Types of Antennas

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1 Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010

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3 Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010

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4 Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010 Wire Antennas Short Dipole Antenna Dipole Antenna λ/2 Dipole Antenna Broadband Dipole Antenna Monopole Antenna Folded Dipole Antenna Loop Antenna

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5 Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010

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6 Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010 Short Dipole Antenna

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7 Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010 Short Dipole Antenna The following points are important w.r.t short wave dipole The fields die off as 1/r, which indicates that the power falls of as The fields are proportional to L, indicating a longer dipole will radiate more power.

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8 Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010 Short Dipole Antenna The fields are proportional to the current amplitude I0. The directivity of a short wave dipole antenna is 1.5 (1.76 dB). The Half-Power Beamwidth is 90 degrees. The polarization of this antenna is linear.

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Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010 9

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Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010 12 Dipole Antenna Normalized radiation patterns for dipoles of various lengths

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Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010 13 Dipole Antenna Dipole directivity as a function of dipole length

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Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010 16 λ/2 Dipole Directivity = 1.64 (2.15dB) HPBW = 78 degrees Radiation pattern is same as shown for a 1 λ length dipole (on slide no. 14), only change being a reduced directivity.

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Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010 17 Broadband Dipole A dipole antenna can be made more broadband by increasing the volume it occupies. This increase in volume can be simply achieved by increasing the thickness of the wires. Eg. Hollow aluminum pipes are used in case of commercial Yagi-Uda antennas rather than a thin wire.

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Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010 19 Monopole Antenna A monopole antenna is one half of a dipole antenna, almost always mounted above some sort of ground plane. Impedance of a monopole is half of the λ/2 dipole. D(monopole) = D(dipole) + 3dB. Were used as antennas in older cell phones.

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Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010 20 Monopole Antenna

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Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010 24 Reflector Antennas Corner Reflector Antenna Parabolic Reflector Antenna/Satellite Dish

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Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010 25 Corner Reflector Antenna Used to increase directivity of an antenna. Here two conductive sheets/plates are placed at the back of the antenna at an angle of 90 degree to each other.

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Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010 27 Corner Reflector Antenna Resulting pattern has same polarization. Increase in directivity by 9-12 dB. Assumption -> Fields behind plates are zero.

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Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010 28

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Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010 29 Parabolic Reflector Antenna/Satellite Dish Characteristics Very high gain Low cross polarization Fractional bandwidth of at least 5% Smaller dishes operate at a freq of 2-28GHz whereas larger dishes operate at VHF band (30-300MHz)

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Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010 30

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Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010 34 Gain pattern of illuminated reflector

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Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010 35 Parabolic Reflector Antenna/Satellite Dish Reflector Feed Mechanisms Prime Focus Feed Cassegrain Feed Gregorian Feed Offset Feed

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Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010 37 Travelling Wave Antennas Helical Antenna Yagi-Uda Antenna

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Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010 40 Helical Antenna For good radiation number of turns should be at least 3 and 0.75λ ≤ C ≤ 1.33 λ . This determines operating bandwidth of helical antenna. Formulae Zin = 140 C λ Axial Ratio (AR) = (2N+1)/2N Gain, G = (6.2*(C^2)*NS)/ (λ^3) HPBW = 52/ C λ(n*S λ) degrees

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Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010 48 Horn Antennas

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Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010 49 Horn Antenna Characteristics Very popular at UHF & higher frequencies. Typical gain of 10-20 dB. Directional radiation pattern. Wide impedance bandwidth. Gain increases and beamwidth decreases as frequency of operation increases. Directivity is roughly equal to gain. E.g. E-plane horn, H-plane horn, Pyramidal horn, Conical horn.

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Aniket Bhalerao [Lecturer] (Dept. of Electronics and Communication Engineering) TCET,Indore Oct. 2010 54 References Antennas (for all application) Third Edition John. D. Kraus, Ronald J. Marhefka [TMH] Antenna Theory: Analysis and Design, 3rd Edition, Constantine A. Balanis [Wiley] Practical Antenna Handbook, Joseph Carr [Mc Graw Hill] Most of the simulations and plots are works of Peter Bevelacqua ( Antenna Engineer at Apple). The others are obtained using FEKO Lite and Ansoft HFSS. 5. Antenna & Wave Propagation, K.D.Prasad [Satya Prakashan]