WO2011073645A2

WO2011073645A2 - Notch antenna

Info

Publication number: WO2011073645A2
Application number: PCT/GB2010/052079
Authority: WO
Inventors: Robert James Clements; James Maximillian Todd
Original assignee: Aerial Research Technology Limited
Priority date: 2009-12-14
Filing date: 2010-12-14
Publication date: 2011-06-23
Also published as: EP2514031A2; EP2514031B1; GB201009752D0; WO2011073645A3; GB0921811D0; GB2476132A; GB201008784D0

Abstract

A notch antenna, plate component thereof and related manufacturing and installation methods are described. The notch antenna is compact, efficient and easy to adjust.

Description

Notch Antenna

Field of the Invention The invention described herein relates to notch antennas, to plate components of notch antennas, and to related manufacturing and installation methods.

Background to the Invention A conventional notch antenna is shown in Figure 1. The antenna comprises a plate P with a notch N, the notch N being coupled to feed line F at a feed point. To give omni-directional polar characteristics at the centre of a desired operating frequency range the width W of the plate P is chosen to be less than a quarter of one wavelength. The notch N is doglegged to allow the notch to be of sufficient length.

However, matching the dimensions of the notch and plate to give high efficiency and omnidirectional polar characteristics across a wide operating frequency range is difficult. Further difficulties arise when this type of antenna is installed close to the ground, near to metallic structures or in other areas where the local permittivity differs from that of free space, as such installations can severely effect antenna operation within the intended operating frequency range.

It is an aim of example embodiments of the invention to address at least one disadvantage of the prior art, whether identified herein, or otherwise.

Summary of the Invention

In a first aspect, the invention described herein provides a notch antenna comprising a first notch coupled to a feed line, and a second notch in use passively excited by a signal supplied to the first notch through the feed line.

In a second aspect, the invention described herein provides a plate component of a notch antenna, the plate comprising a first notch for coupling to a feed line and a second notch arranged to be passively excited by a signal supplied to the first notch.

Suitably, the notch antenna comprises a plate in which the first and second notches are defined. Suitably, the second notch is arranged with the first to be excited, in use, by currents induced around the first notch.

Suitably, the first notch comprises an open end at an edge of the plate, a closed end, and long edges between the open and closed ends. Suitably, the second notch comprises an open end at an edge of the plate, a closed end, and long edges between the open and closed ends.

Suitably, the plate comprises a metallic material. Suitably, the plate comprises a thin, electrically conducting material. Suitably, the plate comprises an elastically deformable material. Suitably, the plate comprises a flexible material. Suitably, the antenna further comprises a cover arranged over one or both faces of the plate. Suitably, the cover is electrically non-conductive. Suitably, the cover is of low electrical permittivity to radio frequency energy within the operating range of the antenna. Suitably, the cover comprises part of a vehicle registration plate.

Suitably, the plate comprises a component selected from a group including: the ground plane of a circuit-board, metal sheet and expanded metal.

Suitably, the plate has a width, x, dimension, a height, z, dimension and a depth, y, dimension. Suitably, the depth of the plate is small in comparison to the width and height. Suitably, the plate is generally rectangular.

Suitably, the width of the plate is equal to or greater than one quarter of one wavelength at the centre of the operating frequency range. Suitably, the width of the plate is selected according to the desired frequency for the centre of the operating range.

Suitably, the first and second notches open on different plate edges. Suitably, the first and second notches open on opposite plate edges. Suitably, the first notch is generally linear. Suitably, the second notch is generally linear. Suitably the first notch comprises long edges aligned with the width dimension of the plate. Suitably, the second notch comprises long edges aligned with the width dimension of the plate.

Suitably, the first notch is of length less than or equal to one fifth of one wavelength at the centre of the operating frequency range. Suitably, the second notch is of length less than one fifth of one wavelength at the centre of the operating frequency range. Suitably, the length of the first and/or second notch is selected with a length according to the desired frequency for the centre of the operating range. Suitably the notch antenna comprises an adjustment portion provided to the second notch to facilitate change to the effective length of the second notch. Suitably, the adjustment portion comprises a conductive patch applied to the second notch, suitably applied across the second notch. Suitably, the adjustment portion is applied at the closed end of the second notch. Suitably, the adjustment portion comprises a piece of adhesive backed tape, preferably adhesive backed metallic tape. Suitably, the adjustment portion is arranged to bridge the second notch with a conducing element in contact with the plate. Suitably, the adjustment portion is arranged to provide a conductor that is capacitively coupled to the plate. Suitably, the adjustment portion comprises an semiconductor component coupled across the second notch. Suitably, the adjustment portion comprises a switching component coupled across the second notch. Suitably, the adjustment portion comprises a PIN diode coupled across the second notch. Suitably, the adjustment portion comprises a plurality of like or unlike components, including one or more selected from the adjustment portions described above. Suitably, the feed line comprises a coaxial feed line. Suitably, the feed line comprises a micro- strip connection across the first notch. Suitably, the antenna comprises a sealed body provided around the plate. Suitably, the sealed body is an insulating body. Suitably, the adjustment portion is provided outside the sealed body. Suitably, the first and second notches are manufactured with different lengths. Suitably, the second notch is longer than the first notch. Suitably, the adjustment portion shortens the effective length of the second notch.

In a third aspect, the invention described herein provides a method of manufacturing a notch antenna comprising the steps of: providing a first notch coupled to a feed line, and providing a second notch in use to be passively excited by a signal supplied to the first notch through the feed line.

Suitably the method further comprises providing an adjustment portion for the second notch to change the effective length of the second notch. Suitably, the method further comprises providing an adjustment portion in the form of a conductive patch applied to the second notch, suitably applied across the second notch. Suitably, the adjustment portion is applied at the closed end of the second notch. Suitably, the adjustment portion comprises a piece of adhesive backed tape, preferably adhesive backed metallic tape. Suitably, the method further comprises providing an adjustment portion in the form of a semiconductor component coupled across the second notch. Suitably, the adjustment portion comprises a switching component coupled across the second notch. Suitably, the adjustment portion comprises a PIN diode coupled across the second notch. Suitably, the adjustment portion comprises a plurality of like or unlike components, including one or more selected from the adjustment portions described above.

In a fourth aspect, the invention described herein provides a notch antenna installation method, the method comprising providing a notch antenna comprising a first notch coupled to a feed line, and a second notch in use passively excited by a signal supplied to the first notch through the feed line, installing the antenna at a desired installation position, and providing an adjustment portion for the second notch to change the effective length of the second notch in response to a detected frequency shift from a desired centre frequency caused by electrical permittivity of the installation position.

Suitably, providing the adjustment portion comprises providing a conductive patch applied to the second notch, suitably applied across the second notch. Suitably, the adjustment portion is applied at the closed end of the second notch. Suitably, the adjustment portion comprises a piece of adhesive backed tape, preferably adhesive backed metallic tape.

According to the invention described herein, there is provided an apparatus and method as set forth in any appended claims. According to the invention described herein, there is provided a notch antenna and a plate component of a notch antenna, each substantially as described herein with reference to the Figures 2 and 3 respectively. Other features of the invention will be apparent from the any dependent claims, and the description which follows.

Brief introduction to the Figures For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which:

Figure 1 shows a schematic front view of a conventional notch antenna;

Figure 2 shows a schematic front view of a notch antenna according to an example embodiment of the invention described herein;

Figure 3 shows a schematic front view of a plate for a notch antenna according to an example embodiment of the invention described herein;

Figure 4 shows the voltage standing wave ratio (VSWR) of a notch antenna according to an example embodiment of the invention described herein, constructed with the plate of Figure 3; and Figures 5 and 6 show radiation patterns of a notch antenna according to an example embodiment of the invention described herein, constructed with the plate of Figure 3. Description of Example Embodiment

The following description is given to aid understanding of the invention described herein, and to describe how embodiments thereof may be constructed. Referring now to Figure 2 there is shown a schematic front view of a notch antenna 10 according to an example embodiment of the invention described herein. The antenna 10 comprises a plate 20, first and second notches 21 ,22 and a feed line 30. The feed line 30 may be fed directly, or alternatively via a BALUN. The first notch 21 is operatively coupled to the feed line 30 at a feed point to receive a signal from the feed line 30 when the antenna 10 is used to transmit. Reciprocity applies when the antenna 10 is used to receive. The second notch 22 is in use passively excited by a signal supplied to the first notch 21 through the feed line 30, or by induced currents in the plate for the receive condition. The feed line 30 is suitably a coaxial line. The plate 20 is generally planar, and generally rectangular with characteristic dimensions of width x, height z, and out of plane depth y, that is an out of plane depth y that is orthogonal to the plane of the paper. The depth of the plate 20 is small in comparison to the width and height.

The first and second notches 21 ,22 are provided in the plate 20 close to one another such that the second notch 22 is excited, in use, by currents induced around the first notch 21 in response to a signal applied to the first notch 21 from the feed line 30, or by induced plate currents in the case or reception.

The first notch 21 comprises an open end 211 at an edge of the plate, a closed end 212, and long edges 213 between the open and closed ends 21 1 ,212. The second notch 22 comprises an open end 221 at an edge of the plate, a closed end 222, and long edges 223 between the open and closed ends 221 ,222. The long edges 213,223 are linear, and are aligned with the width of the plate 20. The open ends 21 1 ,221 of the first and second notches 21 ,22 are located on opposing plate edges. In preferred embodiments the width of the plate 20 is greater than one quarter of one wavelength at the centre of the operating frequency range. In such embodiments the first and second notches 21 ,22 are of length less than one fifth of one wavelength at the centre of the operating frequency range. The plate 20 comprises a metallic material which in example embodiments may be flexible to allow the antenna 10 to be bent out of planar arrangement around a substrate to which it is to be installed. In other example embodiments the plate 20 is arranged with a non-conductive cover arranged over one or both faces of the plate, and for example may be integrated with a cover in the guise of a vehicle registration plate. Flexible plates may for example comprise an electrically conductive metallic mesh, for example expanded metal. Rigid plates may for example comprise a circuit board with its ground plane, or metal sheet. Copper is a particularly suited metal for any of these plate constructions owing to its excellent electrical conduction properties. In the case of either rigid or flexible plate, the antenna produced is conveniently sized and shaped to enable it to be hermetically sealed, thereby reducing the risk of degradation in performance over time due to corrosion or other environmental effects. Furthermore, the relatively simple construction and convenient dimensions enable a relatively robust antenna package to be produced, with the antenna being easily mountable and concealable in a range of applications.

The area around the closed end 222 of the second notch 22 comprises an adjustment portion provided to facilitate change to the effective length of the second notch 22. Initially, the second notch 22 is relatively longer than required. If required, a conductive patch can be applied across the second notch 22 at the closed end 222 thereof, effectively reducing the length of the second notch 22. The change in length of the second notch 22 enables frequency response of the antenna to be easily adjusted to suit its environment. For example, shift in the centre frequency of the desired operating frequency range caused by permittivity of the structure on which the antenna 10 is mounted, or that of nearby metallic structures, can now be compensated for.

In effect, the two linear notches provide a circular polar response with high efficiency over a significant bandwidth range. A high efficiency is achievable over more than a 10% of the bandwidth. Furthermore, since the centre frequency of the antenna can be altered by simply adjusting the length of the unfed second notch 22 there is no need to reposition the feed line when installing and tuning the antenna.

Methods of manufacturing and installing a tuneable notch antenna are now described. The manufacturing method comprises the steps of providing a first notch coupled to a feed line, and providing a second notch in use to be passively excited by a signal supplied to the first notch through the feed line, in the case of transmission. The notch antenna manufacturing method suitably further comprises providing an adjustment portion for the second notch. The adjustment portion is provided along the second notch to enable a change in the effective electrical length of the second notch. The installation method comprises the steps of providing a notch antenna comprising a first notch coupled to a feed line, and a second notch, in use to be passively excited by a signal supplied to the first notch through the feed line, installing the antenna at a desired installation position, and providing an adjustment portion for the second notch to change the effective length of the second notch in response to a detected frequency shift from a desired centre frequency caused by the local environmental effects about the installation position. In both methods the step of providing the adjustment portion comprises providing a piece of adhesive backed metallic tape at the closed end of the second notch. In alternative embodiments the step of providing the adjustment portion comprises providing a suitable electronically activated semiconductor device or devices to bridge the second notch at an appropriate position, for example providing one or more PIN diode switches.

Figure 3 shows a schematic front view of a plate 20 for a tuneable notch antenna according to an example embodiment of the invention described herein. The plate 20 is intended for an antenna designed to operate at a lowest frequency of 405 MHz in free space.

It can be seen in Figure 3 that the unfed notch has been, coincidently, reduced to half the width of the plate to give a modified centre frequency of 430 MHz. By scaling the antenna, example embodiments of the invention described herein are operable over frequencies in the lower UHF band, up to and including the S-Band, for example in the range 0.2GHz to 4GHz.

Figure 4 shows the VSWR of an antenna constructed from the plate of Figure 3, and Figures 5 and 6 show the radiation characteristics of the antenna. Figure 5 shows the pattern in the yz plane and Figure 6 shows the pattern in the xy plane. As will be appreciated, Figures 5 and 6 show radiation patterns similar to those produced by a dipole aligned on the z axis, with the antenna providing a complete 360 degree azimuth radiation pattern.

As above, simple, effective and readily tunable antenna constructions with related componentry, and related method steps have been described, able to produce a notch antenna that operates efficiently over a useful range of frequencies.

Although a few preferred embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the Summary of Invention section and/or any appended claims.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention described herein is not restricted to the details of the foregoing embodiment(sand extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLAIMS:

1. A notch antenna comprising a first notch coupled to a feed line, and a second notch in use passively excited by a signal supplied to the first notch through the feed line.

2. The notch antenna of claim 1 , wherein the second notch is arranged with the first to be excited, in use, by currents induced around the first notch.

3. The notch antenna of claim 1 or 2, comprising a plate in which the first and second notches are d ef i n ed .

4. The notch antenna of claim 3, wherein the first notch comprises an open end at an edge of the plate, a closed end, and long edges between the open and closed ends.

5. The notch antenna of claim 3 or 4, wherein the second notch comprises an open end at an edge of the plate, a closed end, and long edges between the open and closed ends.

6. The notch antenna of claim 3, 4 or 5, wherein the plate comprises a metallic material.

7. The notch antenna of any one of claims 3-6, wherein the plate comprises a thin, electrically conducting material.

8. The notch antenna of any one of claims 3-7, wherein the plate comprises an elastically deformable material.

9. The notch antenna of any one of claims 3-8, wherein the plate comprises a flexible material.

10. The notch antenna of any one of claims 3-9, wherein the antenna further comprises a cover arranged over one or both faces of the plate.

1 1. The notch antenna of claim 10, wherein the cover is electrically non-conductive.

12. The notch antenna of claim 10 or 1 1 , wherein the cover is of low electrical permittivity to radio frequency energy within the operating range of the antenna.

13. The notch antenna of claim 10, 1 1 or 12, wherein the cover comprises part of a vehicle registration plate.

14. The notch antenna of any one of claims 3-13, wherein the plate comprises a component selected from a group including: the ground plane of a circuit-board, metal sheet and expanded metal.

15. The notch antenna of any one of claims 3-14, wherein the plate has a width, x, dimension, a height, z, dimension and a depth, y, dimension, and wherein the depth of the plate is small in comparison to the width and height.

16. The notch antenna of any one of claims 3-15, wherein the plate is generally rectangular.

17. The notch antenna of any one of claims 3-16, wherein the width of the plate is equal to or greater than one quarter of one wavelength at the centre of the operating frequency range.

18. The notch antenna of any one of claims 3-17, wherein the width of the plate is selected according to the desired frequency for the centre of the operating range.

19. The notch antenna of any one of claims 3-18, wherein the first and second notches open on different plate edges.

20. The notch antenna of any one of claims 3-19, wherein the first and second notches open on opposite plate edges.

21. The notch antenna of any one of claims 3-20, wherein the first notch comprises long edges aligned with the width dimension of the plate.

22. The notch antenna of any one of claims 3-21 , wherein the second notch comprises long edges aligned with the width dimension of the plate.

23. The notch antenna of any preceding claim, wherein the first notch is generally linear.

24. The notch antenna of any preceding claim, wherein the second notch is generally linear.

25. The notch antenna of any preceding claim, wherein the first notch is of length less than or equal to one fifth of one wavelength at the centre of the operating frequency range.

26. The notch antenna of any preceding claim, wherein the second notch is of length less than one fifth of one wavelength at the centre of the operating frequency range.

27. The notch antenna of any preceding claim, wherein the length of the first and/or second notch is selected with a length according to the desired frequency for the centre of the operating range.

28. The notch antenna of any preceding claim, comprising an adjustment portion provided to the second notch to facilitate change to the effective length of the second notch.

29. The notch antenna of claim 28, wherein the adjustment portion comprises a conductive patch applied to the second notch.

30. The notch antenna of claim 28 or 29, wherein the adjustment portion comprises a conductive patch applied across the second notch.

31. The notch antenna of any one of claims 28-30, wherein the adjustment portion comprises a conductive patch is applied at the closed end of the second notch.

32. The notch antenna of any one of claims 28-30 wherein the adjustment portion comprises a piece of adhesive backed tape.

33. The notch antenna of claim 32, wherein the adjustment portion comprises a piece of adhesive backed metallic tape.

34. The notch antenna of any one of claims 28-33 wherein the adjustment portion is arranged to bridge the second notch with a conducing element in contact with the plate.

35. The notch antenna of any one of claims 28-34, wherein the adjustment portion is arranged to provide a conductor that is capacitively coupled to the plate.

36. The notch antenna of any one of claims 28-35, wherein the adjustment portion comprises an semiconductor component coupled across the second notch.

37. The notch antenna of any one of claims 28-36, wherein the adjustment portion comprises a switching component coupled across the second notch.

38. The notch antenna of any one of claims 28-37, wherein the adjustment portion comprises a PIN diode coupled across the second notch.

39. The notch antenna of any one of claims 28-37, wherein the adjustment portion comprises a plurality of like or unlike components, including one or more selected from the adjustment portions described above in claims 29-38.

40. The notch antenna of any preceding claim, wherein the feed line comprises a coaxial feed line.

41. The notch antenna of any one of claims 1-39, wherein the feed line comprises a micro- strip connection across the first notch.

42. The notch antenna of any preceding claim, comprising a sealed body provided around the plate.

43. The notch antenna of claim 42, wherein the sealed body is an electrically insulating body.

44. The notch antenna of claim 42 or 43, comprising an adjustment portion is provided outside the sealed body.

45. The notch antenna of any preceding claim, wherein the first and second notches are manufactured with different lengths.

46. The notch antenna of any preceding claim, wherein the second notch is longer than the first notch.

47. The notch antenna of claim 45 or 46, comprising an adjustment portion applied thereto to shorten the effective length of the second notch.

48. A plate component of a notch antenna, the plate comprising a first notch for coupling to a feed line and a second notch arranged to be passively excited by a signal supplied to the first notch.

49. A method of manufacturing a notch antenna comprising the steps of: providing a first notch coupled to a feed line, and providing a second notch in use to be passively excited by a signal supplied to the first notch through the feed line.

50. The method of claim 49, further comprising providing an adjustment portion for the second notch to change the effective length of the second notch.

51. The method of claim 50, further comprising providing an adjustment portion in the form of a conductive patch applied to the second notch

52. The method of claim 51 , comprising providing an adjustment portion across the second notch.

53. The method of claim 51 or 52, comprising providing adjustment portion applied at the closed end of the second notch.

54. The method of any one of claims 51-53, wherein the adjustment portion so provided comprises: a piece of adhesive backed tape; or adhesive backed metallic tape; or a semiconductor component coupled across the second notch; or a switching component coupled across the second notch; or a PIN diode coupled across the second notch; or a plurality of like or unlike components, including one or more selected from the adjustment portions described above in this claim.

55. A notch antenna installation method, the method comprising providing a notch antenna comprising a first notch coupled to a feed line, and a second notch in use passively excited by a signal supplied to the first notch through the feed line, installing the antenna at a desired installation position, and providing an adjustment portion for the second notch to change the effective length of the second notch in response to a detected frequency shift from a desired centre frequency caused by electrical permittivity of the installation position.

56. The method of claim 55, wherein providing the adjustment portion comprises providing a conductive patch applied to the second notch.

57. The method of claim 55 or 56, wherein providing the adjustment portion comprises providing a conductive patch across the second notch.

58. The method of claim 55, 56 or 57, wherein the adjustment portion is applied at the closed end of the second notch.

59. The method of any one of claims 55 to 58, wherein the adjustment portion comprises a piece of adhesive backed tape, or adhesive backed metallic tape; or a semiconductor component coupled across the second notch; or a switching component coupled across the second notch; or a PIN diode coupled across the second notch; or a plurality of like or unlike components, including one or more selected from the adjustment portions described above in this claim.

60. A notch antenna, or a plate component of a notch antenna, each substantially as described herein with reference to the Figures 2 and 3 respectively.