CAD Antenna Designer Feed Networks and Impedance Matching Flashcards

On a Smith Chart, where is a perfect impedance match (Z = Z0) located?

Answer: At the center of the chart

A perfect impedance match corresponds to a normalized impedance of 1 + j0, which is located at the center of the Smith Chart.

What is the input impedance of a lossless transmission line terminated in a short circuit (Z_L = 0) and exactly λ/4 long?

Answer: Infinite (open circuit)

A λ/4 shorted stub presents an open circuit (infinite impedance) at its input because Z_in = Z0²/Z_L → ∞ as Z_L → 0.

What is the approximate return loss for a system with a VSWR of 2:1?

Answer: −9.5 dB

For VSWR = 2:1, Γ = (2−1)/(2+1) = 1/3, giving return loss = −20·log10(1/3) ≈ −9.5 dB.

What is a Wilkinson power divider primarily designed to achieve?

Answer: Equal power splitting with high isolation between output ports

A Wilkinson power divider splits power equally between two output ports while providing high isolation between them, with all ports matched to the system impedance.

What happens to the electrical length of a transmission line when the operating frequency is doubled?

Answer: The electrical length is doubled

Electrical length θ = βl = 2πfl/v_p is directly proportional to frequency, so doubling frequency doubles the electrical length of a fixed physical line.

In a T-junction power divider, what is the primary disadvantage compared to a Wilkinson divider?

Answer: T-junctions provide no isolation between output ports

A T-junction power divider provides no isolation between output ports, meaning signals at one output couple directly to the other, while a Wilkinson divider provides high inter-port isolation.

What does the outermost scale of a Smith Chart typically represent?

Answer: Wavelengths toward generator or toward load

The outer perimeter scale of a Smith Chart represents wavelengths toward the generator or toward the load, used to track impedance changes as a signal moves along a transmission line.