Introduction to Antennas & Radiating Systems Austin Peay State University William Cooke Department of Physics & Astronomy J. Caleb Wherry Department of Computer Science
Outline 2 Introduction What is An Antenna? Transmission Lines Free Space The Antenna How An Antenna Works Radiating from Accelerating Particles Electric and Magnetic Fields Radiation Patterns The /2 Short Dipole Conclusion
What is An Antenna? 4 Transmission Line/Guided Path A transmission line is a path in which a current flows. This line can be a typical circuit, coaxial cable, or any other material with a well-defined, complex impedance. Free Space Free space is made up of fields and void of other matter. These fields carry energy in the form of waves which can travel freely throughout. Antenna An antenna is the interface between the above transmission lines and free space. It takes the current from the transmission lines and converts it to waves which get transmitted into free space, and vice versa.
12 Retarded Current distance z away from poles: Integrating over all dz’s to get E & H components of far field: z dz
13 We can then find the Power by integrating the above field over a large surface of the Poynting vector: Radiation Resistance:
Conclusion 14 Antennas are all around us! Examples listed here are only a small subset of a rich field of study. Antennas’ shape are of great importance in the theory of transmission and receiving of antennas (Optimization theory – Genetic Algorithms). A better understanding of how antennas work gives us an understanding of the electromagnetic radiation into or out of our electronic device. Enjoy your summer!
References 15 Griffiths, D.J. Introduction to Electrodynamics. 3rd ed. Prentice-Hall: Upper Saddle River, NJ. 1999. Kraus, J.D. Antennas. 2nd ed. McGraw-Hill: New York.1988.