Note for ANTENNA ENGINEERING - AE by Abhishek Apoorv

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ANTENNA ENGINEERING

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ANTENNA ENGINEERING (3-1-0) Module-I (14 Hours) Antenna Definition,Principles of Radiation, Basic antenna parameters, Retarded Vector Magnetic Potential, Radiation field from Current element., Current Distribution on a thin Wire. Half wave dipole and Quarterwave monopole. Two-element array. Principle of Pattern Multiplication. Linear Array. Broadside and end fire patterns, Balun. Module-II (12 Hours) Folded Dipole, Yagi Antenna. Frequency Independent Antenna. Log Periodic Dipole array, Secondary Source and Aperture Antennas (Basics & applications). Module-III (10 Hours) Horn Antennas-Pyramidal & Sectoral Horn. Radiation Pattern and Gain of horn antenna. Parabolic Reflector Antenna -Principle, analysis, Radiation Pattern and Gain. Principles of Cassegrain Antenna. Module-IV (08 Hours) Microstrip Antenna – Basic Characteristics, Rectangular Patch, Radiation principle, Feeding Techniques,Cavity model. Antenna Measurements – Radiation Pattern, Gain and Input Impedance. Text Books: 1. Electromagnetic Wave and Radiating system by E. C. Jordan and K.G. Balmain, 10, 11, 12, 13, 14, and 15. 2. Antennas Theory – Analysis and Design by C. Balanis, 2nd Edition, John Willey & Sons Selected portion Ch. 11, 12, 13, 15, and 16. References Books: 1. Antenna Engineering by J. D. Krauss. 2. Antenna Engineering by W. L. Weeks. 3. Antennas and Wave Propagation by G. S. N. Raju, Pearson Education. 4. Antenna & Wave Propagation by R E. Collins.

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ANTENNA DEFINITION: An antenna is defined by Webster’s Dictionary as “a usually metallic device (as a rod or wire) for radiating or receiving radio waves.” The IEEE Standard Definitions of Terms for Antennas (IEEE Std 145–1983)∗ defines the antenna or aerial as “a means for radiating or receiving radio waves.” In other words the antenna is the transitional structure between free-space and a guiding device, as shown in Figure 1.1. The guiding device or transmission line may take the form of a coaxial line or a hollow pipe (waveguide), and it is used to transport electromagnetic energy from the transmitting source to the antenna, or from the antenna to the receiver. In the former case, we have a transmitting antenna and in the latter a receiving antenna. A transmission-line Thevenin equivalent of the antenna system of Figure 1.1 in the transmitting mode is shown in Figure 1.2 where the source is represented by an ideal generator, the transmission line is represented by a line with characteristic impedance Zc, and the antenna is represented by a load ZA [ZA = (RL + Rr ) + jXA] connected to the transmission line. The Thevenin and Norton circuit equivalents of the antenna are also shownin Figure 2.27. The load resistance RL is used to represent the conduction and dielectric losses associated with the antenna structure while Rr , referred to as the radiation resistance, is used to represent radiation by the antenna. The reactance XA is used to represent the imaginary part of the impedance associated with radiation by the antenna. This is discussed more in detail in Sections 2.13 and 2.14. Under ideal conditions, energy generated by the source should be totally transferred to the Radiation resistance Rr , which is used to represent radiation by the antenna. However, in a practical system there are conduction-dielectric losses due to the lossy nature of the transmission line and the antenna, as well as those due to reflections (mismatch) losses at the interface between the line and the antenna. Taking into account the internal impedance of the source and neglecting line and reflection (mismatch) losses, maximum power is delivered to the antenna under conjugate matching.