H-SHAPED STACKED PATCH ANTENNA FOR DUAL BAND OPERATION JA Ansari, P. Singh, and ...

12 Pages·2008·0.19 MB·English

Progress In Electromagnetics Research B, Vol. 5, 291–302, 2008
H-SHAPED STACKED PATCH ANTENNA FOR DUAL
BAND OPERATION
J. A. Ansari, P. Singh, and S. K. Dubey
Department of Electronics & Communication
University of Allahabad
Allahabad, India
R. U. Khan and B. R. Vishvakarma
Department of Electronics Engineering
I. T. BHU
Varanasi 221005, India
Abstract—Analysis of U-slot loaded patch stacked with H-shaped
parasitic elements is given in this paper. It is found that the antenna
exhibits dual resonance and both the resonance frequency (upper and
lower) depends directly on slot width and inversely on slot length.
Bothupperandlowerresonancefrequencyincreasewithincreasingthe
value of h . Typically the bandwidth at lower and upper resonance is
2
found 3.66% and 10.25% respectively. The radiated power at higher
frequency (beamwidth 64◦) is 0.73dB as compared to lower resonance
frequency(beamwidth71◦). Thetheoreticalresultsarecomparedwith
the simulated data obtained from IE3D.
1. INTRODUCTION
In spite of having advantage like light weight, low profile, compact and
cost effective, the conventional microstrip antenna has disadvantages
of narrow bandwidth and low gain. A number of researchers have
tried to minimize these drawbacks of the patch antenna by way of
addition of parasitic elements either laterally or vertically [1], cutting
slot including probe fed U-slot loaded patch antenna [2], double C-
patch antennas [3] and E-shape patch [4]. Among various proposed
methods stacked patch configuration seems to be very promising due
to its capability of providing dual frequency characteristics [5–7] and
wider bandwidth [8,9].
292 Ansari et al.
In the present paper, an analysis of a U-slot loaded patch stacked
with H-shaped patch is carried out. A U-slot loaded patch along with
its initial dimensions provides other parameters such as slot length
and slot width to improve the various antenna characteristics. In the
presentworkvariationofsubstratethicknessisalsostudied. Theentire
investigation is based on equivalent circuit model.
2. THEORETICAL CONSIDERATIONS
The configuration of the proposed antenna is shown in Fig. 1. The
upper element is H-shaped parasitic patch and lower one is the U-
slot loaded patch. Due to the presence of parasitic element in the
stackedpatchantenna,therearetworesonanceassociatedwiththetwo
resonators [10]. The first resonator is considered as a microstrip patch
with dielectric cover which causes a change in resonance frequency as
well as effective dielectric constant (ε ).
ff
Microstrip patch with a dielectric cover is considered as a single
patch with a semi-infinite superstrate with relative permittivity equal
to unity and the single relative dielectric constant (ε ) given as:
s
2ε −1+p
ff
ε =
s
1+p
where
10h
1
p = 1+
W
1e
in which W is the effective width and ε is the effective dielectric
1e ff
constant of the structure [11]. The effective dielectric constant of the
lower substrate is given as
(cid:2) (cid:3)
ε +1 ε +1 12h
s s 1
ε = + 1+ (1)
e1 2 2 W
1
where
h = height between ground plane and lower patch
1
W = width of the patch
1
The equivalent circuit of the simple patch antenna is parallel
combination of resistance (R ), inductance (L ) and capacitance (C )
p p p
(Fig. 2), whose values are defined as [12]
(cid:2) (cid:3)
ε ε (cid:8) W πy
C = 0 e1 1 1 cos−2 0 (2)
p
2h (cid:8)
1 1
Progress In Electromagnetics Research B, Vol. 5, 2008 293
Y
1
s
WE
W Ls X
1
Feed point
wb
WN Ws
(a) U-slot loaded fed patch
2
w
n
d
W
2
side stripes
(b) H-shaped parasitic patch
H-shaped parasitic patch
U-slot loaded fed patch
ε
h εr2 h2
r1 h1
(c) Side view of the proposed antenna
Figure 1. Configuration of stacked patch antenna.
294 Ansari et al.
C
Rp Lp p
Figure 2. Equivalent circuit of patch antenna.
1
L = (3)
p ω2C
1 p
Q
1
R = (4)
p
ω C
1 p
where
√
c ε
Q = e1
1
4f h
1 1
(cid:8) = length of the lower patch
1
y = Y-coordinate of the feed point
o
ω = 2πf
1 1
c
f = √
1
2((cid:8) +2∆(cid:8) ) ε
1 1 eff
c = velocity of light
∆(cid:8) = fringing length for the lower patch
1
When a U-slot is etched into the patch, current distribution
changes which ultimately changes the resonance behaviour of the
patch. This change in the patch adds series inductance (∆L ) and
1
series capacitance (∆C ) in the initial circuit of the patch. Therefore
1
the equivalent circuit of U-slot loaded patch can be given as shown in
Fig. 3, in which the resonance resistance R , ∆L and ∆C are given
1 1 1
as [13–15]
(cid:4) (cid:5)
Q h πy
R = 1 1 cos2 0 (5)
1
πf ε ε W (cid:8) (cid:8)
r eff 0 1 1 eff
1
where (cid:8) is the effective length of the fed patch [16] and can be given
eff
1
as
L
s
(cid:8) = (cid:8)+(sin(πw /(cid:8)))
eff b
1 2
(cid:2) (cid:3)
Z +Z πf L
∆L = 1 2(cid:6) (cid:7) tan 1 s (6)
1
16πf cos−2 πy0 c
1 WE
Progress In Electromagnetics Research B, Vol. 5, 2008 295
L L L L
b b b b
C R1 Lp Cp Cb
b
∆L1 ∆C1
Figure 3. Equivalent circuit of U-slot loaded patch.
where
W = W −W
E 1 N
120π
Z = (cid:6) (cid:7)
1
Ws +1.393+0.667log Ws +1.44
h1 h1
120π
Z = (cid:6) (cid:7)
2
Ws−2s +1.393+0.667log Ws−2s +1.44
h1 h1
∆C is calculated as gap capacitance and given by [14]. The value of
1
C and L are calculated as [15]
b b
C w
b b
= (9.5ε +1.25) +5.2ε +7.0pF/m (7)
w r1 h r1
b (cid:2) 1(cid:3)
2L w
b = 100 4 b −4.21 nH/m (8)
h h
1 1
2.1. Analysis of Stacked Patch Antenna
Considering the top patch as a simple rectangular microstrip patch,
the values of resistance (R ), inductance (L ) and capacitance (C )
2 2 2
can be given as
ε ε (cid:8) W
C = 0 r2 2 2 (9)
2
2h
2
1
L = (10)
2 ω2C
2 2
Q
2
R = (11)
2
ω C
2 2
296 Ansari et al.
where √
c ε
Q = e2
2
4f h
2 2
where
(cid:8) = length of the parasitic patch
2
W = width of the parasitic patch
2
ω = 2πf
2 2
c
f = √
2
2((cid:8) +2∆(cid:8) ) ε
2 2 e2
∆(cid:8) = fringing length for the top patch
2
Whentwosymmetricalnotchesareincorporatedintotheparasitic
patch an H-shaped patch is obtained and the equivalent circuit thus
obtained is shown in Fig. 4(a), in which∆L and ∆C are the
2 2
additionalinductanceandcapacitancerespectivelywhichoriginatedue
to introducing the two notches and R is resonance resistance after
H
∆L ∆C
RH L2 C2
∆L ∆C
(a)
Zn Z
p
L L
m m
C C
m m
(b)
Figure 4. (a) Equivalent circuit of RMSA due to notch effect. (b)
Equivalent circuit of H-shaped parasitic patch.
Progress In Electromagnetics Research B, Vol. 5, 2008 297
cutting the notches into the patch. The value of R can be calculated
H
using Equation (5) and the additional inductance and capacitance can
be given as [16]
(cid:2) (cid:3)
h µ π W
1 0 2
∆L = (12)
2
8 w
n
where µ = 4π10−7H/m.
0
And (cid:2) (cid:3)
W
2
∆C = C (13)
2 s
w
n
where C is the gap capacitance between two side strips [17]. Now
s
the equivalent circuit of H-shaped patch is given as shown in Fig. 4(b)
in which ‘Zn’ is the impedance of the notch incorporated patch and
is calculated from Fig. 4(a), Z is the impedance of the initial patch
p
andC andL arethecapacitiveandinductivecouplingbetweentwo
m m
resonant circuits.
Z
m
Z
Z H
U
Figure 5. Equivalent circuit of proposed stacked patch antenna.
The equivalent circuit of the proposed stacked antenna can be
givenasshowninFig.5,inwhichonlycapacitivecouplingisconsidered
and is given by [18]
(cid:8)
(cid:6) (cid:7) (cid:6) (cid:7) (cid:6) (cid:7)
C +C(cid:3) + C +C(cid:3) 2−4C C(cid:3) 1−k−2
eq eq eq eq eq eq c
C(cid:3) = − (14)
m 2
where
∆C C
1 p
C =
eq
2C +∆C
p 1
∆C C
(cid:3) 2 2
C =
eq 2C +∆C
2 2
and k is the coupling coefficient between two resonators.
c
298 Ansari et al.
Thus the total input impedance can be calculated from Fig. 5 as
Z (Z +Z )
U m H
Z = (15)
in
Z +Z +Z
U H m
InwhichZ andZ aretheimpedancesoflowerandparasiticpatches
U H
calculated from Figs. 3 and 4(b) respectively and Z is the impedance
m
due to mutual coupling between driven patch and parasitic patch.
2.2. Design Specifications of Proposed Antenna
Substrate material used Foam
Dielectric constant (ε , ε ) 1.1
r1 r2
Thickness between ground and lower patch (h ) 6.0mm
1
Thickness between lower and parasitic patch (h ) 5.5mm
2
Length of the fed patch ((cid:8) ) 39.40mm
1
Width of the fed patch (W ) 29.40mm
1
Length of the slot (L ) 15mm
s
Width of the slot (s) 1.2mm
Feed location (x , y ) (0, −5.27mm)
0 0
Length of the parasitic patch ((cid:8) ) 26mm
2
Width of the parasitic patch (W ) 18mm
2
Depth of the notch (w ) 4mm
n
Width of the notch (d) 15mm
3. DISCUSSION OF RESULTS
The variation of return loss with frequency for different slot width
(s) is shown in Fig. 6, for a given value of slot length L = 12mm,
s
h = 6mm, h = 5.5mm. It is observed that the antenna shows
1 2
dual resonance in which both lower and upper resonance frequency
increases with increasing value of slot width and the bandwidth at
upper resonance (10.25%) is higher than the bandwidth at the lower
resonance (3.26%). The bandwidth of the antenna also increases with
slot width whereas at lower resonance it is almost the constant. All
theoretical results are found to be approximately in good agreement
with the simulated results using MOM based IE3D [21].
The variation of return loss with frequency for different value of
slot length (L ) is shown in Fig. 7 for a given value of s = 1.2mm,
s
h = 6mm, h = 5.5mm. It is found that both lower and upper
1 2
resonancefrequencydecreaseswithincreasingslotlengthandtheband
width at the upper resonance (10.25%) is higher as compared to the
Progress In Electromagnetics Research B, Vol. 5, 2008 299
0
s=1.2mm(theoretical)
s=1.2mm(simulated)
s=3.2mm(theoretical)
s=3.2mm(simulated)
-5
b)-10
d
s (
s
o
n l
ur
Ret-15
-20
-25
2 2.5 3 3.5 4 4.5 5 5.5 6
Frequency(Hz) x 109
Figure 6. Variation of return loss with frequency for different slot
width (L = 12mm, h = 6mm, h = 5.5mm).
s 1 2
0
Ls=12mm(theory)
Ls=12mm(simulated)
Ls=14mm(theory)
Ls=14mm(simulated)
-5
-10
Return loss (db)-15
-20
-25
2 2.5 3 3.5 4 4.5 5 5.5 6
Frequency (Hz) x 109
Figure 7. Variation of return loss with frequency for different slot
length (s = 1.2mm, h = 6mm, h = 5.5mm ).
1 2
300 Ansari et al.
0 h2=4mm(theory)
h2=4mm(simulated)
h2=5.5mm(theory)
h2=5.5mm(mimulated)
h2=9mm(theory)
h2=9mm(simulated)
-5
b) -10
d
oss (
n l
ur
Ret -15
-20
-25
2 2.5 3 3.5 4 4.5 5 5.5 6
Frequency (Hz) x 109
Figure 8. Variation of return loss with frequency for different value
of h (L = 12mm, s = 1.2mm, h = 6mm).
2 s 1
0
Theoretical (3.26 GHz)
-2 Theoretical (4.66 GHz)
Simulated (4.66 GHz)
-4
-6
B) -8
wer (d
Relative radiative po---111420
-16
-18
-20
-22
-80 -60 -40 -20 0 20 40 60 80
Angle (degree)
Figure 9. Radiation pattern.
lower resonance (3.66%). It is further observed that the bandwidth
at upper resonance increases with increasing slot length where as it is
almost invariant at lower resonance. The theoretical results are found
to be in good agreement with simulated results using IE3D.