EC1352 ANTENNAS AND WAVE PROPAGATION 3 1 0 100

AIM

To enable the student to study the various types of antennas and wave propagation.

OBJECTIVES

• To study radiation from a current element.

• To study antenna arrays

• To study aperture antennas

• To learn special antennas such as frequency independent and broad band antennas.

• To study radio wave propagation.

UNIT I RADIATION FIELDS OF WIRE ANTENNAS 9

Concept of vector potential. Modification for time varying, retarded case. Fields associated with Hertzian dipole. Power radiated and radiation resistance of current element. Radiation resistance of elementary dipole with linear current distribution. Radiation from half-wave dipole and quarter-

wave monopole. Assumed current distribution for wire antennas. Use of capacity hat and loading coil for short antennas.

UNIT II ANTENNA FUNDAMENTALS AND ANTENNA ARRAYS 9

Definitions: Radiation intensity. Directive gain. Directivity. Power gain. Beam Width. Band Width. Gain and radiation resistance of current element. Half-wave dipole and folded dipole. Reciprocity principle. Effective length and Effective area. Relation between gain effective length and radiation resistance.

Loop Antennas: Radiation from small loop and its radiation resistance. Radiation from a loop with circumference equal to a wavelength and resultant circular polarization on axis.

Helical antenna. Normal mode and axial mode operation.

Antenna Arrays: Expression for electric field from two and three element arrays. Uniform linear array. Method of pattern multiplication. Binomial array. Use of method of images for antennas above ground.

UNIT III TRAVELLING WAVE (WIDEBAND) ANTENNAS 9

Radiation from a traveling wave on a wire. Analysis of Rhombic antenna. Design of Rhombic antennas.

Coupled Antennas: Self and mutual impedance of antennas. Two and three element Yagi antennas. Log periodic antenna. Reason for feeding from end with shorter dipoles and need for transposing the lines. Effects of decreasing α.

UNIT IV APERTURE AND LENS ANTENNAS. 9

Radiation from an elemental area of a plane wave (Huygen’s Source). Radiation from the open end of a coaxial line. Radiation from a rectangular aperture treated as an array of Huygen’s sources. Equivalence of fields of a slot and complementary dipole. Relation between dipole and slot impedances. Method of feeding slot antennas. Thin slot in an infinite cylinder. Field on the axis of an E-Plane sectoral horn. Radiation from circular aperture. Beam Width and Effective area.

Reflector type of antennas (dish antennas). Dielectric lens and metal plane lens antennas. Lumeberg lens. Spherical waves and Biconical antenna.

UNIT V PROPAGATION 9

The three basic types of propagation; ground wave, space wave and sky wave propagation.

Sky wave propagation: Structure of the ionosphere. Effective dielectric constant of ionized region. Mechanism of refraction. Refractive index. Critical frequency. Skip distance. Effect of earth’s magnetic field. Energy loss in the ionosphere due to collisions. Maximum usable frequency. Fading and Diversity reception.

Space wave propagation: Reflection from ground for vertically and horizontally polarized waves. Reflection characteristics of earth. Resultant of direct and reflected ray at the receiver. Duct propagation.

Ground wave propagation: Attenuation characteristics for ground wave propagation. Calculation of field strength at a distance.

TUTORIAL 15

TOTAL : 60

TEXTBOOK

1. E.C.Jordan and Balmain, "Electro Magnetic Waves and Radiating Systems", PHI, 1968, Reprint 2003.

REFERENCES

1. John D.Kraus and Ronalatory Marhefka, "Antennas", Tata McGraw-Hill Book Company, 2002.

2. R.E.Collins, 'Antennas and Radio Propagation ", McGraw-Hill, 1987.

3. Ballany , "Antenna Theory " , John Wiley & Sons, second edition , 2003.

AIM

To enable the student to study the various types of antennas and wave propagation.

OBJECTIVES

• To study radiation from a current element.

• To study antenna arrays

• To study aperture antennas

• To learn special antennas such as frequency independent and broad band antennas.

• To study radio wave propagation.

UNIT I RADIATION FIELDS OF WIRE ANTENNAS 9

Concept of vector potential. Modification for time varying, retarded case. Fields associated with Hertzian dipole. Power radiated and radiation resistance of current element. Radiation resistance of elementary dipole with linear current distribution. Radiation from half-wave dipole and quarter-

wave monopole. Assumed current distribution for wire antennas. Use of capacity hat and loading coil for short antennas.

UNIT II ANTENNA FUNDAMENTALS AND ANTENNA ARRAYS 9

Definitions: Radiation intensity. Directive gain. Directivity. Power gain. Beam Width. Band Width. Gain and radiation resistance of current element. Half-wave dipole and folded dipole. Reciprocity principle. Effective length and Effective area. Relation between gain effective length and radiation resistance.

Loop Antennas: Radiation from small loop and its radiation resistance. Radiation from a loop with circumference equal to a wavelength and resultant circular polarization on axis.

Helical antenna. Normal mode and axial mode operation.

Antenna Arrays: Expression for electric field from two and three element arrays. Uniform linear array. Method of pattern multiplication. Binomial array. Use of method of images for antennas above ground.

UNIT III TRAVELLING WAVE (WIDEBAND) ANTENNAS 9

Radiation from a traveling wave on a wire. Analysis of Rhombic antenna. Design of Rhombic antennas.

Coupled Antennas: Self and mutual impedance of antennas. Two and three element Yagi antennas. Log periodic antenna. Reason for feeding from end with shorter dipoles and need for transposing the lines. Effects of decreasing α.

UNIT IV APERTURE AND LENS ANTENNAS. 9

Radiation from an elemental area of a plane wave (Huygen’s Source). Radiation from the open end of a coaxial line. Radiation from a rectangular aperture treated as an array of Huygen’s sources. Equivalence of fields of a slot and complementary dipole. Relation between dipole and slot impedances. Method of feeding slot antennas. Thin slot in an infinite cylinder. Field on the axis of an E-Plane sectoral horn. Radiation from circular aperture. Beam Width and Effective area.

Reflector type of antennas (dish antennas). Dielectric lens and metal plane lens antennas. Lumeberg lens. Spherical waves and Biconical antenna.

UNIT V PROPAGATION 9

The three basic types of propagation; ground wave, space wave and sky wave propagation.

Sky wave propagation: Structure of the ionosphere. Effective dielectric constant of ionized region. Mechanism of refraction. Refractive index. Critical frequency. Skip distance. Effect of earth’s magnetic field. Energy loss in the ionosphere due to collisions. Maximum usable frequency. Fading and Diversity reception.

Space wave propagation: Reflection from ground for vertically and horizontally polarized waves. Reflection characteristics of earth. Resultant of direct and reflected ray at the receiver. Duct propagation.

Ground wave propagation: Attenuation characteristics for ground wave propagation. Calculation of field strength at a distance.

TUTORIAL 15

TOTAL : 60

TEXTBOOK

1. E.C.Jordan and Balmain, "Electro Magnetic Waves and Radiating Systems", PHI, 1968, Reprint 2003.

REFERENCES

1. John D.Kraus and Ronalatory Marhefka, "Antennas", Tata McGraw-Hill Book Company, 2002.

2. R.E.Collins, 'Antennas and Radio Propagation ", McGraw-Hill, 1987.

3. Ballany , "Antenna Theory " , John Wiley & Sons, second edition , 2003.

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