Consider the following statements:
For a square waveguide of cross section 3 cm × 3 cm it has been found
1. At 6 GHz dominant mode will propagate
2. At 4 GHz all the modes are evanescent
3. At 11 GHz only dominant modes and no higher order mode will propagate
4. At 7 GHz degenerate modes will propagate
Which of the above statements are correct?

Coupling into and out of a traveling-wave tube can be accompanied by a

A. Waveguide match

B. Cavity match

C. Direct coax-helix match

D. All of the above

When it is desired that short-range targets be clearly seen on a pulsed-radar set, it is important that the receiver and display system have

A. A long time constant

B. Low-pass filters

C. The shortest possible time

D. The restricted high-frequency response

The antenna separations (in meters) required for optimum operation of a space diversity system can be calculated from:
where R = effective earth radius (m) and L = path length (m)

A. $${\text{S}} = \frac{{2\lambda {\text{R}}}}{{\text{L}}}$$

B. $${\text{S}} = \frac{{3\lambda {\text{R}}}}{{\text{L}}}$$

C. $${\text{S}} = \frac{{\lambda {\text{R}}}}{{\text{L}}}$$

D. $${\text{S}} = \frac{{\text{L}}}{{\lambda {\text{R}}}}$$

The aquadag coating on the inside of PPI tube is used

A. To focus the beam of primary electrons

B. To shield the electron beam from unidirectional magnetic

C. As a second anode and to prevent the build-up of secondary field

D. All of these