1. An amplifier with a gain of 12 dB, a bandwidth of 150 MHz. A Y-factor method is applied to obtain the noise powers, which are N1 = -70 dBm for T1 = 290 K and N2 = – 73 dBm for T2 = 77 K. This amplifier feeds a receiver with a noise temperature of 850 K. (a) Find the noise figure of the overall system; (b) if the input S/N is 30 dB, what are the S/N at the input and output of the receiver? 2. A GaAs FET has the following scattering parameters at 6 GHz (Z0 = 50 ): s11 = 0.9 45o, s12 = 0.2 120o, s21 = 3.0 60o, s22 = 0.7 45o. (a) Determine the stability and plot the stability circles. (b) Design an amplifier to have a gain of 12 dB. 3. Design a dielectric resonator oscillator, using the series feedback circuit with a coupling factor of 0.1, for a wireless local area network application. This local oscillator operates at f0 = 2.4 GHz using a bipolar transistor in common emitter configuration to drive a 50 load on the base side. The S parameters are (Z0 = 50 ): s11 = 1.8 120o, s12 = 0.4 45o, s21 = 3.8 60o, s22 = 1.1 150o. (a) Calculate and plot the output stability circle, (b) Choose a proper T to determine in (>> 1). Design load and terminating networks. 4. A policeman uses a radar operating at a frequency f = 15 GHz to detect the speed of incoming cars. The detection angle is set at 30o. (a) Find the frequency band of the low frequency bandpass filter to cover speed range from 50 km/hr to 200 km/hr. (b) If a car is detected at a speed of 120 km/hr, but it is detected with an error detection angle of 20o, what should be the accurate car speed? 1
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