antenna

Abstract

Sinusoidal and log-periodic antennas are broadband frequency-independent antennas that advantageously provide similar beamwidths at all operating frequencies. While they can be planar, they have improved directional characteristics when formed on a conical or similar surface. Fabrication of these three-dimensional antenna structures is challenging. Typically, an antenna laminate is wrapped around a frustum-shaped former. Any alignment error can result in a significant reduction in the antenna's high-frequency performance. Additionally, wrapping techniques are limited to frustum-shaped and truncated pyramidal formers. A solution is achieved by providing a dielectric sheet formed as a single, integral part that defines a central common area and radially extending arms. The flexible dielectric sheet supports a metal patterned layer that defines, on each arm, a conductive antenna element that is each fed by a conductive trace provided by a portion of the metal patterned layer formed on the common area. Each arm can be bent at its junction with the common area to fit the shape of the former without affecting the alignment between the arms.

Description

[Technical Field]

[0001] Sinuous and log-periodic antennas are broadband frequency independent antennas, which advantageously provide similar beamwidths at all operating frequencies. [Background technology]

[0002] They may be planar, but may have improved directional characteristics if formed on a conical or similar surface, as disclosed, for example, in US Pat. No. 4,658,262.

[0003] Fabrication of these three-dimensional antenna structures is challenging. Typically, the antenna laminate is wrapped around a frustum-shaped former. Any alignment error can result in a significant reduction in the high frequency performance of the antenna. Additionally, the wrapping technique is limited to frustum-shaped and truncated pyramidal formers.

[0004] The present invention has been devised to ameliorate these problems and allow the manufacture of antennas that can precisely conform to more complex curved surfaces such as ogives for aerodynamic applications.

[0005] RU2663264 relates to a log-periodic antenna comprising two identical planar metal log-periodic structures arranged at an angle to each other. Both log-periodic structures are fabricated in the form of printed circuit boards on one side of a curved, metal-free, flexible foil dielectric plate. The log-periodic structures are excited in antiphase by power lines located along the antenna axis, fabricated in the form of an ultra-wideband symmetrical matching transformer. Summary of the Invention

[0006] According to a first aspect of the present invention, there is provided a sinusoidal and / or log-periodic antenna comprising a relatively flexible dielectric substrate supporting a plurality of conductive antenna elements, the dielectric substrate defining a common area and arms, each arm being separately joined to the common area about a separate joint, each arm providing a first curved surface supporting one of the plurality of conductive antenna elements, and the common area providing a first planar surface supporting conductive traces for connecting each conductive antenna element to a transmission line. The flexible dielectric substrate may be supported on a relatively rigid former. The dielectric substrate may comprise a single, integral part defining the common area and the arms. The single, integral part may support a patterned metal layer providing the plurality of conductive antenna elements and the conductive traces.

[0007] The common region of the dielectric substrate ensures that the angular separation and spacing (e.g., angular spacing) between the antenna elements in the central high frequency region is not compromised when the substrate is mounted onto the former. Preferably, the common region is comprised of a single, integral, continuous piece of dielectric substrate.

[0008] By providing a single integral part that provides the arms and the common area, a patterned metal layer that provides both the conductive elements and the traces can be formed by a single patterning process. The patterned metal layer can define that each trace is electrically connected to its respective conductive element, thereby avoiding the need for soldering or similar processes to electrically connect the conductive elements to the traces.

[0009] The separate arms improve the problem of fitting antenna arms to curved 3D surfaces by allowing for independent local bending of the substrate in a way that is not possible with rectangular or triangular sheets of material placed over the entire former.

[0010] The first curved surface may be an ogive or a quadratic surface, such as a cone, a hemisphere, an ellipse, a paraboloid, or a hybrid or truncated form of one or more of these. The former, if present, may define a second curved surface having substantially the same curvature as the first curved surface. The dielectric substrate may rest on and conform to the second curved surface. The former may include a flat surface that supports the common region of the dielectric substrate.

[0011] To improve the ability of the arms to conform to latitudinal curvature, each arm is formed to be relatively narrow near its junction with the common region and to increase in physical width with increasing distance away from the junction, and the change in physical width may be such that each arm has a substantially constant angular width over its length.

[0012] To further improve the ability of the arms to conform to latitudinal curvatures, each arm may have a profile defining curves and / or characteristics that match the curves and / or characteristics of the profile of the conductive element it supports. For example, in an antenna having a serpentine conductive antenna element, each arm may have a curved profile to mimic the serpentine shape of the antenna element it supports. For example, the profile of the arm may be similar (in the sense of Euclidean geometry) to or geometrically match the profile of the antenna element it supports. For example, in the case of a sinusoidal antenna having sinusoidal conductive antenna elements, the arms may also have a sinusoidal profile. Surprisingly, the arms of a sinusoidal antenna, despite being relatively wide, may conform quite well to surfaces that curve around two orthogonal planes.

[0013] The common region of the dielectric substrate may include an opening for a transmission line to pass through to connect to one or more of the conductive antenna elements, and thus the common region may be comprised of a single, integral, annular piece of dielectric substrate.

[0014] To improve conformance of the dielectric substrate on the former around the area where the second surfaced surface of the former and the flat surface join, the former may define a bridge surface interconnecting the second flat surface and the second curved surface. The bridge surface is preferably curved with a radius of curvature that is smaller than the radius of curvature of the second curved surface. Preferably, the bridge surface has a radius of curvature that decreases between the second curved surface and the flat surface. The bridge surface may extend circumferentially around the entire periphery of the common area.

[0015] The antenna may be a sinusoidal log-periodic antenna. The antenna may be a sinusoidal non-log-periodic antenna. The antenna may be a non-signalous log-periodic antenna.

[0016] The antenna may have four or more arms.

[0017] According to a second aspect of the present invention, there is provided a flexible dielectric substrate supporting conductive antenna elements of a sinusoidal and / or log periodic antenna according to any preceding claim, the flexible dielectric substrate defining a common area and separate arms, each of the separate arms being bonded to the common area, and each arm supporting one of the conductive antenna elements.

[0018] According to a third aspect of the present invention there is provided a method of manufacturing a sinusoidal and / or log-periodic antenna, the method comprising: providing a flexible dielectric substrate supporting the conductive antenna elements of a sinusoidal and / or log-periodic antenna according to any preceding claim, wherein the flexible dielectric substrate defines a common area and separate arms, each of the separate arms being bonded to the common area, each arm supporting one of the conductive antenna elements, and the common area supporting conductive traces for electrically connecting each conductive antenna element to a transmission line; placing a dielectric substrate on or within a former such that the conductive antenna element conforms to a curved surface provided by the former; Equipped with.

[0019] The invention will now be described, by way of example only, with reference to the following drawings, in which: [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a perspective view of a sinusoidal wideband antenna. [Figure 2] FIG. 2 is a plan view of the antenna laminate. [Figure 3] FIG. 3 is a perspective view of the antenna laminate before it is wrapped around the former. [Figure 4] FIG. 4 is a perspective view of a log-periodic wideband antenna. DETAILED DESCRIPTION OF THE INVENTION

[0021] Referring to Figure 1, there is shown a sinusoidal wideband antenna 1. The antenna 1 comprises a plurality, in this example four, of sinusoidal conductive elements 2, each extending radially outward from a planar central region 3 across a curved surface 4. The curved surface 4 may be, for example, a quadric or ogive surface.

[0022] Each conductive element 2 is fed by a transmission line (not shown) that provides a controlled phase difference between one or more of the conductive elements 2. The conductive elements 2 may be paired so that one is fed in antiphase relative to the other.

[0023] Each conductive element 2 is shaped to take a sinusoidal path across the curved surface 4 having a half-wavelength that increases logarithmically with increasing radial distance from the central region 3. This feature provides the antenna 1 with frequency-independent performance. The angular width W of each conductive element 2 is substantially constant over its radial distance from the central region 3. Thus, the physical width of each conductive element 2 increases progressively with increasing radial distance from the central region 3. Alternatively, in an alternative embodiment, the angular width W can be varied to improve antenna performance, as described in U.S. Pat. No. 4,658,262.

[0024] Referring to FIGS. 2 and 3, the antenna 1 is comprised of an antenna laminate sheet 5 supported on a former 6. As shown in FIG.

[0025] The antenna laminate sheet 5 comprises a single, integral piece flexible dielectric substrate 7 that carries a patterned metal layer 8, for example of copper, that defines the conductive elements 2 as well as the feed lines 10. An example of a suitable material for the flexible dielectric substrate 7 is a polyimide such as that sold under the trade name Kapton®.

[0026] 2, the antenna laminate sheet 5 defines a common area 5A and separate arms 5B each extending radially in a different direction away from the common area 5A. Each arm 5B is separately joined to the common area 5A at a location circumferentially spaced from the other arms around the common area 5A. In other words, each joint is angularly separated from the other joints around the common area 5A.

[0027] Each arm 5B bears a portion of the patterned metal layer 8 that defines one of the conductive elements 2. To provide the greatest degree of flexibility, each arm 5B has a profile that is geometrically similar to that of the conductive traces 2, i.e., matches a uniform scaling of the profile of the conductive traces 2. This arrangement results in a boundary 7A of exposed substrate 7 of uniform width around the conductive elements 2. In a variant, the substrate 7 could have a profile that matches the profile of the conductive elements 2, but fabrication of such a design could be difficult because machining directly into or through the metal layer could tear or cut through the metal layer.

[0028] Common area 5A consists of a continuous ring of substrate 7 with a central aperture 9. Common area 5A carries feed lines 10 that connect the antenna elements 2 to transmission line(s) (not shown). Each feed line 10 extends across common area 5A from the radially inner end of its respective antenna element 2 towards aperture 9 to connect to the transmission line (not shown).

[0029] 3, former 6 defines a curved outer surface 6A extending circumferentially about a circular plane 6B, which plane 6B is substantially equal in size to common area 5A. A hole 6C in plane 6B extends completely through former 6 to provide a passage for a transmission line through former 6.

[0030] The former 6 has sufficient rigidity to support the antenna laminate sheet 5 without deformation of its curved outer surface 6A or flat surface 6B. A suitable material for the former is polystyrene, whose light weight is advantageous if the antenna is to be used on an airborne platform.

[0031] Extending circumferentially all around the planar end face 6B is a bridge surface 6D that joins the curved outer surface 6A to the end face 6B. The purpose of the bridge surface 6D is to provide a smooth transition in slope between the curved surface 6A and the end face 6B to aid in the conformance of the antenna laminate sheet 5 on the former 6. The bridge surface 6D may have a single radius of curvature with distance from the planar end face 6B, but preferably has a radius of curvature that decreases as the surface extends radially inward toward the planar end face 6B, as this provides the smoothest transition in slope between the planar end face 6B and the curved surface 6A.

[0032] To assemble the antenna 1, the common area 5A of the laminate sheet 5 is aligned with and seated on the edge surface 6B of the former 6. Each of the arms 5B is then folded onto the curved surface 6A of the former 6 (as illustrated by the arrows in FIG. 3). The laminate sheet 5 is held to the former 6 using a suitable adhesive. The separate, relatively narrow connection of each arm 5B to the common area 5A allows adjacent arms 5B to bend independently around the curved surface 6A in different planes, allowing each arm 5B to conform to the surface 6A despite being circumferentially spaced about the edge surface 6B.

[0033] Additionally, because each arm 5B is joined to the common area 5A, and thus to each other, through a continuous flexible substrate sheet 7, the angular separation between each connection element 2 in the area around the joint is maintained when the antenna laminate sheet 5 is attached to the former 6. This ensures that the desired antenna performance at higher operating frequencies is achievable.

[0034] Transmission lines (not shown), implemented for example using separate coaxial cables, are inserted through former 6 so that their ends protrude through aligned openings 6C, 9 in former 6 and antenna laminate 5. The end of each transmission line is soldered or otherwise bonded to a feed line 10 to electrically connect the transmission line to antenna element 2.

[0035] Note that the antenna of Figures 1-3 is technically a sinusoidal log-periodic antenna, i.e., the way in which the oscillations vary along its length is governed by a logarithmic function. However, to distinguish it from the style of antenna illustrated in Figure 4, described below, it is generally referred to simply as a "sinusoidal" antenna.

[0036] FIG. 4 illustrates a modified antenna 1′ that is identical to the antenna of FIGS. 1-3, except that the conductive elements 2′ of the antenna laminate sheet 5′ have a non-sinusoidal log-periodic shape, commonly referred to simply as log-periodic.

[0037] Variations on the above design are possible, examples are given below.

[0038] The common area may be non-circular in shape.

[0039] Instead of a single central aperture, the common area may comprise multiple separate apertures through which different transmission lines extend.

[0040] The common area may include vias that provide electrical connection between a feed line on a first surface of the laminate sheet and an electrical contact on an opposite facing surface of the laminate sheet for connecting to a transmission line.

[0041] Similarly, the end face of the former may include separate openings for the separate transmission lines.

[0042] The former may be hollow, in which case the laminate sheet may be attached to the interior surface of the former to provide a curved surface.

[0043] The antenna may comprise more or less than four conductive elements.

[0044] The antenna may include a rigid disk-shaped printed circuit board or other rigid disk-shaped electrical connection attached to the underside of the central region that provides an electrical connector between the feed line and the transmission line. The presence of the rigid disk will also help to accurately align the antenna laminate sheet on the former and will robustify the electrical connection from the feed line to the transmission line.

[0045] To prevent damage to the arms of the antenna laminate prior to assembly of the antenna, the laminate may define breakout tabs extending between the radially outer free ends of adjacent arms that may be cut when the laminate is ready to be mounted on the former.

[0046] The principles described above can also be applied to create antennas with sinusoidal antenna elements whose half wavelengths vary by functions other than logarithmic functions, but such antennas are unlikely to have good broadband characteristics.

Claims

1. 1. A sinusoidal and / or log-periodic antenna comprising a relatively flexible dielectric substrate carrying a plurality of conductive antenna elements, the dielectric substrate mechanically supported on a relatively rigid former, the dielectric substrate defining a common area and arms, each arm being separately joined to the common area about a separate joint, each arm providing a first curved surface that supports one of the plurality of conductive antenna elements, the common area providing a first planar surface that supports a conductive trace for connecting each conductive antenna element to a transmission line, the dielectric substrate comprising a single unitary part defining the common area and the arms, the single unitary part supporting a patterned metal layer that provides the plurality of conductive antenna elements and the conductive traces.

2. 2. A sinusoidal and / or log-periodic antenna according to claim 1, wherein each arm has a physical width that increases with increasing distance from its junction with said common region.

3. 3. A sinusoidal and / or log-periodic antenna according to claim 2, wherein each arm has a substantially constant angular width over its length.

4. 4. A sinusoidal and / or log-periodic antenna as claimed in claim 1, 2 or 3, wherein each arm has a profile defining curves and / or characteristics that mimic the curves and / or characteristics of the profile of the conductive element it carries.

5. A sinusoidal and / or log-periodic antenna according to any one of claims 1 to 4, wherein the curved surface is a quadric or ogive surface.

6. 6. A sinusoidal and / or log-periodic antenna according to any one of claims 1 to 5, wherein the common area comprises openings for one or more transmission lines to extend therethrough for electrically connecting to one or more of the conductive antenna elements.

7. 7. A sinusoidal and / or log-periodic antenna as claimed in any preceding claim, wherein the former defines a second curved surface, and the flexible dielectric substrate rests on and conforms to the second curved surface.

8. 8. A sinusoidal and / or log-periodic antenna as claimed in claim 7 when dependent on claim 6, wherein the former comprises an opening aligned with the opening through the common area for the transmission line to extend therethrough for electrically connecting to one or more of the conductive antenna elements.

9. 9. A sinusoidal and / or log-periodic antenna as claimed in any one of claims 6 to 8, wherein the former defines a second plane, and the flexible dielectric substrate is located on and conforms to the second plane.

10. 10. The sinusoidal and / or log-periodic antenna of claim 6, wherein the former defines a bridge surface interconnecting the second planar surface and the second curved surface, the bridge surface having a radius of curvature that is smaller than a radius of curvature of the second curved surface, and the flexible dielectric substrate rests on and conforms to the bridge surface.

11. 11. A sinusoidal and / or log-periodic antenna according to claim 10, wherein the bridge surface has a radius of curvature that decreases between the second curved surface and the planar surface.

12. 12. A flexible dielectric substrate supporting the conductive antenna elements of a sinusoidal and / or log-periodic antenna according to any one of claims 1 to 11, wherein the flexible dielectric substrate defines a common area and separate arms, each of the separate arms being joined to the common area, each arm supporting one of the conductive antenna elements.

13. 1. A method of manufacturing an antenna laminate for a sinusoidal or log-periodic antenna, the method comprising: providing a metal layer on a dielectric substrate to form a laminate; removing metal from the substrate to define separate conductive antenna elements; cutting the antenna laminate so that it defines a common area and separate arms, each of the separate arms being joined to the common area, each arm supporting one of the conductive antenna elements for the antenna; A method comprising:

14. 1. A method of manufacturing a sinusoidal and / or log-periodic antenna, the method comprising: i) providing a flexible dielectric substrate supporting conductive antenna elements of a sinusoidal and / or log-periodic antenna according to any one of claims 1 to 11, wherein the flexible dielectric substrate defines a common area and separate arms, each of the separate arms being bonded to the common area, each arm supporting one of the conductive antenna elements, and the common area supporting conductive traces for electrically connecting each conductive antenna element to a transmission line; ii) placing the dielectric substrate on or in a former such that the conductive antenna element conforms to a curved surface provided by the former; A method comprising:

15. 1. A sinusoidal and / or log-periodic antenna comprising a relatively flexible dielectric substrate supporting a plurality of conductive antenna elements, the dielectric substrate being mechanically supported on a relatively rigid former, the dielectric substrate defining a common area and arms, each arm being separately joined to the common area about a separate joint, each arm providing a first curved surface supporting one of the plurality of conductive antenna elements, the common area providing a first planar surface supporting a conductive trace for connecting each conductive antenna element to a transmission line.

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