15.Design of- RAHUL.fullT

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DESIGN OF COMPACT DUAL-FREQUENCY MICROSTRIP ANTENNA

FOR GSM HANDSETS

RAHUL T. DAHATONDE1

& SHANKAR B. DEOSARKAR2

1Ph. D. Research Scholar, Department of E & TC, Dr. Babasaheb Ambedkar Technological University,

Lonere, Raigad, India

2Professor, Department of E & TC, Dr. Babasaheb Ambedkar, Technological University, Lonere, Raigad, India

ABSTRACT

In this paper, a dual-frequency, compact microstrip antenna, suitable for the GSM-900/1800 (890-960 MHz &

1710-1880 MHz) handset, is proposed. The proposed MSA consists of two separate resonant elements controlling the

lower and upper resonant frequencies. These two resonant elements are integrated with each other using a single feed and ashorting pin to maintain the compact size. Since there are two separate elements governing both the frequencies,

dimensions of each element, position of feed, as well as position and dimensions of shorting pin, give lot of freedom for

tuning the resonant frequencies, input impedance and other performance parameters of MSA. The performance of proposed

MSA is theoretically analyzed using MoM based software IE3D and verified experimentally. It was found that the

theoretical results are matching fairly well with the measured results.

KEYWORDS: Mobile Communication, Dual Frequency Antennas, Compact Size, Shorting Pin

INTRODUCTION

With emergence of multi-band communication applications, such as global systems for the mobile

communications (GSM; 890-960 MHz), the personal communication systems (PCS; 1850-1990 MHz) and universal

mobile telecommunication systems (UMTS; 1920-2170 MHz), etc., compact and multi-band antennas have been in

demand. Microstrip antennas, in addition to their inherent advantages, such as low profile, light weight, low cost, ease of

fabrication, and integration with RF devices, etc. [1], can offer superior multi-band performance. Therefore, multi-band

MSAs with compact size and single feed are very popular in these communication systems.

The dual-frequency operation of MSA is generally achieved by means of reactive-loading antenna or using

multiple radiating elements, each supporting strong currents and radiation at its resonance. Due to use of multiple resonant

elements, often, size of MSA becomes large, making it unsuitable for mounting in handheld transceivers. Therefore, lots of

techniques are proposed in literature [2–7], to reduce size of MSA.

The compact size of MSA is generally achieved by loading antenna in various forms such as, ( a) modifying shape

of radiating patch; (b) use of high dielectric constant substrate or superstrate; (c) use of shorting-pins; and (d ) a

combination of any of above techniques [8–10]. However, each of these techniques has their own advantages and

disadvantages. Modification of the radiating patch shapes is the easiest one and also allows considerable size reduction; but

it actually causes removal of radiating patch area reducing gain and affecting radiation pattern. Use of high dielectric

constant substrates also reduces size of antenna, but it excites surface waves in antennas and increase losses within the

substrate, resulting in narrow bandwidth and poor radiation efficiency. Comparatively, use of shorting-pins is a more

efficient size reduction technique.

International Journal of Electrical and Electronics

Engineering Research (IJEEER)

ISSN 2250-155XVol. 3, Issue 1, Mar 2013, 141-146

© TJPRC Pvt. Ltd.



142 Rahul T. Dahatonde & Shankar B. Deosarkar

In [7], the shorting-pins were modeled and analyzed as short pieces of transmission lines with series inductance

and shunt capacitance. In [11] a dual band MSA with PIFA is proposed for the cellular bands GSM900/1800 using only

one matching network. The network was synthesized using the Simplified Real Frequency Technique, which yields an

‘easy to implement circuit topology’ and realizable component values.

In this paper, a MSA suitable for GSM-900/1800 (890-960 MHz & 1710-1880 MHz), handset with dual-

frequency operation and compact size is proposed. To obtain the dual-frequency operation, MSA is designed to have two

separate resonant elements controlling the lower and upper resonant frequencies, integrated with each other using a single

feed and a shorting pin to maintain the compact size. The performance of proposed MSA is theoretically analyzed using

MoM based software IE3D [12] and verified experimentally.

DESIGN OF MSA

Design of most of the dual-frequency MSAs published in the literature is generally based on the trial and error

method. Due to this, controlling operating frequencies is very difficult. In this paper, there are two separate resonating

elements controlling the lower and upper band frequencies. These two resonators are integrated together with a single feed

and a shorting pin, yielding a compact MSA. Since there are two separate radiating elements governing both the

frequencies, there is lot of freedom for adjusting the resonant frequencies, input impedance and other performance

parameters of MSA by controlling the dimensions of each radiating element, position of feed, as well as position and

dimensions of shorting pin [13].

For any MSA to be effective radiator, in the fundamental TM10 mode, its length should be slightly less than 2λ ,

where λ is the wavelength in the dielectric medium. Here,eff

ε λ λ 0=

where0λ is the free-space wavelength and

eff ε is

the effective dielectric constant of the patch. However, at 900 MHz, MSA even with 4λ length will be too large to be used

for applications such as GSM transceivers. To overcome this, a short-circuited resonator operating at single frequency can

be used. As shown in Fig. 1-a, the proposed dual-frequency MSA consists of two resonating elements, the first inverted-L

shaped resonator (Fig. 1-b) operates at lower frequency of 900 MHz and the other L-shaped resonator (Fig. 1-c) operates at

upper frequency of 1800 MHz. The dimensions of these two radiators (in mm) are as given below:

l1 l2 W 1 W 2 l3 l4 W 3 W 4

18 28 4 10 6 17.5 4 10



Design of Compact Dual-Frequency Microstrip Antenna for GSM Handsets 143

In order to verify their performance, these two resonant elements shown in Fig. 1-b and 1-c were first simulated

separately. Then these two resonators were combined with each other such that they use the same feed point and the

shorting pin to get a MSA shown in Fig. 1-a. This MSA, was fed by a 50Ω coaxial feed line located 1.8mm from the

shorting pin having radius of 0.5mm and was analyzed using Zeland’s MoM based software IE3D [12]. For all

simulations, the FR4 substrate with dielectric constant of 4.47 and thickness of 1.59mm was considered.

Figure 3a: Return Loss Vs Frequency for the Inverted Figure 3b: Return Loss Vs Frequency for the

L-Shaped Radiator (Simulated) L-Shaped Radiator (Simulated)

The return loss Vs frequency curves shown in Fig. 2-a and -b, for the inverted L-shaped radiator in Fig. 1 (b), and

L-shaped radiator in Fig. 1 (c) show that they resonate at lower frequency of 900 MHz and upper frequency of 1800 MHz,

respectively.

The return loss Vs frequency curve shown in Fig. 3-a indicates that the MSA obtained by combing both the

elements, exhibits dual-frequency behavior. The first resonance occurs at 900 MHz and the second resonance occurs at

1800 MHz. The return loss is –19.53 dB and –19.50 dB, respectively at both the resonances. The VSWR (Fig. 3-b) is 1.1

and 1.2, respectively at both the resonances. For both the frequency bands, VSWR is almost 1, which shows close to

perfect matching of antenna with the feed line.

Figure 3a: Return Loss Vs Frequency for Figure 3b: VSWR Vs Frequency for

Dual-Frequency MSA (Simulated) Dual-Frequency MSA (Simulated)




From Smith Chart obtained using software IE3D, the simulated values of input impedance at both the resonances

of this MSA were found to be 45.34Ω and 55.47 Ω, respectively.

EXPERIMENTAL VERIFICATION

In order to experimentally verify the performance of this dual-frequency MSA, it was fabricated on FR4 substrate,as shown in Fig. 4. This fabricated MSA was tested on Agilent Marconi Scalar Network Analyzer 6204 available at Dr.

Babasaheb Ambedkar Technological University, Lonere, Maharashtra.

Figure 4: Photograph of Fabricated Dual-Frequency MSA

Fig. 5-a shows measured values of return loss Vs frequency for this MSA. It can be seen that the fabricated MSA

resonates at two different frequencies. The first resonance occurs at 900.88 MHz and the second resonance occurs at

1836.42 MHz. The return loss at these two resonances is –16.318 dB and –17.548 dB, respectively. Figure 5-b, shows the

measured values of VSWR Vs frequency for this dual-frequency MSA. The VSWR is 1.41 and 1.322 at the first and

second resonances, respectively.

Figure 5a: Return Loss Vs Frequency of Figure 5b: VSWR Vs Frequency of

Dual-Frequency MSA (Measured) Dual-Frequency MSA (Measured)



Design of Compact Dual-Frequency Microstrip Antenna for GSM Handsets 145

The value of input impedance at both the resonances of this dual-frequency MSA was measured to be 43.37Ω and

59.87Ω, respectively from the Smith Chart shown in Figure 5-c. This shows MSA is closely matched with the feed line at

both the resonances.

Figure 5c: Smith Chart of Dual-Frequency MSA (Measured)

Table 1 summarizes simulated and measured values of various performance parameters for this MSA. It can be

observed that the measured values of resonant frequencies and corresponding values of return loss and VSWR at both the

resonances are very close to the simulated values. The slight variation in measured values and simulated values

summarized in Table 1 is due to practical constraints during fabrication of MSA.

Table 1: Summary of Simulated and Measured Values of Various Parameters of MSA

Dual-

Frequency

MSA

Resonant Frequency

(MHz)Return Loss (dB) VSWR Input Impedance (Ω)

Simulated Measured Simulated Measured Simulated Measured Simulated Measured

FirstResonance

900 900.88 -19.53 -16.31 1.1 1.41 45.34 43.37

Second

Resonance1800 1836.42 -19.50 -17.54 1.2 1.32 55.47 59.87

RESULTS AND DISCUSSIONS

The input impedance and other performance parameters of MSA can be adjusted by varying the location of feed

point, as well as location and dimensions of shorting pin. Therefore, location of the feed point, shorting pin and the

spacing between them was obtained by performing exhaustive simulation runs. It was observed that, the matching of MSA

with feed line depends on relative distance between feed point and shorting pin.

The location of shorting pin also affects the mutual coupling between two resonators. The loading effect of these

resonators on each other can be minimized by placing the shorting pin at the edge of both elements. The resonant

frequencies can be adjusted by varying length and width of each resonating element.

The proposed MSA was found to have narrow bandwidth (BW), typically 1% to 2% at both the resonances. This

is due to use of single-layer substrate. The BW could have been increased using multiple-layer substrate, however, it will

also increase weight, dielectric loss, surface wave loss, and extraneous radiations from the probe feed. Also there is a

trade-off between size of MSA and its BW.




CONCLUSIONS

In this paper, a MSA suitable for GSM-900/1800 (890-960 MHz & 1710-1880 MHz), handset with dual-

frequency operation and compact size is proposed. To obtain the dual-frequency operation, MSA is designed to have two

separate resonant elements controlling the lower and upper resonant frequencies, integrated with each other using a single

feed and a shorting pin to maintain the compact size. The performance of proposed MSA is theoretically analyzed using

MoM based software IE3D and verified experimentally. It was found that the theoretical results are matching fairly well

with the measured results.

REFERENCES

1. James, J. R., and P. S. Hall (Eds.), Handbook of Microstrip Antennas, Peter Peregrinus, London, 1989.

2. Delaveaud, C., P. Leveque, and B. Jecko, “New kind of Microstrip antenna: the monopolar wire-patch antenna,”

Electron. Lett., Vol. 30, 1–2, Jan. 1994.

3. Waterhouse, R. B., “Small microstrip patch antenna,” Electron. Lett., Vol. 31, 604–605, Apr. 1995.

4. Waterhouse, R. B., S. D. Targoniski, and D. M. Kokotoff, “Design and performance of small printed antennas,”

IEEE Trans. Antennas Propagat., Vol. 46, No. 11, 1629–1633, Nov. 1998.

5. Waterhouse, R. B. and D. M. Kokotoff, “Novel technique to improve manufacturing ease of shorted patches,”

Microwave Opt. Tech. Lett., 37–40, Jan. 1998.

6. Kan, H. K. and R. B. Waterhouse, “Size reduction technique for shorted patches,” Electron. Lett., Vol. 35, No. 12,

948–949, Jan. 1999.

7. Sanad, M., “Effect of the shorting posts on short circuit microstrip antennas,”Proc. IEEE Antennas Propag.

Symp., 794–797, Seattle, WA, Jun. 1994.

8. Wang, K. L., C. L. Tang, and H. T. Chen, “A compact meandered circular microstrip antenna with a shorting

pin,”Microwave Opt. Tech. Lett., Vol. 15, Issue 3, 147–149, 1997.

9. Wang, Y. J. and C. K. Lee, “Design of dual-frequency Microstrip patch antennas and application for IMT-2000

mobile handsets,” Progress in Electromagnetics Research, Vol. 36, 265–278, 2002.

10. Kuo, Y. L. and K. L. Wang, “Coplanar waveguide-fed folded kinverted F antenna for UMTS application,”

Microwave Opt. Tech. Lett., Vol. 32, Issue 5, 364–366, 2002.

11. P. Lindber, M. Sengul, E. G. Cimen, B. S. Yarman, A. Rydberg, and A. Aksen, “A single matching network

design for a dual band PIFA antenna via simplified real frequency technique” Proc. ‘EuCAP 2006’, Nice, France

6–10 November 2006(ESA SP-626, October2006).

12. IE3D 12.0, Zeland Software Inc., Fremont, CA, USA, 2008.

13. A dual-frequency compact microstrip patch antenna S. C. Gao, L. W. Li, T. S. Yeo, and M. S. Leong, Radio

Science, Volume 36, Number 6, Pages 1669 –1682, November–December 2001.

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