AU2018260969B2 - Radio frequency coupler - Google Patents

Abstract

RADIO FREQUENCY COUPLER The present invention relates to a radio frequency (RF) broadband mains isolated RF coupler which may be used to couple an appliance to an antenna, whilst isolating the antenna from voltages which may be connected to the appliance. For electricity meters, it is often necessary to provide an externally mounted antenna for communicating remotely. The antenna should be isolated from the mains voltage, for safety reasons. A coupler described herein comprises first and second planar strip lines which extend parallel to each other and are mounted wholly within an electrical insulating substrate. The strip lines are curved in the planar extending direction. One radio frequency line is arranged for electrical connection to the appliance side and the other radio frequency line is arranged for connection to an antenna. They are isolated by the insulation. .. ... ..... Q) U-

Description

.. ... ..... Q) U- RADIO FREQUENCY COUPLER

Field of the Invention The present invention relates to an radio frequency (RF)

coupler and, particularly, but not exclusively, to a broadband

mains isolated RF coupler which may be used to couple an

appliance to an antenna, whilst isolating the antenna from

voltages which may be connected to the appliance

Background of the Invention There are a number of applications where a radio frequency

transmitter and/or receiver is mounted in an appliance which

may be connected to an electrical power source. An antenna for

the RF signals may be required to be mounted outside the

appliance and, generally, for safety reasons, should be de

coupled from the appliance power.

It is common nowadays in electricity meters, for example, to

provide a radio transceiver which is arranged to send and

receive data to/from remote locations. Meters and meter

components may be mounted in housings which are impenetrable

.0 to or affect radio signals. It is therefore often necessary to

provide an antenna mounted externally of the meter and to

which the radio transceiver is coupled. The antenna should be

isolated, for safety reasons, from the mains voltage applied

to the meter. There are regulatory standards in various

jurisdictions governing the requirement for isolation between

the antenna and the appliance.

In Australia, for example, a number of electricity meters for

domestic or industrial use may be mounted in a box with a

metallic cover. The metal cover affects radio signals and

therefore an antenna external to the meter and metal cover is

required.

It is known to use antenna couplers mounted internally to

electricity meters. One side of the coupler connects to the

antenna. Another part of the coupler connects to the RF

transceiver. These parts of the coupler are isolated from each

other in order to provide the requisite isolation from the

mains supply connected to the meter components.

Current antenna couplers tend to be bulky and complex. It is

desired to address or alleviate one or more disadvantages or

limitations of the prior art, or to at least provide a useful

alternative.

Summary of the Invention

In accordance with a first aspect, the present invention

provides an antenna coupler for connection of a radiofrequency

antenna to an appliance to which electrical power is applied

during operation, the coupler being arranged to provide

isolation to isolate the antenna from the electrical power to

the appliance, the coupler comprising;

first and second radio frequency planar strip lines

extending in a horizontal direction and parallel to each other

.0 so that inner facing surfaces of the strip lines are spaced

apart opposing each other with a gap between them;

the first and second strip lines being mounted wholly

within an electrical insulating substrate, the insulating

substrate extending in the gap between the inner facing

surfaces and also extending over outer surfaces of each of the

first and second strip lines so that the strip lines are

buried in the insulating substrate;

the first and second planar strip lines are of curved

form in the planar extending direction;

the first radio frequency line being arranged for

electrical connection to the appliance side, and the second radio frequency line being arranged for connection to an antenna.

In an embodiment, both the first and second planar strip lines are curved to form a substantially circular ring. The first and second strip lines therefore form parallel spaced opposed rings. In other embodiments, the ring may not be circular, and may be oval or may be irregularly curved.

In an embodiment, the first planar strip line is connected to the appliance side via a connector and the second planar strip line is also connected to a connector arranged for connection to an antenna.

In an embodiment, the first and second planar strip lines are conductively connected to the respective connectors via strip transmission lines. The strip transmission lines comprise conductive elements which are mounted on the surface of the insulating substrate.

In an embodiment, the connector arranged for connection to the antenna is a coaxial cable connector. In an embodiment, the connector arranged for connection to the appliance side is .0 also a coaxial connector.

In an embodiment, the insulating material is FR4 (an industry glass epoxy laminate). This provides "reinforced insulation" for isolation safety.

Advantageously, the use of curved planar strip lines for coupling, mounted wholly within an insulating substrate, enables the antenna coupler to be of compact form. In embodiments, it is in the order of 30% smaller than other couplers, in embodiments that are applied for standard electricity meters in Australia (240 volts). The embedding of the strip lines in the insulating substrate results in a reduced creepage distance.

In an embodiment, the antenna coupler is mounted within an

appliance housing, separately from other components of the

appliance. It may form a separate circuit board mounted spaced

away from circuit board(s) mounting appliance components. In

an embodiment, the antenna coupler is mounted within the

appliance housing by a coupler mount. The coupler mount

incorporates a cradle on which the insulating substrate is

directly mounted. The cradle forms a cavity about the area

where the planar strip lines extend. This cradle and cavity

arrangement avoids material coming into close range of the

coupler and causing RF interference.

In Accordance with a second aspect, the present invention

further provides an assembly comprising an antenna coupler for

connection of a radio frequency antenna to an appliance to

which electrical power is applied during operation, the

coupler being arranged to provide isolation to isolate the

antenna from the power to the appliance, and a mount for

mounting the antenna coupler within a housing of the

appliance, the antenna coupler comprising a pair of opposed

.0 planar extending strip lines extending in a horizontal

direction, mounted to an insulating substrate, the mount

comprising a cradle arranged to support the insulating

substrate and defining a space which provides a gap between

the insulating substrate and the mount, whereby to avoid RF

interference, which may otherwise be caused by the mount.

In an embodiment, the antenna coupler comprises the antenna

coupler of the first aspect of the invention.

Brief description of the Drawings Features and advantages of the present invention will become

apparent from the following description of embodiments

thereof, by way of example only, with reference to the

accompanying drawings, in which:

Figure 1 a perspective view from below and one side of

an antenna coupler in accordance with an embodiment of the

invention;

Figure 2 is a side-perspective view from below and one

side of the embodiment of Figure 1;

Figure 3 is a plan view from above of the embodiment of

Figure 1;

Figure 4 is a diagram of an antenna coupler of the

embodiment of Figure 1 showing a plan view from below;

Figure 5 is a diagrammatic plan view from above of the

embodiment of Figure 1;

Figure 6 shows a cross-sectional diagrammatic view from

the side of the embodiment of Figure 1;

Figure 7 is a cross-sectional diagrammatic view from one

side of a further embodiment of antenna coupler in accordance

with the invention;

Figure 8 is a diagram illustrating a series of

manufacturing steps in manufacturing an antenna coupler in

accordance with an embodiment;

Figure 9 is a diagram showing an electricity meter with

the embodiment of Figure 1 mounted in place within the

electricity meter, and

Figure 10 is a detail of Figure 11 showing a cross

sectional side view of the antenna coupler mounted in place by

a mount within the meter housing.

Detailed description of Embodiments

An embodiment of antenna coupler in accordance with the present invention will now be described with reference to Figures 1 through 6.

The Figures show an antenna coupler, generally designated by reference numeral 1. In this example embodiment, the antenna coupler 1 is arranged to be mounted in a domestic or industrial electricity meter providing mains electricity to a premises. The antenna coupler 1 is arranged, in operation, to provide isolation to isolate an antenna from the mains electricity power being provided to the meter. In this embodiment, the antenna coupler is designed for a meter which monitors a 240v mains power supply.

In this example, the coupler comprises first and second radio frequency planar strip lines, 2 and 3 which extend in parallel planes spaced apart from each other to form a gap 4 between them.

Both strip lines 2 and 3 are formed within a insulating substrate, in this example being formed of FR4 material.

The insulating substrate 5 wholly contains the planar strip .0 lines within it and essentially forms a plenum within which the planar strip lines are suspended. The applicants have found that the insulation wholly surrounding the strip lines results in less potential for creepage and enables the dimensions of the coupler 1 to be reduced.

In this embodiment, the insulating substrate 5 is formed as a number of layers, with the strip lines being formed as the layers are formed using PCB fabrication techniques (see Figure 8).

In this example, the strip lines are formed of copper.

The strip lines 2, 3 each comprise a pair of curved arms

extending in the planar direction and forming opposed ring

structures. The use of ring formations for the strip lines 2,

3 has been found to optimise the bandwidth of the coupling for

this application. In this example, the opposed strip lines

enable coupling and operation between 700 and 2300 MHz.

In more detail, each of the rings 2, 3 is connected to

connectors 6 and 7 respectively. In this example both

connectors 6 and 7 are radio frequency coaxial cable

connectors. The use of SMT coaxial connectors allows the size

of the coupler to be optimised, without impacting isolation

performance. Connector 7 is an SMA (subminiature version

Acoaxial RF connector) termination and connector 6 is a UFL

(miniature RF connector e.g. HiroseT" UFL connector) termination.

In this example, the planar strip lines 2, 3 are connected to

the respective connectors via transmission lines, which are

generally designated by reference numerals 10 and 11.

The transmission lines between the planar strip lines 2, 3 and

.0 connectors 6, 7 comprise a microstrip transmission line 15

from the connector 6 to a conductive via through hole 16 which

connects to a differential strip line 17 embedded in the

insulation 5 and connects to the first planar strip line 2. A

second arm 17a of the differential strip line connects via

another by way of 18 to a ground conductor 19.

The second planar strip line 3 connects to the antenna

connectors 7 via the connector arrangement 11 which comprises

a micro strip transmission line 20 (Figure 3), via 21 and a

first arm of differential strip line 22. The second arm 22a of

the differential strip line connects to a ground conductor 25

by way of a via 26. Vias 27, 28 connect conductive pads 29, 30

for connector 7 to the ground plane 25. A split 35 is formed in the first strip line ring 2 and a split 36 is formed in the second strip line ring 3.

Dimensions of the coupler are shown clearly in Figures 5 and 6. More particularly, for this embodiment, applied with an electricity meter receiving a 240 voltz mains connection, dimensions are as follows:

• Radius of inner ring of planar strip line 5.6mm

• Outer ring radius 8.8mm • Differential transmission line length 1mm

• Ring split width 160um • PCB size 30 x 20.6mm

• Spacing between planar rings (core material thickness) 0.457mm • Thickness of upper PCB layer and lower PCB layer 0.459mm

The table below, which includes a representation of a circuit schematic for the coupler, includes more detail on dimensions and impedance.

SMA Babeddd Fmbedded Embedded UFL Section To stp Edge-opled koide Edge-CaWld Mcros Te o Momp kmg Cople McroUp

h.aped.nt 5006m 50 Oh- 75 O-50 h- 75 Obs so004 50 Ohr

5 Length 0m 500 LOm m17.6- L0m .00

The above dimensions are particular to this embodiment, for operation with a mains electric meter connected to 240v. It will be appreciated that these dimensions will be changed for other applications and to deal with different frequencies.

The dimensions of the strip lines will change for different frequencies. For example, if we design to meet 1,800 3,500MHz, the dimensions of the planar strip lines will shrink by at least a factor of 2. To support 435MHz, the dimensions will increase by factor of in the order of 2.

The dimensions of the gap between the planar rings can be varied, depending on isolation requirements for the application. For electricity meters, a spacing of between 0.4mm and 0.6mm inclusive covers the various standards requirements.

In operation, the antenna coupler of Figures 1 to 7 is mounted in an electricity meter, as shown in Figures 9 and 10

. Figure 9 shows a domestic electricity meter housing 100. The antenna coupler 1 is supported in a coupler mount 101 positioned at a top part of the meter housing 100. Other meter components are provided in the main part 102 of the housing 100. These components are not shown in Figure 9.

The mount 101 is of plastics in this embodiment. It comprises a U-shaped trough which includes inner walls 120, 121 (see .0 Figure 10) which support the coupler 1 and parts thereof. The walls 120 and 121 also form, with the bottom wall 122, a cavity 123 which extends underneath the coupler 1. The coupler 1 is suspended over the cavity in the portion where the planar strip lines extend. This avoids any RF interference which might otherwise be caused by materials supporting the coupler 1 within the meter housing 100.

Further, walls 150 of the meter housing 100 extend downwardly and projections 151, 152 grip the circuit board of the coupler 1 as shown. An upper cavity 153 is formed by these projections 151, 152 and wall 150.

The mounting 101 operates to suspend and mount the coupler 1

away from the rest of the componentry 102 of the meter.

This embodiment provides a coupler which is generally of a

reduced size and better compactness than the prior art.

Figure 7 illustrates a further embodiment of the coupler,

generally referenced by numeral 200. In this embodiment, the

transmission lines connecting the coaxial connectors to the

planar rings are done away with. This enables the design to be

even more compact. The rings 2, 3 are connected to the

connector 6, 7 by way of vias 8 and 9 respectively. Other vias

(not shown but in the depth direction of Figure 8) connect to

ground.

The vias 8 and 9 are "blind" vias. They do not extend all the

way through the insulating substrate. With this construction

it is easier to satisfy creepage distance requirements.

The differential transmission line and microstrip transmission

line is omitted in this embodiment.

Figure 8 shows a process for manufacturing embodiments,

illustrating a lamination sequence.

The above embodiments are designed for particular application

in an electricity meter. It will be appreciated that the

dimensions of the design may be varied to vary application to

different electricity meters requiring different transceiver

frequencies and/or different requirements power isolation.

Dimensions of the insulation may be increased, for example.

Further, different materials than those described above may be

utilised in different applications. Different insulating

materials from FR4 may be used for example. PCB laminate

materials are numerous. Other common ones are PTFE and

ceramic.

In the above embodiment, the connectors to the internal

appliance circuitry and the external antenna are coaxial.

Different types of connectors may be utilised in other

embodiments. The antenna may be connected directly to the

coupler without coax, for example. The coupler may connect to

other components such as a splitter.

In the above embodiments, all conductors are of copper.

Different conductor materials may be used in other

embodiments.

In the above embodiments, the planar strip lines are formed as

opposing rings. Other shapes may be used. The strip lines may

be oval, for example, in other applications. In yet other

embodiments, strip lines may be curved but of a irregular

curved shape. Other forms may also be applied.

The above embodiments have been designed to meet the standard

safety requirements for IEC 62052-31 in Australia. The coupler

is suitable to couple to transceivers for LTE and RF Mesh

Communications.

In the above embodiment, the coupler is applied with an

.0 electricity meter. It may be applied in other appliances to

provide isolation. It is not limited to electricity meters.

It will be appreciated by persons skilled in the art that

numerous variations and/or modifications may be made to the

invention as shown in the specific embodiments without

departing from the spirit or scope of the invention as broadly

described. The present embodiments are, therefore, to be

considered in all respects as illustrative and not

restrictive.

Throughout this specification and the claims which follow,

unless the context requires otherwise, the word "comprise", and

variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference in this specification to any prior publication (or

information derived from it), or to any matter which is known,

is not, and should not be taken as an acknowledgment or admission

or any form of suggestion that that prior publication (or

information derived from it) or known matter forms part of the

common general knowledge in the field of endeavour to which this

specification relates.

Claims (7)

The claims defining the invention are as follows:

1. An antenna coupler for connection of a radio-frequency antenna to an appliance to which electrical power is applied during operation, the coupler being arranged to provide isolation to isolate the antenna from the electrical power to the appliance, the coupler comprising; first and second radio frequency planar strip lines extending in a horizontal direction and parallel to each other so that inner facing surfaces of the strip lines are spaced apart opposing each other with a gap between them; the first and second strip lines being mounted wholly within an electrical insulating substrate, the insulating substrate extending in the gap between the inner facing surfaces and also extending over outer surfaces of each of the first and second strip lines so that the strip lines are buried in the insulating substrate; the first and second planar strip lines are of curved .0 form in the planar extending direction; the first radio frequency line being arranged for electrical connection to the appliance side, and the second radio frequency line arranged for connection to an antenna.

2. The coupler in accordance with claim 1, wherein the first and second planar strip lines are curved to form a substantially circular ring.

3. The coupler in accordance with either of claim 1 or claim 2, wherein the first and second planar strip lines are conductively connected to the connectors via strip transmission lines.

4. The coupler in accordance with either of claim 1 or

claim 2, wherein the first and second planar strip

lines are conductively connected by way of conductive

vias in the substrate.

5. The coupler in accordance with any one of the

preceding claims, wherein the insulating material is

FR4.

6. An assembly comprising an antenna coupler for

connection of a radio frequency antenna to an

appliance to which electrical power is applied during

operation, the coupler being arranged to provide

isolation to isolate the antenna from the power to the

appliance, and a mount for mounting the antenna

coupler within a housing of the appliance, the antenna

coupler comprising a pair of opposed planar extending

strip lines extending in a horizontal direction,

.0 mounted to an insulating substrate, the mount

comprising a cradle arranged to support the insulating

substrate and defining a space which provides a gap

between the insulating substrate and the mount,

whereby to avoid RF interference, which may otherwise

be caused by the mount.

7. The assembly in accordance with claim 6, wherein the

antenna coupler comprises the antenna coupler of any

one of claims 1 to 5.

6 10 1 18 2 17a 35 11

15 29 28

19 16 26 25 Sheet 1 of 10

17 7

3 21 4

5 27 30

Figure 1

7 30 35

2 6 15 19 Sheet 2 of 10

29 25 7 4 3 5

Figure 2

22a 25 Sheet 3 of 10

22 19 29 20

5 3 1 Figure 3

35 Sheet 4 of 10

Figure 4

Sheet 5 of 10

36

Figure 5

17, 17a 2

25

20 19 Sheet 6 of 10

22, 22a 3 16, 18

Figure 6

200

2

8 9 Sheet 7 of 10

7

3

Figure 7

Sheet 8 of 10

Figure 8

1 100 123 Sheet 9 of 10

7 101

Figure 9

150 152 151 1

153 Sheet 10 of 10

121 120 122 123

Figure 10