Beam-Forming Network Using Switch-line Phase Shifter
S.S.B Omran, M.K.A.Rahim and T Masri
1
Wireless Communication Centre, Faculty of Electrical Engineering,
Universiti Teknologi Malaysia, 81310 Skudai Johore Baharu.
[email protected], [email protected], [email protected]
Abstract - This paper describe the design of beamforming network network using Switch-line phase
shifter. The switch line phase shifter composed of
transmission line and RF switching diode. The
simulation results were compared with the
beamforming using butler matrix. It is proven that this
technique has obtained the same result of the butler
matrix result. The result obtained result from the
design has less phase error, approximately about 2.70.
Using this technique the size of the beamforming also
has been reduced.
Keywords: Beam-forming network (BFN), switched-line,
phase shifter, butler matrix. hybrid coupler, smart antenna
1. Introduction
Beam forming network is a technique to form the
radiation pattern of the antenna array at different angle.
In the receiving system, beam forming can increase the
receiver sensitivity in the direction of wanted signals
and decrease the sensitivity in the direction of
interference and noise. While in a transmitting system,
beam forming can help to increase the power of the
signal at the wanted direction where the signal has to
be sent. When transmitting a signal, a beam forming
controls the phase and relative amplitude of the signal
at each transmitter in order to create a pattern of
constructive and destructive interference in the wave
front. When receiving, the information from different
sensors is combined in such a way that the expected
pattern of radiation is preferentially observed [1].
There are many ways to create the beam
forming of the antenna. One of them technique is to
use the passive elements which is called butler matrix.
These butler matrixes use hybrid couplers and 0 dB
crossovers. Figure 1 shows three different
configuration of 4 x 4 butler matrixes. The most
preferable layout is shown in figure 1 (b), since it
keeps all input and output in the same side using
crossover (or cross couplers). The distances between
output-antenna ports are kept equal to λ/2 the layout.
Figure 1 (c) was designed as an alternative for a
circular array [2]. By using the concept of switchedline phase shifter, a network of beam forming can be
built. This network will have the ability to give the
same result as butler matrix. The concept of the
configuration will be discussed in the next section.
Figure 1 Three different configuration of beamforming
network using butler matrix
2. Switch and Phase Shifter configuration
Switches and phase shifter are the control devices
that provide electronic control of the phase and
amplitude of RF/microwave signals. The control
device can be built by using ferrites or solid-state
device (PIN diodes or FET). Phase shifting and
switching with ferrites are usually accomplished by
changing the magnetic permeability, which occurs
with application of a magnetic biasing field. Ferrite
control devices are heavy, slow and expensive. Solidstate control devices, on the other hand, are small, fast
and inexpensive. The ferrite devices do have some
advantages such as higher power handing and lower
insertion loss[3].
One major application of switches is to build
phase shifters. Figure 2 shows switched-line phase
shifter and its realization using RF PIN diodes. When
the bias is positive, the signal flows through the upper
line with a path length l1. If the bias is negative, the
signal flows through the lower line with a path length
l2. The phase difference between the two bias states is
given as:
2π ( l1 - l2 )
(1)
∆φ =
λg
l1 is the length of first length
l2 is the length of the second length
λg is the operating wavelength
∆φ is the differential phase
1-4244-1435-0/07/$25.00©2007 IEEE
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(a)
Schematic diagram
Figure 4 Switched line phase shifter using two shunt
susceptance and a quarter wave length of transmission
line
(b)
Construction using (PIN) diodes
Figure 2: Switch-line phase shifter.
There are different ways to implement switched-line
phase shifters. The first way is by using Loaded-line
phase shifter, for phase shifter < 45 degrees; it uses
loaded-line phase shifters as shown in figure 3. A
shunt susceptance inductive (-jB) or capacitive (+jB) is
switched in across the line causing a phase shift on the
incident signal [4], [5].
The second way to implement switched-line phase
shifters is by using Reflection Phase shifter [4], [5].
The simplest way is to use a 90-degree hybrid and two
PIN diodes to either short to ground bypassing line
length 2 or switched out thus adding line length 2 and
adding a longer path for the signal to travel. The
schematic of the circuit is shown in Figure 5.
Figure 5 Reflection phase shifter using two PIN diodes to
switch in or out the additional line lengths 2
3. Design Configuration
Figure 3 : Two switched line phase shifter
The loaded-line phase shifters work by adding a shunt
reactance to the micro-strip line in the form of an
inductor or capacitor, causing the incident signal to
undergo a phase shift. To modify the loaded-line phase
shifter, the return loss of loaded-line phase shifters can
be greatly improved by having two shunt susceptances
separated by 90 degrees. If these susceptances are
switched in or out by PIN diodes then a switch is able
to give the difference phase between the lines. Phase
shifter can be made as shown in figure 4.
The beam forming can be designed using these
concepts of switch-line phase shifter. In the design, the
most important thing is to obtain the coupling in each
ports of output with different phases. It can be
obtained by using a 90-degree hybrid coupler. The
trick of changing the phase of output with 2 inputs and
four outputs is by using switch-line phase shifter in the
arms of hybrid coupler.
For each arm in the hybrid coupler, it ease to
achieve by using the switch between two lines as
shown in figure 6, where each line has a different
length to get a different phase.
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(b) output phase at frequency 2.4 GHz
Figure 6 Circuit diagram of beam forming using
switched line phase shifter
4. Simulation, Results and Discussion
The network was designed in such a way that four
different phases with same amplitudes of the excitation
current can be coupled. It consists of two 90° hybrid
coupler, four switches and eight different transmission
lines with different length .The most important thing in
this design is the switch; it will give four different
phases with different state of switch (0,1) is as shown
in the figure 7,8. Figure 7,8 (a) and (b) show the output
phase, while figure 7,8 (c) shows the output power of
S31 , S41, S51 and S61.
The simulation of the design has been done using
Agilent Advanced Design System (ADS).
(c) output power at frequency 2.4 GHz
Figure 7: State – 0 condition for switched line phase
shifter phase and output power
(a) output phase at frequency 2.4 GHz
(a) output phase at frequency 2.4 GHz
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Table 2 shows the simulated results of the
corresponding magnitudes and phase shifts between
the inputs and the outputs of the Butler Matrix. It can
be observed from the results that the coupling values
for each output are almost equal which is about -7.2 to
-8.4dB. It can be observed that the Butler Matrix also
provide constant phase increment between its output
ports which are 45° for port In 1, -135° for port In 2,
135° for port In 3 and -45° for port In 4. These results
show that the output of butler matrix is almost equal to
the output of a switch-line phase shifter.
Table2: The simulated result of Butler Matrix.
(b) output phase at frequency 2.4 GHz
Table 3 shows the comparison between the butler
matrix and the (BFN) suing switch-line phase shifter.
Table 3: The comparison between Butler matrix and
(BFN) using switch-line phase shifter.
(c) output power at frequency 2.4 GHz
Figure 8: State – 1 condition for switched line phase
shifter phase and output power
Table 1, shows the simulation results of the
corresponding power and phase shifts between the
inputs and the outputs of the beam forming network. It
can be observed from the results that the coupling
values for each output are almost equal which is about
-6.3 to -7.6dB. As mentioned previously, the variation
of this value may be due to the different lengths of the
transmission line. It can also be observed that the beam
forming network also provide constant phase
increment between its output ports which are 45° for
port 3, -135° at port 4, 135° at port 5 and -45° at port6.
Table1: The simulated result of switch-line phase shifter.
lines
power
(dB)
Phase
Phase
Power
(dB)
Phase
Phase
A,C
E,G
B,D
F,H
ports
1
2
1
2
Out3
Out4
Out5
Out6
-6.36
-7.47
-6.53
-7.6
1.7º
-91.2º
-48.6º
40.6º
-135º
-45º
-92º
-2.25º
-6.4
-7.6
-87.6º
177.2º
-6.3
-44.4º
-134º
-180º
-88.1º
-41.2º
-47.9º
-7.6
It can be observed that the Beam forming network
using (BFN) Butler Matrix and switch-line phase
shifter provide constant phase increment between its
output ports which are almost the same for both
configurations.
5. Conclusion
The design of a switch-line phase shifter beamforming network with two inputs ports and four
outputs ports has been done to achieve the different
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phase shifter at each output port. A comparison with
another butler matrix has been done and the result
correlates well although there is the difference at the
output port in term of power.
From this simulated
result, we can conclude that this beam-forming
network can be use to change the radiation pattern of
an array antenna, especially in smart antenna design .
Acknowledgement
The authors thank to Ministry of Science Technology
and Innovation (MOSTI) for supporting the research
work, Research Management Centre (RMC), Wireless
Communication Centre Universiti Teknologi Malaysia
(UTM) for the support of paper presentation
References
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Jersey, Jan. 2006.
[2] F. E Fakoukakis, S. G. Diamantis, A. P.
Orfanides, and G. A. Kyriacou ''Development of
an Adaptive and a Switched Beam Smart Antenna
System
for
Wireless
Communication"
Electromagnetic
Research
Symposium,
Hangzhou, China, pp 276- 280, August 2005.
[3] KAI CHANG Texas A & M University '' RF and
Microwave Wireless Systems'' John Wiley &
Sons, Inc, July 2000.
[4] Shiban K. Koul, Bharathi Bhat, "Mcrowave and
Millimeter Wave Phase Shifters", Volume I "
Dielectric and Ferrite Phase shifters" Artech
House Boston London Mei 1991
[5] Shiban K. Koul, Bharathi Bhat, Mcrowave and
Millimeter Wave Phase Shifters, Volume II
''Semiconductor and Delay Line Phase Shifters"
Artech House Boston London ,1991.
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