Patent GB-1243193-A (GB)
Title: Electronic pulse modulation devices
Inventor: HARTNAGEL HANS LUDWIG
IPC: H03K7/08
Filed: 1967-12-07
Abstract: 1,243,193. Pulse modulation systems; aerials; Gunn effect circuits; phase modulation. NATIONAL RESEARCH DEVELOPMENT CORP. 4 Dec., 1968 [7 Dec., 1967; 31 July, 1968], Nos. 55810/67 and 36545/68. Headings H3R, H3T, H4A and H4L. A pulse width modulator operates by virtue of the Gunn or other travelling field domain phenomena. General description.-As shown in Fig. 1, a Gunn device carries a large electrode 12 on one surface of the body 11 and a relatively small electrode 13 on the opposite surface, the electrode 12 being biased negatively with respect to the electrode 13. When the potential across the electrodes exceeds a threshold value E t  a domain will be formed near the electrode 12 and will travel towards the electrode 13 and since the electrode 12 is larger than electrode 13 the electric field will increase towards the electrode 13. This effect can be enhanced by shaping the body 11 to taper from the electrode 12 to the electrode 13. If the applied potential is reduced the field adjacent the electrode 12 can be made smaller than the threshold value at which the domain is formed while being above this value near the electrode 13. Thus there will be a point between electrodes 12, 13 at which the electric field will reach the threshold value and this point may be changed by a variation in the potential across the device. If the electrode 12 is biased positively with respect to electrode 13 the domains will be formed adjacent electrode 13 and will travel towards electrode 12, the field will decrease from electrode 13 to electrode 12 and as before, the field gradient can be enhanced by suitable shaping of the body 11. The electric field can be arranged to fall below a second threshold value E s  at which the domain is extinguished at some point between electrodes 12, 13 and this point can be varied by a variation of potential across the device, the output being in the form of frequency-modulated pulses and when the applied potential is a pulse train the pulse amplitude will control the path length of a domain and hence the duration of the temporary variation in the electrical characteristics of the body 11 and this change may be utilized to derive a corresponding duration modulated pulse in the output 15. The output pulses may be derived from a resonant cavity surrounding the body 11. The biasing potential 14 may be arranged to be insufficient to produce a domain and additional triggering pulses applied across electrodes 12, 13 to form a domain, either the potential 14 or the triggering pulses being varied in amplitude to produce the pulse duration modulation. In a modification, Fig. 3 (not shown), a second small electrode (17) is provided adjacent the electrode (13) and is supplied with triggering pulses, the potential from source 14 being insufficient to form a domain when there is no input on the additional electrode (17). As before either the amplitude of the biasing potential or that of the triggering pulses may be varied to produce the corresponding duration modulated output pulses. In a modification the electrode (17) may consist of a relatively long electrode placed along the side surface of the body (11). Phase modulation.-In a further arrangement, Fig. 5, the duration modulated pulses are differentiated at 57, the resulting spiked pulses triggering a Gunn effect oscillator 58. The input pulses to the pulse duration modulator may also be provided by a Gunn oscillator 51. Thus the phase of the oscillations from the output oscillator 71 in relation to those of the input oscillator depends upon the length of the modulated pulse. The output oscillator may operate at the same frequency as the input source or at a harmonic of it. Phased aerial array.-A plurality of the previously described phase modulators 52, Fig. 7, each provided with an input oscillator 51, are biased individually from a potential divider 73 so that a particular phase relationship exists between the output signals from the oscillators 71 enabling the microwave beam to be swept without having to move any part of the aerial array. Alternatively a single source 51 may be applied to each of the devices 52 in turn via a delay line.