Communications: radio wave antennas – Antennas – Balanced doublet - centerfed
Reexamination Certificate
2002-09-23
2004-02-17
Phan, Tho (Department: 2821)
Communications: radio wave antennas
Antennas
Balanced doublet - centerfed
C343S715000, C343S820000
Reexamination Certificate
active
06693602
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
This application claims the priority of German Patent Document No. 199 55 950.3, filed Nov. 19, 1999, and PCT International Application No. PCT/DE00/04037, filed Nov. 17, 2000, the disclosures of which are expressly incorporated by reference herein.
The invention relates to an antenna system for transmitting and receiving electromagnetic waves, particularly in the short-wave range. Furthermore, the invention relates to a vehicle having such an antenna system which is suitable for a mobile use.
Normally, when antennas are used in a mountainous terrain or when electromagnetic waves are transmitted, particularly in the short-wave range, a radiation of the energy is required which is as vertical or steep as possible. So-called dipole antennas are known as the ideal antennas with a radiation angle which is as vertical as possible. An ideal radiation characteristic occurs particularly in the case of a dipole antenna (abbreviated “dipole”) whose length corresponds to half the wavelength and which is generally called a lambda half dipole (also called &lgr;/2 dipole). The transmission behavior and vice versa the reception behavior of a lambda half dipole is characterized by a largely good omnidirectional characteristic and a relatively large vertical radiation angle. In the case of the lambda half dipole, it is a disadvantage that, for a particularly broad-band use in the short-wave range, for example, of from 2 to 30 MHz, the antenna length fluctuates between 75 and 5 m. Thus, such an antenna system constructed of a lambda half dipole is not suitable for a mobile use. Furthermore, dipole antennas can be used in the lower frequency range only if they are correspondingly damped. This, in turn, is connected with considerable losses which are avoided by providing matching units. However, because of the high requirements with respect to quality and matching precision, these matching units result in very high expenditures. In addition, because of the doubling of impedance values for a short dipole in comparison to the impedance values of a simple rod antenna, matching is hardly possible, so that the use of a dipole antenna for a particularly wide frequency range in the short-wave range is possible only to a limited extent and may even be impossible.
Therefore, frame or loop antennas are normally used. A frame antenna is a so-called short-circuit antenna which, in comparison to the dipole antenna, has, for the most part, good frequency behavior within a wide frequency range, in which case the radiation characteristic is limited with respect to a steep radiation angle. Because of the very high currents of the frame antenna, which are unavoidable in the operation of the antenna system, this frame antenna comprises very high-expenditure motors and electrical components which are fixedly installed. An exchange of components or a fast mounting/demounted of the entire antenna system is therefore not possible or is possible only to a very limited extent.
In European Patent Document EP 0 809 321 A1, an antenna system is described which has two dipole halves which are connected by way of a control unit. The control unit comprises a power divider module, as well as a matching module for each dipole half, as well as a central control unit which is connected with each of the two matching modules and controls them.
It is therefore an object of the invention to indicate an antenna system for a largely broad frequency range, which antenna system has a particularly simple construction, and a radiation characteristic which is as vertical or steep as possible, and is suitable particularly for a mobile use.
This object is achieved according to the invention by means of an antenna system for frequencies particularly in the short-wave range. It comprises two antennas which are mutually connected by way of a control unit and jointly form a dipole antenna. In other words, the two antennas are electrically connected with one another by means of the control unit such that they form a dipole antenna with respect to the beam characteristic. As a result, while the particularly good steep-radiation characteristic of a dipole antenna is utilized, a simple construction of the antenna system is simultaneously permitted.
Expediently, a rod antenna which is constructed as a monopole is in each case provided as the antenna. By connecting two monopoles to form a dipole antenna, on the one hand, the good steep-radiation characteristic in the short-wave range, on which the dipole antenna is based, will be utilized. On the other hand, because of the low input impedance, the use of the rod or monopole antennas permits a largely simple matching of the impedance range, whereby a particularly simple construction of the control unit is ensured.
The control unit and the two antennas are preferably arranged on a carrier element. The carrier element is preferably provided for mounting on a vehicle. A frame or a roof rack, for example, can be used as the carrier element. As a result, the antenna system is particularly easy to mount or to demount. Without being changed, the antenna system can be mounted by means of the carrier element on various vehicles independently of the vehicle type and is therefore suitable for a universal use on mobile vehicles.
Advantageously, for the radiation of a certain frequency, the two antennas are connected with the control unit such that the two antennas can be excited or fed by signals which are phase-rotated by 180° with respect to one another. As a result of the connection of the two antennas to form a common dipole with such an antiphase relationship of the two signals, for the most part good frequency behavior is ensured while the radiation energy is simultaneously as large as possible.
In another advantageous further development of the antenna system, the control unit has a modular construction. The control unit expediently comprises at least one matching module and one power divider module. In this case, the matching module is used for matching the output of the control unit to the respective input impedance of the two antennas. By means of the power divider module, each antenna is fed symmetrically. For this purpose, a signal emitted by a transmitter is separated with a definable power by means of a power divider module; that is, half of each antenna is fed by means of the transmission power emitted by the transmitter. Such a modular construction of the control unit permits a particularly high degree of availability and independence of the antenna system. As an alternative, because of the modular construction of the antenna system, the latter can particularly easily be modified from a dipole arrangement to a simple monopole antenna. In this case, for example, one of the two antennas is deactivated by means of the control unit or is simple separated from the control unit.
In order for the antenna system can be used for a plurality of frequencies in the short-wave range, the matching module for a definable frequency comprises at least one L/C element (L element=coil, C element=capacitor). The matching module preferably includes a measuring unit and a control. By means of the measuring unit, the input impedance pertaining to the given frequency is determined. The control has the effect that, by means of the impedance values determined for the two antennas, correspondingly at least one L/C element and/or the number of so-called network elements required for the matching, such as L-elements, C-elements, is switched active. The tuning or matching operation preferably takes place iteratively for each antenna; that is, in an iterative process, the measured values determined by the measuring unit are supplied to the control for the determination of the number of L/C elements required for the matching. In each iteration cycle, the measured values and/or the number of the L/C elements are determined for both antennas, in which case the mutual dependence of the two antennas as a result of their electric coupling is taken into account. The connection of the
Dey Holger
Haneberg Gerhard
Kombrink Friedemann
Mähr Harry
Crowell & Moring LLP
Eads Radio Communication Systems GmbH & Co. KG
Phan Tho
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