![TELKOMNIKA, Vol.17, No.2, April 2019, pp.573~579
ISSN: 1693-6930, accredited First Grade by Kemenristekdikti, Decree No: 21/E/KPT/2018
DOI: 10.12928/TELKOMNIKA.v17i2.11126 573
Received September 6, 2018; Revised December 6, 2018; Accepted January 4, 2019
Electronically controlled radiation pattern leaky wave
antenna array for (C band) application
Mowafak K. Mohsen*1, M. S. M. Isa2, Z. Zakaria3, A. A. M. Isa4, M. K. Abdulhameed5,
Mothana L. Attiah6, Ahmed M. Dinar7
1,2,3,4,5,6,7
Centre for Telecommunication Research and Innovation (CeTRI), Faculty of Electronic and
Computer Engineering (FKEKK), Universiti Teknikal Malaysia Melaka (UTeM), Malaysia
1,5
Ministry of Higher Education and Scientific Research, University of Kerbala, Iraq
*Corresponding author, e-mail: mowafak.k.m@gmail.com1
, saari@utem.edu.my2
Abstract
This paper provides an insight of a new, leaky-wave antenna (LWA) array. It holds the ability to
digitally steer its beam at a fixed frequency by utilizing only two state of bias voltage. This is done with
acceptable impedance matching while scanning and very little gain variation. Investigation is carried out on
LWAs’ control radiation pattern in steps at a fixed frequency via PIN diodes switches. This study also
presents a novel half-width microstrip LWA (HWMLWA) array. The antenna is made up of the following
basic structures: two elements and reconfigurable control cell with each being comprised of two diodes
and two triangle patches. A double gap capacitor in each unit cell is independently disconnected or
connected via PIN diode switch to achieve fixed-frequency control radiation pattern. The reactance profile
at the microstrip’s free edge and thus the main beam direction is changed once the control-cell states are
changed. The main beam may be directed by the antenna between 61o
and 19o
at 4.2 GHz. C band
achieved the measured peak gain of the antenna of 15 dBi at 4.2 GHz beam scanning range.
Keywords: beam steering, control cell, double gap, HW-LWA array, LWA
Copyright © 2019 Universitas Ahmad Dahlan. All rights reserved.
1. Introduction
Since the proposal of microstrip LWAs (MLWAs) in 1978, considerable interest in its
research followed [1-6]. Due to their large bandwidth, ability to integrate easily with microwave
and millimetre-wave circuits, planar low-profile configuration, inherent beam-scanning abilities
with frequency and narrow beam [7-13], microstrip LWAs continue to be a popular choice. The
equation sin−1(β/ko) gives the main beam’s direction (θ) as measured from the boresight of a
LWA, in which ko refers to the free-space wavenumber while β refers to the phase constant. In
relation to this, the direction that lies at 90 degrees to the plane of the antenna is the boresight.
The main beam direction changes as the value of (β/ko) fluctuates with frequency. Usually,
wireless communication systems function in predefined frequency band although the LWAs
scan the beam via sweeping the operating frequency.
As such, beam scanning at a fixed frequency becomes the desired function. Several
LWAs have been built for the purpose of fixed-frequency scanning, which includes a
multiterminal MLWA [14], Fabry-Perot LWA [15-17], composite left/right-handed (CRLH)
LWA [18], and half-width MLWAs [19]. Since there is a strong attachment of electric field
between the ground plane and microstrip, the fundamental mode of a microstrip line never
radiates. Leaky waves are radiated by some higher-order modes. An electric field-null makes up
the first higher-order mode and a phase reversal along the center of the microstrip.
Considerations of the first higher-order mode’s properties led to the design of a MLWA in which
the center of the microstrip is fixed with a shorting wall. This causes the microstrip line’s width to
be reduced by half. Such antenna is also termed as half-width (HW) microstrip LWA
(HW-MLWA) [20].
The requirement of not exciting anything else apart from the first higher order mode
complicates the feeding process of a traditional microstrip LWA. Beneath the microstrip, the
electric field’s normal component is the mode’s peculiar aspect. As such, excitation can only be
achieved by utilizing two offset feeds that are driven 180 out of phase. Vias that connect a
half-width line with one edge to the plane of the ground and having a single offset feed was](https://image.slidesharecdn.com/411126-200804031930/85/Electronically-controlled-radiation-pattern-leaky-wave-antenna-array-for-C-band-application-1-320.jpg)
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TELKOMNIKA Vol. 17, No. 2, April 2019: 573-579
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recently suggested by Zelinski et al [5]. This arrangement creates an electric wall at a location in
which full-width antenna’s electric field becomes zero. In addition to utilizing a simpler feed
system, this implementation benefits by having only one radiating edge. Lumped capacitors
could be combined to such single edge as suggested by Laheurte and Luxey, in order to give
the required reactance to potentially alter the main beam’s direction towards any angle from
broadside to endfire.
This paper provides an insight into the development of a method that allows a MLWAs
to reach fixed-frequency beam scanning and also suggestions on a novel HW-MLWA array
configuration because the high-gain and the highly directional antenna arrays at the transmitter (TX)
and the receiver (RX) reinforces the suitability of wireless communications [21-24]. That eliminates
the necessity of lumped capacitors. It has two new features: 1) building a systematic control cell
based approach to assess and develop digitally controlled reconfigurable electromagnetic
gadgets which includes antennas, 2) utilizing only two values of bias voltage needed to switch
on and off towards getting impedance-matched fixed frequency beam scanning and high quality.
A binary reconfigurable control cell (covetable between two states) forms the basic structure of
the HW-MLWA. Stacking of some similar unit cells created the HW-MLWA. As detailed in the
following part, alteration of the states of control cells allows fixed frequency steering of the
antenna beam. A total of 12 control cells are used in proposed design each cell is contain two
triangles.
2. Antenna Configuration
The structure proposed is a modified two elements of HW-MLWA with 6 periodic control
cells in each elements as shown in Figure 1 (a). Each element of HW-MLWA is designed on
Rogers RT5880 substrate with εr=2.2, and tanδ=0.0009. Length (L), width (W), and height (h) of
the substrate is 239 mm (3.3347λo), 100 mm (1.4λo), and 1.575 mm, respectively, where λo
denotes the free-space wavelength that is calculated at 4.2GHz. Length and width of the ground
plane has the same respective dimensions of the substrate. The length (lp) and the width (wp) of
microstrip line is 222 mm (3.108λo) and 12 mm (0.168λo), respectively. The proposed
HW-MLWA array is fed from one end of the radiation element using a standard SMA feed and
the outer free corner of each branch is shorted to the ground plane by a via to avoid reflection
and to achieve good impedance matching as demonstrated in Figure 1 (b). Dimensions of the
feed line are optimized according to some parametric studies. The optimum parameter values
for the length (lf) is 4.5 mm and width of the feed (wf1, wf2, wf3 and wf4) are 8.5 mm, 6 mm, 4 mm
and 31 mm, respectively. One edge of microstrip line is connected to the ground using a vias
array, which is placed along the edge of microstrip line. Major purpose of the vias array is to
avoid the propagation of the fundamental transversal electromagnetic (TEM) wave and to
support the propagation of first higher-order mode through the structure [25-26]. The proposed
antenna to shorten the edge of each element are used 145 vias. The design configurations of
these structures have been presented in. The metallized diameter (d) and distance (S) between
the two adjacent vias can be calculated using the following (1), that set the design
rules [27-28].
5.0,2.0
s
d
d o (1)
The distance (S) between the two vias is 1.5 mm, and the value of the diameter (d) of
each via is 0.8 mm. The appropriate gap(n) between the feed and the first via and gap (m)
between the feed and first control cell are 4.9 mm and 48.55 mm, respectively, as shown in
Figure 1 (c). These gaps are required to force the wave toward the microstrip edges and
improve matching impedance [29].
3. Control Cell Configuration
The concept of cascading multiple type of unit cells to create a larger cell has been
previously studied by [30] for nonreconfigurable structures. Major drawback in that approach is
that this design system is nonreconfigurable, which means large cells cannot be operated for
other configurations after fabrication. In this paper, the idea of a reconfigurable control cell is](https://image.slidesharecdn.com/411126-200804031930/85/Electronically-controlled-radiation-pattern-leaky-wave-antenna-array-for-C-band-application-2-320.jpg)
![TELKOMNIKA ISSN: 1693-6930
Electronically controlled radiation pattern leaky wave antenna... (Mowafak K Mohsen)
575
presented, which consists of small reconfigurable unit cells. The design allows to dynamically
change the characteristics and size of the large-cell.
The free edge of microstrip line contains (6) equally spaced control cells of each
element with a space separation between cells (A3) of 9.8 mm. Each cell contains two triangular
patches and the dimension of each triangle is (A1) 20 mm and (A2) 16 mm as shown in
Figure 1 (b). A set of control cell patches, was putted very closer to the microstrip line’s free
edge, leaving a narrow 0.25 mm gap (g1) between them, and the gap between the triangles in
control cell (g2) is 0.2 mm as shown in Figure 1 (b). Each control cell consists of two triangular
patches, two PIN diodes are working as binary switch and two vias that goes through the
substrate than connected to the ground level. The PIN diode is connected with the triangular
patch plan through its p-terminal whereas the n-terminal is connected to a via as shown in
Figure 1 (c). The p-terminal of every diode is attached independently to the positive terminal of
DC power supply using externally controlled switches. The ground plane is connected with the
other terminal (-ve) of the DC supply. When a diode is in ON state, i.e. forward biased, the patch
is connected to the ground and when the diode is in OFF state, i.e. reverse biased, the patch is
isolated from the ground. Having a separate connection to the p-terminal provides an individual
control of the states of each diode. In this way, the patches can be controlled individually. The
total input impedance of the antenna when the PIN diodes are ON can be calculated as [31].
(a)
(b) (c)
Figure 1. Reconfigurable HW-MLWAs array: (a) top view,
(b) microstrip line with control cell, (c) port and feed line for two elements.
4. Results & Discussion
CST Microwave Studio was put into consideration for the development and study of the
proposed antenna. The switches of PIN diode that are utilized for this test are taken as the best
antenna. The diode is forward-biased switch (shown as ‘1’) and the triangle patch lies directly
joined to the ground as positive supply is placed to the PIN diode’s p-terminal. A dc supply’s
positive terminal is joined separately to each PIN-diode’s p-terminal. This permits the state of
each PIN diode to be individually controlled (‘Off’ or ‘On’). When the PIN diodes are in the Off
state (represented as ‘0’), the capacitance between the ground and the free edge of the
microstrip line is lower than when diodes are in the ON state. Lower capacitance causes a main
beam that lies at a greater distance from broadside while the higher capacitance causes the](https://image.slidesharecdn.com/411126-200804031930/85/Electronically-controlled-radiation-pattern-leaky-wave-antenna-array-for-C-band-application-3-320.jpg)
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Electronically controlled radiation pattern leaky wave antenna... (Mowafak K Mohsen)
577
Figure 4. |S11| for the state 5 of the
proposed antenna
Figure 5. Radiation patterns of the proposed antenna
at 4.2GHz for different switch cases in Table 1
The voltage standing wave ratio (VSWR) indicates the impedance matching of antenna.
The value of VSWR should lie between 1 and 2. In Figure 6 shows the VSWR for proposed
HW-MLWA antenna array for five states of switched and Table 2 is contain the value of VSWR
at 4.2 GHz for switches configuration in Table 1, in state no. 1 the value of VSWR is low
because the main beam near of the broadside and in state no. 5 the VSWR is high because the
poor radiation when the main beam steering towards endfire.
As the beam points get nearer to the foresight, the efficiency of a MLWA’s radiation is
high. The radiation efficiency lowers as the beam move towards the endfire [32, 33].
Conversely, as the beam scans the same range at 4.2 GHz, the reconfigurable HW-MLWA’s
radiation efficiency lowers by only 4.181% from 95.6% to 91.479%. As the antenna is properly
similar for all the selected control cell states, the reconfigurable antenna’s total efficiency almost
matches all those states’ radiation efficiency. In both forms of LWA’s, when the beam is steered
towards the direction of end-fire, the lowering of radiation efficiency compensates for the rise in
directivity. In this case, within the context of a proper LWA design, production by this gain
variation may be lower than the industrial standard 3dB limit.
The radiation efficiency of this HW-MLWA is shown in Figure 7 for different main beam
directions. The radiation efficiency is high for the beams directed closer to 39o and the efficiency
decreases when approaching endfire at the main beam direction at 61o.
Table 2. Switch Configurations and VSWR at 4.2 GHz
State No. Switch cases VSWR
1 11-11-11-11-11-11-11-11-11-11-11-11 1.306
2 00-00-00-00-00-00-11-11-11-11-11-11 1.411
3 10-10-10-10-10-10-10-10-10-10-10-10 1.387
4 11-11-11-11-11-11-00-00-00-00-00-00 1.269
5 00-00-00-00-00-00-00-00-00-00-00-00 1.638
Figure 6. VSWA for the HW-MLWA array for the
switches configuration for all cases in for the
switches configuration for all cases Table 2
Figure 7. Efficiency for the HW-MLWA array
for the switches configuration for all cases in
Table1
Frequency (GHz)
3.8 4.0 4.2 4.4 4.6 4.8
S11(dB)
-30
-25
-20
-15
-10
-5
0
Theta (Degree)
0 20 40 60 80 100 120
Directivity(dB)
-30
-20
-10
0
10
20
State 1
State 2
State 3
State 4
State 5
Frequency (GHz)
4.10 4.15 4.20 4.25 4.30
VSWR
0.0
0.5
1.0
1.5
2.0
2.5
3.0
State 1
State 2
State 3
State 4
State 5
Frequency (GHz)
3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0
Efficiency(%)
50
60
70
80
90
100
State 1
State 2
State 3
State4
State 5](https://image.slidesharecdn.com/411126-200804031930/85/Electronically-controlled-radiation-pattern-leaky-wave-antenna-array-for-C-band-application-5-320.jpg)
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5. Conclusion
A new technique to control the radiations of periodic HW-MLWAs array at a 4.2 GHz,
using control cell containing two triangular patches with two PIN diodes, is presented in the
article. The free edge of the microstrip line has been loaded by double gap capacitors, which
are periodic, and PIN diodes has been used to control their connections with the ground plane.
This design helps us to achieve beam scanning while there is no need of lumped capacitors and
we also need not to change the frequency. We have developed a multi-state of control cell
approach to analyses reconfigurable periodic structures and this approach is used for the
design of microwave leaky wave antenna that is reconfigurable. Our current methodology is
helpful for the design and analysis of reconfigurable periodic structure systematically. The
scanning range of the designed antenna is 42o at 4.2 GHz while the peak gain at 4.2 GHz is
15 dBi beam scanning range is realized in C band.
Acknowledgements
This work is fully sponsored by Universiti Teknikal Malaysia Melaka (UTeM)
Postgraduate Zamalah Scheme. The authors would also like to thank Center for Research and
Innovation Management (CRIM), Centre of Excellence, Universiti Teknikal Malaysia Melaka
(UTeM) for their encouragement and help in sponsoring this study.
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Electronically controlled radiation pattern leaky wave antenna array for (C band) application
- 1. TELKOMNIKA, Vol.17, No.2, April 2019, pp.573~579 ISSN: 1693-6930, accredited First Grade by Kemenristekdikti, Decree No: 21/E/KPT/2018 DOI: 10.12928/TELKOMNIKA.v17i2.11126 573 Received September 6, 2018; Revised December 6, 2018; Accepted January 4, 2019 Electronically controlled radiation pattern leaky wave antenna array for (C band) application Mowafak K. Mohsen*1, M. S. M. Isa2, Z. Zakaria3, A. A. M. Isa4, M. K. Abdulhameed5, Mothana L. Attiah6, Ahmed M. Dinar7 1,2,3,4,5,6,7 Centre for Telecommunication Research and Innovation (CeTRI), Faculty of Electronic and Computer Engineering (FKEKK), Universiti Teknikal Malaysia Melaka (UTeM), Malaysia 1,5 Ministry of Higher Education and Scientific Research, University of Kerbala, Iraq *Corresponding author, e-mail: mowafak.k.m@gmail.com1 , saari@utem.edu.my2 Abstract This paper provides an insight of a new, leaky-wave antenna (LWA) array. It holds the ability to digitally steer its beam at a fixed frequency by utilizing only two state of bias voltage. This is done with acceptable impedance matching while scanning and very little gain variation. Investigation is carried out on LWAs’ control radiation pattern in steps at a fixed frequency via PIN diodes switches. This study also presents a novel half-width microstrip LWA (HWMLWA) array. The antenna is made up of the following basic structures: two elements and reconfigurable control cell with each being comprised of two diodes and two triangle patches. A double gap capacitor in each unit cell is independently disconnected or connected via PIN diode switch to achieve fixed-frequency control radiation pattern. The reactance profile at the microstrip’s free edge and thus the main beam direction is changed once the control-cell states are changed. The main beam may be directed by the antenna between 61o and 19o at 4.2 GHz. C band achieved the measured peak gain of the antenna of 15 dBi at 4.2 GHz beam scanning range. Keywords: beam steering, control cell, double gap, HW-LWA array, LWA Copyright © 2019 Universitas Ahmad Dahlan. All rights reserved. 1. Introduction Since the proposal of microstrip LWAs (MLWAs) in 1978, considerable interest in its research followed [1-6]. Due to their large bandwidth, ability to integrate easily with microwave and millimetre-wave circuits, planar low-profile configuration, inherent beam-scanning abilities with frequency and narrow beam [7-13], microstrip LWAs continue to be a popular choice. The equation sin−1(β/ko) gives the main beam’s direction (θ) as measured from the boresight of a LWA, in which ko refers to the free-space wavenumber while β refers to the phase constant. In relation to this, the direction that lies at 90 degrees to the plane of the antenna is the boresight. The main beam direction changes as the value of (β/ko) fluctuates with frequency. Usually, wireless communication systems function in predefined frequency band although the LWAs scan the beam via sweeping the operating frequency. As such, beam scanning at a fixed frequency becomes the desired function. Several LWAs have been built for the purpose of fixed-frequency scanning, which includes a multiterminal MLWA [14], Fabry-Perot LWA [15-17], composite left/right-handed (CRLH) LWA [18], and half-width MLWAs [19]. Since there is a strong attachment of electric field between the ground plane and microstrip, the fundamental mode of a microstrip line never radiates. Leaky waves are radiated by some higher-order modes. An electric field-null makes up the first higher-order mode and a phase reversal along the center of the microstrip. Considerations of the first higher-order mode’s properties led to the design of a MLWA in which the center of the microstrip is fixed with a shorting wall. This causes the microstrip line’s width to be reduced by half. Such antenna is also termed as half-width (HW) microstrip LWA (HW-MLWA) [20]. The requirement of not exciting anything else apart from the first higher order mode complicates the feeding process of a traditional microstrip LWA. Beneath the microstrip, the electric field’s normal component is the mode’s peculiar aspect. As such, excitation can only be achieved by utilizing two offset feeds that are driven 180 out of phase. Vias that connect a half-width line with one edge to the plane of the ground and having a single offset feed was
- 2. ISSN: 1693-6930 TELKOMNIKA Vol. 17, No. 2, April 2019: 573-579 574 recently suggested by Zelinski et al [5]. This arrangement creates an electric wall at a location in which full-width antenna’s electric field becomes zero. In addition to utilizing a simpler feed system, this implementation benefits by having only one radiating edge. Lumped capacitors could be combined to such single edge as suggested by Laheurte and Luxey, in order to give the required reactance to potentially alter the main beam’s direction towards any angle from broadside to endfire. This paper provides an insight into the development of a method that allows a MLWAs to reach fixed-frequency beam scanning and also suggestions on a novel HW-MLWA array configuration because the high-gain and the highly directional antenna arrays at the transmitter (TX) and the receiver (RX) reinforces the suitability of wireless communications [21-24]. That eliminates the necessity of lumped capacitors. It has two new features: 1) building a systematic control cell based approach to assess and develop digitally controlled reconfigurable electromagnetic gadgets which includes antennas, 2) utilizing only two values of bias voltage needed to switch on and off towards getting impedance-matched fixed frequency beam scanning and high quality. A binary reconfigurable control cell (covetable between two states) forms the basic structure of the HW-MLWA. Stacking of some similar unit cells created the HW-MLWA. As detailed in the following part, alteration of the states of control cells allows fixed frequency steering of the antenna beam. A total of 12 control cells are used in proposed design each cell is contain two triangles. 2. Antenna Configuration The structure proposed is a modified two elements of HW-MLWA with 6 periodic control cells in each elements as shown in Figure 1 (a). Each element of HW-MLWA is designed on Rogers RT5880 substrate with εr=2.2, and tanδ=0.0009. Length (L), width (W), and height (h) of the substrate is 239 mm (3.3347λo), 100 mm (1.4λo), and 1.575 mm, respectively, where λo denotes the free-space wavelength that is calculated at 4.2GHz. Length and width of the ground plane has the same respective dimensions of the substrate. The length (lp) and the width (wp) of microstrip line is 222 mm (3.108λo) and 12 mm (0.168λo), respectively. The proposed HW-MLWA array is fed from one end of the radiation element using a standard SMA feed and the outer free corner of each branch is shorted to the ground plane by a via to avoid reflection and to achieve good impedance matching as demonstrated in Figure 1 (b). Dimensions of the feed line are optimized according to some parametric studies. The optimum parameter values for the length (lf) is 4.5 mm and width of the feed (wf1, wf2, wf3 and wf4) are 8.5 mm, 6 mm, 4 mm and 31 mm, respectively. One edge of microstrip line is connected to the ground using a vias array, which is placed along the edge of microstrip line. Major purpose of the vias array is to avoid the propagation of the fundamental transversal electromagnetic (TEM) wave and to support the propagation of first higher-order mode through the structure [25-26]. The proposed antenna to shorten the edge of each element are used 145 vias. The design configurations of these structures have been presented in. The metallized diameter (d) and distance (S) between the two adjacent vias can be calculated using the following (1), that set the design rules [27-28]. 5.0,2.0 s d d o (1) The distance (S) between the two vias is 1.5 mm, and the value of the diameter (d) of each via is 0.8 mm. The appropriate gap(n) between the feed and the first via and gap (m) between the feed and first control cell are 4.9 mm and 48.55 mm, respectively, as shown in Figure 1 (c). These gaps are required to force the wave toward the microstrip edges and improve matching impedance [29]. 3. Control Cell Configuration The concept of cascading multiple type of unit cells to create a larger cell has been previously studied by [30] for nonreconfigurable structures. Major drawback in that approach is that this design system is nonreconfigurable, which means large cells cannot be operated for other configurations after fabrication. In this paper, the idea of a reconfigurable control cell is
- 3. TELKOMNIKA ISSN: 1693-6930 Electronically controlled radiation pattern leaky wave antenna... (Mowafak K Mohsen) 575 presented, which consists of small reconfigurable unit cells. The design allows to dynamically change the characteristics and size of the large-cell. The free edge of microstrip line contains (6) equally spaced control cells of each element with a space separation between cells (A3) of 9.8 mm. Each cell contains two triangular patches and the dimension of each triangle is (A1) 20 mm and (A2) 16 mm as shown in Figure 1 (b). A set of control cell patches, was putted very closer to the microstrip line’s free edge, leaving a narrow 0.25 mm gap (g1) between them, and the gap between the triangles in control cell (g2) is 0.2 mm as shown in Figure 1 (b). Each control cell consists of two triangular patches, two PIN diodes are working as binary switch and two vias that goes through the substrate than connected to the ground level. The PIN diode is connected with the triangular patch plan through its p-terminal whereas the n-terminal is connected to a via as shown in Figure 1 (c). The p-terminal of every diode is attached independently to the positive terminal of DC power supply using externally controlled switches. The ground plane is connected with the other terminal (-ve) of the DC supply. When a diode is in ON state, i.e. forward biased, the patch is connected to the ground and when the diode is in OFF state, i.e. reverse biased, the patch is isolated from the ground. Having a separate connection to the p-terminal provides an individual control of the states of each diode. In this way, the patches can be controlled individually. The total input impedance of the antenna when the PIN diodes are ON can be calculated as [31]. (a) (b) (c) Figure 1. Reconfigurable HW-MLWAs array: (a) top view, (b) microstrip line with control cell, (c) port and feed line for two elements. 4. Results & Discussion CST Microwave Studio was put into consideration for the development and study of the proposed antenna. The switches of PIN diode that are utilized for this test are taken as the best antenna. The diode is forward-biased switch (shown as ‘1’) and the triangle patch lies directly joined to the ground as positive supply is placed to the PIN diode’s p-terminal. A dc supply’s positive terminal is joined separately to each PIN-diode’s p-terminal. This permits the state of each PIN diode to be individually controlled (‘Off’ or ‘On’). When the PIN diodes are in the Off state (represented as ‘0’), the capacitance between the ground and the free edge of the microstrip line is lower than when diodes are in the ON state. Lower capacitance causes a main beam that lies at a greater distance from broadside while the higher capacitance causes the
- 4. ISSN: 1693-6930 TELKOMNIKA Vol. 17, No. 2, April 2019: 573-579 576 main beam to lie nearer to the broadside. Extra control over this reaction profile is attributed to having these control cells in the microstrip’s free-edge. In comparison to the effective capacitance without patches, the longer patches bring out a reduced effective capacitance between the radiating edge and ground. Thus, triangle patches cause the direction of the main beam to be moved towards the endfire. Alterations to the PIN diode switch configuration for a given patch length can further causes changes to the main beam’s direction. The switch cases and corresponding direction of main beams at 4.2 GHz is represented by Table 1. Input reflection coefficients of the five distinct switch settings presented in Table 1 is represented by Figures 2, 3, and 4. They show that for these switch cases, the antenna is highly coordinated at 4.2 GHz. Compared to the capacitance as the switch is Off, the capacitance between the ground plane and free edge of the microstrip line is greater than when the switch is On (1). The admittance profile at the microstrip line’s radiating edge is altered by the change of switch states, and thus causing alterations to the effective β of the structure in Table 1. Figure 5 shows the radiation pattern for the five distinct switch settings. It is observable that for state 1 when all diodes are (ON) than the vias is connected the patch cell with ground plane the main beam direction combine towards (19o) near of broadside. For state 5 when the all diodes are (OFF) than no any connected between patches cell with the ground plane the main beams are directed towards (61o) near of the endfire. Table 1. Switch Configurations and Corresponding Main Beam Directions at 4.2 GHz State No. Switch cases Main Beam Direction (θm) 1 11-11-11-11-11-11-11-11-11-11-11-11 19o 2 00-00-00-00-00-00-11-11-11-11-11-11 23o 3 10-10-10-10-10-10-10-10-10-10-10-10 36o 4 11-11-11-11-11-11-00-00-00-00-00-00 39o 5 00-00-00-00-00-00-00-00-00-00-00-00 61o Frequency (GHz) 3.8 4.0 4.2 4.4 4.6 4.8 S11(dB) -30 -25 -20 -15 -10 -5 0 (a) (b) Figure 2. |S11| for the (a) state 1 and (b) state 2 of the proposed antenna (a) (b) Figure 3. |S11| for the (a) state 3 and (b) state 4 of the proposed antenna Frequency (GHz) 3.8 4.0 4.2 4.4 4.6 4.8 S11(dB) -30 -25 -20 -15 -10 -5 0 5 Frequency (GHz) 3.8 4.0 4.2 4.4 4.6 4.8 S11(dB) -30 -25 -20 -15 -10 -5 0 Frequency (GHz) 3.8 4.0 4.2 4.4 4.6 4.8 S11(dB) -30 -25 -20 -15 -10 -5 0 5
- 5. TELKOMNIKA ISSN: 1693-6930 Electronically controlled radiation pattern leaky wave antenna... (Mowafak K Mohsen) 577 Figure 4. |S11| for the state 5 of the proposed antenna Figure 5. Radiation patterns of the proposed antenna at 4.2GHz for different switch cases in Table 1 The voltage standing wave ratio (VSWR) indicates the impedance matching of antenna. The value of VSWR should lie between 1 and 2. In Figure 6 shows the VSWR for proposed HW-MLWA antenna array for five states of switched and Table 2 is contain the value of VSWR at 4.2 GHz for switches configuration in Table 1, in state no. 1 the value of VSWR is low because the main beam near of the broadside and in state no. 5 the VSWR is high because the poor radiation when the main beam steering towards endfire. As the beam points get nearer to the foresight, the efficiency of a MLWA’s radiation is high. The radiation efficiency lowers as the beam move towards the endfire [32, 33]. Conversely, as the beam scans the same range at 4.2 GHz, the reconfigurable HW-MLWA’s radiation efficiency lowers by only 4.181% from 95.6% to 91.479%. As the antenna is properly similar for all the selected control cell states, the reconfigurable antenna’s total efficiency almost matches all those states’ radiation efficiency. In both forms of LWA’s, when the beam is steered towards the direction of end-fire, the lowering of radiation efficiency compensates for the rise in directivity. In this case, within the context of a proper LWA design, production by this gain variation may be lower than the industrial standard 3dB limit. The radiation efficiency of this HW-MLWA is shown in Figure 7 for different main beam directions. The radiation efficiency is high for the beams directed closer to 39o and the efficiency decreases when approaching endfire at the main beam direction at 61o. Table 2. Switch Configurations and VSWR at 4.2 GHz State No. Switch cases VSWR 1 11-11-11-11-11-11-11-11-11-11-11-11 1.306 2 00-00-00-00-00-00-11-11-11-11-11-11 1.411 3 10-10-10-10-10-10-10-10-10-10-10-10 1.387 4 11-11-11-11-11-11-00-00-00-00-00-00 1.269 5 00-00-00-00-00-00-00-00-00-00-00-00 1.638 Figure 6. VSWA for the HW-MLWA array for the switches configuration for all cases in for the switches configuration for all cases Table 2 Figure 7. Efficiency for the HW-MLWA array for the switches configuration for all cases in Table1 Frequency (GHz) 3.8 4.0 4.2 4.4 4.6 4.8 S11(dB) -30 -25 -20 -15 -10 -5 0 Theta (Degree) 0 20 40 60 80 100 120 Directivity(dB) -30 -20 -10 0 10 20 State 1 State 2 State 3 State 4 State 5 Frequency (GHz) 4.10 4.15 4.20 4.25 4.30 VSWR 0.0 0.5 1.0 1.5 2.0 2.5 3.0 State 1 State 2 State 3 State 4 State 5 Frequency (GHz) 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 Efficiency(%) 50 60 70 80 90 100 State 1 State 2 State 3 State4 State 5
- 6. ISSN: 1693-6930 TELKOMNIKA Vol. 17, No. 2, April 2019: 573-579 578 5. Conclusion A new technique to control the radiations of periodic HW-MLWAs array at a 4.2 GHz, using control cell containing two triangular patches with two PIN diodes, is presented in the article. The free edge of the microstrip line has been loaded by double gap capacitors, which are periodic, and PIN diodes has been used to control their connections with the ground plane. This design helps us to achieve beam scanning while there is no need of lumped capacitors and we also need not to change the frequency. We have developed a multi-state of control cell approach to analyses reconfigurable periodic structures and this approach is used for the design of microwave leaky wave antenna that is reconfigurable. Our current methodology is helpful for the design and analysis of reconfigurable periodic structure systematically. The scanning range of the designed antenna is 42o at 4.2 GHz while the peak gain at 4.2 GHz is 15 dBi beam scanning range is realized in C band. Acknowledgements This work is fully sponsored by Universiti Teknikal Malaysia Melaka (UTeM) Postgraduate Zamalah Scheme. The authors would also like to thank Center for Research and Innovation Management (CRIM), Centre of Excellence, Universiti Teknikal Malaysia Melaka (UTeM) for their encouragement and help in sponsoring this study. References [1] Menzel W. A new travelling wave antenna in microstrip. Proceedings of Microwave Conference, 1978, 8th European 1978: 302-306. [2] Mohsen MK et al. The Fundamental of Leaky Wave Antenna. Journal of Telecommunication, Electronic and Computer Engineering (JTEC). 2018; 10(1): 119–127. [3] Damm C, Maasch M, Gonzalo R, Jakoby R. Tunable Composite RightlLeft-Handed Leaky Wave Antenna Based on a Rectangular Waveguide Using Liquid Crystals. 2010 IEEE MTT-S International Microwave Symposium Digest (MTT). 2010: 13–16. [4] Cheng Y, Wu LS, Tang M, Zhang YP, Mao JF. A Sinusoidally-Modulated Leaky-Wave Antenna with Gapped Graphene Ribbons. IEEE Antennas and Wireless Propagation Letters. 2017; 16: 3000–3004. [5] Dong Y, Itoh T. Realization of a Composite Right/Left-Handed Leaky-Wave Antenna with Circular Polarization. 2010 Asia-Pacific Microwave Conference. 2010: 865–868. [6] Oliner AA. Leakage from higher modes on microstrip line with application to antennas. Radio Science. 1987; 22: 907–912. [7] Abdulhameed MK, Isa MSM, Zakaria Z, Mohsin MK, Attiah ML. Mushroom-Like EBG to Improve Patch Antenna Performance For C-Band Satellite Application. International Journal of Electrical and Computer Engineering (IJECE). 2018; 8(5): 3875–3881. [8] Mohsen MK, Isa MSM, Isa AAM, Zakaria Z, Abdulhameed MK. Control Radiation Pattern for Half Width Microstrip Leaky Wave Antenna by using PIN Diodes. International Journal of Electrical and Computer Engineering. 2018; 8(5): 2959–2966. [9] Geng Y, Wang J, Li Y, Li Z, Chen M, Zhang Z. High-efficiency leaky-wave antenna array with sidelobe suppression and multibeam generation. IEEE Antennas and Wireless Propagation Letters. 2017; 16: 2787–2790. [10] Guzman-Quiros R, Weily AR, Gomez-Tornero JL, Guo YJ. A Fabry-Perot Antenna With Two- Dimensional Electronic Beam Scanning. IEEE Transactions on Antennas and Propagation. 2016; 64(4): 1536–1541. [11] Jackson BDR, Caloz C, Itoh T. Leaky-Wave Antennas. Proceedings of the IEEE. 2012; 100(7). [12] Karmokar DK, Esselle KP, Bird TS. An array of half-width microstrip leaky-wave antennas radiating on boresight. IEEE Antennas and Wireless Propagation Letters. 2015; 14: 112–114. [13] Wu GC, Wang GM, Gao XJ, Liang JG. Wideband dual-element leaky-wave antenna with constant gain and enhanced broadside radiation bandwidth using multilayered composite right/left-handed substrate integrated waveguide. International Journal of RF and Microwave Computer‐Aided Engineering. 2017; 27(3). [14] Li Y, Long Y. Frequency-fixed beam-scanning microstrip leaky-wave antenna with multi-terminals. Electronics Letters. 2006; 42(1): 7–8. [15] Nicholls J, Hum SV. An electronically steerable reflectarray with integrated leaky-wave feed. Antennas and Propagation & USNC/URSI National Radio Science Meeting, 2015 IEEE International Symposium. 2015: 2175–2176.
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