods of mainstream ground penetrating radar, one is the time domain pulse mechanism. Ground penetrating radar, one is a ground penetrating radar with a stepped frequency mechanism. Compared with a ground penetrating radar with a stepped frequency mechanism, the ground penetrating radar with the time domain pulse mechanism has obvious advantages in signal processing, but it is difficult to take into account the resolution. and penetration depth, and the ground penetrating radar of the stepped frequency mechanism can take into account these two points very well.

According to the platform, ground penetrating radar can be divided into vehicle-mounted, air-borne and human-driven, etc.; the workplaces are also relatively diverse, including mountains, plains, deserts and even glaciers; they are also widely used, such as urban building detection, mine detection, archaeology Detection, mineral exploration, personnel search and rescue, etc.; therefore, the smaller the equipment, the better. In order to ensure the penetrability of the ground penetrating radar, the step frequency ground penetrating radar generally chooses the wavelength band with a longer wavelength. At the same time, to ensure high resolution, the radar must have a wider bandwidth, and the antenna is one of the most important components of the radar system. , a miniaturized ultra-wideband antenna is an important guarantee for the performance of stepped frequency ground penetrating radar.

Archimedes helical antenna is a kind of planar broadband antenna. It has the characteristics of simple structure, wide frequency band and good radiation performance. It is a common antenna in ground penetrating radar systems. At present, the two mainstream Archimedes helix antennas are the square Archimedes helix antenna and the circular Archimedes helix antenna. Both have their own advantages and disadvantages. Based on the energy band theory, the square Archimedes helix antenna The size of the circular Archimedes helix antenna is about 22% smaller at the same operating frequency, and the circular polarization performance of the circular Archimedes helix antenna is significantly better than that of the square Archimedes helix in the high frequency band. Therefore, it is very useful to combine the advantages of the two to develop an Archimedes helix antenna that is miniaturized, has good circular polarization performance, wide frequency band, high directivity, and is suitable for stepped frequency ground penetrating radars of various types of carriers. necessary.

SUMMARY OF THE INVENTION

The purpose of the present invention is to solve the above problems, to provide a miniaturized, wide-band, high-directivity Archimedes helical antenna for step-frequency ground penetrating radar. 300mm×300mm, the axial ratio is less than 3dB, the pattern is good, the gain is not less than 3dB, and the return loss S11 is less than -10dB.

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

A novel Archimedes helical antenna for stepped frequency ground penetrating radar, comprising a dielectric substrate, an antenna arm, a wave absorbing material, a reflective cavity, an unbalanced-balanced feeding balun and a coaxial joint; it is characterized in that, The antenna arm is a square double-armed helical antenna sheet with cut corners at all four corners, the cut corners are isosceles right triangles, and the angle of the cut corners decreases from the center to the outside in steps of 0.5-5°/circle. The angle is not greater than 45°; the square double-armed helical antenna sheet with cut corners at all four corners is loaded with terminal resistances at a quarter wavelength of the two arms away from the terminal minimum operating frequency.

Further, the arm width of the antenna arm is not less than 2 mm, and the ratio of the distance between the arms to the arm width is 0.5-1.5.

Further, the antenna arm is arranged on a dielectric substrate, the dielectric substrate is arranged on the top of the reflection cavity, the inner sidewall of the reflection cavity is coated with a wave absorbing material, and an antenna feeding port is provided in the center of the dielectric substrate, and the A via hole is provided at the center of the bottom end of the reflection cavity, and the unbalanced-balanced feeding balun sequentially connects the antenna arm and the coaxial connector through the antenna feeding port and the via hole to realize electrical connection.

It should be further explained that the square double-arm helical antenna sheet with cut corners at all four corners of the present invention, wherein the cut corners are isosceles right triangles, as shown in FIG. The included angle θ formed by the dotted line; the ratio between the arm spacing and the arm width is: L1:L2=0.5～1.5.

According to the radiation characteristics of the Archimedes helix antenna, the present invention radiates electromagnetic waves of different frequencies in different regions, and the frequencies are from high to low from the inside to the outside. Compared with the circular antenna, the size is reduced by about 22% under the same working frequency, but the axial ratio performance of the square antenna is worse than that of the circular antenna. Therefore, the invention adds a cut angle on the basis of the square antenna, which can not only ensure the axial ratio performance of the antenna The size of the antenna is reduced as much as possible, the unidirectional radiation of the antenna is realized by the reflective cavity, and the unbalanced-balanced feeding is realized by the matching balun.

The beneficial effects of the present invention are:

1) The antenna arm of the present invention adopts a square double-arm helical antenna sheet with cut corners at all corners, so that the overall size of the antenna is small, the structure is compact, and the length × width of the antenna is not more than 300mm × 300mm;

2) The antenna of the present invention adopts a variable cut angle size according to different radiation areas, which not only ensures the radiation performance of the antenna but also reduces the size of the antenna to the greatest extent possible;

3) The antenna of the present invention uses a reflective cavity and attaches a wave-absorbing material to the side wall inside the cavity, which reduces the influence of the side wall on the antenna relative to the high-frequency working band, and ensures the antenna’s relative high-frequency working band while realizing the directional radiation of the antenna. Good radiation waveform;

4) The antenna of the present invention is loaded with resistance at the end, which weakens or even eliminates the "ringing effect", thereby reducing the reflection at the end of the antenna, and effectively improving the return loss performance;

5) The working frequency bandwidth of the antenna of the present invention is less than -10dB in the frequency band range of 250MHz to 1600MHz, and has an ultra-wide bandwidth.

Description of drawings

Fig. 1 is the structure top view of the novel Archimedes helix antenna of the present invention;

Fig. 2 is the structural side sectional view of the novel Archimedes helix antenna of the present invention;

Fig. 3 is the partial enlarged schematic diagram of the antenna arm of the present invention;

Among them, 1 is the antenna feed port, 2 is the antenna arm, 3 is the dielectric substrate, 4 is the unbalanced-balanced balun, 5 is the via hole, 6 is the absorbing material, 7 is the balun fixing device, and 8 is the coaxial SMA connector, 9 is the reflection cavity, 10 is the loading resistor, and 11 is the cut angle.

FIG. 4 is a graph of the simulated return loss (S11) curve of the novel Archimedes helical antenna in the embodiment of the present invention.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and examples.

This embodiment provides a new type of Archimedes helical antenna for stepped frequency ground penetrating radar. 9. Unbalanced-balanced feeding balun 4 and coaxial joint 8; the antenna arm 2 is arranged on the dielectric substrate 3, the dielectric substrate 3 is arranged on the top 9 of the reflection cavity, and the inner wall of the reflection cavity 9 is coated with suction Wave material 6, an antenna feed port 1 is provided at the center of the dielectric substrate 3, a via hole 5 is provided at the center of the bottom end of the reflective cavity 9, and the unbalanced-balanced feed balun 4 sequentially passes through the antenna feed port 1 The antenna arm 2 is connected to the coaxial joint 8 with the via hole 5 to realize electrical connection; the coaxial joint 8 is fixed to the reflection cavity 9 through the balun fixing device 7; the antenna arm 2 is a square with cut corners at all corners Double-arm helical antenna sheet, as shown in Figure 3, the cut angle is an isosceles right triangle, the angle of the cut angle decreases from the center to the outside in steps of 1.04°/circle, and the starting angle is 37°; The square double-arm helical antenna sheet with cut corners is loaded with end resistances at the quarter wavelength of the minimum operating frequency between the arms. The size is length × width 300mm × 300mm, and the number of turns is 23.

In this embodiment, on the copper-clad Arlon AR 450 or similar dielectric plate with electrical parameters, a high-precision etching process such as photolithography is used to etch the square-cut antenna arm 2; the wave absorbing material 6 is attached to the On the inner side wall of the reflective cavity 9, the antenna substrate 3 is fixed on the top of the reflective cavity 9 with super glue, the unbalanced-balanced balun 4 is passed through the reflective cavity through hole 5, and the balun fixing device 7 is used to fix it on the reflective cavity 9, then solder it with the antenna arm 2, and then solder the coaxial SMA connector 8 at its end to achieve the electrical connection of the coaxial SMA connector 8 to the unbalanced-balanced balun 4 and then to the square chamfered antenna arm 2 .

In this embodiment, the reflective cavity is made of materials with good electrical conductivity such as copper or aluminum. The length and width of the cavity are conformal to the substrate, and the height is about a quarter of the maximum working wavelength. The inner sidewall of the cavity is pasted with a The minimum operating frequency of the layer is not less than 600MHz; the end is loaded with resistance, the antenna arms are disconnected at about a quarter wavelength from the end of the minimum operating frequency, and the resistance is used to connect them to complete the end resistance loading .

Figure 4 shows the simulated return loss (S11) curve of the new Archimedes helical antenna. The return loss is less than -10dB in the frequency range of 250MHz to 1600MHz, indicating that the antenna has good broadband characteristics.

The above descriptions are only specific embodiments of the present invention, and any feature disclosed in this specification, unless otherwise stated, can be replaced by other equivalent or alternative features with similar purposes; all the disclosed features, or All steps in a method or process, except mutually exclusive features and/or steps, may be combined in any way.

Claims (3)

1. An Archimedes spiral antenna for a stepping frequency ground penetrating radar comprises a dielectric substrate, an antenna arm, a wave absorbing material, a reflecting cavity, an unbalanced-balanced feed balun and a coaxial connector; the antenna is characterized in that the antenna arm is a square double-arm spiral antenna sheet with four corners provided with cutting angles, the cutting angles are isosceles right triangles, the angles of the cutting angles are gradually decreased from the center to the outside by 0.5-5 degrees per circle, and the initial angle is not more than 45 degrees; the square double-arm spiral antenna sheet with the four corners provided with the cutting corners is loaded with terminal resistors at the position which is one quarter wavelength away from the minimum working frequency of the terminals of the double arms; the angle of the chamfer represents the angle formed by connecting two end points on the long edge of the chamfer with the central point of the antenna sheet.

2. An archimedean spiral antenna according to claim 1, wherein the arms of the antenna have an arm width of not less than 2mm and the ratio of the inter-arm spacing to the arm width is 0.5 to 1.5.

3. An archimedean spiral antenna as claimed in claim 1 or 2, wherein the antenna arms are disposed on a dielectric substrate, the dielectric substrate is disposed on the top of the reflection cavity, the inner side wall of the reflection cavity is coated with a wave-absorbing material, an antenna feeding port is formed in the center of the dielectric substrate, a via hole is formed in the center of the bottom of the reflection cavity, and the unbalanced-balanced feeding balun connects the antenna arms to the coaxial connectors through the antenna feeding port and the via hole in order to realize electrical connection.

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