Corner Truncated Microstrip Patch Antenna for

Handheld Wireless Applications

M. Ali Babar Abbasi, Saleem Shahid, M. Rizwan, Munir A. Tarar, Farooq A. Tahir

Samar Mubarakmand Research Institute for Microwave and Millimeter-wave Studies (SMRIMMS)

Department of Electrical Engineering, School of Electrical Engineering & Computer Science (SEECS)

National University of Sciences & Technology (NUST), Islamabad, Pakistan

{11mseemabbasi, saleem.shahid, 11mseemrizwan, munir.tarar, farooq.tahir} @seecs.edu.pk

AbstractThe paper presents a compact microstrip patch antenna for RFID 2.45 GHz, WiMAX 2.5 GHz, LTE Band 7,

Blue tooth, WLAN 2.4 GHz, Zig-Bee, Super Extended C-Band

and license free band applications. Patch with corner truncation

and suitable slots are used to achieve the desired bands. Antenna

size has been reduced significantly and FR4-epoxy is used as

substrate with height=3.2mm and r =4.4 to ensure cost effective fabrication. Proposed antenna is circularly polarized, bandwidth

efficient and compact in size. The antenna performance is

characterized in terms of S parameter, radiation pattern and

current distribution. Simulations are carried out in software such

as HFSS v13 whereas effect of introducing different slots has also gone under discussion.

Keywords micro-strip patch antenna, probe fed, corner truncated, mobile communication systems

I. INTRODUCTION

Conventional microstrip antennas in general have a conducting patch printed on a grounded substrate, and have attractive features of low profile, light weight, easy fabrication, and conformability to mounting hosts [1]. Microstrip patch antennas have narrow bandwidth however bandwidth enhancement is demanded for practical applications. In addition, applications in present day mobile communication systems usually require smaller antenna size in order to meet the miniaturization requirements of mobile units. With the developments of various standards for wireless communications, demand increased for broadband antennas.

Starting with the applications demanded for particular antennas, initially an over view about previously done work is presented. Techniques, their benefits and at the end applications available are discussed. This paper proposes size reduction and frequency adjusting techniques for microstrip antennas by using adequate feeding point and introducing suitable slots upon the current intensity, hence simultaneously improving the radiating properties, return loss, impedance bandwidth and gain.

Today, demand for an antenna is to be compact, and supportive for multi applications. Earlier an optimized microstrip patch antenna with compact size, better radiation efficiency and gain by varying current path was presented [2]. For size reduction, use of shortening pin is also reported [3]. Some other techniques like meandering, aperture coupling, peripheral cuts and tuning stubs are also discussed [1].

A brief discussion on todays research areas in wireless communication will enable us to understand multi application compact designs presented in the literature. These research areas include RFID tags consisting of an antenna combined with an application-specific integrated circuit (ASIC) chip [4],[5]. Bluetooth also is a well-established short-distance (10 meters) wireless communications standard which uses 2.42.484 GHz frequency of ISM band with a bandwidth of 84 MHz [6]. LTE release 10 also promotes the application bands for frequencies from 700-2500 MHz [7]. Wireless local area network (WLAN) requires three bands of frequencies: 2.4GHz (2400-2484 MHz), 5.2GHz (5150-5350 MHz) and 5.8GHz (5725-5825 MHz) [8]. WiMAX 802.16e comprises 3 bands. WiMAX comprises of 2.5 GHz (2.5-2.69 GHz), WiMAX 3.5 GHz (3.3-3.7 GHz) & WiMAX 5.7 GHz (5.2-5.8 GHz) [9]. Above mentioned application bands, and license free bands at 2.4GHz (2403-2483 MHz), 5GHz (5150-5250 MHz, 5250-5350 MHz, 5725-5825 MHz & 5725-5850 MHz) are the areas of prominence of antenna designers.

Our goal is to design a compact microstrip patch antenna of order 4x4 cm2 that could operate in multi-application bands and could perform better in terms of return loss and antenna gain. Geometry outline of proposed antenna is shown in Figure 1.

Figure. 1. Geometry outline of antenna

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Figure. 2. Dimensions of truncated corners.

II. ANTENNA CONFIGURATION

The antenna has been designed on low cost FR4 substrate

with height=3.2mm, r =4.34 and tan =0.016. Patch on grounded substrate shown in Figure 1 along with its

geometrical dimension is a simple probe fed. The feeding

point is greatly dependant on the operating frequency.

Therefore the feeding point is selected to be in adequate

position. Our aim was to ensure better return loss, as well as

accepted band width.

Figure 1 shows initial design with its dimensions. A

rectangular patch was chosen as the radiation element. Initial dimensions of patch were adjusted by general guideline of

antenna design [1]. As IEEE 802.11b and 802.11g standards

utilize the 2.4-GHz ISM band, adaptive frequency for antenna

design has been set to 2.45 GHz.

Two sided corner truncation technique shown in Figure 2

was implemented on both sides of the patch [4], third corner

has been truncated so that better impedance matching across

the operating bands can be obtained. Return loss was

improved up to -27.5 dB at first place as shown in Figure 4.

TABLE I. ANTENNA DIMENTIONS

Edge a b x y

Length (cm) 3.05 2.55 3.83 3.35

Edge c d e f

Length (cm) 0.7 0.65 0.39 1.35

Slot p q r -

Length (cm) 0.6 1.8 1.5 -

Figure. 3. Dimensions and numbering of slots.

Figure. 4. Comparison of simple and corner truncated patch

Size of truncated patch was adjusted such that the

operational bandwidth may include 2.4 2.69 GHz. Secondly, corner truncation also ensured circular polarization of antenna.

Figure 2 shows the design configuration for antenna operating at 2.45 GHz. Measurements in Figure 2. are in cm and

diagonal corners have same dimensions.

For this initial design, a comparison between simple patch

and truncated patch is given in Figure 4. Band of operation for

improved design is 2.38-2.74 GHz. This band comprises

various applications which will be discussed in later section of

this paper.

III. RESULTS AND DISCUSSION

A parametric study has been performed to evaluate the effects of the slots on reflection coefficient. Slots at altering field of J surface have been introduced consecutively to achieve best return loss with maximum bandwidth. So that antenna may tune as per requirements of applications, either reflection coefficient or band width.

By introducing slot 1 and 2, with dimensions in Table I and numbering as shown in Figure 3, reflection coefficient improved significantly. By systematic alteration in length p from 5-10mm, return loss has been improved up to -33.5 dB. Figure 5(a) shows comparison for patch without slot 1 & 2 and with slots at p=6 & 8mm. Results depicts improved return loss for lower frequency band, however, the high frequency band does not show a notable change. Vector and magnitude surface current distribution shown in Figure 6(a) also renders the center of the patch as the main radiating area. Introducing slot 1 and 2 improved radiation particularly at 2.5 GHz which can be witnessed in Figure 5(a) and Figure 6(b).

Since currents along the right truncated edges are flowing in the direction of currents along left truncated. Only center and bottom edge of patch contributes to the radiation. Introducing slot 3 on none radiating mid of patch, hence disturbing the current path, determines new resonant frequency 4.5-5.2 GHz. Altering the length of slot 3 by keeping constant width (1 mm) ensured new application bands for WLAN 5.2, 5.8 and WiMAX 5.8GHz. Length q has been altered from 1mm to 2mm to investigate the symmetric current paths. At q=1, dual band has been achieved resonating at 5.5 GHz and 6.4 GHz. Whereas, application bands of WLAN and WiMAX requires 5.2 to 5.8 GHz. Systematic study for alternation of q depicts

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that at 1.8mm improved reflection coefficient of -35.4dB has been achieved which can be observed from Figure 5(b). In Figure 8(a), two distributed current paths on left and right side of slot 3 introduce new resonant frequency band for several applications.

(a)

(b)

(c)

Figure. 5. Optimization with proposed variation in geometrical configuration

(a) Comparison of measured reflection coefficient on, slot 1 added & slot 1

size adjusted to 6mm (b) with and without slot 2 and 3 (c) with slot 4 added and adjusted

(a) (b)

Figure. 6. Simulated surface current distribution on the conductor. (a) Current flow on corner truncated patch (b) after adding sot 1 and 2.

Introducing slot 4 improved the reflection coefficient up to -38.4 dB and bandwidth up to 2.8 GHz for high frequency band without changing of lower frequency bandwidth. For different lengths of r, upper band can be attuned independently. Significant improvement with respect to resonant frequency and bandwidth has been noted for methodical length variation from 1.5-2.5mm. New acceleration and deceleration of current and path variation can be seen in Figure. 8(b), here additional resonant areas have been introduced on radiator. Comparing Figure 8(b) and results in Figure 5(c) clarifies that multi bands in Figure 5(b) have been blended together to form a wide band as a result of introducing slot 4. For r=1.5mm, antenna promises the best return loss for WLAN 5.2. Comparative analysis for improvements has been tabulated in Table II.

Power transmitted by the antenna is not a problem in wireless communication RF front end design now a days, but direction and far field coverage area does matter. Figure 7 exhibits the measured far-field radiation patterns in the yz and zx planes for three frequencies at 2.45, 5.2 and 5.8 GHz, respectively. Summarized below are the bands of application for proposed antenna from Figure 4 & 5(c), as mentioned in Table II.

1. WLAN (2400-2484 MHz)

2. Blue tooth (2400-2484 MHz)

3. Zig-Bee (2400-2483.5 MHz)

4. RFID (2.45 GHz)

5. License free band (2403-2483)

6. WiMax 2.5 (2500-2690 MHz)

7. LTE Band 7 (2500-2690 MHz)

8. License free bands on 5 GHz

9. WLAN 5.2 (5150-5350 MHz)

10. WiMax 5.8(5200-5800 MHz)

11. WLAN 5.8 (5725-5825 MHz)

12. Super Extended C-Band (4500-7025MHz )

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TABLE II. PARAMETRIC STUDY AND SYSTEMATIC IMPLEMENTATION OF TECHNIQUES ON ANTENNA PATCH.

Steps S(1,1) Parameter Band Width Applications

Rectangular Patch -16.2 dB 150 MHz 1-3

Corner Truncated -27.5 dB 320 MHz 1-7

Adding Slot 1,2 -32.5 dB 320, 1550

MHz 1-8

Adding Slot 3 -34.6 dB 320, 2020

MHz 1-11

Adding Slot 4 -38.4 dB 320, 2800

MHz 1-12

(a) (b)

Figure. 8. Simulated surface current distribution on patch and dual path followed by current (a) after introducing slot 3 (b) after introducing slot 4.

IV. CONCLUSIONS

Theoretical investigations of a single layer single feed microstrip patch antennas have been carried out using finite element method (FEM) based software such as Ansoft HFSS. Design is fairly simple rectangular patch on grounded FR4-epoxy substrate. By introducing cuts on edges and addition of slots in the patch, a size reduction has been achieved with increased band width, multi frequency operation and improved

return loss. Proposed antenna is tunable for required bandwidth and capable of performing reasonable Omni-directional coverage and high radiation efficiencies throughout these bands. Also, compared to previous designs proposed in [2], [4] and [5], proposed antenna is both compact and wideband, results are partially comparable with antennas proposed in [6]-[8]. Antenna is compact, simple in design, cost effective in fabrication as well as flexible for multi operations. It makes proposed antenna solution suitable to be installed within laptops, Tablets or even in ultra-thin hand-held PDAs as an internal antenna for multiband wireless communication systems.

REFERENCES

[1] Kin-Lu Wong, Compact and Broadband Microstrip Antennas, John Wiley & Sons, Inc. New York, 2002.

[2] C. Kamtongdee, N. Wongkasem, A Novel Design of Compact 2.4 GHz Microstrip Antennas, 6th International Conference on Electrical Engineering/Electronics, Computer, Telecommunications and Information Technology (ECTI-CON), 2009.

[3] R. B. Waterhouse, S. D. Targonski, D. M. Kokotoff, Design and performance of small printed antennas, IEEE Transactions on Antennas and Propagation, vol. 46, No. 11, 1998, pp 629 - 33.

[4] Bing Yang Quanyuan Feng, A Patch Antenna for RFID Reader, International Conference on Microwave and Millimeter Wave

Technology (ICMMT), vol. 3, 2008, pp 1044 - 46.

[5] R. A. R. Ibrahim, M. C. E. Yagoub, Practical Novel Design Component of Microstrip Patch Slot Antenna MSPSA for RFID

Applications, 23rd Canadian Conference on Electrical and Computer Engineering (CCECE), 2010, pp 1 5.

[6] Sen, A. Roy, J.S. S.R Bhadra Chaudhuri., Investigations on A Dual-Frequency Micro strip Antenna for Wireless Applications, IEEE International Workshop on Antenna Technology, 2009, pp 1-4.

[7] Pulse Finland Oy, Kempele, Finland, Low Correlation Handset Antenna Configuration for LTE MIMO Applications, International Symposium no Antennas and Propagation Society (APSURSI) IEEE, 2010

[8] I Sarkar, P.P Sarkar, S.K Chowdhury, A Novel Compact, Microstrip Antenna with Multi frequency operations, International Seminar/Workshop on Direct and Inverse Problems of Electromagnetic

and Acoustic Wave Theory, (DIPED) 2009 , pp 147-151.

[9] M. N Khan, S. Ghauri, The WiMax 802.16e physical layer model, IET International Conference on Wireless, Mobile and Multimedia Networks, 2008

(a) (b) (c)

Figure. 7. 2-D Radiation pattern in yz and xz planes, depicting the coverage area for (a) 2.45, (b) 5.2 and (c) 5.8 GHz

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