JPH043684B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a variable length whip antenna using a coaxial transmission line.

Prior Art and Problems Radio communication antennas used in mobile objects such as automobiles are often of the so-called whip type, in which the radiation element is vertical, in order to obtain non-directional radiation characteristics in the horizontal plane. In particular, for mobile objects that travel on the ground, there are many demands for improving the vertical radiation characteristics of the antenna and improving the gain of the antenna in order to expand the communication area. As a means of narrowing down the radiation characteristics in the vertical plane, it is necessary to increase the physical length of the radiating element while making appropriate phase corrections so that the phases of the currents flowing through the vertical radiating elements are as in-phase as possible. .

By the way, an actual vehicle-mounted antenna does not always need to use a large radiating element. For example, in amateur radio, when moving relatively short distances such as driving in the city, a short antenna with a relatively low gain of about λ/4 or 5λ/8 is used, and when driving in the suburbs, a short antenna with a relatively low gain is used. If long-distance communication is desired, an antenna with two or three stages of 5λ/8 radiating elements connected is used.

However, such selective use requires time and effort to replace the entire radiating element at the antenna base, so while it may be fine for enthusiasts, it is not preferable to apply it to, for example, a personal radio antenna that is also used by the general public.

Therefore, the present invention has proposed a whip antenna in which the overall length can be easily varied by making the central conductor hollow and storing an expanding radiating element therein in a freely insertable and removable manner. FIG. 1 shows an example of this, in which 1 is a coaxial transmission line, 2 is its center conductor, and 3 is an outer conductor. The center conductor 2 has a hollow shape, and a λ/2 expansion radiation element (multiplying element) 4 is housed inside the center conductor 2 so as to be freely insertable and removable. The tip of the outer conductor 3 is λ/
4 is folded back to form a skirt portion 5. This λ/4 skirt portion 5 is the ground plane of this antenna, and a λ/2 vertical dipole antenna (basic antenna) 6 is constructed by this skirt portion 5 and a λ/4-long central conductor exposed from here to the tip. Ru. 7 is a λ/2 phase correction coil connected between the lower end of the multiplication element 4 and the sliding member 8, and its periphery is reinforced with a highly rigid dielectric resin 9 or the like. The sliding member 8 is made of the same metal as the center conductor 2 and ensures conductivity between it and the center conductor 2. As shown in Fig. 2, the coil 7 absorbs an electric field E _{2 which is in phase opposite to the electric field E 1 of} the dipole antenna 6 and which is generated in the multiplier element 4 and turns it into an electric field E ₂ ' which is in phase with E ₁ . It is something. Without this coil 7, the electric field _E1 of the antenna 6 would be canceled by the electric field _E2 of the opposite phase, so
Rather, it is better not to use the increasing element 4. If the coil 7 is inserted, the electric field generated in the entire antenna will be
It becomes the sum of E ₁ and E ₂ ′.

With the above-described configuration, the antenna gain can be doubled simply by pulling out the multiplication element 4 as shown in FIG. By pushing the multiplication element 4 into the center conductor 2 when it is not needed, the antenna 6 can function as its own, and its handling is extremely simple. but,
If the center conductor 2 is hollow, rainwater or the like may seep in through the opening at its tip, which may change the characteristic impedance of the coaxial transmission line 1 over a long period of time.

OBJECT OF THE INVENTION The present invention seeks to further improve this point.

Structure of the Invention The present invention comprises a solid coaxial cable extending to a feed point, a hollow basic element connected to the center conductor of the coaxial cable and extending further upward from the feed point, and an outer conductor of the coaxial cable. a conductor that is connected to and extends downward from the feed point and forms a basic dipole antenna together with the basic element; a multi-stage extension element that is telescopically housed within the basic element; and one of the extension elements. The invention is characterized in that it has a phase correction element incorporated in the multiplication element, and the overall gain can be switched depending on whether the multiplication element is used or not. Explain in detail.

Embodiment of the invention FIG. 3 is a block diagram showing an embodiment of the present invention.
is a cross-sectional view when expanded, b is a cross-sectional view when contracted, and c is a perspective view of a single element of the phase correction stage. In this example, a normal coaxial cable, for example, a coaxial cable 10 with a characteristic impedance of 50Ω, is used as the coaxial transmission line. This coaxial cable 10 has its outer sheath removed to expose an outer conductor 11. 12 is a center conductor, and a dielectric material 13 is filled between it and the outer conductor 11. In other words, this coaxial cable 10 is solid.

A metal inner pipe 21 is attached tightly around the coaxial cable 10, and a large diameter outer pipe (conductor) 22 is further disposed around the outer circumference of the metal inner pipe 21. The total length of this outer pipe 22 is λ/4, and corresponds to the skirt portion 5 in FIG. Between both pipes 21 and 22 is power feeding point A
They are connected by a conductive plate 23 on the side. A basic element 31 is fixed to the tip of the center conductor 12 of the coaxial cable 10 with a screw or the like. This element 31 is a conductive cylindrical body provided with a bottom plate 31a, and has a total length of λ/4. This corresponds to the portion of the center conductor 2 in FIG. 1 that protrudes upward from the skirt portion 5. 32 is an element of a phase correction stage that is inserted into and removed from this element 31. This element 32 has a dielectric tubular part 32c interposed between a lower conductive tubular part 32a and an upper conductive tubular part 32b, and a coil 3 for position correction is inserted therein.
2d is embedded and wound. Both ends of the coil are connected to tubular portions 32a, 32b. 33-3
Reference numeral 6 denotes elements whose diameters gradually become smaller, and each can be inserted into and removed from the lower element.

All the expansion elements 32 as shown in Figure 3a.
36 is pulled out, the length from the top of the uppermost element 36 to a part of the element 33 is λ/2, and the length including the remainder of the element 33 to the top of the element 31 is λ/2. be.
However, in the element 32, the length of the extended coil 32d is λ/4, so the length of the dielectric 32c is shorter than that. Incidentally, since the length of the lower tubular portion 32a is λ/8, the remaining λ/8 is the aforementioned remaining portion of the element 33.

The operating principle as an antenna is the same as in Figure 1, so there is a gain of about 4 dB in state a. On the other hand, if all the elements 32 to 36 are accommodated within the basic element 31 as shown in FIG. 1B, the antenna becomes the same as the basic antenna 6 in FIG. The point that the gain can be varied by expanding and contracting the element is the same as in FIG. 1, but in the present invention, the hollow structure is up to the basic element 31, and the coaxial cable 10 below the feed point It has a solid structure filled with Therefore, there is no fear that rainwater or the like will seep into the upper end of the coaxial cable 10 and change the characteristic impedance of the transmission path up to the transmitter/receiver. Incidentally, water that has entered the hollow element 31 can be naturally drained to the outside by making a hole in the bottom plate 31a.

Effects of the Invention As described above, the present invention has the advantage that it is easy to change the gain of a whip antenna using a coaxial transmission line, and the characteristic impedance of the coaxial transmission line does not need to be changed by rainwater or the like.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an example of a variable length whip antenna, FIG. 2 is an explanatory diagram of its electric field distribution, and FIG. 3 is a configuration diagram showing an embodiment of the present invention. In the figure, 10 is a coaxial cable, 11 is an external conductor,
12 is the center conductor, 22 is the outer pipe (conductor), 31
1 is a basic element, 32 to 36 are increasing elements, and 32d is a phase correction coil.

Claims (1)

[Claims] 1. A solid coaxial cable extending to a feed point, and a hollow basic element connected to the center conductor of the coaxial cable and extending further upward from the feed point;
a conductor that is connected to the outer conductor of the coaxial cable and extends downward from the feeding point and forms a basic dipole antenna together with the basic element; and a multi-stage extension element that is expandably and contractably housed within the basic element; A variable length whip antenna comprising a phase correction element built into a part of the extension element, and the overall gain is switched by using or not using the extension element.