Microwave Transistors Quiz - Microwave Engineering

1 Which semiconductor material is most commonly used for high-frequency microwave transistors due to its high electron mobility?

Silicon (Si) Gallium Arsenide (GaAs) Germanium (Ge) Silicon Carbide (SiC)

2 In a GaAs MESFET, what does the "M" in MESFET stand for?

Metal Modulated Multi-channel Microwave

3 What is the primary advantage of HEMT (High Electron Mobility Transistor) over conventional MESFETs?

Lower cost of manufacturing Higher electron mobility due to heterojunction structure Simpler fabrication process Higher breakdown voltage only

4 Calculate the maximum available gain (MAG) if |S21| = 3.5 and |S12| = 0.15 (assuming unilateral approximation is not valid but using the simplified MAG formula).

7.35 dB 14.7 dB 17.4 dB 23.4 dB

5 Which S-parameter is primarily responsible for determining the input reflection coefficient in a transistor amplifier?

S11 S12 S21 S22

6 True or False: In a microwave bipolar transistor, the base thickness must be very small (typically less than 1 μm) to minimize transit time and maximize fT.

True False

7 What is the typical noise figure (NF) range for a low-noise GaAs FET amplifier at X-band frequencies?

0.5 - 1.0 dB 1.5 - 3.0 dB 5.0 - 8.0 dB 10.0 - 15.0 dB

8 For a microwave power transistor, which parameter is most critical for determining the power-added efficiency (PAE)?

Current gain β (hFE) Knee voltage and breakdown voltage Gate capacitance only Substrate resistivity

9 A transistor has S21 = 6∠120° and S12 = 0.2∠-45°. Calculate the Rollett stability factor K if |Δ| = 0.3 (where Δ = S11S22 - S12S21).

0.85 1.15 1.52 2.10

10 Which of the following is the primary limitation of silicon bipolar junction transistors (BJTs) at microwave frequencies above 4 GHz?

Excessive base resistance High collector capacitance and base transit time Low emitter injection efficiency Thermal runaway only

11 In a microwave transistor amplifier design, what condition must be satisfied for unconditional stability?

K > 1 and |Δ| < 1 only K > 1 and |Δ| < 1 and B1 > 0 (where B1 = 1 + |S11|² - |S22|² - |Δ|²) |S11| < 1 and |S22| < 1 only S21 > 10 dB and S12 < -20 dB

12 A GaN HEMT is preferred over GaAs FET for high-power microwave applications primarily because:

It has lower noise figure It has higher breakdown voltage and power density It is cheaper to manufacture It has higher electron mobility at room temperature

🔬 Microwave Transistors Quiz