Download Prelab 3 - The College of Engineering at the University of Utah

Spencer Streeter
ECE 3300
Prelab 3: Monopole Antenna and Single Stub Matching Network
1. Read this lab.
2. Design a quarter wave monopole in air (h= λ/4) at 440 MHz. Length = 17.05 cm
c
3 10 8 m s
 
 0.6818 m
f 440 10 8 Hz
 0.6818 m 102 cm
h 
 17.0455 cm
4
4 1 m


3. Design a single stub matching circuit for a quarter wave monopole antenna. The imaginary part of the antenna
has been adjusted to “zero” by tuning the antenna, so the input impedance is approximately Zant=36.5 ohms. This is
ZL of the transmission line. The matching circuit should use a parallel open circuit stub. The characteristic
impedance of both the transmission line and the stub is 50Ω.
ZL  36.5 
Z01  50 
Z02  50 



1.
Normalize Z L  znL
(plot point on “Smith chart”).
Z L RL  jX L 

Z0
Z0

znL 

1
UNIVERSITY
OF UTAH DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING

50 S. Central Campus Dr | Salt Lake City, UT 84112-9206 | Phone: (801) 581-6941 | Fax: (801) 581-5281 | www.ece.utah.edu
Spencer Streeter
ECE 3300
Prelab 3: Monopole Antenna and Single Stub Matching Network
znL 
2.


3.

36.5  j0 
 0.73  j0
50 
Convert to normalized admittance because evaluating parallel stub matching.
(draw line from center past intersecting point until the line intersects with the border of the Smith chart).
1
znL
y nL 
1
 1.37  j0
 point of a  0.25
 note also its extension to WTG
0.73  j0


Other equivalences for


 Translating to WTG we obtain the wavelength
b  0.363
air 

wire 
c
eff f
(m)
d  aird  0.6818 m0.113  7.70 cm (air)

d  wire d  0.4054 m0.113  5.27 cm (wire)
4.


c
(m)
f
(multiply by Smith Chart WTG wavelength fractions.)



d  b  a  0.363 .25  0.113 m


y nL are as follows :
This step requires the use of the Smith Chart involves using the Smith Chart (I don’t know another way)
For matching, move WTG a distance “d” such y nd has a real part equal to 1 corresponding to 2 solutions.

Find the point where the magnitude of y nL intersects the “matching circle” at 1.0. This is y nd which is of
the form ynd 1 j(some number).
ynd 1 j0.316

We want to obtain
ynin  yns  ynd 1 j0 which we can obtain by taking y nsof opposite sign…
yns  j (some number)
yns   j0.316

5.

Then we find the difference in wavelengths from “open circuit” for admittance to
is…
yns   j0.316 which
l  b  a  0.487 0.0  0.487
l  airl  0.6818 m0.0487 = 3.32 cm

(R  jX)
1 
, Z 0 G  jB, 2
1 
R  X 2 
y nL 

l  wire l  0.4054 m0.0487  1.974 cm
 4. Determine the width of a 50 ohm microstripline. Use Txline (available on the LAB website, this is NOT the same

2
UNIVERSITY OF UTAH DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING
50 S. Central Campus Dr | Salt Lake City, UT 84112-9206 | Phone: (801) 581-6941 | Fax: (801) 581-5281 | www.ece.utah.edu
Spencer Streeter
ECE 3300
Prelab 3: Monopole Antenna and Single Stub Matching Network
software as TLine from the lecture site) to compute the dimensions of the microstrip
using Radio Shack Laminate. The electrical length is not important, since the length of the stub has already been
calculated using the Smith Chart.
Radio Shack Laminate Properties
Dielectric constant 3.6
Loss tangent 0.005
Thickness of the substrate 1.6 mm
Thickness of the metal layer 0.7 mils
Figure 2 - Screen Capture of TXline values
Matlab Code
% Name : Spencer Streeter
% Course : ECE 3300 Lab
% Date : September 29, 2006
% Lab
: Prelab 3
% File(s) : prelab3.m
% Description
% Creates a polar plot of the radiation pattern for a monopole antenna
% Begin
- ---------- - ---------- - ---------- -
clear all;
clc;
% Variable Glossary - ---------- - ---------- - ---------- % pwr = power(theta)
clear all;
clc;
theta=0:.1:2*pi;
pwr=[cos((pi/2).*cos(theta))./sin(theta)].^2;
polar(theta,pwr);
title_top=('Polar plot of the "radiation pattern" for a monopole antenna');
title(title_top);
3
UNIVERSITY OF UTAH DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING
50 S. Central Campus Dr | Salt Lake City, UT 84112-9206 | Phone: (801) 581-6941 | Fax: (801) 581-5281 | www.ece.utah.edu
Spencer Streeter
ECE 3300
Prelab 3: Monopole Antenna and Single Stub Matching Network
filename='figure1';
print( '-dpng', filename);
end;
% End
- ---------- - ---------- - ---------- -
4
UNIVERSITY OF UTAH DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING
50 S. Central Campus Dr | Salt Lake City, UT 84112-9206 | Phone: (801) 581-6941 | Fax: (801) 581-5281 | www.ece.utah.edu