A PIN diode can be used in which of the following microwave applications? RF switch Attenuator Phase shifter Oscillator

Introduction / Context:
Passive, current-controlled components are invaluable in microwave front ends. The PIN diode is one such device used for reconfigurable RF functions without active oscillation.

Given Data / Assumptions:

• Applications listed: switch, attenuator, phase shifter, oscillator.
• We must decide where a PIN diode is functionally appropriate.

Concept / Approach:

PIN diodes act as variable resistors at RF controlled by DC current. This property enables series/shunt switching, attenuator pads (e.g., Pi/T networks), and phase shifters (e.g., switched-line or loaded-line implementations). They do not provide negative resistance and therefore are not used as the active element in oscillators.

Step-by-Step Solution:

Verification / Alternative check:

Common catalog parts are marketed specifically as PIN-diode switches, step attenuators, and phase shifters; oscillators rely on devices like Gunn, IMPATT, BJT, FET, or tunnel diodes.

Why Other Options Are Wrong:

• Including item 4 (oscillator): Mischaracterizes the role of a PIN diode.
• Omitting item 3: Phase control is a standard use case.

Common Pitfalls:

Assuming any diode can oscillate; overlooking biasing and linearity implications in attenuator design.

Final Answer:

1, 2 and 3 only