JPS58123203A - Dual-conductor spiral antenna - Google Patents

Abstract

PURPOSE:To improve the axis-ratio characteristic of a circular polarized wave radiated at a low frequency in an operation frequency band by using two different-length conductors and arranging their outer circumferential terminal parts at asymmetrical positions about the center. CONSTITUTION:An electromagnetic wave radiated from an antenna has a circular polarized wave component radiated while propagating in current band area and a linear polarized wave component radiated by a current in a standing wave state. A spiral conductor 2' is shorter than a spiral conductor 1 and positioned asymmetrically about a center 7 as compared with an outer circumferential terminal part 5. Waves 10, 11, and 12 corresponding to a non-node part of the standing wave are asymmetrical with waves 10'', 11'', and 12'' about the center 7. Therefore, radiated waves by the conductors 1 and 2' have planes of polarization as shown by arrows 20 and 20'' and are linear polarized wave components different in time and space from each other. When those linear polarized wave components are put together, the standing wave on the conductors decreases in amplitude and an electromagnetic field having the same rotational direction with the circular polarized wave is produced.

Description

Detailed Description of the Invention In a spiral antenna that is used as an ultra-wideband antenna and is formed of two conductive strips on an insulating support, for example, the length of these two conductive wires and the position of the outer peripheral end of the conductive wire are The present invention relates to a two-wire spiral antenna characterized in that the circularly polarized wave ratio (hereinafter referred to as circularly polarized wave axis ratio) of the circularly polarized wave radiated from these conductive wires is improved in a low frequency band by selecting these conductors.

A conventional two-strand spiral antenna (hereinafter referred to as an antenna) consists of two conductive wires of equal length spiraling from the center to the outer periphery, and the outer shape is often circular or planar. There are many spiral shapes iζ, such as logarithmic spirals, Archimedean spirals, and special square spirals, all of which are used as ultra-wideband antennas. The operating principles of these antennas are all the same, and will be explained using an Archimedean spiral antenna as an example. 1st
The figure is a plan view showing an example of a conventional square spiral antenna. In FIG. 1, 8 is a disc-shaped insulating support. l
and 2 are four edges formed on the insulating support 8, starting from the ends 6 and 6', respectively, close to the center 7 and ending at the outer peripheral ends s5 and 5.
The ends 6 and 6' and the peripheral ends 5 and 5' are respectively symmetrical with respect to the center 7. Further, the conductive wires 1 and 2 have the same overall length. 3 is a feed line connected to ends 6 and 6' of conductors i11 and 2, conducting currents 4 and 4', respectively! v! 11 and 2. A part of the intermediate part between leads #1 and #2 is shown by a broken line and is omitted.

30 is a circle with radius r=λ/2π, where λ is the wavelength of electromagnetic waves radiated from the conductive wires 1 and 2. Reference numeral 31 indicates a group of circles corresponding to radii that differ slightly in wavelength λ, and is called a current band region. The electromagnetic wave with the wavelength λ is radiated particularly strongly at a portion where the circumference 2tF of the circle 30 is equal to the wavelength λ, and the polarization plane of the radiated electromagnetic wave exhibits circular polarization. Currents 4 and 4' from the feeder line 3 are not attenuated at all inside the current band region 31, and proceed outwards,
1, the radiation is intense and is significantly attenuated. After encountering the current band region, it reaches the outer terminals 5 and 5' with small attenuation and is reflected.

When the outer diameter of the antenna is sufficiently large and the IEtIt band region corresponding to the operating frequency band has a sufficient margin up to the outer diameter of the antenna, the current reaching the terminal end of the outer station will be very small. It's completely ignored.

In a frequency band where such conditions are met, the antenna's radiation characteristics remain constant with respect to frequency changes, so it is used as a wideband antenna for various purposes. However, when this antenna is used in an aircraft or the like, the outer diameter of the antenna is restricted due to the requirement for small size and light weight. The outer diameter of this antenna limits the lower limit of the operating frequency band as described above. That is, as the current band region 31 gradually moves toward the outer circumference and approaches the outer diameter of the antenna, the current that reaches the outer circumferential ends 5 and 5' and is reflected cannot be ignored. To put it simply, the reflected current generates a standing wave on the outer periphery of the antenna, and this standing wave generates a linearly polarized wave component, which deteriorates the axial ratio of the circularly polarized wave. Fortunately, other characteristics of the antenna, such as gain, radiation directivity, and input impedance, are not affected by this reflected current, such as the axial ratio characteristics.

Attenuates the reflected current that causes the axial ratio of circularly polarized waves to steepen.
f operating station; several ideas have been proposed in the past because they can widen the lower limit of the wave number band. For example, attempts have been made to provide non-reflection terminators at the outer ends of conductors 1 and 2, load absorbers, or create a zigzag structure. However, these attempts have had the drawback of not being able to expect significant effects despite the high manufacturing costs and affecting other properties other than the axial ratio.

The present invention eliminates radiation in the low frequency band of the operating frequency band by keeping the lengths of the two conductive wires that make up the spiral antenna at different lengths and by arranging the outer peripheral ends asymmetrically with respect to the center. It is an object of the present invention to provide a two-strand spiral antenna that can improve the axial ratio characteristics of the circle 11 and expand the operable frequency range of the antenna.

According to the present invention, circularly polarized waves with significantly improved axial ratio characteristics in the above-mentioned low frequency band can be obtained, and compared to conventional antennas having the same axial ratio of circularly polarized waves at the same frequency, the antenna has a smaller deafness. It is possible to obtain a large two-strand spiral antenna.

Next, based on the drawings, it is an explanatory diagram illustrating standing waves on the conductive layer of the antenna, comparing an embodiment of the double-strand spiral antenna according to the present invention with a conventional one.

As mentioned above, the electromagnetic waves radiated from the antenna propagate through the current band region and are generated by the combination of the radiated circularly polarized wave component, the reflected wave reflected at the outer end of the conductor, and the traveling wave toward the outer end. There is a linearly polarized wave component radiated by the generated stationary wave state current. The waves whose amplitudes correspond to the lengths of the arrows in Figure 2 are such standing waves.

Figure 2 (2) and (6) show standing waves in conductors 1 and 2,
If the village is the same as in Figure 1, the same village name will be used. Waves 10, 11, and 12 and waves 10', 11', and 12' are the antinodes of the standing wave, respectively. Since the leads 111 and 2 have the same length and the outer ends are at symmetrical positions with respect to the center 7, the positions of the antinodes of the standing waves are also symmetrical with respect to the center 7.

Due to the nature of the standing wave antenna, the radiation waves from the antinode of the standing wave are all in phase, and when combined, the waves shown by arrow 20 and arrow 2
It becomes a linearly polarized wave component with a plane of polarization in the direction shown by . That is, the linearly polarized wave components radiated from the conductors 1 and 2 are vector-added to become a directly polarized wave component with twice the amplitude, resulting in a significant deterioration of the axial ratio of the circularly polarized wave. In this way, in conventional antennas, the axial ratio of circularly polarized waves deteriorates because the standing wave current generates linearly polarized wave components, but the radiated electromagnetic waves due to the standing waves are circularly polarized radiated by the traveling waves in the current band region. The axial ratio sensitivity of circularly polarized waves can be avoided by using means that generates circularly polarized waves in the same direction of rotation as the waves. This is the focus of the present invention.

FIG. 3 is an explanatory diagram of the standing wave distribution on the two-strand spiral antenna 4# according to the present invention. wJ3 Figure ^ is exactly the same drawing as Figure 2 4 and shows the standing wave distribution of Hiromaro 1 Figure 3 (6)
It is shown for comparison. Figure 3 (6) is the second
The state in which the length of the conductor 2 is shortened so that the standing wave of the conductor @2 shown in Figure (6) is at the position where the outer peripheral end ass' is moved by the center angle 0, i.e. !3
This figure shows the standing wave distribution of the conductor * 2 / which is located at an asymmetrical position with respect to the center 7 compared to the outer peripheral end 5 in the figure. Waves 10, 11, and 1 indicate the antinode of a standing wave.
2 are located at asymmetrical positions with respect to the center 7 with respect to waves 10", 11" and 12". The radiated waves by #4 #11 and 2' are directed in the directions indicated by arrows 20 and 20" as described above. They are linearly polarized components that are temporally and spatially different from each other. Now, if we choose orthogonal coordinates with the center 7 as the origin and the direction of the arrow 20 of the conducting wire 1 as the X-axis, and the radiation direction as the two axes, the electric field at an infinite point on the z-axis can be expressed by the following equation.

rB, = te, (A − coa (ωt+φ1) +
cos # * Acos (ωt+φ2))...+1
1 1t;y=l=y(UI IF @ Acos (
* t + φ2) ) ・ ・(2) Here, the old ,
E is the electric field component, Theory 1, positive is the Xg y y-axis direction vector, A is the amplitude, and ω is the angular velocity φ1 and φ
d is the excitation phase, 0 is the angle shown in Figure 3 (81). From equations (1) and (2), the axial ratio Al (of the circularly polarized wave formed by the Denrin class ■1 and old is the following It is calculated as follows.Since the relative phase difference between the electric field components and the former is a gap, φ=01−
=Δφ.

If we set AR=1 in l 2 formula < 37, m II −) can
Δφ=O--(4) The equation (4) is obtained. Formula (3
), it is explained that when -=0, that is, when the arrangement is symmetrical, the axial ratio becomes infinite, and when #~0, the axial ratio rapidly improves. Furthermore, by solving equation (4), it is possible to obtain almost completely circularly polarized waves at a certain specific frequency. Therefore, even if there are standing waves in the four sparse 1 and 2', the arrangement should be asymmetrical (therefore, by combining the linear 1 wave components radiated from the conductors l and 2', 'NL
The effect is that it is possible to configure an electromagnetic field having the same rotation direction as the circularly polarized wave radiated from the flL band region. In addition, the high frequency current flowing through the conductors 111 and 2' is
The phase difference of the reflected current approaches the opposite direction, and the conductor I!■ and the adjacent conductor 1ii2' become closed.The electric force 11 increases, causing harmful radiation. It can be seen qualitatively that it becomes difficult to occur.In other words, 4 Gan 1
and 2' have the effect that the standing wave amplitude on the conductor becomes small due to their asymmetrical arrangement. For these reasons, the axial ratio of circularly polarized waves can be greatly improved at the lower limit of the operating frequency band. So far, we have explained the situation in which the antenna is used when wideband operation is desired, but the conductor 1
By selecting an asymmetrical arrangement of and 2, it is possible to operate in a narrow band and to exhibit the best axial ratio at the desired frequency.

Figure 4 shows the circle gI radiated from the double spiral antenna.
FIG. 3 is an explanatory diagram showing the axial ratio and frequency characteristics of the a-wave. In FIG. 4, the vertical axis shows the axial ratio, and the horizontal axis shows the frequency (GH,). Graph 1jL) shows the characteristics of the conventional antenna, and graph 1jL) shows the characteristics of the conventional antenna.
l is the characteristic of the antenna according to the present invention, which is configured so that the axial ratio is minimized near the frequency 2G)I, and the graph Ic
Similarly, I shows the characteristics of an antenna according to the present invention configured to have a flat axial ratio so as to operate in a wide frequency band. As graph (C1) shows, in this operating frequency range, the operable wave number range has been expanded by nearly 100%.Also, it has been confirmed that many actual feeds do not cause the main effect, and formula (1) and the angle shown in (2) is 40ii
: There is a suitable value for shrimp between 150 degrees and 150 degrees.

Furthermore, in a two-strand spiral antenna, for the purpose of measuring disconnection of the antenna conductor, it is often done to provide a short circuit between both conductors at the end of the outer station.

In such a case, the state of reflection of the high frequency current at the end of the outer periphery will change compared to the previously described open case. However, even in this case, it has been confirmed that the axial ratio of the circular UA wave can still be improved by arranging the outer peripheral end portion asymmetrically with respect to the center as described above.

In this way, the present invention has a structure in which the outer peripheral end of the antenna conductor is open.
It can be applied to any short-circuit condition.

As explained above, this system operates by a simple procedure of keeping the lengths of the two conductors 1 that make up the spiral antenna at different lengths and arranging the outer peripheral ends asymmetrically with respect to the center. It is possible to provide a two-strand spiral antenna that can improve the axial ratio characteristics of circularly polarized waves radiated in a low frequency band and expand the operable frequency band of the antenna.

It should be noted that it is also possible to use the present invention in combination with conventionally used means for improving the axial ratio of circularly polarized waves, and an even better axial ratio can be obtained. Furthermore, the present invention can be applied not only to planar logarithmic spiral antennas and planar rectangular spiral antennas, but also to all spiral antennas having two conductive wires, such as a bell-shaped spiral antenna.

[Brief explanation of drawings]

FIG. 1 is a plan view showing an example of a conventional two-strand spiral antenna, and FIG. 2 is a conventional two-strand spiral antenna 41.
i! The above explanatory diagram of the standing wave distribution and FIG. 3 are explanatory diagrams showing the axial ratio and frequency characteristics of the circularly polarized wave radiated from the double-strand spiral antenna according to the present invention. 1 and 2 and 2'... conductor wire, 3... power supply line, 4 and 4',
...Current, 5 and 5' and 5''...External end, 6 and 6
'... End; 7... Center, 8... Insulating support, 1
0 and 11 and 12 and 10' and 11 'A12' and 10' and 11' and 12'...1
Wave, 20 and 20' and 20' jL a, f@, arrow,
30-...Yen, 31...Current band area, Patent applicant Tokyo Keiki Hayabusa 10 $4f! ! U /jljJ屹行C(tHx) 13

Claims (1)

[Claims] In a spiral antenna composed of two conductive wires that extend spirally from the center to the outer periphery, each of the two conductive wires has a different purpose, and the position of the exclusive outer peripheral end is asymmetrical with respect to the center. A two-striped spiral antenna characterized by a