1. Elements of electromagnetic field theory and guided waves
Modes of a circular cavity
Dipole radiation – Thomson model
Hertzian dipole and its far-zone field
Radiated power and radiation resistance
Magnetic dipole
Linear antenna
Antenna excitation of a rectangular WG

2. Circular resonator
since
Top view
Usually d<2a
Side view:

3. Thompson’s model of dipole radiationz
(t<<t) r r r
t: a, v(t ≥ t)=at
t’=(t-r/c)
rays
Let the charge acquire (+a),
then (-a) and return back, etc.
Series of pulses!
Wave fronts
Oscillating dipole creates a spherical EM wave

4. Hertzian dipole H x z E t’=t-R/c → q R>>l IA ,VA l<<l w
Thomson’s formula: E
t’=t-R/c → q
R>>l
IA ,VA
l<<l
leff w
For phasors it takes form:
Linear charge density
Continuity equation:
Hertzian dipole moment
H=Hf=Eq/h

5. Radiated power and radiation resistance of a short dipole
R>>l
IAleff

6. Magnetic dipole z Hq x Ef R>>l p÷Eq Duality: E H q m÷Hf=-Eq /h
pwm0
m/c
m=m0ISaz S I
<<l 2 -

7. Linear antennas l~(0.25…0.75)l l~(0.5…1.5)l l<<l Hertzian dipole
No radiation
from here
No radiation
from here
l~(0.25…0.75)l
l<<l
l~(0.5…1.5)l
No radiation
from here
Hertzian dipole
(without spheres)
Dipole
linear antenna
Monopole
linear antenna h
(if kh<p)
Imax IA
I(z)
Cable, ground plane, or 2d arm

8. Antenna excitation of WGy
TE10
TM11 b l S0 VA d d z VA
d≈b/2
Consider the monopole excitation
Find Rrad and C10