Journal of Electromagnetic Analysis and Applications, 2012, 4, 410-418
http://dx.doi.org/10.4236/jemaa.2012.410056 Published Online October 2012 (http://www.SciRP.org/journal/jemaa)
1
Different Feeding Techniques of Microstrip Patch
Antennas with Spiral Defected Ground Structure for Size
Reduction and Ultra-Wide Band Operation
Dalia M. Elsheakh, Esmat A. Abdallah
Electronics Research Institute, Giza, Egypt.
Received August 9th, 2012; revised September 10th, 2012; accepted September 20th, 2012
ABSTRACT
Different feeding techniques of microstrip patch antennas with different spiral defected ground structures are presented
in this paper. The investigated structures illustrate some merits in designing multi-electromagnetic band-gap structures
by adjusting the capacitance and changing the inductance through varying the width and length of spiral defected
ground structure. Then by applying the three different spirals shapes (one, two and four arms) as the ground plane of
microstrip patch antenna with different feeding techniques to create multi or ultra wide-band, improve the antenna gain
and reduce the antenna size, it is found that the four arms spiral defected ground structure of microstrip patch antenna
with offset feed gives good performance, electrical size reduction to about 75% as compared to the original patch size
and ultra-wide bandwidth extends from 2 GHz up to 12 GHz with −8 dB impedance bandwidth.
Keywords: Electromagnetic Band-Gap (EBG); Defected Ground Structure (DGS); Microstrip Patch Antenna (MPA)
1. Introduction
The ever increasing demand for low profile wireless
communication antennas directed investigations to artifi-
cial materials with specific electromagnetic properties.
Among those are the man-made metamaterial, band gap
structures (EBG), high impedance surfaces (HIS), and
defected ground structure (DGS) [1-7]. The novel pro-
pagation properties found in EBG structures are pro-
mising for various antenna applications, including mi-
niaturization, coupling reduction in antennas arrays, gain
increase and scanning. This method achieved maximum
performance and minimum dimensions [8]. EBG ma-
terials are periodic structures that are composed of di-
electric, metal or metallo-dielectric materials. These
structures can prevent wave propagation in spatial direc-
tions and at certain frequencies, therefore, they can be
used as spatial and frequency filters. There are several
configurations of EBG structures that can be used in
antenna applications [9]. EBG structures are classified
into four main categories; defected ground structure
(DGS), photonic band-gap structure (PBG), high impe-
dance electromagnetic surfaces (HIS) and artificial mag-
netic conductor (AMC) [8,9]. DGS is composed of one
or few number of periodic cells [10-13].
In particular, the Hilbert-Curve inclusion focuses on
the compactness of the surface. As the number of ite-
rations order increases, the equivalent inductance in-
creases, resulting in lowering the resonant frequency.
With similar idea to the Hilbert-Curve inclusion, a larger
equivalent inductance can also be realized with a larger
number of spiral turns. However, each spiral shape has
different transmission coefficient response, so by adjust-
ing length and width of spiral band gap, we may generate
good operational characteristics at all required bands of
frequencies with small cross polarization, hence stagger-
ed multiband resonant frequencies are generated to create
UWB [8].
In this paper a compact spiral DGS design that pro-
duces multi-electromagnetic band-gap and minimizes the
cross polarization effect is presented (Figure 1). The new
designated antenna provides an impedance bandwidth up
to 10 GHz with S11 < –8dB for practical applications in
the most of modern wireless communication bands, i.e.,
GSM 900 MHz, ISM band, Bluetooth, wireless LAN and
S-band, and the new medical applications.
The performance parameters of three MPA feeding
techniques and integrated with three different spiral shapes
are investigated. The antenna performance parameters as
gain, bandwidth and E and H-plane radiation patterns are
then calculated.

Different Feeding Techniques of Microstrip Patch Antennas with Spiral Defected Ground Structure for Size
Reduction and Ultra-Wide Band Operation
411
2. Spiral Shapes of DGS
The first part of this paper is investigating the perform-
ance of different spiral shapes of ground plane by ob-
taining the reflection and transmission coefficients. The
concept of spiral ground plane like spiral antenna, be-
longs to a category of antennas known as broadband [14].
The term of a broadband is a relative measure of band-
width, and it varies with the circumstances. fU and fL rep-
resent the upper and lower frequencies of operation for
which satisfactory performance is obtained. A broadband
antenna can be characterized by the fact that the imped-
ance and pattern of an antenna do not change signifi-
cantly over about an octave (UL
f
f= 2) or more. Its
smooth physical structure tends to produce a radiation
pattern and input impedance that also change smoothly
with frequency.
In the two arms case, the spiral radiates from a region
where the circumference of the spiral equals one wave-
length. This is called the active region of the spiral. Each
arm of the spiral is fed 180˚ out of phase, so when the
(a) (b) (c)
Figure 1. Microstrip patch antenna with different feeding
techniques: (a) inset feed; (b) center line feed; and (c) offset
feed.
circumference of the spiral is one wavelength the cur-
rents at opposite points on each arm of the spiral add in
phase in the far field. The active region moves around the
antenna with frequency. Since the geometry of a spiral is
smooth, the frequency is smoothly reduced, and the ac-
tive region shifts to locations farther out on the spiral.
Hence, self-scaling occurs and frequency-independent
behavior results [10,15].
The single arm spiral is fed with one source; therefore
it is easier and more convenient to work with. The low
frequency operating point of the spiral is determined
theoretically by the outer radius and is given by Equation
(1) and the high frequency operating point is based on
the inner radius given by Equation (2).
outer
2π
L
C
fr  (1)
inner
2π
U
C
fr  (2)
where rinner and router are the inner and the outer radii, re-
spectively as shown in Figure 2 and C the speed of light.
In practice the low frequency point will be greater than
that predicted by Equation (1) due to reflections from the
end of the spiral. In the active region, points that are one
quarter turn around the spiral are 90˚ out of phase. In
addition, the currents are orthogonal in space and nearly
equal. The radiated field components are orthogonal,
equal in magnitude, and 90˚ out of phase. By this concept,
multi-electromagnetic band gap generated so that the
loweSr band-gap is at router and upper band-gap is at rinner.
The bandwidth of band-gap depends on width of the spiral
arm, dielectric constant and height of substrate when
using 50 Ω broadband transmission lines as shown in
Figure 2.
(a) (b) (c)
Figure 2. The proposed three spiral shape configurations: (a) one arm; (b) two arms; and (c) four arms.

Different Feeding Techniques of Microstrip Patch Antennas with Spiral Defected Ground Structure for Size
Reduction and Ultra-Wide Band Operation
412
The operation of the SDGS surface can be simply ex-
plained by an equivalent LC circuit theory [11-13]. To
increase the value of the equivalent inductor, a single
spiral shape is placed as a ground for RT/D6010 sub-
strate with dielectric constant εr = 10.2 and height 0.043
λ@5.2GHz = 2.5 mm. On the other side the broadband
transmission line is etched to study the performance of
SDGS. Figure 3 shows the magnitudes in dB of the
transmission coefficient for one, two and four arms spiral
shape with different width 0.01 λ, 0.015 λ and 0.02 λ at
5.2 GHz.
246810 12
-40
-30
-20
-10
0
|S
21
| (d B)
Frequency (G Hz)
Transmission coefficient one arm spiral
Large Width Spiral
Medium Width Spiral
Small Width Spiral
(a)
2468101
2
-40
-30
-20
-10
0
|S
21
| (d B)
Frequency (GHz)
Tansmission coefficient two arms
Large spiral width
Medium spiral width
Small spiral width
(b)
246810 12
-40
-30
-20
-10
0
|S
21
| (d B)
Frequency (GHz)
Transmission Coefficient four arms spiral
Large Spiral Width
Medium Spiral Width
Small Spiral Width
(c)
Figure 3. Transmission coefficient response for spiral
ground plane with (a) one arm; (b) two arms; and (c) four
arms at three different widths 0.01 λ, 0.015 λ and 0.02 λ at
5.2 GHz.
Multi-band operation is achieved according to Equa-
tions (1) and (2), in the selected started and ended fre-
quency range. Multi-band gap at resonances can be found
at 3 GHz, 6 GHz and 10 GHz for one arm spiral as
shown in Figure 3(a) while for the two arms spiral the
band gap is created at 1 GHz, 3 GHz, and 11 GHz as
shown in Figure 3(b). In Figure 3(c) the transmission
coefficient responses of the four arms spiral is creating
band-gap resonances at 1 GHz, 4 GHz, 8 GHz and 12
GHz with broaden band gap width. Table s 1 and 2 sum-
marize the effect of the three spirals geometries on the
transmission coefficient.
From previous results (transmission coefficient re-
sponses), one can conclude that the best spiral perform-
ance is the spiral with four arms. Figure 4 shows the
magnitude of reflection and transmission coefficients of
the different spiral shapes. One arm spiral produced high
cross polarization; this is due to the large magnitude of
S11 as shown in Figure 4(a). The value of S11 increases
more than 0.6 at different operating frequencies. The
value of cross-polarization is reduced in the case of spiral
with two arms as shown in Figure 4(b). Low cross-po-
larization is achieved by using four arms spiral as shown
in Figure 4(c).
SDGS shape with small width seems to meet the de-
sired requirement in terms of surface compactness; the
resulting high cross polarization is as shown in Figure
4(a).
To reduce the cross polarization, two spirals are con-
nected. The two arms spiral, as shown in Figures 4(b),
turning into the opposite direction is investigated. To
eliminate the cross polarization, four arms spiral is ex-
plored, as shown in Figure 4(c), each branch has 0.5 mm
width, split from the center and rotates outwards. In con-
trast to the previous designs, if this unit cell is rotated 90˚,
it can exactly recover itself. Therefore, this symmetrical
condition guarantees the same scattering response to the
Table 1. Effect of the different SDGS shape parameters.
Parameters One arm Two arms Four arms
No. of band gaps Less Moderate Large
BW Narrow Moderate Wide
Table 2. Effect of the different SDGS shapes ground plane
on the transmission coefficient.
Increasing Fo of band-gap BW
Spiral width Decrease Increase
Spiral air gap Increase Decrease
Dielectric constantDecrease Decrease
Substrate height Decrease Increase
Spiral turns Decrease Decrease

Different Feeding Techniques of Microstrip Patch Antennas with Spiral Defected Ground Structure for Size
Reduction and Ultra-Wide Band Operation
413
x- and y-polarized incident waves. As a result reduced
cross polarization is observed from this structure as
shown in Figure 4(c). The response of one arm spiral has
large intersect with the threshold value from 0.4 to 0.6, as
shown from Figure 4. For two arms spiral the number of
intersect is reduced, while for four arms spiral the value
of S21 does not exceed 0.3 so the cross-polarization is
reduced.
(a)
(b)
(c)
Figure 4. Reflection and transmission coefficient magnitude
of small width spiral with different shapes: (a) one arm; (b)
two arms; and (c) four arms.
3. Microstrip Patch Antennas Design
MPAs have been studied extensively over the past two
decades because of its low profile structure, light weight
and low cost. They have many advantages over conven-
tional antennas, which make them suitable for a wide
variety of applications. However, narrow bandwidth has
been a major drawback for this type of antennas, so the
second part of this paper is investigating the antenna
performance and improving antenna bandwidth by apply-
ing the three spiral shapes ground plane using the three
feeding techniques for MPA namely inset, offset and
center line feed as shown in Figure 1.
This section starts by investigating the MPA perform-
ance with length L = 6.5 mm and width W = 8 mm, re-
spectively with different feeding techniques (inset, center
and offset feed). The simulated reflection coefficients of
conventional MPA with the different feeding techniques
are shown in Figure 5, as a reference. The best response
for MPA is with that of offset feed. The second step is
applying the three spiral DGS to the ground plane of the
three MPAs with different feedings.
4. MPA with Spiral DGS
MPA with inset feed and different spiral arms ground
plane with large width of spiral ground, equals 1.5 mm
and gap of 1 mm shows that multi-band exist at 2 GHz,
2.45 GHz, 2.6 GHz, 4.5 GHz, 5 GHz, 7 GHz, 11 GHz
and 13 GHz as shown in Figure 6(a).
Reduction in antenna size by 60% as component to the
references antenna is achieved by using medium spiral
width with three types of spiral as shown in Figure 6(b).
However, it has narrower bandwidth as compared to the
conventional MPA, in average around 2.5%. To improve
bandwidth and more size reduction, small size spiral
width is used as shown in Figure 6(c) but it produces
Figure 5. The reflection coefficient of conventional MPA
with different feeding techniques.

Different Feeding Techniques of Microstrip Patch Antennas with Spiral Defected Ground Structure for Size
Reduction and Ultra-Wide Band Operation
414
(a)
(b)
(c)
Figure 6. The simulated reflection coefficient of inset feed
for: (a) large width; (b) medium width; and (c) small width
of the three SDGS shapes.
small antenna gain. The above steps were repeated for
center line feed as shown in Figures 7(a)-(c), respec-
tively at the three different spiral width large, medium
and small with SDGS gap width of 1 mm. One can ob-
serve that as the number of arms increases the number of
antenna resonances increases with achieved size reduc-
tion of about 70%.
The results of repeating the previous steps for offset
feed with different spiral widths are shown in Figures
(a)
(b)
(c)
Figure 7. The simulated reflection coefficient of center feed
MPA with: (a) large width; (b) medium width; and (c) small
width of the three SDGS shapes.
8(a)-(c), respectively. The same observation is obtained
which is as the number of arms increases the number of
antenna resonances increases with antenna size reduction
of about 75% relative to the conventional MPA. The
summarized results of the four turns spiral are introduced
in Table 3.
Table 3 shows that good average antenna bandwidth is

Different Feeding Techniques of Microstrip Patch Antennas with Spiral Defected Ground Structure for Size
Reduction and Ultra-Wide Band Operation
415
obtained for MPA with offset feed, while it gives low
antenna efficiency due to large cross polarization since it
has an asymmetrical structure. The, MPA with center
feed produces medium average bandwidth and large an-
tenna efficiency.
The proposed antennas were fabricated by using pho-
tolithographic technique and the photo of the fabricated
antennas with different feeding technique and spiral shapes
are shown in Figure 9.
MPA with offset feed with different spiral width (large,
medium and small) of four arms spiral are shown in
Figure 10, which shows that there is a good agreement
between simulated and measured results. Radiation pat-
tern is simulated at lower frequency of 2 GHz. From the
results one may conclude that the radiation pattern in the
offset feed structure with small spiral width gives the
best H-plane radiation pattern while large spiral width
gives good E-plane radiation pattern. The results are
shown in Figures 11-13 for inset, center and offset feed,
respectively.
(a)
5. Conclusion
(b)
Compact microstrip patch antennas using different spiral
defected ground structures were proposed. Various
configurations of printed spiral geometries have been
examined to realize compact multi-band operation. The
compactness of antenna size due to electromagnetic
band-gap surface can be achieved by increasing the
equivalent inductance. Asymmetry spiral defected
ground structure as single arm and two arms spiral
exhibit large cross polarization levels. Therefore, the four
arms spiral geometry was proposed and designed to
successfully eliminate the cross polarized fields.
Electrical reduction of microstrip patch antenna by 75%
from original antenna size was achieved. The proposed
compact spiral defected ground structure is a good
candidate for various antenna applications. Staggered
(c)
Figure 8. The simulated reflection coefficient of offset feed
for: (a) large width; (b) medium width; and (c) small width
of three SDGS shapes.
Table 3. Summary of the antennas results for four arms SDGS.
One arm spiral Two arms spiral Four arms spiral
Size Feed
type G (dBi) Eff. BW G (dBi)Eff. BW G (dBi) Eff. BW
Inset feed 1.79 0.9 H 3.47 0.9 M 5.6 0.75 L
Center feed 1.6 0.8 M 2.45 0.7 M 4.75 0.8 L
L
Offset feed 1.8 0.8 L 2.41 0.8 L 5.55 0.7 L
Inset feed 1.7 0.9 L 3.51 0.7 L 3.961 0.6 L
Center feed 1.9 0.8 M 3.5 0.7 M 4.4 0.8 L
M
Offset feed 2 0.7 H 2.8 0.6 H 4.39 0.6 L
Inset feed 2.1 0.8 L 2.91 0.8 L 6.2 0.75 L
Center feed 2.3 0.6 M 3.3 0.6 M 4.4 0.8 L
S
Offset feed 2.5 0.7 H 2.8 0.5 H 3.66 0.5 H
“S = Small spiral width = 0.01λ@5.2 GHz, M = Medium spiral width = 0.015λ@5.2 GHz and L = Large spiral width = 0.02λ@5.2 GHz.
(L = Low (BW < 2.5%), M = Medium (2.5% < BW < 5%) and H = Large BW > 5%).”

Different Feeding Techniques of Microstrip Patch Antennas with Spiral Defected Ground Structure for Size
Reduction and Ultra-Wide Band Operation
416
Figure 9. (a) MPA with different feeding techniques center
line feed, inset feed and offset feed; (b) spiral ground with
four arms with different widths: large, medium and small;
and (c) MPA with spiral ground plane, one arm and two
arms.
(a)
(b)
(c)
Figure 10. Comparison between simulated and measured
reflection coefficient of offset feed MPA with four arms
SDGS: (a) large width; (b) medium width; and (c) small
width.
Figure 11. E-plane and H-plane radiation pattern for three different widths of four arms spiral SDGS for inset feed at 2
GHz.

Different Feeding Techniques of Microstrip Patch Antennas with Spiral Defected Ground Structure for Size
Reduction and Ultra-Wide Band Operation
417
Figure 12. E-plane and H-plane radiation pattern for three different widths of four arms SDGS for center feed at 2 GHz.
Figure 13. E-plane and H-plane radiation pattern for three different widths of four arms SDGS for offset feed at 2 GHz.
multi-band operation was achieved which provided ultra-
wide band at –6dB impedance bandwidth. This antenna
gives an average increase in gain by about 5.6 dBi. Fi-
nally, radiation pattern are investigated and the offset
feed antenna gives the best radiation patterns.
6. Acknowledgements
This work is funded by the National Telecommunication
Regularity Authority, (NTRA), Ministry of Communica-
tion and Information Technology, Egypt.
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