Cellular telephony has grown at an exponential rate in recent years. No longer are car phones the exclusive domain of the limousine set. Now they are becoming commonplace in all types of vehicles.
The associated technology has advanced at a dizzying pace as well. No longer are car phones heavy units bolted to the floors of vehicles. Rather, they are now small lightweight units which take a number of forms. So called "mobile" phones usually are permanently installed in a vehicle. These units must be connected to both the vehicle battery and to an external antenna (which is typically mounted on the windshield of the vehicle). "Portable" phones are adapted to be hand carried and include their own battery packs and antennas. A hybrid form of phone, termed a "transportable" can be connected to a vehicle's battery and external antenna, or it may be disconnected and removed from the vehicle, relying on an internal battery pack and its own antenna for operation.
In strong signal areas, all of these units perform well. In fringe areas, however, the associated antennas become more critical. To maintain good communications from a transportable phone at a fringe location, the unit must generally be connected to the vehicle-mounted antenna, rather than rely on its own. If a portable phone is used from a fringe location, it is best to operate the unit outside of the vehicle, with the phone's antenna in the clear. If either a portable or transportable is operated inside the passenger compartment of a vehicle using its built-in antenna, fringe area performance suffers, since the metal surrounding the passenger compartment interferes with transmission of the radio signals.
It will be recognized that it is tedious to connect and disconnect a transportable telephone to a vehicle antenna each time the phone is taken inside or outside a car. However, such action is necessitated in fringe areas. Similarly, it is troublesome for a user of a portable phone to stop the vehicle, get out, and position the portable's own antenna in the clear in order to maintain clear communications. However, this is the present state of the art.
The present invention overcomes these problems. It permits users of transportable and portable telephones to gain the benefit of a vehicle-mounted antenna without requiring that tedious connections be made or broken each time the telephone is moved into or out of a car. The invention even permits portable telephones which have no provision for connection to an external antenna to gain the benefit of an external, vehicle mounted antenna.
In accordance with the present invention, signals are coupled between a vehicle mounted antenna and a cellular telephone by radio rather than by wire. In one embodiment of the invention, this is achieved by providing an on-glass vehicle antenna with an auxiliary antenna inside the vehicle. Signals are passed to and from the external antenna portion of the on-glass antenna by transmission of signals between the telephone's own antenna and the internal auxiliary antenna portion of the on-glass antenna.
It will be recognized that the invention may be likened to so called "passive repeaters." Such repeaters are known in a number of fields, including relay stations to provide cellular telephone coverage in areas that would otherwise be inaccessible to radio signals, such as inside tunnels. In this application, a high gain antenna, typically a parabolic dish, is mounted outside of the tunnel and is directed towards the nearest cellular broadcasting station. This parabolic antenna is connected by coaxial cable or waveguide to one or more antennas inside the tunnel, thereby providing radio coverage inside the tunnel.
While passive repeaters are a well known technology, no one, to applicants' knowledge, has heretofore applied it to the problem of conveniently using portable and transportable telephones from within the passenger compartments of vehicles. Others skilled in this art failed to arrive at the present invention despite massive research and development efforts in the cellular telephony field by industry leaders in the U.S., Europe and Japan. The nonobviousness of the present invention is illustrated by the unanimity with which it has been overlooked.
The above-described features and advantages of the present invention will be more readily apparent from the following detailed description thereof, which proceeds with reference to the accompanying drawings.