Page 220 - Maxwell House

200 ANTENNA BASICS

It means that -vector constantly rotates in the plane perpendicular to the direction of
+
propagation while shifting along the ( − )-axis. Point your right or left thumb along the
direction of wave propagation and align the curve of your fingers to the direction of rotation of
the field (solid blue curve). If you are successful with the right hand, as Figure 5.1.2
demonstrates, the wave is called Right Handed Circular Polarized (RHCP or RCP in short).

= , = /. Then for the in-phase component of E-vector we obtain

⁄
= ℜ( ) = sincos( − ) − sinsin( − ) � (5.6)
0
−
0
2
2
| | ≡ sin
−
The drawing in Figure 5.1.3 demonstrates the time-space behavior of this vector at any spots
where, as before, sin = sin. Now, -vector constantly rotates in the plane perpendicular
−
to the direction of propagation and instantaneously shifts along the ( − )-axis. Evidently,
you need to use your left hand to estimate
the rotation direction. Such wave is
called Left Handed Circular Polarized
(LHCP or LCP).
The fact that the RHCP and LHCP wave
is the superposition of two LP waves is
quite remarkable. Undoubtedly, a single
CP wave carries the power of two LP
waves while according to (5.5) and (5.6) Figure 5.1.3 LHCP wave illustration
its magnitude is equal to the magnitude
of a single LP wave. Therefore, a transmitted power in principle can be doubled with little
concern for the possible electrical breakdown at a high level of power. Evidently, LP antenna
can receive up to half (with 3 dB loss) energy that comes to it EM wave of CP polarization.

From the above discussion
of equations (5.4) - (5.6),
we can come to the
conclusion that any linearly
polarized wave might be
represented as a
superposition of two
circularly polarized waves
of opposite rotation. In the
Figure 5.1.4 Left-handed elliptical polarized wave most general case, E-vector
could rotate varying its
magnitude as Figure 5.1.4 demonstrates and have so-called elliptical polarization. As soon as
2
2 > > 0 the polarization is right handed while it is left handed when − 2 < < 0.
⁄
⁄
From (5.3) it follows that the elliptically polarized wave can be represented as a superposition
of two LP waves of unequal amplitude (red and green projections on side and bottom wall,
respectively) with the phase shift ≠ 0 as it can be seen in Figure 5.1.4 (just pay attention the

2 Public Domain Image, source with some editing: https://wikispaces.psu.edu/display/RemSens597K/P