Chapter 16 : Antennas

Example 1 : pg 564

In [1]:
#calculate the length of half wave dipole
#page no 564
#given
#prob no. 16.1
#Determination of length of half-wave dipole
#given
f=20.;#Operating freq in MHz
#calculations
L=142.5/f;
#results
print 'The length of half-wave dipole is',L,'m'

The length of half-wave dipole is 7.125 m

Example 2 : pg 566

In [7]:
#calculate the efficiency of dipole antenna 
#page no 566
#prob no. 16.2
#given
#A dipole antenna with radiatn resistance=67ohm & loss resistance 5ohm
Rr=67.;Rl=5;
#calculations
#Determination of efficiency 
eta=Rr/(Rr+Rl);
#results
print 'The efficiency of dipole antenna is',round(eta*100,1),'%'

The efficiency of dipole antenna is 93.1 %

Example 3 : pg 571

In [6]:
#calculate whether the first or second antenna has higher gain 
#page no 569
#prob no. 16.3
#given
#Two antennas with gain 5.3dBi & 4.5dBd
#Converting unit dBd in dBi for comparison
G1_dBi=5.3;G2_dBd=4.5;
G2_dBi=2.14+G2_dBd;
#calculations and results
if G2_dBi > G1_dBi:
    print 'Second antenna with gain=4.5dBd has higher gain'
else:
    print 'First antenna with gain=5.3dBi has higher gain '

Second antenna with gain=4.5dBd has higher gain

Example 4 : pg 571

In [4]:
#calculate the gain
#page no 571
#prob no. 16.4
#given
from math import log10
#A dipole antenna with efficency=85% given
n=0.85;D_dBi=2.14;#Directivity in dBi
#calculations
#Determination of gain in dB
D=10**(D_dBi/10);
G=D*n;#Determination of gain
G_dBi=10*log10(G);#Converting to dBi
#results
print 'The gain is',round(G_dBi,3),'dBi'

The gain is 1.434 dBi

Example 6 : pg 573

In [8]:
#calculate the EIRP in dBm 
#page no 573
#prob no. 16.6
#given
from math import log10
#ERP of Tx statn=17W
ERP=17.;
#calculations
#Determnation of EIRP
ERP_dBm=10*log10(ERP/10**-3);#Converting ERP in dBm
EIRP_dBm=ERP_dBm+2.14;#Converting ERP in EIRP
#results
print 'EIRP in dBm is expressed as',round(EIRP_dBm,3),'dBm'

EIRP in dBm is expressed as 44.444 dBm

Example 7 : pg 582

In [9]:
#calculate the beam width, optimum diameter, spacing, total length 
#page no 582
#prob no. 16.7
#given
from math import pi, log10, sqrt
#a helial antenna with 8 turns with freq=1.2GHz given
N=8.;f=1.2*10**9;c=3*10**8;#Speed of light in m/s
#calculations and results
#a)Determination of optimum diameter of antenna
wav=c/f;
D=wav/pi;
print 'a)1.The optimum diameter for antenna is',D,'m'
S=wav/4;#Determination of spacing for the antenna
print 'a)2.The spacing for the antenna',S,'m'
L=N*S;#Determination of total length of an antenna\
print 'a)3.The total length of an antenna is',L,'m'
#b)Determination of antenna gain in dBi
G=(15*N*S*(pi*D)**2)/(wav**3);
G_dBi=10*log10(G);#Converting in dBi
print 'b)The antenna gain is',G_dBi,'dBi'
#c)determination of beamwidth
theta=((52*wav)/(pi*D))*sqrt(wav/(N*S));
print 'The beamwidth is',theta,'degree'

a)1.The optimum diameter for antenna is 0.0795774715459 m
a)2.The spacing for the antenna 0.0625 m
a)3.The total length of an antenna is 0.5 m
b)The antenna gain is 14.7712125472 dBi
The beamwidth is 36.7695526217 degree

Example 8 : pg 590

In [10]:
#calculate the length and spacing 
#page no 590
#prob no. 16.8
from math import pi,tan
#Design of log periodic antenna to cover freq 100-300MHz & t=0.7,a=30 degree
t=0.7;a=30;
#For good performance converting range to 90MHz to 320MHz
f2=90.;f1=320.;
#Determination of lengths of elements
L1=142.5/f1;#For freq of 320MHz
L2=L1/t;L3=L2/t;L4=L3/t;L5=L4/t;
print 'The length of elements are'
print 'L5=',L5,'m ','L4=',L4,'m ','L3=',L3,'m ','L2=',L2,'m ','L1=',L1,'m '
#Determination of spacing betn elements
D1=L1/(2*tan(a*pi/180./2.));
D2=D1/t;D3=D2/t;D4=D3/t;D5=D4/t;
print 'The spacing between elements are'
print 'D5=',D5,'m','D4=',D4,'m ','D3=',D3,'m ','D2=',D2,'m ','D1=',D1,'m '

The length of elements are
L5= 1.85469596002 m  L4= 1.29828717201 m  L3= 0.908801020408 m  L2= 0.636160714286 m  L1= 0.4453125 m 
The spacing between elements are
D5= 3.46090977769 m D4= 2.42263684438 m  D3= 1.69584579107 m  D2= 1.18709205375 m  D1= 0.830964437623 m

Example 9 : pg 598

In [11]:
#calculate the gain and beamwidth
#page no 598
#prob no. 16.9
from math import pi, log10
#given
#A parabolic antenna with diameter=3m & efficiency=60% operate at 4GHz
D=3.;n=0.6;f=4.*10**9;c=3.*10**8;#Spped of light
#Determination of gain & beamwidth
#calculations and results
wav=c/f;#Determination of free space wavelength
theta=(70.*wav)/D;#Calculaing beamwidth
print 'The beamwidth is',theta,'degree'
G=(n*(pi**2)*(D**2))/wav**2;#Calculating gain
#Converting gain in dBi
G_dBi=10*log10(G);
print 'The gain is',round(G_dBi,3),'dBi'

The beamwidth is 1.75 degree
The gain is 39.766 dBi