Design of U-Slot Rectangular Patch Antenna for Wireless LAN at 2.45GHz

9th International Conference on Microwaves, Antenna, Propagation and Remote Sensing ICMARS-2013, Jodhpur, INDIA, 11th – 14th December, 2013

Design of U-Slot Rectangular Patch Antenna for Wireless LAN at 2.45GHz Panchatapa Bhattacharjee, Vivek Hanumante, Sahadev Roy Department of Electronics & Communication Engineering, NIT, Arunachal Pradesh Yupia, INDIA [email protected] [email protected] [email protected] Abstract—This paper presents design and analysis of an efficient U-Slot Rectangular microstrip patch antenna for the application of Wireless LAN for operating frequency 2.45 GHz.U-shaped slot on the patch of the coaxially fed rectangular patch antenna increase the bandwidth. Parafin with relative permittivity 2.24 and loss tangent 200e-6 was used as Dielectric substrate material with a height of 4.75 mm. The antenna was designed and simulated using FEKO, Electromagnetic solver software. A bandwidth of 374.733 MHz was achieved with a gain of 7.1304 dBi. Performance parameters like VSWR, Reflection coefficient and Impedance are very good in arguments. Both performance and design parameters have been tabulated under.Various tables, graphs showing these comparisons with detailed analysis have been included in this paper. Keywords— Microstrip, U-Slot, Reflection coefficient, VSWR, FEKO

I. INTRODUCTION It is well known that microstrip antennas have very narrow impedance bandwidth, typically a few per cent. One of the methods of widening the bandwidth is to cut a U-shaped slot on the patch of the coaxially fed rectangular patch antenna [l]. Microstrip antennas have been widely used in many modern communication systems, because of its planar profile, and low cost [2].Most of these antennas operate at their fundamental mode TM 01 , which results in broadside beam [3]. The Ushaped slot along with the finite ground plane are used to achieve an excellent impedance matching to increase the bandwidth[4].Being such advantageous, a slot of U-shaped on the rectangular shaped patch antenna is considered for our design. The U-slot introduces a capacitive component to counteract the large input inductance when thick substrate is used [5]. These features have attracted a huge area of interest and have been widely used in satellite communications, aerospace, mobile and many more applications. In this paper basic structure of Microstrip patch antenna was taken under design consideration. Microstrip patch antenna uses a radiating patch of perfectly conducting material separated from the copper ground plane using dielectric substrate material. Coaxial probe feed method, being easy and flexible (as it can be placed at any desired location to match impedance), was considered for our design.

Fig.1.FEKO model of a U-slot Rectangular Patch Antenna

II. DESIGN OF THE ANTENNA The geometry of the above proposed U-slot rectangular patch antenna is described in Fig.1.

Fig.2.Dimensions detail of U-slot Rectangular Patch Antenna

Here the ground plane is of length L g and width W g as with the patch length and width, L and W respectively. The patch consists of a U-slot which has a slot width of D, slot height of C, height of slot from base of the patch H and the width between the upper layer and lower layer of U-slot, E and F respectively.

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III. DESIGN CONSIDERATIONS Here the center frequency f o is taken as 2.45 GHz with lower bound frequency f low as 2.00 GHz and upper bound frequency f high as 2.90 GHz. The antenna was designed for the application of wireless LAN that uses operating frequency 2.45 GHz as per IEEE 802.11b/g standards. Dielectric material PARAFIN with dielectric constant 2.24 and loss tangent 200e-6 was used. Substrate height was taken 4.75 mm to minimize inductive impedance and surface waves [6]. A. Calculation of Patch Dimensions Width of the patch of conducting patch material can be calculated using the below formula [7]: 𝑊𝑊 =

2 𝑐𝑐𝑜𝑜 � 2𝑓𝑓𝑜𝑜 (1 + 𝜀𝜀𝑟𝑟 )

Where c 0 is the free-space velocity of light i.e. 3×108 m/s and ε r is the dielectric constant of material here 2.24. The value of the effective dielectric constant is given by [8]: −1� 2

𝜀𝜀𝑟𝑟 + 1 𝜀𝜀𝑟𝑟 − 1 ℎ + �1 + 12 � 2 2 𝑊𝑊 Where h and W are the height and width of substrate material for an antenna respectively. Length of the patch can be calculated as: 𝑐𝑐𝑜𝑜 − 2𝑑𝑑𝑑𝑑 𝐿𝐿𝑒𝑒𝑒𝑒𝑒𝑒 = 2𝑓𝑓𝑜𝑜 �𝜀𝜀𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 The dL is the length extension due to the fringing field and can be calculated using the equation 𝑊𝑊 �𝜀𝜀𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 + 0.3� � + 0.264� ℎ 𝑑𝑑𝑑𝑑 = 0.412ℎ 𝑊𝑊 �𝜀𝜀𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 − 0.258� � + 0.8� ℎ 𝜀𝜀𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 =

B. Calculation of Ground Dimensions

The ground dimension for the antenna can be calculated as below: Width of the ground is given as: W g = W + 6h Length of ground is given as: L g = L + 6h C. Calculation of U -SLOT parameters Slot thickness E and F is given by [9]: E=F=wavelength of light / 60. Slot width D is given by [9]: D= c 0 /2f low ( ε reff) 1/2-2( L+ dL - E),where c 0 is the speed of light. Slot height C is given by [10]: C=D*0.75 Other parameters are calculated as [10]: ε eff (pp)=( ε r +1)/2 +(ε r -1)/2 * {1+(12*T)/(D-2F)}-1/2, where , ‘T’ is the thickness of dielectric substrate. 2d L-E-H =0.824*T [(ε eff (pp) +0.3){(D-2F)/T +0.262}]/ [(ε eff (pp) -0.258) {(D-2F)/T +0.813}]

The height of slot from base H is given as [6]: H=L-E+2d L-E-H -1/ {ε eff (pp)} 1/2[c/f high -(2C +D)], where c is speed of light. H. Feeding Technique & Location The most common technique Coaxial-probe feeding was used for microstrip patch antennas. The main advantage of this type of feeding scheme is that the feed can be placed at any desired location inside the patch in order to match with its input impedance [8]. The impedance match will depend on its location on the patch. Feed point locations in order to match 50 ohm impedance were calculated using the following equation [11]: Along the width of patch: 𝑊𝑊 𝑋𝑋𝑓𝑓 = 2 Along the length of patch: 𝑌𝑌𝑓𝑓 = 𝑌𝑌0 − 𝑑𝑑𝑑𝑑 𝐿𝐿

Where 𝑌𝑌0 = cos −1 � 𝜋𝜋

50 𝑍𝑍0

Z 0s =�50 ∗ 𝑍𝑍𝐼𝐼𝐼𝐼 𝜀𝜀𝑟𝑟 2 𝐿𝐿 𝑍𝑍𝐼𝐼𝐼𝐼 = 90 ∗ ( )2 𝜀𝜀𝑟𝑟 − 1 𝑊𝑊 The calculated feed point coordinates are X f =24.05 and Y f =11.04. However this equation only provides an approximation. Impedance matching was achieved after a lot of iteration, the exact co-ordinates are given in Table I. TABLE I DESIGN PARAMETERS

Normal Patch Readings Width (W) (mm)

48.10

Length (L) (mm)

38.38

Width of Ground(W g ) (mm)

76.6

Length of Ground (L g )(mm) 66.88 Feed point location (original) (24.05,11.04) (mm) U Slot Patch Readings Slot Width (D)(mm)

23.3796

Slot Height(C)(mm)

17.5347

Height of Slot From Base (H)(mm)

14.146

Slot Thickness (E=F) (mm) Feed point taken iterations)(mm)

2.04 (after

(24.05,8.5)

IV. SIMULATION & RESULTS This antenna was designed and simulated using Electromagnetic solver software FEKO which uses Method of Moment (MoM) technique. The feed point location using the earlier mentioned formula was calculated at (24.05, 11.04). But the best impedance matching was obtained at feed point location (24.05, 8.5), where the impedance was found to be 49.9834 Ω. At this feed point the VSWR and Reflection

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coefficient were also found minimum. The Table II presents the performance parameters of antenna. TABLE II COMPARISON OF PERFORMANCE PARAMETERS

Performance Parameters Resonance Frequency (GHz)

2.3218

Gain ( dBi )

7.31074

Impedance (Ω)

49.9834

VSWR (absolute value)

1.01285

Reflection Coefficient (dB)

-43.9004

-3 dB Bandwidth (MHz)

374.773

-10 dB Bandwidth(MHz) -3dB Half Power width(deg)

117.491 Beam-

123.504

Fig.4. Magnitude of the Reflection Coefficient (dB)

The antenna was found to be resonating at 2.3218GHz with a gain of 7.31074 dBi. The values of VSWR and Reflection coefficient are very low and close enough to ideal values. The bandwidth 374.773 MHz is a very good figure in the context of patch antennas. Bandwidth (BW) % can be calculated as follows[9]: BW (%) = ((f high -f low )/ f 0 ) * 100 BW (%) = (0.9/2.450) * 100 BW (%) = 36.73469% Hence a bandwidth with 36.73469% was achieved. The following graphs show the plots of various performance parameters. Figure 8 shows the 3-D radiation pattern of antenna.

.

Fig.5. Absolute value of VSWR

Fig.3.Gain of the antenna Fig.6. -3dB Bandwidth

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ACKNOWLEDGMENT We would like to express our sincere gratitude towards Prof.(Dr.)C.T. Bhunia, Director, NIT AP, Dr. Pinaki Chakraborty, Dean (R&D) and all the Professors and staffs of the Department of Electronics & Communication Engineering of NIT AP for their kind support and motivation in carrying out this study. REFERENCES [1] [2]

Fig.7.Polar Plot and -3db Half powerbeamwidth

[3] [4]

[5]

[6] [7]

[8]

[9] Fig.8 -3 db Radiation Pattern side view [10]

V. CONCLUSIONS Nowadays, microstrip patch antenna is an attractive candidate with low profile, light weight, conformability, and easy fabrication properties [12].The antenna designed for the purpose of Wireless LAN communication purpose at the frequency of 2.45GHz holds good for the performance parameters. The VSWR and return loss have been minimized and a very good bandwidth and gain are obtained. Also the antenna is compact in size and can be used for various applications. Hugely, U-slot antennas are designed for wideband, multiband or frequency tuning operation [13].

[11]

[12]

[13]

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Design of U-Slot Rectangular Patch Antenna for Wireless LAN at 2.45GHz

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