Abstract:
A vehicle antenna system incorporated into at least one side-view mirror of a vehicle includes a forward directed antenna and a rearward directed antenna to transmit and receive signals over corresponding forward and rearward-directed detection fields, respectively. The antennas act as directional transmitters and/or receivers, and a processing circuit discriminates between signals from different antennas without requiring any of the antennas to transmit identification signals to the processing circuit. Signal discrimination is conducted in part by sequentially selecting each antenna to obtain a corresponding antenna signal and, if required for a particular application, comparing the obtained signal with previously obtained antenna signals. The vehicle antenna system can be used, for example, in conjunction with tire pressure sensors to detect low tire pressure in a particular tire.

Description:
FIELD OF THE INVENTION 
     The invention relates to an antenna system for a vehicle for monitoring various vehicle internal diagnostic functions and for transmitting/receiving to and from remote transmitting/receiving stations external to the vehicle. More particularly, the antenna system relates to exterior rear view mirror mounted antennas on the vehicle which can be directionally activated to detect or transmit selected signals. 
     BACKGROUND ART 
     Insufficiently inflated or over-inflated tires for vehicles present an often unknown danger to drivers and passengers of the vehicles. This improper inflation can cause poor handling, poor traction, reduced fuel efficiency and can cause tire failures if left improperly inflated for a period of time. A visual inspection of a vehicle&#39;s tires can provide some indication of the level of inflation of the tires. However, this method is extremely inaccurate and newer “run flat” tires often retain some degree of structural integrity even after losing inflation pressure making a visual inspection of the internal tire pressure nearly impossible. Further, it is suspected that many vehicle owners often neglect to examine the level of inflation in their vehicle&#39;s tires for extended periods of time. Therefore, it is desirable to provide a vehicle with an internal tire pressure sensing system for determining the level of inflation in the vehicle&#39;s tires and alerting the operator if the level is outside a preselected operating range. 
     Several solutions to the problem of detecting and monitoring tire pressure have been proposed in the past. Typically, known tire pressure sensors include a transmitter mounted within the tire (often to the wheel) adjacent to, or integral with, a valve stem therefor. Because the tire pressure sensors detect and transmit a value proportional to the pressure in the tire, this value is typically normalized to compensate for variations in the ambient temperature to prevent inaccurate readings due to air expansion from temperature variations. Further, tires tend to heat up after extended periods of use, also requiring correction for temperature variations. Some examples of tire pressure sensors which include correction for temperature variations are taught by U.S. Pat. Nos. 4,567,459, 4,703,650, and 4,966,034. 
     Due to the physical constraints presented by the location of the tire pressure sensor within the tire and the impracticability of running wire leads from the tire pressure sensor to a control unit within the vehicle, it is desirable to employ a wireless transmission system to relay the data output by the tire pressure sensor to the control unit. In addition to the above-mentioned patents, examples of wireless transmission systems employing means such as radio transmitters are shown in U.S. Pat. Nos. 4,510,484, 4,554,527, and 5,061,917. The tire pressure sensors can include a wireless transmitter-such as that shown in U.S. Pat. No. 4,978,941. In addition to radio transmissions, each of the vehicle&#39;s tires can be coded with a unique digital value such as that shown in U.S. Pat. Nos. 5,001,457 and 5,061,917. 
     Referring now to the drawings and to  FIG. 1  in particular, a vehicle  10  is shown having a generally well-known configuration: four ground-engaging wheels  12  with a spare tire  14  located in a trunk portion  16  of the vehicle  10 . The vehicle  10  is also provided with conventional windshields, one forward windshield  18  and one rearward windshield  20 . The forward windshield  18  is provided with a conventional rear view mirror  22 . A driver-side external rear view mirror  24  and a passenger-side rear view mirror are located adjacent the forward windshield  18 , typically positioned on corresponding front doors (not shown) of the vehicle  10 . Each of the external mirrors  24  and  26  is preferably provided with an antenna system. An example of a prior art antenna system in which a radio frequency antenna is mounted within an exterior mirror for a vehicle is shown in commonly-assigned U.S. Pat. No. 5,504,478 to Knapp, issued Apr. 2, 1996 and is incorporated herein by reference. 
     Several problems have been encountered with the known wireless tire pressure sensor systems. These systems require internal calibration to ensure proper display of information and typically need recalibration if transmitters (or the tires they are mounted to) are replaced or rotated. This calibration and recalibration is an inevitable consequence of the requirement for a uniquely coded transmitter corresponding to the location of the tire on the vehicle. Thus, the system knows if it is detecting a front drivers-side tire pressure, a rear passengers-side tire pressure, etc., depending upon the code detected by the system. 
     U.S. Pat. No. 5,600,301 shows an example of a remote tire pressure sensing system wherein each of the tire pressure sensors has a transmitter provided with a unique code at manufacture. 
       FIG. 2  is a perspective view of an example of a wheel  12  for the vehicle  10  provided with a prior art tire pressure sensor  28  adapted to send a signal detectable by an antenna system on one of the external rear view mirrors  24  and  26 . Each of the wheels  12  (and the spare tire  14 ) of the vehicle  10  are preferably provided with a tire pressure sensor  28  which is adapted to transmit a signal corresponding to the pressure within the wheel  12  (or the spare tire  14 ). 
     The tire pressure sensor  28  is shown in greater detail in FIG.  3  and preferably comprises a body  30  having a valve stem  32 . The valve stem  32  is used to inflate or exhaust pressurized air from within the wheel  12  (when encased by a conventional tire). The body  30  preferably contains a well-known pressure sensor and circuitry adapted to transmit a signal corresponding to the pressure detected by the tire pressure sensor  28 . Each tire pressure sensor  28  thereby must transmit the unique code in addition to the pressure signal to a receiver at different intervals to provide an indication of the tire pressure in each of the tires. 
     One problem with the above-described system is that an initialization procedure must be performed to determine the location of each particular tire pressure sensor on the vehicle. Each transmitter is designed to transmit tire pressure and identification data when a magnet is held in close proximity. The initialization process is performed by placing the receiver in a learning mode and then triggering the transmitter in each tire pressure sensor with a magnet in a predetermined sequence. In this manner, the receiver can associate each tire pressure sensor&#39;s unique code during the initialization sequence to determine the tire&#39;s relative position on the vehicle. As an example, the initialization is begun by triggering the front driver-side tire transmitter first and then triggering each of the other tire transmitters in a counterclockwise sequence around the vehicle. 
     Several additional problems have been encountered with this prior art system. First, each transmitter requires a magnetic sensor to “activate” it during the initialization process adding cost to the transmitter and requiring additional space within the transmitter. 
     Second, the system must be recalibrated when tires are rotated or replaced causing inconvenience to the vehicle operator and necessitating at least one performance of the initialization process to enable the receiver to “relearn” the location of the tire pressure sensors. 
     Third, the receiving antenna is likely required to be omni-directional and centrally located within the vehicle, requiring increased signal strength from each transmitter due to the signal shielding effect from the vehicle&#39;s structure, including radio frequency shielding windows such as “tinted”, low e value windows, requiring higher transmitter power and/or a higher receiver sensitivity. A higher power transmitter can reduce battery life and add to the system cost. A higher receiver sensitivity can increase cost and increase susceptibility to unwanted signals. 
     Fourth, because the transmitters are not synchronized, it is possible that two or more transmissions could occur at nearly the same instant, making the transmitted signals undecipherable, especially with a centrally-located antenna. 
     Fifth, the transmitter in each tire pressure sensor in the system described above requires a unique code so that the receiver can distinguish each transmitter&#39;s relative position after initialization. As the number of vehicles equipped with these types of tire pressure sensing systems increases, a data frame of increased length (typically additional digits or characters) would be required to ensure uniqueness, thereby decreasing battery life due to increased use. 
     Sixth, with systems having an omni-directional antenna, the instant vehicle and vehicles adjacent to it would result in cross-detection of tire pressure sensor transmissions between adjacent vehicles resulting in erroneous pressure data. 
     Further, wireless transmission of other vehicle diagnostic data is becoming more common which increases the probability that the various signals transmitted around the vehicle&#39;s interior and exterior will cause interference and thus reduce the effectiveness of the various wireless transmission systems. Also, while attention has been paid in the past to selection of appropriate transmission frequencies to avoid interference from other radio frequency sources, particular problems are presented by remote control systems, such as keyless entry systems, garage door openers, etc., which are becoming more and more widely implemented. These exterior transmission signals can also cause additional interference and require additional antenna arrays to be built into the vehicle receiving systems. 
     SUMMARY OF THE INVENTION 
     Accordingly, a vehicle antenna system according to the present invention monitors various vehicle internal diagnostic functions as well as enables signal receptions/transmissions to remote transmitting/receiving stations external to the vehicle. In one aspect, the antenna system relates to a system having a directional antenna mounted to each exterior rear-view mirror on the vehicle which can be selectively directionally adjusted to detect the various vehicle internal diagnostic functions, e.g., tire pressure, as well as directed externally of the vehicle to enable communications with systems remote from the vehicle. 
     The antenna system provided on the vehicle external mirrors can be used to improve apparent electromagnetic signal strength for various vehicular applications, e.g., detecting signals generated by a tire pressure sensor adapted to emit a radio frequency signal proportional to the pressure contained in a vehicle tire. The antenna system can also be used to discriminate signal transmission source locations. 
     The antenna system comprises forward and rearward directed antenna elements in the vehicle&#39;s exterior mirror housings and, optionally, an antenna in the interior rear view mirror housing and combinations thereof. A receiver can be provided within the vehicle which is interconnected to the antenna system so that each antenna in the system can be selectively switched in or out of the vehicle&#39;s receiver and transmitter circuits, respectively. 
     There are several applications which can employ the antenna system described herein to advantage. For example, multiple receiving antennas can be used to discriminate the individual locations of multiple transmitters, e.g., tire pressure sensor signaling devices. Multiple receiving antennas can be used to expand the reception range of a transmitted signal, e.g., remote keyless entry (RKE) signals. Multiple transmitting antennas can be used to expand transmission range and coverage, e.g., transmitting an amplified garage door opener signal. A pre-selected transmitting antenna can be used to control transmission directionality, e.g., to transmit to a receiver such as a parking ramp gate, radio-controlled parking meter or an automated toll collection booth. Other vehicular applications for which this antenna array could be utilized include, but are not limited to, cellular telephone signal reception, roadway navigation, location and information, traffic control, safety, security, parking, and vehicular identification and statistical information, e.g., traffic counting applications. These and other uses will be described below in greater detail after the structural components and functions are identified with reference to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top schematic view of a vehicle having a prior art antenna system provided in both outside rear view mirrors and a vehicle internal diagnostic sensing system comprising a transmitting antenna interconnected with a tire pressure sensor in each of road-engaging tires thereon and in a spare tire provided therewith in a trunk portion of the vehicle; 
         FIG. 2  is a perspective view of a wheel for the vehicle of  FIG. 1  provided with a prior art tire pressure sensor adapted to send a signal to the antenna system of one of the outside rear view mirrors of  FIG. 1 ; 
         FIG. 3  is an enlarged, perspective view of the prior art tire pressure sensor of  FIG. 2 ; 
         FIG. 4  is a top schematic view in a similar orientation as  FIG. 1  showing a schematic representation of a transmitting antenna provided on each of the tire pressure sensors of the vehicle internal diagnostic sensing system and a schematic representation of a receiving antenna according to the invention shown on each of the outside rear view mirrors of the vehicle; 
         FIG. 5  is a top schematic view in a similar orientation as  FIG. 1  showing antenna transmitting fields for the tire pressure sensors in each of the road-engaging wheels thereon and a forward- and rearwardly-directed antenna detecting field for the antenna system provided on the driver side rear view mirror; 
         FIG. 6  is a top schematic view in a similar orientation as  FIG. 5  showing the detecting field of the driver-side rear view mirror directed in the forward direction; 
         FIG. 7  is a top schematic view in a similar orientation as  FIG. 5  showing the detecting field of the driver-side rear view mirror directed in the rearward direction; 
         FIG. 8  is a schematic view of a control circuit for a single antenna system provided on one of the rear view mirrors; 
         FIG. 9  is a schematic view of the control circuit of  FIG. 8  modified to support multiple forwardly- and rearwardly-directed antennas on the driver-side rear view mirror as well as forwardly- and rearwardly-directed rear view mirrors on the passenger-side rear view mirror; 
         FIG. 10  is a schematic view of the control circuit of  FIG. 9  modified to show matching networks provided on each of the antenna systems for the drivers- and passenger-side rear view mirrors as well as an antenna switching network to independently control the antenna system on the rear view mirrors; 
         FIG. 10A  is a schematic view of an alternative arrangement of the control circuit of  FIG. 10  modified to show a digital system for determining the peak signal detected by the circuit; 
         FIG. 10B  is a schematic view of another alternative arrangement of the control circuit of  FIG. 10  modified to show an automatic gain control adjuster for a receiver in the circuit for determining the peak signal detected by the circuit; 
         FIG. 11  is a front perspective view of a vehicle with an antenna system located on an external mirror provided on an hydraulic lift in a service station whereby the antenna system on the vehicle transmits vehicle diagnostic data to a vehicle diagnostic computer located adjacent thereto; 
         FIG. 12  is a front perspective view of a vehicle located adjacent a garage provided with a garage door opener whereby an antenna system located on an exterior mirror of the vehicle can transmit a signal to actuate the garage door opener; 
         FIG. 13  is a perspective view of a vehicle located on a cross street having signal lamps interconnected to a traffic control system whereby the vehicle antenna system can transmit its presence to the traffic control system; 
         FIG. 14  is a perspective view of a vehicle located on a first cross street and an approaching emergency vehicle located on a second cross street whereby antenna systems on the passenger vehicle and the emergency vehicle interact with a traffic control system to provide increased safety and prevent passenger vehicle collisions with emergency vehicles; 
         FIG. 15  is a perspective of a vehicle operator actuating a remote keyless entry system to send a wireless signal to actuate locking or ignition systems on a vehicle via an antenna system on an external mirror; 
         FIG. 16  shows a perspective view of a vehicle having an antenna system on an external mirror located adjacent to a gating system having a movable gate provided with a receiving antenna whereby the vehicle antenna system can transmit data to the gating system antenna denoting the presence of the vehicle and signaling the gate to open or close and providing any access codes required by the gating system; 
         FIG. 17  is a perspective view of a vehicle having an antenna system on an external mirror located adjacent to a parking meter having an antenna system whereby the vehicle can transmit data to the parking meter to provide payment for charges for the parking meter or instruct the parking meter of the presence of a car with handicap access therefor; 
         FIG. 18  is a perspective view of a vehicle with an antenna system on an external mirror sending cellular telephone signals between the vehicle and a cellular telephone tower provided with an antenna system thereon; and 
         FIG. 19  is a perspective view of a vehicle having an antenna system on an external mirror transmitting and receiving global positioning data from a satellite with an antenna system thereon. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 4  is a top schematic view in a similar orientation as  FIG. 1  showing one embodiment of the present invention as a schematic representation of a tire pressure transmitting antenna  42  provided on each of the tire pressure sensors  28  of the vehicle  10 . It will be understood that the transmitting antenna  42  is a conventional component of the tire pressure sensor shown in  FIGS. 2 and 3 . 
       FIG. 4  also shows an antenna system  40  according to the invention on each external mirror  24  and  26  comprising a forwardly-directed antenna  44  and a rearwardly-directed antenna  46 . Each of the antennas  44  and  46  can comprise a dielectric or metallic coating on glass for the mirrors  24  and  26  (such as in an electrochromic mirror), a wire antenna provided within the mirror housing, or any other well-known conventional monopole, dipole, helical, patch or other antennas known in the art. Many variations in the types of antennas  44  and  46  are contemplated without departing from the scope of this invention. 
     Each of the antennas  44  and  46  is adapted to detect a signal from a remote source within a particular localized area of the particular antenna  44 ,  46 .  FIG. 5  shows example signal detection fields  48  and  50  for the antennas  44  and  46 , respectively. It will be understood that, although the signal detection fields  48  and  50  are shown only for the antennas  44  and  46  of the antenna system  40  of the driver-side mirror  24 , the fields  48  and  50  are similarly oriented for the passenger-side mirror  26 .  FIG. 5  also shows examples of typical forward and rearward transmission fields  52  and  54 , respectively, for the transmitting antenna  42  in each of the tire pressure sensors  28  on the wheels  12  and the spare tire  14 . 
     It should be noted that the forward signal detection field  48  of the antenna system  40  of the driver-side external mirror  24  preferably substantially overlaps the forward transmission field  52  of the tire pressure sensor  28  on the forward driver-side wheel  12 . The rearward signal detection field  50  preferably substantially overlaps the rearward transmission field  54  of the tire pressure sensor  28  on the rearward driver-side wheel  12 . Accordingly, although not shown in  FIG. 5 , the fields  48  and  50  of the antenna system  40  of the passenger-side external mirror  26  preferably substantially overlap the fields  52  and  54  of the tire pressure sensors  28  on the passenger-side wheels  12  as well. 
     It is an important feature of the invention that the antennas  44  and  46  of the antenna system  40  be interconnected to a matching network (as is known in the art) which maximizes the received signal strength so that a signal from a particular antenna can be detected and processed most accurately. Along these lines,  FIGS. 6 and 7  show the forwardly- and rearwardly-directed antennas  44  and  46 , respectively, being actuated wherein one of the antennas  44  and  46  is actuated while the other is not. A detection of the tire pressure in a particular wheel  12  can thereby be more accurately obtained. 
     For example,  FIG. 6  shows the forwardly-directed antenna  44  being actuated by the presence of only the forward signal detection field  48  which provides an indication of the tire pressure in only the forward driver-side wheel  12 . It will be understood that the particular selected antenna may detect other signals during processing, but that the antenna is interconnected to a “peak detection” circuit which enables a controller to discriminate signal strengths and attenuate unwanted signals such as by reducing receiver gain. Conversely,  FIG. 7  shows the rearwardly-directed antenna  46  being actuated by the presence of only the rearward signal detection field  50  which provides an indication of the tire pressure in only the rear driver-side wheel  12 . 
     Of course, the antenna system  40  is preferably interconnected to a circuit which is described in greater detail in FIG.  8 .  FIG. 8  shows a schematic example of a simplified circuit for a single antenna  44  or  46  of the antenna system  40 . The antenna  44 ,  46  is operably interconnected to a control circuit  60  via a receiver/detector circuit  62  which is a conventional component used to relay antenna signals. Any signal detected from the antenna  44 ,  46  is sent by the receiver/detector circuit  62  to the control circuit  60 . 
     The control circuit  60  can also convert the signal to a pressure value and output a display of the detected pressure value or limit on a visual or audio indicator  64  so that the vehicle operator can interpret the results. The control circuit  60  compares the pressure value with a predetermined desired pressure value. The predetermined pressure value can be set according to tire manufacturer&#39;s specifications, vehicle ride specifications and the like. If the detected pressure value exceeds or is less than the predetermined pressure value (or range) by a preselected amount, a warning message can be displayed or sounded on the indicator  64  to alert the vehicle operator of an unsafe tire pressure condition. 
       FIG. 9  is a schematic view of the circuit of  FIG. 8  modified so that the control circuit  60 , receiver/detector circuit  62  and the indicator  64  can be selectively interconnected to each of the antennas  44  and  46  of the antenna systems  40  provided on the driver-side and passenger-side mirrors  24  and  26  by an antenna matching/switching network  66 . It will be understood that elements common to both FIG.  8  and  FIG. 9  are referred to with common reference numerals. 
     As shown in  FIG. 9 , the matching/switching network  66  is interconnected to the driver-side antennas  44  and  46  by connections  68  and  70  and to the passenger-side antennas  44  and  46  by connections  72  and  74 , respectively. Additionally, the control circuit  60  is interconnected to the network  66  by a feedback loop  76 . The antenna matching/switching network  66  functions to accept the signal from the antennas  44  and  46  and to send the appropriate signal to the receiver and detector circuit  62 . The feedback loop  76  from the control circuit  60  to the matching/switching network  66  enables the control circuit  60  to specify which of the antennas to actively accept a signal from, preferably when a strong signal from one of the antennas  44  and  46  is detected. 
     It will be understood that it has been found that the matching network  66  provides additional accuracy in the signal processing of the system  40  but is not an essential component depending upon the type of antennas  44  and  46  employed as well as other factors such as the length and type of connecting wiring, etc. 
       FIG. 10  shows the control circuit of  FIG. 9  which has been expanded to show internal components of the matching/switching network, shown in box form by reference numeral  66 , and internal components of the receiver and detector circuit  62  and control circuit  60  also outlined by a box denoted by reference numerals  60 ,  62 . The matching/switching network  66  includes a pair of matching networks  78  and  80  extending between each of the antennas  44  and  46  and an antenna switching network  82 . Each of the matching networks  78  and  80  is interconnected by a connection  84 . The matching networks  78  are interconnected to a corresponding connection  68 ,  70 ,  72  and  74  of the antennas  44  and  46  of the driver-side mirror  24  and the antennas  44  and  46  of the antenna system  40  of the passenger-side mirror  26 , respectively. Each of the matching networks  80  is interconnected to the antenna switching network  82  by corresponding connections  86 ,  88 ,  90  and  92 , respectively. 
     The matching networks  78  and  80  are generally provided to ensure that the signal generated by the antennas  44  and  46  are matched to that required by the antenna switching network  82 . Namely, the characteristics of the signals generated by the antennas, i.e., impedance, capacitance and inductance, are matched by the matching networks  78  and  80  and provided to the antenna switching network  82  through the connections  86 - 92 . If the signals between the antennas  44  and  46  and the antenna switching network  82  do not require matching, the matching networks  78  and  80  and their corresponding interconnection  84  are not required. Preferably, at least one of the matching networks  78  and  80  match the antenna characteristics with the input of the receiver and detector circuit  62 , which will be further described in great detail below. 
       FIG. 10  also shows the control circuit  60  and receiver and detector circuit  62  shown in greater detail. A box  60 ,  62  is formed around the receiver and detector circuit  62  and the control circuit  60 . As described above, the output of the control circuit  60  is interconnected to the indicator  64  by a connection  94 . The antenna switching network  82  is interconnected to a receiver  96  of the receiver and detector circuit  62  by a connection  98 . The receiver  96  accepts an analog signal from the antenna switching network  82  through connection  98 , typically a radio frequency signal in the application described herein and performs demodulation on the signal received from the antenna switching network  82  through the connection  98 . 
     The receiver  96  has an output connection  100  interconnected to a detector  102 . The detector  102  is preferably an amplitude detector which can convert the signal received from the receiver  96  through the connection  100  into a signal ready for processing, such as a pulse width modulated signal. 
     The detector  102  has an output connection  104  which is interconnected to a controller  106 . The controller  106  deciphers the signal received from the detector  102  and performs the storage and comparator functions described above and outputs any tire pressure values and/or alerts to the indicator  64  through the connection  94 . It will be understood that conventional display drivers, adapters, voltage level shifters, etc. are interconnected to the output connection  104  as needed to condition the signal(s) at  94  for the alarm/indicators  64 . 
     The circuit of  FIG. 10  is also able to discriminate between the several antenna signals received through the antenna matching/switching network  66 . To further this function, the detector  102  is provided with a feedback connection  108  which splits at node  110  and provides inputs into the receiver  96  through connection  112  and to a peak detector  114  through a connection  116 . The peak detector  114  has an output connection  118  which is interconnected to the controller  106  through an optional analog-to-digital converter  120  to the extent that the output from the peak detector  114  requires conversion to a digital signal by the A/D converter  120 . 
     It will be understood that a digital system can be implemented without departing from the teachings of this specification. For example, the A/D converter  120  could be removed from its location in  FIG. 10 and a  D/A converter (not shown) could be located on the feedback loop  76  to the extent analog signals are received by the receiver  96 . In any event, the schematic shown in  FIG. 10  is by example only and a variety of circuits for accomplishing the functions of the components thereof can be employed without departing from the scope of this invention. 
       FIG. 10A  is a schematic view of such an alternative arrangement of the control circuit of  FIG. 10  modified to show a digital system for determining the peak signal detected by the circuit. The peak detector  114  and A/D converter  120  have been replaced with a D/A converter  114 A located between connections  112 A and  122 A. 
       FIG. 10B  is a schematic view of another alternative arrangement of the control circuit of  FIG. 10  modified to show an automatic gain control adjuster  114 B located between connections  112 B and  122 B for the receiver  96  in the circuit for determining the peak signal detected by the circuit. In operation, the gain control adjuster  114 B is actuated, thereby changing the gain of the receiver  96 , until only one signal is detected by the detector  98 , thus ensuring that the signal with the highest signal strength is detected. 
     Returning to  FIG. 10 , the controller  106  has a feedback connection  122  interconnected to a reset portion  124  of the peak detector  114  whereby, upon a signal from the controller  106 , the reset portion  124  of the peak detector  114  erases any stored peak detection data detected from the signal received from the detector  108  through connection  116 . The feedback loop  76  from the controller  106  to the antenna switching network  82  operates to permit the controller  106  to send a signal to the antenna switching network  82  to select a signal from a particular antenna  44 ,  46 , from a particular mirror  24 ,  26  through the connection  98  to the receiver  96 . 
     The method of operation of the antenna system for detecting a signal received by the antennas  44  and  46  of the antenna system  40  provided on each of the driver-side and passenger-side mirrors  24  and  26  will now be described. 
     Typically, tire pressure sensors  28  transmit frames of data several times over predetermined time intervals. However, to conserve battery power, these data frames are often transmitted at sporadic intervals depending upon various factors, such as the speed of the rotation of the wheel and delays between changes of speed, etc. The signals from the antennas  44 ,  46  on each of the mirrors  24  and  26  are continually sent through connections  68 - 74  into the antenna matching/switching network  66 . The signals are matched by any matching networks  78  and  80  present within the matching/switching network  86  and sent to the antenna switching network  82  through connections  86 - 92 , respectively. 
     The antenna switching network  82  serially selects one of the signals provided through connections  86 ,  88 ,  90  and  92  and outputs the signal through connection  98  into the receiver  96 . The receiver  96  amplifies and filters the received signal and outputs the signal through connection  100  to the detector  102 . The detector  102  detects the amplitude of the received signal and converts the received signal to a pulse information signal and outputs the information signal through connection  104  to the controller  106 . Also, the detector  102  outputs a reception strength signal through connection  108  to the receiver  112 . This return of the reception strength signal from the detector  102  to the receiver  96  through the connections  108  and  112  acts as a quick-response “gain control” to adjust the gain of the signal detected by the receiver  96  to correct for strong or weak signals received by the receiver  96  from the antenna switching network  82 . 
     The reception strength signal from the detector  102  is also sent through connection  108  and connection  116  to the peak detector  114  which compares the peak amplitude of the reception strength signal provided by the detector  102  to previous peaks detected by the peak detector  114 . The peak detector  114  outputs the peak amplitude through connection  118  and A/D converter  120  to the controller  106 . The detector  102  also outputs the reception strength signal through connections  104  to the controller  106 . 
     Normally, the controller  106  would sequentially switch the source antenna  44 ,  46  (i.e., “scan” the available antennas), until an information signal is received through connection  104  by the controller  106 . The controller  106  then records the peak signal value received through the converter  120  from each of the antennas  44 ,  46 —resetting the peak detector  114  each time another antenna  44 ,  46  is switched into the circuit. The controller  106  “locks” on to the antenna  44 ,  46  from which the peak signal was received (i.e., produced the greatest reception strength signal through converter  120  detected by the controller  106 ) and records the information signal (through connection  104 ) from that antenna  44 ,  46 . When a frame of data has thereby been collected, system  40  updates the particular portion of the indicator  64  associated with that particular antenna  44 ,  46  used to collect the data frame. The controller  106  can also additionally use partial or complete data frames to verify the validity of the information signal, e.g., to protect against false indicators from nearly vehicles. The controller  106  then returns to the scan mode. 
     Generally, the controller  106  compares the information signal provided by the detector  102  through connection  104  to the peak signal sent by the peak detector  114  through the connection  118  and the optional A/D converter  120 . The controller then saves the detected information signal  104  in memory and scans the signals from the remaining antennas  44  and  46  and receives a signal through connection  98  from the antenna switching network  82  in similar manners. 
     If the signal sent by the antenna switching network is not equal to the peak signal sent by the peak detector  114 , the controller cycles through the signals received by the receiver/detector circuit  62  until the signal sent by the detector  102  through connection  104  to the controller  106  equals the peak signal sent through connection  108  and optional A/D converter  120  by the peak detector  114 . The strongest signal from the multiple antennas has thereby been identified. 
     At this point, the controller sends a signal through connection  122  to the reset portion  124  of the peak detector  114  to set the peak value saved in the peak detector  114  to zero. At the same time, the controller  106  sends a signal through feedback loop  76  to instruct the antenna switching network  82  to accept a signal from the antenna whose signal equals the peak for an extended period of time. Thus, a full data frame from the peak signal antenna can be detected. 
     Once a full data frame is detected by the controller  106 , the controller  106  outputs the tire pressure value to the indicator  64  through connection  94 . Further, the controller  106  can also perform the comparison to predetermined tire pressure values to determine whether the tire pressure value is outside a predetermined range and should provide an alert to the vehicle operator. 
     This type of sequential scanning approach to processing signals received from mirrors located on vehicle antennas is far more beneficial than those systems known in the prior art. For example, because the antenna switching network  82  is instructed to detect the strongest signal received from the four antennas, the antenna system  40  works much more on a “directional” basis rather than a “sensor specific” basis. Put more simply, the system of the present invention does not require each tire pressure sensor to transmit a specific identification code. In actuality, the particular identification number of a tire pressure sensor is irrelevant (although an identification code does help to discriminate false signals from tires on vehicles nearby to the vehicle at issue). Rather, the tire pressure sensing system senses the signal from each antenna, directionally determines if a signal is being detected by a particular antenna and activates that antenna and deactivates the other antennas of the system so that the tire pressure sensing system directionally adjusts based upon the strength of a signal received by a particular antenna. 
     The following paragraphs summarize various applications for the inventive antenna system. These applications relate both to the monitoring of internal vehicle settings, calibrations, and other diagnostics as well as communications with sources external to the vehicle and remote therefrom. 
     With regard to the monitoring of internal vehicle diagnostics, the antenna system can be used in connection with the tire pressure monitoring system as described above. Further, as shown in  FIG. 1 , an antenna system  200 , as described herein, provided on an external mirror  202  of a vehicle  204  can be used in connection with a vehicle diagnostic computer  206  provided with a transceiver schematically represented by reference numeral  208 . In the example shown in  FIG. 11 , the vehicle  204  is shown in a typical hydraulic lift  210  extending upwardly from a ground surface  212  on which typical vehicle tire grooves  214  arc provided as are well known to be located in service stations. In use, the antenna system  200  can be interconnected to a diagnostic computer (not shown) internal to the vehicle  204  which is adapted to transmit relevant vehicle diagnostic data to the vehicle diagnostic computer  206 . The antenna system  200  can be actuated to provide the vehicle diagnostic data in a number of ways. For example, the vehicle  204  could be provided with a user-actuated button or switch to signal the vehicle diagnostic computer to send the vehicle diagnostic data via the antenna system  200 . Alternatively, the vehicle diagnostic computer  206  provided in the service station and the environment of  FIG. 11  can be actuated by a service station attendant to transmit an actuation signal through the transceiver  208  to the antenna system  200  to instruct the vehicle diagnostic computer to send a return signal with the vehicle diagnostic data. 
     The antenna system described herein can also be used to transmit a signal through the antenna system to a receiver located remote from the vehicle. The following paragraphs describe these various uses. 
       FIG. 12  shows a vehicle  220  parked on a driveway  222  adjacent a typical garage  224 . The garage  224  is provided with a vertically-movable garage door  226  interconnected to a garage door opener  228  shown in the broken-away portion of FIG.  12 . The garage door opener  228  can be any conventional garage door opener interconnected to the garage door  226  by a drive system  230  such as a chain, pulley, gear, screw, etc. The vehicle  220  has been provided with an antenna system  232  as previously described which is capable of sending an actuation signal to the garage door opener  228  to signal the garage door  226  to be moved to an open or a closed position via the drive system  230 . The garage door opener  228  is typically provided with a receiving antenna system  234  capable of receiving a signal from the antenna system  232  on the vehicle  220  and signaling the garage door opener  228  to move the garage door  226  in the desired direction. If more than one antenna is provided in the antenna system  232 , the antennae can be sequentially activated to increase the quality and breadth of the signal to the garage door opener  228 . 
     Preferably, the antenna system  232  of the vehicle  220  is equipped with a “learn” circuit (not shown) capable of receiving a signal from a conventional garage door opener as is well known in the art and saving the signal so that the signal can be transmitted via the antenna system  232  to the receiving antenna  234  of the garage door opener  228 . Preferably, the antenna system  232  on the vehicle  220  can thereafter be selectively actuated by a user to send the garage door opening signal to the receiving antenna  234  on the garage door opener  228  when the vehicle  220  is in sufficient proximity to the garage  224 . 
       FIG. 13  shows another use for the antenna system described herein for use in transmitting a signal to a traffic light control system  240  such as those typically provided on a pole  242  adjacent an intersection of a first street  244  and a cross street  246 . Typically, the first cross street  244  is provided with a first traffic signal  248  having red, yellow, and green signal lamps  250 ,  252 , and  254 , respectively. The second cross street  246  is typically provided with a second traffic signal  256  also w provided with red, yellow, and green signal lamps  258 ,  260 , and  262 , respectively. The significance to vehicle operators of the signal lamps  248  and  256  is well known and need not be described. The first and second traffic signal lamps  248  and  256  are interconnected by conduit  260  from each of the signal lamps  248  and  256  to the pole  242  and to the traffic control system  240 . 
     The traffic control system  240  is preferably provided with a receiving antenna  266  adapted to receive a signal from an antenna system  268  mounted to an external mirror  270  of a vehicle  272 . The antenna system  268  can preferably program to intermittently send a “presence” signal as the vehicle  272  is driven. To the extent that the receiving antenna  266  of the traffic control system  240  is located in sufficient proximity to the antenna system  268  on the vehicle  272 , the traffic control system  240  can evaluate the number of vehicles and their location relative to the traffic control system  240  on the pole  242  and make a determination of which of the red, yellow and green signal lamps to activate on the first and second traffic signal lamps  248  and  256 . 
     Thus, if the vehicle  272  were the only vehicle on the cross street  244  and no vehicles were located in sufficient proximity on the second cross street  246 , the first signal lamp  248  could have its green signal lamp  254  actuated by the traffic control system  240  and the red signal lamp  258  on the second traffic signal lamp  256  could be actuated to allow the vehicle  272  to pass unimpeded without encountering a red light. Thus, the potential for gridlock and traffic jams is reduced. Further, the traffic control system  240  could be adapted to monitor and/or transmit statistical data on the numbers of cars passing through the intersection of the first and second cross streets  244  and  246  whereby traffic could be controlled in a city or regional area on a map or scale. 
     The antenna system described herein can also be used to receive signals from a transmitting antenna. Various uses of the antenna system to receive these signals will now be described. 
       FIG. 14  shows a perspective view of a vehicle  280  provided with an antenna system  282  on an external mirror  284  as described herein located on a first cross street  286 . An emergency vehicle  288  provided with an antenna system  290  on an external U mirror  292  as described herein is located on a second cross street  294 . A pole  296  is provided which has a first cantilever arm  298  having a first traffic signal lamp  300  provided with conventional red, yellow, and green lamps  302 ,  304 , and  306 , respectively. The pole  296  also has a second cantilever arm  308  provided with a second traffic signal lamp  310  provided with conventional red, yellow, and green lamps  312 ,  314 , and  316 . The operation of these traffic signal lamps is well known. The pole  296  is also provided with a traffic control system  318  having an antenna system  320  thereon. 
     The antenna system  290  on the emergency vehicle  288  can operate in one of two ways. First, the antenna system  290  can be actuated with sirens  322  of the emergency vehicle  288  to transmit a first signal  324  to the antenna system  320  on the traffic control signal  318  to ensure that the second traffic signal  310  actuates the green signal lamp  316  so that the emergency vehicle  288  can pass unimpeded along the second cross street  294  through the intersection defined with the first cross street  286 . Simultaneous with the actuation of the green signal lamp  316  on the second traffic signal  310 , the red signal lamp  302  on the first traffic signal lamp can be actuated to signal vehicles on the first cross street such as the vehicle  280  to stop their forward progress and allow the emergency vehicle  288  to pass. The antenna system  290  on the emergency vehicle  288  can also be adapted to send a second signal  326  detectable by the antenna system  282  on the vehicle  280  that the emergency vehicle  288  is in the area and to alert the driver of the vehicle  280 . This system can be extremely beneficial if obstructing objects such as the tree  328  located adjacent the cross streets  286  and  294  obstructs the line-of-sight of the drivers of the passenger vehicle  280  and emergency vehicle  288 . Thus, accidents between passenger vehicles and emergency vehicles could be reduced by the signals sent by the cooperating antenna systems  282 ,  290 , and  320  of the passenger vehicle  280 , emergency vehicle  288  and traffic control system  318 , respectively. 
     The antenna system described herein can also be used as a receiving antenna for vehicle remote security and operation devices such as remote keyless entry (RKE) systems. The RKE systems are well known in the art as a handheld console wherein an operator of a vehicle can press certain buttons to lock and unlock the doors of the vehicle, set off a vehicle alarm or perhaps remotely actuate the ignition system of the vehicle. 
     As shown in  FIG. 15 , a vehicle  330  is shown parked on a ground surface  332 . The vehicle  330  is provided with an antenna system  334  on an external mirror  336  as described herein. A vehicle operator  338  is shown standing remote from the vehicle  330  holding an RKE device  340  capable of sending a signal  342  detectable by the antenna system  334  on the external mirror  336  to the extent that the RKE device  340  is located in sufficient proximity to the vehicle  330 . 
     The antenna system  334  can be provided with circuitry which “learns” the signal  342  to be transmitted by the RKE device  340  to perform the functions discussed above. Contrary to known RKE devices currently employed, any receiving antennas are typically located within the vehicle interior or within the vehicle frame and do not typically effectively receive the low-powered radio frequency signal of an RKE device  340 . 
     The antenna system  334  located externally with respect to the vehicle  330  such as on the external mirror  336  provides much greater detection of the signal  342  of the RKE device  340 , thus allowing the vehicle operator  338  to lock or unlock the vehicle doors, set off an alarm or actuate the vehicle ignition system from greater distances. 
     The antenna system described herein can also be used in a “bi-directional” manner, i.e., to transmit and receive signals to and from a device located remotely from a vehicle. Examples of various uses of this type are described in the following paragraphs. 
       FIG. 16  shows a vehicle  350  having an antenna system  352  on an external mirror  354  as described herein employed in connection with a parking ramp, parking lot or toll booth  356  whereby the vehicle  350  is allowed to proceed on a roadway  358  pending the entry into the gating system  356 . The gating system  356  comprises a housing  360  with a movable gate  362  between a first position whereby the gate  362  obstructs the vehicle&#39;s progress  350  along the roadway  358  and a second position shown in phantom lines in  FIG. 16  whereby the gate  362  is open and the vehicle  350  may proceed along the roadway  358 . 
     Examples of these gating systems  356  can be found in parking lots, parking ramps and toll booths and are well known in the art. The gating system  356  of  FIG. 16  has been provided with an antenna system  364  capable of receiving a signal from the antenna system  352  on the vehicle  350  to the extent that the vehicle  350  is located in sufficient proximity to the gating system  356 . The signal  366  between the antenna system  352  on the vehicle  350  and the antenna system  364  on the gating system  356  could transmit an actuation signal to instruct the gating system  356  to move the gate  362  between the open and closed positions or provide a “key card access” signal consisting of a particular identification code of an access card owned by the operator of the vehicle  350 . 
     This feature would eliminate the requirement that operator of the vehicle  350  extend his/her arm out of the vehicle  350  interior to place or slide the access card within a card reader located in prior art gating systems. Rather, the operator of the vehicle  350  could merely actuate the antenna system  352  to send the identification code contained in the access card to the antenna system  364  on the gating system  356  to alter the position of the gate  362 . The vehicle  350  could include a card reader slot (not shown) interconnected to learning circuitry whereby the operator of the vehicle  350  could selectively send the signal of a particular actuator card to the gating system  356  (e.g., if the operator of the vehicle  350  had more than one access card for various parking ramps or lots). For commercial, charge-by-the-hour or -day parking ramps, the operator of the vehicle  350  could also insert his/her credit card into the card reader slot to instruct the antenna system  352  to transmit credit card information to the antenna system  364  on the gating system  356  so that the operator of the vehicle  350  was charged for the time in the parking lot or ramp or toll both. Thus, the requirement for parking ramp or toll both attendants would be eliminated and the charges for the parking ramp, lot or toll both could be automatically charged to the credit card account of the operator of the vehicle  350 . 
     The concept described in the above paragraph with respect to a parking ramp, parking lot, or toll booth could also apply to a vehicle  370  provided with an antenna system  372  for an external mirror  374  as described above located on a roadway  376  adjacent a curb  378  having a parking meter  380  provided with an antenna system  382  as shown in FIG.  17 . Thus, as described above, the operator of the vehicle  370  could transmit credit card or handicap access information to the antenna system  382  on the parking meter  380  to have charges for the parking ramp applied to a credit card or indicate handicap access to the parking meter and avoid incurring charges on the parking meter  380 . 
       FIG. 18  shows a perspective view of a vehicle  390  travelling on a roadway  392  provided with an antenna system  394  located on a vehicle exterior mirror  396 . A cellular telephone tower  398  provided with several antenna systems  400  thereon. The antenna system  394  on the vehicle  390  is interconnected to a cellular telephone (not shown) located within the vehicle  390  whereby the antenna system  394  can transmit and receive a signal  402  to the receiving antenna system  400  on the cellular telephone tower  398 . Rather than requiring an additional or specialized antenna for the cellular telephone located within a vehicle, the antenna system  394  can be actuated when the cellular telephone within the vehicle  290  is used to allow outgoing and incoming telephone calls. Thus, the antenna system  394  can provide an antenna for the cellular telephone located within the vehicle  390  without requiring an unsightly additional antenna or an antenna of reduced effectiveness provided internally of the vehicle  390 . 
       FIG. 19  shows a vehicle  410  travelling on a roadway  412  having an antenna system  414  provided on an external mirror  416  of the vehicle  410 . A satellite  418  is shown in orbit above the vehicle  410  and preferably has an antenna system  420  interconnected to a global positioning satellite (GPS) system which is a well known system for locating an object longitudinally and latitudinally anywhere on the earth. The antenna system  414  on the vehicle  410  is preferably interconnected to a GPS device (not shown) located within the vehicle  410  whereby the antenna system  414  can transmit and receive a signal from the antenna system  420  and the satellite  418  to enable a GPS device located within the vehicle interior to display the location of the vehicle  410  without requiring additional antenna systems provided for the vehicle  410 . 
     While particular embodiments of the invention have been shown, it will be understood, of course, that the invention is not limited thereto since modifications may be made by those skilled in the art, particularly in light of the foregoing teachings. Reasonable variation and modification are possible within the scope of the foregoing disclosure of the invention without departing from the spirit of the invention.