Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2000-05-31
2001-09-11
Phan, Tho G (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S770000
Reexamination Certificate
active
06288679
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an antenna structure for transmitting and receiving electromagnetic signals in general and, specifically, to transmission and reception within the Global System for Mobile Communications Standards (GSM).
BACKGROUND OF THE RELATED ART
In the course of a continuously increasing need for communication and mobility, transmission techniques using electromagnetic signals are of particular interest. The rapidly expanding field of mobile radio which operates, for example, using the Global System for Mobile Communications Standard (GSM), represents an important application of such transmission techniques. So-called base stations are used as connecting nodes in order to set up a connection between two mobile radio subscribers or one mobile radio subscriber and a communication subscriber in the fixed network. In order to ensure that simultaneous transmission and reception are guaranteed at all times on an existing connection the GSM Standard provides two separate frequency bands for transmitting and receiving the electromagnetic signals. For example, base stations using the GSM 900 Standard transmit in the 925 to 960 MHz frequency band, and receive in the 880 to 915 MHz frequency band. In order to transmit and receive the signals, a typical base station has a transmitting/receiving antenna in addition to transmitting and receiving amplifiers. This transmitting/receiving antenna in consequence has to cover the entire frequency range from 880 MHz to 960 MHz, that is to say has to have a minimum bandwidth of 80 MHz.
Dipole antennas or planar antenna structures, so-called patch antennas, are normally used for such applications. Both antenna types typically have one port for inputting the signals to be transmitted and for outputting the received signals. A so-called duplex filter or duplexer is used in order to use the antenna simultaneously for transmission and reception operation in adjacent transmitting and receiving frequency bands. The duplexer is essentially a frequency filter, in order to split the transmission and received signals between the transmission path and reception path on the basis of the frequency bands. For this purpose, the duplexer typically has three connections, one each for the antenna, the transmitter and the receiver. This results in separate ports at the duplexer for the connection of the transmitter and of the receiver (in this context, see also FIG.
8
).
Since the signal levels of the transmitted and received signals are generally very different, the duplexer must have a very high attenuation for the transmitted frequencies at the receiver port, in order to avoid overdriving and blocking of the receiver, and thus a reduction in the receiver sensitivity. In addition, the received frequencies must also be heavily attenuated at the transmission port, since the so-called wideband noise from the transmitter may fall in the reception band. The losses in the duplexer resulting from the high level of mutual attenuation required in consequence lead in an extremely disadvantageous manner to a reduction in the effective transmission power, and to a reduction in the receiver sensitivity.
The joint use of a typical antenna structure with one port for transmission and reception operation also results in limitations regarding the line impedances used. The optimum impedances for coupling the antenna structure to the transmitter and to the receiver cannot be chosen independently of one another. Normally, the duplex filters do not carry out any impedance transformation, so that the antenna structure, transmitter and receiver have the same impedance. A real impedance of 50 ohms is frequently selected for all the ports, as a compromise.
A semiconductor is normally used as the power output stage in the transmission path, typically having a low output impedance, and the impedance is thus transformed up to 50 ohm by means of a matching network. Owing to the transmitter and receiver having the same impedance, direct noise matching between the antenna structure and the first amplifier stage is not possible in the reception path either. A matching network is typically likewise used in order to transform the impedance of the coupling to the antenna structure to the optimum source impedance to achieve a minimum noise factor. However, losses in the matching networks result in a further disadvantageous reduction in the reception sensitivity and the transmission power. In general, matching networks also have the disadvantage that, as additional components, they result in costs and a space requirement.
Further disadvantages result in particular for the use of planar patch antennas, since planar antenna structures have relatively narrow bandwidths, so that it is impossible to use them for applications with wide bandwidth requirements. In this case, it is disadvantageous that the bandwidth of a normal antenna structure with one port has to cover the entire frequency range from the lowest to the highest operating frequency, which entire range comprises at least the width of the sum of the bandwidths of the transmission and reception bands, that is typically even wider, however, since there is also a guard band between the transmission band and the reception band.
Although antennas having two ports are already known, these structures are dimensioned such that the same frequency range is output at both ports. In these antennas, two mutually orthogonal polarizations are output from the same resonator. When so-called “dual polarized” structures are used in transmitting/receiving systems, a duplex filter is then connected downstream of each of the two ports, which once again leads to the series of disadvantages described above.
SUMMARY OF THE INVENTION
One object of the invention is thus to provide an antenna structure for transmitting and receiving electromagnetic signals, which avoids at least some of the disadvantages of the prior art.
A further object of the invention is to provide an antenna structure which ensures decoupling between the transmission path and reception path and, in particular, separate ports for the connection of the transmitter and the receiver.
The object is achieved in a surprisingly simple manner just by the features of Claim
1
. Preferred developments are the subject matter of the dependent claims.
The antenna structure according to the invention comprises a first and a second conductive element, which are at a distance from one another and essentially form a resonator for electromagnetic oscillations. The antenna structure furthermore comprises a first and a second coupling. The first coupling comprises a port via which signals in a transmission band are preferably input into the resonator, and the second coupling comprises a port, via which signals in a reception band are preferably output. In this case, the impedance of the first coupling for frequencies from the transmission band is matched to a transmitting device, and the impedance of the second coupling for frequencies from the reception band is matched to a receiving device. The antenna structure according to the invention thus simultaneously allows signals to be transmitted in the transmission band and to be received in the reception band, and to be assigned to the transmitting device and the receiving device via the two separate ports. Thus, advantageously, there is no need for any additional frequency filter, in the form of a duplex filter, between the antenna structure and the transmitting and receiving devices.
The frequency selectivity which is provided by the duplex filter for conventional transmitting/receiving antennas, in order to split the frequency range on the basis of the transmission band and reception band, is thus achieved just by the antenna structure, according to the invention, itself. Losses are thus avoided, which leads to an improvement in the reception sensitivity and the effective transmitted power.
Furthermore, the two couplings and the two resonant axes of the antenna structure can be optimized independently of one another, which allows line
Fischer Georg
Manzione Louis Thomas
Tsai Ming-Ju
Goo J.
Lucent Technologies - Inc.
Phan Tho G
LandOfFree
Single element antenna structure with high isolation does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Single element antenna structure with high isolation, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Single element antenna structure with high isolation will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2521390