Communications: radio wave antennas – Antennas – Plural separate diverse type
Reexamination Certificate
2000-09-29
2003-04-29
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Plural separate diverse type
C343S893000, C343S7000MS
Reexamination Certificate
active
06556173
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an integrated multiport antenna for increasing information rates of wireless communication networks.
2. Description of the Related Art
One of the more critical pieces of equipment in a communication network and, in particular, in a wireless communication network is the antenna. Antennas are used to convey information (i.e., transmit and receive information) in the form of electromagnetic waves over communication links of a network.
The owners and/or operators of communication networks, i.e., the service providers, are constantly searching for methods and equipment that can meet the changing needs of their subscribers. Subscribers of communication networks, including wireless communication networks, require higher information throughput in order to exploit the expanding range of services being provided by current communication networks. For example, wireless communication subscribers are now able to have simultaneous access to data networks such as the Internet and to telephony networks such as the Public Switched Telephone Network (PSTN). Also, service providers are constantly investigating new techniques that would allow them to increase their information throughput. Information throughput is the amount of information—usually measured in bits per second—successfully conveyed (transmitted and received) over a communication channel. Information throughput can be increased in a number of well known manners. One way is by increasing the power of the transmitted signals. A second way is by expanding the frequency range (i.e., bandwidth) over which the communication is established. However, both power and bandwidth are limited by certain factors such as governmental and standards organization that regulate such factors. In addition, for portable devices, power is limited by battery life.
An approach which circumvents the power and bandwidth limitations is to increase the number of antennas used to transmit and receive communication signals. Typically, the antennas are arranged as an array of antennas. Three of the more general ways of using antenna arrays are (a) phased array applications (b) spatial diversity techniques and (c) Multiple Input Multiple Output (MIMO) techniques. A phased array comprises an antenna array coupled to a device, which controls the relative phase of the signal in each antenna in order to form a focused beam in a particular direction in space. Spatial diversity is the selection of a particular antenna or a group antennas of the array to transmit or receive signals in order to improve information throughput. In a spatially diverse structure the antenna array is typically coupled to a receive diversity device that utilizes one of many combining techniques, such as Maximum Ratio Combining, switching, or many others well known to those skilled in the art. Unlike phased arrays and spatial diversity techniques wherein one or a group of antennas are used to transmit and/or receive a single signal, a technique called Multiple Input Multiple Output (MIMO) is used whereby the antenna array coupled to a signal processing device is used to transmit and/or receive multiple distinct signals. One example of a MIMO system is the BLAST (Bell Labs LAyered Space Time) system conceived by Lucent Technologies headquartered in Murray Hill, N.J.
In many cases, as the number of antennas in a transmit and/or receive array (e.g., BLAST system) is increased, the information throughput of the system also increases; G. J. Foschini and M. Gans,
Wireless Commun.
6, 311 (1998). Typically the amount of space available for the antenna array is limited. In particular, the space limitation is very critical for portable wireless devices (e.g., cell phones, Personal Digital Assistants (PDA)). Thus, increasing the number of antennas in an array of limited space decreases the spacing between individual antennas in the array. The reduced spacing between antennas typically causes signal correlation to occur between signals received from different antennas. Signal correlation reduces the gain in information throughput obtained by the use of MIMO techniques; A. L. Moustakas et al.,
Science
287, 287 (2000).
In particular, received signal correlation is a phenomenon whereby the variations in the parameters (i.e., amplitude and phase) of a first signal of a first antenna track the variations in the parameters of a second signal of a second antenna in the vicinity of the first antenna;
Microwave Mobile Communications,
W. J. Jakes (ed.), chapter 1, IEEE Press, New York (1974). Correlation is quantitatively defined in terms of at least two signals. When any two signals s
1
(t) and s
2
(t) are being transmitted or received, the degree of correlation between these two signals is given by the absolute value of the following expression:
∫
t
1
t
2
s
1
(
t
)
s
2
(
t
)
*
ⅆ
t
∫
t
1
t
2
&LeftBracketingBar;
s
1
(
t
)
&RightBracketingBar;
2
ⅆ
t
∫
t
1
t
2
&LeftBracketingBar;
s
2
(
t
)
&RightBracketingBar;
2
ⅆ
t
where s
2
*(t) corresponds to the complex conjugate of s
2
(t) and t
1
and t
2
are times selected in accordance to rules well known to those skilled in the pertinent art. When two signals have low correlations or are uncorrelated, the above integral becomes relatively-small.
The correlation between received signals can be determined by the correlation of the radiation patterns of the antennas receiving the signals. As it is known to those skilled in the art, the radiation pattern of a particular antenna or cluster of antennas fed through a port, is the relative amplitude, direction and phase of the electromagnetic field in the far field region radiated at each direction. The radiation patterns are reciprocal in that they show the relative amplitude, phase and direction of a field transmitted from an antenna as well as the sensitivity of that antenna to incoming radiation from the same direction. The radiation pattern can be measured experimentally in an anechoic chamber, or calculated numerically with the use of a programmed computer.
The correlation function of two radiation patterns is a useful measure of the degree of their overlap. It is defined as the magnitude of
∫
ⅆ
k
E
⇀
1
(
k
)
·
(
E
⇀
2
(
k
)
)
*
∫
ⅆ
k
&LeftBracketingBar;
E
⇀
1
(
k
)
&RightBracketingBar;
2
∫
ⅆ
k
&LeftBracketingBar;
E
⇀
2
(
k
)
&RightBracketingBar;
2
where E
1
(k) and E
2
(k) are the far field vector electric fields at direction k of the radiated field at a given frequency due to ports
1
and
2
respectively and E
2
(k)* is the complex conjugate of the far field vector electric field at direction k due to port
2
. The correlation between radiation patterns can be calculated based on the experimentally determined or numerically calculated individual-radiation patterns.
When two antennas are placed sufficiently far from each other, the correlation of their radiation patterns at the same frequency will be very small. A result of this effect is that the received signal from two antennas spaced sufficiently apart will be independent. The radiation pattern of a port of an antenna generally depends on many factors. A port is a part of the antenna at which a signal is applied to produce electromagnetic radiation or a point on the antenna from which a signal is obtained as the result of electromagnetic radiation impinging on the antenna. The factors affecting the radiation pattern of a port of an antenna include the placement of the port, the materials from which the port and antenna are constructed, structure and shape of the antenna, the relative position of the antenna in an antenna array, the relative position of the antenna within a communications device, as well as the position of other objects proximately spaced to the antenna. The reason for this dependence is the electr
Moustakas Aris L
Safar Hugo F
Simon Steven H
Stoytchev Marin
Agere Systems Inc.
Chen Shih-Chao
Ligon John
Wong Don
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