1. Permit pin-point focusing
2. Reduce the bulk of the lens
3. Increase the bandwidth of the lense
4. Correct the curvature of the wave front from a horn that is too short
Reduce the bulk of the lens
1. Allow the feed to be placed at a convenient
2. Allow the use of a small sized reflector
3. Increase the antenna directivity
4. None of the above
Allow the feed to be placed at a convenient
1. 100 km
2. 150 km
3. 200 km
4. 400 km
400 km
1. 250 km to 400 km
2. 150 km to 250 km
3. 50 km to 150 km
4. 15 km to 50 km
250 km to 400 km
1. Of low power requirement
2. They are least prone to distortion
3. They penetrate the ionosphere easily
4. The transmission antennas are of convenient
They penetrate the ionosphere easily
1. Space waves
2. Surface waves
3. Sky waves
4. Ground waves
Space waves
1. Diurnal variation
2. Seasonal variation
3. Ionospheric variation
4. None of the above
Ionospheric variation
1. More than unity
2. Less than unity
3. Equal to unit
4. Either more or less than unity depending on the electron concentration
Less than unity
1. High-frequencies
2. Ultra-high frequencies
3. Microwave frequencies
4. Optical frequencies
High-frequencies
1. 160 km
2. 140 km
3. 120 km
4. 60 km
160 km