Flexible vehicle antenna

An antenna adapted to be mounted to a motor vehicle for receiving digital audio signals from a satellite. The antenna includes a base configured to be secured to a vehicle, and an elongated mast constructed of a polymer material and including at least one antenna-forming conductor extending along the mast to receive signals. A spring member flexibly connects the elongated mast to the base, and an elastomeric cover extends between the base and the elongated mast and envelops the spring member. A flexible conductor is connected to the antenna-forming conductor and extends through the elastomeric cover.

TECHNICAL FIELD
 The present invention relates to an antenna that is suitable for mounting
 on a mobile vehicle, such as an automobile, truck, or other motor vehicle.
 BACKGROUND OF THE INVENTION
 Various antennas for mounting to motor vehicles have been developed. For
 example, "whip-type" antennas having a flexible fiberglass or Teflon rod
 with a helically-wound conductor for receiving radio signals have been
 developed. Mobile vehicle antennas often employ a flexible mounting base
 to allow for impact with an object. For example, U.S. Pat. No. 4,393,383
 to Yamashita discloses a spring-mounted antenna including a coaxial cable
 and a flexible body portion surrounding the coaxial cable. Also, global
 positioning satellite (GPS) navigators having quadrifilar helical antennas
 have been developed. For example, U.S. Pat. No. 5,198,831 discloses a GPS
 navigator that may be vehicle mounted, and includes a tubular, quadrifilar
 antenna structure. Further, various window mounted or film type antennas
 for vehicles have been developed. Examples of such antennas are disclosed
 in U.S. Pat. Nos. 5,739,794; 5,714,959; 5,648,785; 5,610,619; and
 5,528,314.
 SUMMARY OF THE INVENTION
 One aspect of the present invention is an antenna adapted to be mounted to
 a motor vehicle for receiving digital audio signals from a satellite. The
 antenna includes a base configured to be secured to a vehicle, and an
 elongated mast constructed of a polymer material and including at least
 one antenna-forming conductor extending along the mast to receive signals.
 A spring member flexibly connects the elongated mast to the base, and an
 elastomeric cover extends between the base and the elongated mast and
 envelops the spring member. A flexible conductor is connected to the
 antenna-forming conductor and extends through the elastomeric cover.
 Another aspect of the present invention is an antenna for receiving digital
 signals from a satellite. The antenna includes a base configured to be
 secured to a motor vehicle. An elongated mast constructed of a dielectric
 material has a generally cylindrical outer surface, and defines a base
 end. Four elongated antenna conductors are disposed on the outer surface
 of the elongated mast and form a quadrifilar helical antenna. Each antenna
 conductors has an electrical feed point adjacent the base end of the
 elongated mast. The feed points are progressively phased by about ninety
 degrees relative to one another. A flexible member connects the elongated
 mast to the base and biases the mast into a use position. The antenna
 further includes a flexible elongated conductor and a phase network
 positioned adjacent the base end of the mast and electrically connecting
 the electrical feed points of the elongated antenna conductors to the
 flexible cable.
 Yet another aspect of the present invention is an antenna for mounting on a
 motor vehicle for receiving digital signals from a satellite. The antenna
 includes a base having an electronics case with a cavity adapted to
 receive electronic components therein. The electronics case has an inner
 shell made of a rigid material forming the cavity, and an outer cover of
 an elastomeric material enveloping the inner shell and forming a gasket
 configured to seal the cavity when the electronics case is mounted to a
 vehicle. An elongated mast is secured to the base, and at least one
 elongated antenna conductor extends along the mast to receive signals.
 These and other features, advantages and objects of the present invention
 will be further understood and appreciated by those skilled in the art by
 reference to the following specification, claims and appended drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 For purposes of description herein, the terms "upper," "lower," "right,"
 "left," "rear," "front," "vertical," "horizontal," and derivatives thereof
 shall relate to the invention as oriented in FIG. 1. However, it is to be
 understood that the invention may assume various alternative orientations
 and step sequences, except where expressly specified to the contrary. It
 is also to be understood that the specific devices and processes
 illustrated in the attached drawings and described in the following
 specification are simply exemplary embodiments of the inventive concepts
 defined in the appended claims. Hence, specific dimensions and other
 physical characteristics relating to the embodiments disclosed herein are
 not to be considered as limiting, unless the claims expressly state
 otherwise.
 Referring to FIG. 1, an antenna 1 is illustrated according to the present
 invention. Antenna 1 is adapted to be mounted to a motor vehicle 2 for
 receiving digital audio signals from one or more remote transmitters, such
 as a satellite or land-based transmitters. Antenna 1 includes a base 3
 configured to be secured to the vehicle 2. An elongated mast 4 is
 constructed of a polymer material, and includes at least one
 antenna-forming conductor 5 extending along the mast to receive signals. A
 flexible member, such as a coil spring 6 flexibly connects the elongated
 mast 4 to the base 3, and an elastomeric cover 7 extends between the base
 3 and the elongated mast 4 and envelops the coil spring 6. A flexible
 conductor such as coaxial cable 8 is connected to the antenna-forming
 conductor 5, and extends through the coil spring 6 and elastomeric cover
 7.
 Mast 4 is molded from a polymer material, such as VALOX.RTM. thermoplastic
 resin, available from General Electric Company, and has a generally
 tubular construction. A MYLAR.RTM. film 9 includes four copper traces
 forming four conductors 5 to form a quadrifilar antenna element 10 that is
 positioned within the tubular mast 4 (see also FIG. 6). The substrate/film
 9 with copper traces 5 is wrapped around and bonded to the mast 4 with
 traces 5 forming a spiral around mast 4. Each trace extends at angle "A"
 of about 65 degrees in a preferred embodiment. According to one example,
 mast 4 has a diameter of 9.5 mm, and the quadrifilar antenna element 10
 has an overall length A of 120.7mm. The four conductors 5 form four
 electrical feed points 11. A phase network 12 is electrically connected to
 the feed points 11, and combines the four feed points into one antenna
 input that is connected to the coaxial cable 8. As described in more
 detail below, phase network 12 is formed on the substrate film 9 in the
 same manner as traces 5. The phase network 12 could be a microstrip phase
 circuit, a discrete hybrid coupler network, or other phase network. The
 phase network 12 is soldered or otherwise electrically connected to the
 coaxial cable 8, thereby allowing connection to the electronics in the
 case 20.
 Coil spring 6 is secured to the lower end 13 of mast 4, and flexibly mounts
 the antenna to the mounting member 15. Mounting member 15, like mast 4, is
 also preferably made of a VALOX.RTM. polymer material. Coaxial cable 8
 extends through coil spring 6, and elastomeric cover 7 is molded over the
 spring 6 to provide flexibility to allow the mast 4 to deflect in the
 event of impact with a foreign object. Cover 7 is preferably made of a
 SANTOPRENE.RTM. thermoplastic elastomer, or other suitable flexible
 material. An elastomeric seal 16 may extend around mounting member 15 to
 provide a seal against a cover 17. Cover 17 includes a threaded opening
 that receives threaded end 18 of mounting member 15. Coaxial cable 8 is
 connected to the phase network 12, and extends through the coil spring 6,
 and mounting member 15. An SMB or other RF connector connects to a circuit
 board 22 in electronics case 20.
 With further reference to FIGS. 3 and 4, electronics case 20 includes a
 hard inner shell 23 formed of a zinc diecast or other suitable material.
 The conductive shell 23 ensures that the antenna components are shielded
 from feedback. An elastomeric outer shell 24 extends over the hard inner
 shell 23, and forms a gasket surface 25 that seals against an outer
 surface 26 of a motor vehicle 2. An extension 27 of inner shell 23 extends
 downwardly through an opening 30 in the outer layer 29 of motor vehicle 2,
 and a second SMB connector 28 extends through the extension 27, and
 connects to the circuit board 22. Electronics case 20 forms a cavity 31
 for receiving electronics components, including circuit board 22. A
 recessed edge 32 extends around the perimeter 33 of cavity 31, and circuit
 board 22 rests on edge 32 when installed. A plurality of fasteners or
 other suitable fasteners 34 or other suitable connectors are utilized to
 secure cover 17 to the electronics case 20. Cover 17 has a smooth, shallow
 dome-like shape, with a perimeter 35 that fits closely against the surface
 26 of the vehicle 2 to provide a smooth, unobtrusive appearance. Cover 17
 may be designed to conform to the surface shape of various vehicles, such
 that antenna 1 can be readily mounted to the roof or other location on a
 variety of vehicles by utilizing a cover 17 conforming to the surface
 contour of a particular vehicle.
 With reference to FIG. 5, copper antenna traces 5 and the phase network 12
 are formed on a thin flexible substrate 9. The overall length "L" of the
 substrate 9 is 251.3 mm, and the antenna section 39 of the substrate 9 has
 a width "W" of 27.3 mm. The rectangular circuit portion 38 of the
 substrate 9 forms a centerline "C" that extends at an angle "B" of 25
 degrees relative to the antenna traces 5. When assembled, centerline C
 extends parallel to the centerline of mast 4. In a preferred embodiment,
 traces 5 have a width of 2.5 mm, and the substrate is Mylar, Kapton or
 other flexible material. The phase network 12 includes a plurality of
 delay lines 40 that provide input for the coaxial cable 8. Such phase
 networks are generally known, and an example is illustrated in U.S. Pat.
 No. 5,198,831 entitled "Personal Positioning Satellite Navigator With
 Printed Quadrifilar Helical Antenna" to Burrell et al. Although the
 Burrell '831 phase circuit has a generally similar construction, the phase
 circuit 12 of the present invention is designed to process satellite
 signals in the 2.3-2.4 GHz range. The phase network 12 feeds into a
 tab-like connector 41 that is configured to connect to a R6316 cable. When
 assembled, connector 41 extends into the cavity 43 (FIG. 6) of mast 4.
 During assembly, the elongated portion 39 of substrate/film 9 with traces
 5 is rolled to form a tube. The tubular mast 4 is then molded over the
 tubular film 9. Because the circuit board 22 and related electronics are
 remote from the mast 4, mast 4 can be constructed with a relatively small
 outer diameter, thus providing a compact antenna suitable for use with
 automobiles, trucks, and the like.
 A second embodiment 101 of the antenna is illustrated in FIG. 7. Antenna
 assembly 101 is similar to antenna 1 described above in FIGS. 1-6. Mast
 104 includes a quadrifilar antenna element 10 formed on a flexible
 substrate 9, phase network 12, coil spring 6 and flexible cover 7 that are
 substantially identical as described above in connection with FIGS. 1-5.
 However, antenna assembly 101 includes an SMB or other RF connector 121
 that is secured to the base portion 145 of mast 104. A coaxial jumper
 cable assembly 147 is assembled with the cover 117 with the upper
 connector 148 positioned within the threaded protrusion 146 of cover 117.
 Connector 148 provides a waterproof seal to prevent entry of moisture. The
 base 103 may be assembled and secured to a motor vehicle, such that the
 mast assembly 104 can be installed or removed by threading the mast 104
 onto the threaded protrusion 146. The SMB connector 121 simultaneously
 threads onto the connector 148, thereby facilitating installation/removal
 of mast 104 from base 103. This arrangement permits the mast 104 to be
 easily removed, for example, for shifting of the motor vehicle.
 Base assembly 103 includes a circuit board 122 and electronics case 120.
 When assembled, the connector 149 of cable 147 is connected to the circuit
 board 122. Electronics case 120 is similar to electronics case 20
 described above. However, electronics case 120 does not include an
 elastomeric outer shell. Rather, a first gasket 150 is sandwiched between
 the upper surface 153 of electronics case 120 and inner surface 154 of
 cover 117 to ensure that the circuit board 122 is sealed off rain, dust,
 or other such elements. Threaded screws 152 are utilized to secure the
 electronics case 120 to the cover 117 and compress gasket 150. Electronics
 case 120 includes a downwardly extending threaded extension 157 that
 extends through an opening in the surface layer 26 of the motor vehicle
 when assembled. A threaded nut 155 and sleeve 156 are received on the
 threaded extension 157, and draw the electronics case 120 and cover 117
 downwardly against a second gasket 151 that is thereby sandwiched between
 the cover 117 and the surface layer 26 of the motor vehicle. Threaded
 extension 157 includes a passageway for routing of cable 159. Cable
 assembly 159 includes a connector 160 that is connected to the circuit
 board 122, with the end portion 161 of cable assembly 159 extending
 through the threaded nut 155, sleeve 156, gasket 151, and the threaded
 extension 157.
 The present antenna provides a quadrifilar antenna element configured to
 receive a digital audio signal transmittal from a satellite or other
 remote location. Advantageously, the antenna mast may be removed for
 shipping of the vehicle. Further, the flexible mount reduces the
 likelihood of damage if the antenna strikes, for example, overhead
 structures in parking garages or the like. The phase network provides a
 connection to the coaxial cable, with the coaxial cable providing a
 flexible conductor. The elastomeric cover 7 extends over the coil spring 6
 to provide a smooth, uncluttered appearance. The electronics case
 arrangement and cover provide a waterproof seal for the electronic
 components, while permitting the antenna to be readily mounted to various
 vehicles having different surface contours. A base cover having the proper
 shape for mounting to a particular vehicle may be utilized to mount the
 mast assembly to a variety of different vehicles. Further, if required the
 antenna 1 can be easily unscrewed from the base to prevent damage, such as
 during shipping of the motor vehicle.
 It will be understood by those who practice the invention and those skilled
 in the art, that various modifications and improvements may be made to the
 invention without departing from the spirit of the disclosed concept. The
 scope of protection afforded is to be determined by the claims and by the
 breadth of interpretation allowed by law.