Question

Direction: Given question consists of two statements, one labeled as the 'Assertion (A)' and the other as 'Reason (R)'. You are to examine these two statements carefully and select the answers to these items using the codes given below.

Assertion (A): A unique property of TM_on modes in circular waveguides is a rapid decrease in attenuation with increasing frequency.

Reason (R): The circular waveguides find application in long low-loss communication.

1. Both A and R are individually true and R is the correct explanation of A
2. Both A and R are individually true but R is NOT the correct explanation of A
3. A is true but R is false
4. A is false but R is true

Answer 1

Correct Answer - Option 4 : A is false but R is true

The assertion statement is wrong as the unique feature of the circular waveguide is that some of the higher-order modes (TE0n ) have a particularly low loss.

The magnetic field distribution for these modes generates lower current levels on the walls of the waveguide than the other waveguide modes.

Therefore, a circular waveguide carrying this mode is commonly used when signals are sent over relatively long distances (microwave antennas on tall towers).

SOME IMPORTANT POINTS ABOUT CIRCULAR WAVEGUIDE-

The dominant mode of the circular waveguide is TE11.

The cutoff frequency of dominant mode is-1.841*c/2*pie*r

Where r=radius of circular waveguide

Some other applications of the circular waveguide are the following-

Circular waveguide is used in applications requiring rotation, such as for a rotary joint in a radar antenna