Communications: radio wave antennas – Antennas – Balanced doublet - centerfed
Reexamination Certificate
1997-03-05
2001-12-04
Wimer, Michael C. (Department: 2821)
Communications: radio wave antennas
Antennas
Balanced doublet - centerfed
C343S797000
Reexamination Certificate
active
06326932
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to antennas. 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 antennas for radio transmission and reception.
Conventional television antennas are generally quite bulky and unsightly. In order to achieve best performance, outdoor antennas are preferred, for example, roof mounted antennas. 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 antennas are commonly smaller than outdoor antennas 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-1 302 644. 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.
SUMMARY OF THE INVENTION
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 antennas 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.
REFERENCES:
patent: 2552816 (1951-05-01), Root
patent: 2615005 (1952-10-01), White
patent: 3025524 (1962-03-01), Thies
patent: 3541559 (1970-11-01), Evans
patent: 3641576 (1972-02-01), Farbanish
patent: 3721990 (1973-03-01), Gibson et al.
patent: 3815141 (1974-06-01), Kigler
patent: 4860019 (1989-08-01), Jiang et al.
patent: 0257657 A2 (1988-03-01), None
patent: 1302644 (1973-01-01), None
Wimer Michael C.
Woodcock & Washburn LLP
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