Design of a 90⁰ switched line phase shifter for phased array antennas

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 03 Issue: 10 | Oct-2014, Available @ http://www.ijret.org 137
DESIGN OF A 90⁰ SWITCHED LINE PHASE SHIFTER FOR PHASED
ARRAY ANTENNAS
S Gowri Shankar1
, K Viswavardhan Reddy2
1
Department of Telecommunication Engineering, RV College of Engineering, Bangalore, India
2
Department of Telecommunication Engineering, RV College of Engineering, Bangalore, India
Abstract
Phase shifters are considered as the most vital subsystem for an antenna in any transceivers or RADARs. As the name suggests
that, these components provide phase shift for the input signal, with respect to the reference signal at its output without any loss
or modifications in the amplitude of input. In this work, an attempt has been made to design a 90⁰ phase shifter based on switched
line type. The phase shifter is designed to implement on a microstrip circuit type. The frequency considered for the operation is 1
GHz. Agilent’s ADS (Advanced Design Simulation) software tool was used for designing and simulating the switched line phase
shifter. The ADS software is widely used for designing and the simulation of microwave circuits and its components. Initially the
circuit was designed with ideal switch models, which are readily available in ADS. Then independent single pole double throw
switches were designed and simulated again. Parameters like return loss and insertion loss were considered as main parameters
and then the designs were optimized to achieve the best possible return loss and insertion loss.
Keywords - Phase shifters, SPDT switches, Switched line.
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1. INTRODUCTION
The phase of an electromagnetic wave of a given frequency
can be shifted when propagating through a transmission line
by the use of Phase Shifters [1]. In the field of electronics, it
is often necessary to change the phase of the signals. RF and
Microwave Phase Shifters have many applications in
various equipments such as phase discriminators, beam
forming networks, power dividers, linearization of power
amplifiers and phase array antennas [2].
Phase Shifters can be separated into two categories:
Reciprocal and Non-Reciprocal [3]. The reciprocal phase
shifter is not directionally sensitive, which means that the
phase shift in the direction of both transmit and receive is
same. Therefore, with the of use reciprocal phase shifters,
switching of phase states between transmit and receive is
not required. On the other side with the use of a
nonreciprocal phase shifter, switching of phase states
between transmit and receive is required.
Optimal transmitting and receiving properties are required
to be provided by the modern radio communication systems
for an effective utilization of transmission channels. Thus
focusing on the antennas, this requires electronically
steerable radio patterns, that can be achieved by the phased
array antennas [4]. One of the most important part of the
phased array antennas are the phase shifters. Differential
signal phase shift of antenna's will be determined by the
phase shifters. “Switched-line Phase Shifter” [5] is one of
the most important type of Phase Shifter based on the diodes
and their phase shift corresponds to the length difference
between two switched transmission lines [4]. Thus by
changing the bias point of a pin-diode from forward to
reverse direction and vice versa, the switching procedure is
obtained. Digital-to-Analog conversion is not required
because the phase shift can be controlled digitally with the
use of this method.
2. MOTIVATION
In the area of applications like phased array antennas and
communication antennas, there is a need of beam forming
configurations for effectively having a directional radiation
of electromagnetic waves. This can be achieved by using
multiple antenna radiating elements with varied phase inputs
of signal rather than using single element. In such cases the
phase shifters come into play as the name suggests shifting
the phase of the input signal to required amount. Also, in the
Defence areas where RADARs are used to the great extent
in finding the enemy’s path and to detect early warnings of
any threat, the RADAR system must itself be concealed
from the enemies. So in such scenarios static radar with
electronic beam steering offers more stealth compared to
conventional mechanical beam steering RADARs. Due to
these reasons an attempt has been made to study and design
a 90⁰ switched line phase shifter.
The objectives of this work is to design a 90⁰ switched line
phase shifter for phase shifting purpose and to design the
circuit keeping in mind for implementation on micro strip
line on a standard FR-4 substrate. For this we simulate and
design its operation on Agilent’s Advanced Design System
software. Some of the specifications of the microwave 2-
port device that were considered for the design are:
Operating frequency of 1 GHz, Return loss better than 20
dB, Insertion loss ranging within -1 to 0 dB.

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3. MICROSTRIP LINES
Microstrip transmission lines consists of a conductive strip
of width "W" and thickness "t" and a wider ground plane,
separated by a dielectric layer (a.k.a. the "substrate") of
thickness "H" [6] as shown in the fig 1. Especially for
microwave integrated circuits and MMICs, the most
popularly used microwave transmission line is Microstrip
and the major advantage of microstrip over stripline is that
all active components can be mounted on top of the board.
Fig 1 Microstrip line
The design equations associated for the design of microstrip
lines is given as
For,
𝑊
𝐻
≥ 1
𝜀𝑒 =
𝜀+1
2
+
𝜀−1
2
1
1+12
𝐻
𝑊
+ 0.04 1 −
𝐻
𝑊
2
. (1)
Where ε is substrate permittivity and εe is effective
permittivity.
Z0 =
120 𝜋
𝜀𝑒 [
𝑊
𝐻
+1.393+
2
3
ln(1.444+
𝑊
𝐻
)]
ohms. (2)
Where Z0 is characteristic impedance.
From the equations 1&2, for the specification of using FR-4
substrate that carries permittivity of 4.8 and also considering
the market availability of 0.06 in standard thickness
substrate, we perform the calculations. So H = 0.06 in = 1.5
mm W=3 mm.
The values are assumed, so that the W/H ratio is more than
1 for design and simplification of calculation. Below is the
table 1 representing microstrip line dimensions for ease of
understanding the iterations carried out to get proper values
of W and H for 50 ohms characteristic impedance.
Table.1. Microstrip line dimensions
W(mm) H(mm) W/H Permittivity Z0(ohms)
3 1.5 2 3.618 46.98
3 1 3 3.75 36.133
1.8 1 1.8 3.586 50.044
Thus the final dimensions taken are depicted in the below
fig 2.
Fig.2 Microstrip line dimensions
4. PHASE SHIFTERS
Phase shifters find numerous applications in testing and
measurement systems, but the most significant use is in
phased array antennas. Where the antenna beam can be
steered in space by electronically controlled phase shifters.
There are basically three types of PIN diode phase shifters:
 Switched line,
 Loaded line, and
 Reflection.
The basic schematic of switched-line phase shifter is shown
in the below fig 3, which is the most straightforward type
using two, Single Pole Double Throw (SPDT) switches to
route the signal flow between one of two transmission lines
of different length. The differential phase shift between the
two paths is given by the equation 3.
ΔФ=β(l2- I1) (3)
Fig.3. Basic schematic of switched line phase shifter
Where, β is the propagation constant of the line. If the
transmission lines are TEM (or quasi-TEM, like micro strip),
this phase shift is a linear function of frequency which
implies a true time delay between the input and output ports.
The insertion loss of the switched line phase shifter is equal
to the loss of the SPDT switches plus line losses. The
switched-line phase shifter is usually designed for discrete
binary phase shifts of Δφ= 180◦, 90◦, 45◦, etc.
5. DESIGN AND IMPLEMENTATION
Advanced Design System (ADS) [7] is an electronic design
automation software system developed by Agilent EEsof
EDA a unit of Agilent Technologies now formally called as
Keysight Technologies. It provides an integrated design
environment to designers for RF electronic products such as
mobile phones, pagers, wireless networks, satellite
communications, radar systems, and high-speed data links.

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The following procedure is used for the design of a 90
degree switched line phase shifter for the simulation:
 Initially started with design of suitable microstrip
line dimensions based on availability from market
so widely available substrate FR-4 was chosen with
1mm of thickness.
 Corresponding microstrip line design equations
were employed to come up with width of the line.
 Based on basic schematics of switched line phase
shifter a design consisting of measured width for the
microstrip line and line difference for phase shift
was carried out.
 The above mentioned design was completed using
ideal SPDT switch that was available inbuilt in ADS
tool.
 Its return loss and insertion loss were taken down
after the simulation and plotted.
 Then a design of SPDT switch was performed using
the specifications of already available discrete
electronic component of PIN diode that is vital for
switch design.
 The PIN diode MA4PH301 from MAcom
technologies was used as reference for the new
switch design where the actual PIN diode’s
specifications were fed into the ADS tool for further
analysis.
 The corresponding circuitry for the SPDT switch
was designed along with required DC blocking
capacitors and chokes to operate at a frequency of 1
GHz.
 Further optimizations were done on the values of RF
chokes and DC blocking capacitors using repeated
simulations using ADS inbuilt optimization tool.
 Finally the return loss and insertion loss values were
plotted and readings were recorded.
Design of Basic Phase Shifter
As a first step in modelling, the standard switched line
phase shifter has been modelled in ADS with the
dimensions line difference of 3.423 cm. The analysis setup
has been made for the frequency range 500 MHz -1.5 GHz.
Return loss parameters are simulated. The simulated return
loss is better than 30 dB at the 1 GHz frequency. The phase
shifter modelled in ADS and simulated return loss is shown
in fig 4 and 4.1 respectively.
The figure 4 shows the basic design of switched line phase
shifter using ADS’s inbuilt SPDT switch and note that two
options like S parameter simulation for return loss and
insertion loss and transient simulation block for time
domain results is seen and the phase shift of output
waveforms are also employed.
The fig 4.1 indicates the ideal values observed for the design
of phase shifter to give a phase shift of 90 degrees. As seen
in circuit diagram the ideal SPDT switched employed, so
the graph gives a quite linear curve in either cases delivering
good return loss more than 30 dB and good insertion loss
maintained at less than 1 dB.
Fig. 4 Switched line phase shifter model on ADS
Fig 4.1 Switched line phase shifter return loss(left) and
insertion loss(right)
Design of Phase Shifter Based on Real SPDT
Switch
As a second step in modeling, the standard switched line
phase shifter for 90 degrees was designed again using real
design based on PIN diodes whose part number is
MA4PH301-146 from MA com technology. The design of
SPDT switch involved usage of two of those PIN diodes.
The PIN diode’s specifications like reverse voltage,
minimum operating frequency, total capacitance, series
resistance and delay time was entered in ADS tool to
customize the given PIN diode for modeled SPDT switch is
depicted in fig 5 below.
The complete schematic of Switched line phase shifter for
90 degrees phase shift is shown in the fig 6a and 6b. As it
can been seen that there are 4 PIN diodes used 2 each for an
SPDT switch and corresponding DC blocking capacitors
and RF chokes. The circuit diagram is split into two part for
better understanding, as single diagram is large in dimension
on a single page.

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Fig 5 SPDT switch using PIN diode with specifications
Fig. 6a Final circuit schematic

_______________________________________________________________________________________
Fig.6b. Final circuit schematic
Next the results based on S parameters are summarized and
got an -21.22 dB of return loss and 0.806 dB of insertion
loss which were the targeted specification and performance
to achieve at the beginning. The wave forms are shown in
fig 7 which chows steep dip at 1 GHz of frequency for
return loss and an insertion loss less than 1 dB at the
targeted frequency.
Fig.7 Final Switched line phase shifter return loss (left) and
insertion loss (right)
And a diagram of tabulated values observed throughout the
simulation is as shown in the table 2 and is given for
reference based on which the graphs are displayed above.

_______________________________________________________________________________________
Table.2. Tabulated values from simulation for return loss (left) and insertion loss (right)
6. CONCLUSIONS AND FUTURE SCOPE
Successfully modelled the 90 degree switched line phase
shifter using own design of SPDT switch at 1 GHz
operating frequency. Return loss obtained were well within
the target values namely -21.22 dB and insertion loss less
than 1 dB in magnitude where we got 0.806 dB. Valuable
insight on design using Agilent’s ADS tool was gained and
technically understood the methods and procedures for
optimizing the microwave circuits. Future scope will
include the designed schematic can be implemented
practically on further optimizations using discrete
components on a circuit board.
The discrete components can be converted to stub elements
and radial stubs to make it friendly to implement in the form
of microstrip circuitry and further optimizations can be
processed to reduce the complexity and size.
REFERENCES
[1] Merrilskolnik, “Radar Handbook”, 3rd edition, Page
13.51
[2] http://www.qsl.net/va3iul/Phase_Shifters/Phase_Shi
fters.pdf
[3] S.Navin Andrew Prince, P.Muthukumaran,
N.Jagatheesh, "Design and Implementation of Two
1-Bit Switched Line Phase Shifter", IEEE
International Conference on Advanced
Communication Control and Computing
Technologies (ICACCCT)., 2014., ISBN No. 978-1-
4799-3914.
[4] M. Schühler, C. Schmidt, J. Weber, R. Wansch, and
M. A. Hein "Phase Shifters based on PIN-Diodes
and Varactors: Two Concepts by Comparison", 51st
Internationales Wissenschaftliches Kolloquium,
Technische Universität Ilmenau., September 11 -
15., 2006.
[5] R.V. Garver, “Broad-Band Diode phase Shifters”,
IEEE Transaction on microwave theory and
techniques, vol 20, no. 5, pp 314-323 May 1972.
[6] Siti Mariam Binti Zakaria, "Re-configurable patch
antennas", University Teknikal Malaysia Melaka,
Page No. 9, May 2008.
[7] http://www.keysight.com/en/pc-1297113/advanced-
design-system-ads?cc=IN&lc=eng

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