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International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: 02 26
112902-8383 IJET-IJENS @ April 2011 IJENS I J E N S
Abstract— In this paper, influence of Circularly Split Ring
Resonators with its accompanying circular microstrip patch
antenna are investigated. Proposing a 5850 to 7075 MHz band of
working frequency, by means of microwave laminate RT/D 5880
(εr = 2.2 and thickness of 1.82 mm). The antenna is wholly
organized into three layers consisting of circular copper sheet as
ground plane, an undersized main radiator for where signal will
pass through to resonate and ended with designed split rings
entrenched on layer three laminate. All layers are separated by an
air gap, simulated and optimized carefully using Microwave
Studio of Computer Simulation Technology Suite (CST).
Provided that, dimension of air gap, split ring quantity and
entrenched split ring width are monitored as key controllers. Via
transient solver, it presents corresponding S-parameter results
and provides 3D view farfield. Thus demonstrating how each key
controllers influence the antenna in terms of bandwidth,
directivity, gain and efficiency produced. These works conclude
that adaptation of split rings can enhance and improve this
particular antenna.
Index Term— CCSRRs, CMS, CSMA, SRR
I. INTRODUCTION
High Altitude Platform Station (HAPS) has been proposed to
achieve full broadband coverage as stated in Malaysia’s
National Broadband Plan (NBP) [1]. In Malaysia, HAPS are to
be allocated and operated in the frequency spectrum of 5850-
7075 MHz to support operations in fixed and mobile services
[2]. HAPS allow several advantages. Signal interference of
HAPS depends on the antenna’s radiation pattern rather than
terrain features of coverage area. HAPS also have larger
system capacity, which allow implementation of more efficient
and effective resource management [3]. HAPS is placed at 10
to 20 km above earth surface, serves a ground area of 60 km
diameter, with elevation angle from ground up set at 30
degree [4-5]. Tuning
proposed antenna in terms of its return loss, bandwidth, return
loss, gain and directivity are the main tasks analyzed in this
paper. Few HAPS antennas are made available and are still in
experimental phase due to different working frequencies yet to
be finalized by ITU regulations. Current research on HAPS
antennas employ array patch antennas to obtain broadband
operation, due to its multi beam latency for higher frequencies
such as from 20-30 GHz [7].
Microstrip patch antenna exhibits very narrow bandwidth,
making it unsuitable for the HAPS operation. Wide bandwidth
requirements can be achievable by simulating and optimizing
suitable physical antenna design parameters. Circular
microstrip antenna (CMSA) design proposed in this paper
utilizes low relative permittivity (εr) laminates values.
Substrate thicknesses are selected and optimized to fulfill
targeted bandwidth and gain values. Combination of
Complementary Circularly Split Ring Resonators and CMSA
elements are expected to result in broader bandwidth and
boosting other related s-parameter output. Here, by means of
circular outline structure give no pointed edges and such gives
less fringing effect [8] while at the same time increasing height
of substrate (the middle air gap) can help increase the
bandwidth and sustain VSWR lower than 2:1 via stacked
multiresonator MSA concept applied here [9]. Significantly,
CSRR [10] is being blended together with all CMSA on layer
three. Here CCSRR was periodically multiplied and its size
incremented throughout the copper area, not as typically found
with other present left-handed structures. Study of this CCSRR
involvement was also found beneficial as it helped to
minimized and eliminates unwanted backlobes.
II. PROCEDURE FOR PAPER SUBMISSION
A. Basic Calculation
This paper segment reports of proposed CSMA-CSRR
antenna designs concept. Aiming to achieve suitable antenna
structure with decent bandwidth, return loss and gain
requirements. Fundamental equation of a typical rectangular
patch is analyzed. Then equivalent area of this rectangular
patch is converted to an equivalent circular area form. By
selecting the starting point, middle point and end point of
operating frequencies 5.85, 6.4375, and 7.075 GHz
respectively, rectangular patch width can then be derived using
equation (1).
Effective relative permittivity is derived by using equation
(2). Estimation of the extended incremental lengths of patch,
ΔL is obtained by using equations 3 and 4. Actual length value
is derived from equation 5. In the equations, W is width of
patch or microstrip line, εr is dielectric constant of substrate, h
is thickness of substrate and t is thickness of metallic patch
conductor. These derived parameters are listed in Table I
Preliminary Study of Circularly Split Ring
Resonators Entrenched within Circular
Microstrip Antenna
A. A. M. Ezanuddin, M. F. Malek, and P. J. Soh
International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: 02 27
112902-8383 IJET-IJENS @ April 2011 IJENS I J E N S
TABLE I
CALCULATION OF THE BASIC SHAPE OF WIDTH AND LENGTH.
Frequency
(MHz)
W
(mm) εreff
ΔL
(mm)
L
(mm)
Le
(mm)
5850 19.38 2.27 1.05 14.87 16.9
6430 17.65 2.26 1.05 13.37 15.4
7025 16.14 2.25 1.05 12.12 14.8
1
2
21
2
2
1
r
o
roo fr
v
frW
(1)
2
1
1212
1
2
1
W
hrrreff
(2)
)8.0)(258.0(
)264.0)(1(
412.0
h
Wh
W
h
L
reff
reff
(3)
LL 2
2
(4)
LLLe 2 (5)
Equation 6 derives the dimension parameters of a
circularly shaped microstrip antenna (CMSA), by using the
dimension parameters obtained from the basic rectangular
patch (RMSA).
222 )1.1/()
1()(
4ln1)('
t
W
h
t
tWW
(6)
Effective radius, ae of the CMSA can be obtained by using
equations 7, 8 and 9.
4
3
1
2
3
4exp)62(6
W
hF
(7)
2
'
21
'ln
2
W
h
W
hF
hWe
(8)
2
1
eee
WLa (9)
Table II illustrates effective CMSA radius for the three
frequencies 5.85 GHz, 6.4375 GHz and 7.075 GHz
respectively.
TABLE II
EFFECTIVE RADIUS (AE) TAKING INTO ACCOUNT OF THE DISPERSION EFFECT.
Frequency
(MHz) W’(cm) F We(mm) ae(mm)
5850 19.49 6.035 24.56 11.524
6430 17.76 6.031 22.75 10.275
7075 16.25 6.026 21.16 10.009
Common SRR Fig. 1 itself can be described as an LC
resonant tank (10) [17] (becoming low pass filter), the
resonant frequency is as showed below in Figure 1. SRR
design below also is to improve roll-off of the binomial return
loss, thus a set of SRRs with resonant frequency f1 near the
conventional filter cut-off frequency fc would be required.
Thus in order to improve roll-off and gain a deeper line drop,
multiple SRR or an array of SRRs will be required.
LcCcfc
2
1 (10)
Fig. 1. Layout of general split ring resonator and its equivalent
ciruit.
B. Design One
Design One antenna consists of an 11.0 mm radius etched
circular copper which is coaxially fed at the midpoint. This
antenna is expected to resonate at lower than -10 dB along
targeted bandwidth. Observed in Figure 2, center main circular
radiating element is then accompanied by four more parasitic
elements of similar dimensions. Additions of these parasitic
elements are to increase the bandwidth and better return loss
following the mutual coupling after effect. This is due to larger
copper area present with additional parasitic elements. Figure
3 shows S11 parameters values of four different scenarios (i.e.
with different number of parasitic elements from 0 to 4). A
high dielectric laminate of Rogers RO3010 type (εr = 10.2, 40
mm radius) was initially used for the simulations and analysis.
International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: 02 28
112902-8383 IJET-IJENS @ April 2011 IJENS I J E N S
With four parasitic elements, the signal appears to worsen as
all five circular shapes acts more like a reflector.
Design One seem unable to resonate at desired frequency
and suffers from high attenuation and power loss, contributed
from long feeding coaxial dimension. Figure 4 is one 3D plot
on 2D plane showing E-Field in carpet form. Dark region
represents strong electric field being deflected away by ground
plane. This in turn, has altered the total farfield in Figure 5, to
radiate in reverse direction.
Fig. 2. Diagram of the investigated single layer antenna with 4 parasitic
elements.
Fig. 3. Parametric study of Design One antenna as the parasitic elements
increases.
Fig 4. Carpet plot type of the E-Field at 5.585 GHz shows that darker
region of electric energy being bounced back from the ground plane.
Fig. 5. When most energy is bounced back, its directivity changes towards
the rear along the z-axis with minimal signal at the front.
C. Design Two
Second antenna blueprint (Design Two) utilizes an
additional second layer of lesser or equal valued dielectric
constant and greater substrate thickness. By expecting this
design being able to store more energy, permitting lower
effective dielectric value, which results in better return loss
(S11 parameters) and bandwidth enhancement.
Fig. 6. Diagram of investigated two layer antenna with four parasitic
elements.
Fig. 7. E-Field strength showed by the darker part area.
Worsen and shifted 1 4
Strong electrical field
Not radiating at
desired direction.
Darker region are
located at the front.
International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: 02 29
112902-8383 IJET-IJENS @ April 2011 IJENS I J E N S
Fig. 8. Isoline plot shows E-Field flow of Design Two antenna, with most
energy situated in between the substrates.
Fig. 9. Farfield resulted in direction changes with a second substrate.
Figure 6 illustrates two layers antenna design with its E-
Field output Figure 7, carpet plot differentiated by dark and
light green color contour zone. Substrate (Layer One) addition
has allowed energy to flow and kept forward. Introduction of
an air gap has also created an area for driven energy
occupation in order to resonate designed circular microstrip
seen in Figure 8. Next, Figure 9 holds the resulted farfield,
which is now totally opposite of what in Figure 5.
Briefly, a capacitive region was created upon similar
laminate addition and disallowing energy bouncing off by
ground plane. Thus energy from port successfully resounds
above microstrip and at the same time more focus beam was
generated in Figure 9. Figure 10 illustrates S11 parameter
results for two layer antennas with different number of
parasitic elements added on the upper layer. With addition of
more parasitic elements, bandwidth and resonant frequency
values increases. Wider resonance band values are achievable
by manipulating air gap spacing.
Fig. 10. Return loss of two layer antenna by increasing quantity of
parasitic elements.
D. Design Three
Third antenna plan (Design Three) operates on three layers
substrates. Figure 11 shows diagram of suggested three layers
antenna design. Layer 1, 2 and 3 are the lower, intermediate
and upper layers, respectively. Center located main radiator
and four parasitic elements are incorporated onto the upper
layer (layer 3). Essential parameters of the antenna have been
obtained and configured by a series of computerized parameter
sweep, which resulted of an optimum spacing required to
achieve good S11 parameters. Spacing variations between
substrates show that with larger spacing (air gaps) [11, 13]
resulted in larger bandwidth but seriously altering signal and
energy flow seen in Figure 12 and far field Figure 13. Figure
14 shows S11 parameters results for different number of
parasitic elements (from 0 to 4) and plot shows that bandwidth
can be enhanced by having four parasitic elements while
maintaining structure formation.
Fig. 11. Diagram of the investigated three layer antenna (air gaped) with 4
parasitic elements.
Port
Energy stored to
resonate CMSA.
Radiate at desired
direction.
Signal deepens with
four elements.
1
4
International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: 02 30
112902-8383 IJET-IJENS @ April 2011 IJENS I J E N S
Fig. 12. Combination of three substrates has worsened the energy flow
and it dominates more at rear region rather than above the structured
CMSA.
Fig. 13. Farfield shows the strongest signal has once again reverted.
Fig. 14. Return loss of three layered antenna widens by increasing
quantity of parasitic elements.
E. Design Four
Fourth antenna design (Design Four) a further investigation
from Design Two, consists of a smaller circular copper sheet
acting as main radiator with continuous wave and signal fed
through coaxial cable positioned at intermediate layer (layer
2)[18], as shown in Figure 15. This smaller circular copper
sheet [15] replaces center piece laminate present in previous
designs. Such placement permits upper copper (A calculated)
with its corresponding parasitic elements (B and C) to be
magnetically and electrically coupled, thus, producing a
wideband characteristics. S11 results are plotted in Figure 16
and its simulated farfield pattern of this design (Design Four)
shows higher directivity towards 900 theta angle, as shown in
Figure 17. However, it suffers from low gain (< 4.5 dB) and
noticeable minor sidelobes and backlobes near the ground
plane.
Fig. 15. Design four before including circular split ring resonator.
Fig. 16. Return loss drop not reaching the 7.0 GHz point obtained with
non-CSRR CSMA.
Fig. 17.Farfield produced side beam and less directive ≤4dBi.
Energy wasted at the rear.
Four elements
Side lobes
International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: 02 31
112902-8383 IJET-IJENS @ April 2011 IJENS I J E N S
Fig. 18. Surface current found at every CMSA edge producing mutual
coupling.
Fig. 19. Side view of Design Four E-Field, with every red-yellow region
representing same frequency frame.
Due to these dissimilar CMS placed close together of less
than a lambda, it happens to generate mutual coupling, Figure
18, and this leads to energy multiplication. Fairly strong gain
signal are found unevenly positioned. Supporting this is in
Figure 19, noticeable at third layer edges. Electrical field are
more intense and yields out unwanted side beams. Bandwidth
expansions are both affected by the optimized air gap and
aforementioned factors.
F. Design Five
Previous antenna (Design Four) is then incorporated with
complementary circular split ring resonator (CCSSR) shape on
layer 3, as shown in Figure 20. In this antenna (Design Five),
CCSSR design is repeated by gradually incrementing it to fully
occupy every circular copper areas available on layer 3.
Similarly, layer 2 is significantly reduced to a 10 mm diameter
of circular copper sheet to acquire more energy in resonating
all slots. The split ring design shown seems to improve the
overall results of the antenna. Figure 21 illustrate S11
parameters results of CCSSR involvement. Results indicate a
wide bandwidth enlargement covering more than 5850 – 7075
MHz, which is better than results obtained using the non-
CCSSR type design in Figure 16.
Applying CCSRR resulted in wider bandwidth, enhances
antenna gain and directivity (from < 4.5 dB to 6 dB),
minimizes minor backlobes and retains the directive features
of having the strongest main beams perpendicularly positioned
(z-direction). Figure 22 shows outcome result of less than 2:1
for Voltage Standing Wave Ratio (VSWR) [12] for CCSRR
type design.
Contrast to Figure 18 with current surging along outer
CMSA edges, CCSRR inserted, Figure 23 boosted more
current intensity and value from middle slots to the outer rim.
Such energy combination raises frequency related electrical
points, Figure 24 and gave more improvement.
Fig. 20. Begins with a few and then the entire copper element were fully
occupied with CCSRR
Fig. 21. Return loss obtained is wider with CCSRR
Fig. 22. Corresponding VSWR of prototype with CCSRR.
Fig. 23. Stronger and more current found flowing within slotted surfaces.
Mutual coupling
Intense E-Field
Current value rises
International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: 02 32
112902-8383 IJET-IJENS @ April 2011 IJENS I J E N S
Fig. 24. More CCSRR slots created more high value electrical points.
G. Design Six
Design 6 in Figure 25, advances on to additional CMS set
close to strong current flow based on Figure 23, and by
removing non-copper laminate areas at layer 3, Figure 26. It is
to capture and reduce surface current on none copper areas of
layer three and forming air-way for supplied signal to induce
more CCSRR structures. This in turn, enhances and deepens
S11 output, Figure 27. Stable and evenly flowed electric field
and surface currents resulted to higher gain value of ≥7 dB, as
shown in Figure 28.
Fig. 25. Layout view of Design Six with additional CMSA.
Fig. 26. Numbers are locations of removed substrate.
Fig. 27. CCSRR and selected laminate area removal permits extensive
bandwidth starting from 4.7055 GHz up to 7.411 GHz.
Fig. 28. Simulated farfield at 5.85 GHz with ≥7 dBi directivity.
Design six exhibits average ≥6.5 dB gain, ≥6.5 dBi
directivity and 80% of radiation efficiency and total efficiency.
along 5850 to 7075 MHz span. Blending in CCSRR, there are
no minor backlobe, irregular electrical, magnetic and current
surface flow as in Figure 29. Substrate removal repairs these,
Figure 30 which gave out electrical rise from 12393V/m to
15265 V/m of peak voltage.
Fig. 29. Design Five produces unevenly flowing E-Field.
Electrical points
Additional CMSA
(1)Substrates removed
1
1
1
1
International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: 02 33
112902-8383 IJET-IJENS @ April 2011 IJENS I J E N S
Fig. 30. Design Six E-Field flow improved after designated substrates
locations are eliminated.
III. PARAMETRIC STUDIES
Fig. 31. Parametric study of altering air gap dimensions.(a) Height at
4.5 mm (b) Height at 9 mm.
As stated earlier, dimension of air gap, split ring quantity
and entrenched split ring width are monitored as key
controllers. Increase of air gap (h) causes fringing fields from
edges to increase and thus further decreases CMS radius to air
gap ratio. This in turn drops effective dielectric value and
hence deepens resonance frequency. Eleven samples prepared
from 0 to 9 mm in Figure 31, shows this is true making
selecting dimensions (h) from 4.5 mm onwards are reasonable
in accomplishing band expansion.
Haps_v2_f01
Haps_v2_f02
Haps_v2_f03
Haps_v2_f04
Haps_v2_f05
Haps_v2_f06
Fig. 32. Six samples of CCSRR addition to the CSMA structure.
Two of many slots purposes are to lengthen excited surface
current path and introduce reactive loading to yield dual band
operation where here it is revised to widen band span. Figure
32 displays six CCSRR quantity incremental formations and
with its corresponding gain studies in Figure 33. From one
slots Figure 32 Haps_v2_f01, gain produced fluctuated and not
stable. It deteriorate more at complementary two slots up till
reaching Haps_v2_f06, gain reading are found to be higher
and less wavering in between 5 to 6 dB.
Fig. 33. Comparison of six restructured antennas with CCSRR formation.
(a) One slot(s), (b) Full slot(s).
Existent and width (w) of CCSRR does affect the antenna
impedance matching and bandwidth. Creating slot [17] of
smaller area looks to performing better seeing as since
electrical and current flow more intensely and adds up
together. Figure 34, illustrate an six samples parametric study
beginning from 0.34 mm to 0.43 mm. More widely it gets,
more ripple occurs and making impedance matching not
properly tuned to targeted frequency. 0.34 mm was chosen
given that the output signal had fewer ripples, smoothly below
-10 dB and deepens resonance frequency [19].
a
b
a
b
International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: 02 34
112902-8383 IJET-IJENS @ April 2011 IJENS I J E N S
Fig. 34. Parametric study of altering CCSRR width.
Fig. 35. Simulating the designed antenna with available microwave
laminates.
Next step is to simulate gain performance of proposed
antenna over more diverse laminate types (different epsilon
and thickness). Five different laminates types to be simulated
are Taconic RF300300C1/C1, Taconic TLX906207/C1/C1,
Taconic TLY30200CH/CH, RogersRO3010 and Rogers
RT/D5880. Gain result of these different lamina types are
shown in Figure 35. For Rogers RT5880 (εr = 2.2), gain
fluctuates in the region of 5.5 to 7 dB. For Taconic
TLY30200CH/CH (εr = 2.33) the gain fluctuates from 4.75 to
6.6 dB. For Taconic TLX906207CI/CI (εr = 2.5), the gain
fluctuates from 4.8 to 6.75 dB. For Taconic RF300300C1/C1
(εr = 3.0), the gain fluctuates from 4 to 6 dB. For
RogersRO3010 (εr = 10.2), the gain fluctuates from 5.8 to 7.1
dB. Thus, layer three copper is designed using a thicker low
dielectric substrate (using RT 5880) to enhance bandwidth. Air
gap is increased to make total height of the antenna larger,
which reduces effective dielectric constant experienced by top
IV. RADIATION PATTERN
Polar plot serve straightforward options to investigate
Design Six antenna behaviour right from E-field versus H-field
theta and phi cut. Generally, linear polarization happen when
two orthogonal linear components that are in time phase or
1800 out of phase. In Figure 36, displays five frequency spots
at 900 theta cut. E-field and H-field are statistically unrelated
hence making Design Six one of linear polarization devices.
Similarly, as in Figure 37, E-field versus H-field at 900 phi cut,
same conditions are met.
In a 50 ohm system, 0 dB is equivalent to 0.224 V or 1.0
mW. Figure 38 is one polar plot resulted again at 900 theta cut.
Vigilantly, two locations ranging from 300 to 600 (A), and
from 3000 to 3300 (B) placed the 0 dB readings.
Fig. 36. E-field versus H-field at azimuth 900 theta cut. (a) Whole E-
field, (b) Whole H-field.
Fig. 37. E-field versus H-field at elevation 900 phi cut. (a) Entire E-
filed, (b) Entire H-field.
Fig. 38.Maximum = 0 dB, each arrows represent main radiation
direction.
Through simulation, power pattern can also be analysed at
each frequency. If in theory, 0 dB equals to 1.0 mW, here by
linear scaling the antenna produces, of receiving and
b
a
a
b
A
B
International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: 02 35
112902-8383 IJET-IJENS @ April 2011 IJENS I J E N S
transmitting power varying from as low as 0.097 VA/m2 to
0.39 VA/m2 all along 5850 to 7075 MHz span.
Fig. 39. Initial fabricated antenna CCSRR.
As a way to compare between simulation and fabricated
CCSSR design. Figure 39, 40, 41 and 42, presents an initial
result of the fabricated antenna, measured antenna return loss,
the measured antenna phase and the measured VSWR.
Fig. 40. Measured return loss.
Fig. 41. Corresponding measured fabricated antenna phase.
Fig. 42. Corresponding measured fabricated antenna VSWR.
V. CONCLUSIONS
Demonstrated via computer simulation, with manipulating
dimension of air gap, split ring quantity and entrenched split
ring width are monitored candidly improve antenna
characteristics and widen pass targeted band span.
Incorporation of circular split ring structure here has also
being electrically and magnetically improved due to coupling,
impedance matching and attaining better return greater than -
10 dB throughout 5.85 GHz to 7.075 GHz. Given that each
copper been re-shaped on microwave laminate (layer three)
was manipulated from no split ring slots to with one, it still
shows a circularly copper slots perform much better in terms
of total S-parameter and total efficiency.
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