Communications: radio wave antennas – Antennas – With vehicle
Reexamination Certificate
1997-06-18
2001-07-31
Le, Hoanganh (Department: 2821)
Communications: radio wave antennas
Antennas
With vehicle
C343S704000, C343S711000, C343S712000
Reexamination Certificate
active
06268832
ABSTRACT:
The present invention relates to antennas. The antennas to which this invention relates will most typically find application in a vehicle and can be used for VHF radio reception in the range of 76-110 MHz. However, antennas of the present invention may be used in other circumstances and other ranges (VHF otherwise) and are not restricted to use with audio broadcasts.
A motor vehicle, being a cage of metal, is internally largely shielded from external radio signals. It is thus necessary to provide an antenna for a radio receiver operating within the vehicle.
Traditionally, antennas for motor vehicles comprise a metal mast or rod which projects, in use, from the vehicle body. The disadvantages of these-have been long-recognised, such that technology has been available for many years whereby an antenna can be formed from conductive elements on a glass pane of the vehicle such as those used for rear-screen heating. Such antennas, in their broadest sense, will be referred to herein as window mounted antennas.
One reason why window mounted antennas are not universally used is that their cost is greater than the equivalent metal mast or rod antenna. This has not been due to the cost of providing a special glass pane; this is negligible. Rather, this has been due to the cost of the interface circuitry required. Most particularly, the interface circuitry has included active components for amplification of the signal received to a level suitable for feeding to a radio receiver.
An additional disadvantage of window mounted antennas (which conventionally include active components) is that the signal-to-noise ratio of the output from such antennas has not been as good as that of traditional mast types.
Various attempts have been made to improve the performance of window mounted antennas. These have included variations in the interface circuitry, changes to the pattern of conductive elements, and providing separate conductive elements dedicated to radio reception and which play no part in heating the window. However, these attempts have not removed the above disadvantages.
The primary aim of the present invention is to provide a window mounted antenna, particularly but not exclusively for VHF reception in cars, which has a lower cost and better performance than has hitherto been available.
In arriving at the present invention, the applicants have recognised that there has been acceptance that a window mounted antenna will be disadvantaged through being mounted within a conductive surround of uncontrolled behaviour at radio frequencies. A rear screen of a vehicle has properties similar to a slot, in a ground plane, but its resonance properties are uncontrolled and correspond only by coincidence with frequencies of signals to be received. Previously, attempts have been made to improve the signal derived from a disadvantageously disposed antenna. However, this has constituted an appeasement of the symptoms of inherent deficiencies rather than any attempt to remove them.
By the present invention, there is provided an antenna for receiving radio signals in a vehicle within a desired frequency range comprising an array of conductive elements disposed on a window pane, characterised in that the elements are disposed to define a radio reception zone between boundary conductive paths, each boundary conductive path being a part of a respective loop tuned to resonate at a frequency within the desired frequency range, the boundary conductive paths isolating the reception zone from the periphery of the pane to mitigate the effects on the receptor zone of image current flowing in the periphery of the aperture and such that the antenna is favourably matched to radio signals within the desired frequency range.
By realising that the antenna must be considered to act as a system in conjunction with its immediate surroundings, the applicants have been able to provide an antenna which generates from the outset signals which are of high quality. Particularly in the case of a metal vehicle the interaction between the antenna and the surrounding vehicle body is highly significant. In many embodiments, the signals can be of sufficient magnitude to be useable by a radio receiver without amplification.
Preferably, the elements are disposed such that a reception zone is created in the array which at least partially compensates for the effects of canceling image currents in the conductive material of the vehicle. In this manner, the reception zone can be configured as required to of-far high quality reception of signals. In such embodiments, a connection may conveniently be made to one or more elements within the reception zone from which connection an output signal is obtained.
In embodiments of the last-preceding paragraph, the reception zone may be defined between a pair of boundary conductive paths, each of which is part of a conductive loop tuned to resonate at a frequency within the desired reception range, Each of such loops advantageously has an external connection (for example, to a surrounding vehicle body) of low impedance at a frequency within the desired reception range. The external connection can, for example, comprise a series-resonant circuit, or an open-circuit (1+2n)&lgr;/4 transmission line, to implement a short circuit at the frequency of operation. (Alternatively, a short circuit transmission time of n&lgr;/2 may be used.) Such transmission lines have the advantage that they can be formed as a conductive path on the window pane. In any case, the connection advantageously is of high impedance to low frequencies and to DC.
Each boundary conductive path, as defined above, is preferably connected to the respective connection to the vehicle body through multiple conductive paths, these multiple paths each being of length approximately one quarter of the wavelength of a signal to be received while propagating within the window pane. These multiple paths are conveniently substantially parallel to one another and the boundary conductive path comprises elements interconnecting adjacent ones of the multiple paths.
The multiple paths are typically formed by heating elements for the window pant. In such embodiments, the boundary conductive path conveniently comprises a plurality of conductive elements interconnecting adjacent heating elements. In such embodiments, the interconnecting elements are advantageously disposed such that they interconnect points of substantially equal potential of the electrical heating supply. In this way, substantially no heating current will flow through them, allowing them to be formed as fine conductors.
In an antenna of the present invention, typically all of the conductive paths are formed by printing or deposition onto the pane.
In a second of its aspects, the invention provides a glass pane for a vehicle comprising an array of conductive elements disposed to constitute a heater for the pane and an antenna for receiving radio signals of a desired range of frequencies; the array comprising a plurality of parallel heating elements extending between a pair of bus bars, and a plurality of interconnecting elements each extending between adjacent heating elements, the interconnecting elements being disposed to be at a high impedance locus for signals in the desired range with respect to a connection point on one of the busbars.
Such a glass pane may be fitted to a motor vehicle during manufacture to provide that vehicle with an antenna for receiving radio broadcasts.
In a glass pane embodying the invention, the distance from a connection point along the conductive path defined by the busbars and the heating elements to each interconnecting element may typically be approximately one quarter of the wavelength of the signals of the desired frequency propagating within the glass pane, although other distances may be used and compensated for in the design. It is to be remembered that such signals will be propagating at a speed substantially less than (for example 60% of) their speed in free space.
The array of conductors typically includes an output conductive element connected t
Davies John
Twort Keith Jeremy
BSH Industries Limited
Le Hoang-anh
Shoemaker and Mattare Ltd.
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