EP603 Microwave Devices

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1 EP603 Microwave Devices TOPIC 3 MICROWAVE MEASUREMENTS

2 Lesson Learning outcomes 1. Draw the block diagram of instrument in microwave testing 2. Explain the function of each block and overall measurement process: - Frequency measurement wave meter - VSWR measurement slotted line - Power measurement - Bolometer/ Crystal Rectifier

3 Microwave Test Equipment Power Meter Microwave sources Isolator Altenuator Wave Meter Directional Coupler Terminator Tuner Slotted Section VSWR

4 Uwave source Block Function a generator or a device that produce carrier wave in microwave spectrum. Isolator To allow the wave to pass by in one direction only. The wave which travel in opposite direction will be attenuated. The purpose is to block the reflected wave produced in the system travel back to the generator/source. Attenuator To control the power level in the system to a suitable value. Wave meter To measure the frequency in the system Directional Coupler To divide the signal with certain ratio to Power meter for power measurement

5 The function.. Power meter To measure power in the system Slotted Line Used with Diode Detector to sampled the strength of the signal and sent to VSWR display. VSWR display To show the value of VSWR generated in the system Tuner To allow the correct frequency exist in the system Termination To terminate the system with match or short circuit or open circuit or complex load.

6 The types of measurement Frequency Measurement - Wave meter Power Measurement Directional coupler Measurement of VSWR Slotted section.

7 # 1 FREQUENCY MEASUREMENT Identify the value of production of the correct frequency. Measurement Methods Electromecanikal Slotted line / resonant cavities Electronic Frequency Beating Technique

8 Structure of wave meter with resonant cavity

9 Electromechanical method Using a resonant cavity is a hollow cylinder. The movement in the plunger => changes in the volume of voids =>change in the frequency of the duct cavity. Plunger displacement is measured by a micrometer. Result from the macro-meters will be used in the calibration frequency chart to get the frequency value in Hertz.

10 Electronic Methods Zero Beating Technique. A constant frequency, for example 10MHz will amplified and will be connected to the harmonic generator to produce 'Frequency Comb of standards. " Has a high accuracy. When the signal had been amplified and connected to the harmonic generator, the waveform will have distortion (harmonic distortion). Harmonic distortion of the spectrum that will generate harmonics from the original frequency.

11 #2 Power Measurement Measurement of the high level (> 1W), using a calorie meter. Measurement of medium level ( 1W), using coupling direction, attenuation and power meters. Measurement of low levels ( 10mW), the sensitivity of heating energy.

12 Measurement of low-level Bolometer divided into: -Beratter -Thermistor Using a bridge circuit with one resistor is Bolometer / Termokupel

13 BARATTER Ω THERMISTOR Ω W Conductor with a coefficient Temperature resistance when it is positive is it absorbing power, the temperature will increase and the resistance increases. W Conductor with a coefficient Temperature resistance is negative when it absorbing power, the temperature will increase and resistance decreases. Smooth strings Streamer Changes in linear barriers Semi-solid materials More durable Resistance change is not linear

14 Wheatstone bridge circuit Galvanometer / = 0, t hen Rs can be adjusted. Unbalanced currents will be measured in terms of power measurement

15 Measurement of high-power High power normally in radar system. Tools = calorimeter wattmeter. power dissipated as heat and increase of temperature will measured.

16 Measuerement of VSWR The measure voltage in line not match. (load resistance not same with a input resistence) Have a reflaction.

17 Reversal Voltage will cause a change the voltage value along the line. V Vmax Vmin t

18 VSWR V max V min VSWR = Vmax / Vmin VSWR = If fully reflection. VSWR = 1,. where no reflection occurs.

19 Measuerement of VSWR Detector Meter Source signal Pad Slotted Line Tool in testing Matched load

20 Microwave Measurement Grede There were 2 grade measurements in the microwave. Grade 1: Measurements for get values (data) that has the error <5%. Grade 2: Measurement only to see the microwave act.

21 quiz?

22 WHAT IS GRAPHIC EQUIPMENT PREVIOUSLY BEEN INTRODUCED?

23 Lesson Learning Outcomes

24 SMITH CHART Is a graphical tool for calculating the transmission line. It was proposed by PH Smith, and known as the polar impedance diagram. It includes information about the impedance, reflection coefficient and VSWR on the microwave circuit.

25 SMITH chart A network analyzer (HP 8720A) showing a Smith chart.

26 Smith circle base VSWR circle base Barrier circle

27 Smith interest Plot real value, imagine and complex something load. Get VSWR value. To find input impedance in which interior point transmission line whether with short circuit termination or open circuit.

28 Smith Chart Scale Scale A Representing resistance to flow where value conductivity = 0, located on the left.

29 Smith Chart Scale. Scale B - The susceptance place on the circle

30 Smith Chart Scale Scale C - The scale represents the greatest longdistance wave has normalized. The distance along the transmission lines can be shown by using this scale. - Distance to the load is counter-clockwise according to the distance and the generator is clockwise.

31 Scale D - Constant Resistance & Conductance - Used to put the complex impedance & help solve the problem using the smith chart. Smith Chart Scale

32 Impedance Plot To plot the complex impedance as Z = R jx then: - Normalize the first part of the real & imaginary Put the real value of the normalized on the horizontal line (scale A). Put the imagenary value that has been normalized to the constant curve reactance. (Scale D). Crosses between (iii) and (iv) is impedance place that has been normalized.

33 Example 1 ZL Zo If one lines terminated with load impedance ZL =200+j300 and the characteristic impedance value is 100, plot above CS. 200 j

34 ZL Zo 200 j

35 VSWR Plot 1. Normalize the load and plot on the Smith Chart. 2. Make a circle with a radius of 1.0 centered on the point of touching the point was made earlier. 3. Intersection of the circle with value scale A (right side) is VSWR value.

36 Example 2 Find the value of the VSWR for transmission line with load impedance ZL = 50 - j 100. Characteristic impedance of the line is 75

37 Y plot, with Z given by 1. Normalize the load and plot on the Smith Chart. 2. Plot the VSWR. 3. Draw a line from a point 1.0 until it touches circle VSWR on the part opposite direction. 4. This intersection indicates value that had been normalized.

38 Example 3 By using the Smith chart, calculate the value of a move YL from a impedance value ZL = 50 + j100. Characteristic impedance of the transmission line is 50.

39 Search input impedance in transmission line that terminated by a short open circuit.

40 Open Circuit & Short Circuit On the Smith Chart, the position of short circuit (resistance = 0) located on the left (Point A) and the position of an open circuit line (resistivity = ), is located on the right (Point B). D1

41 To determine the distance from the scale C to a point on a transmission line with impedance input + jx Normalized impedance value Plot that point in scale that outermost. From 1.0 points, draw a line that touches the point + jx Read the distance. To convert the reading in units of cm, the wavelength of a determined frequency must be known.

42 EXAMPLE 4 Find the length of transmission line terminated by a short circuit. The desired input impedance is j75 with 7Ghz operating frequency, characteristic impedance is 50.

43 Solution Normalized impedance input zl = j75/50 = j 1.5 so; D1 = = (4.29) = 0.669cm Make a straight line from 1.0 to point j1.5 With value λ = c/f = 3x10 8 / 7x10 9 = 4.29 cm

44 EXAMPLE 5 Find the input impedance at a distance of 15cm from an open circuit with characteristic impedance 50 dan frequency = 400 MHz.

45 Penyelesaian λ = c/f = 3x10 8 / 400 x10 6 = 0.75 m = 75 cm 1 λ = 75 cm? λ = 15 cm :. 15/75 = 0.2 λ Since the open circuit starting with the 0.25 λ, then; D2 = 0.25 λ λ = 0.45 λ Make a straight line from point D2 to the center of the circle and read the normalized impedance. zl = ZL /Zo = - j0.32 :. ZL = - j0.32 (50) = - j16

46 THE END READY FOR THE QUIZ 3

Dhanalakshmi College of Engineering Department of ECE EC6701 RF and Microwave Engineering Unit 5 Microwave Measurements Part A

Dhanalakshmi College of Engineering Department of ECE EC6701 RF and Microwave Engineering Unit 5 Microwave Measurements Part A 1. What is the principle by which high power measurements could be done by