GB2121611A

GB2121611A - Offsettable antenna for a portable radio transceiver

Info

Publication number: GB2121611A
Application number: GB08312467A
Authority: GB
Inventors: Joel Jeannolle; Gilbert Maillard
Original assignee: Thomson CSF SA
Current assignee: Thales SA
Priority date: 1982-05-14
Filing date: 1983-05-06
Publication date: 1983-12-21
Also published as: GB8312467D0; FR2527013A1; FR2527013B1; IT8367535A0; IT8353319V0; IT1162860B

Abstract

The antenna comprises an electrically conductive support member 4 having a pointed part 5 for inserting the antenna into the ground 6 and a radiating element 7 secured to the support member end opposite to the pointed part 5 by way of a junction box 8 enabling high- frequency energization of the dipole embodied by the radiating element 7 and the support member 4. The member 4 may be metal, or may be rigid plastics provided with an electrical conductor. Use: Offsettable antenna for a portable transceiver operating in the VHF range of the order of 26 MHZ or more. <IMAGE>

Description

SPECIFICATION Offsettable antenna for a portable radio transceiver This invention relates to an offsetable antenna or a portable radio transmitter and/or receiver.

Conventionally, antennas of this kind are attached to the frame of the transmitter and/or receiver set, with the advantage for operating purposes of having a readily transportable operating unit. However, at operating frequencies in the VHF range of the order of 26 MHz and above some of the electromagnetic energy radiated by the antenna is absorbed by the person who is carrying or operating the set and who is close to it. This loss of power causes modifications in the antenna radiation diagram and in a reduction of the range which the antenna can provide.

One way of obviating this disadvantage is to separate the radiating element of the antenna geographically from the set and the person carrying it and connecting the radiating element to the set by a coaxial line.

Accordingly, the radiating element is kept vertical above the ground by guys and the radiating dipole previously embodied by the antenna and the set chassis is embodied by a conductor network spread out like a sheet or layer on the ground. In such cases the set chassis or the ground layer of conductors acts as what is commonly referred to in radio as a radio counterweight to the radiating element.

Unfortunately, this system is highly impracticale since installation of the antenna calls for multiple manipulations and bulky accessories which are heavy to transport.

Another system, used for radio stations on board vehicles, is to instal the antenna at the top of a "discone" and "ground plane" mast; unfortunately, this kind of installation, the equipment for which is heavy and bulky, cannot be transposed to provide transmission and reception installations readily portable by the carrier or user of the transmitter and/or receiver when no vehicle is available and the carrier of the set has to move in difficult geographical terrain.

The object of the invention is to obviate these disadvantages by means of an antenna for a portable transmitter and/or receiver set, the antenna being readily installable at a distance from the set and being compact and light enough for convenience of transport while being large enough to be unobtrusive and rugged and suitable for use in all kinds of terrain including the most difficult geographical regions.

The invention accordingly relates to an offsettable antenna for a portable radio transmitter and/or receiver, characterised in that it comprises an electrically conductive support member having a pointed part for inserting the antenna into the ground and a radiating element secured to the support member end opposite to the pointed part by way of a junction box enabling high-frequency energization of the dipole embodied by the radiating element and the support member.

The invention will be more clearly understood, and other features will become apparent if reference is made to the following description taken together with the accompanying drawings wherein: Figure 1 shows an example of a transceive installation comprising an antenna according to the invention; Figure 2 shows an embodiment of a metal support member connected to the junction box, and Figure 3 shows a possible embodiment of a matching circuit disposed in the junction box.

The installation shown in Fig. 1 comprises a transceiver set 1 connected by a coaxial cable 2 to an antenna 3 according to the invention.

The antenna 3 comprises a metal support member 4 having a pointed part 5 enabling the antenna to be enaged in the ground 6 and a radiating element 7 secured to the support member end opposite to the pointed part 5 by way of a junction box 8. The same enables the radio dipole formed by the radiating element 7 and the support member 4 to be energized with high-frequency electromagnetic energy and accordingly connects the element 7 and member 4 to one end of the cable 2, whose other end is connected to the transceive antenna socket of the set 1.

The member 4 is shown in Fig. 2 and comprises a picket or stake or the like 10 and, thereabove, a rod or a cylindrical tube 11.

The picket 10 comprises a conical member 1 2 which is the pointed part 5, a connector 1 3 and an intermediate tube 1 4 disposed between the conical member 1 2 and the connector 1 3. The conical member 1 2 has at its base 1 2a a cylindrical part 1 5 engaging in end 1 4a of the tube 14 and a shoulder 1 6 on which the tube end 1 4a bears. One or more screws 1 7 or any similar securing means secure the tube end 1 4a to the cylindrical part 15.

The connector 1 3 is in two cylindrical parts 18, 19 separated by a shoulder 20. The generatrices of the cylinders formed by the parts 18, 1 9 have the same directions. The cylindrical part 1 8 engages in the tube end 1 4h to bring the same into bearing engagement on the shoulder 20 and is secured in this position on the tube end 1 4b by at least one clamping screw (not shown) or any other similar securing means. The cylindrical part 1 9 has its end face 21 opposite the shoulder slightly convex so that it can if necessary be hammered when the picket 10 is driven into the ground without any risk of damage to the connector 13.

The cylindrical tube 11 has two ends 11 a, 11 b and is pierced on its cylindrical surface with an aperture 21 bis through which the coaxial cable 2 can extent. The cylindrical tube 11 is disposed releasably above and in extension of the longitudinal axis of the picket 10 by means of the connector 13, the cylindrical part 1 9 thereof engaging freely in the end part 11 a of tube 11.

For improved electrical continuity between the picket 10 and the tube 11 an electrical conductor (not shown) can be secured to the respective cylindrical surfaces of the picket 10 and tube 11.

The junction box 8, also shown in Fig. 2, comprises a support member 22, circuits 23 for matching the antenna 3 to the coaxial cable 2 and an insulated cylindrical casing 24, for instance, of bakelite, around the circuits 23. The support member 22 comprises a base 25 for securing the box 8 to the tube end 11 b and a support plate 26 for the matching circuits 23. The base 25 has a shoulder 27 between two cylindrical parts 28 and 29, the generatrices of the formed cylinders having the same direction. The part 28 engages in the tube end 11 b. The same and the part 28 are held together by at least one clamping screw or any other similar securing means (not shown). The part 29 has a gasket 30 and engages in end 24a of the insulated cylindrical casing 24.The base 25 is also formed with an aperture 31 which extends in the direction of the generatrices of the corresponding cylinders of the parts 28, 29 and through which the end of the coaxial cable 2 can extend for connection to the matching circuit 23. The base 25 also has a top plane part 32 which is at the end of the cylindrical part 29 and which is perpendicular to the direction of the generatrices of the cylinder corresponding to the part 29, on which the plate 26 rests. An insulated plate 33, for instance, of Bakelite (RTM), is applied to the top part 32 by a clamping screw 33 bis. The top end 24b of the casing 24 is closed by a sealing plug or the like 34 whose top end 35 is tapped to receive a screwthreaded terminal part 36 of the radiating element 7 of the antenna. Bottom part 37 of plug 34 is cylindrical and engages in the casing top end 24b.

When the plug 34 engages in the end 24b of the junction box 8, the top end 24b of the casing 24 is in contact with a shoulder 38 of the plug 34, the shoulder 38 being disposed between the plug top part 35 and the plug bottom part 37.

The matching circuits 23 are shown in Fig.

3. They comprise an inductance 23a and a capacitor 23b. The inductance 23a has one end connected to a connecting terminal 39 which is disposed at the bottom end of the plug 34 to provide an electrical connection between the end of the inductance 23a and the end 36 of the radiating element 7. The inductance 23a has a second end which is electrically connected to a terminal 41 disposed on the insulating plate 32, terminal 41 being connected to the inner conductor of the coaxial cable 2. The first end of inductance 23a is also electrically connected to one side of the capacitor 23b, the other side of which is connected to the metalwork of the support element 4 by way of a terminal 40 formed by a solid thimble secured to the top part of the base 22 by means of the screw 33 bis. The outer sheath of the coaxial cable 2 is also electrically connected to the earth terminal 40.Consequently, the electromagnetic energy transmitted by the transmitter 1 is transmitted to the radiating elements 7 by way of the inductance 23a and across the capacitor 23b.

The elements 23a, 23b are adjusted to match the antenna for the required passband.

The required passband can also be obtained by an appropriate choice of the dimensions of the radiator element 7 and support member 4, for the Q-factor of the antenna can be reduced if the diameter of the elements 7 and the diameter of the member 4 are different from one another. Also, by adjusting the length of the intermediate tube 11 appropriately, if necessary by using a number of intermediate tubes, the antenna tapping point can be varied, a step which is equivalent to shifting the junction box 8 along the antenna axis and thus energizing the antenna asymmetrically and increasing the non-reactive component of antenna impedance, with the result of an appreciable reduction in the Q-factor of the antenna and a consequent increase in its passband.

The antenna hereinbefore described can provide a radiation of vertically polarized electromagnetic waves with an omnidirectional radiation pattern in azimuth. Of course, different antennas can be provided if the radiating element 7 is given a shape and a structure other than those hereinbefore described. More particularly, the radiating element can take tile form of an elongated straight or flexible conductor or of a stretched conductor wire or be embodied by a number of elements adapted to engage one in another, for instance, telescopically.

Other constructional variants of the invention are possible too; for instance, the picket or stake or the like 10 can be a unitary member and, instead of hollow cylindrical tubes, solid rods or bars interconnected, for instance, by sleeves or bushes or the like can be used. Another possibility is for the casing of the junction box to be metallic and for its base 25 and support member 26 to be insulating, to insulate from one another the two dipole parts formed by the radiating element 7 and the support member 4. The latter, instead of being of metal, can be made over all or some of its length of an such as a plastics of sufficient rigidity, so that the stake 10 or the like can be forced into the ground without damage. In this latter case an electrical conductor must be disposed on the periphery or inside the support member 4 in order to form with the radiating element 7 the radio dipole of the antenna.

Claims

1. An offsettable antenna for a portable radio transmitter and/or receiver, characterised in that it comprises an electrically conductive support member (4) having a pointed part (5) for inserting the antenna into the ground (6) and a radiating element (7) secured to the support member end opposite to the pointed part (5) by way of a junction box (8) enabling high-frequency energization of the dipole embodied by the radiating element (7) and the support member (4).

2. An antenna according to claim 1, characterised in that the support member (4) comprises a picket (10) insertable into the ground and having at least one intermediate rod (11) above it.

3. An antenna according to claim 2, characterised in that the intermediate rod (11) is disposed releasably above the picket (10).

4. An antenna according to claims 2 and 3, characterised in that the radiating element is a substantially straight elongated conductor so arranged that the longitudinal axes of the radiating element (7) and picket (10) extend in substantially the same direction.

5. An antenna according to any of claims 1 to 4, characterised in that the junction box (8) has an asymmetrical intermediate position between the ends formed by the pointed part (5) and the antenna end distal from the pointed part, to widen the antenna pass band.

6. An antenna according to any of claims 1 to 5, characterised in that the sections of the radiating element (7) and support member (4) which embody the dipole are made different from one another to widen the antenna pass band.

7. An antenna according to any of the previous claims, characterised in that the length of the support member (4) is adjustable.

8. An antenna according to any of the previous claims, characterised in that the junction box (8) comprises a matching circuit (23) for acting on the antenna pass band.

9. An antenna according to any of the previous claims, characterised in that the high-frequency energy is supplied to the junction box through a coaxial cable (2).

10. An antenna according to any of the previous claims, characterised in that the picket (10) has a pointed part (5, 12), a connector (13) and an intermediate tube (14) disposed between the pointed part (5) and the connector (13).

11. An antenna substantially as hereinbefore defined with reference to and as illustrated in the accompanying drawings.