Transmission line
• Two or more conductors separated by some insulating medium (two-wire, coaxial, microstrip, etc.).
• Normal operating mode is the TEM or quasi-TEM mode (can support TE and TM modes but these modes are typically undesirable).
• No cutoff frequency for the TEM mode. Transmission lines can transmit signals from DC up to high frequency.
• Significant signal attenuation at high frequencies due to conductor and dielectric losses.
• Small cross-section transmission lines (like coaxial cables) can only transmit low power levels due to the relatively high fields concentrated at specific locations within the device (field levels are limited by dielectric breakdown).
• Large cross-section transmission lines (like power transmission lines) can transmit high power
levels.
Waveguide
1. Metal waveguides are typically one enclosed conductor filled with an insulating medium (rectangular, circular) while a dielectric waveguide consists of multiple dielectrics.
2.Operating modes are TE or TM modes (cannot support a TEM mode).
3. Must operate the waveguide at a frequency above the respective TE or TM mode cutoff frequency
for that mode to propagate.
4. Lower signal attenuation at high frequencies than transmission lines.
5. Metal waveguides can transmit high power levels. The fields of the propagating wave are spread
more uniformly over a larger cross-se ctional area than the small cross-section transmission line.
6. Large cross-section (low frequency) waveguides are impractical due to large size and high cost.
For more infomation please visit www.antennatutorials.com
sir,
ReplyDeletei am doing my pg project on antennas.
i wrote a program for simple broadside array..
clc;
clear all;
close all;
disp('CALCULATION OF AF WITH 3D PLOT, HPBW,FNBW,GAIN AND DIRECTIVITY FOR BROADSIDE ARRAY (BETA=0)');
N=input('ENTER THE NUMBER OF ELEMENTS: ');
d=input('ENTER THE INTER-ELEMENT SPACING IN LAMBDA: ');
%x=input('ENTER THE ODD VALUE VALUE OF SINE POWER FOR UNIDIRECTIONAL PATTERN: ');
for theta=1:360
deg2rad(theta)=theta*pi/180;
psi=pi*d*cos(deg2rad(theta));
AF(theta)=((sin(N*psi))/(N*sin(psi)));
end;
disp('DIRECTIVITY=');dir=2*N*d;disp(dir);
disp('HALF POWER BEAMWIDTH=');hpbw=2*((pi/2)-acos(1.391/(pi*N*d)));hpbw=hpbw*180/pi;disp(hpbw);
disp('FIRST-NULL BEAMWIDTH=');fnbw=2*((pi/2)-acos(1/N*d));fnbw=fnbw*180/pi;disp(fnbw);
ee=input('ENTER ELECTRIAL EFFECIENCY FOR CALCULATING GAIN: ');disp('GAIN=');gain=dir*ee;disp(gain);
theta=1:1:360;
plot(theta,AF);title('RECTANGULAR PLOT');grid on;
xlabel('THETA');ylabel('ARRAY FACTOR');
figure();
polar(deg2rad,AF);title('POLAR PLOT');
%3D PLOT CLACULATION
theta=linspace(0,2*pi,100);
phi=linspace(0,2*pi,100);
[T,P]=meshgrid(theta,phi);
PSY=2.*pi.*d.*cos(T);
AF3=(1/N.*sin(N/2.*PSY)./sin(1/2.*PSY));
[X,Y,Z]=sph2cart(T,P,AF3);
figure(3);
surfc(X,Y,Z)
title('3D PLOT');
xlabel('THETA');ylabel('PHI');zlabel('AF in db');
in the above program i am getting AF in normalised form..but i want them in decible please help me. i even tried wit db(AF) but i didnot get.
please help me.
when i check in some books the AF are in negative values.. y so?can Af be in negatives?
You are stupid.
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