# chapter07:Microwave Measurements¶

## Example 7.1, Page number 278¶

In [1]:
#calculate VSWR
#chapter-7 page 278 example 7.1

import math
a=4.##Length of Waveguide in cm
f=10.**10.##Frequency in Hz
x=0.1##distance between twice minimum power points in cm
c=3.*10.**10.##Velocity of Light in cm/sec

#CALCULATION
wc=2.*a##Cutoff wavelength in TE10 mode in cms
w0=(c/f)##Free space wavelength in cms
wg=(w0/math.sqrt(1-(w0/wc)**2.))##Guide wavelength in cms
S=(wg/(x*(math.pi)))##Voltage Standing Wave Ratio(VSWR) for double minimum method

#OUTPUT
print '%s %.1f' %('\nFor double minimum method, Voltage Standing Wave Ratio(VSWR) is S=',S)#

For double minimum method, Voltage Standing Wave Ratio(VSWR) is S= 10.3


## Example 7.2, Page number 279¶

In [2]:
#calculate reflected power and VSWR
#chapter-7 page 279 example 7.2
import math
x=3##O/P incident power from first directional coupler in mW
y=0.1##O/P reflected power from second directional coupler in mW

#CALCULATION
Pi=x*100.##Incident Power in mW
Pr=y*100.##Reflected Power in mW
p=math.sqrt(Pr/Pi)##Reflection Coefficient
S=((1+p)/(1-p))##Voltage Standing Wave Ratio(VSWR)

#OUTPUT
print '%s %.f %s %s %.2f' %('\nReflected Power is Pr=',Pr,'mW','\nVoltage Standing Wave Ratio(VSWR)in the main waveguide is S=',S)#

Reflected Power is Pr= 10 mW
Voltage Standing Wave Ratio(VSWR)in the main waveguide is S= 1.45


## Example 7.3, Page number 279¶

In [3]:
#calculate VSWR
import math

#Variable declaration
Pr = 0.15*10**-3     #reflected power(W)
Pi = 2.5*10**-3      #incident power(W)

#Calculations
rho = math.sqrt(Pr/Pi)
s = (1+rho)/(1-rho)

#Results
print "VSWR =",round(s,2)

VSWR = 1.65


## Example 7.4, Page number 279¶

In [4]:
#calculate reflected power
import math

#Variable declaration
s = 2.                    #VSWR
Pi = 4.5*10**-3*1000      #incident power(W)
c = 30                    #couplers

#Calculations
#s = (1+rho)/(1-rho)
rho = (s-1)/(s+1)
Pr = rho**2*Pi

#Results
print "Reflected power =",Pr,"W"

Reflected power = 0.5 W