L- Probe Fed Microstrip Antenna

L- Probe Fed Microstrip Antenna

International Journal of Engineering Research & Technology (IJERT)

ISSN: 2278-0181

Vol. 2 Issue 6, June – 2013

S. D. Lokhande R. C. Jaiswal A. S. Bhalerao

LMISOI PICT Pune

S.D. Lokhande:- Author is currently working as Professor & Head of Department (Electronics Engineering) in Singhgad College of Engg., Pune. He has completed his M.E. in the year of 1996 & Ph.D. in Electronics Engineering in the year of 2006. He has 21 years of experience in teaching field. He is Life Member of Instrumentation Society of India (LMISOI). His research interest is in the fields of Neural Networks, Machine Intelligence, System Identification and Control.

R.C. Jaiswal:- Author is currently working as Asst. Professor ( Electronics & Telecommunication Engineering Dept.) in PICT, Pune. He has completed his M.E. in the year of 2004 & pursuing Ph.D. in Electronics Engineering. He has 14 years of experience in teaching field. His research interest is in the fields of Networking, Neural Networks, Machine Learning.

A.S.Bhalerao:- Author is pursuing M.E. (Microwave) in Pune Institute of Computer Technology, Pune, under the guidance of Prof. R.C. Jaiswal. His research interest is in the fields of Microwave Communication, Microstrip Antenna.

Abstract

Two layered substrate antennas are used to enhance the bandwidth. The bottom patch is fed with a coaxial line, and the top parasitic patch is excited due to electromagnetic coupling with the bottom patch. The strip loaded slotted broadband microstrip antenna is fed by an L-strip feed line to achieve impedance matching and has an overall dimension of 42× 55× 3.2 mm2. Operating

frequency range of antenna is from 4.96 GHz to

5.76 GHz when the horizontal arm of L-probe is on right side. The antenna gives bandwidth of 15%. The gain of antenna is 5.50 dBi. We get further increase in bandwidth when there are two symmetrical rectangular strips incorporated in hexagonal slot. The bandwidth of antenna obtained is 25% (1.2 GHz) which is much higher than earlier two geometries. We get 43% increase in bandwidth. Also, gain of antenna increases by 11% (6.09 dBi).

1. Introduction

   Microstrip antennas (often called patch antennas) are widely used in the microwave frequency region because of their simplicity and compatibility with printed-circuit technology, making them easy to manufacture either as stand- alone elements or as elements of arrays. In its simplest form a MSA consists of a patch of metal, usually rectangular or circular (though other shapes are sometimes used) on top of a grounded substrate. [1]

   The origin of MSA apparently dates back to 1953, when Deschamp proposed the use of microstrip feed lines to feed an array of printed antenna elements. The printed antenna elements introduced there were not microstrip patches, but flared planar horns. The microstrip patch antenna was first introduced by Munson in a symposium paper in 1972, which was followed by a journal paper in 1974. These papers discussed both the wraparound microstrip antenna and the rectangular patch. Shortly after Munsons symposium paper, Howell also discussed rectangular patch antennas in another symposium paper in which he credits Munson with the basic idea by referencing a private communication. [1]

   Conventional microstrip antennas in general have a conducting patch printed on a grounded microwave substrate, and have the attractive features of low profile, light weight, easy

   fabriAcabtisotnr,aacntd conformability to mounting hosts. However, microstrip antennas inherently have a

   narrow bandwidth, and bandwidth enhancement is usually 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. Thus, size reduction and bandwidth enhancement are becoming major design considerations for practical applications of microstrip antennas. For this reason, studies to achieve compact and broadband operations of microstrip antennas have greatly increased [2], [3]. Lot of researches has been carried out for enhancing the bandwidth of microstrip antennas.

   The technique for widening the bandwidth of a microstrip antenna using thick substrate is of interest due to its possible single-layered structure. Increasing the substrate thickness increases the bandwidth of microstrip antennas. When the thickness exceeds about 0.05 o, the increased inductance of the feed deteriorates 50 ohm impedance matching. This problem can be avoided by modifying the feed in to the form of an L shape, in which the increased inductive reactance of the probe is suppressed by the capacitance of the L-feed. Besides providing good impedance matching characteristics, the L-probe excites higher order modes which further enhance the bandwidth [4], [5].

2. Antenna Design

   The geometry of the proposed antenna is shown in Fig. 1 & Fig 2. The prototype is fabricated on a substrate of relative dielectric constant r=4.4 and thickness h=1.6 mm. Initially a hexagonal slot of dimension 14.3 mm is etched on a square microstrip antenna of

   42 mm

   55 mm

   55 mm

   44.5 mm

   44.5 mm

   15 mm

   3 mm

   Fig 1. Bottom Substrate

   dimension 35×35 mm2.[6] In order to achieve proper impedance matching, a rectangular strip of length (L3)= 4.7 mm and width 3 mm is incorporated symmetrically on the top portion of the slot. The antenna is electromagnetically coupled using a printed L shaped microstrip transmission line having a horizontal length of 15mm, vertical length 44.5 mm and width 3 mm printed on the same substrate. Two different configurations of antenna are discussed:- (1) With single rectangular strip & (2) With two rectangular strips.

   35 mm

   For this antenna, VSWR against frequency graph is shown in Fig 3. The gain of antenna is 5.50 dbi.

   For the antenna having two rectangular strips, the return loss below -10dB has started from 4.50GHz and the same characteristics has been shown till 5.70 GHz, as shown in Fig 5. The simulated bandwidth of antenna is 1.2 GHz. For the measured result, the return loss below -10db is from

   4.37 GHz to 5.5 GHz. Hence, the measured bandwidth is 1.13 GHz. So, we get very good agreement with simulated & practical results. The VSWR bandwidth of antenna is 1.2 GHz, shown in Fig 6. The measured gain of antenna is 6.06 dbi.

   14.3 mm

   14.3 mm

   35 mm

   35 mm

   4.7 mm

   4.7 mm

   3 mm

   Fig 2. Top Substrate

3. Result & Discussion

   The simulated & the experimental results of antenna are measured using Ansoft HFSS version

   13.0 & HP8510C Network Analyzer, respectively. As we know for proper transmission of signal by antenna, the S11 parameter of antenna should be less than -10dB. For the antenna having only one rectangular strip, the return loss below -10dB has started from 4.96 GHz and the same characteristics has been shown till 5.76Ghz as shown in Fig 4. The VSWR bandwidth of antenna is 840MHz.

   3.00

   2.00

   -5.00

   -10.00

   Reflection Coefficient S11(db)

   Reflection Coefficient S11(db)

   -15.00

   -20.00

   -25.00

   -30.00

   -35.00

   -40.00

   -45.00

   -50.00

   0.00

   -2.50

   Reflection Coefficient, db

   Reflection Coefficient, db

   -5.00

   -7.50

   -10.00

   -12.50

   -15.00

   VSWR

   VSWR

   -17.50

   4.70 4.90 5.10 5.30 5.50 5.70 5.90 6.00

   <>Freq [GHz]

   Fig 4. Simulated reflection coefficient vs frequency for single strip

   4.00 4.25 4.50 4.75 5.00 5.25 5.50 5.75 6.00

   Freq [GHz]

   Fig 5. Simulated reflection coefficient vs frequency for two strips

   1.00

   0.00

   4.70 4.90 5.10 5.30 5.50 5.70 5.90 6.00

   Freq [GHz]

   Fig 3. Simulated VSWR vs frequency for single strip

   Fig. 7, shows the effect of change in length (L3) of the rectangular slot on the bandwidth as well as reflection coefficient of the antenna. As the length increases, the return loss characteristics of the antenna improves. The bandwidth of antenna increases upto 2.7 GHz when the length incresed by 1mm. a indicates change in length of L3.

   9.00

   8.00

   7.00

   6.00

   VSWR

   VSWR

   5.00

   4.00

   3.00

   2.00

   1.00

   4.00 4.25 4.50 4.75

   5.00

   Freq [GHz]

   5.25 5.50 5.75 6.00

   frequency of 5.1 GHz, which is much higher than earlier geometry. We get 43% increase in bandwidth when two rectangular strips are incorporated symmetrically on hexagonal patch. Also, gain of antenna increases by 10% (6.06 dBi). So, antenna having two rectangular strips is more efficient than single strip.

   The parametric analysis of the antenna having two rectangular strips incorporated symmetrically on hexagonal patch shows that, there is further increase in bandwidth as we increase the length of rectangular strip (L3). For L3= 4.7mm we get bandwidth of 1.2 GHz. As we increase L3, the return loss characteristics of antenna improves. Bandwidth up to 2.7 GHz is obtainable, which can be used in wideband imaging applications. Good agreement is

   0.00

   -5.00

   Reflection Coefficient, db

   Reflection Coefficient, db

   -10.00

   -15.00

   -20.00

   -25.00

   Fig 6. Simulated VSWR vs frequency for two

   strips

   Curve Info

   a='0.2mm'

   a='0.4mm'

   a='0.6mm'

   a='0.8mm' a='1mm'

   4.00 4.50 5.00 5.50 6.00 6.50 7.00 7.50 8.00

   Freq [GHz]

   Fig 7. Variation of S11 parameter with change in length of rectangular strip

   achieved between simulated & measured results.

   5. References

   1. David M. Pozar, A Review of Microstrip Antennas: History, Operation, Development, and Applications, May 1996.

   2. G. Kumar and K. C. Gupta, Broad-band microstrip antenna using additional resonators gap-coupled to the radiating edges, IEEE Trans. Antennas Propag., vol. 32, no. 12, pp. 13751379, 1984.

   3. C. K. Aanandan, P. Mohanan, and K. G. Nair, Broad-band gap coupled microstrip antenna, IEEE Trans. Antennas Propag., vol. 38, no. 10, pp. 1581 1586, 1990.

   4. M. A. Matin, B. S. Sharif, and C. C. Tsimenidis, Probe fed stacked patch antenna for wideband applications, IEEE Trans. Antennas Propag., vol. 55, no. 8, pp. 23852388, 2007.

4. Conclusion

L-probe fed slotted single patch microstrip antenna is designed. The patch has a dimension of 35×35 mm2 when printed on a substrate of dielectric constant 4.4 and thickness 1.6 mm. Operating frequency range of antenna is from

4.96 GHz to 5.76 GHz when the horizontal arm of L-probe is on right side. The antenna gives bandwidth of 15% (840 MHz) with centre frequency of 5.41 GHz. The gain of antenna is

5.50 dBi.

We get further increase in bandwidth when there are two symmetrical rectangular strips incorporated in hexagonal slot. The bandwidth of antenna obtained is 24% (1.2 GHz) with centre

1. M. Gopikrishna, D. D. Krishna, C. K. Aanandan, P. Mohanan, and K. Vasudevan, Design of a compact semi-elliptic monopole slot elements,IEEE Trans. Antennas Propag., vol. 55, no. 4, pp. 11961199, 2007.

2. V. P. Sarin, M. S. Nishamol, D. Tony, C. K. Aanandan,,P. Mohanan, and K. Vasudevan A Broadband -Strip Fed Printed Microstrip Antenna, IEEE Trans Antennas Propag., vol.59, NO. 1, January 2011,pp.281-284.