Microwave pulse compression using a helically corrugated waveguide

Abstract

Abstract-There has been a drive in recent years to produce ultra-high power short microwave pulses f or a range of applications. These hig h power pulses can be produced by microwave pulse com pression. Sweepfrequency based microwave pulse co mpression using smooth bore hollow waveguides is one technique of passive pulse compression, however at very high pow ers this method has some limitation due to i ts operation close to cut-off. A special helical corrugation of a circular waveguide ensures an eigenwave with strongly frequency dependant group velocity far from cut-off, which makes the helically corrugated waveguide attractive for u se as a passive pulse com pressor for very high pow er amplifiers and oscillators. The results of proof-of-principle experiments and calculations of the wave dispersion using a PIC code are presented. In the ex periments a 70ns 1kW pulse from a conventional TWT was compressed in a 2 metre long helical waveguide. The compressed pulse had a peak power of 10.9k W and duration of 3n s. In order to find the optimum pulse compression ratio the w aveguide's dispersion characteristics m ust be w ell known. The dispersion of the helix was calculated using the PIC code MAGIC and verified using an experimental technique. Future work detailing plans to produce short ultra-high power (GW) pulses will be discussed.

Helically corrugated waveguide microwave pulse compression experiments

“…The 3-fold helical corrugation [2] couples a pair of partial modes of the smoothbore circular waveguide having significantly different group velocities: TE 2,1 mode close to cut-off and TE 1,1 far from cut-off. At non-zero amplitude of corrugation, resonant coupling between the modes occurs when their axial and azimuthal wave numbers satisfy the Bragg conditions resulting in the operating eigenmode [3]. As a result, in the frequency region of their resonant coupling, the resultant eigenmode has a strong frequency dependent group velocity which is favourable for pulse compression [4].…”

“…The reciprocal set-up is required on the output side of the pulse compressor to obtain the compressed TE 1,1 wave. Using coupled wave theory [3] the eigenwave dispersion was calculated for the interaction of the two electromagnetic waves present in the 5-fold helix; the TE 3,1 and TE 2,2 . A vector network analyzer ( Figure 4) was used to measure the phase of the eigenwave.…”

Investigation on the Microwave Pulse Signal Compression With NGD Circuit

“…Owing to the great interest for the development of radar and communication systems, the PC has been used to improve the range resolution. In other respects, a microwave pulse compressor based on a passive resonant cavity has been investigated by several authors [13][14][15], in order to increase microwave power. The prerequisites are that the compressor cavity must present a high Q-factor, the constituting waveguides should operate with an oversized mode of the field in order to increase the power strength, and the power microwave sources should be narrow-band.…”

Simulations of Ka-band waveguide components for use in a gyro-travelling wave amplifier

“…Helically corrugated waveguide interaction regions [2][3][4][5][6][7][8][9] (Figure 1) radically alter the dispersion relation of the interacting mode such that it matches the electron beam dispersion over a broad range of frequencies. This decreases the sensitivity to electron velocity spread, increases the stability to parasitic selfoscillations and improves the frequency bandwidth.…”