Design of ultra wideband antenna with triple band notch for minimum EMI

Abstract

In this paper, a compact design and analysis of ultra wideband (UWB) microstrip patch antenna with defected ground structure is proposed It's main feature is reduced electromagnetic interference and wide bandwidth. This design has the ability to work between 1.5 GHz and 10.75 GHz, with four notch frequencies. Here almost the whole UWB is covered except ISM band, Wi-Fi for 2.4 and 5 GHz, and some more applications. The proposed design consists of compact sized microstrip line fed patch antenna having dimension of 12.45 × 16 mm2 with U slot on the ground plane.

Full text

DESIGN OF ULTRA WIDEBAND
ANTENNA WITH TRIPLE BAND NOTCH
FOR MINIMUM EMI
Pramod Singh
1
and Rekha Aggarwal
2
1
Department of Electronics and Communication, MIET Meerut,
Meerut, Uttar Pradesh, India; Corresponding author:
pramodnsit@gmail.com
2
Department of Electronics and Communication, AMITY School of
Engineering, New Delhi, New Delhi, India
Received 22 October 2015
ABSTRACT: In this paper, a compact design and analysis of ultra
wideband (UWB) microstrip patch antenna with defected ground struc-
ture is proposed It’s main feature is reduced electromagnetic interfer-
ence and wide bandwidth. This design has the ability to work between
1.5 GHz and 10.75 GHz, with four notch frequencies. Here almost the
whole UWB is covered except ISM band, Wi-Fi for 2.4 and 5 GHz, and
some more applications. The proposed design consists of compact sized
microstrip line fed patch antenna having dimension of 12.45 316 mm
2
with U slot on the ground plane. V
C2016 Wiley Periodicals, Inc.
Microwave Opt Technol Lett 58:1521–1525, 2016; View this article
online at wileyonlinelibrary.com. DOI 10.1002/mop.29851
Key words: microstrip; antenna; ultra wide band; electromagnetic
interference; U slot
1. INTRODUCTION
In modern communication systems, the demand of broadband
antennas has increased for use at high frequency for high data
rate transmission. Printed antenna has the ability to operate in
broad frequency range. Such antennas are conformal in shape
and have the ability to be hidden inside packages making them
well suited for consumer applications. Microstrip antenna is the
most frequently used printed antenna which has such abilities. It
has several advantages over other antenna types such as: low
fabrication cost, linear and circular polarizations are possible
with simple feed, can be easily integrated with microwave inte-
grated circuits, etc [1]. Microstrip antennas are used in many
applications over the broad frequency range from 100 MHz to
50 GHz, but narrow bandwidth is its major drawback.
In 2002, FCC (Federal Communication Commission) has
declared the frequency band 3.1–10.6 GHz for ultra wideband
(UWB) [2]. UWB antennas have attracted a lot of research
interests due to large number of applications existing in UWB
frequency band. Major issue with the UWB antenna system is
electromagnetic interference (EMI) from existing frequency
bands of various narrow band applications. Allocated frequency
bands in UWB are:
IEEE 802.16 (Wi-Fi) has the frequency: 2.3 GHz, 2.5 GHz,
and 3.5 GHz for different regions.
IEEE 802.11 (WLAN) used in five different frequency
ranges: 2.4 GHz, 3.6 GHz, 4.9 GHz, 5 GHz, and 5.9 GHz.
X band for downlink satellite communication: 7.25–7.75 GHz.
In the design of UWB antennas, this EMI problem must be
considered to have better efficiency. Therefore, UWB antenna
must have notches which can reject these unwanted frequency
bands. Thus, main purpose of this design is to present an UWB
antenna with compact size that can cover almost the entire
UWB having minimum interference with existing narrowband
applications in the same band.
For reduced EMI, the frequency bands of existing applica-
tions must be removed from UWB. Therefore, the operation of
UWB antenna must be multiband. There are two options for
design of compact and multiband operation: defected ground
structures (DGS) and electromagnetic band gap structures
(EBG) generally known as photonic band gap structures (PBG)
[3]. The photonic band gap structures are periodic structures
etched in the ground plane and has the ability of unwanted fre-
quency rejection and circuit size reduction. On the other hand,
DGS is not a periodic structure but one or few etched structures
located on the ground plane. The use of PBG in the design of
microwave and millimeter wave components is difficult due to
difficulties in modeling. But modeling of DGS structures are rel-
atively simple and hence these structures are preferred over
PBG structures in the design of microwave circuits.
Researchers have proposed several ideas for designing of
UWB antenna with minimum EMI. Use of DGS to increase
bandwidth and introduce notch bands has been emerged as most
common option. There are several possible DGS patterns such
as rectangular, square, circular, dumbbell, spiral, L-shaped, con-
centric ring, U-shaped and V-shaped, hairpin DGS, hexagonal
DGS, cross shaped DGS, and combined structures have been
appeared in the literature. A shovel-shaped DGS in a printed
monopole to provide band notch characteristics has also been
used [4]. In a different approach, L shaped stripes has been pro-
posed to provide triple frequency monopole antenna [5]. A
UWB antenna with hook-shaped DGS has been used to provide
triple band notch characteristics [6].
2. DESIGN OF PROPOSED STRUCTURE
Microstrip patch antenna has various possible shapes such as
rectangular, circular, square, triangular, etc. Here, rectangular
shape is chosen which is the most frequently used. The design
parameters for this antenna are width Wand length Lof the
patch over a ground plane with width W
g
and length L
g
, sub-
strate thickness h, and dielectric constant of substrate e
r
. The
width Wof the patch can be given as [5].
W5c
2frffiffiffiffiffiffiffiffiffiffi
2
er11
r(1)
where cis the velocity of light and f
r
is the resonant frequency.
Due to fringing effect the effective length of patch is differ-
ent from actual length which can be given as
L5c
2frffiffiffiffiffiffiffiffi
ereff
p22DL(2)
where,
ereff 5er11
2
1er21
21112 h
w

1=2
for w=h>1 (3)
and,
DL50:412hereff 10:3ðÞ
w
h1:264

ereff 20:258ðÞ
w
h10:8
 (4)
The proposed structure is designed on FR
4
substrate which has
thickness (h) of 1.6 mm and dielectric constant (e
r
) of 4.4. For a
resonant frequency (f
r
) of 5.5 GHz, the patch width is 16 mm
and effective length (L
eff
) of the patch is 12.45 mm, with strip
line feed as shown in Figure 1(a). Feed line is located at a
DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 58, No. 7, July 2016 1521

distance of 2.46 mm (x
f
) from the center of the patch. The
dimension of ground plane is 28.1 332 mm2
:To achieve wide-
band operation with notches on some frequencies, U slot on the
ground plane is cut as shown in Figure 1(b). Prototype of the
proposed structure is shown in Figure 2 and equivalent circuit in
Figure 3. For simulation purpose, electromagnetic solver, Ansoft
HFSS is used which numerically investigates and optimizes the
proposed structure. At first, simple rectangular patch antenna is
used with normal ground plan with no slots. The plot of return
loss is shown in the Figure 4.
There are various periodic structures that can limit the wave
propagation in the certain frequency bands. To obtain multiband
operation in UWB, defect in the ground plane is introduced in
three steps. In the first step, a slot parallel to the length of the
ground plane is introduced. Due to this slot wider bandwidth is
obtained as shown in the Figure 5. When a vertical slot is also
Figure 1 (a) Front view of proposed antenna. (b) Back view of
proposed antenna. [Color figure can be viewed in the online issue, which
is available at wileyonlinelibrary.com]
Figure 2 Prototype of microstrip antenna with DGS. [Color figure can
be viewed in the online issue, which is available at wileyonlinelibrary.com]
Figure 3 Equivalent circuit of patch antenna with DGS. [Color figure
can be viewed in the online issue, which is available at wileyonlinelibrary.
com]
Figure 4 S
11
plot of patch antenna with no slot
1522 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 58, No. 7, July 2016 DOI 10.1002/mop

cut along with this horizontal slot it is observed that the reso-
nant frequency is shifted in the direction of the vertical slot
shown in Figures 6 and 7. If two vertical slots are used along
with this horizontal slot (U slot) then the desired plot is obtained
which covers UWB and leave frequencies allocated for other
services to avoid electromagnetic interference (EMI) as shown
in Figure 8. In UWB it is required to eliminate frequencies from
2.3 to 3.5 GHz for Wi-Fi and WLAN applications.
3. ANALYSIS OF PROPOSED STRUCTURE
For analyzing the proposed structure transmission line model is
used. In this model, the equivalent circuit of a simple patch
antenna is parallel combination of resistance R
1
, inductance L
1
,
and capacitance C
1
. These values can be defined as [6]
C15eoeeLW
2hcos22pxf
L
 (5)
L151
x2
rC1
(6)
and,
R15Qr
xrC1
(7)
where Q
r
can be given as
Qr5cffiffiffiffi
ee
p
frh(8)
Figure 5 S
11
plot of patch antenna with horizontal slot
Figure 6 S
11
plot of patch antenna with horizontal slot and left verti-
cal slot
Figure 7 S
11
plot of patch antenna with horizontal slot and right verti-
cal slot. [Color figure can be viewed in the online issue, which is avail-
able at wileyonlinelibrary.com]
Figure 8 S
11
plot of patch antenna with horizontal slot and left and
right vertical slot (U slot). [Color figure can be viewed in the online
issue, which is available at wileyonlinelibrary.com]
Figure 9 Plot of VSWR. [Color figure can be viewed in the online
issue, which is available at wileyonlinelibrary.com]
TABLE 1 Performance of four resonant frequencies
Resonant
Frequencies
Return
Loss (in dB)
Frequency
Band (in GHz) Bandwidth
1.85 GHz 219.5 1.5–2.2 40%
4.15 GHz 213 4–4.3 7.23%
6.5 GHz 231.7 6–7 15.4%
9.5 GHz 223.25 8.2–10.68 26%
DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 58, No. 7, July 2016 1523

Due to etching of slots in the ground plane, current distribution
in the ground plane changes resulting in the introduction of
equivalent inductance and capacitance. So DGS structure acts
like L
1
C
1
resonant circuit coupled to microstrip line as shown in
Figure 3. Thus the defect produced in the ground plane provides
band rejection characteristics from the resonance property
[7–10]. The cut off frequency of this resonant circuit is mainly
dependent on the etched slot. The inductance L
S
and capacitance
C
S
of this resonant circuit can be given as:
LS51
4pf2
rCS
(9)
CS5fc
4pZ0ðf2
r2f2
cÞ(10)
4. RESULTS AND DISCUSSION
Simulation of the proposed antenna structure is performed using
ANSOFT HFSS. Figure 7 shows the proposed fabricated
antenna. From the simulation results it is seen that the patch
antenna without any slot has a single resonant frequency at
7 GHz and the bandwidth is around 3%. On introducing a hori-
zontal slot the bandwidth at 7 GHz is increased to 21% and one
more resonant frequency at 9.5 GHz is obtained with a band-
width of 6%. In the next step, a vertical slot is also cut along
with the horizontal slot. There are three resonant frequencies at
6.66 GHz, 3.3 GHz, and 9.8 GHz with bandwidths of 15.14%,
50%, and 9.5%.
For the proposed structure with U slot, four resonant frequen-
cies are obtained at 1.8 GHz, 4.19 GHz, 6.72 GHz, and 9.5 GHz.
Bandwidths, frequency range, and return loss at these frequencies
are shown in Table 1. The VSWR performance is shown in Fig-
ure 9 and the radiation pattern of patch with DGS is also shown
in Figure 10. Entire frequency range of the proposed structure is
from 1.5 GHz to 10.6 GHz in four sub-bands with three notches.
First sub-band is from 1.49 GHz to 2.21 GHz, then a notch band
from 2.21 GHz to 4 GHz for Wi-Fi and WLAN applications. Sec-
ond sub-band is from 4 GHz to 4.3 GHz and after that there is
notch band from 4.3 GHz to 6 GHz for WLAN (5.18–
5.825 GHz). Third sub-band is from 6 GHz to 7 GHz and then
stop-band from 7 GHz to 8.15 GHz for downlink satellite appli-
cations in X band. Last sub-band is from 8.15 GHz to 10.68 GHz.
5. CONCLUSION
A novel DGS shapes for stripline feed microstrip patch antenna
are designed, analyzed, and fabricated on ground plane of micro-
strip patch antenna. The resulting structure is compact in size and
shows significant bandwidth enhancement. Simulations are done
using HFSS and the results are verified through measurements.
Due to the use of DGS the UWB range is divided in four frequency
bands with four resonance frequencies: 1.8 GHz, 4.19 GHz,
6.7 GHz, and 9.5GHz. These bands have sufficient bandwidths
and interference with other applications is also avoided.
REFERENCES
1. R. Garg, P. Bhartia, I. Bahl, and A. Ittipiboon, Microstrip Antenna
Design Handbook, Artech House, Dedham, MA, 2002.
2. H. Schantz, A brief history of UWB antennas, In: 2003 IEEE Con-
ference on Ultra Wideband Systems and Technologies, Nov. 16–19,
2003, pp. 209–213.
3. H. Elftouh, N.A. Touhami, M. Aghoutane, S. El Amrani, A. Tazon,
and M. Boussouis, Miniaturized microstrip patch antenna with defected
ground structure, Prog Electromagn Res C 55 (2014), 25–33.
Figure 10 E-plane (red) and H-plane (blue) plots of radiation pattern of proposed structure for four resonant frequencies. [Color figure can be viewed
in the online issue, which is available at wileyonlinelibrary.com]
1524 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 58, No. 7, July 2016 DOI 10.1002/mop

4. A. Nouri and G.R. Dadashzadeh, A compact UWB band-notched
printed monopole antenna with defected ground structure, IEEE
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microstrip-fed monopole antenna using defected ground structure,
IEEE Trans Antennas Propag 59 (2011).
6. L. Wen Tao and S. Xiao Wei, and Y. Qiang Hei, Novel planar
UWB monopole antenna with triple band-notched characteristics,
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defected ground structure, Prog Electromagn Res B 7 (2008).
8. C.A. Balanis, Antenna Theory—Analysis and Design, Wiley, New
York, NY, 1997.
9. M.S. Joung, J.S. Park, and H.S. Kim, A novel modeling method for
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10. J.S. Park, J.H. Kim, J.H. Lee, and S.H. Kim, and S.H. Myung, A
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V
C2016 Wiley Periodicals, Inc.
A 1.12 GHz TO 2 GHz WIDE-
TUNING-RANGE VCO WITH DYNAMIC
COUPLING STRUCTURES
Yong-Bo Xiang, Guang-Ming Wang, Xu-Chun Zhang, and
Jiangang Liang
Air Force Engineering University, Xian, China; Corresponding author:
micsearcherl23@126.com
Received 22 October 2015
ABSTRACT: This paper presents a continuous wide-tuning-range VCO
with 56.4% frequency tuning ratio (FTR). Both a dynamic coupling reso-
nator structure and a dynamic feedback amplifying circuit are proposed
to maintain the wide-tuning range for the VCO. The dynamic coupling
promises stable loaded Q factor and wider tuning range, while the
dynamic feedback amplifying circuit assured the oscillating condition
across the large frequency tuning range. There are three voltage tunable
structures in the proposed, all of which are controlled by the same tun-
ing voltage, so it is easy to be controlled and can be phase locked by a
phase-lock-loop (PLL). The VCO results in a tuning range from
1.12 GHz to 2.00 GHz at 0 15 V tuning voltage. The measured out-
put power is 4.0 6.37 dBm within the tuning range. The measured
phase noise is 294.24 298.66 dBc/Hz at 100 kHz frequency offset
and 2118.07 2123.41 dBc/Hz at 1 MHz frequency offset respectively
within the tuning range. V
C2016 Wiley Periodicals, Inc. Microwave Opt
Technol Lett 58:1525–1529, 2016; View this article online at
wileyonlinelibrary.com. DOI 10.1002/mop.29850
Key words: VCO; varactor; resonator; phase noise; wide band
1. INTRODUCTION
Recently many papers have researched on Wide-tuning-range
VCOs. To achieve wider tuning range, many papers adopted
switchable structures in integrated VCOs. Among which the
switched-varactor bank [1] and switched-capacitor bank [2]
structures are most widely used in wide-tuning-range VCOs,
wide frequency tuning ratio (FTR) about 20% could be easily
achieved by using these structures. The switchable gate-biased
active core [2] in the VCO operating in two different modes has
achieved a FTR about 41%. The VCO with switchable-
inductive-tuning method [3] has achieved 14.2% FTR with
62dB phase noise variation. For even wider FTR, the multiport
LC-ladder VCO with multiple operation modes [4–11] may be
used, each mode is only responsible for a part of the frequency
range, large FTR more than 100% could be easily achieved by
using this structure, a three-port-LC-ladder resonator VCO with
158% actual frequency tuning range has been reported [4]. The
switch tuning VCO could be easily fulfilled by integrated cir-
cuit, but is not easy for non-integrated VCOs since the complex
structure. Non-integrated wide-tuning-range VCOs with
advanced techniques have been researched. A VCO with a tuna-
ble substrate integrated waveguide (SIW) resonator [7] shows
both low phase noise (2109 dBc/Hz at 100 kHz offset) and
wide FTR about 26% (1.7 GHz 2.2 GHz); a pulsed-mode
operation Colpitts VCO [8] shows a FTR about 28% (7.2 GHz
9.5 GHz).
This paper presents a continuous wide-tuning-range VCO with
56.4% actual FTR (1.12–2.00 GHz) under 0 5 V tuning voltage
without any switchable structure. Both a dynamic coupling resona-
tor structure and a dynamic reflecting network are proposed to
maintain the wide-tuning range and the stable performance for the
VCO. There are three voltage tunable structures controlled by the
same tuning voltage, so it is easy to be controlled. The output
power of the VCO is from 4.0 dBm to 6.37 dBm, and the measured
phase noise is 294.24 298.66 dBc/Hz at 100 kHz frequency off-
set and 2118.07 2123.41 dBc/Hz at 1 MHz frequency offset
respectively within the tuning range.
2. DESIGN CONSIDERATIONS FOR THE VCO
To enhance the FTR of a VCO, large capacitance ratio varactors
are adopted. Since the capacitance ratio of a varactor is limited,
the switched-capacitor bank [2] the switched-varactor bank [1]
structures are adopted to achieve larger capacitance ratio. But
we may found that the FTR of the VCO is much smaller than
the capacitance tuning ratio of the varactor. That is because
when to build a continuous wide-tuning-range VCO, larger cou-
pling capacitance for the LC resonator is usually adopted, so
that the energy coupling from the resonator is sufficient within
the whole tuning range. But the large coupling capacitance
degrades the tuning range of the resonator since all the loaded
capacitors are responsible for the resonance frequency, and the
Q factor of the loaded resonator will also be degraded, which
result in poor phase noise performance for the VCO. Further-
more, when the capacitance tuning ratio of the varactor is too
large, the VCO may stop oscillating at some frequency band, as
the oscillating conditions are hard to be fully satisfied within
the whole tuning range.
So, there are two main problems for a continuous wide-
tuning-range VCO consequently. The first problem is how to
achieve a wide-tuning resonator. The second is how to maintain
the oscillating conditions within the wide-tuning range. To solve
the problems, a dynamic coupling resonator structure and a
dynamic reflecting amplifying structure are proposed. To dem-
onstrate the validity of the proposed structure, a traditional VCO
as Figure 1 shows and the proposed VCO as Figure 2 shows are
compared.
2.1. Dynamic Coupling Resonator
To satisfy the wide tuning, the fixed coupling capacitance as
shown in Figure 1 should be a little large, otherwise the cou-
pling capacitance will be too small for low resonance frequency,
and the VCO will not oscillating. But the large coupling capaci-
tance will induce two problems: the first is it degrades the Q
factor of the resonator, the second is it reduces the tunable
DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 58, No. 7, July 2016 1525