Consider the following applications

1. Switch
2. Attenuator
3. Phase shifter
4. Oscillator

In which of the above can a PIN diode be used?

A PIN diode has an intrinsic (i) layer between p and n layers. When reverse bias is applied depletion layers are formed at p-i and i-n junctions.

The effective/width of depletion layer increases by the width of i layer. It can be used as a voltage controlled attenuator.

At high frequencies the rectification effect ceases and impedance of diode is effectively that of i layer.

This impedance varies with the applied bias. It is used in high frequency switching circuits, limiters, modulators etc.

The quantities required to be measured in microwave circuits are frequency, power and impedance.

Microwave frequency measurement is done by slotted line, resonant cavities and transfer oscillator.

Microwave power measurement uses bolometers and micromave power meters.

A self balancing bridge working on the principle of power substitution is commomly used.

Microwave impedance measurement is done by measurement of reflection coefficient and VSWR.

A slotted line and probe is a basic tool for these measurements.' Network analyser enables rapid impedance measurement over a broad frequency range.

Power handling capacity ? (voltage)² and is inversely proportional to f² max.

A balun gives 4 : 1 impedance transformation.

Hollow metallic enclosures exhibit resonance behaviour when excited by electromagnetic field.

These enclosures are called cavity resonators.

Time required for microwave cooking is much less than the time required for conventional cooking.

Coplanar arms are decoupled.

Z₀₁ provides series inductances and teflon filled low impedance line Z₀₂ provides shunt capacitance.

1 x 10^-6 x 1000 = 0.001.