Wide band antenna

Abstract

A method of manufacturing and an antenna having an upper and lower loop. Upper loop comprising a first conductive loop defined by an upper conductor and a first conductive blade tapering outwardly to form a flare portion adjacent a distal end of the upper conductor. Lower loop comprising a second conductive loop defined by a base conductor and a second conductive blade tapering outwardly forming a flare portion adjacent a distal end of the base conductor. First and second conductive blades defining, between their facing edges, a notch opening outwardly from a feed region. Upper loop further comprising an elongate conductive vane extending at an angle from a first location on the upper conductor to a second location on the first conductive blade defining a pair of loops within the upper loop.

Claims

1. A method of manufacturing a travelling wave antenna element, comprising the steps of: selecting a desired operating frequency range and selecting a predetermined required performance characteristic of said antenna element, wherein said predetermined required performance characteristic comprises at least one of impedance bandwidth, directive gain, and efficiency; and forming an antenna component having an upper and lower conductive loop by: providing a first conductive loop element defined by an upper conductor and a first conductive blade member that tapers outwardly to form a flare portion adjacent a distal end of said upper conductor; providing a second conductive loop element defined by a base conductor and a second conductive blade member that tapers outwardly to form a flare portion adjacent a distal end of said base conductor; placing said first and second conductive loop elements adjacent to each other such that outer edges of the first and second conductive blade members face each other to define a notch therebetween which opens outwardly from a feed region; providing an elongate vane between a first location on said upper conductor and a second location on said first conductive blade to define a pair of loops within said first conductive loop element; wherein selecting the second location is a function of the length of the upper conductor, and wherein the second location on the first blade member is at least of the length of the upper conductor; and matching an impedance of said antenna component, at said desired operating frequency range, to a transmission line to be connected at said feed region thereof; wherein said step of providing said elongate conductive vane comprises: selecting a minimum distance of said second location from said feed region at which said impedance match is maintained and said performance characteristic is attained, and placing said conductive vane within said first conductive loop element such that it extends from said selected second location on said first conductive blade to a first location on said upper conductor; and/or selecting an angle of inclination of said conductive vane within said first conductive loop at which said performance characteristic is attained, and placing said conductive vane at said selected angle of inclination between said first location on said upper conductor and said second location on said first conductive blade.

2. The method according to claim 1, wherein the distance of the second location from the feed region is between and of the length of the upper conductor.

3. The method according to claim 1, wherein the conductive vane is inclined outwardly, away from the feed region, such that the distance of the first location from the proximal end of the upper conductor is greater than that of the second location from the feed region.

4. The method according to claim 1, wherein the conductive vane is curved along at least a portion of its length.

5. The method according to claim 1, comprising the step of selecting the distance of the first location from the proximal end of the upper conductor as a function of the length of the upper conductor and in accordance with the selected second location.

6. The method according to claim 5, wherein, when the distance of the second location from the feed region is of the length of the upper conductor, the distance of the first location from the proximal end of the upper conductor is or of the length of the upper conductor.

7. The method according to claim 5, wherein the first location is between and along the length of the upper conductor from its proximal end.

8. The method according to claim 1, comprising the step of selecting the length of the upper conductor and/or the base conductor according to a selected desired cut-off frequency of the antenna element.

9. The method according to claim 8, comprising the steps of selecting a cut-off frequency of the antenna element, and selecting the peripheral dimensions of the upper loop such that, combined, they are substantially equal to a wavelength corresponding to the selected cut-off frequency.

10. An antenna element manufactured substantially in accordance with the method of claim 1, and comprising an upper loop and a lower loop, said upper loop comprising a first conductive loop element defined by an upper conductor and a first conductive blade member that tapers outwardly to form a flare portion adjacent a distal end of said upper conductor, said lower loop comprising a second conductive loop element defined by a base conductor and a second conductive blade member that tapers outwardly to form a flare portion adjacent a distal end of said base conductor, said first and second conductive blade members defining, between their facing edges, a notch which opens outwardly from a feed region, said upper loop further comprising an elongate conductive vane extending at an angle from a first location on said upper conductor to a second location on said first conductive blade to define a pair of loops within said upper loop, wherein an impedance of said antenna element substantially matches, at said desired operating frequency range, an impedance of a transmission line to be connected at said feed region thereof; and: said conductive vane is located within said upper loop such that it extends from a selected second location on said first conductive blade to a first location on said upper conductor, said selected second location corresponding to a minimum distance from said feed region at which said impedance match is maintained; and/or said conductive vane is located at a selected angle of inclination between said first location on said upper conductor and said second location on said first conductive blade to attain a selected desired characteristic of said antenna element.

11. The wide band antenna comprising an array of antenna elements according to claim 10.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other aspects of the present invention will be apparent from the following specific description, in which embodiments of the present invention are described, by way of examples only, and with reference to the accompanying drawings, in which:

(2) FIG. 1A is a schematic perspective view of an antenna element according to the prior art;

(3) FIG. 1B is a close-up schematic view of the feed region of the antenna element of FIG. 1A;

(4) FIG. 2 is a schematic side view of an antenna element according to an exemplary embodiment of the present invention;

(5) FIGS. 3A to 3E illustrate schematically various configurations of an antenna element according to an exemplary embodiment of the present invention, with progressively increasing distances of the conductive vane from the feed region of the antenna element;

(6) FIG. 4 is a graphical representation of test results for each of the five configurations illustrated in FIG. 3;

(7) FIG. 5 is a graphical representation of calculations of performance from an antenna element according to an exemplary embodiment of the present invention compared with test results from two antenna elements according to the prior art;

(8) FIGS. 6(F) to 6(J) illustrate various configurations of an antenna element according to an exemplary embodiment of the present invention, with progressively increasing inclinations of the conductive vane; and

(9) FIG. 7 is a graphical representation of calculations of performance for each of the five configurations illustrated in FIG. 6.

DETAILED DESCRIPTION

(10) In the following exemplary embodiments, an antenna is configured to be driven by microwave frequency oscillators (MFOs). However, it will appreciated that the present invention is not intended to be limited in this regard and that other multi-frequency pulsed energy sources can be used.

(11) Throughout the specification, references are made to components being outward or inward. The term outward has been used to indicate a direction that is towards the medium into which the antenna radiates (often referred to as boresight), and inward is used to indicate the opposite direction, i.e. away from the medium into which the antenna radiates. Furthermore, relative terms such as upper and lower, and row and column, are used for convenience to distinguish between components so as to better explain the invention, so no absolute orientation is intended from the use of such terms alone.

(12) Ultra Wide band (UWB) radiating systems with a peak power of around 10.sup.10 W are necessary for many applications. As explained above, creation of this type of radiating system has been achieved on the basis of multi element arrays with a peak radiation power of a single array element of around 0.1-1 GW.

(13) An antenna element has been proposed for this purpose in Koshelev, et al, High-Power Ultrawideband Radiation Source with Multielement Array Antenna, in Proceedings of the 13th International symposium on High Current Electronics, Tomsk, Russia, July 2004. The described antenna element comprises an upper loop and a lower loop. The upper loop comprises a conductive loop defined by a first elongate conductor and a first conductive blade member that tapers outwardly to form a flare portion adjacent a distal end of the first elongate conductor. The lower loop comprises a conductive loop element defined by a second elongate conductor and a second conductive blade member that tapers outwardly to form a flare portion adjacent a distal end of the second elongate conductor, with the first and second conductive blade members defining, between their facing edges, a notch which opens outwardly from a feed region. It is to be appreciated that the term distal used above and hereinafter is intended with reference to the feed region, i.e. outward from the feed region, and the term proximal used above and hereinafter is intended with reference to the feed region, i.e. closer or closest to the feed region. An antenna comprising a 44 array of such antenna elements is described, wherein the source comprises a pulse generator feeding the antenna via four co-axial transmission lines (i.e. one feeding each row of antenna elements).

(14) This type of antenna element was further explored by Godard, A., et al, A transient UWB Antenna Array Used with Complex Impedance Surfaces, Hindawi, International Journal of Antennas and Propagation, Vol. 2010, wherein a modified antenna element is proposed that includes a conductive vane extending at an angle from the first conductive blade member to the upper elongate conductor so as to form a pair of adjacent loops. Such an antenna element is illustrated schematically in FIG. 1A of the drawings, in which it can be seen that the element comprises an upper loop 1 comprising a first conductive loop element 2 and a lower loop 3 comprising a second conductive loop element 4. The conductive loop element 2 of the upper loop 1 comprises an elongate upper conductor 9 and a first conductive blade member 10, the first conductive blade member tapering outwardly from a feed region 7 to the distal end of the upper conductor 9 to form a first flare 11. The conductive loop element 4 of the lower loop 3 comprises an elongate base conductor 5, oriented substantially parallel to the upper conductor 9, and a second conductive blade member 6 which tapers outwardly from the feed region 7 to the distal end of the base conductor 5 to form a second flare 8.

(15) A conductive vane 12 extends at an angle across the conductive loop of the monopole member, between the second blade member and the upper conductor, the vane 12 being inclined outwardly, i.e. away from the feed region 7. The feed region 7 is defined at a back plate 13. The connection or transition between the first blade member 6 and the inner surface of the back plate 13 is designed to achieve a good impedance match (S11 parameter lower the 10 dB) over a desired frequency band (300 MHz-3 GHz). As shown in FIG. 1B of the drawings, the transition is formed of two sections: a first section 14 formed of metal and a second, central section 15 formed of, for example, PTFE, that provides high-voltage resistance.

(16) However, it will be appreciated, that the described antenna element is intended for a specific use and frequency range, and has been developed and optimised for that use and frequency range. In contrast, an object of aspects of the present invention is to provide a method of antenna design that permits the design of an antenna element with a specified cut-off frequency, and permits the performance of such an antenna element or a wide band antenna comprising an array of such elements to be optimised according to specified characteristics, without increasing the dimensions of the antenna element to levels that would make it impractical for many applications.

(17) The object of the above-mentioned reference (Godard) is to present a miniature antenna element which can be shown to have a cut-off frequency of 363 MHz. This characteristic is determined by the external characteristics of the antenna element, i.e. height H, length L and width W. In order to reduce the cut-off frequency of the element, it would be necessary to increase the external dimensions significantly, with the result that the antenna element, and any resulting multi-element array antenna would have impractically large dimensions for many applications, and may have an inadequate performance at various frequency ranges. Using the design calculations employed by Godard et al, a cut-off frequency of around 100 MHz, would require an antenna element of dimensions:

(18) W=3000/10=300 mm

(19) H=3000/5=600 mm

(20) L=3000/3.85=780 mm

(21) Thus, the width of each antenna element would have to be 300 mm. However, this also has additional drawbacks in terms of heat dissipation and, therefore, a negative effect on efficiency of the antenna element. Also, such dimensions may make it difficult to impedance-match the antenna element, or a multi-element antenna, to the transmission lines(s), which is a significant drawback as the feed design is, in many cases, critical to driving the antenna. Furthermore, such dimensions would not provide an optimised performance at specified frequencies and frequency ranges, and no methods or techniques are proposed in the prior art for solving these issues.

(22) It is, therefore, an object of aspects of the invention to provide a method of antenna design, wherein its performance can be optimised at a specified operational frequency range and with reduced dimensions compared with known techniques.

(23) In accordance with invention, this object may be achieved by altering the location and/or the inclination of the conductive vane defining the double loop in the upper loop of an antenna element of the type described above.

(24) Referring to FIG. 2, in an exemplary embodiment of the invention, the antenna element structure proposed is of the type described above, but having the following dimensions:

(25) W=200 mm;

(26) H=600 mm;

(27) L=1000 mm;

(28) which dimensions are selected to provide a cut-off frequency of 100 MHz.

(29) In a method of manufacture according to an exemplary embodiment of the invention, impedance matching is performed to match the impedance of the antenna element to the transmission line of the desired radiation source (in a known manner) and the feed region 7 is thus optimised. Next, a selected operating frequency range for which the antenna element performance is to be optimised is selected. In this example, the frequency range is 400-700 MHz.

(30) The inventors have determined that by selecting the location of the conductive vane 12, the performance of the antenna element in the operating frequency range 400-700 MHz can be optimised (in terms of return loss and efficiency.

(31) Referring to FIG. 3 of the drawings, 5 possible locations of the conductive vane are illustrated, as A, B, C, D and E respectively. The inventors have determined, through extensive innovative input, that the key aspect of this element of the design method is the distance from the feed region 7 of the end of the conductive vane 12 where it meets the blade member of 10. In each of the five illustrated tests A-E, the inclination of the vane 12, outward, is substantially the same, at less than 10 degrees relative to a vertical axis defined by the back plate 13, and the above-mentioned distance from the feed region 7 of the vane 12 where it meets the blade member 10 is made progressively larger.

(32) As illustrated in FIG. 4 of the drawings, it can be seen that if this distance is too small, the impedance match is degraded and the return loss (S11) is increased above an acceptable level at some frequencies. However, it can be seen that the performance of the antenna in the frequency range 400-700 MHz is significantly improved in tests B, C and D at least (i.e. with the above-mentioned distance between about L/6 and 5L/8.

(33) This performance can be seen in FIG. 5 (reference 3) in comparison to that achieved with a comparably sized antenna element having (1) a single loop (Koshelev) and (2) a much larger double loop (Godard), wherein the above-mentioned distance is L/4 and the inclination of the vane is such that the distance of the other end of the vane from the proximal end of the upper conductor is L/2.

(34) Referring now to FIG. 6 of the drawings, having determined the optimum distance from the feed region of the conductive vane where it meets the blade member, the inventors have determined that the performance of the antenna element can be further optimised by changing the length of the inner loop (closest to the feed region). In effect, this method step comprises selecting an inclination of the conductive vane (outward) relative to the vertical axis defined by the back plate, or (equally) selecting the distance from the proximal end of the upper conductor of the conductive vane where it meets the upper conductor.

(35) In the examples shown in FIG. 6, each of the configurations tested has a bottom distance (from the feed region) of around L/6 (corresponding to Test B of FIG. 3), and each of the test configurations has a progressively larger loop length, ranging from about L/5 in test (F) to around 4L/5 in test (J). Thus, as shown in the calculated results illustrated in FIG. 7 of the drawings, the performance of the antenna element can be optimised for a specified operating frequency range (in this case, 400-700 MHz) by maintaining the minimum bottom distance of the conductive vane (whilst maintaining the required impedance match), but increasing the size of the inner loop by increasing the top distance (from the proximal end of the upper conductor) or inclination of the conductive vane. In view of the increased length of the upper and/or lower loops in comparison to the above-referenced Godard design, the antenna performance is further optimised by the methods proposed herein.

(36) Thus, more generally, the cut-off frequency of the antenna can be selected and the loop length/dimensions selected to achieve that selected cut-off frequency. The performance of the resultant antenna can then be optimised for a specified frequency range or ranges using methods according to exemplary embodiments of the present invention.

(37) It will be apparent to a person skilled in the art, from the foregoing description, that modifications and variations can be made to the described embodiments without departing from the scope of the invention as defined by the appended claims. The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of this disclosure. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.