Practical_Antenna_Handbook_0071639586

C h a p t e r 2 0 : M i c r o w a v e W a v e g u i d e s a n d A n t e n n a s 455
Antenna
a
b
c
Figure 20.9A Antenna radiator in capped waveguide.
• Free-space velocity c
• Group velocity v g
• Phase velocity v p
0111057 FIG 18-09A
Of course, c is the velocity of propagation in unbounded free space, 3 × 10 8 m/s.
The group velocity is the straight-line velocity of propagation of the wave down the
centerline (z axis) of the waveguides. The value of V g is always less than c, because the
actual path length taken, as the wave bounces back and forth, is longer than the straight-
B
/ 4
a
g/ 4
0
A
a
V g
C
Figure 20.9B Wave propagation in waveguide.