GB2148604A

GB2148604A - Monopole aerial

Info

Publication number: GB2148604A
Application number: GB08327811A
Authority: GB
Inventors: Ronald Henry Charles Jolly
Original assignee: Plessey Co Ltd
Current assignee: Plessey Co Ltd
Priority date: 1983-10-18
Filing date: 1983-10-18
Publication date: 1985-05-30
Also published as: GB2148604B; GB8327811D0

Abstract

A monopole aerial comprising a plurality of capacitively coupled conductive elements at least one pair of which (1 and 2) comprise conductive end portions fitted within a conductive sleeve (3) which is lined with insulation material (4), which insulation material (4) serves electrically to insulate the elements (1 and 2) from the sleeve (3) and from each other. A matching circuit is disclosed (Fig. 3). <IMAGE>

Description

SPECIFICATION Monopole aerial This invention relates to radio antennas and more especially it relates to monopole aerials.

Due to the impedence variation of aerials over a given frequency band such as the HF or VHF bands for example, it is necessary to provide between an aerial and radio equipment with which it is operatively associated, an impedence matching unit the characteristics of which should ideally be modified in accordance with a frequency received if matching is to be optimised.

In order to reduce the impedence variations over a frequency band of interest so that the band can be covered with one matching unit, it is known to provide aerials comprising a plurality of capacitively coupled elements.

It is an object of the present invention to provide a monopole aerial having elements electrically linked by means of an improved capacitive coupling.

According to the present invention a monopole aerial comprises a plurality of capacitively coupled conductive elements at least one pair of which elements comprise conductive end portions fitted within a conductive sleeve which is lined with insulating material, which insulating material serves to electrically insulate the elements from the sleeve and from each other.

The end portions of the elements of the pair may be substantially the same diameter.

The end portions may be cylindrical and the sleeve may be tubular.

The insulation material may be arranged to define between the elements an insulative partition.

The insulation material may be internally screw threaded at one end of the sleeve to accept complementary external screw threads provided on one end of an aerial element.

The insulation at the other end of the sleeve remote from the internally screw threaded end may be arranged to define a tubular portion which extends from within the sleeve to beyond the end of the sleeve.

The tubular portion which extends beyond the end of the sleeve may be tapered away from the sleeve.

One embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a somewhat schematic sectional view of two aerial elements capacitively and mechanically coupled by means of a sleeve: Figure 2 is a sectional view of a sleeve for coupling two aerial elements; and, Figure 3 is a circuit diagram of a matching unit associated with a monopole aerial.

Referring now to Fig. 1, two conductive elements 1 and 2 which form a part of a monopole aerial are linked together by means of a conductive sleeve 3 within which a ferrule 4 of insulating material is fitted. The ferule 4 of insulating material, is formed to receive the elements 1 and 2 with a tight push fit and as well as serving to insulate the elements 1 and 2 from the sleeve 3 it serves also to insulate the elements 1 and 2 from each other. The sleeve 3 may be made of brass and the elements 1 and 2 may be made of copper plated steel.

In an alternative embodiment of the invention, a sleeve 5 may be used as shown in Fig.

3 which includes a core 6 of insulating material which at one end is provided with a tapped hole 7 which includes internal screw threads 8. The internal screw threads 8 are arranged to mate with complimentary external screw threads formed on an aerial element not shown. At the end of the insulative core 6 remote from the hole 7 a bore 9 is provided having a generally circular cross section, the walls of the bore 9 being defined by a tubular portion 10 which is arranged to taper away from the sleeve 5.

In use of the sleeve shown in Fig. 3 an upper aerial element is screwed into the screw threads 8 within the hole 7 and a lower aerial element is fitted with a tight push fit into the bore 9.

It can be seen from Fig. 3 that when aerial elements are fitted within the sleeve 5 they are insulated from the sleeve and from each other and are capacitively coupled by reason of the proximity effect of the sleeve.

A monopole aerial comprising elements capacitively coupled as just before described with reference to Fig. 1 and Fig. 2 may be used to define a monopole aerial 11 as shown in Fig. 3 which is arranged to be coupled via a matching unit to radio apparatus with which it is operatively associated. The matching unit comprises a T filter which includes serially connected inductors 1 2 and 1 3 and a shunt capacitor 14. The T filter is coupled to the monopole aerial 11 via a coaxial line 15, the screen 1 6 of which is connected to an earth rail 17 via conductors 18 and 19. In use, the monopole aerial 11 is coupled to radio apparatus via a socket 18 which is connected to the inductor 1 2 of the T filter.

By constructing a monopole aerial with aerial elements capacitively coupled as herein before described, radio apparatus may be fed from a monopole aerial 11 via a single matching unit of the kind described with reference to Fig. 3.

1. A monopole aerial comprising a plurality of capacitively coupled conductive elements at least one pair of which elements comprise conductive end portions fitted within a conductive sleeve which is lined with insulating material, which insulating serves to electrically insulate the elements of a pair

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Monopole aerial This invention relates to radio antennas and more especially it relates to monopole aerials. Due to the impedence variation of aerials over a given frequency band such as the HF or VHF bands for example, it is necessary to provide between an aerial and radio equipment with which it is operatively associated, an impedence matching unit the characteristics of which should ideally be modified in accordance with a frequency received if matching is to be optimised. In order to reduce the impedence variations over a frequency band of interest so that the band can be covered with one matching unit, it is known to provide aerials comprising a plurality of capacitively coupled elements. It is an object of the present invention to provide a monopole aerial having elements electrically linked by means of an improved capacitive coupling. According to the present invention a monopole aerial comprises a plurality of capacitively coupled conductive elements at least one pair of which elements comprise conductive end portions fitted within a conductive sleeve which is lined with insulating material, which insulating material serves to electrically insulate the elements from the sleeve and from each other. The end portions of the elements of the pair may be substantially the same diameter. The end portions may be cylindrical and the sleeve may be tubular. The insulation material may be arranged to define between the elements an insulative partition. The insulation material may be internally screw threaded at one end of the sleeve to accept complementary external screw threads provided on one end of an aerial element. The insulation at the other end of the sleeve remote from the internally screw threaded end may be arranged to define a tubular portion which extends from within the sleeve to beyond the end of the sleeve. The tubular portion which extends beyond the end of the sleeve may be tapered away from the sleeve. One embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a somewhat schematic sectional view of two aerial elements capacitively and mechanically coupled by means of a sleeve: Figure 2 is a sectional view of a sleeve for coupling two aerial elements; and, Figure 3 is a circuit diagram of a matching unit associated with a monopole aerial. Referring now to Fig. 1, two conductive elements 1 and 2 which form a part of a monopole aerial are linked together by means of a conductive sleeve 3 within which a ferrule 4 of insulating material is fitted. The ferule 4 of insulating material, is formed to receive the elements 1 and 2 with a tight push fit and as well as serving to insulate the elements 1 and 2 from the sleeve 3 it serves also to insulate the elements 1 and 2 from each other. The sleeve 3 may be made of brass and the elements 1 and 2 may be made of copper plated steel. In an alternative embodiment of the invention, a sleeve 5 may be used as shown in Fig. 3 which includes a core 6 of insulating material which at one end is provided with a tapped hole 7 which includes internal screw threads 8. The internal screw threads 8 are arranged to mate with complimentary external screw threads formed on an aerial element not shown. At the end of the insulative core 6 remote from the hole 7 a bore 9 is provided having a generally circular cross section, the walls of the bore 9 being defined by a tubular portion 10 which is arranged to taper away from the sleeve 5. In use of the sleeve shown in Fig. 3 an upper aerial element is screwed into the screw threads 8 within the hole 7 and a lower aerial element is fitted with a tight push fit into the bore 9. It can be seen from Fig. 3 that when aerial elements are fitted within the sleeve 5 they are insulated from the sleeve and from each other and are capacitively coupled by reason of the proximity effect of the sleeve. A monopole aerial comprising elements capacitively coupled as just before described with reference to Fig. 1 and Fig. 2 may be used to define a monopole aerial 11 as shown in Fig. 3 which is arranged to be coupled via a matching unit to radio apparatus with which it is operatively associated. The matching unit comprises a T filter which includes serially connected inductors 1 2 and 1 3 and a shunt capacitor 14. The T filter is coupled to the monopole aerial 11 via a coaxial line 15, the screen 1 6 of which is connected to an earth rail 17 via conductors 18 and 19. In use, the monopole aerial 11 is coupled to radio apparatus via a socket 18 which is connected to the inductor 1 2 of the T filter. By constructing a monopole aerial with aerial elements capacitively coupled as herein before described, radio apparatus may be fed from a monopole aerial 11 via a single matching unit of the kind described with reference to Fig. 3. CLAIMS

1. A monopole aerial comprising a plurality of capacitively coupled conductive elements at least one pair of which elements comprise conductive end portions fitted within a conductive sleeve which is lined with insulating material, which insulating serves to electrically insulate the elements of a pair from the sleeve and from each other.

2. A monopole aerial as claimed in claim 1 wherein the end portions of the elements of a pair are of substantially the same diameter.

3. A monopole aerial as claimed in claim 1 or claim 2 wherein the end portions are cylindrical and the sleeve is tubular, the sleeve being effective to support the elements of a pair in juxtaposed positional relationship.

4. A monopole aerial as claimed in any preceding claim wherein the insulation material is arranged to define between the elements an insulative partition.

5. A monopole aerial as claimed in any preceding claim wherein the insulation material is internally screw threaded at one end of the sleeve to accept complementary external screw threads provided on one end of an element.

6. A monopole aerial as claimed in claim 5 wherein the insulation at that end of the sleeve remote from the internally screw threaded end is arranged to define a tubular portion which extends from within the sleeve to beyond the end of the sleeve.

7. A monopole aerial as claimed in claim 6 wherein the tubular portion which extends beyond the end of the sleeve is tapered away from the sleeve.

8. A monopole aerial substantially as herein before described with reference to the accompanying drawings.