Int. J. Electron. Commun.

(AEÜ) 139 (2021) 153891

Contents lists available at ScienceDirect

International Journal of Electronics and Communications

journal homepage: www.elsevier.com/locate/aeue

Regular paper

A CPW-fed rectangular nested loop antenna for penta band

wireless applications
R. Samson Daniel
Department of ECE, K. Ramakrishnan College of Engineering, Samayapuram, Tiruchirappalli, India

A R T I C L E I N F O A B S T R A C T

Keywords: A miniaturized coplanar waveguide (CPW) fed rectangular nested loop antenna is proposed for penta band
CPW-fed wireless applications. Multiband and antenna compactness are obtained by using rectangular loop resonators.
Multiband The proposed antenna has been optimized by increasing the number of loop iterations. The designed antenna
Rectangular loops
comprises four rectangular loops, it constructs the antenna to excite 1.01 GHz, 1.67 GHz, 2.30 GHz, 2.92 GHz
LC quasi-static design equations
and 3.48 GHz frequency bands. The fabricated geometry has a dimension of 30 × 30 × 1.6 mm3, which is
developed on a low-cost Flame Retardant-4 substrate having εr = 4.4 and tanδ = 0.02. The resonance behavior of
the proposed antenna is verified by employing LC quasi-static design equations. The measured reflection coef­
ficient and far-field pattern are exhibited to support the performance of the designed antenna for wireless
applications.

1. Introduction [14]. Electromagnetic band gap (EBG) structures are used for attaining
high isolation in multiband antenna design due to reducing the mutual
In recent scenario, flourishing wireless devices are prominent role in coupling between the antenna components [15]. In [16], the rectangular
the advanced communication systems. Planar antennas are developing and square shaped slots are created in the conductor patch to radiate the
as an important contributor in wireless devices such as mobile phones, multiband. The rectangular slot is used to build the dual-band (middle
Bluetooth and biomedical devices owing to the small size, multiband, and upper) resonances, while the square shaped slot is used to radiate
high performance and cost effectiveness [1]. Numerous design meth­ lower resonance. Multiple symmetrical hexagonal complementary split
odologies have been proposed for achieving multiband abilities such as ring resonators are introduced in a radiation patch for attaining the
fractal geometry [2], metamaterial [3], loading slots [4] and modified multiband and compact size of the antenna [19]. The CPW-fed planar
ground plane [5]. Nested loop configurations have been evolving as a antennas are used to acquire effective miniaturization and multiband
big candidate in advance wireless communication. It offers wider response [20].
bandwidth [6], multiband [7] and impedance matching [8] character­ In this article, CPW-fed nested loop antenna is developed for GSM
istics along with shrinkage of antenna size. CPW-fed is used to recognize (1.01 GHz and 1.67 GHz), WLAN (2.30 GHz and 2.92 GHz) and WiMAX
a quarter wave transformer for obtaining impedance matching [9]. (3.48 GHz) applications. The proposed loop antenna has an electrical
Nested loop resonators induce magnetic coupling between the mutual size of 0.101 λ0 × 0.101 λ0 × 0.005λ0 , where λ0 is the wavelength at
inductances to drive the radiating modes. The structural alignment of lower resonance frequency of1.01 GHz. Due to the nested loop config­
nested loop yields various current orientations for acquiring multiband uration, the capacitance is governed by the electrically coupled, while
[10]. Loop resonator plays a paramount role to create the lower radi­ the mutual inductance is governed by magnetic coupling for generating
ating modes for designing electrically small antenna. penta band resonance behavior. The CPW-fed has been synthesized to
Furthermore, multiband planar antennas have been developing by attain impedance matching. The designed loop antenna has substantial
crinkle fractal structure [11] and radiating element [12]. An offset CPW- benefits, involving better reflection coefficient characteristics, multi­
fed asymmetric E-shaped patch can be used to optimize the performance band and compact size. This article has unique attention, which com­
of the antenna, such as impedance matching, multiband and circular prises quasi-static LC tank circuit analysis of rectangular loop resonance
polarization [13]. CPW-fed square spiral patch with L-shaped strips can frequency and correlated with already reported antennas
be produced multiband characteristics and wider impedance bandwidth [1–4,7,9,10,12,17].

E-mail address: samson.rapheal@gmail.com.

https://doi.org/10.1016/j.aeue.2021.153891
Received 1 April 2021; Accepted 6 July 2021
Available online 22 July 2021
1434-8411/© 2021 Elsevier GmbH. All rights reserved.
R. Samson Daniel AEUE - International Journal of Electronics and Communications 139 (2021) 153891

Fig. 1. Design evolution of the designed loop antenna.

Table.1
Geometrical values of the proposed antenna.
Parameters Dimensions (mm)

30
L 30
l1 12.2
w1 9.5
l2 11.4
w2 8.7
l3 10.6
w3 8
l4 9.8
w4 7.1
Lg 12.3
wf 3
S 0.3

Fig. 2. Pictorial view of the designed antenna.

2. Antenna design and simulated results

The geometry of the proposed antenna is designed from a narrow

band single rectangular loop CPW-fed antenna as depicted in the design
(A) of Fig. 1. It offers a narrow resonance at 1.66 GHz. This fundamental
resonance frequency has been estimated using [16]
L1 = 2l1 + w1 + 2Δleff (1)

where the fringe field depth Δleff is equal to the FR-4 substrate thickness
(h = 1.6 mm), l1 = 12.2 mm and w1 = 9.5 mm is the length and width of
the conventional rectangular loop (N = 1). Therefore, L1 = 42.7 mm and
the fundamental resonance frequency is given by:

c 3 × 108
fr = √̅̅̅̅ = √̅̅̅̅̅̅̅ = 1.67GHz (2)
2L1 εr 2 × 42.7 × 10− 3 4.4

From this examination, it is identified that the conventional rectan­ Fig. 3. S11 (dB) characteristics of the design evolution.
gular loop resonator produces resonance at 1.67 GHz, which validates
with simulated resonant frequency of 1.66 GHz.
characteristics along with 92% of size reduction. The pictorial view of
To acquire multiband resonance characteristics from this narrow
the designed antenna is described in Fig. 2 and its parameters are given
resonance, the nested rectangular loops are introduced as shown in the
in Table 1.
design (B) of Fig. 1. The rectangular loops are capable of constructing
All simulations have been conducted using electromagnetic software
multiband owing to the loop configuration. The width of the rectangular
HFSS V.13.0. The S11 (dB) characteristics of the single rectangular loop
loop and spacing between the loops is kept constant value of 0.2 mm for
CPW-fed antenna (A) and proposed geometry (B) are illustrated in Fig. 3.
uniformity. Now, the proposed antenna yields penta band resonance

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Table 2
Performance evaluation of the number of rectangular loops.
Number of Resonance Return Frequency Impedance
rectangular frequency loss (dB) range (GHz) bandwidth
loops (GHz) (MHz)

N=1 1.66 − 20 1.58− 1.74 160

N=2 2.06 − 13 2.03− 2.08 50
3.25 − 23 3.08− 3.45 370
N=3 1.34 − 21 1.33− 1.36 30
2.18 − 33 2.13− 2.21 80
2.95 − 33 2.85− 3.06 210
3.78 − 10 − −
N=4 1.01 − 25 1.00− 1.02 20
1.67 − 38 1.65− 1.69 40
2.30 − 22 2.26− 2.34 80
2.92 − 45 2.84− 2.98 140
3.48 − 14 3.43− 3.54 110

resonance at 1.01 GHz, 1.67 GHz, 2.30 GHz, 2.92 GHz and 3.48 GHz
with better impedance matching.
From this analysis, by increasing the number of rectangular loops is
used to achieve penta band and better impedance matching, which is
estimated in Table 2. In the Fig. 5(a)–(e) perspective view of electric
field distribution and corresponding vector current distribution has been
illustrated. From absolute electric field distribution, it is perceived that
maximum field distribution exists on the loops. From vector current
distribution, it is understood that in the rectangular loops, current mo­
tion in the opposite orientation, which supports the opposite side loop
configuration property [17].

3. Quasi-static analysis of rectangular loop

The designed loop antenna and its LC prototype [18] are described in
Fig. 6. The LC tank circuit model is represented for 50 Ω CPW-fed
transmission line, outer rectangular loop (N = 1) and nested rectan­
gular loops (N = 2,3,4). Here, Lf is the length of the CPW-fed trans­
mission line, Rf is the loss resistance of CPW-fed, characteristic
impedance (Z0 = 50 Ω), lumped components (R1 , C1 , L1 ) of the outer
rectangular loop and Cc is the gap capacitance between the rectangular
Fig. 4. S11 (dB) characteristics of the number of loop resonators (a) N = 1, N =
loops. The inductance (L2 , L3 , L4 ) values are governed by nested rect­
2 and (b) N = 3, N = 4.
angular loops (N = 2,3,4) and corresponding capacitance values (C2 , C3 ,
C4 ) are governed by spacing between the rectangular loops.
It is explained that, the proposed geometry offers penta band at 1.01 After fashioning nested rectangular loop resonators, the new reso­
GHz, 1.67 GHz, 2.30 GHz, 2.92 GHz and 3.48 GHz. This resonance nance frequencies are generated along with better impedance matching.
behavior has been confirmed by exploration of the rectangular loop Therefore, the LC tank circuit model has been focused on N = 2, N = 3
resonators under four cases: (a) Rectangular loop with N = 1, (b) and N = 4. The new resonance frequency is estimated by [19]
Rectangular loop with N = 2, (c) Rectangular loop with N = 3 and (d)
Rectangular loop with N = 4. Fig. 4(a) and 4(b) shows the S11 (dB) fL =
1
√̅̅̅̅̅̅̅̅̅̅̅ (3)
characteristics of the number of loop resonators with a corresponding 2π LL CL
inset image, which illustrates the rectangular loop configurations. As the
image depicts that, rectangular loop with N = 1 produces a narrow N− 1
WhereCL = [2L − (2N − 1) (W + S) ]C0
resonance at 1.66 GHz. The rectangular loop with N = 2 offers a new 2
resonance frequency of 3.25 GHz and shifts the narrow resonance from (√̅̅̅̅̅̅̅̅̅̅̅̅̅̅ )
1.66 GHz to 2.06 GHz. Therefore, the rectangular loop with N = 2 K 1 − K2 S
2
C0 = ε 0 andk =
generates two resonance frequencies of 2.06 GHz and 3.25 GHz. The K(k) W + S2
rectangular loop with N = 3 yields two resonances at 1.34 GHz and 3.78
[ ( ) ]
GHz. Also, it shifts the resonance from 2.06 GHz to 2.18 GHz and from 0⋅98
LL = 4μ0 L − (N − 1) (S + W)ln + 1⋅84ρ
3.25 GHz to 2.95 GHz. Hence, the rectangular loop with N = 3 create the ρ
quad band resonance at 1.34 GHz, 2.18 GHz, 2.95 GHz and 3.78 GHz. To
acquire penta band along with better impedance matching, the rectan­ (N − 1)(W + S)
ρ =
gular loop with N = 4 are introduced. It creates a new resonance fre­ 1 − (N − 1)(W + S)
quency of 1.01 GHz at lower frequency region and shifts the resonance
Here, average length of the rectangular loop (L), the width of the
frequencies from 1.34 GHz to 1.67 GHz, from 2.18 GHz to 2.30 GHz,
rectangular loop (W = 0.2 mm), spacing between the loops (S = 0.2
from 2.95 GHz to 2.92 GHz and from 3.78 GHz to 3.48 GHz. Thus, the
mm), N is the number of rectangular loops and K is the first order elliptic
proposed antenna (rectangular loop with N = 4) provides penta band
integral of the first kind identity K(k). This LC quasi-static design

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R. Samson Daniel AEUE - International Journal of Electronics and Communications 139 (2021) 153891

Fig. 5. Perspective view of electric field distribution and corresponding vector current distribution at (a) 1.01 GHz, (b) 1.67 GHz, (c) 2.30 GHz, (d) 2.92 GHz and (e)
3.48 GHz.

equations are computed by the MATLAB code to calculate the resonant Thus, the third loop resonance frequency is f3 = 2π√1̅̅̅̅̅̅̅̅
L C
= 1.33 GHz.
3 3
frequency of rectangular loop owing to LC values.
For, N = 4 (Fourth Loop) Average Length (L) = l4 +W 2
4
= 8.45 mm
For, N = 2 (Second Loop) Average Length (L) = l2 +W 2
= 10.05 mm
2 Hence, L4 = 7.8013×10− 08 (Henry) and C4 = 3.1352×10− 13 (Farad).
Hence, L2 = 4.6315×10− 08 (Henry) and C2 = 5.2253 ×10− 14 (Farad). Thus, the fourth loop resonance frequency is f4 = 2π√1̅̅̅̅̅̅̅̅ = 1.02 GHz.
Thus, the second loop resonance frequency is f2 = 2π√1̅̅̅̅̅̅̅̅ = 3.24 GHz.
L C 4 4
L C 2 2 From this LC quasi-static examination, it is observed that second
For, N = 3 (Third Loop) Average Length (L) = l3 +W
2
3
= 9.3 mm loop, third loop and fourth loop produce the resonance at 3.24 GHz,
Hence, L3 = 7.6736×10− 08 (Henry) and C3 = 1.8579×10− 13 (Farad). 1.33 GHz and 1.02 GHz, respectively. It supports the simulated S11 (dB)

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R. Samson Daniel AEUE - International Journal of Electronics and Communications 139 (2021) 153891

Fig. 5. (continued).

Fig. 6. Proposed loop antenna and its LC tank circuit model.

at N = 2, N = 3 and N = 4. Similarly, Table 2 describes the same. prominent role in radiation behavior and antenna impedance. The feed
width is increased from 2 mm to 3 mm in steps of 0.5 mm and the
4. Parametric study corresponding input reflection coefficient plot is described in Fig. 8. It
explains that, by increasing the width of the feed line, the characteristics
To perceive the effects of structural configurations on the resonance, impedance Z0 = 50 Ω is achieved. Thus, the optimum feed width Wf = 3
a parametric study has been examined. The S11 (dB) behavior of the mm is assigned for the designed antenna.
( ) ( )
length of the ground plane Lg , the width of the feed Wf and spacing Furthermore, Fig. 9 indicates the S11 (dB) of the designed antenna
between the ground plane and feed line (S) are revealed in this section. with spacing between the ground plane and feed line (S). It shows that,
( )
The variations in the length of the ground plane Lg are explained in as the value of ‘S’ increases from 0.1 mm to 0.3 mm, the impedance
Fig. 7. The ground plane length is changed from 10.3 mm to 12.3 mm matching is also obtained gradually. Therefore, the maximum possible
with incremental step of 1 mm. As the length of the ground plane Lg
( ) value of S = 0.3 mm is chosen to attain penta band resonance fre­
quencies of 1.01 GHz, 1.67 GHz, 2.30 GHz, 2.92 GHz and 3.48 GHz. The
increases, the input refection coefficient values are enhanced. Although,
input reflection coefficient plots for rectangular loops greater than N = 4
the optimum ground plane length Lg = 12.3 mm is selected for better
( ) is illustrated in Fig. 10. It reveals that, if the number of loops is greater
impedance matching. The width of the CPW-fed Wf executes
than N = 4 the performance of the antenna is decreased. Hence, the

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R. Samson Daniel AEUE - International Journal of Electronics and Communications 139 (2021) 153891

Fig. 7. S11 (dB) plots for various ‘Lg ’ values.

Fig. 10. S11 (dB) plots for N = 4 and N = 5.

Fig. 8. S11 (dB) plots for various ‘Wf ’ values.

Fig. 11. Efficiency of the proposed antenna.

number of loops is fixed at N = 4 for the proposed antenna design. The

radiation efficiency of the designed antenna is represented in Fig. 11.
The radiation efficiencies are 72, 73, 72, 73 and 75% at 1.01 GHz, 1.67
GHz, 2.30 GHz, 2.92 GHz and 3.48 GHz, respectively.
In this design, the rectangular loop resonators are used as the main
radiating element, which supports the antenna size reduction. When the
size of the antenna is miniaturized, it affects the radiation behavior,
leading to a reduction in the gain.
The comparison of proposed CPW-fed loop antenna with earlier
published antennas indexed in literature is displayed in Table 3. It de­
scribes that the prototype antenna has a minimum aperture area to
obtain penta band characteristics for GSM, WLAN and WiMAX appli­
cations. Also, this article emphasizes the verification of resonance fre­
quency using LC quasi-static design equations, which are computed by
MATLAB code.

5. Measurement results

The snapshot of the fabricated prototype has been displayed in

Fig. 9. S11 (dB) plots for various ‘S’ values. Fig. 12. The reflection coefficient of the fabricated antenna is experi­
mentally verified by Anritsu VNA MS2027C setup model as shown in
Fig. 13. Fig. 14 represents the simulated and measured S11 (dB) of the
designed antenna, both data congruence to each other. The directional

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R. Samson Daniel AEUE - International Journal of Electronics and Communications 139 (2021) 153891

Table 3
Comparison of proposed CPW-fed loop antenna with earlier published antennas.
Reference Year Patch detail Substrate dimensions L Resonance frequencies (GHz) Gain (dBi) Quasi-static LC
× W (mm2) analysis

[1] 2019 Rectangular and circular SIW cavities loaded 48 × 52 5.2 and 5.8 GHz 6.97 and 6.2 dBi Not Analyzed
with circular slots
[2] 2020 Hexagonal sierpinski gasket fractal 50 × 50 3.46, 8.28, 12.26, 17.21, 23.40 6, 8.37, 9.65, 9, 7.84 Not Analyzed
and 26.01 GHz and 9.34 dBi
[3] 2018 Metamaterial antenna with modified split ring 25 × 20 3.2 and 3.9 1.72 and 3.41 dBi Not Analyzed
resonator (SRR)
[4] 2019 Rectangular patch loaded with L-slots and 50 × 50 1.25, 1.48, 1.8, 2.25, and 2.9 1, 1.07, 1.1, 1.3 and Not Analyzed
inverted L-slots GHz 1.35 dBi
[7] 2019 Hexagonal nested loop fractal antenna with L- 40 × 32 1.7, 2.4, 3.1, 4.5 and 6 1.6, 2.15, 2.79 and Not Analyzed
shaped slot on the ground plane 3.8 dBi
[9] 2020 Elliptical patch loaded with circular ring slots 45 × 35 2.4, 3.5, 5.5 and 5.8 GHz 5.40 dBi Not Analyzed
[10] 2018 Sierpinski fractal carpet with metamaterial 40 × 40 3.5 and 5.8 GHz 2.5 and 3.5 dBi Not Analyzed
[12] 2019 CPW-fed square patch with radiating element 28 × 22 2.45, 4.45 and 7.4 GHz 2.92, 4.13 and 5.85 Not Analyzed
dBi
[17] 2019 Two SRR rings and an inverted L-shaped stub 30 × 17 2.45 GHz 1.86 dBi Not Analyzed
Proposed CPW-fed rectangular nested loop antenna 30 × 30 1.01, 1.67, 2.30, 2.92 and 1.80, 2.02, 2.12, 3.74 Analyzed
3.48 GHz and 2.64 dBi

ability of proposed antenna is explained by its far-field patterns. Fig. 15

(a)–(e) shows the simulated and measured patterns of the elevation
plane (Y-Z) and azimuthal plane (X-Z) of measured resonance fre­
quencies at 1.01 GHz, 1.65 GHz, 2.32 GHz, 2.89 GHz and 3.37 GHz,

Fig. 12. Snapshot of the fabricated prototype.

Fig. 14. Simulated and measured S11 (dB) of the designed antenna.

Fig. 13. (a) Measurement setup model and (b) S11 (dB) characteristics from VNA MS2027C.

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R. Samson Daniel AEUE - International Journal of Electronics and Communications 139 (2021) 153891

Fig. 15. Radiation patterns of the proposed antenna (a) 1.01 GHz, (b) 1.65 GHz, (c) 2.32 GHz, (d) 2.89 GHz and (e) 3.37 GHz.

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