The frequency of oscillation in a backward wave oscillator can be changed by

Since the two wire radiators are at 90° to each other, they have to be excited 90° out of phase with each other.

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.

Artificial transmission lines have many applications. One of the applications is to simulate an actual line in the laboratory.

A quarter wave line o.c. at far end behaves as a series tuned circuit.

It is somewhat similar to TWT and can deliver microwave power over a wide frequency band.

It has an electron gun and a helix structure. However the interaction between electron beam and RF wave is different than in TWT.

The growing RF wave travels in opposite direction to the electron beam.

The frequency of wave can be changed by changing the voltage which controls the beam velocity.

Moreover the amplitude of oscillations can be decreased continuously to zero by changing the beam current.

It features are:

1. Frequency range - 1 GHz to 1000 GHz.

2. Power output - 10 mV to 150 mW (continuous wave) 250kW (pulsed).

It is used as signal source in transmitters and instruments.

Matched load means no reflections.

In a travelling wave both x and t increase simultaneously so that a constant phase point moves in the direction of positive (or negative) x.

Shunt conductance can be neglected in most of calculations.

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

E_x = ± Z_TM H_y

E_y = ± Z_TM H_x

where E₀ is the amplitude of the wave.

The expressions for ?, ?_c, f_c, ?_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.