GB2148605A - Whip aerial - Google Patents

Abstract

A whip monopole aerial comprising a plurality of capacitively coupled conductive elements wherein at least one pair of elements (1 and 2) comprise conductive end portions which are adapted to fit coaxially one within the other, the end portions being spaced apart and insulated from each other by means of an insulative sleeve (3). <IMAGE>

Description

SPECIFICATION Whip aerial This invention relates to radio antennas and more especially it relates to whip 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 the 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 whip aerial having elements electrically linked by means of an improved capacitive coupling.

According to the present invention a whip monopole aerial comprises a plurality of capacitively coupled conductive elements wherein at least one pair of elements comprise conductive end portions which are adapted to fit coaxially one within the other, the end portions being spaced apart and insulated from each other by means of an insulated sleeve.

The end portions may be generally circular in cross section and the sleeve may be tubular.

One end portion may comprise a conductive tube within which the sleeve is fitted.

The whip aerial may be operatively associated with a matching unit via which it is adapted to be coupled to radio apparatus.

The matching unit may comprise a T circuit comprising two serially connected inductors and a shunt capacitor, the T circuit being arranged to be fed at one end from an aerial via a coaxial coupling line and arranged to feed radio apparatus at the other end.

One embodiment of the invention will now be described solely by way of example with reference to the accompanying drawing in which: Figure 1 is a somewhat schematic exploded plan view of the end portions of a pair of elements forming part of a whip aerial and in which; Figure 2 is a circuit diagram of a matching unit coupled to a whip aerial.

Referring now to the drawing, a whip aerial comprises a plurality of elements which are serially interconnected and capacitively coupled. The manner in which each pair of adjacent elements are coupled is shown in Fig. 2.

Referring now to Fig. 2 a pair of conductive aerial elements 1 and 2 are arranged to fit coaxially one within the other.

The element 1 comprises a hollow metal tube within which is fitted a tubular insulative sleeve 3. The sleeve 3 may be made of any suitable insulative material and the tube 1 may be copper, brass plated steel, or aluminium. The element 2 comprises an end portion 4 of reduced diameter which is arranged to be a push fit within the insulated sleeve 3.

Thus it will be appreciated that a capacitive coupling is thereby provided between the aerial elements 1 and 2 due to the fact that the end portion 4 of the element 2 overlaps with the end portion of the element 1 which is covered by the sleeve 3. Adjacent elements of a whip aerial (not shown in detail) are similarly fabricated to produce a whip aerial in which all elements are capacitively coupled.

A whip aerial including elements capacitively coupled as just before described may be arranged to feed radio apparatus via a matching circuit as shown in Fig. 2. The matching circuit comprises a pair of serially connected inductors 6 and 7 which in combination with a capacitor 8 define a T circuit. The T circuit is coupled at one end to a socket 9 and at the other end to a coaxial line 10 the screen of which is connected via conductors 11 to an earth line 12. The coaxial line 10 is coupled to a whip aerial 13.

Since the elements of the aerial are capacitively coupled radio apparatus coupled to the aerial via the socket 9 will work satisfactorily over a wide frequency band with a single matching unit of the kind just before described.

1. A whip monopole aerial comprising a pluraity of capacitively coupled conductive elements wherein at least one pair of elements comprises conductive end portions which are adapted to fit co-axially one within the other the end portions being spaced apart and insulated from each other by means of an insulative sleeve.

2. A whip monopole aerial as claimed in claim 1 wherein the end portions are generally circular in cross-section and the sleeve is tubular.

3. A whip monopole aerial as claimed in claim 1 or claim 2 wherein one end portion comprises a conductive tube within which the sleeve is fitted.

4. A whip monopole aerial as claimed in any preceding claim operatively associated with a matching unit via which it is adapted to be coupled to radio apparatus.

5. A whip monopole aerial as claimed in claim 4 wherein the matching unit comprises a T-circuit including two serially connecting inductors and a shunt capacitor, the T-circuit being arranged to be fed at one end thereof from an aerial via a co-axial coupling line and arranged to feed radio apparatus at the other end.

6. A whip monopole aerial substantially as

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

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Whip aerial This invention relates to radio antennas and more especially it relates to whip 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 the 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 whip aerial having elements electrically linked by means of an improved capacitive coupling. According to the present invention a whip monopole aerial comprises a plurality of capacitively coupled conductive elements wherein at least one pair of elements comprise conductive end portions which are adapted to fit coaxially one within the other, the end portions being spaced apart and insulated from each other by means of an insulated sleeve. The end portions may be generally circular in cross section and the sleeve may be tubular. One end portion may comprise a conductive tube within which the sleeve is fitted. The whip aerial may be operatively associated with a matching unit via which it is adapted to be coupled to radio apparatus. The matching unit may comprise a T circuit comprising two serially connected inductors and a shunt capacitor, the T circuit being arranged to be fed at one end from an aerial via a coaxial coupling line and arranged to feed radio apparatus at the other end. One embodiment of the invention will now be described solely by way of example with reference to the accompanying drawing in which: Figure 1 is a somewhat schematic exploded plan view of the end portions of a pair of elements forming part of a whip aerial and in which; Figure 2 is a circuit diagram of a matching unit coupled to a whip aerial. Referring now to the drawing, a whip aerial comprises a plurality of elements which are serially interconnected and capacitively coupled. The manner in which each pair of adjacent elements are coupled is shown in Fig. 2. Referring now to Fig. 2 a pair of conductive aerial elements 1 and 2 are arranged to fit coaxially one within the other. The element 1 comprises a hollow metal tube within which is fitted a tubular insulative sleeve 3. The sleeve 3 may be made of any suitable insulative material and the tube 1 may be copper, brass plated steel, or aluminium. The element 2 comprises an end portion 4 of reduced diameter which is arranged to be a push fit within the insulated sleeve 3. Thus it will be appreciated that a capacitive coupling is thereby provided between the aerial elements 1 and 2 due to the fact that the end portion 4 of the element 2 overlaps with the end portion of the element 1 which is covered by the sleeve 3. Adjacent elements of a whip aerial (not shown in detail) are similarly fabricated to produce a whip aerial in which all elements are capacitively coupled. A whip aerial including elements capacitively coupled as just before described may be arranged to feed radio apparatus via a matching circuit as shown in Fig. 2. The matching circuit comprises a pair of serially connected inductors 6 and 7 which in combination with a capacitor 8 define a T circuit. The T circuit is coupled at one end to a socket 9 and at the other end to a coaxial line 10 the screen of which is connected via conductors 11 to an earth line 12. The coaxial line 10 is coupled to a whip aerial 13. Since the elements of the aerial are capacitively coupled radio apparatus coupled to the aerial via the socket 9 will work satisfactorily over a wide frequency band with a single matching unit of the kind just before described. CLAIMS

1. A whip monopole aerial comprising a pluraity of capacitively coupled conductive elements wherein at least one pair of elements comprises conductive end portions which are adapted to fit co-axially one within the other the end portions being spaced apart and insulated from each other by means of an insulative sleeve.

2. A whip monopole aerial as claimed in claim 1 wherein the end portions are generally circular in cross-section and the sleeve is tubular.

3. A whip monopole aerial as claimed in claim 1 or claim 2 wherein one end portion comprises a conductive tube within which the sleeve is fitted.

4. A whip monopole aerial as claimed in any preceding claim operatively associated with a matching unit via which it is adapted to be coupled to radio apparatus.

5. A whip monopole aerial as claimed in claim 4 wherein the matching unit comprises a T-circuit including two serially connecting inductors and a shunt capacitor, the T-circuit being arranged to be fed at one end thereof from an aerial via a co-axial coupling line and arranged to feed radio apparatus at the other end.

6. A whip monopole aerial substantially as hereinbefore described with reference to the accompanying drawing.

7. A whip monopole aerial in operative association with a matching unit and substantially as hereinbefore described with reference to the accompanying drawing.