icrostrip stacked shortedpatches, the use of various

icrostrip patch antennas are popular for theirwell-known attractive features of low profile, lightweight, and compatibility with monolithicmicrowave integrated circuits (MMICs). Because of theirattractive feature they are in great demand in wirelesscommunication applications. The main disadvantage ofthis microstrip antenna narrow bandwidth, which is dueto the resonant nature of the patch structure.4Conventional microstrip antennas in general have aconducting patch printed on a grounded microwavesubstrate, and have the attractive features of low profile,light weight, easy fabrication, and conformability tomounting hosts.1 However, conventional microstrippatch antenna suffers from very narrow bandwidth,typically about 5% bandwidth with respect to the centerfrequency. This poses a design challenge for themicrostrip antenna designer to meet the broadbandtechniques 3. To overcome this problem of narrowbandwidth, many proposals and techniques have beenanalyzed and investigated such as probe fed stackedantenna, microstrip patch antennas on electrically thicksubstrate, slotted patch antenna and stacked shortedpatches, the use of various impedance matching andfeeding techniques, the use of multiple resonators. 14The development of antenna for wirelesscommunication also requires an antenna with more thanone operating frequency. This is due to many reasons,mainly because there are various wirelesscommunication systems and many telecommunicationoperators using various frequencies. Therefore oneantenna that has multiband characteristic is moreAuthor ?: Research Scholar, MEWAR University, Rajasthan, India.e-mail: [email protected] ? : Principal, Madan Mohan Malviya Engineering College,Gorakhpur (U.P), India. e-mail: [email protected] than having one antenna for each frequencyband. 7 Our aim is to increase the operatingbandwidth the simulation has been carried out by IE3D.So we want an antenna which offers a low profile, widebandwidth, compact antenna element. Among thesestandards, the following frequency bands can bementioned: (1) PCS-1900 requires a band of 1.85–1.99GHz; (2) IEEE 802.11b/g requires a band of 2.4–2.484GHz; (3) IEEE 802.11a requires a band of 5.15–5.35GHz and an additional band of 5.725–5.825 GHz; (4)HiperLAN2 requires a band of 5.47–5.725 GHz besidesthe band of 5.15–5.35 GHz. 2, 6, 7, 12To overcome the above problem, a microstripantenna structure with a typical Kite symbol shapedpatch is proposed which exhibits good enhancedimpedance bandwidth of up to 76.53% depending uponthe radius of probe.II. Antenna DesignThe dielectric constant of the substrate isclosely related to the size and the bandwidth of themicrostrip antenna. Low dielectric constant of thesubstrate produces larger bandwidth, The resonantfrequency of microstrip antenna and the size of theradiation patch can be similar to the following formulaswhile the high dielectric constant of the substrate resultsin smaller size of antenna 1.The Length of groundplane of Antenna is 24 mm and Width is 28.2 mm, L & Wof the patch is 14 mm & 18.6 mm the radius of thecoaxial probe feed is taken as 0.5 mm. The materialused for substrate is glass epoxy with dielectric constantof 4.2, loss tangent .0012 and substrate height of 1.6mm. The proposed structure is shown in fig 1.The patch width, effective dielectric constant,the length extension and also patch length are given byr fW c2 ?= (1)where c is the velocity of light, r? is the dielectricconstant of substrate, f is the antenna workingfrequency, W is the patch non resonant width, and theeffective dielectric constant is eff ? given as,( ) ( ) 211 102121 ??????? +?++=Wr r Heff? ?? (2)