Polarization

1. Polarization • According to the IEEE Standard Definitions for Antennas, the polarization of a radiated wave is defined as “that property of a radiated electromagnetic wave describing the time-varying direction and relative magnitude of the electric field vector; specifically, the figure traced as a function of time by the extremity of the vector at a fixed location in space, and the sense in which it is traced, as observed along the direction of propagation.” • Polarization is the curve traced out by the end point of the arrow representing the instantaneous electric field.

2. The field must be observed along the direction of propagation.

3. If E-field vector at a point in space as a function of time is directed along a line, normal to the direction of propagation, the field is linearly polarized. • If E-field trace is an ellipse, elliptically polarized. • CW rotation of E-field is right-hand polarization, CCW as left-hand polarization.

5. Linear Polarization • In Fig 4-10, a plane wave in +z direction, • Examine the variation of E-field vector E at z=0. 3 cases • Ex0+=0, Ey0+=0 and φx= φy= φ(Fig. 4-10, 4-11, 4-12)

7. Circular Polarization • The tip of the electric field vector traces out a circular locus in space. • RHCP (Clockwise) : Ex.1

9. RHCP: Ex.2

10. LHCP(CCW): Ex 1

11. LHCP: Ex2

13. Elliptical Polarization

14. If ER>EL  AR: negative, RH circular component is stronger than the LH circular component RHEP • If ER<EL  AR: positive, LH circular component is stronger than the RH circular component LHEP