Microwave Communication - Section 1

 = coulomb |sec|m² = current density

In a klystron the resonant structure limits the bandwidth.

A TWT is a broadband device. Its main components are electron gun (to produce the electron beam) and a structure supporting the slow electromagnetic wave.

The velocity of wave propagation along the helix structure is less than velocity of light.

The beam and wave travel along the structure at the same speed.

Thus interaction occurs between beam and wave and the beam delivers energy to the RF wave.

Therefore the signal gets strengthened and amplified output is delivered at the other end of tube.

The main features of TWT are :

1. Frequency range - 0.5 GHz to 90 GHz

2. Power output - 5 mW at low frequencies(less than 20 GHz) 250 kW (continuous wave) at 3 GHz 10 MW (pulsed) at 3 GHz

3. Efficiency - about 5 to 20%

4. Noise - about 5 dB for low power TWT 25 dB for high power TWT

TWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc.

H_z = 0

where E₀ is the amplitude of the wave.

The expressions for β, λ_c, f_c, λ_g, a are the same as for TE waves.

For TM wave the lowest cut off frequency in rectangular wave guide is for TM₁₁ mode.

If , the cutoff frequency for TM₁₁ mode is about 12% more than that for TE₂₀ mode.

Since all ports matched, input SWR = 1. No power is reflected and P_in = P₄ = 1 W.

This power splits between ports 1 and 2. Therefore P₁ = P₂ = 0.5 Ω, P₃ = 0.

and is independent of line lengt