Microwave pulse compression using 3-fold and 5-fold helically corrugated waveguides

The use of an over-moded circular waveguide with helical corrugations of its inner surface as a dispersive medium enables compression of frequency-modulated microwave pulses. The helical corrugation couples a pair of partial modes of the circular waveguide having significantly different group velocities. As a result of the resonant coupling an eigenmode of the helically corrugated waveguide appears which has a strongly frequency dependent group velocity, which is favourable for the pulse compression. Two helically corrugated waveguide structures were investigated as sweep-frequency microwave pulse compressors for X-band microwave radiation. The investigation comprised the analytical, numerical and experimental study of the eigenwave and group velocity dispersion characteristics for the 3-fold and 5-fold helically corrugated waveguide compressors. Sweep-frequency based microwave pulse compression experiments were carried out at low (mW) and medium (kW) power levels. A 3-fold helically corrugated waveguide system resonantly coupled the fasttravelling counter-rotating TE1,1 mode and TE2,1 near cut-off mode. A 5.6 kW, 80 ns input pulse with 5 % frequency modulation from a conventional TWT was compressed to a maximum peak power of 140 kW, 1.5 ns pulse resulting in a peak power amplification of 22.5 ± 2.5 times, where 42 ± 5 % of the input energy was compressed to the main body of the output pulse. A larger diameter 5-fold helically corrugated waveguide system was designed to compress microwave pulses with frequency-modulation within the frequency interval 9.0 GHz to 9.6 GHz and simultaneously provide low reflection of the input radiation within a frequency interval of 8.0 GHz to 10.0 GHz. The 5-fold helically corrugated waveguide resonantly coupled the fast-travelling counter-rotating TE3,1 mode and TE2,2 near cut-off mode. An input pulse of 5.8 kW, 85 ns duration was compressed to a maximum peak power of 144 kW, 1.5 ns pulse resulting in a peak power compression ratio of 22.3 ± 2.5 and compression efficiency of 40 ± 5 %.The use of an over-moded circular waveguide with helical corrugations of its inner surface as a dispersive medium enables compression of frequency-modulated microwave pulses. The helical corrugation couples a pair of partial modes of the circular waveguide having significantly different group velocities. As a result of the resonant coupling an eigenmode of the helically corrugated waveguide appears which has a strongly frequency dependent group velocity, which is favourable for the pulse compression. Two helically corrugated waveguide structures were investigated as sweep-frequency microwave pulse compressors for X-band microwave radiation. The investigation comprised the analytical, numerical and experimental study of the eigenwave and group velocity dispersion characteristics for the 3-fold and 5-fold helically corrugated waveguide compressors. Sweep-frequency based microwave pulse compression experiments were carried out at low (mW) and medium (kW) power levels. A 3-fold helically corrugated waveguide system resonantly coupled the fasttravelling counter-rotating TE1,1 mode and TE2,1 near cut-off mode. A 5.6 kW, 80 ns input pulse with 5 % frequency modulation from a conventional TWT was compressed to a maximum peak power of 140 kW, 1.5 ns pulse resulting in a peak power amplification of 22.5 ± 2.5 times, where 42 ± 5 % of the input energy was compressed to the main body of the output pulse. A larger diameter 5-fold helically corrugated waveguide system was designed to compress microwave pulses with frequency-modulation within the frequency interval 9.0 GHz to 9.6 GHz and simultaneously provide low reflection of the input radiation within a frequency interval of 8.0 GHz to 10.0 GHz. The 5-fold helically corrugated waveguide resonantly coupled the fast-travelling counter-rotating TE3,1 mode and TE2,2 near cut-off mode. An input pulse of 5.8 kW, 85 ns duration was compressed to a maximum peak power of 144 kW, 1.5 ns pulse resulting in a peak power compression ratio of 22.3 ± 2.5 and compression efficiency of 40 ± 5 %