Monolithic Microwave Integrated Circuit Mid-term Exam
Date : 2019/11/7 Total Gardes : 100 (Close Book : 60 ; Open Book : 40)
Part 1 : Closed Book (1.5 hr)
1. (a) Determine the S parameters of the two-port network shown in Fig. 1. (5%)
(b) Show that the impedance along a transmission line repeats itself at every λ/2
distance. That is, (2 %)
(c) Why do we generate the small signal model of an FET in a small signal
amplifier design rather than simply use the measured S-parameters? (3 %)
Fig. 1
2. (a) Please determine the K factor and |S22| are greater or smaller than 1 in Fig. 2(a)
and Fig. 2(b) if the shadow areas stand for the stable region. (5%)
(b) Two output stability circles are shown in Fig. 2(c) and Fig. 2(d). Determine the
K factor (>1 or <1) and the stable region for the load reflection coefficient. (5%)
Fig. 2(a) Fig. 2(b)
Fig. 2(c) Fig. 2(d)
3. (a) Calculate the reflection coefficient from the 100 Ω load and the VSWR in the
λ/4 line in Fig. 3. (5 %)
(b) Calculate V (0), PAVS, and the power delivered to the 100 Ω load. (5 %)
Fig. 3
4. (a) The input portion of a microwave amplifier is shown in Fig. 4. Calculate
(VSWR)IN if ΓIN = 0.545∠-77.7°. (5 %)
(b) Verify that Za is 50 Ω when Γs = ΓIN*. (5 %)
Fig. 4
5. (a) Show the noise figure for a 3-stage amplifier is given by
𝐹2 −1 𝐹3 −1
𝐹3−𝑠𝑡𝑎𝑔𝑒 = 𝐹1 + +𝐺
𝐺𝐴1 𝐴1 𝐺𝐴2
where F1, F2, F3 are the noise figure of the first, second and third stage
respectively, and GA1 and GA2 are the power gains of the first and the second stage
respectively. (5 %)
(b) There are four amplifiers with their noise figure and power gain shown in Table
1. Please choose three of them and decide the order to design a 3-stage amplifier with
the best overall noise figure. (5 %)
(c) The balanced amplifier structure is illustrated in Fig. 3. If the two amplfiers are
identical and the power gain and noise figure are G (dB) and F (dB) respectively.
Assuming the 90o couplers are lossless and all ports are matched, the overall noise
figure is (A) F-3 (B)F (C)F+3 (D)F+6 (unit : dB) and why ? (5 %)
Fig. 3
6. List three approaches to design broadband amplifiers and compare the advantages
and disadvantages of these approaches. (5%)
