1. RF Theory: An Introduction
Philip Weber MSc (Astronomy)
USAF MARS (SMD PA) / SHARES

2. Electromagnetism

3. Electricity and Magnetism
James Clerk Maxwell developed the Maxwell Equations that predicted the existence and operations of radio and television waves
Radio waves were not actually discovered by Hertz, in 1888

4. Introduction
Wave motion is the transfer of energy from a source to receiver without transfer of matter
James Clerk Maxwell (1860) first discovered electromagnetic waves
Atoms vibrate and in turn radiate vibrations of electromagnetic energy
If the temperature is high enough, the emissions are light
Every physical object in the Universe emits radiation in proportion to the rate of molecular and atomic vibratory motion

5. Moving Charges Cause Magnetic Field

6. Electromagnetic Spectrum
All electromagnetic waves travel the same speed in a vacuum
Different waves have differing frequency and wavelength
Frequency is how many times something happens in a specific time period
Wavelength is how long the wave is relative to a known measurement system
As frequency increases, wavelength decreases

7. Properties of Waves

8. Anatomy of a Wave

9. Electromagnetic Wave

10. Relationship Between Wavelength and Frequency

11. Distribution of Electromagnetic Radiation

12. Distribution of Electromagnetic Radiation

14. Energy and Penetrability of Radiation
Higher the frequency (shorter wavelength) the higher the energy
Radio waves penetrate the air, but not metals
Radio propagation produced by waves bouncing off the ionosphere (skip versus line of sight)
Infrared (IR or heat waves) passes through dry air but not moist air
Visible light passes through glass but IR does not
X-rays penetrate virtually any substance, but with absorbtion
Every substance, depending on its atomic structure, absorbs, reflects, or emits radiation uniquely.

15. Interaction of Radiation and Matter
REFLECTION – bouncing of waves off a surface
REFRACTION – bending of waves through a medium
DIFFRACTION – spreading of waves through a slit
INTERFERENCE – result of waves meeting
POLARIZATION – wave oscillating in one plane only
EXPOSURE – Interaction of light waves with silver

16. Philip Weber MSc (Astronomy) USAF MARS (SMD PA) / SHARES
DIPOLE ANTENNA THEORY
Philip Weber MSc (Astronomy)
USAF MARS (SMD PA) / SHARES

17. Types of Antennas Wire antennas Aperture antennas Array antennas
Reflector antennas
Lens antennas
Patch antennas

18. Introduction (Cont’d..)
Common types of antennas:

19. Radiation Mechanism

20. Basic Antenna Parameters
Radiation pattern: The relative distribution of radiated power as a function of direction in space – an (hypothetical) isotropic antenna radiates equally in all directions.
Gain G : The ratio of the radiated power in the maximum direction to the radiated power of an isotropic antenna. The gain of an antenna represents the ability to focus its beam in a particular direction – an isotropic antenna has a gain of 0 dB.

21. Basic Antenna Parameters
Radiation Resistance RA: The equivalent resistance which would dissipate the same amount of power as the antenna radiates.
Input impedance ZA : The ratio of the voltage to the current at the antenna terminals (Thevenin equivalent circuit).
Polarization: The direction of the E-field.

22. Typical ½ Wavelength Dipole

24. ½ Wave Dipole

25. Some popular forms of dipole antennas

26. Radiation Pattern of an Infinitesimal Dipole

27. Radiation Pattern of a Thin Dipole

28. 4.3 Dipole Antennas Dipole Antennas
A drawback to Hertzian dipole as a practical antenna is its small radiation resistance. A longer will have higher radiation resistance, becomes more efficient. It as an L long conductor conveniently placed along the z axis with current distribution i(z,t).

30. Dipole Antennas (Cont’d..)
3D and 2D amplitude patterns for a thin dipole of l=1.25λ

31. Dipole Antennas (Cont’d..)
Therefore, the normalized power density is:
The current distribution and normalized radiation pattern for a half wave dipole antenna.

32. Dipole Antennas (Cont’d..)

33. Dipole antennas

34. Yagi Uda Array Antennas (Cont’d..)