FIELD OF THE INVENTION 
     The present invention relates to the field of cellular telephony, and more particularly relates to mobile antennas used with cellular telephones. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     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 &#34;mobile&#34; 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). &#34;Portable&#34; phones are adapted to be hand carried and include their own battery packs and antennas. A hybrid form of phone, termed a &#34;transportable&#34; can be connected to a vehicle&#39;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&#39;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&#39;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&#39;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 &#34;passive repeaters.&#34; 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&#39; 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 non-obviousness 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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of an antenna system according to one embodiment of the present invention. 
     FIG. 2 is a schematic illustration of the antenna system of FIG. 1 used in the passenger compartment of a vehicle in conjunction with a portable cellular telephone. 
     FIG. 3 is an illustration of an antenna system according to a second embodiment of the present invention. 
     FIG. 4 is an illustration of an antenna system according to a third embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     To provide a comprehensive disclosure without unduly lengthening this specification, applicants incorporate by reference the disclosures of U.S. Pat. Nos. 4,862,183, 4,804,969, 4,794,319, 4,764,773 (Larsen), 4,658,259 (Blaese), 4,238,799 (Parfitt), 4,089,817, 4,028,704, 2,829,367 and 2,206,820. 
     As illustrated by the above-referenced patents, vehicle mounted antennas are typically fed by one of two techniques: direct feed or through-the glass coupling (inductive or capacitive). In direct feed systems, there is an electrical connection from the feed line to the antenna. This connection is usually made by a cable that passes through a hole drilled in the vehicle body. Through-the-glass coupling is most commonly used for cellular vehicle antennas since no hole need be drilled in the vehicle. 
     Through-the-glass coupling systems usually take one of two forms. In the first, a low impedance presented by the transmission line (connecting to the telephone) is transformed up to match a high impedance presented by the external antenna. The Larsen and Parfitt patents illustrate this technique. In the Larsen system, the transformation up to the high impedance is performed on the side of the glass outside the vehicle; the through-the-glass coupling is performed at a low impedance. In the Parfitt system, the transformation up to the high impedance is performed on the side of the glass inside the vehicle; the through-the-glass coupling is performed at a high impedance. 
     In the second type of through-the-glass coupling, a low impedance presented by the transmission line is coupled directly to a low impedance antenna without any impedance transformation. The Blaese patent illustrates this technique. 
     The present invention is applicable to all of these through-the-glass techniques, as well as to traditional direct feed techniques. For expository convenience, the invention will be illustrated with reference to the Larsen system. 
     Referring to FIG. 1, an antenna system 10 according to the present invention includes an external radiator 12, an internal auxiliary antenna 14, and some means 16 for coupling energy therebetween. In the illustrated embodiment, the internal auxiliary antenna comprises a dipole dimensioned to present a low resonant impedance in the cellular telephone frequency band. Each leg 14a, 14b of the dipole is connected to an inside capacitive coupling plate 18a, 18b. These inside capacitive coupling plates, in turn, are mounted to an inside surface 20 of a vehicle windshield 22. 
     On an outside surface 24 of the vehicle windshield 22, opposite the inside coupling plates 18a, 18b, are mounted corresponding outside capacitive coupling plates 26a, 26b. These plates, in turn, are connected to an impedance transformation network 28, which here comprises a series-coupled inductor 30 and capacitor 32. The inductor 30 is tuned to match a high resonant impedance presented by the external radiator 12 to the low impedance coupled through the vehicle windshield from the low impedance internal auxiliary antenna 14. 
     Referring now to FIG. 2, the antenna 10 of the present invention is shown mounted on the rear windshield of a vehicle 34. Inside the passenger compartment of the vehicle is a portable or transportable telephone 36 with its own antenna 38. Signals broadcast from the telephone antenna 38 are picked up by the internal auxiliary antenna 14 and rebroadcast outside the passenger compartment using the external radiator 12. Similarly, signals received by the external radiator 12 are rebroadcast inside the vehicle by the antenna 14 and received by the telephone antenna 38. 
     The internal auxiliary antenna may be oriented to achieve vertical or horizontal polarization. Surprisingly, best results are often achieved with horizontal polarization, despite the fact that the telephone antenna with which it is communicating is generally vertically polarized. 
     In another embodiment of the invention (FIGS. 3 and 4), the antenna system may be adapted for removable mounting on the top of a vehicle window. A spring-plastic U-shaped clip 50 can slide down over the top edge of a partially-rolled down window 52. The internal auxiliary antenna can be mounted to the inside portion 54 of the clip. The external radiator can be mounted to the outside portion 56 of the clip. Coupling from the internal antenna to the external radiator can be accomplished by a transmission line 58 molded into the plastic clip that connects the two (FIG. 3). Alternatively, a capacitive or inductive coupling arrangement can be used, with one coupling component 26 attached to the outside portion of the clip and the other coupling component 18 attached to the inside portion of the clip (FIG. 4). 
     It will be recognized that in either of the two foregoing arrangements (i.e. coupling from the internal antenna to the external radiator by a transmission line or coupling through inductive/capacitive components), no powered circuitry is involved. In other words, the coupling is passive. 
     If desired, a vehicle may be provided with two or more antenna systems according to the present invention. By using a plurality of such antenna systems, a directional radiation pattern is achieved. Unlike most phased arrays, the directional characteristics here are dependent not only on the spacings of the radiators relative to each other, but also on the location of the portable or transportable telephone&#39;s antenna within the array of internal antennas. By moving the telephone within the car, the relative phasings of the signals driving the radiators are altered, changing the net radiation pattern. Thus, by use of a plurality of antenna systems according to the present invention, it is possible to provide a steerable phased array--steerable simply by moving the telephone inside the vehicle. 
     CONCLUSION 
     It will be recognized that the foregoing embodiments permit transportable phones to gain the benefit of an external vehicle-mounted antenna without having to connect or disconnect the antenna each time the telephone is moved to or from the vehicle. The invention similarly permits portable phones, which often cannot connect to an external antenna even by cable, to easily utilize an external antenna. 
     Having described and illustrated the principles of our invention with reference to several embodiments thereof, it will be apparent that the invention can be modified in arrangement and detail without departing from such principles. For example, while the invention has been illustrated with reference to an embodiment in which the internal auxiliary antenna is a dipole and presents a low impedance, in other embodiments other interior antenna configurations may be used, some of which present high impedances. Similarly, while the invention has been illustrated with reference to an embodiment in which an inductor/capacitor matching network is used outside the glass, a variety of other matching arrangements may be used on either side of the glass, or no matching network at all may be required. Of course, the invention may also be applied to direct feed antennas by directly connecting the internal auxiliary antenna to the external radiator, as was noted in connection with the second embodiment. Similarly, if a vehicle is provided with a direct feed radiator mounted on the vehicle trunk, an auxiliary antenna may be positioned within the passenger compartment of the vehicle and connected to the external radiator by cabling. 
     In view of the variety of embodiments to which the principles of our invention may be applied, it should be recognized that the detailed embodiments are illustrative only and should not be taken as limiting the scope of our invention. Instead, we claim as our invention all such embodiments as may come within the scope and spirit of the following claims and equivalents thereto.
A mobile cellular antenna system includes an auxiliary antenna that is positioned inside the passenger compartment of a vehicle and is coupled to the radiator on the exterior of the vehicle. This arrangement permits users of portable or transportable cellular telephones with built-in antennas to gain transmission and reception advantage from the exterior antenna while operating from within the passenger compartment.