Antenna system

Abstract

 An antenna system particularly intended for tactical communications comprises an antenna (10) of loop form including a plurality of separable sections (11, 12) and means (14, 15) for applying an electrical drive signal across ends of the loop (10).

Description

[0001] This invention relates to loop antennas and in particular but not exclusively to loop antennas which are collapsible.

[0002] Currently, when tactical communications are required, there are two modes of H.F. communication, namely ground wave propagation and skywave propagation. In the ground wave mode, propagation is typically up to about 30 km, and skywave mode propagation covers the range 100 km upwards. There is therefore a skip distance in the range 30 - 100 km where neither mode provides good communication. In addition, current ground wave transmitters employ a whip antenna of 4 m or so mounted on a vehicle. Such antennas are susceptible to damage due to their height and furthermore may indicate the presence of an otherwise hidden vehicle. Current skywave transmitters require that a half wave dipole wire antenna be erected, typically consisting of radiating elements some 150 metres long. It will be appreciated that this arrangement is difficult to erect quickly.

[0003] It is thus an object of this invention to provide an antenna which with appropriate mode and frequency management is capable of providing transmissions over short, medium and long ranges. It is a further aim of this invention to provide such an antenna which is readily portable.

[0004] According to this invention, an antenna system comprises an antenna of loop form including a plurality of separable sections and means for applying an electrical drive signal across ends of the loop.

[0005] Preferably, said sections are of a common unit length, and interconnected by several corner elements.

[0006] In one arrangement said loop antenna is of generally rectangular shape.

[0007] Advantageously said loop antenna includes tuner apparatus connected thereto for matching the impedance of said loop with that of the signal transmitter.

[0008] Further aspects will become apparent from the following description which is by way of example only, reference being made to the accompaning drawing illustrating a tactical high frequency antenna system.

[0009] Referring to the drawing, the antenna system includes a rectangular loop antenna 10 which is made up of interchangeable sections 11 a-f of electrically conducting material. The sections 11a-d are of common unit length, typically about 1 m long whilst the sections 11e and 11f are of different length. Each of the sections 11a-f is adapted to allow end-to-end connection with another section. In one embodiment respective ends of the sections are swaged to form reduced diameter portions which fit snugly within respective other ends of the adjacent section. Electrically conducting corner pieces 12a-c connect adjacent ones of the sections 11a-f at 90° to each other. Stands 13 are provided for supporting the loop antenna in a stable condition on the ground.

[0010] An automatic tuning unit 14 takes the place of a corner piece 12 and is connected between two sections 11e and 11f to allow the impedance of the loop antenna to be matched with that of the H.F. transceiver 15.

[0011] The system also includes an add-on interface 16 which is capable of tuning a range of existing whip antennas 17, 17' etc. when only short range ground wave communication is required. A switch on the side of the interface unit 16 selects the correct whip configuration and the automatic tuning capability of the unit 14 tunes the configuration.

[0012] This combination of the loop and whip systems with a common tuning unit provides a capability for operation either on a vehicle or remote from it. The need for antennas or conspicuous tall masts is removed by the use of the loop for frequencies about 10MHz.

[0013] In normal use, the loop antenna will be disassembled and stored with the automatic tunign unit. By making the loop antenna from several sections, the antenna may be transported by one man. Also, by adding further sections 11 the height and width dimensions of the loop may be adjusted in units of 1 m to suit the particular characteristics required.

[0014] As well as being used on the ground, the loop antenna may also be secured to a land or sea vehicle. In this case there is no need for the loop to be disassembled for storage. Instead it may form a permanent feature of the vehicle, for example, being attached to the side of the vehicle with the plane of the loop generally vertical.

Claims

1. An antenna system comprising an antenna (10) of loop form including a plurality of separable sections (11, 12) and means (14) for applying an electrical drive signal across ends of the loop.

2. A system according to claim 1, wherein the sections consist of elongate elements (11) and corner elements (12).

3. A system according to claim 1 or 2, wherein the loop antenna (10) is of generally rectangular shape.

4. A system according to any preceding claim, wherein the system includes a tuning apparatus (14) connected to the loop antenna for matching the impedance of the loop antenna with that of a signal transmitter (15).

5. A system according to claim 4, wherein the tuning apparatus (14) is arranged to form a corner element (12) of the loop antenna and co-operates with two of the separable sections (11).

6. A system according to any one of the preceding claims, including stands (13) to support the loop antenna (10) in an upright plane.

Drawing