Patent Document

BACKGROUND  
       [0001]     Typically, mobile tracking and messaging antennas for mobile tracking and messaging systems, such as that used with Qualcomm Incorporated&#39;s OmniTRACS® system, are housed within a radome. A radome is an enclosed housing, usually made of a low-loss dielectric material that serves to protect antennas mounted on ground-based vehicles, ships, airplanes and the like without significantly altering the electrical performance of the enclosed antennas.  
         [0002]     Transit buses and heavy industrial equipment having tracking and messaging systems are well suited for use with radomes. The dielectric material of the radome is usually made of a plastic material having a thickness on the order of the wavelength associated with an antenna used therewith.  
         [0003]     Mobile tracking of equipment, such as industrial vehicles, can involve the Global Positioning System (GPS) which can be used to track vehicles using a number of low earth orbiting satellites.  
         [0004]      FIG. 1  illustrates a three-dimensional perspective view of a prior art messaging and tracking antenna setup, including an antenna assembly, referenced herein as antenna communications unit (ACU)  2 . ACU  2  in conjunction with circuitry, not shown, is a mobile transceiver. The ACU, when in installed in vehicles, such as trucks, allows two-way communication between drivers and logistic centers. GPS patch antenna  4 , mounted to ground plane  5 , provides reception of GPS signals which, for instance, allow truck systems controllers to know the location of a truck and its cargo. Patch antenna  4  and ground plane  5  are disposed on cast aluminum base  6  covered by radome  8 . Base  6  of ACU  2  can be mounted to a vehicle (e.g., tractor cab). Radome  8  can be attached to base  6  preferably a using v-clamp. Rotating messaging antenna  10  which is well-suited for digital communications involving geostationary satellites, particularly involving code division multiple access (CDMA), is rotatable on pedestal  11  about axis  12  through radome  8  in a plane between peak  14  of radome  8  and base  6 . Antenna  10  of  FIG. 2  is illustrated as a horn antenna. A system of this type can, for example, use an uplink (transmit) frequency band of 14.0-14.5 GHz while the downlink (receive) frequencies range from 11.7-12.2 GHz. In an effort to improve satellite communications, antenna  10  rotates toward a satellite in connection with communication therewith.  
         [0005]     While the messaging antenna is capable of movement to increase transmission and reception signal strength, the GPS antenna is stationary. In order to optimize GPS performance, it is desirable to locate the GPS antenna in clear line of sight to the GPS satellite constellation.  
         [0006]     A method and apparatus for improving the GPS satellite reception is needed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  illustrates a three-dimensional perspective view of a prior art messaging and tracking antenna setup, which forms antenna communications unit (ACU).  
         [0008]      FIG. 2  presents a three-dimensional perspective view of a patch antenna connected to a radome. 
     
    
       [0009]     Applicable reference numerals have been carried forward.  
       DETAILED DESCRIPTION  
       [0010]     In order to improve GPS satellite reception, in one embodiment, the GPS antenna is moved from the base of the ACU as shown in  FIG. 1  to being attached to the radome itself as shown in  FIG. 2 .  FIG. 2  presents a three-dimensional perspective view of patch antenna  4  connected to radome  8 . The radome is preferably fabricated using a method of thermoforming. Thermoforming is a manufacturing process which transforms a thin thermoplastic sheet or film into a formed component. In one method of thermoforming, a sheet or film is heated between infrared heaters to its forming temperature and then is stretched over a temperature-controlled, single-surface metal mold. The sheet or film is held against the mold until it cools.  
         [0011]     With reference still to  FIG. 2 , GPS patch antenna  4  lies within thermoformed antenna cup  16  which is adhered to radome  8  by adhesive ring  20 . Circular shaped ground plane  17  is adhered to cup  16  by a second adhesive ring (not shown). A soldered connection  14  of predetermined length joins ground plane  17  to patch antenna  4 . The length of connection  14  has bearing on the gain associated with antenna  4 . GPS coaxial antenna cable  22  is connected to ground plane  17  and is adhered to and along a wall of radome  8  enclosing, among other things, patch antenna  4  and rotating messaging antenna  10 . Cable  22  is connected at another end to circuitry  21  within the transceiver formed by ACU  2 . In one aspect, radome  8  is preferably constructed from a thin polycarbonate. However, the thin-walled thermoformed radome is not conducive toward allowing radome attachment of cup  16  and cable  22  by way of rivet, other conventional threaded fasteners (e.g., screws) or other commonly available measures since the thermoplastic can easily crack in connection with such measures, thus creating a moisture ingress path from the region of penetration. This is particularly deleterious to ACU  2  since base  6  and radome  8 , in one aspect, are sealed to help isolate ACU  2  from the surrounding environment. In experimental tests, ultrasonic weld and solvent bond methods of adhesion of cup  16  to radome  8  proved unacceptable, causing radome  8  to become embrittled. Adhesion of cup  16  and cable  22  using 3M™ VHB™ 5952 pressure sensitive adhesive tape obviated any need for screws, rivets, and silicones.  
         [0012]     One challenge in implementing the attachment of cable  22  and cup  16 , containing patch antenna  4 , to radome  8  lie in identifying a robust mount that would be able to withstand years of fatigue in an outdoor mobile application while potentially being exposed to the Earth&#39;s most extreme climates. ACU  2  is frequently deployed in harsh, inhospitable regions of the world and as such, it must operate reliably when exposed to diverse climatic conditions offered by high humidity scenarios encountered in the Amazon River basin, extreme heat typical of desserts in the American southwest and rugged terrain and winter temperatures reaching −40° C. in northern Alaska. The method of attachment would be subjected to rapid excursions in temperature, extended exposure to hot and cold extremes, and high impact stress at severe cold temperatures. Preferably, the bonding agent used for adherence would have low water absorption properties and demonstrate a high degree of radio frequency (RF) transparency over a range of frequencies.  
         [0013]     After much experimental testing, adhesion to radome  8  was obtained using a double-sided adhesive tape. It was determined that commercially available 3M™ VHB™ 5952 tape was best suited to adhere cup  16 , containing patch antenna  4 , and GPS antenna cable  22  to radome  8 . 3M™ VHB™ 5952 is a very high bond, double-sided acrylic foam tape. As illustrated in  FIG. 2 , two strips of tape  24  are applied to adhere cable  22  to the enclosing wall of radome  8 . As shown, cable  22  is captured under a strap fastened to radome  8  with two ends of tape  24 . Tape  24  is deformable so as to securely affix cable  22  to the surface of radome  8  through the foam surface. Adhesive ring  20  is a double-sided adhesive used to secure cup  16  on one side and radome  8  on the other, made from 3M™ VHB™ 5952 tape in a preferred embodiment. A smaller adhesive ring (not shown) is likewise a double-sided adhesive ring made from 3M™ VHB™ 5952 tape which secures ground plane  17  to cup  16 .  
       EXAMPLES  
       [0014]     The high performance tape holding the GPS antenna cup to the radome was required to demonstrate durability under a number of stringent tests. A primary goal of this testing was to observe the stress responses of the tape in order to maintain its suitability and long-term reliability in the radome mounted GPS application.  
         [0015]     Thermal shock tests were performed to determine the ability of the high performance tape to withstand sudden changes in temperature. Specifically, vibration tests were conducted to demonstrate the capacity of the tape to withstand the dynamic stress typically encountered in a usage environment. Vibration tests over hot and cold temperatures were also performed to demonstrate the ability of the tape to survive under conditions most likely to cause tensile or shear failures.  
         [0016]     Heavy impact tests were done to meet limited market requirements contemplated for customers concerned with vandalism. Further, aggressive side impact tests were performed to assure that a low-hanging tree branch striking the side of the radome would not result in adhesion failure.  
         [0017]     The present embodiments are further illustrated by the following examples demonstrating the testing undergone by the foregoing described adhesive tape in which the tape held its bond during such testing. It was determined that an improved bond could be obtained using an adhesion promoter during adhesion of cup  16  and cable  22  to radome  8 . Further, thermal shock testing demonstrated improved results by increasing the surface area of the affixed tape.  
         [0018]     Accumulated Stress Test  
         [0019]     Fifteen thermal shock cycles in an air-to-air thermal shock chamber (−50° C. to +85° C.) followed by 9 hr 5.2 (root mean squared) RMS random vibe (10-1000 Hz) and a quantity of 54, 20 G amplitude bump shocks (half sine, 11 ms).  
         [0020]     Simultaneous Temperature and Vibration  
         [0021]     Cold random vibration (1 hr. 5.2 gRMS, 10-1000 Hz) performed in the vertical axis while ACUs were held at 50° C. (worst case condition due to reduced tensile strength of the tape at cold temperature). Hot vibration (1 hr, 5.2 gRMS, 10-1000 Hz) performed in the horizontal axis while ACUs were held at +85° C. (worst case condition due to reduced tape shear strength at high temperature).  
         [0022]     Temperature-Humidity Cycling  
         [0023]     −40° C. to +70° C. and 90% relative humidity (RH), 8 hr cycle, 17 day duration.  
         [0024]     Storage Temperature Cycling  
         [0025]     −50° C. to +85° C., 8 hr cycle, 17 day duration.  
         [0026]     Ambient Top-Down Impact  
         [0027]     Three strikes from a 20 oz mass hitting the radome at an impact speed of 28 mph.  
         [0028]     Cold Top-Down Impact  
         [0029]     Three radome strikes from a 20 oz mass dropped 12 in. (free-fall) while ACU is cold (−50°).  
         [0030]     Ambient Side Impact  
         [0031]     One strike from a spring-loaded bar hitting the radome at an impact speed of 25 mph.  
         [0032]     Cold Side Impact  
         [0033]     One strike from a spring-loaded bar hitting the radome at an impact speed of 25 mp while the ACU is cold (50° C.).  
         [0034]     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. For example, messaging antenna  10  of  FIG. 2  can represent a phased array antenna. Further, although, described herein with reference to a transceiver, the foregoing embodiments can be modified to operate with solely a receiver or solely a transmitter. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.

Technology Category: 5