Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2000-07-20
2001-08-28
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S795000, C343S824000
Reexamination Certificate
active
06281849
ABSTRACT:
The field of the invention is that of microwave antennas.
More precisely, the invention relates to a printed bi-polarization antenna as well as a corresponding network of antennas.
The antenna according to this invention has numerous applications. For example, it can be used as a probe in a device for testing an antenna by measurement of radio wave radiation. It will be recalled that such devices notably enable one to make forecasts of radio wave coverage, to carry out measurements on equipment (mobile or otherwise) with a view to establishing conformity to standards, to check the security of transmitted, wanted signals and to make measurements used for the study of the interactions between radio waves a n d people.
It may also be used in the field of telecommunications, for example in the base stations of a radio communications system (GSM or otherwise), or in a multi-media satellite receiver.
In all these applications, in a traditional way it is desirable that the antenna used has an omnidirectional radiation diagram (as close as possible to an infinitesimal dipole), a broad band width and excellent purity of polarization.
In the context of this invention, it is desirable, in addition, that the antenna should be a double polarization antenna. In effect, it has been noted that this type of duplex polarization antenna is in oeneral use.
Because of this general use, it is also true that an antenna test device requires the use of duplex polarization probes, that is to say, probes capable of measuring two orthogonal components of an electrical field. In effect, the measurement carried out by the test device must, in particular, provide the characteristics of the antenna under test, under polarization isolation conditions. It can therefore be understood that the probe itself must have excellent isolation between its accesses and provide cross-over polarization levels that are very low.
Traditionally, as measurement probes, open or horn guide type antennas are used. However these have a large “thickness” (5 to 10 wavelengths &lgr;) which has a redhibitory effect when used in frequency bands below 3 GHz.
So as to resolve this problem of space and size, certain attempts have been made to use printed technology. In effect, one of the major interesting features of this technology is to permit the production of antennas that occupy only a small volume (the thickness remaining generally of the order of &lgr;/4) and have a low weight. In addition, through the literature, numerous structures for printed, duplex polarization antennas are known.
However, in practice, at the present time, no printed bi-polarization antenna exists that has an omni-directional radiation diagram, a broad band width and excellent polarization purity. In effect, they are all, at the present time, based on metallic resonant patches powered by coupling (lines or punched out slits in a ground plane) or by contact (coaxial probes). However the use of resonant patches unfortunately leads to reduced band widths (rarely more than 20% with the SWR (Stationary Wave Ratio) less than 2). Known printed antennas only meet two out of the three criteria (namely an omni-directional radiation diagram and purity of polarization), and are therefore not suitable for the applications mentioned above.
An objective of the invention is to remedy these various disadvantages in the state of the technology.
More precisely, one of the objectives of this invention is to provide a printed bi-polarization antenna having not only an omni-directional radiation diagram and excellent polarization purity, but also a broad band width (for example greater than 50% with the SWR<2).
The invention also has the objective of providing such an antenna capable of operating in circular polarization.
Another objective of the invention is to provide such an antenna having augmented directional selectivity.
These various objectives and others that will become apparent in what follows, are achieved in accordance with the invention using a printed bi-polarization antenna comprising:
first, second and third superimposed substrate plates;
a first metal deposit, situated on the external face of said first plate which defines at least one first radiating element of the dipole type, in the form of a T, the horizontal bar of said T being constituted by two radiating lateral strands separated by a coupling slit;
a first power supply line pursuant to a first polarization, situated between said first and second substrate plates and supplying power to said at least one first radiating element;
a second metal deposit, situated on the external face of said third substrate and defining at least one second radiating element of the dipole type, in the form of a T, the horizontal bar of said T being constituted by two radiating lateral strands separated by a coupling slit;
a second power supply line pursuant to a second polarization, situated between said second and third substrate plates and supplying power to said at least one second radiating element.
The general principle of the invention consists therefore of superimposing at least one first printed T-shaped dipole and at least one second printed T-shaped dipole, each having a distinct polarization. Thereby, a structure with three substrate layers and four metal coating layers (two for the radiating elements and two for the power supply lines) is obtained. This topology avoids physical intersections between the power supply lines and therefore limits the dangers of parasitic couplings.
In this way, the bi-polarization antenna according to the invention benefits from all the advantages associated with the printed T-shaped mono-polarization dipole, namely low volume, easy mechanical maintenance, an omni-directional radiation diagram and a broad band width (greater than 50% with SWR<2).In addition it is a technology that is simple to implement.
For a detailed description of the printed T-shaped dipole, reference can be made, in particular to French patent No. 93 14276, the text of which is introduced here as a reference.
It should be noted that the small volume occupied by the antenna according to the invention (in particular its small thickness) makes it particularly suitable for the test devices mentioned above and particularly for near-field devices. It may be recalled that the latter enable one to measure the radio field emitted at a short distance through the use of a n electronic apparatus (under test). Such measurements aim to provide better knowledge of propagation phenomena at short distance from electronic equipment and enable one to provide evidence of interactions between the waves radiated by the equipment and the human body (which is often made difficult by the extreme proximity of the equipment).
In a preferred embodiment of the invention, said first metal deposit defines two first radiating elements of the dipole type, each in the shape of a T and joined to one another through the free end of the vertical bar of each T. Said first power supply line has two arms each supplying one of the two first radiating elements. Said second metal deposition defines two second radiating elements of the dipole type, each in the shape of a T and joined to one another through the free end of the vertical bar of each T. Said second power supply line has two arms each supplying one of the two second radiating elements.
By joining radiating elements in a T, associated two b y two, with one and the same polarization, geometric symmetry is introduced which enables improvements to be made in the purity of polarization (cross-over polarization levels which are very small) and in the isolation between accesses.
Preferably, the longitudinal axis of the Ts of said first radiating elements is offset by about 90° with respect to the longitudinal axis of the Ts of said second radiating elements.
In this way, a level of additional symmetry is introduced which allows improvements to be made in the purity of polarization and the isolation between accesses.
In an advantageous way, the vertical bar of the T of each radiating element consti
France Telecom
Merchant & Gould P,C,
Nguyen Hoang
Wong Don
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