GB1593552A

GB1593552A - Radio aerials

Info

Publication number: GB1593552A
Application number: GB562277A
Authority: GB
Original assignee: Plessey Co Ltd
Current assignee: Plessey Co Ltd
Priority date: 1978-01-19
Filing date: 1978-01-19
Publication date: 1981-07-15

Description

(54) IMPROVEMENTS IN OR RELATING TO RADIO AERIALS (71) We, THE PLESSEY COMPANY LIMITED, a British Company of Vicarage Lane, Ilford, Essex, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in an by the following statement:- This invention relates to Radio Aerials.

According to the present invention an aerial comprises a loop arranged substantially orthogonally with respect to a monopole, the monopole comprising an outer conductor connected to one end of the loop and arranged to screen an inner conductor connected to the other end of the loop, the ends of the inner and outer conductors remote from the loop being connected to first and second terminal means respectively, whereby a pair of polarisation diversity signals are provided in use of the aerial.

In use of an aerial according to the present invention the terminals of the aerial may be connected to a diversity combiner whereby polarisation diversity reception is facilitated. Thus the signal from the loop developed between the inner and outer conductors or the inner conductor and a ground plane constitues one input for the combiner and the signal from the monopole developed between the outer conductor and a ground-plane constitutes the other input for the combiner.

The loop may comprise one or more turns. The loop may define any suitable shape but in one embodiment a circular loop is provided comprising one generally circular turn with the monopole disposed orthogonally with respect to the plane of the loop and positioned at the centre of the loop.

The inner and outer conductors may comprise screened cable which may be rigid or flexible coaxial cable.

The grdund plane may . be in effect: replaced by- an additional aerial system which may be of identical or similar form to an aerial according to the present invention so that the combination acts as a balanced or a partially balanced version of the aerial according to the invention and resembles a dipole rather than a monopole.

The arrangement may comprise a balanced system wherein the connections between the loops and the coaxial or other screened cables are adapted and arranged so as to result in an additive i.e. reinforcing combination of the output signals from the two loops.

The aerial may have operatively associated with it impedance conversion means whereby output signals suitable for matching the input impedance of a diversity combiner are provided. Such a combiner may have an input impedance of 50 or 75 ohms.

The impedance conversion means may comprise tranformers and/or amplifiers which may be solid state devices.

According to one embodiment of the invention, two loops and a dipole may be provided, the dipole comprising two sections of outer conductor connected one to one end of each loop, the outer conductor sections serving to screen an inner conductor connected between the ends of the loops remote the outer conductor, the first terminal means comprising terminals for facilitating connection to the inner conductor and the second terminal means comprising terminals for facilitating connection to the two sections of the outer conductor, whereby the pair of diversity signals are provided.

The first terminal means may in this case comprise two terminals connected one to the centre of the inner condudtor and one connected to the ground plane, and the second terminal means may comprise transformer means whereby the output from the two outer conductors with respect to earth is provided.

Some embodiments of-the invention will now.be described by way of example with reference to the drawing accompanying the complete specification in which Figure 1 is a generally schematic diagram of a loop/monopole aerial suitable for polarisation diversity reception and in which, Figure 2 is a generally schematic diagram comprising two -loops and a dipole suitable for polarisation diversity reception.

Referring now to Figure 1, the aerial comprises a generally circular loop 1 connected by means of conductors 2 to an outer conductor 3 of a coaxial cable which defines a monopole and between which and a ground plane 4 one of two diversity signals is generated the other end of the loop being connected to the inner conductor 5 of the coaxial cable. Thus two diversity output signals from the aerial are provided, one being developed between the inner conductor 5 and the adjacent end of the outer conductor 3 and the other being developed between the outer conductor 3 and the ground plane 4. Thus it will be appreciated that the aerial comprises a loop and a monopole which are responsive to signals in orthogonal planes of polaristation.

Such an aerial may therefore find application where the plane of polarisation is not predictable and for h.f. signal reception over distances which are such that ionespheric bounce occurs such that there is no permanent preferred - or predictable plane or polarisation. Application in boats and ships, land bases, ground vehicles and possibly aircraft is envisaged.

Referring now to Figure 2, an aerial is shown comprising two loops 6 and 7 one end of each of which is connected via an inner conductor 8 to a terminal 9. The inner conductor 8 is screened by two sections 10 and 11 of outer conductor which defined a dipole. the sections 10 and 11 of the dipole are connected to one winding 12 of a transformer a centre tap of which is connected to earth via a capacitor 13. A primary winding 14 of the transformer is connected to a pair of terminals 15 across which an output signal from the dipole is provided. Signals from the loops are developed between the terminal 9 and a terminal 16 which is connected to earth.

It is well known that diversity reception improves considerably the reliability of radio receiving systems in the presence of multi-path fading and the known techniques developed for implementing such systems will not be described herein. Diversity reception is of particular value in the h.f.

band and because of the long wave length involved there is growing interest in the use of short active aerials. An active aerial is defined as an aerial in which the aerial terminals are adapted to feed associated tuned circuits via a wideband impedance matching amplifier. Thus an aerial which might normally be unsuitable because its output impedance can not simply be made acceptably compatible over relatively large bandwidths with aerial tuning units, may be used in association with a suitable wideband impedance matching amplifier and the combination of the matching amplifier and the aerial is often described as an active aerial.

The present invention provides a compact means of providing for polarisation diversity reception and especially of providing for such reception by means of a relatively minor modification to a short active aerial.

Diversity reception based on orthogonal polarisation can be achieved by the use of a vertical monopole and a horizontal loop, as just before described, wherein the former accepts vertically polarised energy and the latter accepts horizontally polarised energy arriving from an azimuthal direction.

In use of an aerial as described with reference to Figure 1 the e.m.f. generated on reception of a signal between the base of the monopole and the ground plane 4 or some other suitable reference point, constitutes the normal monopole aerial output voltage which is utilised as one diversity signal and in the case of a short active aerial is applied via appropriate coupling means to a suitable impedance converter, which may be a high input impedance/low output impedance amplifier.

The e.m.f. generated at the base of the aerial between the inner conductor 5 and the outer conductor 4 of the coaxial line provides the other polarisation diversity signal and is also applied to a suitable impedance converter which in this case would normally be a low impedance device with a high output impedance. The two signals thus produced may then be processed and combined by any known method to exploit the advantages of diversity reception.

It will be appreciated that provided the dimensions of the loop are small compared with the wavelength of the signal being received, the loop acts substantially as a captive "hat" for the vertical monopole.

WHAT WE CLAIM IS: 1. An aerial comprising a loop arranged substantially orthogonally with respect to a monopole, the monopole comprising an outer conductor connected to one end of the loope and arranged to screen an inner conductor connected to the other end of the loop, the ends of the inner and outer conductors remote from the loop being connected to first and second terminal means respectively whereby a pair of polarization diversity signals are provided in use of the aerial.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. reference to the drawing accompanying the complete specification in which Figure 1 is a generally schematic diagram of a loop/monopole aerial suitable for polarisation diversity reception and in which, Figure 2 is a generally schematic diagram comprising two -loops and a dipole suitable for polarisation diversity reception. Referring now to Figure 1, the aerial comprises a generally circular loop 1 connected by means of conductors 2 to an outer conductor 3 of a coaxial cable which defines a monopole and between which and a ground plane 4 one of two diversity signals is generated the other end of the loop being connected to the inner conductor 5 of the coaxial cable. Thus two diversity output signals from the aerial are provided, one being developed between the inner conductor 5 and the adjacent end of the outer conductor 3 and the other being developed between the outer conductor 3 and the ground plane 4. Thus it will be appreciated that the aerial comprises a loop and a monopole which are responsive to signals in orthogonal planes of polaristation. Such an aerial may therefore find application where the plane of polarisation is not predictable and for h.f. signal reception over distances which are such that ionespheric bounce occurs such that there is no permanent preferred - or predictable plane or polarisation. Application in boats and ships, land bases, ground vehicles and possibly aircraft is envisaged. Referring now to Figure 2, an aerial is shown comprising two loops 6 and 7 one end of each of which is connected via an inner conductor 8 to a terminal 9. The inner conductor 8 is screened by two sections 10 and 11 of outer conductor which defined a dipole. the sections 10 and 11 of the dipole are connected to one winding 12 of a transformer a centre tap of which is connected to earth via a capacitor 13. A primary winding 14 of the transformer is connected to a pair of terminals 15 across which an output signal from the dipole is provided. Signals from the loops are developed between the terminal 9 and a terminal 16 which is connected to earth. It is well known that diversity reception improves considerably the reliability of radio receiving systems in the presence of multi-path fading and the known techniques developed for implementing such systems will not be described herein. Diversity reception is of particular value in the h.f. band and because of the long wave length involved there is growing interest in the use of short active aerials. An active aerial is defined as an aerial in which the aerial terminals are adapted to feed associated tuned circuits via a wideband impedance matching amplifier. Thus an aerial which might normally be unsuitable because its output impedance can not simply be made acceptably compatible over relatively large bandwidths with aerial tuning units, may be used in association with a suitable wideband impedance matching amplifier and the combination of the matching amplifier and the aerial is often described as an active aerial. The present invention provides a compact means of providing for polarisation diversity reception and especially of providing for such reception by means of a relatively minor modification to a short active aerial. Diversity reception based on orthogonal polarisation can be achieved by the use of a vertical monopole and a horizontal loop, as just before described, wherein the former accepts vertically polarised energy and the latter accepts horizontally polarised energy arriving from an azimuthal direction. In use of an aerial as described with reference to Figure 1 the e.m.f. generated on reception of a signal between the base of the monopole and the ground plane 4 or some other suitable reference point, constitutes the normal monopole aerial output voltage which is utilised as one diversity signal and in the case of a short active aerial is applied via appropriate coupling means to a suitable impedance converter, which may be a high input impedance/low output impedance amplifier. The e.m.f. generated at the base of the aerial between the inner conductor 5 and the outer conductor 4 of the coaxial line provides the other polarisation diversity signal and is also applied to a suitable impedance converter which in this case would normally be a low impedance device with a high output impedance. The two signals thus produced may then be processed and combined by any known method to exploit the advantages of diversity reception. It will be appreciated that provided the dimensions of the loop are small compared with the wavelength of the signal being received, the loop acts substantially as a captive "hat" for the vertical monopole. WHAT WE CLAIM IS:

1. An aerial comprising a loop arranged substantially orthogonally with respect to a monopole, the monopole comprising an outer conductor connected to one end of the loope and arranged to screen an inner conductor connected to the other end of the loop, the ends of the inner and outer conductors remote from the loop being connected to first and second terminal means respectively whereby a pair of polarization diversity signals are provided in use of the aerial.

2. An aerial as claimed in claim 1

operatively associated with a diversity combiner whereby polarization of diversity reception is facilitated.

3. An aerial as claimed in claim 2, wherein one input for the combiner is developed between the inner conductor and a ground plane, the other input for the combiner being developed between the outer conductor and the ground plane.

4. An aerial as claimed in claim 2, wherein one input signal for the combiner is developed between the inner and outer conductors, the other input signal for the combiner being developed between the outer conductor and ground plane.

5. An aerial as claimed in any preceding claim wherein the loop comprises a plurality of turns.

6. An aerial as claimed in any preceding claim wherein the loop is circular the monopole being disposed orthogonally with respect to the plane of the loop and positioned at the centre of the loop.

7. An aerial as claimed in any preceding claim wherein the inner and outer conductors comprise the conductors of a coaxial line.

8. An aerial as claimed in claim 1 or claim 2 comprising two loops and two monopoles aligned to form a dipole.

9. An aerial as claimed in claim 8 wherein the two loops and the two monopoles are dimensionally similar and thereby define a balanced aerial arrangement.

10. An aerial as claimed in claim 8 or claim 9 wherein the aerial has operatively associated with its impedance conversion means whereby signals suitable for matching the impedance of the diversity combiner are provided.

11. An aerial as claimed in claim 10 wherein the impedance conversion means comprises a transformer and/or amplifiers.

12. An aerial as claimed in any of claims 8 to 11 wherein the dipole comprises two aligned sections of coaxial line, the outer conductor sections the said line being connected respectively to one end of each loop, and serving to screen two adjoined inner conductor sections of the line which are connected respectively at opposing ends between the ends of the loops remote from the outer conductor, the first terminal means comprising terminals facilitating connection to the inner conductor and the second terminal means comprising terminals facilitating connections to the two sections of the outer conductor whereby the pair of diversity signals are provided.

13. An aerial as claimed in claim 12 wherein the first terminal means comprises two terminals connected one to adjoined ends of the inner conductor and one to earth or a ground plane and wherein the second terminal means comprises the primary winding ends of a transformer a centre top of which is earthed thereby to provide at a secondary winding an output from the two outer conductors.

14. An aerial substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

15. An aerial substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.