ANTENNA DEVICE HAVING MAGNETIC FASTENING MEANS AND GROUND COUPLING MEANS CAPABLE OF OPERATING AT MULTIPLE FREQUENCIES

Abstract: An antenna device for microwave radio communication comprising feed connection means (5) having a hot conductor and a ground conductor for connecting said device to a radio transceiver, magnetic fastening means (25) having first and second opposed sides for fastening at its first side the device to a steel body to be acting as a ground plane means, conductive ground coupling means connected to the ground conductor, radiator means (16-20) including a helical filter means (19) and connected to the hot conductor. The ground coupling means including said magnetic fastening means (25) and a metal member (23) adjacent to the second side of the magnetic fastening means (25), wherein the metal member (23) and the magnetic fastening means (25) being arranged so as to provide radio frequency contact to the steel body to be acting as a ground plane.

Description: ANTENNA DEVICE HAVING MAGNETIC FASTENING MEANS AND GROUND COUPLING MEANS CAPABLE OF OPERATING AT MULTIPLE FREQUENCIES Field of the invention The invention relates to an antenna device for micro wave radio communication comprising feed connection means having a hot conductor and a ground conductor for connecting said device to a radio transceiver, magnetic fastening means having first and second opposed sides for fastening at its first side said device to a steel body to be acting as a ground plane means conductive ground coupling means connected to said ground conductor, radiator means connected to said hot conductor . Related prior art Antenna devices have been marketed and sold by the applicant in a single band version under Order No. 1140.3 form the prior art closest to the invention. However, those antenna devices fail to provide a desired dual band operability and include a relatively complicated and environmentally sensitive arrangement of a base portion. Summary of the invention In view of the above, the main object of the invention to provide an improved durable and cost-effective antenna device, in particular including magnetic fastening means and being operative at two frequency bands. This object is attained by device of the appended claims. The dependent claims recite various enhancements of the invention in attaining above mentioned objects. Several different types of ground structures may be employed alternatively in the invention, as will be evident from the detailed description below. Brief description of the drawings It should be noted that the drawings are not necessarily drawn to exact shape, scale and proportions, but are intended to provide and facilitate understanding of the invention in order for a skilled person to apply the invention. The sole figure of the drawing shows the in a partially sectional view a preferred embodiment of an antenna device according to the invention and a ground plane to which it is to be fastened. The antenna means is generally rotationally symmetrical in relation to a longitudinal axis, except in an arrangement for entering a cable into the device. Description of preferred embodiments With reference to the figure, the depicted antenna device has a base portion 1 and a radiator portion 2. The antenna device in the disclosed embodiment is intended to serve as an auxiliary antenna for a hand portable mobile telephone (not shown) when traveling in an automobile having a body including a steel panel 3 acting as a ground plane. The steel panel generally includes an external protective layer 4, such as paint. In such use the mobile telephone is connected via a coaxial cable 5, shown partially, to the inventive antenna device . The base portion 1 and the radiator portion 2 are to be interlocked by threaded means 6 and 7 of the respective portions 1 and 2 so that surfaces 8 and 9 abut each other. Further, surface 10 of the base portion 1 is to abut the steel panel 3. In operation the base portion 1 thus erects the radiator portion 2 generally perpendicularly of the steel panel 3 externally of the automobile body. An automobile roof is preferred as the ground plane, but various other ground plane means are possible to use. The base portion 1 includes a first non-conductive housing 11 that hermetically seals an internal cavity 12 formed therein. Specifically, it is preferred for durability reasons that the housing 11 forms integrally the surface 10 that is to physically contact the steel panel 3. The base portion 3 further includes a cable aperture 13 and a radiator aperture 14. The cable 5 being entered fixedly through the cable aperture, a center conductor 15 of the cable 5 is connected to a first lower rod radiator portion 16. The portion 16 is further connected to a second lower rod radiator portion 17. The portion 17 is further connected to a third lower rod radiator portion 18. The portion 18 is further connected to a helix radiator portion 19. The portion 19 is further connected to an upper rod radiator portion 20. The portions 17 - 20 are enclosed in a second non-conductive housing 21. An outer conductor 22 of the cable 5 is contacted and held fixedly by a generally circular fastening steel plate 23 by means of fastening tab means 24 formed integrally in the plate 23. The tab means 24 holds and contacts the outer conductor 22 by pressure achieved through deformation or, possibly, soldering is used. The plate 23 is arranged in parallel to the surface 10. Between the plate 23 and the surface 10 there is provided a disk magnet 25 that is to fasten the antenna means to the steel panel 3 by means of magnetic attraction. Also, the plate 23 is held closely to the magnet disk 25 by means of magnetic attraction. Thus, the outer conductor 22 is coupled conductively and capacitively to the steel panel 3. The preferred antenna device operate at frequencies in the order of 1 MHz. Consequently a sufficient coupling between the outer conductor 22 and the steel panel 3 is achievable by only a few square centimeters of capacitor area of the plate 23 and the magnet 25. The antenna means is intended for operation within a lower and an upper, or more, relatively widely separated frequency bands, for example, frequency bands about 900 and 1800 MHz, respectively. Such dual band operation is achieved in the invention by means of a distributed parallel resonance circuit formed by the helix radiator portion 19. The portion 19 essentially passes signals in the lower frequency band and blocks those of the upper frequency band. The function of portion 19 is achieved by selecting appropriate axial length, winding diameter, thread thickness, and pitch thereof such that capacitances between the helix turns provide cut off at the upper band. It is essential to the dual band operation of the antenna to select the helix pitch and thread diameter, such that the pitch is essentially equal to or greater than the thread diameter, in order to cope with variations in manufacturing and possible deformation of the portion 19 due to physical impact. At the lower band, the portions 16 - 20 provide the combined radiator, while, at the upper band, the portions 16 - 18 and a fraction of portion 19 only provide the combined antenna function. Thus, a blocking filter function of the upper band is achieved by means of the helix. Tests and simulations have shown that an antenna constructed in accordance with the one depicted in the drawings performs well in dual band operation, in the GSM 900 MHz and DCS 1800 MHz systems, having the following dimensions: 0.5 mm diameter of thread in portions 18, 19, 20; 39.5 mm total length of portions 16, 17, 18; 3 mm outer diameter, 1 mm pitch and 13.5 turns of helix portion 19. The magnet disc 25, the plate 23, and surface 10 are designed to provide a sufficient attraction and friction force when the antenna device is mounted on an automobile roof. It is to be understood that the inventive concept and scope of the invention are defined by the appended claims only.

Claims: Claims 1. Ground plane dependent antenna device for micro wave radio communication comprising: - feed connection means having a hot conductor and a ground conductor for connecting said device to a radio transceiver, - magnetic fastening means having first and second opposed sides for fastening at its first side said device to a steel body to be acting as a ground plane means, - conductive ground coupling means connected to said ground conductor, - radiator means connected to said hot conductor, - said ground coupling means including said magnetic fastening means and a metal member adjacent to said second side of said magnetic fastening means, - said metal member and said magnetic fastening means being arranged so as to provide radio frequency contact to the steel body to be acting as a ground plane, characterized by - a housing forming integrally a surface that is to physically contact said ground plane means, said housing thereby providing a hermetic enclosure of said magnetic fastening means . 2. Device of claim 1, wherein - said metal member alone and in one piece provides RF contact between said outer conductor and said magnetic fastening means, 3. Device of any preceding claim, wherein - said feed connection means includes a coaxial cable having an inner conductor and an outer conductor forming said hot and ground conductors, respectively, - said metal member is conductively connected to said outer conductor. 4. Device of any preceding claim, wherein - said metal member includes a deformed portion providing by pressure a conductive contact to said ground conductor. 5. Device of any preceding claim, wherein - said metal member exhibits a conductive connection to said magnetic fastening means. 6. Device of any preceding claim, wherein - said connection between said metal member and said magnetic fastening means is established through magnetic attraction. 7. Device of any preceding claim, wherein - said metal member is made of steel. 8. Device of any preceding claim, further comprising: - radiator means connected to said hot conductor and providing operability at first and second frequencies, - said radiator means including first and second elongated radiating portions, - parallel resonance means spacing axially said first and second radiating portions and providing a radio frequency path at said first frequency and a radio frequency block at said second frequency, - said parallel resonance means being helically configured and including plural consecutive turns, - each of said consecutive turns being arranged to form an inductance and capacitance connected in parallel such that said path and block are attained. 9. Device of claim 8, further comprising: - a wire forming at least part of said first elongated portion, said helically configured parallel resonance means, and said second elongated portion. 10. Device of claim 8 or 9, wherein - said helically configured parallel resonance means having a pitch and a conductor cross-sectional dimension (diameter of said wire) , - said pitch being greater than or equal to said cross- sectional dimension.

Inventors: ENGWALL ERIK, JOHANNISSON EDDIE, SHALALVAND HASSAN, STROEMSTEDT PATRIK, ENGWALL, ERIK, JOHANNISSON, EDDIE, SHALALVAND, HASSAN, STROEMSTEDT, PATRIK
Applicants: ALLGON AB, ENGWALL ERIK, JOHANNISSON EDDIE, SHALALVAND HASSAN, STROEMSTEDT PATRIK, ENGWALL, ERIK, JOHANNISSON, EDDIE, SHALALVAND, HASSAN, STROEMSTEDT, PATRIK
Application year: 1999
Main classification: H01Q1
IPC codes: H01Q1, H01Q5, H01Q9