Design of A Circularly Polarized E-shaped Patch Antenna with Enhanced Bandwidth for 2.4 GHz WLAN Applications

Transcription

1 VNU Jounal of Science: Comp. Science & Com. Eng., Vol. 31, No. 2 (2015) 1-7 Design of A Ciculaly Polaized E-shaped Patch Antenna with Enhanced Bandwidth fo 2.4 GHz WLAN Applications Hong Van Tam 1, Luong Vinh Quoc Danh *,2 1 Vinaphone Company, Vietnam 2 Depatment of Electonics and Telecommunication Engineeing, College of Engineeing Technology, Can Tho Univesity, Vietnam Abstact This pape pesents the design of a wideband ciculaly polaized E-shaped patch antenna fo 2.4-GHz wieless local aea netwoks (WLAN) applications. The poposed antenna is a modified fom of the conventional ciculaly polaized E-shaped patch antenna. By incopoating additional slots into the antenna patch, the impedance bandwidth and etun loss of the ciculaly polaized antenna ae impoved by about 6.5% and 12 db, espectively. Measuements of the fabicated antennas show good ageement with simulated esults Published by VNU Jounal of Science. Manuscipt communication: eceived 30 Apil 2014, evised 04 May 2015, accepted 25 June 2015 Coesponding autho: Luong Vinh Quoc Danh, lvqdanh@ctu.edu.vn Keywods: Axial Ratio, Cicula Polaization, E-shaped Patch, WLAN. 1. Intoduction Ciculaly-polaized antennas have been employed in many moden wieless communication systems such as navigation, satellite communication systems, adio fequency identification (RFID), WLAN and WiMAX. One of the attactive advantages of the ciculaly polaized antennas is that they can educe tansmission loss caused by the misalignment between antennas of tansmitte and eceive. In addition, cicula polaization povides bette ability to combat multi-path fading poblem and thus enhances oveall system pefomance. In [1], the authos have pesented a ciculaly polaized E-shaped patch antenna with unequal slots that offes wideband axial atio bandwidth compaed to the U-slot patch antennas. The design intoduced in [1] has povided a simple appoach to achieve ciculaly polaized adiating fields fom a single-feed micostip antenna without the necessity of it being squae o come-timmed. In [2], the size and position of the slots of the E-shaped patch antenna have been tuned to impove the impedance bandwidth and etun loss. The esults fom [2] have shown that the 10 db impedance bandwidth of about 21.6% was obtained ( GHz), with a lowest value of S 11 of 17.5 db in the GHz band. The axial-atio of this antenna was kept below 3 db in the 2.4 GHz WLAN band. In this pape, we pesent the design of a modified E-shaped patch antenna that offes

2 2 H.V. Tam, L.V.Q. Danh / VNU Jounal of Science: Comp. Science & Com. Eng., Vol. 31, No. 2 (2015) 1-7 wide impedance bandwidth and bette etun loss compaed to the conventional one. By popely incopoating additional slots to the E- shaped patch, the impedance bandwidth and etun loss S 11 of the poposed antenna ae impoved by about 6.5% and 12 db, espectively. The axial atio emains below 3 db in the 2.4 GHz WLAN band. Measuements of the fabicated antennas show good ageement with simulated esults. 2. Featues of the E-shaped Patch Antennas Fig. 1 pesents the geomety of the conventional E-shaped patch antenna [1] and the modified one. As shown in Fig. 1b, compaed to the conventional E-shaped patch antenna, the poposed antenna has 3 additional slots incopoated into the patch. Two slots having length of d 1 and width of d 2 ae made on the top and bottom ams of the E-shaped patch and anothe slot having length of d 3 and width of d 4 is added to the cente of the patch. The dimension and position of the slots ae key paametes in contolling the antenna bandwidth. They should be appopiately chosen to obtain the achievable bandwidth. The pinciple of the bandwidth impovement can be explained using equivalent cicuits of the patch. Fig. 2 illustates the fundamental idea of the wideband mechanism of the E-shaped patch antenna. The uppe and lowe pats of the patch can be modeled as the L 1 C 1 and L 2 C 2 esonant cicuits, espectively [3]. When the additional slots ae incopoated into the lowe and uppe ams of the E-shaped patch, the values of L and C in the esonant cicuits ae changed. By tuning the length d 1, width d 2 and position P 1 of the slots, the esonant featue of the L 1 C 1 and L 2 C 2 esonant cicuits can be alteed to extend the impedance bandwidth of the antenna. 3. E-shaped Patch Antenna Design fo 2.4 GHz WLAN Applications The initial paametes of the ectangula micostip patch antenna defined in [4] ae used in the fist step of the design pocess. The width W of the ectangula patch is: W c = 2 ε +1 f (1) whee f is the esonant fequency of the antenna. The actual length L of the patch: c L = 2 L f ε eff (2) Extended length of the patch L (accoding to the Hammestad fomula): ( ε L = h ( ε eff eff W + 0.3) h W 0.258) h Effective pemittivity of the patch ε eff : 1 2 (3) ε + 1 ε 1 h ε = (4) eff W Coaxial-pobe feeding is located at the distance F fom the edge of the patch: F = y 0 = cos = 16.4 ( mm) π (5) In the second step, we follow the design pocedue descibed in [1] to simulate and optimize the E-shaped patch antenna with two unequal slots fo 2.4 GHz fequency band. As the last stage, thee paallel slots ae incopoated into the E-shaped patch to impove esonant featue of the patch antenna: two

3 H.V. Tam, L.V.Q. Danh / VNU Jounal of Science: Comp. Science & Com. Eng., Vol. 31, No. 2 (2015) identical slots ae added to the uppe and lowe ams of the E-shaped patch; and one small slot is cut at the middle of the patch. The taget of this step is (a) to extend the impedance bandwidth of the antenna and simultaneously maintain the axial-atio level below 3 db ove the desied fequency band, and (b) to align the axial-atio and impedance bandwidths togethe. Dimensions and positions of the additional slots ae tuned to meet the design goal. It can be seen D fom Fig. 3 and Fig. 4 that the dimensions of the two slots in the uppe and lowe ams of the patch keep an impotant ole in widening impedance bandwidth of the antenna. They ae symmetically placed about the y-axis to maintain the othogonality of cuents on the patch. Besides, the thid slot cut at the cente of the patch can be used to contol the level of etun loss S 11, as pesented in Fig. 5 and Fig. 6. (c) Fig. 1. Geomety and dimensions of the E-shaped patch antenna: (a) the conventional fom, (b) the poposed antenna, and (c) side view of the antenna. Fig. 2. Resonance mechanism of the E-shaped patch antenna.

4 4 H.V. Tam, L.V.Q. Danh / VNU Jounal of Science: Comp. Science & Com. Eng., Vol. 31, No. 2 (2015) 1-7 w Fig. 3. Simulated esults of etun loss S 11 at diffeent values of d 1 while othe paametes ae fixed. Fig. 6. Simulated etun loss S 11 at diffeent values of d 4 while othe paametes ae fixed. The optimized dimensions of the poposed antenna ae detemined though paametic analysis, and ae listed in Table I. Antenna simulations ae pefomed using the ANSYS High Fequency Stuctue Simulato (HFSS) [5]. TABLE I THE DIMENSIONS OF THE PROPOSED CIRCULARLY POLARIZED E- SHAPED PATCH (IN MM). L W h F W s L s1 L s P P 1 d 1 d 2 d 3 d 4 L g W g Fig. 4. Simulated esults of etun loss S 11 at diffeent values of d 2 while othe paametes ae fixed. Fig. 5. Simulated etun loss S 11 at diffeent values of d 3 while othe paametes ae fixed. The calculated fa-field 2-D and 3-D adiation pattens of the antenna at 2.44 GHz ae plotted in Fig. 7. It can be seen that the halfpowe beam width of the designed antenna is about 60 degees. The calculated peak gain of the antenna is 9.7 dbi at the cente of the 2.4 GHz WLAN band. The simulated etun loss S 11 esults ae depicted in Fig. 8, whee the etun loss of poposed antenna is impoved by about 12 db compaed to that of the conventional E-shaped patch antenna in [2]. It can also be seen fom Fig. 9 that the calculated axial-atio of the designed antenna emains below 3 db in the 2.4 GHz WLAN band. It is woth noting that the

5 H.V. Tam, L.V.Q. Danh / VNU Jounal of Science: Comp. Science & Com. Eng., Vol. 31, No. 2 (2015) etun loss of the conventional antenna can be impoved futhe. Howeve, this impovement will lead to the eduction of the 3-dB axial atio bandwidth of the antenna. Compaisons of the left-hand cicula polaization (LHCP) and ight-hand cicula polaization (RHCP) pattens in the xz plane at 2.44 GHz ae shown in Fig. 10. The cuent distibution on the E- shaped patch of the poposed antenna is pesented in Fig. 11. Fig. 8. Compaison of etun loss S 11 between the conventional E-shaped patch antenna (dash line) and the poposed antenna (solid line). (a) Fig. 9. Compaison of axial atio between the conventional E-shaped patch antenna (dash line) and the poposed antenna (solid line). 4. Expeimental Results A pototype of the poposed antenna was fabicated and measued. The font view of the antenna pototype is shown in Fig. 12. (b) Fig. 7. Simulated (a) 2-D and (b) 3-D adiation pattens of the poposed antenna at 2.44 GHz. Fig. 13 shows the measued etun loss S 11 of the poposed antenna (dash lines) compaed to the simulated ones (solid lines). As shown in

6 6 H.V. Tam, L.V.Q. Danh / VNU Jounal of Science: Comp. Science & Com. Eng., Vol. 31, No. 2 (2015) 1-7 Fig. 13, thoughout the WLAN fequency band ( GHz), the values of S 11 ae bette than 22.5 db. The lowest value of S 11 of about 31 db was obtained at 2.42 GHz. The measued esults agee well with the simulated ones. Measuements wee pefomed using the Anitsu Antenna Analyze S331D. In ode to veify the antenna pefomance in pactical applications, the designed antenna was connected to the antenna connecto of a commecial 2.4-GHz WLAN access point (D- Link DIR-600) seving as a tansmitte, and a laptop compute was employed as a eceive. The NetStumble softwae [6] installed on the compute was used to measue the WLAN signal stength tansmitted fom the access point. The measuements wee caied out unde non-line-of-sight condition. It can be seen fom Fig. 14 that the poposed antenna geatly impoves WLAN signal eception compaed to that of the 2-dBi omnidiectional one. Pefomance compaisons between the two E-shaped patch antennas ae summaized in Table II. Fig. 11. Cuent distibution on the patch of the poposed antenna. Fig. 12. Font view of the pototype of the poposed E-shaped patch antenna. Table II Antenna Pefomance Compaison Fig. 10. The adiation pattens of left-hand cicula polaization (ed) and ight-hand cicula polaization (blue) in the xz plane. Paametes Impedance bandwidth Lowest value of S11 Conventional E-shaped patch antenna [2] The poposed antenna 21.62% ( GHz) 28.15% ( GHz) 17.5 db 30 db Axial-atio bandwidth 2.72% ( GHz) 4.1% ( GHz) Peak gain 9.7dBi 9.7dBi

7 H.V. Tam, L.V.Q. Danh / VNU Jounal of Science: Comp. Science & Com. Eng., Vol. 31, No. 2 (2015) Conclusion Fig. 13. Measued and simulated etun loss S 11 of the poposed antenna. Poposed antenna 2-dBi Omni. antenna Fig. 14. Compaed antenna gains unde non-line-ofsight condition. The ciculaly polaized E-shaped patch antenna with impoved bandwidth is pesented in this pape. The poposed E-shaped patch has been designed, fabicated, and measued fo the 2.4-GHz WLAN band. Compaed to the conventional E-shaped patch antenna, the 10 db impedance bandwidth and etun loss of the poposed antenna ae impoved by about 6.5% and 12 db, espectively. The axial atio of the antenna emains below 3 db in the 2.4 GHz fequency band. The poposed antenna is expected to be suitable fo 2.4-GHz WLAN applications and othe wieless communication systems opeating in the GHz fequency ange. Refeences [1] Ahmed Khide, Kai Fang Lee, Fan Yang, and Atef Elshebeni, Wideband Ciculaly Polaized E- Shaped Patch Antenna fo Wieless Applications, IEEE Antennas and Popagation Magazine, Vol. 52, No.5, Octobe [2] Tam Hong-Van, Quoc-Danh Luong Vinh, A Ciculaly Polaized E-Shaped Patch Antenna with Impoved Bandwidth fo 2.4-GHz WLAN Applications", Poc. of the Fist NAFOSTED Confeence on Infomation and Compute Science 2014 (NICS'14), Mach 2014, Hanoi, pp [3] Fan Yang, Xue-Xia Zhang, Xiaoning Ye, and Yahya Rahmat-Samii, Wide-band E-shaped patch antennas fo wieless communications, IEEE Tansactions on Antennas and Popagation, Vol. 49, Issue 7, pp , July [4] Constantine A. Balanis, Antenna Theoy Analysis and Design, Thid Edition, John Wiley & Sons, Inc., [5] ANSYS HFSS softwae. Available: [6] Netstumble softwae. Available: