preliminary study of circularly split ring resonators ...ijens.org/vol 11 i 02/112902-8383...

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



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.



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.



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



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



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



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



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



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



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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