PLANAR ANTENNA ON ELECTRICALLY-INSULATING SHEET

Abstract: A generally planar TV antenna having preferably at least two pairs of spaced-apart electrically conductive lands (3, 5; 7, 9) disposed on a sheet of electrically-insulating material (1) and method of manufacturing such antenna by providing the lands by hot foil blocking onto the sheet. The foil may also be formed by sputtering to the desired thickness.

Description: Planar antenna on electrically-insulating sheet This invention relates to antennae. In one form it relates to an antenna which is particularly suitable for, but not limited to, receiving television signals. The invention is also applicable to antennae for radio transmission and reception. Conventional television antennae are generally quite bulky and unsightly. In order to achieve best performance, outdoor antennae are preferred, for example, roof mounted antennae. However, these can be inconvenient to mount securely, and difficult to maintain. In the event of a storm, an outdoor antenna may easily become mis-aligned, or it may suffer damage. Indoor antennae are commonly smaller than outdoor antennae for aesthetic reasons. However, their small size limits their efficiency, which means that they are generally suitable for reception only in areas where the television signals are strong. A tuned Yagi antenna has additional elements to increase gain, but this achieves high gain only along the front-rear direction of the antenna. Thus the antenna is highly directional and is also susceptible to receiving rear-reflected signals to cause ghosting. Typically the acceptance angle of a Yagi antenna is only about 20 degrees. A lightweight FM-VHF-UHF antenna consisting of strip conductors disposed on a flexible plastics sheet has been proposed, see GB-A-1302644. The antenna is in 3 sections, one having the strip conductors disposed in a log periodic array, with the other two sections having the strip conductors disposed each in a Yagi-Uda array. The present invention is concerned with providing a generally planar antenna of improved design, of compact size yet with sufficient gain for domestic television reception. According to the present invention there is provided a generally planar antenna as specified in the claims hereinafter. The antenna of the invention comprises at least one, and preferably at least two pairs of spaced-apart electrically-conducting lands acting as dipoles disposed on an electrically-insulating sheet material. The antenna is designed to be deployed vertically broadside on to a transmitter generating horizontally- polarized signals. The antenna can be employed on its side, horizontally, for vertically-polarized signals. The sheet material may be flexible (e.g. of plastics material) or it may be relatively rigid - for example a stiff cardboard sheet. The electrically-conductive lands may be formed by a variety of means (e.g. printing, laminating, etching, evaporation) , but preferably they are formed of foil (e.g. aluminium foil) hot pressed onto the sheet material. An antenna feed arrangement is associated with one pair of lands, other pairs of lands (if present) act as a reflector. Three pairs of lands may be employed side-by- side with the feed being taken from any pair, for example the centre pair. With a vertically disposed antenna the feed is preferably taken from the bottom of the antenna. Each pair of lands is preferably spaced-apart from and symmetrical about an imaginary line on the sheet material. The first pair of lands may form a first symmetric shape with each further pair forming the same or different symmetric shapes. Each land is a substantially two-dimensional area with an x-axis parallel to the imaginary line and a y-axis orthogonal thereto, with the maximum x-dimension of each land being approximately the same or similar to the maximum y-dimension. In other words each land extends substantially in both x- and y-directions - in contrast to a thin strip. Each land may be generally rectangular or trapezoidal. The shape and dimensions of the lands, and their spacing, will vary the output of the antenna. The lands do not need to be disposed on the same side of the sheet material although this is preferred. A land of one pair may be capacitively coupled to a land of another pair (e.g. diagonally if two pairs of lands are side-by-side) . This may be achieved by having these lands on opposite sides of the sheet material and extending the foil in a thin strip from one such land towards a similar strip from the other land (on the opposite side of the sheet) until the strips overlap capacitively. The sheet material acts as the capacitive dielectric. In order to improve performance, means may be provided, such as a clip, for shorting together any pair of the lands not coupled to the antenna feed means. In certain circumstances this has proven to increase television band selectivity. The shorting may be controlled by a switch or by simply removing the clip. If desired, to improve performance two or more antennae of the invention can be coupled together and stacked in series. If the antenna is compact enough, it will be possible to integrate it with a domestic television receiver - for example in or on the back of the receiver or even (if the conductive lands are sufficiently thin and optically transmissive) on the viewing face of the cathode ray tube. A preferred antenna according to the invention, for use with a domestic television receiver, will now be described by way of example with reference to the accompanying drawing. The drawing shows the antenna face-on. The antenna comprises a sheet 1 of stiff cardboard to which has been laminated by hot foil blocking four spaced aluminium foil lands 3,5,7 and 9. The aluminium foil is approximately 200 x 10 "10 metres in thickness, which gives an electrical resistance of about 1.5 ohms per square. The foil is overcoated with an electrically-insulating lacquer. The arrangement may be manufactured by sputtering aluminium to the desired thickness onto a lacquer-coated backing surface. The aluminium is then coated with adhesive and the combination hot foil blocked onto the sheet 1 with the adhesive adjacent the sheet. The backing surface is peeled away to leave the sheet 1, lands 3, 5, 7, 9 and lacquer overcoating bonded together. Each pair of lands 3,5 and 7,9 is spaced apart from and is symmetrical about an imaginary line x-x on sheet 1. The antenna is designed for use in a vertical plane, e.g. mounted against a wall, and the feed for television signals can be obtained from either pair of lands. With the lands shaped as shown, taking feeds from lands 3,5 is effective for television bands A,B whereas feeds from lands 7,9 is more efficient for bands C,D. The feed (shown to lands 3,5) consists of a clip 11 which presses a pair of strip conductors 13, 15 down onto the lacquer at adjacent corners of the lands 3,5. The contact to the aluminium foil is capacitive through the intervening lacquer (it can also be a direct metal-to-metal contact, without intervening lacquer) . Shorting the non- fed pair of lands (7,9 as shown) can improve band selectivity, and this can be achieved by shorting across a small area 17 of exposed foil on each land. The lands are spaced-apart in the y-direction (orthogonal to x-x) by 1 cm. Lands 3,5 each have a maximum y-dimension of 22 cm and a maximum x-dimension of 12 cm. Lands 7,9 have a maximum y- dimension of 22 cm and a maximum x-dimension of 18 cm. At their closest approach lands 3,5 are spaced from lands 7,9 by 15 cm in the x-direction (parallel to x-x) . In a further embodiment which is a variant of that illustrated, the two lands 7 and 9 are merged to form one contiguous land extending transverse to x-x and symmetrically relative thereto, to act as a single reflector to lands 3 and 5.

Claims: CLAIMS:- 1. A generally planar or sheet antenna comprising: a sheet of electrically-insulating material, at least one pair of spaced-apart electrically- conducting lands disposed on said sheet, and antenna feed means comprising first and second feed elements for forming respective feed connections to each of the two lands in one pair of said lands. 2. An antenna according to claim 1 in which each pair of lands is symmetric about, and spaced-apart from, an imaginary line on the sheet material. 3. An antenna according to claim 2 wherein a first pair of lands form first symmetric shapes and a second pair of lands form second symmetric shapes. 4. An antenna according to claim 2 or 3 wherein each land is two-dimensional with an x-axis parallel to the imaginary line and a y-axis orthogonal thereto, the maximum dimension of each land in its x-direction being approximately the same or similar to its maximum dimension in its y-direction. 5. An antenna according to any of claims 1 to 4 wherein each land is generally rectangular or trapezoidal. 6. An antenna according to any of claims 1 to 5 comprising two pairs of lands with means enabling the antenna feed means to connect to either of said pairs of lands. 7. An antenna according to any of claims 1 to 6 comprising three pairs of lands side-by-side with means enabling the antenna feed means to connect to the middle pair of lands. 8. An antenna according to claim 2 wherein a pair of lands form first symmetric shapes and a single land is provided, spaced from said symmetric pair, and disposed symmetrically about said imaginary line. 9. An antenna according to any of claims 1 to 8 wherein each land comprises a conductive foil attached to the sheet material and having an electrically-insulating coating thereover. 10. An antenna according to any of claims l to 9 wherein the antenna feed means capacitively couples to the respective lands. 11. An antenna according to claim 10 wherein the antenna feed means comprises a clip for attachment to the sheet material and for urging the feed elements into the capacitive coupling arrangement to the respective lands. 12. A generally planar or sheet antenna as claimed in any of claims 1 to 11 when disposed vertically within or on a television receiver. 13. Use of an antenna according to any of claims 1 to 11 when wall-mounted. 14. A method of manufacturing an antenna as claimed in claim 1 which includes providing the lands by hot foil blocking onto the sheet material. 15. A method according to claim 14 wherein the foil is formed by sputtering. 16. A method according to claim 14 or 15 wherein the foil is approximately 200 x 10 "10 metres thick.

Inventors: MANNAN MICHAEL, MANNAN, MICHAEL
Applicants: MANNAN MICHAEL, MANNAN, MICHAEL
Application year: 1995
Main classification: H01Q1
IPC codes: H01Q1, H01Q9