Backward-wave oscillator

The backward wave oscillators were demonstrated in 1951, M-type by Bernard Epsztein [1] and O-type by Rudolf Kompfner.

However, frequency-agile radars can hop frequencies fast enough to force the jammer to use barrage jamming, diluting its output power over a wide band and significantly impairing its efficiency.

The electron current is a function of the details of the gun, and is generally orders of magnitude more powerful than the input RF signal.

This basic pattern is repeated along the length of the tube so the waveguide passes across the beam several times, forming a series of S-shapes.

[2] In a traditional TWT, the speed of propagation of the signal in the induction system has to be similar to that of the electrons in the beam.

This places limits on the selection of wavelengths the device can amplify, based on the physical construction of the wires or resonant chambers.

The complex serpentine waveguide places strict limits on the bandwidth of the input signal, such that a standing wave is formed within the guide.

However, at long range the amount of energy from the original radar broadcast that reaches the aircraft is only a few watts at most, so the carcinotron can overpower them.

[2] The system was so powerful that it was found that a carcinotron operating on an aircraft would begin to be effective even before it rose above the radar horizon.

As it approached the station, the signal would also begin to appear in the antenna's sidelobes, creating further areas that were blanked out by noise.

At close range, on the order of 100 miles (160 km), the entire radar display would be completely filled with noise, rendering it useless.

Airborne radars had the advantage that they could approach the aircraft carrying the jammer, and, eventually, the huge output from their transmitter would "burn through" the jamming.

The carcinotron could still sweep through the entire band, but then it would be broadcasting on the same frequency as the radar only at random times, reducing its effectiveness.

According to Floquet's theorem (see Floquet theory), the RF electric field E(z,t) can be described at an angular frequency ω, by a sum of an infinity of "spatial or space harmonics" En where the wave number or propagation constant kn of each harmonic is expressed as z being the direction of propagation, p the pitch of the circuit and n an integer.

Two examples of slow-wave circuit characteristics are shown, in the ω-k or Brillouin diagram: A periodic structure can support both forward and backward space harmonics, which are not modes of the field, and cannot exist independently, even if a beam can be coupled to only one of them.

The sole electrode is more negative than the cathode, in order to avoid collecting those electrons having gained energy while interacting with the slow-wave space harmonic.

Nevertheless, its ability to be phase- or frequency-locked has been demonstrated, leading to successful operation as a heterodyne local oscillator.

Measurements on submillimeter-wave BWO's (de Graauw et al., 1978) have shown that a signal-to-noise ratio of 120 dB per MHz could be expected in this wavelength range.