WO2005053088A1

WO2005053088A1 - Compact dual band antenna

Info

Publication number: WO2005053088A1
Application number: PCT/DK2003/000810
Authority: WO
Inventors: Poul Erik Schou-Pedersen
Original assignee: Kamstrup A/S
Priority date: 2003-11-26
Filing date: 2003-11-26
Publication date: 2005-06-09
Also published as: AU2003281991A1; DE20380353U1

Abstract

The invention relates to a balanced dual band antenna comprising a plane microstrip part and a plane electrically conductive ground plane part arranged substantially parallel to each other. A resonator of the antenna exhibits a ½-wavelength first resonance within the frequency interval 400-500 MHz and exhibits a ¾-wavelength second resonance within the frequency interval 800-1000MHz. Preferably, the microstrip part is formed by a printed circuit board with electrically conductive paths. The antenna may be adapted for example for a lower frequency of 444MHz and a higher frequency of 910MHz (GSM). Preferably, the antenna is provided with a protecting cover. The antenna may be used with an associated consumption meter adapted for wireless transmission of measured consumed quantity. The antenna according to the invention exhibits a high efficiency and it is generally insensitive to mounting positions close to a surface etc.

Description

COMPACT DUAL BAND ANTENNA

Field of the invention

The present invention relates to the field of dual band antennas. More specifically the invention relates to balanced dual band microstrip or patch antennas. In addition, the invention relates to a consumption meter with means for wireless transmission of a measured consumed quantity.

Background of the invention

Wireless reading of consumption meters, such as water, heat or electricity meters, positioned in a house of a consumer has a number of advantages. However, most often antennas adapted to function in the normal frequency range for this purpose, 400-1000 MHz, are bulky and vulnerable to mechanical impacts. In addition, efficiency of such antennas is normally highly depending on their position relative to other objects, such as the presence of for instance a brick wall or a metal door. This is essential since transmitting power in such wireless reading system is often very limited, such as 25 mW transmitting power or lower. Therefore, for several reasons such antennas are generally not suited for mounting, for example, on a wall of a consumer's house.

A large number of compact microstrip or patch antennas are known within mobile communication. However, such antennas are designed to suit very different goals and they are therefore not suited for the above-mentioned applications.

Summary of the invention

It may be seen as an object of the present invention to provide a compact and robust antenna adapted for the frequency range 400-1000 MHz. The antenna must be adapted to exhibit a high efficiency in different mounting environments.

The above mentioned object is complied with by providing in a first aspect a balanced dual band antenna comprising - at least one path of electrically conductive material disposed on a surface of a substantially plane and electrically non-conductive substrate, and - a substantially plane first member of electrically conductive material, wherein the substantially plane substrate and the substantially plane first member are aligned and arranged substantially parallel to each other with a non-conductive second member being arranged between the substantially plane substrate and the substantially plane first member.

The non-conductive second member may form part of the non-conductive substrate. The at least one path of electrically conductive material may be disposed so as to form a dual band dipole antenna. The at least one path of electrically conductive material may form, together with substantially plane first member, first and second resonators. The first resonator may exhibit a 1/2-wavelength resonance within the frequency interval 400-500 MHz and the second resonator may exhibit a 3/4-wavelength resonance within the frequency interval 800-1000 MHz.

An additional electrical connection to the at least one path of electrically conductive material may be disposed on the surface of the substantially plane substrate. The additional electrical connection may disposed through a hole in the substantially plane substrate.

A distance between the substantially plane first member and the substantially plane substrate is preferably within the interval 1-50 mm.

Preferably, the substantially plane substrate is formed by a single-sided printed circuit board (PCB), and the at least one path of electrically conductive material is formed by a copper path. The substantially plane first member may be a metal plate, such as a stainless steel plate. The substantially plane first member may have a substantially circular shape.

Preferably, the antenna further comprises a casing for housing at least the substantially plane and electrically non-conductive substrate. The casing may comprise an electrically non-conductive cover, and an electrically conductive lid for covering an opening in the non- conductive cover. The lid for covering the opening in the non-conductive cover may be formed by the substantially plane first member. The casing may comprise means for ensuring a predefined distance between the substantially plane substrate and the substantially plane first member. The means for ensuring the predefined distance may be monolithically integrated with the cover. The cover may be formed by plastic materials, PVC, or rubber.

According to a second aspect, the invention provides a consumption meter for measuring a quantity value corresponding to a consumed quantity and transmitting said quantity wirelessly to an associated receiver, the consumption meter comprising: - means for measuring the quantity value, and - means for transmitting the measured quantity value to the associated receiver, wherein the means for transmitting the measured quantity value comprises a balanced dual band antenna according to the first aspect.

The balanced dual band antenna may be arranged externally to the means for measuring the quantity value. Preferably, the consumption meter comprises means for receiving a wireless signal from the associated transmitter using the balanced dual band antenna.

The consumption meter may be adapted to measure an amount of water, heat, electricity or gas. The dual band properties of the balanced dual band antenna may be utilised for frequency diversity transmission or reception of wireless signals.

Brief description of drawings

In the following the invention is described in details with reference to the accompanying figures of which

Fig. 1 shows a cross section sketch of a preferred antenna device embodiment,

Fig. 2 shows a layout of a microstrip part of a preferred antenna,

Fig. 3 shows an exploded view of a preferred embodiment,

Fig. 4 shows a cross section sketch of a protecting cover with means for mounting the microstrip part and the ground plane part of the antenna,

Fig. 5 shows a preferred shape of the antenna mounted in various positions on outer surfaces of a house, and

Fig. 6 shows an antenna with a cover having a preferred shape.

While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims.

Detailed description of the invention

In the following the antenna according to the present invention will be described in connection with a preferred use, namely connected to an associated consumption meter adapted for wireless reading by a consumption supplier. From a central station the supplier can contact each individual consumer's meter and request a measured value. For the best possible radiation the antenna may be positioned on an exterior surface of the consumer's house.

Fig. 1 shows a dual band antenna device according to the present invention. A microstrip part of the antenna is formed by a plane printed circuit board (PCB) substrate 1 with paths 2 of electrically conducting material thereon. If preferred, the substrate 1 may be formed by other dielectric materials. The paths 2 form the radiating elements of the antenna, and these paths 2 may be formed by a metal such as copper, aluminium, brass, or silver. The paths 2 may further have a layer of a protecting material such as a layer of lacquer. The substrate 1 is arranged at a distance d relative to a plane metal sheet 3 forming a ground plane part of the antenna. The metal sheet 3 serves as a shielding element so as to shield the antenna from an object on which it is mounted. Preferably, the metal sheet extends at least as large as a region covered by the paths 2. Preferably, the plane PCB forming the microstrip part of the antenna is arranged parallel to the sheet of metal forming the ground plane part of the antenna. Preferably, the paths 2 are positioned on an upper surface of the substrate 1, whereas a lower surface of the substrate 1 faces the metal sheet 3. The metal sheet may be formed by metals such as iron, stainless steel, aluminium etc. Preferably, a gap formed between a lower surface of the substrate 1 and a surface of the metal sheet 3 is filled with atmospheric air. If preferred, the gap may be filled with other dielectrics.

The antenna shown in Fig. 1 is externally connected via a coaxial cable 4 through a hole in the metal sheet 3. Electrical conductors of the cable 4 are connected to the paths 2 via a connector 5 attached to the substrate 1 so as to allow a mechanically stable design being resistive to damage of the termination of the antenna, a damage that may cause the antenna to malfunction. The electrical conductors of the cable 4 are connected to the paths 2 by soldering, welding or by means of electrically conductive adhesives.

A cover 6 of an electrically non-conductive material is shown to protect internal parts of the antenna. Preferably, the cover 6 forms the entire external surface of the antenna when mounted with the metal sheet 3 against a flat surface. Hereby, an external part of the antenna can be formed robust against various mechanical impacts thus yielding a reliable design with a high resistance against malfunction and with a low risk for mechanical breakdown and the need for costly repair. The cover 6 may be fabricated in various nonconducting materials, such as various plastic materials, or rubber.

Fig. 2 shows a preferred layout of the microstrip part of the antenna, i.e. layout of electrically conductive paths 10 on a surface of a substrate 15. The shape of the substrate may in principle have any shape such as rectangular, circular or quadratic. A first 11 part of the path is dedicated to a first frequency band whereas a second path 12 is dedicated to a second frequency band. Contact point 13 is soldered to an inner conductor of a connecting coaxial cable 4, and contact point 14 is soldered to a shielding conductor of the connecting coaxial cable 4. The lengths of the paths 11,12 are dictated by the desired frequencies. The two paths 11,12 are each folded so as to provide the required path length while occupying only a limited region of the substrate 15, hereby enabling a compact design of the total antenna.

The antenna according to the invention will exhibit a 1/2-wavelength resonator characteristics at a first frequency and a 3/4-wavelength resonator at a second frequency. The antenna exhibits a narrow frequency pass band. Hereby, unwanted signals are effectively attenuated thus allowing a receiver/transmitter part of an associated consumption meter to be very simple without the need for complicated filters. The detailed design of the microstrip part of the antenna, such as to adapt the design to different frequencies, is an iterative process with efficiency (gain) and bandwith as important parameters.

Due to the presence of the metal sheet forming a ground plane, an antenna according to the invention exhibits a radiation pattern which is generally insensitive to its mounting position, also in positions where the antenna is closer to a rigid surface than 1/4- wavelength. This ensures a high efficiency regardsless of the structure of a mounting surface or the distance thereto.

The embodiment shown in Fig. 2 is designed to a first band of 444 MHz, i.e. the ISM band, and a second band of 910 MHz, i.e. the GSM band. Alternative shapes of electrically conductive paths may be chosen thus allowing the antenna to be tuned to various frequency bands. For use with an associated consumption meter, it may be preferred to design the antenna for a first, lower, frequency being associated with a local wireless network supported by a consumption supplier, whereas a second, higher, frequency allows the antenna to transmit/receive via the GSM network. Hereby, the same antenna design may be mass produced for use for consumers situated within a coverage area of the local supplier wireless network, whereas remotely situated consumers may have their consumption meters read with the same type of antenna but via the GSM network. Another embodiment may be tuned to a lower frequency band of 434 MHz and a higher frequency band of 868 MHz. The dual band property may for any embodiment be utilised for frequency diversity purposes.

Following the above, a single type of antenna according to the invention may be installed at all consumers coupled to a supplier's consumption net. Consumers within a coverage of the supplier's wireless net may use this net, whereas consumers out of the range of this net may have their meter read via the GSM net. This eliminates the need for costly on-site measurements at each consumer for deciding if the supplier's net can be used or if a GSM antenna should be installed instead. However, it may be preferred to produce consumption meters with changeable transmitter/receiver modules. If later performed tests show that the supplier's net is insufficient to reach a consumer, then it is only necessary to change the transmitter/receiver module in the meter of this consumer to a GSM module but without the need for changing the antenna once installed. In this way it is possible to adapt an individual consumer's system with a minimum of installing costs.

Fig. 3 shows an exploded version of a preferred embodiment adapted for the frequency bands 444 MHz and 910 MHz (GSM). A cover 26 of the antenna has a generally round shape and a diameter of 12 cm. The height of the cover is approximately 2.5 cm.

In the embodiment shown in Fig. 3 the cover 26 is die cast in a plastics and it has on its inner side various protrusions so as to fix a microstrip part 21 and a ground plane part 23 when the antenna is assembled. The microstrip part 21 is formed by a generally plane and rectangular PCB. The ground plane part 23 is formed by plane a sheet of metal which is generally round in shape so as to fit the round shape of the cover 26. The ground plane part 23 has a hole in its centre so as to allow termination of the microstrip part 21. Two distance pieces 27 serve to fix the microstrip part 21 and the ground plane part 23 at a predetermined distance. In addition, the distance pieces 27 serve, together with protrusions on the inner side of the cover 26, to keep the microstrip part 21 and the ground plane part 23 substantially parallel to each other.

The embodiment shown in Fig. 3 is especially suited for mounting on a flat surface such as a wall or a consumption meter door. The metal sheet part of the antenna will then be mounted close to the flat surface, and if preferred the metal sheet may be provided with means for fixing the antenna to the flat surface so as to allow a quick and reliable installing of the antenna.

Fig. 4 shows a cross section sketch of an alternative embodiment of a cover with built-in fixing means 41, 42. With respect to low cost mass production the distance d shown in Fig. 2, is critical in order to obtain a precise tuning of the resonance frequencies of the antenna. In Fig. 4 the cover has distance pieces 41 for fixing the microstrip part of the antenna and distance pieces 42 for fixing the ground plane part of the antenna. Preferably, the cover is monolithically die cast in a plastic material. A monolithically die cast cover can provide very precise fixing means so as to ensure that the distance d between the microstrip part and the ground plane part is precise - also in low cost production series without the need for manual adjustments. Thus, the antenna can be manufactured with very few components and it is therefore suited for large scale low cost production. The microstrip part and the ground plane part may be attached to the fixing means of the cover by means of screws, adhesives or by fusing. The fixing means may also comprise taps for click means for locking the microstrip part and the ground plane part into position, once they have been positioned mounted.

Fig. 5 shows a selection of positions that may be used for an antenna in connection with an outer surface of a house 100 of a consumer. Since transmitting and receiving performance of an antenna according to the invention is generally insensitive to a surface on which it is mounted, the antenna may be positioned in a large variety of external positions of the consumer's dwelling. The antenna may be mounted on any type of materials such as brick, concrete, wood or metal.

In Fig. 5 an antenna 101 is positioned on a vertical surface, namely a wall of the house 100. In case the antenna 101 is to be connected to an indoor positioned meter device this position may be preferred since connection cabling may be lead through a hole in the wall just behind the antenna and thus the cabling may be invisible. Preferably, a cabling hole in the metal sheet 3 of the antenna is aligned with a hole in the wall, thus enabling a mounting close to the surface of the wall without the need for bending the cable. In Fig. 5 an antenna 102 is mounted on a horizontal surface, namely under an overhang of the roof of the house 100. An antenna 103 is positioned on a consumption meter door of an externally accessible consumption meter, such door often being a metal door. This position of the antenna 103 may be preferred since only a short cable is necessary for connecting the antenna 103 to the consumption meter. The cable may be lead through a hole in the meter door.

Lower part of Fig. 5 shows a cross section of an antenna 104 mounted on a flat surface 110, such as a brick wall of a house, a wood board of a fence or a metal door of a consumption meter. The cover of the antenna 104 may be given various shapes, however it will be appreciated that a generally smooth shape without sharp edges will provide the mechanically most robust design. In addition, it is preferred that the antenna 104 has a shape enabling the cover to fit close to the surface 110 on which the antenna 104 is mounted. If preferred, the cover may be provided with a seal so as to provide a waterproof mounting to the surface 104.

In preferred embodiments the antenna has an unobtrusive appearance which is enabled due to the general design of the transmitting/receiving parts of the antenna being very compact. Preferably, the cover part, i.e. the visual part of the antenna, has a smooth shape and a generally smooth surface. Preferably, the shape of the cover part is round and flat thus doing the antenna generally insensitive to mechanical impacts that may accidentally occur, such as a football or a ladder hitting the antenna. The cover may be produced in a material having a preferred colour, or the cover may be painted so as to have a preferred colour. The colour may be selected so as to match the surface on which the antenna is mounted, thus making the antenna less visible and therefore more acceptable for mounting in visible positions on dwellings.

Fig. 6 shows three different perspectives of an antenna with a cover having a preferred shape. The antenna in Fig. 6 is shown fastened to a plate, such as for example when mounted on the metal door of a consumption meter.

The antenna according to the invention may be used connected to an associated consumption meter systems such as water, heat or electric consumption meters. However, the general functionality of the design allows a wide range of other applications that may profit from a compact and robust design in combination with a controlled radiation pattern under various mounting environments.

Claims

1. A balanced dual band antenna comprising

- at least one path of electrically conductive material disposed on a surface of a substantially plane and electrically non-conductive substrate, and

- a substantially plane first member of electrically conductive material,

wherein the substantially plane substrate and the substantially plane first member are aligned and arranged substantially parallel to each other with a non-conductive second member being arranged between the substantially plane substrate and the substantially plane first member.

2. A balanced dual band antenna according to claim 1, wherein the non-conductive second member forms part of the non-conductive substrate.

3. A balanced dual band antenna according to claims 1 or 2, wherein the at least one path of electrically conductive material is disposed so as to form a dual band dipole antenna.

4. A balanced dual band antenna according to any of claims 1-3, wherein the at least one path of electrically conductive material forms, together with substantially plane first member, first and second resonators.

5. A balanced dual band antenna according to claim 4, wherein the first resonator exhibits a 1/2-wavelength resonance within the frequency interval 400-500 MHz and the second resonator exhibits a 3/4-wavelength resonance within the frequency interval 800-1000 MHz.

6. A balanced dual band antenna according to any of the preceding claims, wherein an additional electrical connection to the at least one path of electrically conductive material is disposed on the surface of the substantially plane substrate.

7. A balanced dual band antenna according to claim 6, wherein the additional electrical connection is disposed through a hole in the substantially plane substrate.

8. A balanced dual band antenna according to any of the preceding claims, wherein a distance between the substantially plane first member and the substantially plane substrate is within the interval 1-50 mm.

9. A balanced dual band antenna according to any of the preceding claims, wherein the substantially plane substrate is formed by a single-sided PCB, and wherein the at least one path of electrically conductive material is formed by a copper path.

10. A balanced dual band antenna according to any of the preceding claims, wherein the substantially plane first member is a metal plate, such as a stainless steel plate.

11. A balanced dual band antenna according to any of the preceding claims, further 5 comprising a casing for housing at least the substantially plane and electrically non- conductive substrate.

12. A balanced dual band antenna according to claim 11, wherein the casing comprises an electrically non-conductive cover, and an electrically conductive lid for covering an opening

10 in the non-conductive cover.

13. A balanced dual band antenna according to claim 12, wherein the lid for covering the opening in the non-conductive cover is formed by the substantially plane first member.

15 14. A balanced dual band antenna according to any of claims 11-13, wherein the casing comprises means for ensuring a predefined distance between the substantially plane substrate and the substantially plane first member.

15. A balanced dual band antenna according to claim 14, wherein the means for ensuring 20 the predefined distance is monolithically integrated with the cover.

16. A balanced dual band antenna according to any of claims 12-15, wherein the cover is formed by a material selected from the group consisting of: plastic materials, PVC, and rubber.

25 17. A balanced dual band antenna according to any of the preceding claims, wherein the substantially plane first member has a substantially circular shape.

18. A consumption meter for measuring a quantity value corresponding to a consumed 30 quantity and transmitting said quantity wirelessly to an associated receiver, the consumption meter comprising:

- means for measuring the quantity value, and

35 - means for transmitting the measured quantity value to the associated receiver, wherein the means for transmitting the measured quantity value comprises a balanced dual band antenna according to any of claims 1-17.

40 19. A consumption meter according to claim 18, wherein the balanced dual band antenna is arranged externally to the means for measuring the quantity value.

20. A consumption meter according to claim 18 or 19, further comprising means for receiving a wireless signal from the associated transmitter using the balanced dual band antenna.

21. A consumption meter according to any of claims 18-20, wherein consumption meter is adapted to measure an amount of water.

22. A consumption meter according to any of claims 18-20, wherein consumption meter is adapted to measure an amount of heat.

23. A consumption meter according to any of claims 18-20, wherein the consumption meter is adapted to measure an amount of electricity.

24. A consumption meter according to any of claims 18-20, wherein consumption meter is adapted to measure an amount of gas.

25. A consumption meter according to any of claims 18-24, wherein the dual band properties of the balanced dual band antenna is utilised for frequency diversity transmission or reception of wireless signals.