37 questions and answers
What are cross field device? What role does the dc magnetic field play in their normal operation?
The cavity magnetron is a cross field device. Here the electric field between anode and cathode is radial whereas the magnetic field produced by a permanent magnet is axial.
What do you mean by cut off frequency of a waveguide? On what factor does the cut off frequency of a waveguide depend? Derive expression in support it.
Several modes of electromagnetic waves, corresponding to the solution of the Maxwell’s equations, propagate inside a waveguide. A given waveguide has a definite cut-off frequency for each allowed mode.
What is strip line?
Strip lines are essentially modifications of the two wire lines and coaxial line. These are basically planar transmission lines that are widely used at frequency from 100 MHz to 100 GHz.
What is microstrip line? What are the advantages and disadvantages of microstrip line? Show the electric and magnetic field lines of microstrip line explain the working principle of a microstrip antenna.
Microstrip line is an unsymmetrical strip line that is nothing but a parallel plate transmission line having dielectric substrate, the one face of which is metalized ground and the other face has a thin conducting strip of certain with 'w' and thickness 't'.
Define the quality factor. On what factors does the cut-off frequency of a rectangular waveguide depend? Derive expressions in support of your answer.
The quality factor (Q) of any resonant or anti resonant circuit is a measure of frequency selectivity and it defined by the equation
Write short note on Microwave Power Measurement
Microwave power measurement devices can be divided into two categories: devices such as detector , bolometer and tocouples, whose resistance changes with the applied power and calorimeters in which the temperature rise of a known quantity of liquid being used as a load measured.
Write short notes on
At microwave frequency, the value of L and C will be so small that they cannot be practically realizable. At microwave the cavity resonator the cavity resonator can generate oscillation like L.C tuned circuit. When a short is placed across the waveguide, the wave reflected by the short, forms a standing wave along with the incident wave.
Write short note on Magnetron Oscillator.
The magnetron cross section view and field distribution inside the magnetron are presented in Fig. 38(a) and 2 respectiv. The reason behind the development of magnetron tube was the requirement of high power during the time of 2nd world war though it was invented by Hull in 1921. The basic structure of a magnetron is a number of identical resonators arranged in a cylindrical pattern around a cylindrical cathode.
What is a slow wave structure? Why does the TWT need such a structure? Explain the beam and RF interaction in such wave tube.
The slow wave structures are a special type of circuits, used in microwave tubes to reduce the wave velocity in a certain direction so that a prolonged interaction between the electron beam and the signal wave may take place.
Compare and contrast the bunching operation in a two cavity klystron and reflex klystron.
The Klystron tube operates on the principle of velocity modulation inst of current density modulation employed in conventional tubes. The idea of Klystron Amplifier was introduced by Varian brothers in 1939. The typical diagram of two cavity Klystron amplifier is depicted in Fig. 31. It consists of electron gun, buncher cavity, catcher cavity and collector. Electrons emitted by the cathode are focused by one or more focusing electrodes kept in front of the cathode.
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