CN103943949B - The fractal miniaturization method of Axial-mode cylindrical helical antenna - Google Patents

Abstract

The invention discloses the fractal miniaturization method of a kind of Axial-mode cylindrical helical antenna, it comprises the following steps: step one, constructs a fractal curve；Step 2, constitutes longer, a periodically fractal curve；Step 3, draws a cylinder；Step 4, by the periodicity fractal curve that constructs in step 2 along its starting point rotation alpha counterclockwise or π α angle；Step 5, forms circle dextrorotation or a left-handed cylindrical screw；Step 6, merges M and encloses one fractal helical strips of fractal spiralization；Step 7, becomes, by the helical strips that the M in step 6 encloses, the metal conduction band that thickness is T；Step 8, places circular concentric copper coin；Step 9, the initial end at fractal helix increases λ/4 impedance transformer.The present invention makes the axial mode operating frequency of helical antenna reduce, thus realizes compact in size.

Description

Fractal Miniaturization Method of Axial Mode Cylindrical Helical Antenna

technical field

The invention relates to an antenna and a fractal miniaturization method thereof, which is a fractal miniaturization method of an axial-mode cylindrical helical antenna, in particular a Gesip-Piano fractal miniaturization method of an axial-mode cylindrical helical antenna .

Background technique

Circularly polarized waves have the advantages of anti-ionospheric Faraday magnetic effect, good target recognition ability, strong anti-interference ability, good communication link robustness (Robustness), and low requirements for antenna installation. , radio astronomy, radar detection, electronic reconnaissance/countermeasures, electronic warfare and other fields have been widely used. Circularly polarized waves are usually generated by circularly polarized antennas or circular polarizers. Conventional circularly polarized antennas use two excitation feeds with equal amplitudes, orthogonal phases, and orthogonal directions to generate circularly polarized waves, so the axial ratio bandwidth and circularly polarized beamwidth are usually very narrow, such as circularly polarized microstrip antenna, circularly polarized patch antenna, etc. In contrast, the helical antenna relies on its own helical structure to achieve circularly polarized radiation. It has a wide axial ratio bandwidth and circularly polarized beam width, good in-band axial ratio and gain flatness. It is a typical The wideband circularly polarized antenna has good practical value. Therefore, since its invention more than half a century ago, helical antennas have been extensively studied and have gained extensive engineering applications. However, it is still a very difficult task to design a helical antenna with wide bandwidth, high gain, high-purity circular polarization, low profile, compact structure, and small size that meets practical needs. Common spiral antennas include planar spiral antennas (Spiral), such as Archimedes spiral antennas, planar equiangular spiral antennas and involute spiral antennas, and space spiral antennas (Helix), such as cylindrical spiral antennas, conical spiral antennas, spherical/elliptical Spherical helical antenna, etc.

Like any other type of antenna, the helical antenna also has a physical size comparable to the working wavelength. For example, the outer diameter of the planar helical antenna is proportional to its lowest working wavelength, and the diameter of the axial mode cylindrical helical antenna is about 1/π times the working wavelength. . In the microwave and millimeter wave frequency bands, the physical size of the helical antenna is small, but in the lower frequency bands such as UHF, VHF, HF, and LF, the size of the helical antenna will become so large and bulky that it cannot be used. In addition, although the input impedance of the conventional cylindrical helical antenna (CHA) is almost a constant in the band, it is not ideal purely resistive, and the imaginary part presents a large capacitive component, which is difficult to match. Therefore, reducing the physical size so that it can be applied to lower frequency bands and realizing pure resistive impedance to improve matching characteristics have become important topics in the research field of helical antennas.

Contents of the invention

The technical problem to be solved by the present invention is to provide a fractal miniaturization method of an axial-mode cylindrical helical antenna, which reduces the diameter of the helical antenna and reduces the working frequency of the axial mode of the helical antenna, thereby realizing size miniaturization.

The present invention solves the above-mentioned technical problems through the following technical solutions: a fractal miniaturization method of an axial-mode cylindrical helical antenna, which is characterized in that it comprises the following steps:

Step 1: Construct a fractal curve with width W and horizontal length L ₀ on the XOZ plane. The ratio of horizontal length l _i to vertical length m _i of each iteration I _i is δ _i = l _i /m _i , i is the number of iterations I _i ;

Step 2, on the XOZ plane, connect N such fractal curves end to end to form a longer, periodic fractal curve, whose horizontal total length L is equal to the length of a circle of spirals C=L=N·L ₀ ;

Step 3, in the Cartesian coordinate system, draw a cylinder whose bottom surface is located on the XOY plane, arranged along the +Z axis, with a diameter of D=C/π and a height of H;

Step four, on the XOZ plane, rotate the periodic fractal curve constructed in step two counterclockwise along its starting point by an angle of α;

Step five, conform the Gesip-Piano fractal curve rotated by α angle to the surface of the cylinder in step three to form a right-handed cylindrical helix; if you want to form a left-handed cylindrical helix, then in step four, counterclockwise The rotation angle should be π-α;

Step 6, copy M copies of a right-handed or left-handed spiral in step 5 along the +Z axis, and then merge M circles of fractal spirals to form a fractal spiral strip;

Step 7, changing the spiral strip of M circles in step 6 into a metal conduction band with a thickness of T;

Step 8, place a concentric circular copper plate with a diameter of D _g and a thickness of h at a distance d from the bottom of the fractal cylinder spiral, as a feeder floor and reflector;

Step 9: Add a λ/4 impedance converter at the initial end of the fractal spiral, whose characteristic impedance is determined by the input impedance of the helical antenna and the characteristic impedance of the coaxial line; It is connected to one end of the impedance transformer, and the outer conductor is connected to the floor.

Preferably, the materials of the helix of the helical antenna, the impedance transformation section and the floor can be selected from various types of metals.

Preferably, the helical antenna is directly wound from a metal wire, or printed on a flat flexible substrate and then wound onto a cylinder.

Preferably, the main geometric parameters of the helical antenna include: the number of iterations of the fractal curve, the length of the initial body, the width of the wire, the length ratio of the horizontal and vertical broken lines, the number of fractal units per spiral, the total number of turns of the spiral, the diameter of the spiral, and the pitch of the spiral , Helix angle.

Preferably, the width of the wire gradually narrows as the number of iterations and the number of units per turn increase.

The positive progress effect of the present invention is that: the present invention can realize continuous increase of the circumference of a single-turn helix while keeping the diameter constant, thereby reducing its working frequency and realizing miniaturization.

Description of drawings

Fig. 1 is a schematic diagram of the definition of the spherical coordinate system adopted by the antenna model;

Figure 2(a) to Figure 2(d) are schematic diagrams of Guiseppe PeanoCurve for each iteration; Figure 2(a) represents the initial body or zero iterations, and Figure 2(b) represents One iteration, Figure 2(c) represents the second iteration, and Figure 2(d) represents the third iteration;

Fig. 3 is the schematic diagram of N unit I ₁ iteration Gesip Peano periodic fractal curve;

Figure 4 is a schematic diagram of the N unit period Gesip-Piano curve rotated by α or (π-α) angle (gray-conformal cylinder);

Figure 5(a) is a schematic diagram of the front view of the M-circle Gesip Peano helical antenna (GPHMA) and cylindrical helical antenna (CHA) without impedance converter;

Figure 5(b) is a schematic side view of the M-circle Gesip-Piano helical antenna (GPHMA) and the cylindrical helical antenna (CHA) without impedance transformers;

6 is a schematic diagram of an M-circle Gesip Piano cylindrical helical antenna (GPHMA) with a quarter-wavelength impedance converter;

Fig. 7 is the schematic diagram of the input impedance Z _in (f) of the N=4, M=8 ring Gesip Peano helical antenna (GPHMA) and cylindrical helical antenna (CHA) without impedance converter;

Fig. 8 is a schematic diagram of the reflection coefficient |S ₁₁ (f)| of N=4, M=8 circle Gesip Peano helical antenna (GPHMA) and cylindrical helical antenna (CHA) without impedance converter;

Fig. 9(a) is a schematic diagram of the axial gain G(f) of N=4, M=8 circle Gesip Peano helical antenna (GPHMA) and cylindrical helical antenna (CHA) without impedance converter;

Figure 9(b) is a schematic diagram of the axial-to-axial ratio AR(f) of the N=4, M=8-turn Gesip Peano helical antenna (GPHMA) and cylindrical helical antenna (CHA) without impedance converters;

Fig. 10(a) is the pattern of the cylindrical helical antenna (CHA) with N=4, M=8 coils without impedance converter at f _L =2.63GHz;

Figure 10(b) is the directivity diagram of the N=4, M=8-turn cylindrical helical antenna (CHA) at f _H =4.23GHz without impedance converter;

Fig. 11(a) is the pattern of the N=4, M=8-turn Gesip Piano helical antenna (GPHMA) at f _L =2.02GHz without impedance converter;

Fig. 11(b) is the pattern of the N=4, M=8-turn Gesip Piano helical antenna (GPHMA) at f _H =3.02GHz without impedance converter;

Fig. 12 is a schematic diagram of the input impedance Z _in (f) of the N=4, M=8 ring Gesip Piano helical antenna (GPHMA) with a quarter-wavelength impedance converter;

Fig. 13 is a schematic diagram of the reflection coefficient |S ₁₁ (f)| of the N=4, M=8 ring Gesip Piano helical antenna (GPHMA) with a quarter-wavelength impedance converter;

Fig. 14 is a schematic diagram of the axial gain frequency characteristic G(f) of the N=4, M=8 ring Gesip Piano helical antenna (GPHMA) with a quarter-wavelength impedance converter;

Fig. 15 is a schematic diagram of the axial ratio frequency characteristic AR(f) of the N=4, M=8 ring Gesip Piano helical antenna (GPHMA) with a quarter-wavelength impedance converter;

Fig. 16(a) is the pattern of the N=4, M=8 circle Gesip Piano helical antenna (GPHMA) with a quarter-wavelength impedance converter at f _L =2.02GHz;

Fig. 16(b) is the pattern at f _H =3.02GHz of the N=4, M=8-turn Gesip Piano helical antenna (GPHMA) with a quarter-wavelength impedance converter.

The accompanying drawings are used to further illustrate and understand the present invention, and constitute a part of the description, together with the examples of the present invention, are used to explain the present invention, but do not constitute a limitation to the present invention.

detailed description

In the following, a miniaturized Geseppe Peano helical antenna (GPHMA) is specifically designed based on I ₁ (one iteration) Guiseppe Peano Curve, and corresponding drawings are given to illustrate the present invention in detail. It should be noted that the preferred implementation examples described here are only used to illustrate and explain the present invention, and are not used to limit or limit the present invention.

As shown in Figure 6, the antenna structure that the present invention adopts comprises Gesip Peano fractal helix 1, quarter-wavelength air microstrip impedance converter 2, conformal cylinder 3, metal disk 4, and 50Ω standard coaxial cable 5.

The Gesip Peano fractal miniaturization design method of the axial modulus cylindrical helical antenna is introduced in detail below, that is, the fractal miniaturization method of the axial modulus cylindrical helical antenna includes the following steps:

Step 1, construct a Gesip-Piano fractal curve with a width of W and a horizontal length of _L0 on the XOZ plane, as shown in Figure 1 and Figure 2(a)-(d) (l _i and m _i respectively is the horizontal length and vertical length of I _iterations ). Wherein, the ratio of the horizontal length l _i to the vertical length m _i of each iteration I _i is δ _i = l _i /m _i (i is the number of iterations I _i ).

Step 2, on the XOZ plane, connect N such Gesip-Piano fractal curves end to end to form a longer, periodic fractal curve, and its total horizontal length L is equal to the length of a circle of spiral C=L= N·L ₀ , as shown in Fig. 3 .

Step 3: In the Cartesian coordinate system, draw a cylinder whose bottom surface is located on the XOY plane, arranged along the +Z axis, with a diameter of D=C/π and a height of H, as shown in Figure 4.

Step 4: Rotate the XOZ plane and the periodic gridhip-Piano fractal curve constructed in step 2 counterclockwise along its starting point by an angle α (ie, the helix angle), as shown in Figure 4.

Step five, conform the Gesip-Piano fractal curve rotated by α angle to the surface of the cylinder in step three, forming a circle of right-handed cylindrical helix (RHCP), as shown in Fig. 5(a), Fig. 5( b) as shown (wherein, W ₁ represents the width of the helical wire, T represents the thickness of the helical wire, α represents the helix angle, S represents the pitch, D represents the diameter of the helix, C represents the length of the single-turn helix; D _g represents the diameter of the floor, h represents the thickness of the floor, d represents the height of the helix start from the ground); if a left-handed cylindrical helix (LHCP) is to be formed, the counterclockwise rotation angle in step 4 should be (π-α), as shown in Figure 4.

Step 6, copy M copies of a right-handed or left-handed spiral in step 5 along the +Z axis, and then merge M circles of fractal spirals to form a fractal spiral strip, as shown in Figure 5(a) and Figure 5(b) Show.

In step seven, the M-circle fractal spiral strip in step six is changed into a metal conduction strip with a thickness of T, and the material is set to pure copper, as shown in Fig. 5(a) and Fig. 5(b).

Step eight, place a concentric circular copper plate with a diameter of D _g and a thickness of h at a distance d from the bottom of the fractal cylinder spiral, as a feeder floor and reflector, as shown in Figure 5(a) and Figure 5(b) Show.

Step nine, add a λ/4 impedance converter at the initial end of the fractal spiral, and its characteristic impedance Z ₀ is determined by the input impedance Z _in of the helical antenna and the characteristic impedance Z _c of the coaxial line, namely Then, a 50Ω coaxial cable is used to directly feed power, the inner conductor is connected to one end of the impedance transformer, and the outer conductor is connected to the floor, as shown in Figure 6 (here N=4, M=8, W ₁ =1.5mm, T =1.5mm, α=12o, S=17.57mm, D=26.31mm, H=140.56mm, C=82.65mm; D _g =150mm, h=1mm, d=6.2mm).

According to the above steps, we can get the helix length of Gessi Pupiano's helix GPMHA as follows (1):

L=M·C=M·N·[4.5·(L ₀ /3.5)+4·(L ₀ /3.5)·(m ₁ /l ₁ )]

=M·N·{(L ₀ /3.5)·[4.5+4·δ ₁ ]}

={[4.5+4·δ ₁ ]/3.5}·M·N·L ₀ ……………………………………(1)

The helix length of the cylindrical helical CHA is as follows (2):

L'=M·N·L ₀ ………………………………………………(2)

The ratio of the lengths of the two spirals is as follows (3):

$\frac{\mathrm{<span\; class="notranslate">\; L</span>}}{{\mathrm{<span\; class="notranslate">\; L</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 4.5</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 3.5</span>}}<span\; class="notranslate">\; ></span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Aiming at the present situation that the helical antenna is a circularly polarized antenna with excellent performance, the impedance is not purely resistive, and the size is too large to be practical at low frequencies, the present invention focuses on using fractal curves to realize the axial mode (Axial-mode) The miniaturization method of the cylindrical helical antenna is to replace the conventional smooth helix with the Guiseppe Peano fractal curve (Guiseppe Peano Curve), so as to achieve physical size reduction and matching performance improvement. Due to the space-filling property of the fractal curve, the physical length of the fractal curve becomes longer with the increase of the number of iterations, but the overall size of the antenna remains constant. Under variable circumstances, the circumference C of the single-turn helix is continuously increased, thereby reducing its operating frequency. In addition, fractal also has self-loading and self-resonance characteristics, which can realize impedance self-matching, and has been widely used in various antenna designs, that is, we are familiar with fractal antennas. Naturally, we consider applying fractals to the miniaturization design of cylindrical helical antennas. Studies have shown that the diameter of the axial-mode cylindrical helical antenna is reduced by at least 33% after Gesip Piano fractal design, and it can be further reduced with the adjustment of structural parameters. At the same time, the pure resistance of the in-band impedance is improved, the frequency consistency is more significant, and the matching is easier and more ideal.

The Guiseppe Peano fractal curve (Guiseppe Peano Curve) involved in the present invention is not limited to one iteration I ₁ selected as an example, but includes various iterations, such as the second iteration I ₂ , three iterations I ₃ ... N iterations I _N (N is a natural number) and so on. The main geometric parameters of the Gesip-Piano fractal spiral antenna are: the number of iterations I _i of the fractal curve, the initial body length L ₀ , the wire width W _i (or diameter D _i ), the length ratio of horizontal and vertical broken lines δ _i , and each The number of fractal units N of the spiral, the total number of spiral turns M, the diameter of the spiral D, the pitch of the spiral S, and the helix angle α. Both the vertical height H of the fractal spiral and the total length L of the spiral are determined by the above parameters. The Gesip Piano fractal helical antenna can be wound directly from a metal wire, or printed on a flat flexible substrate and then wound onto a cylinder. The wire width W _i (or diameter D _i ) becomes narrower as the number of iterations I _i and the number of cells per circle N increase, so as to prevent adjacent fold lines from intersecting or overlapping each other. The operating frequency f _c of the Gesip Peano fractal helical antenna is determined according to the selection of the initial body length L ₀ , the number of iterations I _i and the diameter of the cylinder D, the gain G, the axial ratio AR and the bandwidth BW are related to the coil The number M is related. The more turns M, the greater the gain G, the smaller the axial ratio AR and the bandwidth BW, and vice versa. The input impedance Z _in of the Gesip Piano fractal helical antenna is not ideal 50Ω, so a microstrip impedance transformation section needs to be connected in series at the beginning of the helical wire, and the filling medium between the metal strip and the floor can be air or other Dielectric medium, its characteristic impedance Z ₀ is jointly determined by Z _in and coaxial line characteristic impedance Z _c , that is The metal floor and reflector of the helical antenna is placed at a distance d behind the bottom of the helix. Its diameter is D _g (or side length L _g ), and its thickness is h. The horizontal position is concentric with the helical cylinder, and its shape can be circular, square or regular polygon. The helical antenna is fed by a 50Ω standard coaxial line. The coaxial line passes through the via hole on the metal floor, the inner conductor thereof is connected to the beginning of the impedance transformer, and the outer conductor is connected to the metal floor by welding. For a firm and easy connection, drill holes in the floor and install an SMA connector on the back. The coaxial cable is directly connected to the SMA connector through the nut, and the inner and outer conductors of the SMA head are respectively connected to the impedance transformation section and the floor. The helix of the helical antenna, the impedance transformation section and the material of the floor can be selected from various metals, such as good conductors such as pure copper, brass, pure aluminum, stainless steel, etc., and they can be selected from the same metal material or different metal materials respectively. Because the weight of the helical conductor itself will cause axial deformation of the fractal helix, it is often necessary to install a tree-shaped plastic or wooden support above the floor, and each turn of the helix will be supported by a horizontal short pile of the support, thereby supporting the entire metal helix The weight of the thread.

In the present embodiment, the specific parameters of the non-impedance transformer and the impedance transformer with a quarter wavelength are as follows: The simulated performance parameters of the helical antenna (CHA) and the Gessip Peano helical antenna (GPHMA) with a quarter impedance transformer are shown in Figure 7-16.

As shown in FIG. 7 , it is a schematic diagram of the input impedance Z _in (f) of the N=4, M=8-turn Gesip Peano helical antenna (GPHMA) and the cylindrical helical antenna (CHA) without an impedance converter. Among them, the horizontal axis (X axis) is the frequency, the unit is GHz, the vertical axis (Y axis) is the input impedance, the unit is Ω; the solid line represents GPHMA, the dotted line represents CHA; the smooth line represents the real part, and the dotted line represents the imaginary Department; f _L represents the lowest operating frequency, f _H represents the highest operating frequency, BW represents the percentage bandwidth;

As shown in Fig. 8, the reflection coefficient |S ₁₁ (f)| schematic diagram. Among them, the horizontal axis (X axis) is the frequency, the unit is GHz, the vertical axis (Y axis) is the reflection coefficient amplitude |S ₁₁ |, the unit is dB; the solid line represents GPHMA, the dotted line represents CHA; f _L represents the lowest operating frequency, f _H represents the highest operating frequency, BW represents the percentage bandwidth;

As shown in Fig. 9(a), it is the axial gain G(f) of N=4, M=8 circle Gesip Peano helical antenna (GPHMA) and cylindrical helical antenna (CHA) without impedance converter schematic diagram. Among them, the horizontal axis (X axis) is the frequency, the unit is GHz, the vertical axis (Y axis) is the axial gain G, the unit is dBi; the solid line indicates GPHMA, the dotted line indicates CHA; f _L indicates the minimum operating frequency, and f _H indicates The highest working frequency, f _U means the upper limit frequency, BW means the percentage bandwidth;

As shown in Figure 9(b), it is the axial-to-axial ratio AR(f ) schematic diagram. Among them, the horizontal axis (X axis) is the frequency, the unit is GHz, the vertical axis (Y axis) is the axial ratio AR, the unit is dB; the solid line indicates GPHMA, the dotted line indicates CHA; f _L indicates the minimum operating frequency, f _H Indicates the highest operating frequency, f _U indicates the upper limit frequency, BW indicates the percentage bandwidth;

As shown in Fig. 10(a), it is the directivity diagram of the N=4, M=8-turn cylindrical helical antenna (CHA) at f _L =2.63GHz without impedance converter. Among them, the horizontal axis (X axis) is the elevation angle Theta in degrees (°), the vertical axis (Y axis) is the gain G in dBi; the solid line indicates Phi=0° (XOZ plane), and the dotted line indicates Phi=90 ° (YOZ plane); the smooth line represents the co-polarization component LHCP, and the dotted line represents the cross-polarization component RHCP;

As shown in Fig. 10(b), it is the pattern of the N=4, M=8-turn cylindrical helical antenna (CHA) at f _H =4.23GHz without impedance converter. Among them, the horizontal axis (X axis) is the elevation angle Theta in degrees (°), the vertical axis (Y axis) is the gain G in dBi; the solid line indicates Phi=0° (XOZ plane), and the dotted line indicates Phi=90 ° (YOZ plane); the smooth line represents the co-polarization component LHCP, and the dotted line represents the cross-polarization component RHCP;

As shown in Fig. 11(a), it is the pattern of the N=4, M=8-turn Gesip Piano helical antenna (GPHMA) at f _L =2.02GHz without impedance converter. Among them, the horizontal axis (X axis) is the elevation angle Theta in degrees (°), the vertical axis (Y axis) is the gain G in dBi; the solid line indicates Phi=0° (XOZ plane), and the dotted line indicates Phi=90 ° (YOZ plane); the smooth line represents the co-polarization component LHCP, and the dotted line represents the cross-polarization component RHCP;

As shown in Fig. 11(b), it is the pattern of the N=4, M=8-turn Gesip Piano helical antenna (GPHMA) at f _H =3.02GHz without impedance converter. Among them, the horizontal axis (X axis) is the elevation angle Theta in degrees (°), the vertical axis (Y axis) is the gain G in dBi; the solid line indicates Phi=0° (XOZ plane), and the dotted line indicates Phi=90 ° (YOZ plane); the smooth line represents the co-polarization component LHCP, and the dotted line represents the cross-polarization component RHCP;

As shown in FIG. 12 , it is a schematic diagram of the input impedance Z _in (f) of the N=4, M=8-turn Gesip Piano helical antenna (GPHMA) with a quarter-wavelength impedance converter. Among them, the horizontal axis (X axis) is the frequency, the unit is GHz, the vertical axis (Y axis) is the input impedance, the unit is Ω; the solid line indicates the real part, and the dotted line indicates the imaginary part;

As shown in Fig. 13, it is a schematic diagram of the reflection coefficient |S ₁₁ (f)| of the N=4, M=8-turn Gesip Piano helical antenna (GPHMA) with a quarter-wavelength impedance converter. Among them, the horizontal axis (X axis) is the frequency, the unit is GHz, and the vertical axis (Y axis) is the reflection coefficient amplitude |S ₁₁ |, the unit is dB;

As shown in FIG. 14 , it is a schematic diagram of the axial gain-frequency characteristic G(f) of the N=4, M=8-turn Gesip Piano helical antenna (GPHMA) with a quarter-wavelength impedance converter. Among them, the horizontal axis (X axis) is the frequency, the unit is GHz, the vertical axis (Y axis) is the axial real gain G, the unit is dBi; f _L represents the lowest operating frequency, f _H represents the highest operating frequency, and BW represents the percentage bandwidth ;

As shown in Figure 15, it is a schematic diagram of the axial ratio frequency characteristic AR(f) of the N=4, M=8-turn Gesip Piano helical antenna (GPHMA) with a quarter-wavelength impedance converter . Among them, the horizontal axis (X axis) is the frequency, the unit is GHz, the vertical axis (Y axis) is the axial ratio AR, the unit is dB; f _L represents the lowest operating frequency, f _H represents the highest operating frequency, and BW represents the percentage bandwidth ;

As shown in Fig. 16(a), it is the pattern at f _L =2.02GHz of the N=4, M=8-turn Gesip Piano helical antenna (GPHMA) with a quarter-wavelength impedance transformer. Among them, the circumferential axis is the elevation angle Theta, the unit is degree (°), the radial axis is the gain G, the unit is dBi; the solid line indicates Phi=0° (XOZ plane), and the dotted line indicates Phi=90° (YOZ plane); The smooth line represents the co-polarization component LHCP, and the dotted line represents the cross-polarization component RHCP;

As shown in Figure 16(b), it is the pattern of the N=4, M=8-turn Gesip Piano helical antenna (GPHMA) with a quarter-wavelength impedance transformer at f _H =3.02GHz. Among them, the circumferential axis is the elevation angle Theta, the unit is degree (°), the radial axis is the gain G, the unit is dBi; the solid line indicates Phi=0° (XOZ plane), and the dotted line indicates Phi=90° (YOZ plane); The smooth line represents the co-polarization component LHCP, and the dotted line represents the cross-polarization component RHCP;

To sum up, the method of the present invention can reduce the diameter of the axial mode helical antenna (CHA), thereby realizing miniaturization. At the same time, other characteristics of the antenna such as gain, polarization, axial ratio, efficiency, etc. remain basically unchanged, but the bandwidth will be slightly reduced accordingly. This is an inherent property and shortcoming of fractal miniaturized antennas. Nevertheless, the reduction effect of the method on the size of the helical antenna is still very significant and practical. In addition, the method of the invention has the advantages of easy design, easy matching and easy processing.

The above are only preferred examples of the method of the present invention, and are not intended to limit the present invention. For researchers or those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of protection declared by the present invention.

Claims (1)

1. the fractal miniaturization method of an Axial-mode cylindrical helical antenna, it is characterised in that it includes Following steps:

Step one, one width of XOZ planar configuration be W, horizontal length be L₀Fractal curve, Each iteration I_iHorizontal length l_iWith vertical length m_iRatio be δ_i=l_i/m_i, i is iterations；

Step 2, in XOZ plane, joins end to end such for N bar fractal curve, constitutes one more Long, periodically fractal curve, its horizontal total length L is equal to a circle spiral line length C=L=N L₀；

Step 3, under rectangular coordinate system, draws a bottom surface and is positioned at XOY plane, edge+Z axis row Row, diameter D=C/ π, the cylinder of a height of H；

Step 4, in XOZ plane, by the periodicity fractal curve that constructs in step 2 along its starting point Rotation alpha angle counterclockwise；

Step 5, by conformal for the Ge Xipu Piano fractal curve after rotation alpha angle in step 3 Periphery, forms a circle dextrorotation cylindrical screw；If forming left-handed cylindrical screw, then step In four, rotated counterclockwise by angle should be π-α；

Step 6, replicates M part by the circle dextrorotation in step 5 or left-turn spiral edge+Z axis, then closes And M encloses one fractal helical strips of fractal spiralization；

Step 7, becomes, by the helical strips that the M in step 6 encloses, the metal conduction band that thickness is T；

Step 8, is placing an a diameter of D at fractal cylindrical screw bottom d_g, thickness be the concentric of h Circular copper plate, is used as feed floor and holds concurrently reflecting plate；

Step 9, the initial end at fractal helix increases λ/4 impedance transformer, its characteristic impedance Determined with coaxial line characteristic impedance by the input impedance of helical antenna；Then, use 50 Ω coaxial lines straight Connecing feed, its inner wire is connected with impedance transformer one end, and outer conductor is connected with floor；

The helix material of described helical antenna, each metalloid of impedance transformer material selection；

Described helical antenna is that the direct coiling of plain conductor forms, or is printed on planar flexible substrate and rolls up On cylinder；

The main geometric parameters of described helical antenna has: the iterations of fractal curve, initial body length L₀, conductor width, anyhow broken line length compare δ_i, often enclose the fractal unit number of spiral, spiral number of total coils, Screw diameter, spiral coil are away from, lead angle；

Described conductor width increases with iterations and every coil unit number and becomes narrow gradually.