JNTU III B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008
( Common to Electronics & Communication Engineering and Electronics &
1. (a) A rectangular guide of inner dimensions 2.5 cm × 1.2 cm is to propagate energy in TE10 mode. Calculate the cut off frequency. If the frequency of signal is 1.2 times this cut off frequency, compute the guide wave length, phase velocity and wave impedance. Derive the relations used.
(b) Prove that for any wave guide.
1_2 = 1_g2 + 1_c2
2. (a) Derive the Q for TM111 mode of rectangular cavity assuming lossy conducting
walls and lossless dielectric.
(b) The quality factor of micro strip line is reciprocal of the dielectric loss tangent ? and is relatively constant with frequency. Prove this statement.
3. (a) Derive the expression for the coupling and directivity of a two hole directional
(b) There are two identical directional couplers connected back to back to sample
incident and reflected powers. The outputs of the couplers are 12 mw and 0.12mw respectively. What is the VSWR in the guide.
4. (a) Explain the principle of operation of an isolator? What is the significance of
using isolator in microwave circuits.
(b) Why are S – parameters used at microwave frequencies explain. Give the properties of S -parameters.
5. (a) What are the limitations of conventional tubes at microwave frequencies. Describe the construction & working of two cavity klystron amplifier.
(b) A reflex klystron having an accelerated field of 300v oscillates at a frequency of
10GHZ with a retarding field of 500v. If its cavity is retured to 9GHZ. What must be the new value of retarding field fro oscillations in the same mode to take place?
6. (a) Draw a labeled schematic diagram of Helix TWT & show that output power
gain of TWT is G = -9.54 + 47.3 NC db
(b) A TWT has the following parameters Vo=3KV , Io = 4mA, f = 10 GHz, Zo= 30 & N=50. Calculate the
i. Gain parameter
ii. Power gain in db.
7. (a) Derive the equation for power output & efficiency of IMPATT diode.
(b) Determine the conductivity of n-type Ga As Gunn diode if
Electron density n = 1018 cm?3
Electron density at lower valley nl = 1010 cm?3
Electron density at upper valley nu = 108 cm?3
Temperature T = 300oK.
8. (a) The cablibrated power from a generator as read at the power meter is 25mw.
When a 3dB attenuator with a VSWR of 1.3/1 is inserted between the generator and detector what value should the power meter read.
(b) Compare the power ratio and RF substitution methods of measuring attenuation provided by the microwave component.