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Microwave Engineering Lab Questions​
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Date 13/10/2025
1.​ Define VSWR.
VSWR (voltage standing wave ratio) is the ratio of the maximum field minimum field strength of standing
waves.
2.​ What is reflection coefficient?
It is the ratio of reflected voltage to incident voltage on standing waves.
3.​ Write the relation between VSWR and reflection coefficient.
S=(1+K)/(1-K) Where S-standing wave ratio; K - Reflection coefficient.
4.​ Write the values of VSWR for open circuit, short circuit & matched load.
Open/closed circuit: VSWR = ∞
Matched load: VSWR = 1
5.​ What is a matched load?
A matched load is a load whose impedance is exactly equal to the characteristic impedance of the
transmission line to which it is connected.
For instance, connecting a 50 Ω load to a 50 Ω line ensures the signal travels without reflection.
6.​ What are the main components of a microwave bench setup and why do we tune the microwave
bench?
Microwave source ( klystron), isolator, attenuator, slotted line, detector mount, and VSWR meter.
Benches are tuned so that they minimize reflections and maximize detected power.
When this condition is met, maximum power is transferred from the transmission line to the load, and no
reflections occur along the line.
7.​ What is the purpose of the Klystron Power Supply?
It provides the required DC voltages to operate the reflex klystron tube and generate microwave
oscillations.
8.​ Why is the reflector voltage negative?
It repels the electrons back toward the cavity, enabling electron bunching and sustained oscillations.
9.​ What is a Gunn diode and why is it used?
A Gunn diode is a bulk semiconductor device (usually made of Gallium Arsenide, GaAs) that exhibits
negative differential resistance when a certain threshold voltage is applied.
It is used to generate microwave frequencies. When properly biased, high-field domains are formed inside
the diode that travel through the material due to transit-time effects, producing continuous microwave
oscillations.
10.​ How do you determine the wavelength of the microwave in the setup?
By measuring the distance between two successive minima or maxima in the standing wave pattern on the
slotted line.
11.​ What is a circulator and how does it work?
A non-reciprocal three(or four)-port device that routes power from port 1→2, 2→3, 3→1 (in that order).
Uses ferrite and magnetic biasing for non-reciprocity.
12.​ Define insertion loss and isolation.
Insertion loss — loss of forward power (dB) when device is inserted. Isolation — how much unwanted
reverse power is attenuated (dB).