Communications: radio wave antennas – Antennas – Spiral or helical type
Patent
1998-06-01
2000-06-13
Wong, Don
Communications: radio wave antennas
Antennas
Spiral or helical type
343906, H01Q 124
Patent
active
060755008
DESCRIPTION:
BRIEF SUMMARY
This application is National Stage of International Application PCT/SE/96/01488 Under 35 USC 371, filed Nov. 15, 1996.
FIELD OF THE INVENTION
The present invention relates to a compact antenna means intended for mobile or portable radio devices such as cellular telephones, portable computers and terminals having a radio communication function, and similar devices. The invention also relates to a connection means or externally connecting the compact antenna means to a transmission line to enable a further connection to an auxiliary antenna or other signal source.
The electrical length and the physical length of an antenna can be different. Some electronic communication devices, such as American cellular phones are operating from the 824 MHz to the 894 MHz band. Broad band width antennas are desired for devices that work in either one band or that work in multiple bands if the device is multifunctional. A quarter wavelength long dipole means that the electrical length of one half of the dipole is a quarter of the wavelength for which the dipole antenna is designed. At a frequency of 1 GHz the wavelength in free space is approximately 30 cm which means that each end of a quarter wave dipole is approximately 7.5 cm long. An antenna which is electrically one quarter wavelength long has similar complex Return-Loss values as a cylindrical dipole. The complex S11-parameter values of a cylindrical dipole are described in many books such as the "Jasik, Antenna Engineering Handbook". The physical length of an antenna can be reduced by winding the cylindrical dipole (for example: a wire) into a helical shape or a zigzag shape. Any oval cross section shapes geometrically between those two (round and flat) extremes are also possible. Besides having good S11-Parameter values the antenna should have horizontal gain characteristics. The electrical horizontal gain of an antenna increases with its electrical length up to the point at which it is one half a wavelength. The Return Loss values (also called the S11-parameter), on the other hand, has its optimum electrical length approximately one quarter wavelength when no matching circuit is used. Therefore many antenna assemblies use a quarter wavelength antenna without a matching circuit. Others use an electrical 3/8 wavelength antenna or 1/2 wavelength antenna with a matching circuit between the antenna and the Receiving/Transmitting Duplexer device. Most of the electronic devices use transmission lines with 50 Ohm, or 200 Ohm resistance such as a RG58 coaxline. Typically, at the present time, the frequency bands that the afore mentioned antennas operate in are between 100 MHz and 3 GHz.
In many applications, the plastic housing of the electronic communication device is protected against interference problems by an electrically conductive shielding. This shielding protects the internal devices from unwanted external electromagnetic waves and also protects other nearby electrical equipment from interference that is generated inside the device itself. This shielding can be used as one a part of the dipole antenna. It can also act as an electrical ground plane depending on its size.
DESCRIPTION OF PRIOR ART
The prior art documents U.S. Pat. Nos. 4,868,576, 5,446,469, 5,479,178, 5,504,494, 5,262,792, WO 95/08853, EP-A1-0 590 534 all disclose antenna means including helical antenna structures. However, in spite the fact that a helical antenna structure provides a more compact configuration than, e.g., a straight radiator antenna, it suffers from several drawbacks. The gain and bandwidth is typically smaller. In addition, the volume occupied by a helical structure is still considerable, since the helix requires a relatively large diameter in order to attain a satisfactory antenna function.
The volume of the helix is calculated by the Formula: r*r*pi*h. Where r is the radius and h the height. The radius cannot be decreased since the height then becomes either too large to be practical or the electrical length or the antenna is changing, i.e., getting longer or shorter than a
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Johnson Howard William
Kurz Hans Peter
Allgon AB
Chen Shih-Chao
Wong Don
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