The document discusses phase weighting techniques for synthesizing shaped radiation patterns in base station antenna arrays. It presents an algorithm that uses genetic optimization and particle swarm optimization to determine the phase weights needed to generate a desired shaped pattern. This is achieved by first using statistical sampling to get an initial approximation, then refining it with the optimization algorithms. Examples are given showing shaped patterns produced that meet requirements like low sidelobe levels and filled nulls. Phase-only weighting is preferred over amplitude weighting because it is easier to implement physically in the antenna feed network.

1. Phase Weighting of Shaped Pattern for Base Station
Antenna Arrays
Mei WANG1
, Wei JIANG1
, ZhenGuo LIU2
and YanChang GUO1
1. Nanjing Research Institute of Electronics Technology, Nanjing 210013, China
2. State Key Lab. Millimeter Waves, Southeast University, Nanjing 210096, China
liuzhenguo@seu.edu.cn
Abstract- With the advent of the 3G mobile
telecommunication system, the antenna array of the base
station is required to be smart and intelligent. And the
antenna pattern should be shaped to have filled nulls over
the down side and low sidelobe levels over the upper side.
Phase weighting of shaped pattern for base station
antenna arrays is presented. It is achieved by using the
combination of the genetic optimization and particle
swarm optimization and statistically sampled optimization
algorithms. Phase weighting is easy to be implemented in
the feed network of the antenna and efficient for the
engineering practice. It is preferred in the antenna design.
The example is given and the associated figure also shown.
I. INTRODUCTION
In mobile communication sYstem CAPACITY of channel
is a serious problem because of the increase of consumers It
can be seen as a typical shaped pattern of the antenna array for
the base station system. which makes the efficient frequency
reuse more important To decrease the frequency reuse
distance, base station antennas in a cellular system are often
required to radiate a shaped-beam pattern. The general view
figure of the required pattern is shown in Fig.1. This shaped
beam has as low level as possible toward the interference zone
where the same frequency is used. At the same time, it has as
high a level as possible toward the service zone to keep
suitable signal strength and the null points must be filled to
avoid blind spot The problem of synthesizing shaped-beam
patterns has received much attention over the years, and many
synthesis methods have been presented [1-7]. Because the
excitation phase of an array element can be easily designed, in
this paper, we synthesize the shaped-beam pattern by
controlling only the excitation phases of the array elements. In
addition, the excitation amplitudes are symmetric and the
ratios of maximum and minimum amplitude are small, so that
the arrays can easily be realized.
In this paper, we first apply the phase weighting method
to achieve the start phase and then apply the Genetic
optimization algorithm (GA) and particle swarm optimization
(PSO) algorithm to find the second phase.
II. DESIGN REQUIREMENTS
Now an example is given. An antenna array in the base
station is consisted of N=18 elements. It is uniformly
distributed with spacing d= /2, where is the wavelength in
the free space. In the pattern of the antenna, the side lobe level
is required to be less than -18dB over [- 0, -30 ], less than -
15dB over (-30 ,-90 ], less than -12dB over [-90 ,-180 ], and
more than -15dB over [ 0, 20 ], where 0 is the first null
position.
We can see that in the pattern, over the upper side the
side lobe level is required to be less than -18dB, -15 dB and -
12dB. It is because of that the element factor can be
considered and the increased side lobe level in the array factor
can be reduced. And the first filled null at the down side in the
pattern is lifted to more than -15dB to reduce the blind area.
The general view figure of the required pattern is shown in
Fig.1. It can be seen as a typical shaped pattern of the antenna
array for the base station system.
a
b
Figure.1 (a) base station system, (b) shaped pattern
CJMW2011 Proceedings
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2. III. THE PHASE WEIGHTING ALGORITHM OF THE SHAPED
ANTENNA PATTERN
To obtain the shaped antenna pattern, there are several
methods to calculate the related weights []. Recently, the
genetic optimization, particle swarm optimization and
statistically sampled optimization techniques and some others
are frequently used to synthesis shaped patterns. In general,
the obtained results show that the weights for the shaped
pattern are complex, i.e. they consists of the amplitudes and
phases. Usually, it is not easy to be implemented in the feed
network of the antenna. It is desired to use the phase-only
weight to achieved the shaped pattern. Obviously, the change
of the phase only needs the change of the feedline length.
Then the cost and complexity of the feedline will be reduced.
Assume a linear array has N elements and it is uniformly
distributed. The spacing between adjacent elements is d. Then
the pattern of the array can be written as
1
1
( ) ( ) exp[ ( ) ]
2
N
n
N
E f j n u (1)
where ( )f is the pattern of the element in array,
2
sinu d , is the observation angle, which is shown
in Fig.2.
-200 -150 -100 -50 0 50 100 150 200
-30
-25
-20
-15
-10
-5
0
theta (degree)
radiationpattern
Figure 2 Radiation pattern of a uniformly array with 18 element
If there are different phases at the elements and the pattern of
the array will be as follows
1
1
( ) ( ) exp[ ( ) ]
2
N
n
n
N
E f j n u (2)
where n at the nth element is the phase to be determined to
form the desired shaped pattern. The set of
1
n s is the target
set to synthesis.
At first, an ideal shaped pattern can be obtained and
written as [8-9]
0
1
1
( ) exp[ ( ) ]
2
N
n n
n
N
E I j n u (3)
where nI and n are the desired amplitude and phase at the
nth element in the array.
Then, we utilize the one bit phase weighting [] to
approximate the ideal pattern. Statistically, we have
1 2
1
1
( ) ( ) exp[ ( ) ] exp[ ( )]
2
N
n n
n
N
E f j n u j
(4)
where
1 2
n n n .
As the first approximation, let
2
1
0
1
n n
n
n
n
with probability p
with probability p
(5)
Then
1
exp ( ) 1 (1 ) 2 1n n n n nj p p p I (6)
and
1
2
n
n
I
p (7).
Therefore, the statistically sampled optimization
algorithm can be used to search the optimized phases
1
n s.
The obtained pattern (8)
1
1
1
( ) ( ) exp[ ( ) ]
2
N
n
n
N
E f j n u (8)
sometimes may not be good enough to close to the ideal
shaped pattern. So we can use the genetic optimization and the
particle swarm optimization algorithms to further search the
optimized set of phases as the resultant solution.
IV. COMPUTATION RESULTS
In the Fig.3, 4, 5, the shaped patterns are shown as the
computed examples, where we assume the element pattern
( ) cosf , (9)
if the array is without ground plate. For these examples, there
are the different solutions for the different local optimization
points and various objectives. In Fig.3, we can see the side-
lobe level over upper side is less than -20dB and the depth of
the first filled null over the down side is higher than -14dB. In
Fig.4 and Fig.5 the situation are similar, but the side lobe level
over the down side is higher than that in Fig.3.The required
parameters are achieved and very good.
If we have ground plate in the array antenna, we can
assume the element pattern in array is written as
( ) cos( / 2)f (10)
With the formula (10), the computation results are shown in
Fig.6. In this figure it is obviously that the grat-lobe is
suppressed, and the side-lobe level also meets the requirement
for the shaped pattern.
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3. -150 -100 -50 0 50 100 150
-30
-25
-20
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-10
-5
0
theta (degree)
radiationpattern(dB)
Figure 3. Shaped pattern, Example 1
-150 -100 -50 0 50 100 150
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0
theta (degree)
radiationpattern(dB)
Figure 4. Shaped pattern, Example 2
-150 -100 -50 0 50 100 150
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0
theta (degree)
radiationpattern(dB)
Figure 5. Shaped pattern, Example 3
-150 -100 -50 0 50 100 150
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0
theta (degree)
radiationpattern(dB)
Figure 6. Shaped pattern, Example 4
V. CONCLUSIONS
Employing a shaped pattern for a base station antenna is
preferable because the shaped pattern in a service area is
capable of providing a sufficiently constant received power
level for mobile users and uniform receiving power levels in
spite of the cell edge while imparting only a slight interference
power level to other adjacent cells. In order to realize the
shaped beam pattern, a lot of methods have been presented,
including the amplitude or/and phase weighting. In this paper,
a shaped pattern basestation antenna with simple phase
weighting method integrating with GA and PSO optimization
is proposed. First upper sidelobe surppression and null-filling
are also obtained in broadband range with the highest possible
gain. The simulation results agree well with experiment.
.
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[4] H. J. Orchard, R.S. Elliott, and G.J. Stern, Optimising the synthesis of
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H, Microwave, Opt. & Antennas, 1983
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theta (degree)
radiationpattern(dB)
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