EP0817306A2 - Antennes de véhicule - Google Patents

Antennes de véhicule Download PDF

Info

Publication number
EP0817306A2
EP0817306A2 EP97304100A EP97304100A EP0817306A2 EP 0817306 A2 EP0817306 A2 EP 0817306A2 EP 97304100 A EP97304100 A EP 97304100A EP 97304100 A EP97304100 A EP 97304100A EP 0817306 A2 EP0817306 A2 EP 0817306A2
Authority
EP
European Patent Office
Prior art keywords
vehicle
base
antenna
exterior surface
radio
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP97304100A
Other languages
German (de)
English (en)
Other versions
EP0817306A3 (fr
EP0817306B1 (fr
Inventor
Milan Cvetkovic
John Francis Kennedy
Robert Lane
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Ford Werke GmbH
Ford France SA
Ford Motor Co Ltd
Ford Motor Co
Original Assignee
Ford Werke GmbH
Ford France SA
Ford Motor Co Ltd
Ford Motor Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ford Werke GmbH, Ford France SA, Ford Motor Co Ltd, Ford Motor Co filed Critical Ford Werke GmbH
Publication of EP0817306A2 publication Critical patent/EP0817306A2/fr
Publication of EP0817306A3 publication Critical patent/EP0817306A3/fr
Application granted granted Critical
Publication of EP0817306B1 publication Critical patent/EP0817306B1/fr
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00—Details of, or arrangements associated with, antennas
    • H01Q1/27—Adaptation for use in or on movable bodies
    • H01Q1/32—Adaptation for use in or on road or rail vehicles
    • H01Q1/325—Adaptation for use in or on road or rail vehicles characterised by the location of the antenna on the vehicle
    • H01Q1/3275—Adaptation for use in or on road or rail vehicles characterised by the location of the antenna on the vehicle mounted on a horizontal surface of the vehicle, e.g. on roof, hood, trunk
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00—Details of, or arrangements associated with, antennas
    • H01Q1/12—Supports; Mounting means
    • H01Q1/1207—Supports; Mounting means for fastening a rigid aerial element
    • H01Q1/1214—Supports; Mounting means for fastening a rigid aerial element through a wall
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00—Details of, or arrangements associated with, antennas
    • H01Q1/12—Supports; Mounting means
    • H01Q1/1271—Supports; Mounting means for mounting on windscreens
    • H01Q1/1285—Supports; Mounting means for mounting on windscreens with capacitive feeding through the windscreen

Definitions

  • the invention relates to an improved radio antenna for a vehicle and in particular to a monopole antenna for a motor vehicle.
  • the majority of vehicles manufactured today are fitted with a radio antenna for reception of FM radio broadcasts.
  • the most common type of antenna is the monopole antenna. This may be placed on the front or rear wing, on the A pillar or centre line of the car roof.
  • Such antenna may consist of a fixed length rod or be telescopic.
  • the length and orientation of a monopole antenna relative to the vehicle bodywork play a critical part in determining the radio reception qualities in the FM band (87.5 - 108 MHz).
  • the complex impedance of the antenna varies as a function of antenna length (at a given frequency).
  • the antenna impedance must be matched to the input impedance of the radio to which it is connected.
  • near optimum impedance occurs when the physical length of the antenna is approximately equal to one quarter of the wavelength of the desired radio signal.
  • This type of antenna provides good sensitivity and is referred to as a quarter wave monopole, whose length is usually chosen to be a quarter wave at the centre of the band (98 MHz) which works out to be approximately 0.75 metres.
  • a quarter wave monopole antenna would be too large for the vehicle. Not only would the length of the antenna itself be unwieldy, the longer an antenna is the larger its diameter needs to be for structural support and rigidity. A large diameter may detract from the appearance of the vehicle and increase the drag coefficient and wind noise. Thus it is necessary in a number of vehicles to be able to produce an efficient monopole antenna which is shorter than a quarter wave. This is known as an electrically short antenna.
  • impedance matching network Prior art systems have been developed which use an additional electronic circuit at the output of the antenna known as an impedance matching network.
  • the purpose of such a network is to maximise the transfer of power available from the antenna to the receiver by matching the complex impedance of the antenna to the receiver input impedance. If a perfect complex conjugate impedance match between the antenna and radio can be achieved, and the matching network is loss less, then all the power available from the antenna will be transferred to the receiver. Such a system would ensure that the performance of an electrically short antenna would match that of the quarter wave monopole.
  • the matching network typically consists of a number of passive electrical components such as capacitors and inductors in a suitable circuit configuration connected to the output of the antenna. Due to the necessity to buy and then package additional electrical component, any such matching network always adds to the total cost of an electrically short antenna system.
  • a number of vehicle antennas have been proposed which include along the length of the mast, a coil which acts as an inductor, electrically in series with the antenna mast.
  • Typical antennas of this type are described in DE 3931807 and US 4462033.
  • Glass mounted antennas for mobile telephones sometimes use the glass as a capacitive coupling between the mast and the telephone.
  • the antenna mast is coupled to a metal plate which is mounted on the exterior surface of the glass, and a similar metal plate, mounted on the interior surface of the glass is connected to the telephone.
  • a capacitor can be provided by using the vehicle body as a plate of the capacitor coupled to ground.
  • CA 950978 is a non standard antenna in the form of a horizontal rod mounted spaced from the rear of the vehicle where the air between the rod and the vehicle body acts as the dielectric.
  • An antenna base which is capacitively mounted upon the body via a dielectric layer is also described in W092/10865. In this system the antenna base and coaxial cable are arranged such that the coaxial cable is capacitively coupled to ground via the dielectric layer.
  • a radio antenna for a vehicle, for mounting upon the body of the vehicle and for electrical connection to a coaxial cable coupled to the radio system of the vehicle, the antenna comprising a mast for receiving radio signals, a base for mounting upon the exterior surface of the vehicle and means for electrically coupling the base to the coaxial cable of the vehicle, the mast being mounted on the base via an electrically conductive coil spring member, one end of the mast being mounted upon and electrically connected with one end of the spring member, the other end of the spring member being mounted upon and electrically connected with the electrically conductive base, and the base including a mounting surface covered by an insulating base layer for contacting the body of the vehicle and sealing the gap between the base and the body such that when the antenna is mounted upon the vehicle the electrically conductive base does not touch and is not in direct electrical contact with the body of the vehicle, but there is a capacitive connection between the base and the vehicle body via the insulating base layer.
  • the matching network is intrinsically built into the physical structure of the antenna. No discrete electrical components are used in the design which means that the total cost of the electrically short antenna is effectively reduced while improving the radio reception capability.
  • the coil spring acts as an inductor to artificially increase the electrical length of the antenna, while at the same time providing mechanical flexibility which helps with car wash robustness and avoiding the effects of vandalism.
  • the electrically conductive base, the insulating base layer and the body of the vehicle together act as a capacitor.
  • the capacitance is obtained through the capacitive effect between the footprint of the antenna base and the body work of the vehicle separated by non-conducting material.
  • the capacitor thus formed couples the base of the inductor to ground. However there is still a direct connection between the inductor and the coaxial cable.
  • non-conducting material may comprise a non-water absorbent rubber grommet which at the same time as acting as the dielectric for the capacitor also acts as a very effective water seal.
  • the base can be a substantially solid piece of conductive material.
  • the base is die cast.
  • the insulating base material may be plastic exhibiting properties of non-compressibility and imperviousness to moisture whilst at the same time having a time invariant dielectric constant and being physically stable over the typical temperature range encountered in automotive applications.
  • the insulating base layer comprises a central plastic piece and a slightly thicker non water absorbent rubber section around the circumference of the plastic thus providing a combination of non-compressibility provided by the plastic and water seal from the rubber seal which compresses to the thickness of the plastic part.
  • the spring coil member is of steel whose characteristics have been chosen to give the required stiffness of spring and spring inductance. More preferably the steel spring is copper plated to minimise the ohmic losses of the network.
  • an inductance of approximately 290nH and capacitance of 10pF are suitable for the matching network. It has been found that a spring having 8mm diameter and 18mm long supplies the required inductance and the capacitance may be achieved using a base footprint area of 200mm 2 and a dielectric seal lmm thick whose relative permativity is approximately 2.3.
  • the means for mounting the antenna to the exterior surface of the vehicle comprises an electrically conductive screw passing through a cylindrical bore in the exterior surface and being surrounded by an insulating sleeve such that the screw is in contact with the base but insulated from the exterior panel and the insulating base layer, the head of the screw being for connecting to the coaxial cable thus supplying means to couple the base to the coaxial cable without providing a direct connection between the base and the exterior surface.
  • the screw acts as the means for coupling the base to the coaxial cable but also acts as means for mounting the base on the vehicle.
  • the antenna of the prior art is not illustrated. It comprises a roof mounted electrically short monopole antenna which is 0.48 metres long having an impedance matching network illustrated in Figure 1 packaged in the base of the antenna.
  • the matching network consists of only one component, an inductor coil 1 which is coupled between the antenna 3 and coaxial cable 5.
  • the coaxial cable 5 is coupled to the radio system of the vehicle and is also connected to earth 7.
  • the graph of figure 2 illustrates the measured data of mismatch loss versus frequency of this antenna with and without the matching network. Mismatch loss is a measurable expressed in decibels (dB) which quantifies the degradation of power transfer from the antenna into a specified load impedance (75 ohms in this case) due to differences between antenna and load impedances.
  • dB decibels
  • FIG. 4 illustrates an example of a radio antenna in accordance with the invention, while figure 3 illustrates the equivalent electric circuit.
  • the antenna 9 is for mounting upon an exterior surface 11 of the vehicle for electrical connection to a coaxial cable 13 coupled to the radio system (not shown) of the vehicle.
  • the antenna 9 comprises a mast 15 for receiving radio signals and a base 17 for mounting upon the exterior surface 11 of the vehicle. Means 19 electrically and mechanically couple the base 17 to the coaxial cable 13 of the vehicle.
  • the mast 15 is mounted upon the base 17 via an electrically conductive coil spring 21, one end 23 of the mast being mounted upon and electrically connected with one end 25 of the spring member.
  • the other end 27 of the coil spring member is mounted upon and electrically connected with the electrically conductive base 17.
  • the base 17 includes a mounting surface 29 covered by an insulating base layer 31 for contacting the exterior surface 11 of the vehicle such that when the antenna is mounted upon the vehicle as shown in figure 4 the electrically conductive base 17 is not in direct electrical contact with the exterior surface 11 of the vehicle.
  • a metallic disc 33 of the same diameter as the coil spring 21 At the end 23 of the mast 15 is a metallic disc 33 of the same diameter as the coil spring 21. At the other end 27 of the coil spring is an internally threaded metallic member 35.
  • the metal disc 33 spring 21 and metallic member 35 all sit within annular sleeve 37 which is flexible and plastic. Around this is non water absorbent rubber cover 39.
  • the internally threaded member 35 mates with threaded stud 41 which extends from base 17 and is externally screw threaded.
  • a plastic cover 43 covers the base 17. In this case the base 17 is part spherical with a semi-spherical cut-out 45. Because this is a simple solid without requiring mounting of any further electrical components the base 17 is die cast.
  • the antenna base 17 is secured to the panel 11 by screw 19 which is electrically conductive.
  • the screw 19 sits within insulating nut 47 which includes a cylindrical bore for accommodating the screw 19.
  • the screw 19 passes through bore 49 in panel 11 through the semi-spherical cut-out 45 and screws into 17.
  • the semi-spherical cut-out 45 provides tolerance for mounting the screw into the base.
  • the surface 29 of the base 17 can be seen clearly in figure 5.
  • An auxiliary connection 51 couples the panel 11 to co-axial cable 13. This provides a simple but effective antenna impedance matching network which is equivalent to that depicted in figure 3 but is built into the physical structure of the antenna avoiding the cost of using discrete electrical components. It should be noted that details of the attachment method of the antenna base to the coaxial cable are not described in detail here since they are well known and apparent to the skilled addressee of the specification.
  • Figure 6 illustrates the measured mismatch loss of this prototype antenna compared to that of the prior art in which a significant improvement can be observed.
  • the antenna described does not have its lowest point of mismatch loss exactly at mid-band position indicating that minor adjustments to the spring inductance and base capacitance may be needed. However it shows a 2.55 to 2.0DB improvement over the bottom half of the FM band (87.5-98 MHz) and 2.0 to 0.75 dB improvement over the top half of the FM band (98-108 MHz). At the point of minimum mismatch loss shows a 2.3 dB improvement over the current antenna design. Mismatch loss reduction is not the only benefit offered in terms of perceived radio reception quality.
  • a further parameter associated with reception quality is audio signal to noise ratio (S/N) at the output of the radio and figure 6shows a typical graph of FM tuner audio S/N versus radio frequency RF input level.
  • the graph has two sections. The first section of the graph has a slope of 3.5 while the second section has a slope of 1.
  • the point of inflexion is known as the FM threshold point which occurs when the carrier to noise ratio of the FM signal reaches about 10, a condition which typically occurs at about 99 dBm or 2.42 uV RF signal level. Below threshold there is a rapid rise in audio signal to noise ratio as the radio frequency level increases.
  • the rate of signal to noise improvement is approximately 3.5 dB for every 1 dB increase in RF signal level.
  • the rate of signal to noise improvement reduces to 1 dB for every 1 dB increase in RF signal level.
  • the graph indicates that under weak signal conditions (below threshold and typically in the signal range 1-2.5 uV) the correct impedance matching between satisfaction and can represent the difference between an antenna and radio is of critical importance to ensure higher audio signal to noise ratios and hence better reception quality. For every dB of mismatch loss improvement one can expect an increase of 3.5 dB in audio signal to noise. Comparing the current antenna to the prior art the invention enables the following audio S/N improvement to be achieved over 1-2.5 uV RF input level range: 8.7-7 dB improvement over bottom half of the FM band 7-2.6 dB improvement over top half of the FM band.
  • the signal to noise improvement can contribute a significant amount to customer unlistenable and acceptable radio signal.
  • Other benefits of improved impedance matching at stronger signal levels are that the effects of multipath nulls which manifest themselves as audio spits are reduced since the radio is capable of recovering more of the signal out of the nulls.
  • the physical characteristics of the spring and the antenna base can be chosen to give the required inductance and capacitance or the antenna impedance matching circuit and also the required mechanical properties of the antenna.

Landscapes

  • Engineering & Computer Science (AREA)
  • Remote Sensing (AREA)
  • Details Of Aerials (AREA)
  • Support Of Aerials (AREA)
EP19970304100 1996-06-19 1997-06-12 Antennes de véhicule Expired - Lifetime EP0817306B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GBGB9612826.9A GB9612826D0 (en) 1996-06-19 1996-06-19 Improved vehicular radio antennas
GB9612826 1996-06-19

Publications (3)

Publication Number Publication Date
EP0817306A2 true EP0817306A2 (fr) 1998-01-07
EP0817306A3 EP0817306A3 (fr) 1999-04-28
EP0817306B1 EP0817306B1 (fr) 2004-09-29

Family

ID=10795550

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19970304100 Expired - Lifetime EP0817306B1 (fr) 1996-06-19 1997-06-12 Antennes de véhicule

Country Status (3)

Country Link
EP (1) EP0817306B1 (fr)
DE (1) DE69730908D1 (fr)
GB (1) GB9612826D0 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102004011662A1 (de) * 2004-03-10 2005-10-13 Daimlerchrysler Ag Antennenbefestigungsanordnung
US7193572B2 (en) 2002-05-16 2007-03-20 Kathrein-Werke Kg Roof antenna for motor vehicles
WO2009016076A1 (fr) * 2007-07-30 2009-02-05 Advanced Automotive Antennas, S.L. Système d'adaptation d'antenne pour des véhicules à moteur
CN102694239A (zh) * 2012-05-30 2012-09-26 泰兴市迅达通讯器材有限公司 一种双频全向天线

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4058811A (en) * 1976-03-22 1977-11-15 Motorola, Inc. Encapsulated base for whip antenna
US4184160A (en) * 1978-03-15 1980-01-15 Affronti Victor A Antenna roof mount for vehicles
US4794319A (en) * 1986-07-03 1988-12-27 Alliance Research Corporation Glass mounted antenna
US4825217A (en) * 1987-10-19 1989-04-25 Tae Lim Electronics Co., Ltd. Car phone antenna assembly
WO1992010865A1 (fr) * 1990-12-05 1992-06-25 Les Wallen Manufacturing Limited Bases d'antenne isolees

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4058811A (en) * 1976-03-22 1977-11-15 Motorola, Inc. Encapsulated base for whip antenna
US4184160A (en) * 1978-03-15 1980-01-15 Affronti Victor A Antenna roof mount for vehicles
US4794319A (en) * 1986-07-03 1988-12-27 Alliance Research Corporation Glass mounted antenna
US4825217A (en) * 1987-10-19 1989-04-25 Tae Lim Electronics Co., Ltd. Car phone antenna assembly
WO1992010865A1 (fr) * 1990-12-05 1992-06-25 Les Wallen Manufacturing Limited Bases d'antenne isolees

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7193572B2 (en) 2002-05-16 2007-03-20 Kathrein-Werke Kg Roof antenna for motor vehicles
DE102004011662A1 (de) * 2004-03-10 2005-10-13 Daimlerchrysler Ag Antennenbefestigungsanordnung
DE102004011662B4 (de) * 2004-03-10 2006-04-20 Daimlerchrysler Ag Antennenbefestigungsanordnung
WO2009016076A1 (fr) * 2007-07-30 2009-02-05 Advanced Automotive Antennas, S.L. Système d'adaptation d'antenne pour des véhicules à moteur
EP2026473A1 (fr) * 2007-07-30 2009-02-18 Advanced Automotive Antennas, S.L. Antenne avec système de correspondance d'impédance pour véhicules automobiles
CN102694239A (zh) * 2012-05-30 2012-09-26 泰兴市迅达通讯器材有限公司 一种双频全向天线

Also Published As

Publication number Publication date
EP0817306A3 (fr) 1999-04-28
EP0817306B1 (fr) 2004-09-29
GB9612826D0 (en) 1996-08-21
DE69730908D1 (de) 2004-11-04

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