Communications: directive radio wave systems and devices (e.g. – Directive – Including a steerable array
Reexamination Certificate
1999-10-25
2002-01-08
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a steerable array
C342S374000
Reexamination Certificate
active
06337659
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an antenna system, more particularly to an enhanced phased array base station antenna system having distributed low power amplifiers for mobile and wireless communication such as digital cellular communication, personal communication service (PCS), wireless local loop, local point multi distribution system and trunk radio service.
2. Prior Art of the Invention
In order to provide a wireless service, a base station antenna system transmits radio frequency signal through a transmitting antenna to a mobile station and receives signals radiated from a mobile station. From the advents of the aforementioned cellular mobile communications, there have been various kinds of efforts for cost-saving and improving service quality through the base station antenna system.
FIGS. 1A and 1B
show a conventional antenna system for a base station in accordance with the prior art.
The antenna system comprises a transmitting antenna
13
, a receiving antenna
14
, a transmitting or receiving antenna
17
and a bracket
18
. The base station comprises a high power amplifier
11
and a low noise amplifier
16
. The antenna system is coupled to the base station through radio frequency cables
12
and
15
.
Referring to
FIGS. 1A and 1B
, in a forward direction from the base station to the mobile station, a signal to be transmitted is amplified by the high power amplifier
11
in the base station, sent to the transmitting antenna
13
placed on an antenna tower through the radio frequency cable
12
and radiated through the transmitting antenna
13
.
In a reverse direction, a radio frequency signal radiated from the mobile station is received by the receiving antenna
14
and sent to the low noise amplifier
16
located inside of the base station through the radio frequency cable
15
. Since the reverse direction signals are easily corrupted by the multi-path propagation environments (refers to ‘fading’), an additional reverse direction path from receiving antenna
14
′ to low noise amplifier
16
′ is needed to cope with fading phenomena. This technique is called as space diversity.
FIG. 2
is a block diagram illustrating a conventional dual polarized antenna system.
The dual polarized antenna system comprises a duplexer
23
and a transmitting and receiving antenna
24
and a receiving antenna
25
. The base station comprises a high power amplifier
21
and low noise amplifiers
27
and
29
. The dual polarized antenna system is coupled to the base station through radio frequency cables
22
,
26
and
28
.
Referring to
FIG. 2
, in a forward direction, a signal to be transmitted is amplified by the high power amplifier
21
in the base station, sent to the transmitting and receiving antenna
24
placed on an antenna tower through the radio frequency cable
22
and the duplexer
23
and radiated through the transmitting antenna
24
.
In a reverse direction, a radio frequency signal radiated from the mobile station is received by the receiving antennas
24
and
25
sent to the low noise amplifier
27
and
29
located inside of the base station through the radio frequency cables
26
and
28
. This technique gives an alternative reverse direction path that is necessary to cope with fading. This technique is called as polarization diversity.
In the prior art, the radio frequency cable
12
,
15
,
22
,
26
or
28
usually runs several tens meters from the huge antenna tower to the inside of the base station. The long radio frequency cable unnecessarily consumes more than a half (3 dB) of the transmission power. To keep field intensity necessary to the mobile station in a cell, an amplifier in a forward path should output a higher power than that necessary to compensate loss within the cables. However, as output of the power amplifier becomes higher, the amplifier becomes more expensive and larger. Also, the efficiency of the amplifier becomes worse. As the efficiency of the amplifier is low, unnecessary power dissipated as heat is increased, and thereby there needs a cooling fan or air conditioner in order to balance the heat, which causes noise pollution and additional prime power consumption.
The life span of the high power amplifier with low efficiency is short. Also, if the amplifier goes wrong, communication service is severely deteriorated and even absolutely interrupted. During the service, one can often find those kinds of service interruption. In order to avoid this, one usually needs a dummy high power amplifier additionally.
In the prior antenna system, power loss due to several tens meter radio frequency cable decreases receiving sensitivity or signal to noise ratio in a reverse path from the mobile station to the base station as well as in a forward path. Accordingly, it becomes a main reason to need an excessively specified low noise amplifier in the noise figure and gain for preventing the communication quality from being degraded, thereby the system's cost increasing.
On the other hand, in the cellular communication service such as CDMA (Code Division Multiple Access) or GSM (Global System for Mobile communication) service, if a signal radiated from a base station may be spilled over into the adjacent cell, which acts as an interference to subscribers there. The interference signal deteriorates communication quality. In this case, there needs down-tilt of the base station antenna. However, if an antenna is too much down-tilted, the coverage of the cell may be too small and the antenna pattern may be distorted in the broadside region within the cell. On the contrary, the base station antenna located on the hilly region needs to be up-tilted. Likewise, the tilt control is frequently required in the optimization of the air interface network.
In the prior art, when tilt control is required, a crew rents a crane and climbs up to the antenna tower and turns the mechanical bracket
18
to adjust the tilt angle and checks again. It is very cumbersome as well as expensive. Furthermore, it may cause an unexpected accident in a rainy or snowy day. On the whole, the mechanical down-tilt control in a prior art has been a burdensome problem preventing the optimization of the air interface network in most of the cellular communications.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide an enhanced base station antenna system reducing power consumption in forward direction.
Another object of the present invention is to provide an enhanced base station antenna system providing higher reliability in forward direction.
Further another object of the present invention is to provide an enhanced base station antenna system improving communication quality in reverse direction.
Still another object of the present invention is to provide a polarization diversity phased array base station antenna system which gives reduction of power consumption and high reliability in forward direction and improves communication quality in reverse direction.
Still another object of the present invention is to provide a cost-saving base station antenna system.
In accordance with an aspect of the invention, there is provided an antenna system for radiating a signal in a base station, comprising: a phased array means for selecting an input signal through one of a plurality of beam ports, for dividing the input signal into a plurality of signals and for outputting the plurality of signals through a plurality of array ports, each of the signal having a linear phase difference according to difference of propagation path; a switching means for receiving the input signal from a base station, for selecting one of the plurality of beam ports of said phased array means and for transmitting the input signal to the selected beam port, responsive to a control signal transmitted from the base station; a plurality of low power amplifying means for low power amplifying the plurality of signals inputted from the plurality of array ports of said phased array means; and phased array radiating means for radiat
Gamma Nu, Inc.
Greenblum & Bernstein P.L.C.
Phan Dao
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