# Chapter 3 : Radiation and Antennas¶

## Example 3.1,Page Number 158¶

In :
from __future__ import division
from sympy import Symbol
from math import pi

Lm = Symbol("Lm'")# defining Lm as lambda
dl = Lm/40 # dipole length
Rr = 80*(pi)**(2)*(dl/Lm)**2
print "radiation resistance of dipole in ohm if dl = Lm/40 :",round(Rr,3)
dl = Lm/60 # dipole length
Rr = 80*(pi)**(2)*(dl/Lm)**2
print "radiation resistance of dipole in ohm if dl = Lm/60 :",round(Rr,3)
dl = Lm/80 # dipole length
Rr = 80*(pi)**(2)*(dl/Lm)**2
print "radiation resistance of dipole in ohm if dl = Lm/80 :",round(Rr,3)

radiation resistance of dipole in ohm if dl = Lm/40 : 0.493
radiation resistance of dipole in ohm if dl = Lm/60 : 0.219
radiation resistance of dipole in ohm if dl = Lm/80 : 0.123


## Example 3.3,Page Number 160¶

In :
from __future__ import division
from sympy import Symbol
from math import pi,sqrt

#variable declaration

Pr = 1 #power in watt
Eta0 = 120*(pi) # constant

#calculations
I = sqrt(Pr/73) # current in A
r = Symbol('r')
E_max = 60*I/r
RI = (r**2*E_max**2)/Eta0 # radiation intensity
Gd_max = (4*(pi)*(RI))/Pr

#result
print "Directivity of a half wave dipole is:",round(Gd_max,3)

Directivity of a half wave dipole is: 1.644


## Example 3.4,Page Number 160¶

In :
#variable declaration

Rr=300 # radiation resistance in ohm
I=3 # in A

#calculations
#formula: Pr=I**2*R
Pr=I**2*Rr # power radiated in watt

#result
print "power radiated by antenna in watts:",Pr

power radiated by antenna in watts: 2700


## Example 3.5,Page Number 161¶

In :
from __future__ import division
from math import pi

#variable delaration

f = 500 #frequency in mega hertz
f = 500*10**6 #frequency in hertz
c = 3*10**8 #speed of light in m/s
Gdmax = 1.644 # directivity of a half wave dipole

#calculations
lamda = c/f #wavelength in meter
Ae = ((lamda)**2*Gdmax)/(4*(pi)) # Effective area in m**2

#result
print "effective area of half wave dipole in m**2:",round(Ae,3)

effective area of half wave dipole in m**2: 0.047


## Example 3.6,Page Number 161¶

In :
from __future__ import division
from math import pi

#variable delaration
f = 100 #frequency in Mhz
f = 100*10**6 #frequency in hertz
c = 3*10**8 #speed of light in m/s
D = 1.5 # directivity

#calculations
lamda = c/f #wavelength in meter
Ae = (lamda**2*D)/(4*(pi)) # effective area in m**2

#result
print "Effective area of hertezian dipole in m**2:",round(Ae,2)

Effective area of hertezian dipole in m**2: 1.07