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8/9/2019 Miniaturized Z-shaped UWB Antenna
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Miniaturized Z-shaped Micro-strip Ultra-wideband Antenna
Prepared By:
Sagar Kumar Dhar
ID: g201206700
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Table of Contents
Abstract ........................................................................................................................................... 4
Introduction ..................................................................................................................................... 4
Literature Review............................................................................................................................ 6
UWB Antenna Technique ............................................................................................................. 10
Antenna Miniaturization Technique ............................................................................................. 11
Proposed Antenna Structure ......................................................................................................... 11
Miniaturization Using L shaped Slot ............................................................................................ 12
Scaled and Parametric Analysis .................................................................................................... 13
Future Works ................................................................................................................................ 15
Conclusion .................................................................................................................................... 15
References ..................................................................................................................................... 16
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List of Figures
Figure 1 Possible UWB communication application ...................................................................... 5
Figure 2 Dual ring UWB antenna [8] ............................................................................................. 6
Figure 3 UWB Antenna: top view (left) and bottom view (right) [9] ............................................ 7
Figure 4 Square Ring UWB Antenna [10] ...................................................................................... 7
Figure 5 Reconfigurable UWB Antenna [11] ................................................................................. 8
Figure 6 UWB monopole antenna [12] ........................................................................................... 8
Figure 7 Z shaped compact narrow band antenna .......................................................................... 9
Figure 8 Z shaped UWB antenna structure [14] ............................................................................. 9
Figure 9 Multiband Z-shaped antenna [15] .................................................................................. 10
Figure 10 Proposed Antenna Structure ......................................................................................... 11
Figure 11 Return loss plot S11...................................................................................................... 12
Figure 12 Miniaturization Using L-shaped slot ............................................................................ 13
Figure 13 Return loss plot of miniaturized antenna ...................................................................... 13
Figure 14 Scaled structure for parametric analysis ....................................................................... 14
Figure 15 Parametric simulation of rectangular ring .................................................................... 14
List of Tables
Table 1 FCC Restrictions [2] .......................................................................................................... 5
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Abstract
Micro-strip UWB antennas are highly desirable cause of their unique features such as low cost,
low weight, simple structure and small size where UWB antennas are required in the many
today’s wireless communication system cause of their advantages such as high data rate, spatial
resolution in radar and imaging technique. A miniaturized UWB antenna with high gain and
omnidirectional radiation pattern is required for all of these systems for seamless operation. In
this work, a miniaturized Z-shaped antenna is proposed in the range of 1.72 to 2.94 GHz which
covers the 2.4 GHz WLAN application having fractional bandwidth of 52% and of the size
18mm*25mm. 17% size reduction is observed using an L-shaped slot in the Z-shaped patch.
However, more fraction bandwidth and size reduction is possible and to cover the whole
3.1GHz-10.6GHz range is desirable.
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Introduction
Ultra-wideband (UWB) systems are associated with larger bandwidth typically refer to the
systems having fractional bandwidth greater than or equal to 20% [1]. Due to its extremely wider
operating bandwidth, such systems are potential for high data rate communication, can provide
high spatial resolution and resistant to multipath fading. But there are Federal Communication
Commission (FCC) restrictions for UWB emission. According to FCC rules, UWB unlicensed
commercial application should follow the emission limits shown in Table I and according to this
rules, highest allowed UWB emission is in the range of 0.5-0.96GHz and 3.1-10.6GHz and the
maximum allowable emission is -41.3dBm/MHz [1]. This restriction in emission limits the range
of operation of UWB system which typically lies in the range of 10m or a few 10m. However,
within the range, portable and handheld devices have good opportunity to communicate with
higher data rate even in Gbps range. Figure 1 shows such possible applications of UWB system
in portable devices like laptop, mobile, projector, printer etc. as WLAN communication system.
Table 1 FCC Restrictions [2]
Frequency
(GHz)
Max.
Power in
dBm/MHz
Frequency
(GHz)
Max.
Power in
dBm/MHz
0.5-0.96 -41.3 1.99-3.1 -51.3
0.96-1.61 -75.3 3.1-10.6 -41.3
1.61-1.99 -53.3 10.6-50.6 -51.3
Figure 1 Possible UWB communication application
On the other hand, cause of high band width, UWB systems can provide high spatial resolution
and high resistant to multipath fading which are useful for low range wireless and wearable
biosensors, contactless remote healthcare system, imaging and radar systems [3], [4], [5], [6].
However, all these lucrative features of wireless communication system requires UWB antenna
at the same time for unaltered system performance.
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On the other hand, commercial UWB systems require small low-cost antennas with
omnidirectional radiation patterns and large bandwidth. It is a well-known fact that planner
antennas present really appealing physical features, such as simple structure, small size and low
cost than any other antenna types. Due to all these interesting characteristics, micro-strip
antennas are extremely attractive to be used in emerging UWB applications and growing
research activity is being focused on them. In this work, a miniaturized Z-shaped UWB antenna
is presented for WLAN application in the range of 1.72 to 2.94 GHz which covers the 2.4 GHz
WLAN application having fractional bandwidth of 52% and of the size 18mm*25mm.
Literature Review
In literature, different UWB antennas can be found but for seamless operation throughout the
band, a UWB antenna should show high gain and linear phase at the operating band. Moreover,
for the portable and handheld devices, miniaturized UWB antennas are highly recommendable.
But reduction in size reduces the bandwidth and gain which causes the uttermost challenge in
UWB Antenna design. In this work, among different UWB antenna technique, slotted patch
geometry are chosen to be worked with and related literature review in this perspective is
presented.
[7] presents an annual ring UWB antenna in the range of 2.8 to 12.3GHz and also provide almost
omnidirectional radiation pattern. But the size of the antenna in this work presented is large
which is 44mm×44mm. [8] presents a dual ring UWB antenna in the range of 31 to 42.8GHz
with fractional bandwidth which used slotted patch technique for UWB realization. The
technique behind the structure presented in [8] is using two radiator rings radiate in adjacent
bands provides wideband together shown in Figure 2.
Figure 2 Dual ring UWB antenna [8]
[9] presents triple band UWB antenna at 3.5/5.5/7.2GHz which also used slotted technique for
UWB realization. In this work, pair of C shaped and one U shaped slot in the radiating patch are
used and dual I shaped slots are used in the ground plane as shown in the Figure 3. The size of
the antenna is larger which is 32mm×28mm : 0.384λ *0.336 λ at 3.5GHz.
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Figure 3 UWB Antenna: top view (left) and bottom view (right) [9]
[10] presents band notched square ring UWB antenna in the range of 3-14.6GHz which has
fractional bandwidth of 130% using pairs of T shaped patch in the radiating element and π
shaped patch in the ground plane. This work also present relatively low sized structure of
12mm×18mm: 0.18λ *0.25 λ at 4.2 GHz and also provide omnidirectional radiation pattern.
Figure 4 Square Ring UWB Antenna [10]
[11] presents on the other hand a reconfigurable UWB antenna possible to tune within the range
3.7 to 4.2GHz and 5.15 to 5.825 GHz electronically. Low fractional bandwidth is offered by this
structure with larger size of 45mm×40mm: 0.55 λ *0.49 λ at 3.7GHz. This work also used slotted
technique for UWB realization needed to be improved with the size.
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Figure 5 Reconfigurable UWB Antenna [11]
[12] presents a compact ring monopole UWB antenna in the range of 3.1-10.6GHz with the size
of 20mm×30mm can be reduced in dimensions.
Figure 6 UWB monopole antenna [12]
[13] presents a Z shaped antenna structure with the size of 10mm×11mm: 0.1λ×0.1λ which
works at around 2.4GHz but provides very narrow bandwidth and can be modified for UWB
applications.
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Figure 7 Z shaped compact narrow band antenna
[14] presents another Z-shaped antenna oriented inversely for UWB realization provides
frequency of operation in the range of 2.9 to 5.6GHz which covers the 5GHz WLAN and
3.5GHz WiMax. Size of the antenna was 40mm*40mm: 0.47λ *0.47 λ at 3.5GHz which is larger
comparatively and needed to be improved for USB type devices or so on.
Figure 8 Z shaped UWB antenna structure [14]
[15] presents multiband Z-shaped antenna structure operate at 2.5 GHz, 3.5GHz and 5.7GHz
with the size of 33m×28mm: 0.28 λ *0.23 λ at 2.5GHz. However, the structure can be improved
for UWB systems with proper slotted technique.
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Figure 9 Multiband Z-shaped antenna [15]
Among all of the works reviewed, it is evident that slotted patch technique can be a possible
solution for UWB antenna realization with excellent gain and omnidirectional radiation pattern.
In this work, a new miniaturized Z-shaped UWB antenna structure is designed and analyzed
which provides frequency of operation in the range of 1.72 to 2.94 GHz which covers the 2.4
GHz WLAN application having fractional bandwidth of 52% and of the size 18mm*25mm.
UWB Antenna Technique
Ultra-wideband antennas with high gain and omnidirectional radiation pattern are highly
desirable for WLAN application and other imaging and radar technology. Due to attractive
features of the micro-strip antenna, UWB antennas are highly desired to be built on micro-strip
structure. But micro-strip structures are by default single frequency structure which throws a big
challenge in UWB antenna realization in micro-strip structure. However, over the years some
techniques are applied for UWB antenna realization from narrow band micro strip antennas:
1. L shaped probe
2. Slotted patch
3. Electromagnetic band gap (EBG) structure loading
4. Fractal structure
Among all of these four techniques, slotted patch is mostly used and desirable cause of its cost
effectiveness and planar structure. In this work, this technique is adopted for transforming a
narrow band Z antenna to a UWB antenna structure.
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Antenna Miniaturization Technique
Miniaturized antenna refers to the electrically small antenna i.e. the physical length is smaller
than the corresponding wavelength at operational frequency [16]. Miniaturized antennas are
highly desirable for modern wireless communication system. But, reduction in size reduces the
bandwidth and gain which is the uttermost challenge in the miniaturized UWB antenna design.
Several miniaturization techniques can be used such as:
1. Loading the antenna with high contrast materials (high permittivity material)
2. Modifying antenna geometry and shape
3. Loading the antenna with lumped element to compensate the large reactance part of
the antenna impedance when size is reduced.
4. Use of meta-materials
In this work, modification in antenna structure is chosen to be worked with since it’s the most
convenient and intelligent manner that will provide low cost as well as rugged and small design.
Proposed Antenna Structure
In this work, a miniaturized Z-shaped UWB antenna is presented for WLAN application in the
range of 1.72 to 2.94 GHz which covers the 2.4 GHz WLAN application having fractional
bandwidth of 52% and of the size 18mm*25mm, material used: FR4. Figure 10 and Figure 11
show the proposed antenna structure and its return loss S11 plot consecutively.
Figure 10 Proposed Antenna Structure
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Figure 11 Return loss plot S11
The key features of the proposed antenna are listed below:
• Operating Frequency Band: 1.72GHz to 2.94GHz
• Fractional Bandwidth: 52%
• Size: 18mm*25mm: 0.13 λ *0.18 λ at 2.18GHz
•
Lowest size ever reported
• Can Cover WLAN at 2.4GHz band
Miniaturization Using L shaped Slot
Once the Z shaped antenna resonates at 2.18 GHz, introducing an L shaped slot in the Z shaped
patch, reduces the center frequency to the 2GHz instead of 2.18 GHz which provides
miniaturization and size of the antenna becomes 0.12λ×0.16λ which indicated 18% of size
reduction. So, L shaped slot provides 18% miniaturization which is attractive very much. In
Figure 12, L shaped slotted Z-shaped UWB antenna is shown and its return loss plot is shown inFigure 13.
0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00Freq [GHz]
-30.00
-25.00
-20.00
-15.00
-10.00
-5.00
0.00
d B ( S ( 1 , 1
) )
HFSSDesign1XY Plot 2 ANSOFT
MX2: 2.9400
MX1: 1.7201
m1
-10.0986 -10.0096
1.2199
Curve Info
dB(S(1,1))Setup1 : Sw eep
Name X Y
m1 2.1800 -26.6421
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Figure 12 Miniaturization Using L-shaped slot
Figure 13 Return loss plot of miniaturized antenna
Scaled and Parametric Analysis
The Z-shaped structure is a narrowband structure by nature. In this work, the narrowband Z-
shaped structure is turned into a UWB antenna using rectangular ring. The optimum size of the
rectangular ring for better return loss and UWB feature is set by parametric analysis in HFSS
13.0. The parametric simulation is shown in Figure 14. In this simulation, the structure is also
scaled to : 14mm*18mm which provides the ultrawideband in the range of 2.3to 3.8GHz at the
center frequency of 2.9GHz.
0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00Freq [GHz]
-25.00
-20.00
-15.00
-10.00
-5.00
0.00
d B ( S ( 1 , 1
) )
HFSSDesign1XY Plot 2 ANSOFT
MX2: 2.6552
MX1: 1.6500
m1
-10.0011 -10.0049
1.0052
Curve Info
dB(S(1,1))Setup1 : Sw eep
Name X Y
m1 2.0600 -23.2432
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Figure 14 Scaled structure for parametric analysis
Figure 15 Parametric simulation of rectangular ring
0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00
Freq [GHz]
-30.00
-25.00
-20.00
-15.00
-10.00
-5.00
0.00
d B ( S ( 1 , 1 ) )
HFSSDesign1XY Plot 1 ANSOFT
MX1: 2.3000
MX2: 3.8200
-10.6706 -10.6606-10.3293-10.1038-9.6702 -9.4223
-10.0191
-7.4977-6.2323
-5.4870 -5.3081-4.2690
1.5200
Curve Info
dB(S(1,1))Setup1 : Sweepk='10mm'
dB(S(1,1))Setup1 : Sweepk='15mm'
dB(S(1,1))Setup1 : Sweepk='20mm'
dB(S(1,1))Setup1 : Sweepk='25mm'
dB(S(1,1))Setup1 : Sweepk='30mm'
dB(S(1,1))Setup1 : Sweepk='35mm'
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Future Works
In this work, a new Z-shaped UWB antenna is investigated with UWB and miniaturization
technique and successfully simulated. However, the structure can be improved for higher
features such as:
•
Can be optimized for larger bandwidth without changing its size so that same antenna can
cover the LTE, GSM, WLAN, WiMax as well as ISM band
• This antenna structure can be a good candidate for MIMO system: uncoupled behavior of
the antenna can be tested.
• Further miniaturization can be offered by slow wave loading using passive or active
elements
Conclusion
In this work, a miniaturized Z-shaped UWB antenna is presented for WLAN application in the
range of 1.72 to 2.94 GHz which covers the 2.4 GHz WLAN application having fractional
bandwidth of 52% and of the size 18mm*25mm. Miniaturization using an L shaped slot in the
patch is realized which gives 17% reduction in size. Successful simulation results in the HFSS 13
ensure the feasibility of such structures for real time implementation. However, it is also possible
to improve the fractional bandwidth with proper slotted patch design without affecting size is
highly desirable.
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