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Performance Improvement of RMSA using Different Substrates

Suraj Rabindranath1, M. Utkala Prakash2, Chetana. D3& Prof. Mahesh M. Gadag4

Department of Electronics and Communication Engineering, SDMCET, Dharwad, Karnataka, India. E-mail: 1surajrabindranath@gmail.com, 2itsutkalaprakash@gmail.com, 3chetanadeshnur@gmail.com,

4mahgadag@gmail.com

ABSTRACT— To Study the behavioral characteristics of the microstrip patch antennas with different dielectric substrates such as Glass epoxy, FR-4 and RT-Duroid. The paper gives the comparative study of Rectangular Microstrip Patch Antenna’s of different dielectric substrates for design parameters like Return loss, Bandwidth, Gain, Directivity and Efficiency at 2.5GHz. Different dielectric materials have different relative permittivity and this varies the radiating capability of antennas.

INDEX TERMS—Bandwidth, Directivity, Efficiency, FR-4, Gain, IE3D, Plastic radome, Return loss, RMSA and RT-duroid.

I . INTRODUCTION The rectangular microstrip patch antenna, is a type of radio

antenna with a low profile characteristic [4]. A patch antenna is usually constructed on a dielectric substrate and lithography processes is used to make printed circuit boards. Microstrip patch antenna can be mounted on a flat surface. It consists of a flat rectangular sheet or "patch" of metal, mounted over a larger sheet of metal called a ground plane [3]. The assembly is usually contained inside a plastic radome, which protects the antenna structure from damage. Patch antennas are simple to fabricate and easy to modify and customize. They are the original type of microstrip antenna. The two metal sheets together form a resonant piece of microstrip transmission line with a length of approximately one-half wavelength of the radio waves.

\ Substrate

Fig. 1 Top view of rectangular microstrip patch antenna

Fig. 2 Side view of rectangular microstrip patch antenna The behavioural characteristics of the microstrip patch

antennas with different dielectric substrates are analyzed in this paper. The different dielectric materials used are Glass epoxy, RT- duroid and FR4. For the behavioural analysis of EM waves IE3D simulator is used and RMSA is designed at 2.5GHz operating frequency.

TABLE I Dielectric substrates and its relative permittivity

Dielectric Substrate Glass epoxy

FR-4 RT duroid

Relative Permittivity 4.4 4.0 3.2

The above Fig-2 shows the different dielectric materials with their respective permittivity. Here FR-4 means Flame retardant and is a grade designation assigned to glass-reinforced epoxy laminate sheets, P C B , rods and tubes, FR-4 is composite material composed of woven fiber-glass cloth with an epoxy resins that is fame resistant. RT-duroid is a glass microfiber reinforced composites. The RT-duroid is used because of its features such as isotropic, lowest electrical loss for reinforced material, excellent chemical resistance.

II. DESIGN OF R M S A

Design of R M S A includes calculation of different physical parameters of microstrip patch antenna such as, thickness, length, width, strip width, inset width, inset depth, feed length and total length.

Considering 2.5GHz as operating frequency, all the physical parameters of patch antenna are calculated using standard design equations. The strip impedance is considered as 50Ω. Any E M waves travel slowly in a medium than in free space. Hence the effective length of the strip is considered in calculating the strip width and length to get 50Ω impedance. This effective length is called as electric length and is

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calculated using velocity factor and half wavelength. Thus calculated strip line is fed at the point where the impedance of patch matches with that of feed line. The depth to which the feed line is fed is called as inset depth. The difference between total strip length and inset depth is feed length.

A. Design Equations The following are the equation used to calculate the design parameters of Rectangular Microstrip Patch Antenna [1].

1. Practical Width of half-wave patch antenna

W = 1

2frµöeö f2 εο + 1

2. Effective dielectric constant 1

er + 1 e r - 1 h ~2 W eeff = — + — 1 + 12— , τ - > 1

3. Extension of length due to fringing effect M/

AL = 0.412ft (ee// + 0.3 -+0 .264

4. Actual length

{teff - 0.258 - + 0.8

2ΔΖ, 2/ r^ ereff^fiweo

5. Effective length Leff = L + 2ΔΖ,

6. Input impedance of half-wavelength patch

Zin = 90 er2 Z^2

er - 1 W Ω

7. Inset Depth considering feed impedance as 50 Ω

8. Velocity factor

9. Electric length

yo = — cos

Vf

Zin

eeff

Electric Length = Vf%X -

10. Feed length F = Total strip length — Inset Depth

TABLE II Dimensions obtained for antennas from design equations

Parameter εr

Height Length Width

Glass epoxy 4.4 1.588mm 28.246mm 36.515mm

FR-4 4 1.4mm 29.677mm 37.947mm

RT- Duroid 3.2 0.762mm 33.358mm 41.404mm

Patch length Patch width Inset depth

15.664mm 1.457mm 10.514mm

17.113mm 2.874mm 10.728mm

20.998mm 1.819mm 11.973mm

III . SOFTWARE & SIMULATION

The software used for the design of R M S A is Z E A L A N D IE3D. Microstrip patch antennas are simulated for different dielectric substrates. The values obtained are analyzed and compared graphically.

A. Sofware-IE3D Z E L A N D I E 3 D is software based on M O M solution of

integral equation which has an excellent accuracy for frequency domain analysis. For the simple structures like rectangular and circular I E 3 D is the best suited software. This software helps to detect the most accurate circuit resonance, quantify circuit noise and determine E M radiation pattern. I E 3 D is also used to improvise design quality and reduce E M design cost.

Simulation of 3 patches is made using Zealand I E 3 D software. The physical parameters calculated using standard equations are used in software. Rectangular patches of calculated length and width, Strips of calculated length and width and inset depth as calculated are accurately used in software to design the patch and verify its results.

Once the patches are designed simulated results for return loss is observed. Return loss is defined as loss in power in strip due to reflections at feeding point. A reflection at feeding point occurs due impedance mismatch. Hence inset depth of the patch should be readjusted to get perfect impedance match and least return loss at operating frequency of 2.5GHz.

Also 3 D power pattern view for different patches is made in software. Comparative study is made in software as well as in hardware fabricated patches.

B. Simulation Results Simulation result of Glass epoxy with 1.588mm thickness

Fig. 3 shows the Return loss graph of Glass Epoxy with thickness 1.588mm and bandwidth obtained is 40MHz.

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Simulation result of FR-4 with 1.4mm thickness I V . FABRICATION

Fig. 4 shows the Return loss graph of FR-4 with thickness 1.4mm and bandwidth obtained is 55MHz.

Simulation result of RT- Duroid with 0.762mm thickness

Fig. 5 The Return loss of RT- Duroid with thickness 0.762mm and bandwidth obtained is 70MHz.

As mentioned earlier the dimensions of the antennas are calculated using design equations. With the dimensions calculated a patch is simulated and verified using Zealand IE3D simulator. Necessary optimizations are made for inset depth to get accurate resonating frequency (here 2.5 GHz) and return loss. After optimization the mask is prepared with this optimized physical dimensions and stacked to the substrate. Thus formed prototype is dipped into the Ferric chloride solution and unmasked metal layer over the substrate is etched out. After etching out the metal layer in unmasked region, mask is removed and is cleaned using cleansing agent. Thus antennas are designed. Finally designed antennas are tested and compared with the simulation results.

Fig. 7 Fabricated patch on Glass Epoxy.

Fig. 8 Fabricated patch on FR-4.

Fig. 6 The field pattern view for RT- Duroid and blue colour represen t s ga in in db.

Fig. 9 Fabricated patch on R T - Duroid.

V . TESTING

The fabricated antennas are tested in the laboratory to analyze the performance of antennas and compare the results obtained with that of simulation. Also, the performances of antennas using different relative permittivity material as substrates are studied.

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Also the performances of fabricated antennas are proved to be satisfactory in comparison with the simulation results.

Fig. 10 Laboratory setup for testing all the designed patches.

The designed patch is mounted on tripod and connected to a microwave source (indicated by left half of the Fig. 10) and a common receiver patch is used with all the designed patches that is connected to VSWR meter (indicated by right half of Fig.10). The distance maintained between transmitter and receiver is 15cms. The practical results obtained from the patch are plotted taking frequency on x-axis and output power on y-axis as shown in the fig

RT-Duroid FR-4

80

70

60

50

40

30

20

10

Glass epoxy

i i i r r r m m ι ιι

Fig. 11 Graph showing the plot output power of 3 antennas in db with respect to frequencies.

V I . COMPARATIVE STUDY

The comparison graph of gain and directivity for different substrate antenna is obtained from simulator. The performance of RT-Duroid is proved to be better than FR-4 which is better than Glass epoxy which can be viewed in the figure below.

Fig. 11 Graph showing comparisons of gain of antennas with different dielectric substrate.

Fig. 12 Graph showing comparisons of directivity of antennas with different dielectric substrate.

TABLE III Comparison of antennas performance from simulation results

Antenna

Glass Epoxy FR- 4

RT- Duroid

Bandwidth (MHz)

40 55 70

Return loss (dB) -36 -40 -42

VSWR

1.06 1.08 1.05

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TABLE IV Comparison of antennas performance from ractical testing

Antenna

Glass Epoxy FR- 4

RT-Duroid

Bandwidth (MHz) 35.54 49.8 50.5

Output Power (dB) -34.7 -32.2 -30

VSWR

1.06 1.08 1.25

Chetana. D, author of this paper, is a student of final year engineering in the department of Electronics and Communication at SDMCET, Dharwad. Field of interest includes Wireless Communication, Cryptography, Optical Fiber Communications and Applied Mathematics.

VII . CONCLUSION

The patch antenna with different relative permittivity and heights are designed, simulated and tested for the performance. It is found that antenna with thicker substrates and lesser relative permittivity has optimum performance.

REFERENCES

[1] C. A. Balanis, “Microstrip Antennas”, in Antenna Theory, Analysis and Design, ed., John Wiley & sons, New york, 2008, pp.723-752.

[2] Emtalk online calculator is used for Microstrip Patch Antennas design. Available: http://www.emtalk.com

[3] Prof. Mahesh M. Gadag, Mr. Dundesh S. Kamshetty, Mr. Suresh L. Yogi, “Design of Different Feeding Techniques of Rectangular Microstrip Antenna for 2.4GHz RFID Applications Using IE3D”, in Proc. of the Intl. Conf. on Advances in Computer, Electronics and Electrical Engineering, 978-981-07-1847-3, city, state, year, pp.522­525.

[4] Prof. Mahesh M. Gadag, Mr. Dundesh S. Kamshetty, Mr. Suresh L. Yogi, Mr. Vinayak C. D, “Design and Comparative Study of Different Feeding Mechanisms for Microstrip Antenna for Wireless Communication”, International Conference on Computational Intelligence and Computing Research (IEEEICCIC), 978-1-61284-693-4/11, city, 2011, pp.638-641.

[5] Prof. Mahesh M. Gadag, Ms. Lubna F Shaikh, Ms. Aahaladika, Mr. Kundan Kumar, “Rectangular Microstrip Antenna using Air-Coupled Parasitic Patches for Bandwidth Improvement”, International Conference on Electronics and Communication Engineering, 978-93-81693-56-8, Vizag, 2012, pp.45-49.

[6] Referred website, en.wikipedia.org.

Prof. Mahesh M. Gadag, author of this paper, received Bachelor of Engineering in Electronics and Communication Engineering in 1987 and M. Tech from NITK, Suratkal in 1992. Worked as Assistant Professor at defense University, Ethiopia and as Associate Professor at Al-Fateh University, Tripoli. Currently working as Assistant professor at SDMCET, Dharwad. Field of research include RF and microwave communication.

Suraj Rabindranath, author of this paper, is a final year student in the department of Electronics and Communication Engineering at SDMCET, Dharwad. His Fields of interests includes VLSI, Embedded Systems, Microwave & Antenna Engineering, Cryptography, Robotics and Artificial Intelligence.

M. Utkala Prakash, author of this paper, is pursuing Bachelor degree in Electronics and Communication Engineering at SDMCET, Dharwad. Field of interest includes Computer Communication Networks, Network infrastructure, Satellite communication, RFID, Electromagnetic Theory, Operating Systems, Cryptography and Radar systems.