Electronically reconfigurable beam steering array antenna using switched line phase shifter

Electronically Reconfigurable Beam Steering
Array Antenna using Switched Line Phase
Shifter
Hayat Errifi
PhD student, EEA & TI Laboratory
Faculty of Sciences and Technologies
Hassan II University of Casablanca, Morocco
Abdennaceur Baghdad, Abdelmajid Badri,
Aicha Sahel
Professors, EEA & TI Laboratory
Faculty of Sciences and Technologies
Hassan II University of Casablanca, Morocco
Abstract— Beam-steering antennas are the ideal solution for a
variety of system applications, it is most commonly achieved
through using phased arrays, where phase shifters are used to
control the relative of the main-beam. In this paper, a low-cost
directive beam-steering phased array (DBS-PA) antenna using
switched line phase shifters is demonstrated. The proposed
DBS-PA antenna has four micro-strip patch antennas, three
power dividers and four phase shifters printed on the same
Rogers RT-Durroid substrate with a dielectric constant of 2.2
with dimensions of 8 x 3.5 cm. The phased array antenna has a
directivity of 15 dBi and the main beam direction can be
switched between the angles of ±30 degrees with a 3dB beam-
width of 25 degrees. All design and simulations have been
carried out using Agilent AdS and Ansoft HFSS software tools.
The frequency considered for the operation is 10 GHz.
Index Terms— Phase shifters; Switched line; Beam steering;
Patch antenna; Phased arrays; Return loss; Directivity.
I. 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 phased array antennas
[2]. Optimal transmitting and receiving properties are
required to be provided by the modern radio communication
systems for an effective use of transmission channels. Thus
focusing on the antennas, this requires electronically
steerable radio patterns that can be achieved by the phased
array antennas [3,4]. One of the most important part of the
phased array antennas are the phase shifters. This last will
determine differential signal phase shift of antenna.
“Switched-line Phase Shifter” [5, 6] 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].
978-1-5386-2123-3/17/$31.00 ©2017 IEEE
Thus by changing the bias point of a pin-diode from
forward to reverse direction and vice versa, the switching
procedure is obtained. Therefore, by placing a phase shifter
on each radiating element allows the antenna beam to be
electronically steered without physically moving the antenna
element as shown in Fig1.
Fig 1. A Standard phased array antenna system
This research is focuses on the beam-steering patch
antenna radiation pattern which suitable for point-to-point
communication system that requires high gain and directivity
characteristics [7]. The objectives is to design and simulate a
switched line phase shifter for integration on micro-strip
array antenna circuit [8].
All designs and simulations have been carried out using
Advanced Design System software (ADS) and High
Frequency Structure Simulator tool (HFSS). The rest of the
paper is organized as follow: Section II presents the design
specifications of the proposed switched line phase shifter.
Section III present the simulated geometry of the microstrip
phased array antenna system. The simulated results are
discussed in Section IV and finally Section V provides the
conclusion and future works.
II. SWITCHED LINE PHASE SHIFTER
Phase shifters find numerous applications in testing and
measurement systems, but the most significant use is in
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phased array antennas. Where the antenna beam can be
steered in space by electronically controlled phase shifters.
There are three types of PIN diode phase shifters:
Switched line
Loaded line
Reflection.
The aim of the realization of this switched line phase shifter
(SLPS) based on PIN diodes is to integrate it into a microstrip
adaptive antenna array dedicated to X band applications. The
substrate used is RT-Duroid with the following
carracteristiques: thickness: 0.79 mm εr: 2.2 and tgδ: 0.02.
The schematic of SLPS is shown in Fig 2, which is the most
straightforward type using four Single Pole Single Throw
(SPST) 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:
ΔФ= β (L2- L1) (1)
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 real time delay between the input and output ports. The
insertion loss of the switched line phase shifter is equal to the
loss of the SPST switches plus line losses.
Fig 2. Basic schematic of switched line phase shifter
Fig. 4 SLPS circuit designed by ADS
The switch SPST shown in Fig. 3 is considered as the
basic circuit of the SLPS architecture. It can transmit or block
the microwave signal [9]. The diode chosen for this
application is PIN HPND sold by Hewlett-Packard [10]. In
forward bias, the diode is equivalent to a series resistance
characterizing the loss of contact: Rs = 1.5Ω. In reverse bias,
the equivalent circuit is a capacitance in parallel: Ct = 25pF.
Fig 3. SPST Switch in parallel designed by ADS
Therefore, when the circuit is in reverse bias, the RF
signal is transmitted to the output and when the circuit is
biased in direct, the RF signal is blocked. The SPST
architecture is extended to make the proposed SLPS, the
switch has two output branches in which four diodes are
connected in parallel, and each branch has its own bias circuit
as is well illustrated in Fig. 4
This switch can route the signal to a path of two
transmission lines having different length (L1 and L2). The
switching time of these diodes is 2nsec. The bias voltage is -
10V, 10V. The coupling capacitors are selected high value as
not to disrupt the transmission of RF energy [11].
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Next, the results based on S parameters are summarized,
and got an -23.66 dB of return loss and -0.9 dB of insertion
loss; which were the targeted specification and performance
to achieve at the beginning. The waveforms are shown in fig
5, which shows steep dip at 10 GHz of frequency for return
loss and an insertion loss maintained at less than 1 dB at the
targeted frequency.
Fig 5. Switched line phase shifter return loss and insertion loss
III. MICROSTRIP PHASED ARRAY ANTENNA
Microstrip patch antennas are important as single
radiating elements but their major advantages are realized in
application requiring moderate size arrays [12]. The primary
radiator antenna is designed at frequency of 10 GHz which
gives single patch antenna (SPA) as shown in Fig. 6. The
dimensions of the patch are calculated using formulae found
in [13-14] and their values are stored in TABLE I.
TABLE I. DIMENSIONS OF SPA
Parameter
Value (mm)
Substrate type
Roger RT-Durroid
Substrate length
27.93
Substrate width
35.58
Substrate thickness
0.79
Patch width
11.86
Patch length
9.31
Feed-line width
2.408
Quarter wavelength
transformer width
0.5
Fig 6. Geometry of SPA
The proposed directive beam-steering phased array (DBS-
PA) antenna is developed from four SPA as shown in Fig. 7.
All elements are homogenous which has similar dimensions
and characteristics as well.
Fig 7. Geometry of the proposed DBS-P
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The dimension of the DBS-PA antenna is 3.5x8 cm. The
inter-element spacing (IES) of radiating elements must be
determined precisely in order to get the better antenna
performance. The IES is realized to half of wavelength (λ/2)
in most array cases. The feed network is composed of three
T-junction power dividers and four microstrip SLPS printed
on the same Rogers RT-Durroid substrate with a dielectric
constant of 2.2 and thickness of 0.79 mm. The phase shifters
are outlined by red circles and there are labelled as S1, S2, S3
and S4.
With in-phase feeding to the patch antennas, the beam
direction of the array is perpendicular to the substrate (0°). To
achieve beam steering, the microstrip switched line phase
shifters are used to reconfigure the delay feeding line between
the patches.
The SLPS is comprised of two microctrip line segments of
different length (L1 = 5.7 mm and L2 = 8.5 mm for S1), (L1 =
5.7 mm and L2’ = 10 mm for S2), (L1 = 5.7 mm and L2” = 12.4
mm for S3) and (L1 = 5.7 mm and L2”’ = 15 mm for S4).
Selectively connected to the transmission line, RF input, RF
output, four PIN diodes D1, D2, D3, and D4. Only one arm
should be ON at a time. When the PIN diodes D1 and D3 are
ON while PIN diodes D2 and D4 are OFF, the reference delay
line L1 is in the circuit. When the PIN diodes D2 and D4 are
ON while PIN diodes D1 and D3 are OFF, the delay line (L2,
L2’, L2”, or L2”’) is in the circuit [15]. By switching the signal
between the two microstrip lines, it is possible to realize a
specific phase shift.
IV. SIMULATION RESULTS & DISCUSSION
In antenna design, firstly, the researcher needs to
determine the application of the antenna development in
order to fix the antenna‘s operation frequency.
Fig 8. Comparison of radiation pattern by certain phase shifters
configuration in polar plot
This research focused on the 10 GHz operating frequency
of telecommunication satellite and radar systems. The
presented DBS-PA antenna is competent to perform beam
shape ability with sustain frequency operating. This can be
done by the SLPS configuration as summarized in TABLE II.
We can choose from any one of L1 or (L2, L2’, L2”, L2”’) as a
reference line and the other is delay line. There are five
parametric analysis to be considered which are operating
frequency, directivity, beam-width at -3dB, lobe direction
and radiation efficiency.
TABLE II. SLPS CONFIGURATION
Type
of
phase
shifter
SLPS
Phase shifter status
Case 1
Case 2
Case 3
Case 4
Micro-
strip
switche
d line
phase
shifter
S1
D1 and D3
ON (L1)
D1 and D3
ON (L1)
D1 and D3
ON (L1)
D2 and D4
ON (L2)
S2
D1 and D3
ON (L1)
D1 and D3
ON (L1)
D2 and D4
ON (L2’)
D2 and D4
ON (L2’)
S3
D1 and D3
ON (L1)
D2 and D4
ON (L2”)
D2 and D4
ON (L2”)
D2 and D4
ON (L2”)
S4
D1 and D3
ON (L1)
D2 and D4
ON (L2”’)
D2 and D4
ON (L2’”)
D2 and D4
ON (L2’”)
Operating
Freq (GHz)
9.88
9.88
10
10
Lobe Direction
(deg.)
0°
10°
20°
30°
Directivity
(dBi)
15
15.35
15.35
12.2
HPBW
(deg.)
23°
30°
30°
25°
Radiation
efficiency (%)
90
93
93
89
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Fig 9. Comparison of radiation pattern by certain phase shifters
configuration in rectangular plot
Directional beam steering from -30° to +30° has been
observed. To illustrate this beam steering, seven different
beam steering angles at -30°, -20°, -10°, 0°, 10°, 20° and 30°
are simulated and presented. The E-plane radiation patterns
of the DBS-PA antenna are shown in Fig. 8 and Fig. 9. The
scanning ability is 60° with different delay paths. There is an
improvement in terms of directivity. This has been clearly
compared in Fig. 8 which all cases have high directivity of up
to 15 dBi. Single patch provide directivity up to 7 dBi, here
directivity is increased significantly by 8 dBi using array
structure. Besides, the half power beam width (HPBW) is
small for all beam steering angles, so the radiation beam
becomes narrow and more directive.
Fig. 10 Comparison of reflection coefficient by certain phase shifters
configuration
It is important for the phased array to have good
impedance matching at all beam steering angles. To verify
this impedance matching, return losses for the proposed
DBS-PA antenna at beam steering angles of 0°, 10°, 20° and
30° are plotted in Fig. 10
This figure illustrates the reflection coefficient result under
the tolerable S11 of less than -10dB for phase shifters
configuration. It is observed that very good impedance
matching is maintained across all the beam steering angles
with small discrepancy in frequency due to the shift line
lengths.
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