Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2000-08-15
2001-09-11
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S711000, C342S359000
Reexamination Certificate
active
06288678
ABSTRACT:
It is well-known that the so called CTM (Cordless Terminal Mobility) has been recently more and more developed in the telephone field, due to the extension to a whole town of the function of DECT (Digital Enhanced Cordless Telecommunication) apparatuses—namely of cordless telephone apparatuses which function in confined areas—achieved by means of a direct connection to central apparatuses of the fixed network.
It is also well-known that the DECT standard, which was created for small areas and for indoor use, reaches its limits when employed in large areas and outdoors.
The low power of the radio signal is one of the most obvious limitations. The weakness of such a signal together with the use of a relatively high frequency, meaning a high likelihood of reflections and interferences, makes communication precarious as soon as the distance between the base station RFP (Radio Fixed Part) and the user's Mobile PP (Portable Part) increases.
The interference to be taken into account in the DECT standard is not caused by signals with the same frequency, coming from different base stations, as in the GSM standard.
This is because the choice of the transmission frequencies is made automatically and dynamically by the RFP-PP system, by sensing the frequencies used by adjacent systems, using a different frequency, so as to avoid at the beginning this kind of interference. (The synchronism between base stations, typical of the DECT standard, ensures the correct sensing of the frequencies already used).
Destructive interference in the DECT standards is determined by signals coming from the same source, with the same amplitude, but reaching the antenna with opposite phase: this is caused by the existence of multiple signal paths from the transmitter to the receiver, characterized by reflections in different directions, with different path lengths, but with a similar attenuation.
Communication by reflection is particularly relevant in DECT standards, because of the high frequency used (the wavelength is comparable with the size of objects present in the town environment) and of the comparatively low location (4-6 meters) of base stations from the ground, that does not allow the illumination of users from above.
The presence of common obstacles, like buildings, trees and vehicles, leads to very diversified multiple paths, with a high likelihood of phase shifts and delays. Small changes in the PP position (of the order of a few wavelengths) are sufficient to come out of the opposite phase condition, and thus of interference, or to get into it. This is the reason why is it not uncommon to see DECT users moving and turning the PP in an attempt to obtain the best signal (i.e. with the highest power and free from interferences).
The solutions adopted in existing installations consist in reducing the area covered by a single base station RFP, to enhance the average level of the available radio signal, and in making use of the so called “antenna diversity” to obviate interferences.
However, to reduce the area covered by a single RFP means increasing the number of the RFP required by the system, with evidently higher installation and maintenance costs.
The antenna diversity is obtained by making use of two antennas positioned at least two wavelengths apart, if their polarization is the same, or even less if their polarization is different. Such diversity should ensure that, in case the signal received by one antenna is attenuated by reflected, interfering signals, the other antenna receives a signal that can be utilized, because of different geometric conditions leading to different interference conditions.
The use of polarization diversity (vertical polarization and horizontal polarization) to obtain antenna diversity cannot be avoided if both antennas have to be contained within the same case as the electronic part, and if the overall dimensions of the whole base station have to fulfil market requirements (maximum dimension below 300 mm and volume below 5 liters).
On the other hand, the polarization of the wave impinging on the RFP antennas cannot be predicted (because it is determined by the PP orientation and the effects of consecutive reflections). Therefore, a linearly polarized antenna is not always able to receive the maximum of the available field: from this point of view, a circular polarization antenna is certainly more effective.
The best use of the antenna diversity, however implemented, is now the object of much research, aiming at the development of algorithms, mainly based on statistical models of the environment in which the RFP's will operate.
Of course, following this route, any possible solution which might be reached will suffer from a close dependence on the environment and be affected by the precariousness of the statistical data.
The present invention follows a totally different route—and fully original, at least in the DECT technology—which is based on the idea of letting the antenna of base stations search for the best communication, which search is nowadays carried out by the user in difficulty.
To realize such an idea, it has been observed that the search for the best communication is normally carried out by the user by altering the geometric configuration of the RFP-environment-PP system, by moving and turning the PP, and by making use of the information resulting from these changes. By perfect analogy, the RFP must change the configuration and the orientation of its antenna to search for the optimal geometric configuration of the RFP-environment-PP system, through real changes and the use of the information obtained as a consequence of the changes, rather than through statistical considerations.
In other words, it is not the user who must search for the antenna, but rather, it is up to the antenna to find and follow the user, and this can be obtained by seeking the antenna configuration which maximizes the signal and minimizes the effects of a possible interference.
The notion that the directional characteristic of the fixed base station in a mobile radio telephone system can be matched to the current location of a mobile user has been already disclosed in WO-A-o6/29836, describing a system which manages a multiplicity of elementary, narrow lobe antennas, each with different orientation, choosing time to time the elementary antenna among said multiplicity of antennas which is best orientated to be matched to the mobile station of the user.
The present invention reaches the same aim, but advantageously using, instead of a multiplicity of elementary antennas, a sole antenna consisting of a plurality of “patches”, in which, varying the phase between “patch” and “patch”, the orientation and the width of the antenna lobe are changed, to obtain the wished best connection with the mobile user. This antenna may be in fact omnidirectional in a horizontal half plane or be with narrow lobe and orientated in a very good way, with a reduced size, compatible with the DECT standards.
More precisely the antenna according to the present invention, intended for cellular telephone communication systems and in particular for base stations (RFP) of DECT standards is characterized in that it is formed as a multimode, adaptive, dual antenna, apt to take up both a narrow lobe configuration, with variable orientation on an horizontal plane (azimuthal plane), and an omnidirectional configuration on an horizontal half-plane, the two antennas composing said dual antenna being similar, integrated on the same dielectric substrate, and working simultaneously with two different roles (traffic support; search for optimal orientation), said roles being exchanged at every receipt-transmission cycle.
Advantageously, both said antennas forming the dual antenna consist of a set of “patches”, phase shifters being interposed between them and being produced by identical technology on the same substrate.
The two component antennas may be provided on the same substrate either with discrete sets of patches and phase shifters, or with discrete sets of phase shifters and with common patches, used with diff
Nguyen Hoang
Nixon & Vanderhye P.C.
Telefonaktiebolaget LM Ericsson (publ)
Wong Don
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