GB2212985A - Slotted antenna - Google Patents

Abstract

An antenna comprises an elongate central conducting core surrounded by a series of outer conductors (5) which are separated from each other to provide slots (4) and which are spaced from the core and carried by annular dielectric supports (2). Dielectric spacers (3) are located in each of the slots (4) and prevent the outer conductors (6) and supports (2) from sliding along the central core. <IMAGE>

Description

SLOTTED ANTENNA Field of the Invention The invention relates to antennae.

Summary of the Invention According to the invention an antenna comprises an elongate conducting core; two or more hollow, tubular outer conductors which are coaxial with the core, separated from the core by a dielectric, and which lie along the core so as to define a coaxial transmission line with one or more slots; means for supporting the tubes in position relative to each other and to the core; means for connecting the antenna to a transmitter or a receiver.

The antenna may with particular advantage be used to transmit or receive signals in the microwave range of frequencies.

The invention provides an effective and robust antenna which may be easily, and therefore relatively inexpensively, constructed.

Preferably the means for supporting the antenna's tubular outer conductors in position relative to each other and to the conducting core comprise the dielectric between each outer tube and the core; and a dielectric sleeve which embraces the core in each slot.

Preferably the antenna is terminated in an end outer conductor which includes a conducting surface which extends from the circumference of the outer conductor to .make contact with the conducting core.

This end formation may be achieved using a solid cylindrical conductor with a central bore through which the central core passes, and short circuits the transmission line.

Alternatively the conducting core of the antenna terminates within the dielectric inside an end tube, so that the transmission line is terminated in an open circuit.

Brief Description of the Accompanying Drawings Figure 1 of the drawings shows in sectional side elevation an antenna embodying the invention.

Figure 2 shows an alternative end formation for the antenna of Figure 1.

Description.of the Preferred Embodiment The antenna shown in Figure 1 of the drawings operates in the microwave range of frequencies, that is the frequencies in the region of 5 GHz. The antenna has a plurality of hollow tubular outer conductors 5 and a cylindrical end conductor 6.

Each outer conductor 5 is separated from the elongate central conducting core 1 by an annular dielectric support 2. Each dielectric support 2 is attached to its corresponding outer conductor 5 by means of a suitable adhesive, and or by indenting the surface of the outer conductor 5 so that it grips the dielectric support 2. The end conductor 6 is held in position on the central core 1 by means of a screw which passes through a threaded radial hole in the end conductor 6 and bears against the central core 1. A similar arrangement may be used to fasten the outer conductors 5 to the dielectric 2. The outer conductors are coaxial with the core 1.

The outer conductors 5 and the end conductor 6 define between 5hem a number of radiating slots 4. A plastic dielectric spacing sleeve 3 surrounds the central core 1 in each of the slots 4 and prevent the outer conductors 6 from sliding along the central core 1. The materials forming the sleeves 3 and the supports 2 can be selected from a number of known alternatives.

The antenna is connected to a receiver or a transmitter by a coaxial connector at the base 7 of the transmitter.

The means for inputting a signal into the antenna so that it acts as a transmitter will be apparent to the skilled addressee of this specification.

For transmission of radiation whose mains lobe is perpendicular to the axis of the core 1, the spacing between each adjacent pair of slots is equal (to within 1%) to the wavelength of electromagnetic radiation propagating in the antenna.

The angle of elevation of the main lobe of radiation may be adjusted by adjusting the inter-slot spacing. This adjustment may be achieved by using different lengths of sleeves 3.

Figure 2 shows the alternative end piece which has an outer conductor 8 separated from the core 1 by the dielectric 2.

The inside diameter of the outer conductor 8 must be less than half the critical wavelength of the waveguide.

Claims (7)

CLAIMS:

1. An antenna comprising an elongate conducting core; two or more hollow, tubular outer conductors which are coaxial with the core, separated from the core by a dielectric, and which lie along the core so as to define a coaxial transmission line with one or more slots; means for supporting the tubes in position relative to each other and to the core; and means for connecting the antenna to a transmitter or a receiver.

2. An antenna according to claim 1 in which the means for supporting the tubular outer conductors in position relative to each other and to the conducting core comprise the dielectric between each outer tube and the core.

3. An antenna according to claim 1 or claim 2 in which, within the or each slot, there is a dielectric sleeve which embraces the core.

4. An antenna according to any one of the preceding claims which is terminated in an end outer conductor which includes a conducting surface which extends from the circumference of the outer conductor to make contact with the conducting core.

5. An antenna according to claim 4, in which said end formation is achieved using a solid cylindrical conductor with a central bore through which the central core passes, and shortcircuits the transmission line.

6. An antenna according to any one of claims 1 to 3, in which the conducting core terminates within the dielectric inside an end tube, so that the transmission line - is terminated in an open circuit.

7. A microwave antenna substantially as hereinbefore described with reference to and as shown in the accompanying drawings.