CHAPTER 1

INTRODUCTION ___________________________________________________________________________

1.1 General Background

An antenna is a system which converts electromagnetic waves to electrical currents and

voltages and vice versa. As shown in Figure 1.2 (a) & (b), there are different types of

antennas such as dipole, monopole and helical wire antennas that are used for low frequency

operated radio, TV and mobile phones applications. Since these antennas were supported by

single operating band and also mounted outside of the device, the overall size of the system

had become very large. In order to resolve these issues especially for the handheld wireless

communication devices, in the year 1953, a brand new technology named as ‘microstrip

antennas’ was introduced by the Deschamps [Balanis 1989]. However, the practical

development of these antennas took around twenty years due to technology limitations. As

shown in Figure 1.2 (c) & (d), by using microstrip antenna technology, all modern devices

are having features of inbuilt antenna that supports multiple frequency bands. The list of

various targeted frequency bands/communication protocols that are regulated by Federal

Communication Commission [FCC report, 2002] and International Telecommunication

Union (ITU) are given in Table 1.1. The following section gives a brief discussion about

microstrip antennas and its feeding techniques with their advantages and limitations.

(a) (b) (c) (d)

Figure 1.2 Different Types of Antennas on (a) Motorola DynaTAC 8000X Mobile Phone

(b) Linksys WAP55AG, WLAN Access Point. [Zhang, 2011] (c) - (d) Inbuilt

Multi-Band Antennas in Nokia (www.nokia.co.in) and Apple Phone

(www.apple.com)

Table 1.1 Various Commonly Used Wireless Communication Protocols Define by FCC

and ITU

SR.No Service Name Frequency Band Application

1. DCS 1800 1.71-1.880 GHz Digital communication system

2. PCS 1900 1.85-1.99 GHz Personal Communication System

3. WiBro 2300 2.30-2.39 GHz Wireless Broadband

4. LTE 2300 2.30-2.40 GHz Long Term Evolution

5. Bluetooth 2.40-2.48 GHz Bluetooth

6. WLAN IEEE 802.1 b/g 2.40-2.484 GHz Wireless Local Area Network

7. RFID 2.446-2.454 GHz Radio Frequency identification

8. LTE 2500 2.50-2.69 GHz Long Term Evolution

9. WiMAX

2.50-2.69 GHz Worldwide Interoperability for

Microwave Access

10. WLAN IEEE 802.11 a 5.15–5.35 GHz &

5.72–5.82 GHz

Wireless Local Area Network

11. ISM 2.4

ISM 5.2

ISM 5.8

2.40-2.484 GHz

5.150-5.350 GHz

5.725-5.825 GHz

Industrial, Scientific, Medical

12. WiMAX IEEE 802.16

3.4-3.6 GHz &

5.25–5.85 GHz

Worldwide Interoperability for

Microwave Access

13. ELAN/ HIPERLAN2 5.470-5.725 GHz Europe Local Area Network

14. US Public Safety 4.940-4.990 GHz US Public Safety

15. X-band 7.5-8.5 GHz X-band satellite Applications

16. ITU 8 GHz 8.02-8.4 GHz ITU applications

17. UWB 3.1-10.6 GHz Ultra wide band communication

1.1.1 Microstrip Antenna

As given in Figure 1.3, the simple structure of a microstrip antenna contains a radiator or

radiating element on one side and a ground plane on the other side of the substrate. Based on

the design requirements, the radiating patch can take different geometries [Balanis, 2005]

such as hexagonal, ring sector, square, dipole, rectangular, circular, circular ring, triangle and

elliptical as shown in Figure 1.4. These printed antennas are having principle advantages of

simple structure, light weight, low fabrication cost and simple to integrate with RF circuits,

low scattering loss and conformability to planar and non planar structures. Due to these major

advantages, microstrip antenna has become one of the best choices for mobile

communication, satellite communication, spacecraft, telemetry, biomedical and missile

applications [Balanis, 2005; Balanis 1989; Garg 2001 and James, 1980].

Figure 1.3 Basic Geometry of a Patch Antenna [Balanis, 2005]

Figure 1.4 Different Geometries of Microstrip Antenna [Balanis, 2005]

Along with the numerous advantages, microstrip antennas have limitations of [Balanis, 2005]

narrow bandwidth, low radiation efficiency, high Q factor, poor isolation and poor

polarization purity. In the recent years, researchers have focused on developing advanced

technologies to minimize these drawbacks.

1.1.2 Feeding Methods

Since the radiating branches are considered on one side of the dielectric substrate, the RF

energy may be fed directly to the patch by attaching a conducting strip on the same side

called as microstrip line feed (Figure 1.5(a)) and if the radiating element and ground plane are

connected to a coaxial connector via a hole then it that type of feeding is called as coaxial line

feed technique (Figure 1.5(b)). The advantages of these two types of feeding schemes [Bahl,

1980; Carver, 1981; Balanis, 1989; Garg, 2001; Deepu, 2010 and Abutarboush, 2011] are that

feeding can be chosen at any position of the radiator in order to achieve desired 50Ω

characteristic impedance. If the microstrip antenna is excited by using the concept of

electromagnetic wave coupling to transfer energy between feedline and patch without

physical contact, then such techniques are called as aperture coupling (Figure 1.5(c)) or

proximity coupling feeding techniques depending on the ground plane location (Figure

1.5(d)). The major drawbacks of these two feeding techniques are that it is very difficult to

fabricate multiple layers [Bahl, 1980; Carver, 1981; Balanis 1989 and Garg 2001].

Figure 1.5 Types of Microstrip Feeding Techniques

Even though the above mentioned microstrip antenna feeding techniques are having so many

advantages, due to double sided printing/via hole feeding, it faces difficulties with the

integration of active devices and MMICs. This has created a greater interest in the design of

uniplanar antennas. Uniplanar antennas can be conveniently designed on the one side of a

lossless substrate, which makes fabrication and integration of active devices much easier. The

most widely used uniplanar antennas are the coplanar wave guide fed designs.

1.1.3 Coplanar Waveguide (CPW)-Fed Antenna

The CPW-fed antenna [Abutarboush, 2011] consists of a radiating patch and a signal strip

bounded by twin lateral ground strips separated by a small gap. The entire structure can be

design and fabricate on the one side of the dielectric material as shown in the Figure 1.6. The

major advantages are small size with simple structure, low cost due to uniplanar design,

wider bandwidth, low dispersion and radiation loss.

Figure 1.6 Coplanar Wave Guide Fed Rectangular Shaped Antenna

1.1.4 Asymmetric Coplanar Strip (ACS)-Fed Antenna

As shown in Figure 1.7, an ACS is a modification of the CPW-fed planar antenna. In

comparison to general CPW-fed monopole antenna, an ACS-fed structure will have smaller

size [Deepu et al. 2007; Deepu et al. 2009 and Deepu, 2010] by considering only half of the

ground plane of CPW-fed structure. Owing to the simple structure, ease of fabrication and

uniplanar structure, it is a more advantageous feeding technique for compact multi-band

antenna design.

Figure 1.7 Schematic of the Asymmetric Coplanar Strip (ACS) Fed Antenna

1.2 Parameters of an Antenna

A brief discussion on various parameters that are used to evaluate an antenna performance is

given in this section.

1.2.1 Return Loss (S11) and Impedance Bandwidth (BW)

The return loss (S11) can be defined as the ratio of the voltages of incident and reflected wave

[Deepu, 2010; Zhang, 2011 and Abutarboush, 2011]. The range of frequencies for which the

VSWR is 2 or S11 ≤ -10 dB can be considered as the bandwidth of an antenna (Figure 1.8).

The expression for percentage of bandwidth is generally expressed as

where, f1 and f2 are lower and higher -10 dB points and f0 is the centre frequency.

Figure 1.8 Impedance Bandwidth

1.2.2 Radiation Patterns

According to IEEE standard definition [Bahl, 1980; Carver, 1981; Balanis 1989; Garg 2001

and Balanis, 2005], an antenna radiation pattern can be defined as “A mathematical function

or a graphical representation of antenna parameters such as field intensity, flux density and

gain as a function of space coordinates”. As shown in Figure 1.9, various parts of radiation

patterns are referred as main lobe, back lobe and side lobes. Based on the desired

applications, electromagnetic field patterns can be omnidirectional as given in Figure 1.10(a)

(power radiates in all directions) or bidirectional (power radiates in particular direction) as

shown in Figure 1.10(b).

Figure 1.9 Radiation Pattern of an Antenna

Figure 1.10 (a) Omnidirectional Field Pattern and (b) Bi-directional field pattern

1.2.3 Directivity

Antenna directivity can be defined as “the ratio of the field intensity concentrated in a given

direction to the average field intensity distributed over all directions” [Balanis, 2005].

1.2.4 Gain

For a given antenna, gain of an antenna (Abutarboush, 2011) is defined as “the ratio of power

radiated or received by an antenna in a desired direction, to the power radiated or received by

an standard isotropic antenna”, considering both antennas are provided with same power.

1.3 Literature Review

Nowadays, compact multi band antennas are the key elements in every advanced wireless

communication systems. In particular, antennas that support multiple wireless

communication standards are of great interest to the researchers, designers and engineers due

to their wide range of applications. This section gives a detailed literature review on various

printed single and multi-band antennas that were designed by using microstrip feeding, cpw-

feeding and ACS-feeding techniques. An overview of the topics covered in this section is

given in Figure 1.11.

Figure 1.11 Classification of Literature Review Based on Operating Bands and Feeding

1.3.1 Single Band Antennas

In the year 2002, the FCC released a licensed-free ultra wide band (UWB) frequency

spectrum ranging from 3.1 to 10.6 GHz for high data rate short distance wireless

communication systems [FCC, 2002]. As shown in Figure 1.12, there are two standard

approaches [Lee et al. 2009] for designing UWB systems i.e. DS-CDMA and MB-OFDM.

The standard DS-CDMA approach divides the full band into three modes of operation i.e.

low band consisting of frequency ranging from 3.1-5.15 GHz, and high band consisting of

frequencies ranging from 5.82 GHz to 10.6 GHz and mixed band consisting of frequencies

ranging from 3.1 GHz-10.6 GHz.

Figure 1.12 Frequency Spectrums of MB-OFDM and DS-CDMA (two standard

approaches for designing UWB systems)

The MB-OFDM approach classifies its 7.5 GHz UWB bandwidth into fourteen sub-bands

each with an impedance bandwidth of 528 MHz. The first three sub-bands (3.168 GHz to

4.752 GHz) are decided as compulsory modes (Group A) in the system due to its high data

rate feature (Batra, 2003). To implement the MB-OFDM/DS-CDMA approach, single-

band/UWB antennas of compact size, omnidirectional radiation patterns and constant gain are

required. Recently, various antenna geometries/structures for MB-OFDM / low band DS-

CDMA systems with a frequency range of 3.1 GHz to 4.8 GHz / 3.1 GHz to 5.15 GHz have

been reported in the literature.

Chair et al. (2004) designed a CPW-fed rectangular slot monopole antenna with U-shaped

strip for UWB applications. In the antenna design, a substrate having large dimensions of 100

x 100 mm2

was considered. To achieve compact size antenna, Liang et al. (2005) proposed a

new design strategy without compromising on antenna performance characteristics like

impedance bandwidth and omnidirectional radiation patterns. The printed antenna was having

a circular disc radiating patch having an impedance bandwidth of 7 GHz with a substrate size

of 50 x 42 mm2. Chan and Huang (2006) developed a novel 26 mm 41.8 mm size coplanar

waveguide (CPW)-fed balanced wideband dipole antenna having an impedance bandwidth of

4 GHz from 3-7 GHz for UWB applications. The reported antenna was having limitations of

narrow bandwidth and being large in size.

Sadat et al. (2007) proposed a novel square ring slot antenna that covers wide frequency band

starting from 3.1 GHz to 10.6 GHz. Even though the reported antenna covers wider

impedance bandwidth, it occupies a very large area of 120 x 100 mm2. To achieve small size

antenna, Azenui et al. (2007) designed a printed crescent-shape monopole antenna fed by

microstrip line having overall dimensions of 45 x 21.5 mm2 for ultrawideband (3–10 GHz)

applications. Park et al. (2008) and Lee (2008) reported two different novel compact UWB

antennas targeted for 3.1 GHz to 5.2 GHz DS-CDMA/MB-OFDM applications; the overall

size of the antennas were 600 mm2 and 900 mm

2 respectively.

In order to reduce the size of an antenna, Song et al. (2008) designed a monopole structure

with two symmetrical strips to achieve 3.1-4.8 GHz frequency band operation with a size of

600 mm2 including radiating elements and ground plane. Similarly, Lee (2009) proposed a

narrow band, large size rectangular patch antenna (100 x 40 mm2) that uses coupling concept

for UWB DS-CDMA/MB-OFDM applications. Kumar and Chaubey (2011); Kumar and

Malathi (2011) proposed two UWB antennas based on the concept of fractal geometry. By

using pentagonal and diamond shape CPW-feeding structure, wide bandwidths of 10.3 GHz

from 4.69 GHz to 15 GHz and 4.2 GHz from 2.0 GHz to 6.2 GHz were achieved. Both the

designs were targeted for UWB applications having overall dimensions of 31 mm 32 mm

and 50 mm x 67 mm respectively. Recently, a 90 x 90 mm2 size, rectangular slot antenna was

proposed by Mitra et al. (2012) and a 35.5 x 34 mm2 size, circular patch antenna with beveled

stubs was reported by Ershadh et al. (2014) for broadband communication system

applications.

A detailed comparative study of the reported antennas in terms of its performance

characteristics are given in Table.1.2. From the table, it can be seen that many of these

reported designs are having either complex structures or large size and in addition to these

drawbacks, very few reported antennas were covering entire UWB band. This makes them

very difficult to use for broadband wireless communication system applications.

S.No Literature Antenna

purpose

Size (mm2) Total area

(mm2)

Operating frequency band

1. Chair et al. (2004) Single-Band 100 x 100 10000 2.799.48 GHz

2. Jianxin et al. (2005) Single-Band 50 x 42 2100 2.789.78 GHz

3. Chan et al. (2006) Single-Band 26 x 41.8 1086.8 37 GHz

4. Ma et al. (2006) Single-Band 66.1 x 44 2908.4 3.112 GHz

5. Zaker et al. (2007) Single-Band 26.5 x 23 609.5 3.510.7 GHz

6. Sadat et al. (2007) Single-Band 120 x 100 12000 3.110.6 GHz

7. Azenui et al. (2007) Single-Band 45 x 21.5 967.5 3.010 GHz

8. Dastranj et al. (2008) Single-Band 85 x 85 7225 2.811.4 GHz

9. Dawood et al. (2008) Single-Band 100 x 100 10000 3.110.6 GHz

10 Park et al. (2008) Single-Band 20 x 30 600 3.14.8 GHz

11. Lee et al. (2008) Single-Band 30 x 30 900 3.15.2 GHz

12. Song et al. (2008) Single-Band 20 x 30 600 3.14.8 GHz

13. Lee et al. (2009) Single-Band 40 x 100 4000 35.5 GHz

14. Sarin et al. (2009) Single-Band 55 x 42 2310 4.36.33GHz

15. Dastranj et al. (2010a) Single-Band 85 x 85 7225 2.8515.12 GHz

16. Dastranj et al. (2010b) Single-Band 85 x 85 7225 2.814 GHz

17. Kumar et al.(2011) Single-Band 31 x 32 992 4.6915 GHz

18. Kumar et al.(2011) Single-Band 50 x 67 3350 2.06.2 GHz

19. Mitra et al. (2012) Single-Band 90 x 90 8100 4.716.14 GHz

20. Ershadh et al. (2014) Single-Band 35.5 x 34 1207 3.015 GHz

Table 1.2 Comparison of Reference Antennas in terms of Size and Impedance Bandwidth

(It can be seen that the reported designs are having either complex structures with large size

and in addition to these drawbacks, very few reported antennas were covering entire UWB

band)

1.3.2 Multi Band Antennas

In this section, various multi-band antennas that have been designed based on CPW and

microstrip feeding techniques are presented.

1.3.2.1 Coplanar Waveguide (CPW)-Fed Antennas

As explained in the previous section, a CPW-fed planar antenna consists of a radiating

element and a signal strip bounded by twin lateral ground strips separated by a small gap. The

entire structure can be designed and fabricated on single side of a dielectric material. So, the

major advantages are small size with simple structure, low cost due to uniplanar design,

wider bandwidth, low dispersion and radiation loss. A detailed discussion on various CPW-

fed multi-band antennas that were reported in the literature is given in the following sections.

Liu et al. (2004) presented a 20 x 30 mm2 size meandered patch antenna for dual frequency

operation. The proposed antenna consists of CPW feeding with uniplanar rectangular

radiating element. The antenna provides a -10 dB impedance bandwidth of 260 MHz from

1.92–2.18 GHz and 710 MHz from 4.99–5.7 GHz, respectively, which can support both the

UMTS and WLAN bands. Though the reported structure was simple, it was not able to cover

3.5 GHz WiMAX band. In order to integrate 3.5 GHz WiMAX band, Song et al. (2007)

designed a triangular shape CPW-fed multiband antenna for WLAN/WiMAX applications.

Adjustable strips were used to enhance the impedance bandwidth in the higher frequency

band. Even though the reported antenna covers wider impedance bandwidth, it occupies a

very large area of 840 mm2.

Krishna et al. (2008) designed a 28.5x 33.5 mm2 size fractal monopole antenna for dual

frequency WLAN and WiMAX applications. The achieved operating bands were from 2.38

to 3.95 GHz and 4.95 to 6.05 GHz. A 40 x 35 mm2 dual-band antenna having a U-shaped

open stub was proposed by Lee et al. (2009b) to cover the 2.45 GHz WLAN and the 3.1-5.2

GHz DS-UWB applications. Similarly, Liu et al. (2010a) reported a 22 x 41 mm2 size tri-

band monopole antenna suitable for 2.4/5.0 GHz WLAN and WiMAX applications. In the

reported design, by inserting a U-shaped strip into a monopole, two resonances for WLAN

band were achieved and by integrating two symmetrical L-shaped slits into a defect ground-

plane, another resonance at WiMAX band was achieved. Again these reported designs were

having limitations of large size and complex structure.

A simple monopole printed CPW-fed antenna was presented by Chu et al. (2010) for wireless

communication applications. The reported antenna supports dual operating frequencies that

resonate at 2.5 GHz and 5 GHz respectively to support all the WLAN and WiMAX frequency

standards. Liu et al. (2010b) proposed a 30 x 25 mm2 size monopole antenna, which consists

of simple rectangular patch geometry. By properly choosing the optimized electrical lengths

of radiating slots, dual frequency operation of 2.4/5.0 GHz WLAN and 4–8 GHz C-band

operations was obtained. Even though both the reported antennas cover wider impedance

bandwidth, it occupies a very large area.

Huang et al. (2011) design and developed a novel monopole slot antenna with embedded

rectangular parasitic elements for dual-band applications. Though the reported antenna was

having wider impedance bandwidth, it was having drawback of large dimensions i.e. 30 x 50

mm2 including ground plane. In order to support, all the frequency standards of WLAN and

WiMAX, a slot monopole antenna (Hu et al. (2011)) with tri-band frequency of operation

was obtained. The reported antenna has three operating band from 2.34–2.82 GHz, 3.16–4.06

GHz, and 4.69–5.37 GHz respectively, which can cover WLAN and WiMAX bands.

Lin et al. (2012) reported a very large size (50 x 50 mm2) rhombus shaped slot antenna for

dual frequency operation. By properly selecting the feeding structure and rectangular strips,

two independent resonant frequencies having -10 dB bandwidths of 607 MHz resonated at

2.45 GHz and 1451 MHz resonated at 5.5 GHz were achieved. To reduce the size of the

antenna, a single layer CPW-fed antenna with tri-frequency operation for WLAN and

WiMAX applications was presented by Zhang et al. (2012). The proposed structure

comprised of planar rectangular patch element embedded with dual U-shaped slot. Also it is

having a simple uniplanar structure and occupies an area of 450 mm2 including ground

planes. In order to cover RFID band along with the WLAN band, Teng et al. (2012) proposed

a CPW-fed triangular shaped antenna with a dimensions of 28 x 26 mm2. In the design, a Π-

shaped slot and a T-shaped strip were introduced to generate two separate impedance

bandwidths ranging from 2.36-2.50 GHz and from 5.01-6.33 GHz respectively. Though the

reported structure was small and simple, it was not able to cover 3.5 GHz WiMAX band.

Huang et al. (2014) proposed a multi-band CPW-fed antenna for various wireless

communication applications. By using three different radiating elements namely, folded open

stub, L-shaped open stub, and Y-shaped resonator, triple operating bands working at

2.5/3.5/5.5 GHz was achieved. Similarly, to meet WLAN and WiMAX applications, a bow

tie shaped CPW-fed slot antenna was proposed by Tsai (2014). In the reported design, an M-

shaped patch at the centre of the slot is used as a radiating element. The developed antenna

achieves a dual frequency operation from 2.26-2.57 GHz and 4.81-6.56 GHz and has

dimensions of 60mm x 45mm. Again the reported design was having limitations of large size

and narrow impedance bandwidth.

A detailed comparative study of the recently reported CPW-fed multi-band antennas in terms

of its performance characteristics are given in Table.1.3. From the table, it is seen that even

though the CPW feeding is having many advantages such as uniplanar structure, simple to

design and has less cost of fabrication (one side printing), all the reported antennas are having

drawbacks of large size, narrow bandwidth and limited frequency of operation.

1.3.2.2 Microstrip-Fed Antennas

Various multi-band printed monopole antennas that have been designed by using the concept

of microstrip feeding technique are discussed in this section.

Kuo et al. (2003) designed and fabricated a printed microstrip-fed double-T shaped antenna

for WLAN system applications. The reported antenna comprised of dual T-shaped radiating

elements that can excite two independent resonant modes for the desired operations. The

proposed antenna has two independent impedance bandwidths that cover 2.17-2.56 GHz and

5.13-5.23 GHz bands respectively. Though the reported geometry has a simple structure with

wide operating band, the proposed antenna size was quite large with the ground plane itself

measuring 75 mm x 50 mm.

Yildirim (2006) developed a monopole antenna fed by microstrip line for WLAN/ Bluetooth

and UWB applications. Two rectangular shaped strips having different lengths generated two

independent resonance frequencies. The proposed monopole antenna has an operating

bandwidth of 484 MHz from 2.4-2.484 GHz and 5.5 GHz from 4.5-11.0 GHz. Though the

reported structure was simple, it was not able to integrate 3.5 GHz WiMAX communication

protocol and also it occupies a large area 800 mm2. Zhao et al. (2007) designed and fabricated

a 32 x 16 mm2 size meandered printed antenna that can work for 2.4/5 GHz WLAN systems.

By integrating multiple radiating branches or strips to the monopole structure, dual operating

bands with omnidirectional radiation patterns were achieved. But at the same time reported

antenna was not able to cover 3.5 GHz WiMAX frequency standard.

Reference Type Size (mm2) Area

(mm2)

Bandwidth Gain

(dBi)

Liu et al. (2004) Dual-band 20 x 30 600 1.92–2.18 GHz and 4.99–5.7 GHz 2.2

Song et al. (2007) Dual-band 35 x 24 840 2.36-2.50 GHz and 3.40–6.41 GHz 2.7

Krishna et al (2008) Dual-band 33.5 x 28.5 954.75 2.38 to 3.95 GHz and 4.95–6.05 GHz 2.0

Lee et al (2009b) Dual-band 40 x 35 1400 2.2–2.55 GHz, 3.0 –5.6 GHz 2.0

Liu et al. (2010a) Tri-band 22 x 41 902 2.32-3.27 GHz, 3.27-3.75 GHz & 4.96-6.02 GHz 3.5

Zhao et al. (2010) Tri-band 40 x 40 1600 2.28-2.58 GHz,3.38-3.66 GHz and 5.07-5.86GHz 3.3

Chu et al. (2010) Dual-band 28 x 33 924 2.24–2.81 GHz and 3.35–6.51 GHz 2.4

Liu et al. (2010b) Dual-band 30 x 25 750 2.34–2.55 GHz and 4.8–9.62 GHz 3.5

Zhuo et al. (2011) Dual-band 20 x 25 500 2.25-2.48 GHz and 5.0- 6.2 GHz 2.4

Huang et al. (2011) Dual-band 50 x 30 1500 2386–2510 MHz and 4878–6002 MHz 2.6

Hu et al. (2011) Tri-band 28 x 32 896 2.3-2.8 GHz, 3.1-4.0 GHz and 4.6-5.3 GHz 3.0

Lin et al. (2012) Dual-band 50 x 50 2500 2384–2991 MHz and 4959–6410 MHz 3.5

Zhang et al. (2012) Tri-band 25 x 18 450 2.37-2.53 GHz, 3.34-3.82 GHz & 4.23-6.88 GHz 3.7

Teng et al. (2012) Tri-band 28 x 26 728 2.36-2.50 GHz and 5.01-6.33 GHz 3.0

Sun et al. (2012) Quad-band 25 x 20 500 2.4–2.5GHz, 3.3–3.6 GHz, 5.15–5.3 & 5.7–5.8 GHz 2.5

Shu et al. (2012) Tri-band 31 x 21 651 2.33-2.83 GHz, 3.27-3.97 GHz & 4.3-6.67 GHz 2.7

Liu et al. (2012) Tri-band 23 x 36.5 839.5 2.33-2.76 GHz, 3.05-3.88 GHz & 5.57-5.88 GHz 2.8

Xu et al (2012) Tri-band 35 x 25 875 2.34-2.50 GHz, 3.1-3.82 GHz and 5.13-5.89 GHz 2.4

Liu et al. (2014) Dual-band 25 x 50 1250 3.4–3.6 GHz and 8–15 GHz --

Huang et al. (2014) Tri-band 30 x 18 540 2.39-2.69, 3.38-3.73 and 5.0-5.99 GHz 3.3

Tsai (2014) Dual-band 60 x 45 2700 2.26-2.57 GHz and 4.81-6.56 GHz 3.2

Chen et al. (2014) Tri-band 18 x 28 504 2.36-2.58 GHz,3.36-3.83 GHz & 4.83-6.29 GHz 2.7

Kumar et al. (2014) Dual-band 34 x 30 1020 2.3-2.5 GHz and 2.9-15.0 GHz 2.5

Table 1.3 Comparison of Referenced CPW-fed Multi-band Antennas (It is seen that even

though the CPW feeding is having many advantages such as uniplanar structure, simple to

design and have less cost of fabrication (one side printing), all the reported antennas are

having drawbacks of large size/narrow bandwidth and limited frequency of operation)

Thomas and Sreenivasan (2009) have proposed a multi-band antenna that can support several

communication standards such as WLAN and WiMAX applications. The reported antenna

design consists of a rectangular radiating element, trapezoidal shaped ground plane and

microstrip feed line. The reported design was having limitation of large size of 1140 mm2.

Mahatthanajatuphat et al. (2009) investigated the working of a rhombic monopole antenna

that was designed by using fractal geometry technique. The designed antenna was intended to

support advanced wireless communication standards such as PCS 1800 MHz, UMTS 2100

MHz, 2.4/5 GHz WLAN frequency bands. Even though the reported antenna has wide

impedance bandwidth, it is very difficult to integrate with modern communication devices

due to its large dimensions of 5310 mm2. Dang et al. (2010) have developed a simple

structured slot antenna based on microstrip feeding for WLAN and WiMAX applications.

The design is composed of a signal strip, and a slotted ground plane. The experimental results

show that that the reported tri-band design can provide multiple independent frequency bands

resonated at 2.7 GHz, at 3.5 GHz, and at 5.6 GHz respectively. Again the reported design was

also having limitation of large size.

Similarly, Dong et al. (2010) designed and developed a novel geometry of a planar antenna

that offers multiband operation in the bands of both the IEEE 802.11 a/b/g and WiMAX

bands. The reported design is having a circular radiating patch with two rectangular slits. By

using the inverted U-shaped slot, a pair of rectangular slits, and the hexagon-shaped slot, the

resonance frequencies and bandwidths of three independent frequency bands were tuned and

controlled. Measurement results show that the reported antenna can cover three desired

frequency bands of WLAN (2.4-2.4835, 5.15-5.875 GHz) and WiMAX (3.3-3.7 GHz). Even

though the reported antenna covers multiple frequency bands with wider impedance

bandwidth, it occupies a very large area of 975 mm2.

By using Defective Ground Structure (DGS) concept, Liu et al. (2011) developed a compact

tri-frequency microstrip monopole antenna. The reported antenna consisted of a rectangular

radiator with two L-shaped branches. The developed antenna operates over the three different

frequency ranges from 2.14–2.52 GHz, 2.82–3.74 GHz, and 5.15–6.02 GHz, making it

suitable for WLAN and WiMAX applications. In their paper, Papantonis and Episkopou

(2011) developed a novel 2.5 shaped printed antenna for WLAN applications. The reported

design provides a bandwidth of 403MHz (2.184 GHz-2.587 GHz) in the first operating band

and 4004MHz (3.880 GHz-7.884 GHz) in the second operating band, respectively. Again

these reported designs were having limitations of large size and complex structure.

Some other designs like rectangular patch with L-shape slot and stub [Xiong et al. (2012)],

rhombic shaped slot antenna [Xie et al. (2012)], L and E-shaped antenna [Sun et al. (2012)],

rectangular ring with L-shaped strip [Yuan et al. (2013)], an arc shaped strips antenna [Yoon

(2014b)], swastika antenna [Samsuzzaman et al. (2014)], microstrip patch antenna with

defected ground plane [Kaur and Khanna (2014)] and a tri-band monopole antenna with L-

shaped strip and a meandered strip [Ren et al. (2015)] were reported for multi-band

applications. Many of these reported designs are having either complex structures or large

size and in addition to these drawbacks, very few reported antennas with large size are

covering desired WLAN and WiMAX frequency bands.

A detailed comparison in terms of parameters like size, type, total area occupied and

frequency of operation of the reported antennas are given in Table 1.4. From the table it has

been observed that, all of these reported designs are having either complex structures or large

in size, in addition to the this some of the reported large size antennas are covering only few

WLAN/WiMAX operating bands. None of the reported antennas satisfy all the requirements

of a modern portable wireless communication system. This leads to a limited access of service

in LTE,WLAN, WiMAX, Bluetooth and US public safety frequency bands. Hence these

reported antennas are very difficult to integrate with RF/MMIC circuits.

Table 1.4 Comparison of Referenced Microstrip Multi-Band Antennas

Reference Type Size

(mm2)

Area

(mm2)

Operating Bands Gain

(dBi)

Kuo et al. (2003) Dual-band 75 x 75 5625 2.11–2.68 GHz and 5.15–5.46 GHz 1.4

Yildirim (2006) Dual-band 20 x 40 800 2.4–2.5 GHz and 4.5-11 GHz --

Zhao et al. (2007) Dual-band 16 x 32 512 2.2–2.5 GHz and 4.8–7.2 GHz 3.5

Thomas et al. (2009) Tri-band 38 x 30 1140 2.23–2.65 GHz and 3.24–6.95 GHz 2.5

Mahatthanajatuphat

et al. (2009)

Dual-band 59 x 90 5310 1.9-2.7 GHz and 4.3-6.1 GHz 2.4

Basaran et al. (2009) Dual-band 32 x 20 640 2.4–2.484 GHz and 5.151–5.825 GHz --

Dong et al. (2010) Tri-band 25 x 39 975 2.4–2.484 GHz, 3.15-3.89 and 5.13-6.23 GHz 3.3

Dang et al. (2010) Tri-band 35 x 30 1050 2.4–3.0 GHz, 3.25–3.68 and 4.9–6.2 GHz 3.5

Reference Type Size

(mm2)

Area

(mm2)

Operating Bands Gain

(dBi)

Rathore et al. (2010) Dual-band 45 x 35 1575 2.40-2.484 GHz and 5.15-5.35 GHz --

Ghalibafan et al. (2010) Dual-band 100 x 100 10000 2.40-2.48 GHz and 3.6-3.9 GHz --

Ren et al. (2011) Tri-band 14 x 34 476 2.4-2.5 GHz, 3.4-3.6 GHz, and 5.7-6.0 GHz 1.7

Pei et al. (2011) Tri-band 38 x 25 950 2.4–2.7 GHz, 3.1–4.15 GHz & 4.93–5.89 GHz 1.85

Papatonis et al. (2011) Dual-band 48 x 30 1440 2.18-2.58 GHz & 3.9-7.8 GHz 2.2

Liu et al. (2011) Tri-band 20 x 30 600 2.14–2.52 GHz, 2.82–3.74 and 5.15–6.02 GHz 2.0

Sun et al. (2012) Dual-band 40 x 30 1200 2.39-2.51 GHz and 5.0-6.1 GHz 1.0

Xiong et al. (2012) Tri-band 17 x 30 510 2.4-2.67 GHz, 3.26-3.8 GHz, and 5.0-7.0 GHz 2.0

Xie et al. (2012) Dual-band 40 x 40 1600 3.15–3.70 GHz and 5.05–5.97 GHz 4.0

Sayidmarie et al. (2012) Dual-band 42 x 24 1008 2.3-2.66 GHz and 4.5-6.0 GHz 2.2

Mehdipour et al. (2012) Tri-band 22 x 29 638 2.4-2.6 GHz, 3.4-3.75 and 5.0-6.3 GHz 1.5

Flores-Leal et al. (2012) Dual-band 40 x 40 1600 2.4–2.484 GHz and 5.151–5.825 GHz 1.6

Yuan et al. (2013) Tri-band 21 x 33 693 2.39-2.51 GHz, 3.26-4.15 and 5.0-6.43 GHz 2.5

Sim et al. (2014) Dual-band 30 x 45 1350 2.14-2.75 GHz and 5.05-6.16 GHz 3.3

Kaur et al. (2014) Dual-band 70 x 60 4200 3.34–3.54 GHz and 4.90–6.26 GHz --

Huang et al. (2014) Tri-band 20 x 30 600 2.4-2.74 GHz, 3.41-3.75 and 5.24-5.88 GHz 2.0

Yoon et al. (2014a) Tri-band 25 x 40 1000 1.93–3.16 GHz, 3.40–4.15 and 5.15–6.0 GHz 1.1

Lin et al. (2014) Dual-band 35 x 20 700 2.4-2.5 GHz and 5.0-6.0 GHz 2.9

Yoon et al. (2014b) Tri-band 28 x 40 1120 2.2-2.6 GHz,3.3-4.2 GHz and 5.06-7.07 GHz 3.0

Samsuzzaman et al.

(2014)

Dual-band 40 x 40 1600 2.28–3.23GHz, 3.28–3.94GHz &5.0–6.17GHz 3.5

Sun et al. (2014) Dual-band 25 x 25 525 2.38–2.51 GHz and 4.79–5.98 GHz 2.5

Liu et al. (2014) Tri-band 34 x 28 952 2.36-2.91 GHz, 3.27-4.06 and 5.07 -5.88 GHz 3.0

Ren et al. (2015) Tri-band 38 x 20 760 2.32–2.51 GHz, 3.0–3.95 and 5.4–5.95 GHz 3.1

Kumar et al. (2015) Tri-band 35 x 24 840 2.2-2.4 GHz, 2.8-3.3 and 3.55-11.6 GHz 1.0

Table 1.4 Comparison of Referenced Microstrip Multi-Band Antennas (It can be seen

that, all of these reported designs are having either complex structures or large in size, in

addition to the this some of the reported large size antennas are covering only few

WLAN/WiMAX operating bands)

1.3.2.3 ACS-Fed Antennas

To decrease the overall size of an antenna, some designs have been reported in Deepu et al.

(2007); Song et al. (2008); Deepu et al. (2009); Ashkarali et al. (2012) and Li et al. (2013) by

using the new concept called Asymmetric Coplanar Strip (ACS)-feeding. In comparison to

general CPW-fed antenna, an ACS-fed antenna structure will consume only 50% area by

considering only half of the ground plane of CPW-fed structure. Table 1.5 shows the

comparison of size, operating bands and average peak gains of the reported antennas. It was

found that most of the reported ACS-fed dual-band antennas were compact in size but again

they are having drawbacks of complex structure, narrow bandwidth and limited/no access of

5.2 GHz WLAN and 3.5/5.5 GHz WiMAX frequency band services.

Published

Literature

Antenna

Size (mm2)

Antenna Purpose

Antenna

Type

Average Peak

Gains (dBi)

WLAN

WiMAX

Deepu et al. (2007)

28 x 30

2.4/5.2/5.8 GHz

3.5 GHz

Dual-band

~ 2.1

Song et al. (2008)

31 x 15

2.4/5.2/5.8 GHz

----

Tri-band

~ 2.4

Deepu et al. (2009)

21 x 19

2.4/5.2 GHz

----

Dual-band

~ 1.9

Ashkarali et al.

(2012)

37.5 x 24

2.4 GHz

----

Dual-band

~ 1.21

Li. B et al. (2013)

35 x 19

2.4/5.2/5.8 GHz

3.5/5.5 GHz

Tri-band

~ 2.2

Table 1.5 Comparison of Referenced ACS-fed Multi-Band Antennas (It can be seen that

many of the reported ACS-fed dual-band antennas were compact in size but again they are

having drawbacks of complex structure, narrow bandwidth and limited/no access of 5.2 GHz

WLAN and 3.5/5.5 GHz WiMAX band services)

1.4 Objective of Study

Based on the literature review and from the presented comparative tables, it is observed that

CPW-fed, microstrip and ACS-fed techniques are having several advantages such as compact

size with wider impedance bandwidth, uniplanar structure and less fabrication cost (one side

printing in case of CPW and ACS-fed). However, most of the reported designs are having

limitations of large size, complex structure and narrow bandwidth/ limited frequency of

operation. Hence the primary objective of this research work is to design and develop novel

small size, simple structured multi band antennas based on advanced feeding techniques

(ACS, CPW and microstrip) to fulfill the portable wireless communication system

requirements.

The research mainly focuses on achieving the following objectives:

Design and development of small printed monopole multi-band antennas by using

advanced feeding techniques (i.e ACS, CPW and microstrip feeding).

Targetting to integrate many modern communication standards such as WLAN,

WiMAX, PCS/DCS/LTE, Bluetooth, WiBro, 8 GHz ITU/satellite system band and

US public safety bands into a single antenna.

Targetting to integrate 2.4 GHz WLAN/Bluetooth band 3.1-10.6 GHz UWB band

into a single compact antenna, which can be used for portable medical and point to

point high data rate communication system applications.

Achieving unique feactures such as compact size, independent tunability of each

resonant frequency and omnidirectional radiation patterns with desired peak gains.

1.5 Organization of the Thesis

This Thesis has been organized into five Chapters. Brief description of the contents of each

chapter is as under.

Chapter-1 discusses about basic introduction of single-band and multi-band antennas with

detailed literature review and objectives.

Chapter-2 presents design of two compact antennas using ACS feeding technique. The first

antenna is used for dual frequency operation that serves for LTE, WLAN and

WiMAX applications. Whereas the second antenna with triple operating bands is

designed for PCS, WLAN and WiMAX applications. Finally, experimental

`results along with the independent resonant frequency tuning property is

presented.

Chapter-3 presents a novel technique to design compact tri-band antennas for LTE,

WLAN/WiMAX and ITU applications. A detailed study of the proposed multi-

band antennas with its experimental results is presented. Both the antennas

presented in this chapter are aimed to fullfill desired objectives such as small

size, simple structure, wider impedance bandwidth, independent tunability of

resonant frequency and omnidirectional radiation patterns with acceptable peak

gains and radiation efficiency.

Chapter-4 presentes details of a simple structured dual-band antenna using Coplanar

Waveguide (CPW) feeding technique. The use of mirror C-shaped and stair case

shaped radiating patchs are explained in detail. The experimental results are

validated using simulation studies performed by CST microwave studio package.

Chapter-5 deals with the design and optimization of a very small size triangular shaped

patch antenna for dual frequency WLAN and UWB applications. Further

simulated design was validated experimentally by using vector network analyser

and performance characteristics like radiation patterns and peak gains are studied.

Chapter-6 presents the summary of the research work, its results and conclusions with its

future scope.