Communications: radio wave antennas – Antennas – With coupling network or impedance in the leadin
Reexamination Certificate
2002-08-30
2004-09-07
Vannucci, James (Department: 2821)
Communications: radio wave antennas
Antennas
With coupling network or impedance in the leadin
C343S757000
Reexamination Certificate
active
06788268
ABSTRACT:
BACKGROUND OF THE INVENTION
In the area of wireless communications, time division multiple access (TDMA) and code division multiple access (CDMA) protocols are used for communicating from a base station to a mobile station. The TDMA technology uses a single frequency for transmitting and receiving signals, while the CDMA systems use one frequency band for transmitting signals and another frequency band for receiving signals. In both cases, multipath can be a source of interference.
FIG. 1
is an example environment
100
in which multipath is typically present. The environment
100
includes a first antenna tower
105
a
and a second antenna tower
105
b
. Each antenna tower
105
a
,
105
b
has an associated base station (not shown). The environment
100
further includes a first office building
110
a
and a second office building
110
b
. In the first office building
110
a
, a subscriber unit
115
is within range of signals from both antenna towers
105
a
,
105
b.
There are several signaling paths from the antenna towers
105
a
,
105
b
to the subscriber unit
115
. A first signaling path
120
is a direct signaling path from the first antenna tower
105
a
to the subscriber unit
115
. A second signaling path
125
includes a reflection off the second office building
110
b
as the respective signal travels from the first antenna tower
105
a
to the subscriber unit
115
. A third signaling path
130
is a direct signaling path from the second antenna tower
105
b
to the subscriber unit
115
.
The first signaling path
120
is in the direction of the first antenna tower
105
a
. The subscriber unit
115
does not know where the first antenna tower
105
a
is located. The subscriber unit
115
can only point (i.e., direct a beam) in the direction of the strongest desired signal, if the subscriber signal is equipped with a steering antenna. The strongest desired signal is in the direction between the locations of the first antenna tower
105
a
and second office building
110
b.
In direction finding (DF), multipath tends to be harmful because it masks the true direction of the signal. The component of the multipath that is in-phase with the first signaling path
120
is actually helpful, and thus, the direction change is inconsequential. So, multipath is not all interference. However, the third signaling path
130
is all interference because it is not the same signal as being transmitted on the first signaling path and can never be in-phase with the signal on the first signaling path.
If the subscriber unit
115
employs a phased array antenna, it can use the phased array antenna to steer an associated antenna beam toward the first antenna tower
105
a
, or, in the case of multipath as just described, in the direction of the strongest desired signal. Additionally, the phased array antenna may be used to steer the associated antenna beam to receive signals from only the direct signaling path
120
from the first antenna tower
105
a
to remove the multipath effects (i.e., signal fading) caused by the second signal
125
or interference caused by the third signaling path
130
.
FIG. 2
is a block diagram of the phased array antenna used by the subscriber unit
115
of
FIG. 1
capable of steering the associated beam, where the steering is done by phase shifting the RF signals to/from the antenna elements composing the array antenna
200
. The phased array antenna
200
is composed of antenna sub-assemblies
205
. Each antenna sub-assembly
205
includes an antenna element
210
, duplexer
215
, and phase shifter
220
. A control signal
225
is used to adjust the phase shifts imposed by each of the phase shifters
220
.
In transmission mode, the sub-assemblies
205
of phased array antenna
200
receives a signal
230
. The signal is phase shifted by the phase shifters
220
in a manner where, when the beams of all the antenna elements
210
are combined, the resulting effective beam (not shown) is directed as defined by the control signals
225
. The signal
230
passes from the phase shifters
220
to the antenna elements
210
via the duplexes
215
, which are in a transmit mode.
In receive mode, the antenna elements
210
receive RF signals most strongly from a direction defined by the same control signals
225
. The antenna elements
210
provide the received signals to the duplexes
215
, which are set in a receive mode to allow the received RF signal to pass to the phase shifters
220
. The phase shifters
220
provide signals
230
, which have been phase shifted, to a summer (not shown) to reconstruct the signal. The reconstructed signal is thereafter processed by a receiver (not shown).
SUMMARY OF THE INVENTION
Recently, experiments to determine optimal gain between a subscriber unit and antenna tower have shown that, when using transmission signals of different frequencies, the optimum signaling direction varies for the different frequencies. In CDMA technology, as defined for a subscriber unit, the receive (R
x
) signals range between 1930-1990 MHz, and the transmission (T
x
) signals span from 1850-1910 MHz. Further tests were conducted to determine whether the optimum signaling paths differ for the T
x
and R
x
signals of the CDMA technology, as in the case of transmitting signals having different frequencies. These further experiments proved that, in fact, the optimum signaling paths between a subscriber unit and base station antenna tower are frequency dependent, affecting signaling paths of T
x
and R
x
signals.
At least one reason for different optimum signaling directions for signals at different frequencies has been determined to be caused by different angles of refraction as the signals travel between the antenna tower and the subscriber unit antenna. For example, in CDMA technology, when the T
x
and R
x
signals travel through a glass of an office building window, the T
x
signals “bend” at a first angle and the R
x
signals “bend” at a second angle. The different angles of refraction may also result in the signals taking multiple paths inside an office in which the subscriber unit resides. Further, the T
x
and R
x
signals bend around objects external from the office building at different angles, which can be another source of difference in transmission paths. The net result of differences in angles and multipath is at best a reduction in signal-to-noise ratio (SNR) and at worst an interference causing disruption in communication.
In directional antenna technology, there is an assumption that the optimum directions of the signals traveling in the forward and reverse links are along the same path. Thus, once a direction has been selected, typically based on R
x
signal-to-noise ratio (SNR), the selected direction is used for both T
x
and R
x
signals. While the selected direction may have been found to be optimal for one of the links, the selected direction of the antenna directivity may be sub-optimal for the other link, as learned during the experiments discussed above.
In general, the present invention provides a subscriber unit with an ability to transmit and receive signals in different directions simultaneously to allow for optimum gain in both directions. In this way, refraction and multipath effects resulting from communication signals operating at different frequencies can be compensated for to improve gain in both the forward and reverse links.
Accordingly, one embodiment of the present invention includes a directive antenna having plural antenna elements arranged in an antenna array. Frequency selective components are coupled to respective antenna elements, where the frequency selective components provide simultaneous frequency discrimination. At least two weighting structures are coupled to the frequency selective components to produce independently steerable beams having spectrally separated signals.
In an alternative embodiment, the present invention includes a directive antenna having plural antenna elements arranged in a parasitic antenna array. Frequency selective components are connected to a first subset of the antenna elem
Chiang Bing
Gainey Kenneth M.
Proctor, Jr. James A.
Hamilton Brook Smith & Reynolds P.C.
IPR Licensing Inc.
Vannucci James
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