CHAPTER 1 INTRODUCTION. (a) (b) (c) (d)

Transcription

1 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 ( and Apple Phone (

2 Table 1.1 Various Commonly Used Wireless Communication Protocols Define by FCC and ITU SR.No Service Name Frequency Band Application 1. DCS GHz Digital communication system 2. PCS GHz Personal Communication System 3. WiBro GHz Wireless Broadband 4. LTE GHz Long Term Evolution 5. Bluetooth GHz Bluetooth 6. WLAN IEEE b/g GHz Wireless Local Area Network 7. RFID GHz Radio Frequency identification 8. LTE GHz Long Term Evolution 9. WiMAX GHz Worldwide Interoperability for Microwave Access 10. WLAN IEEE a GHz & GHz Wireless Local Area Network 11. ISM GHz ISM GHz Industrial, Scientific, Medical ISM GHz 12. WiMAX IEEE GHz & GHz Worldwide Interoperability for Microwave Access 13. ELAN/ HIPERLAN GHz Europe Local Area Network 14. US Public Safety GHz US Public Safety 15. X-band GHz X-band satellite Applications 16. ITU 8 GHz GHz ITU applications 17. UWB GHz Ultra wide band communication

3 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.

4 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

5 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 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 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 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.

6 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 Return Loss (S 11 ) and Impedance Bandwidth (BW) The return loss (S 11 ) 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, f 1 and f 2 are lower and higher -10 db points and f 0 is the centre frequency. Figure 1.8 Impedance Bandwidth

7 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

8 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] 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, cpwfeeding and ACS-feeding techniques. An overview of the topics covered in this section is given in Figure Figure 1.11 Classification of Literature Review Based on Operating Bands and Feeding

9 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 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 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, singleband/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 mm 2 was considered. To achieve compact size antenna, Liang et al. (2005) proposed a

10 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 mm 2. 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 mm 2. 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 mm 2 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 mm 2 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 GHz frequency band operation with a size of 600 mm 2 including radiating elements and ground plane. Similarly, Lee (2009) proposed a narrow band, large size rectangular patch antenna (100 x 40 mm 2 ) 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 mm 2 size, rectangular slot antenna was proposed by Mitra et al. (2012) and a 35.5 x 34 mm 2 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

11 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 Size (mm 2 ) Total area Operating frequency band purpose (mm 2 ) 1. Chair et al. (2004) Single-Band 100 x GHz 2. Jianxin et al. (2005) Single-Band 50 x GHz 3. Chan et al. (2006) Single-Band 26 x GHz 4. Ma et al. (2006) Single-Band 66.1 x GHz 5. Zaker et al. (2007) Single-Band 26.5 x GHz 6. Sadat et al. (2007) Single-Band 120 x GHz 7. Azenui et al. (2007) Single-Band 45 x GHz 8. Dastranj et al. (2008) Single-Band 85 x GHz 9. Dawood et al. (2008) Single-Band 100 x GHz 10 Park et al. (2008) Single-Band 20 x GHz 11. Lee et al. (2008) Single-Band 30 x GHz 12. Song et al. (2008) Single-Band 20 x GHz 13. Lee et al. (2009) Single-Band 40 x GHz 14. Sarin et al. (2009) Single-Band 55 x GHz 15. Dastranj et al. (2010a) Single-Band 85 x GHz 16. Dastranj et al. (2010b) Single-Band 85 x GHz 17. Kumar et al.(2011) Single-Band 31 x GHz 18. Kumar et al.(2011) Single-Band 50 x GHz 19. Mitra et al. (2012) Single-Band 90 x GHz 20. Ershadh et al. (2014) Single-Band 35.5 x 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)

12 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 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 CPWfed multi-band antennas that were reported in the literature is given in the following sections. Liu et al. (2004) presented a 20 x 30 mm 2 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 GHz and 710 MHz from 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 mm 2. Krishna et al. (2008) designed a 28.5x 33.5 mm 2 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 mm 2 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 GHz DS-UWB applications. Similarly, Liu et al. (2010a) reported a 22 x 41 mm 2 size triband 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 groundplane, another resonance at WiMAX band was achieved. Again these reported designs were having limitations of large size and complex structure.

13 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 mm 2 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 mm 2 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 GHz, GHz, and GHz respectively, which can cover WLAN and WiMAX bands. Lin et al. (2012) reported a very large size (50 x 50 mm 2 ) 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 mm 2 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 mm 2. In the design, a Π- shaped slot and a T-shaped strip were introduced to generate two separate impedance bandwidths ranging from GHz and from 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

14 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 GHz and 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 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 GHz and 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 GHz and 5.5 GHz from 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 mm 2. Zhao et al. (2007) designed and fabricated a 32 x 16 mm 2 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.

15 Reference Type Size (mm 2 ) Area (mm 2 ) Bandwidth Gain (dbi) Liu et al. (2004) Dual-band 20 x GHz and GHz 2.2 Song et al. (2007) Dual-band 35 x GHz and GHz 2.7 Krishna et al (2008) Dual-band 33.5 x to 3.95 GHz and GHz 2.0 Lee et al (2009b) Dual-band 40 x GHz, GHz 2.0 Liu et al. (2010a) Tri-band 22 x GHz, GHz & GHz 3.5 Zhao et al. (2010) Tri-band 40 x GHz, GHz and GHz 3.3 Chu et al. (2010) Dual-band 28 x GHz and GHz 2.4 Liu et al. (2010b) Dual-band 30 x GHz and GHz 3.5 Zhuo et al. (2011) Dual-band 20 x GHz and GHz 2.4 Huang et al. (2011) Dual-band 50 x MHz and MHz 2.6 Hu et al. (2011) Tri-band 28 x GHz, GHz and GHz 3.0 Lin et al. (2012) Dual-band 50 x MHz and MHz 3.5 Zhang et al. (2012) Tri-band 25 x GHz, GHz & GHz 3.7 Teng et al. (2012) Tri-band 28 x GHz and GHz 3.0 Sun et al. (2012) Quad-band 25 x GHz, GHz, & GHz 2.5 Shu et al. (2012) Tri-band 31 x GHz, GHz & GHz 2.7 Liu et al. (2012) Tri-band 23 x GHz, GHz & GHz 2.8 Xu et al (2012) Tri-band 35 x GHz, GHz and GHz 2.4 Liu et al. (2014) Dual-band 25 x GHz and 8 15 GHz -- Huang et al. (2014) Tri-band 30 x , and GHz 3.3 Tsai (2014) Dual-band 60 x GHz and GHz 3.2 Chen et al. (2014) Tri-band 18 x GHz, GHz & GHz 2.7 Kumar et al. (2014) Dual-band 34 x GHz and 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)

16 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 mm 2. 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 mm 2. 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 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 ( , GHz) and WiMAX ( GHz). Even though the reported antenna covers multiple frequency bands with wider impedance bandwidth, it occupies a very large area of 975 mm 2. 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 GHz, GHz, and 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 GHz) in the first operating band

17 and 4004MHz (3.880 GHz 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 Area Operating Bands Gain (mm 2 ) (mm 2 ) (dbi) Kuo et al. (2003) Dual-band 75 x GHz and GHz 1.4 Yildirim (2006) Dual-band 20 x GHz and GHz -- Zhao et al. (2007) Dual-band 16 x GHz and GHz 3.5 Thomas et al. (2009) Tri-band 38 x GHz and GHz 2.5 Mahatthanajatuphat et al. (2009) Dual-band 59 x GHz and GHz 2.4 Basaran et al. (2009) Dual-band 32 x GHz and GHz -- Dong et al. (2010) Tri-band 25 x GHz, and GHz 3.3 Dang et al. (2010) Tri-band 35 x GHz, and GHz 3.5

18 Reference Type Size Area Operating Bands Gain (mm 2 ) (mm 2 ) (dbi) Rathore et al. (2010) Dual-band 45 x GHz and GHz -- Ghalibafan et al. (2010) Dual-band 100 x GHz and GHz -- Ren et al. (2011) Tri-band 14 x GHz, GHz, and GHz 1.7 Pei et al. (2011) Tri-band 38 x GHz, GHz & GHz 1.85 Papatonis et al. (2011) Dual-band 48 x GHz & GHz 2.2 Liu et al. (2011) Tri-band 20 x GHz, and GHz 2.0 Sun et al. (2012) Dual-band 40 x GHz and GHz 1.0 Xiong et al. (2012) Tri-band 17 x GHz, GHz, and GHz 2.0 Xie et al. (2012) Dual-band 40 x GHz and GHz 4.0 Sayidmarie et al. (2012) Dual-band 42 x GHz and GHz 2.2 Mehdipour et al. (2012) Tri-band 22 x GHz, and GHz 1.5 Flores-Leal et al. (2012) Dual-band 40 x GHz and GHz 1.6 Yuan et al. (2013) Tri-band 21 x GHz, and GHz 2.5 Sim et al. (2014) Dual-band 30 x GHz and GHz 3.3 Kaur et al. (2014) Dual-band 70 x GHz and GHz -- Huang et al. (2014) Tri-band 20 x GHz, and GHz 2.0 Yoon et al. (2014a) Tri-band 25 x GHz, and GHz 1.1 Lin et al. (2014) Dual-band 35 x GHz and GHz 2.9 Yoon et al. (2014b) Tri-band 28 x GHz, GHz and GHz 3.0 Samsuzzaman et al. (2014) Dual-band 40 x GHz, GHz & GHz 3.5 Sun et al. (2014) Dual-band 25 x GHz and GHz 2.5 Liu et al. (2014) Tri-band 34 x GHz, and GHz 3.0 Ren et al. (2015) Tri-band 38 x GHz, and GHz 3.1 Kumar et al. (2015) Tri-band 35 x GHz, and 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)

19 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 (mm 2 ) Antenna Purpose Antenna Type Average Peak Gains (dbi) WLAN WiMAX Deepu et al. (2007) 28 x /5.2/5.8 GHz 3.5 GHz Dual-band ~ 2.1 Song et al. (2008) 31 x /5.2/5.8 GHz ---- Tri-band ~ 2.4 Deepu et al. (2009) 21 x /5.2 GHz ---- Dual-band ~ 1.9 Ashkarali et al. (2012) 37.5 x GHz ---- Dual-band ~ 1.21 Li. B et al. (2013) 35 x /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)

20 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 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

21 `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 multiband 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.

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