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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 102 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 m0.113 7.70 cm (air) d wire d 0.4054 m0.113 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 m0.0487 = 3.32 cm (R jX) 1 , Z 0 G jB, 2 1 R X 2 y nL l wire l 0.4054 m0.0487 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