Exam 7: Microwave Network Noise Figure, Oscillator Circuits, and Negative Resistance Devices

Quartz crystal and tourmaline used in oscillators work on the principle of:

In a microwave oscillator, a load of 50+50j is connected across a negative resistance device of impedance -50-50j. Steady state oscillation is not achieved in the oscillator.

For a Wilkinson power divider of insertion loss L and the coupler is matched to the external circuitry, and then the gain of the coupler in terms of insertion loss is:

In transistor oscillators, FET and BJT are used. Instability is achieved by:

Any device with negative impedance as its characteristic property can be called:

One condition to be satisfied in an oscillator circuit so that stable oscillations are produced is:

For achieving steady state oscillation, the condition to be satisfied in terms of reflection coefficients is:

To achieve stable oscillation, Zin + ZL=0 is the only necessary and sufficient condition to be satisfied by the microwave oscillator.

Expression for over all noise figure of a mismatched amplifier is:

The equivalent circuit of a quartz crystal has LCR arm capacitance of 12nF and inductance of 3mH and parallel arm capacitance of 4nF. Parallel resonant frequency for the circuit is:

In an oscillator, the resonant feedback circuit must have must have a low Q in order to achieve stable oscillation.

Noise equivalent temperature of a 2 stage cascade network is given by:

In microwave oscillators, negative resistance transistors and diodes are used in order to generate oscillations in the circuit.

Noise equivalent temperature of Wilkinson coupler having a gain of 1/2L is given as:

Parallel resonant frequency of quartz crystal is given by:

In transistor oscillators, the requirement of a negative resistance device is satisfied using a varactor diode.

A quartz crystals equivalent circuit is a series LCR circuit and has a series resonant frequency.

Noise figure can be defined for any microwave network irrespective of any other constraints.

In the plot of reactance v/s frequency of a crystal oscillator, the reactance between series resonant frequency and parallel resonant frequency is:

In the equivalent circuit of a quartz crystal, LCR arm has an inductance of 4 mH and capacitor has a value of 4nF, then the series resonant frequency of the oscillator is: