Which one of the following is a transferred electron device?

Cassegrain feed is used with a parabolic reflector to:

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:

Consider the following statements:
In a magic Tee,
1. Collinear arms are isolated from each other.
2. One of the collinear arms is isolated from E-arm.
3. The collinear arms is isolated from H-arm.
4. E-arm and H-arm are isolated from each other of these statements, correct answers are: