2011 ijet-ijens preliminary study of circularly split ring
TRANSCRIPT
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International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: 02 27
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Abstract In this paper, influence of Circularly Split RingResonators 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
(r = 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 byan 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 TermsCCSRRs, CMS, CSMA, SRR
I. INTRODUCTIONigh Altitude Platform Station (HAPS) has been proposed
to achieve full broadband coverage as stated in
Malaysias 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
antennas 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, withelevation angle from ground up set at 30 degree [4-5]. Tuning
Manuscript received February 25, 2011.
A.A.M. Ezanuddin is with the School of Computer and Communication
Engineering, Universiti Malaysia Perlis, Perlis, Malaysia (phone: 6012-688-
2674; fax: 303-555-5555; e-mail: [email protected]).
M. F. Malek is with the School of Electrical System Engineering,
Uinversiti Malaysia Perlis, Perlis, Malaysia (e-mail: [email protected].
P. J. Soh is is with the School of Computer and Communication
Engineering, Uinversiti Malaysia Perlis, Perlis, Malaysia (e-mail:
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 (r) 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 thebandwidth 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 FORPAPERSUBMISSIONA.
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).
Preliminary Study of Circularly Split Ring
Resonators Entrenched within Circular
Microstrip Antenna
A. A. M. Ezanuddin, M. F. Malek, and P. J. Soh
H
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Effective relative permittivity is derived by using equation
(2). Estimation of the extended incremental lengths of patch,
L is obtained by using equations 3 and 4. Actual length
value is derived from equation 5. In the equations, Wis width
of patch or microstrip line, r 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 1
TABLE1
CALCULATION OF THE BASIC SHAPE OF WIDTH AND LENGTH.
Frequency
(MHz)
W
(mm)reff
L
(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 22
(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 2 illustrates effective CMSA radius for the three
frequencies 5.85 GHz, 6.4375 GHz and 7.075 GHz
respectively.
TABLE 2
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 theconventional 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 equivalentciruit.
B. Design OneDesign 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
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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 (r = 10.2, 40 mm radius) was initially used for
the simulations and analysis. 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 lowereffective 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.
Worsen and shifted1 4
Strong electrical field
Not radiating at
desired direction.
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Fig7. E-Field strength showed by the darker part area.
Fig8. Isoline plot shows E-Field flow of Design Two antenna, with most
energy situated in between the substrates.
Fig9. 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.
Darker region are
located at the front.
Port
Energy stored to
resonate CMSA.
Radiate at desireddirection.
Signal deepens with
four elements.
1
4
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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, itsuffers 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
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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 andaforementioned 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
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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 deepensS11 output, Figure 27. Stable and evenly flowed electric field
and surface currents resulted to higher gain value of7 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 7dBi 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
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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 incrementalformations 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
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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 simulatedare 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 (r = 2.2), gain
fluctuates in the region of 5.5 to 7 dB. For Taconic
TLY30200CH/CH (r = 2.33) the gain fluctuates from 4.75 to
6.6 dB. For Taconic TLX906207CI/CI (r = 2.5), the gain
fluctuates from 4.8 to 6.75 dB. For Taconic RF300300C1/C1
(r = 3.0), the gain fluctuates from 4 to 6 dB. For
RogersRO3010 (r = 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 PATTERNPolar 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
transmitting power varying from as low as 0.097 VA/m2 to
0.39 VA/m2 all along 5850 to 7075 MHz span.
b
a
a
b
A
B
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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. CONCLUSIONSDemonstrated 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 alsobeing 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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[19]Heba B. El-Shaarawy, Fabio Coccettti, Robert Plana, Mostafa El-Said andEssam A. Hashish, Defected Ground Structures (DGS) and UniplanarCompact- Photonic Band Gap (UC PBG) Structures for Reducing the
Size and Enhancing the Out-of-Band Rejection of Microstrip Bandpass
Ring Resonator Filters, WSEAS Transactions on Communications, Issue
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