37 questions and answers
Describe the operation of an ideal four port ‘directional coupler’. Define ‘Coupling’ and ‘Directivity’ in the context of a directional coupler.
The directional coupler consists of two transmission lines or waveguides coupled together by fringing fields, or in case of a waveguide, by means of a small slot in such a manner that an incident wave on one line is partly transferred to the other with particular directional properties.
What is scattering Parameters? Why is it used in microwave Network?
Any two port networks are represented by a special type of parameter by which reflection co- efficient or transmission co – efficient of any network is measured. This special type of parameter is called scattering parameter of S - parameter.
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. The permanent magnet is placed such that the magnetic lines are parallel to the vertical cathode and perpendicular to the electric field between cathode and anode.
Explain PIN diode and give its application.
The p-i-n diode is a stack of a very highly doped p+- layer, and nearly intrinsic layer i and a very highly doped n+ layer. The variable element is resistances are Ri, that is related to the i- layer thickness.
Explain the tunneling action in a tunnel diode.
Tunnel diode is specially made p-n junction device which exhibits negative resistance over part of the forward bias characteristics. It has extremely heaving doping on both sides of the junction and an abrupt transition from the p – side to the n- side.
What is bunching? Explain with proper diagram. Deduce the expression for the minimum length at which the first bunch will be formed.
Electrons in the electron beam produced in the cathode – anode region of the Klystron and accelerated by a d.c anode voltage passing through a pair of buncher grids, across which an R.F voltage exist are either accelerated or decelerated depending on the part of the cycle during which they cross the gap.
Write a short note on Bathe hole coupler.
Bathe hole coupler has a single centre offset hole in the common broad wall of the two guides and the coupling between port 1 and 3 is controlled by the offset of the hole i.e., the angle θ between the axis of the two guides determines the amount of coupling.
What is the advantage of heterojunction bipolar transistor (HBT) over BJT? Describe the advantage of operational mechanism of HBT.
The advantage of heterojunction bipolar transistor over BJT is High speed switch device and enhancement of output power.
Derive the expression for the condition for negative differential mobility of transferred effect on devices.
The generation of negative resistance in a Gunn diode is explained by the valley current. The passive electronic device absorbed or dissipated power and active devices generated the power. Power across the passive devices is I2R and across the active devices is -I2R.
Distinguish between group velocity and phase velocity.
If there is modulation in the carrier, the modulation envelope actually travels at velocity slower than that of carrier alone and of course slower than speed of light. The velocity of modulation envelope is called the group velocity Vg.
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