Antennas and Microwave Engineering MCQs | Page - 16

Explanation: expression for noise of a two port network considering the noise due to transmission line and other lossy components is gktb + gnadded. here, g is the gain of the system. nadded is the noise generated by the transmission line, as if it appeared at the input terminals of the line.

Explanation: noise equivalent temperature of a 2 stage cascade network is given by te1

Explanation: to evaluate the noise figure of the coupler, third port is terminated with known impedance. then the coupler becomes a two port device. since the coupler is matched, Гs=0 and Гout=s22=0. so the available gain is │s21│2. this is equal to 1/2l from the available data.

Explanation: noise equivalent temperature of the wilkinson coupler is found using the relation

Explanation: the overall noise figure of a

Explanation: in an oscillator a total of 3600 of phase shift is to be achieved in the entire circuit to produce oscillations. the transistor used in the oscillator circuit must produce a phase shift of 1800 to achieve stable oscillations. hence this condition has to be satisfied by the oscillator.

Explanation: if the resonant feedback circuit has a high q, so that there is random phase shift with frequency, the oscillator will have good frequency stability.

Explanation: quartz crystals work on the principle of piezo electric effect. when electrical energy is applied to these crystals, they vibrate in a direction perpendicular to the application of energy producing oscillations.

Explanation: a quartz crystal has an equivalent circuit such that a series lcr network is in parallel with a capacitor. a quartz crystal thus has both series and parallel resonant frequencies.

Explanation: in the plot of reactance v/s frequency of a crystal oscillator, the reactance between series resonant frequency and parallel resonant frequency is inductive. in this region between the series and parallel and series resonant frequencies, the operating point of the crystal is fixed and hence can be used as part of other circuits.