CHAPTER 3 ( SMITH CHART )

WEEK 7 TO 9, STUDENT HAS FINISH CHAPTER 3 WHICH IS SMITH CHART.

Define Smith Chart.

A special polar diagram containing constantresistance circles, constantreactance circles, circles of constant standing-wave ratio, and radius lines representing constant lineangle; used in solving transmission-line and waveguide problems.

THIS IS SMITH CHART

WHAT IS IN SMITH CHART?

1) NORMALIZED RESISTANCE CIRCLE

2) NORMALIZED REACTANCE CURVE

3) SCALE FOR TRANMISSION LINE DISTANCE

4) RADIALLY SCALED PARAMETER

STUDENT HAS LEARN HOW TO DRAW VSWR CIRCLE

1. Determine the normalized load impedance

2. Mark on Smith Chart the normalized load impedance

3. Use a compass to draw a circle from the center to the marked load

STUDENT ALSO KNOW  Position of load ZL from input impedance Zin and input admittance Yin AND

Position of input impedance Zin and input admittance Yin from load ZL.

THE POSITION IF IN SMITH CHART

Finding the input impedance at any distance from the load

1)The load impedance is first normalized and is located on the Smith chart. 

2)The VSWR circle is drawn for the load. 

3)A line is drawn from the 1.0 point through the load to the outer wavelength scale. 

4)To locate the input impedance on a Smith chart of the transmission line at any given distance from the load, advance in clockwise direction (TOWARDS GENERATOR) from the located point, a distance in wavelength equal to the distance to the new location on the transmission line.

STUDENT ALSO LEARN HOW TO FIND THE Position of Vmaximum and Vminimum of standing wave

STUDENT ALSO LEARN ABOUT SINGLE STUB

# impedance of the transmission line, there are no reflections back down the line; mismatched loads cause reflections back down the line. If the waves are time varying voltages and currents, standing waves are set up. 

#These resonance conditions can cause large voltage buildup, resulting in insulation breakdown and damage to the line and transmitting source. 

#Single stub impedance matching Impedance matching can be achieved by inserting another transmission line (stub) as shown in the diagram below :

# There are two design parameters for single stub matching: 

                   -The location of the stub with reference to the load dstub 

                   -The length of the stub line Lstub 

#Any load impedance can be matched to the line by using single stub technique. The drawback of this approach is that if the load is changed, the location of insertion may have to be moved. 

#The transmission line realizing the stub is normally terminated by a short or by an open circuit. In many cases it is also convenient to select the same characteristic impedance used for the main line, although this is not necessary. The choice of open or shorted stub may depend in practice on a number of factors. 

#A short circuited stub is less prone to leakage of electromagnetic radiation and is somewhat easier to realize. On the other hand, an open circuited stub may be more practical for certain types of transmission lines, for example microstrips where one would have to drill the insulating substrate to short circuit the two conductors of the line.

AFTER FINISH THE CHAPTER 3, STUDENT DEP4A HAS TRY A FEW QUESTIONS ABOUT SMITH CHART