Question Bank DEPARTMENT OF ELECTRONICS AND COMMUNICATION SUBJECT- MICROWAVE ENGINEERING(EEC-603) Unit-III 1. What are the high frequency limitations of conventional tubes? Explain clearly. 2. Explain with suitable sketch the operation of two-cavity Klystron amplifier. explain the concept of velocity and current modulations. 3. Explain how velocity modulation creates density modulation in a Klystron amplifier. How does the reflex Klystron differ from amplifier Klystron? 4. Explain with schematic diagram the operation of Reflex Klystron Oscillator. Draw Applegate diagram for the Reflex Klystron Oscillator. 5. Obtain relation between repeller voltage and frequency of operation of Reflex Klystron Oscillator.. 6. What are modes in Reflex Klystron oscillator? Sketch output power and frequency of Klystron versus repeller voltage for Reflex Klystron. 7. Derive an expression for the efficiency of the Klystron amplifier. 8. A two-cavity Klystron amplifier has the following parameters: Vo = 1000V, Ro = 40 K ohms, Io = 25 ma, f = 3 GHz. Gap spacing in either cavity (d) = 1 mm. Spacing between the two cavities (L) = 4 cms. Effective shunt impedance, excluding beam loading (Rsh) = 3 p K ohms. Find (i) The input gap voltage to give maximum voltage (V2) (ii) The voltage gain, neglecting the beam loading in the output cavity, (iii) The efficiency of the amplifier, neglecting beam loading. (Ans: 96.5V, 8.595, 46.2%) 9. A two-cavity Klystron operates at 4.5GHz. The dc beam voltage is 10KV. Cavity gap spacing is 2mm. For a given input, the magnitude of the gap voltage is 100V. Calculate the time the electrons are in the gap, the transit angle, and the range of velocities of electrons as they leave the gap region. (Ans. 33.7 psec, 0.95 rad, 0.598x108m/s and 0.588x108 m/s). 10. Describe with suitable diagram the following Microwave (i) Travelling wave tube (TWT) (ii) Magnetron. 11. A Reflex Klystron is operating at 9GHz and the mode number n is 2. Calculate the transit time in secs.
12. What is a re-entrant cavity? Explain it. In Reflex Klystron, the re-entrant cavity is resonant at 9 GHz. The half power frequencies are separated? 15 MHz from the centre frequency. Calculate the loaded Q for the cavity. 13. Describe qualitatively the mechanism of operation of a travelling wave tube amplifier. How the oscillations are prevented in practice. 14. What is a slow wave structure? Give some typical structures, which support slow waves. 15. Explain the working of a magnetron oscillator. With the help of the Rieke diagram, discuss its performance under varying load conditions. What is the typical range of efficiencies obtainable in a magnetron? 16. What is strapping of Magnetrons? Describe the techniques used in magnetrons for mode separation and for tuning its output frequency. 17. What is meant by π-mode operation in a magnetron? Describe how strapping separates the? mode from other possible modes. 18. With the aid of a sketch, explain the operation of a backward-wave oscillator (BWO). 19. A cylindrical magnetron has the following parameters. Inner radius = 0.15m Outer radius = 0.45m Magnetic flux density = 1.2 milliwebers/m2 (a) Calculate the Hull cut off voltage (b) Determine the cut off magnetic flux density of the beam voltage is 6KV. UNIT-I 1. The guide wavelength of copper rectangular waveguide with 10GHz is 1.2λ. The guide is required to transmit 500W. If (b/a)=0.5, compute Emax, current density in each wall of waveguide, attenuation. 2. If a = 3 cm and b = 1.2 cm, calculate the cutoff frequencies of the TE10, TE01, and TE11 modes, assuming that the waveguide is filled with air. Calculate the guide wavelength, the phase velocity, and the group velocity, for propagating signals having a frequency 100MHz above the TE10 mode cutoff frequency. [35%] 3. Find the field component present in TM 11 mode of propagation? 4. For a rectangular waveguide of internal dimension 7.214 X 3.404 cm operating at 5GHz, find out the propagation constant and phase velocity for TE 10 and TE 11 mode of propagation. 5. What are various types of attenuation taking place in any waveguide? 6. An air filled cylindrical waveguide of internal diameter 5cm supports TE 11 mode of propagation. If p 11 = 1.84 find out the cut-off frequency, guide wavelength and wave impedance at 3GHz.
7. Define quality factor of any resonator. Design a rectangular cavity to have resonant frequency of 10.2GHz having dimensions a = d and b = a/2. 8. Why there is non-existence of TEM modes in a rectangular waveguides? Explain 9. Write short notes on:- Microstrip lines 10. Derive the expression for field equations under TM mode in rectangular waveguide. 11. Show that the TM 01 and TM 10 mode in a rectangular waveguide do not exist. 12. A rectangular waveguide is designed to propagate the dominant mode TE 10 at a frequency of 5GHz. The cut-off frequency is 0.8 of the signal frequency. The ratio of the guide height to width is 2. The time average power flowing through the guide is 1KW. Determine the magnitude of electric and magnetic intensities in the guide and indicate where these occur in the guide. 13. An air-filled circular waveguide is to be operated at a frequency of 6GHz and is to have dimension such that f c = 0.8f for the dominant mode. Determine- A)Diameter of the guide.b)wavelength λ g and the phase velocity v g in the guide. 14. Explain how rectangular waveguide can act as a High Pass Filter. 15. Write short notes on:- Waveguide excitation 16. Write short notes on:- Dominant and degenerate modes. UNIT II 1. Explain the working of a multi-hole directional coupler and define the following terms in reference to a multi-hole directional coupler - i) Directivity ii) Coupling factor. 2. What are S-parameters? Derive S-parameter of Hybrid Tee if all the ports of the Tee are matched and power is incident from port 3 only? 3. What is Circulator? How can a four port Circulator be realized using two magic tee & a Gyrator? 4. Name the reciprocal and non-reciprocal microwave devices. Explain any one. 5. What do you mean by E-plane and H-plane Tee? Compare their propagation characteristics.
6. Write short notes on :Hybrid Ring 7. Determine the scattering parameter for a 10dB directional coupler. The directivity D = 30dB. Assume that it is lossless and the VSWR at each port is 1.0 under matched conditions. Designate the ports in the main guide as 1 and 2 while the ports in the auxiliary guide as 3 and 4. 8. What is attenuation? Name various types of attenuators. Discuss any one type. 9. Describe the principle and mechanism of operation of rotary attenuator. 10. Describe in detail the principle and working in of a rotary phase changer. 11. Write short notes on (A) Variable and fixed attenuators (B) Slotted waveguide section. 12. Derive the S-matrix for a loss-less reciprocal, 4-port directional coupler. 13. Explain Faraday rotation in ferrites. What is the expression for rotation per unit length? Mention its uses. 14. The input power to a 20dB attenuator is 100mW. Find the output power and the power absorbed by the attenuator. 15. A 5 db waveguide attenuator is specified as having a VSWR of 1.2. Assuming that it is reciprocal, find its S-parameters. 16. Determine s-parameters of a 10dB directional coupler of directional coupler of directivity 30dB.Assuming directivity of coupler loss-less VSWR at each port under matched condition is unity. UNIT-IV 1. Explain the working of the following: i) IMPATT ii) Microwave Bipolar Transistor Diode iii) Tunnel Diode. 2. What is transferred electron effect and how it is used for generation of microwave signal in Gunn diode. Compare it with tunnel diode. 3. Describe the Ridley-Watkins-Hilsum theory. 4. List and explain two performance characteristics of MASER. 5. Explain the differences between microwave transistors and transferred electron devices (TEDs).
6. Describe the following: (i) Gunn effect, (ii) high-field domain theory, (iii) Two- Valley theory. 7. Define negative differential mobility, and state the necessary conditions for transferred electron effect to occur. 8. Describe the modes of operation for Gunn diodes. 9. For a transit-time domain mode, the domain velocity is equal to the carrier drift velocity and is about 107 cm/s. Determine the drift length of the diode at a frequency of 8GHz. 10. Describe how a gunn diode can be used in an oscillator circuit. 11. Describe the following (a) Read diode 12. Explain the construction and working of IMPATT diode. 13. Explain how necessary conditions are achieved for the oscillators to take place In IMPATT Diode. 14. Describe the following: (c) TRAPATT diode (d) BARITT diode 15. An IMPATT diode has a drift length of 2?m. Calculate (i) the drift time of the carriers, and (ii) the operating frequency of the IMPATT diode. 16. Describe an oscillator circuit using IMPATT diode. UNIT 5 1. Discuss methods for measurement of low and high microwave power. 2. How VSWR of the unknown load is measured with the help of a slotted wave carriage using microwave bench set-up. Draw of the block diagram of the set-up. 3. Explain double minimum method for measurement of VSWR. 4. Explain Attenuation loss measurement. 5. Explain the various methods of measuring Microwave frequencies. 6. Explain the working principle of Microwave Power Meter. 7. Explain the various methods of measuring microwave power. 8. Explain the various methods of measuring Wavelength. 9. Explain the various methods of measuring Impedance. 10. Explain Insertion loss measurement.