Consider the following statements relating to problem of mounting the bolometer in a waveguide for microwave power measurement.
1. The first requirement in the mounting is that the mount and bolometer match the impedance of the waveguide and this can completely be solved by incorporating tuning elements.
2. The operating resistance of the bolometer, determined by the point of operation may be used as one of the variables in impedance matching and is chosen to be about equal to the characteristic impedance of the waveguide.
3. Mechanically it is very difficult to ensure that the bolometer is subjected to the microwave power and at the same time arranged so that it can be connected in low frequency bridge circuit.
4. A stub and short-circuited section behind the bolometer are introduced for cancelling reflections at frequencies different from the centre frequency and thus to increase the bandwidth of the mount. Of the above statements:

Consider the following statements associated with microstrip patch antennas:
1. The microstrip patch behaves more like a leaky cavity rather than like a radiator and thus is not is highly efficient antenna.
2. They are broadband antennas and are well suited for mm-waves.
3. They can be adapted for radiation of circularly polarised waves.
The correct ones of these statements are:

Cassegrain feed is used with a parabolic reflector to:

Which of the following statements about parabolic reflector systems are correct?
1. A front-fed shallow parabolic reflector antenna requires a feed horn with narrow radiation pattern relative to that for a deep dish
2. The noise temperature of a Cassegrain system is the highest when it looks at the horizon
3. The noise temperature of a front-fed parabolic antenna is the lowest when it looks at the Zenith
4. The sidelobe level of a parabolic reflector is highest for uniform aperture illumination
Select the correct answer using the codes given below:

The slow-wave structure of TWT is provided with an attenuator. Which one of the following is the function of such an attenuator?