Selenia Industrie Elettroniche Associate S.p.a.

Selenia Industrie Eletroniche Associate, S.p.a.

Selenia-industrie Elettrotechniche Associate S.p.a.

Ennio Giaccari

Gaspare Galati

Egidio D'Addio

Roberto Pace

Piero Cervone

Voltage regulator which can compensate for the output voltage variation of a line modulator for use in transmitters for radar applications. The voltage variation in question is due to the modulation induced by the radar repetition frequency. This regulator is essentially made up of a network (1,2,3,4,5,6,7) which varies the value of the input signal to a comparator 8 in relation to a signal which is proportional to the variation of repetition frequency.

Voltage regulator for use in transmitters for radar applications

A digital MTD processor interposed between a coherent video detector and a signal extractor of a surveillance radar comprises a plurality of Doppler filters connected in parallel to the video-detector output, including a zero filter, working into respective modulus extractors connected by way of respective threshold circuits to a common OR gate. Each threshold circuit includes a fixed-threshold comparator and an adaptive-threshold comparator with inputs connected in parallel to the output of the associated modulus extractor, either of these comparators being connectable to the OR gate via a switch controlled with the aid of a rain-clutter map so that the adaptive threshold is used only during exploration of regions with heavy rain. A ground-clutter map, which can be updated on the basis of level measurements performed on the output of the zero filter, controls the selective loading of each Doppler filter with one of three preselected sets of weights depending on the intensity of the ground clutter in the region being explored. Where ground clutter is heavy, the threshold circuit of the zero filter may be cut off from the OR gate. Both the fixed and the adaptive thresholds can be incremented in response to a command from the signal extractor generated upon the occurrence of an excessive number of false alarms.

Adaptive MTD digital processor for surveillance radar

A radar, e.g. as used for the surveillance of aerial navigation, has a receiver feeding incomimg echo signals to several Doppler filters in parallel, the output signal of each filter beign passed to a utilization stage through a respective attenuator connected to the filter output in parallel with an associated area processor. The latter comprises a pulse counter synchronized with the scanning motion of the radar antenna to register the number of echoes received in successive sweeps from different zones into which the surveyed space is divided in distance and azimuth. Upon the last sweep of a sector encompassing a group of such zones, the contents of respective cells of a sector memory loaded by the pulse counter are compared with a first threshold. If the number of echoes stored in such a cell exceeds that threshold, a count written in an assigned cell of a scan memory is incremented; if it does not, the count is decremented. A delayed reading of the scan memory, during a subsequent antenna rotation, determines the setting of the associated attenuator during the sweep of any zone. The attenuator includes a delay line from which the signal amplitudes appearing in the output of the corresponding Doppler filter during recurrent sweeps of the same zone are simultaneously recovered and averaged; the result is multiplied by a factor selected by comparison with a second threshold in the associated area processor on the basis of the numerical value read out from the corresponding cell of the scan memory.

Circuit arrangement for post-detection suppression of spurious radar

A device for suppressing second-time-around echoes from far-out clutter in an MTI pulse radar lies in shunt with a digital signal processor connected to the receiver output of the radar whose transmitter includes a power oscillator maintaining phase coherence only for the duration of an outgoing pulse. In order to minimize the occurrence of blind speeds, the oscillator is triggered for different pulse-repetition frequencies of predetermined values in alternate scanning intervals each lasting for an antenna rotation by half a beamwidth. Echoes from a group of radar pulses emitted in one interval are accumulated and then compared in magnitude with accumulated echoes from another such group emitted in an adjoining interval. If these magnitudes--relatively adjusted to compensate for the different numbers of pulses per group--are substantially equal over a sequence of antenna revolutions, they are classified as due to second-time-around clutter echoes and the output signal of the processor is eliminated for the corresponding scanning intervals.

Suppressor of second-time-around clutter echoes for MTI pulse radar

A receiving section of a surveillance radar equipped with a power oscillator in its transmitting section comprises several registers for the storage of values, perferably in complex digital form, representing the starting phase of a continuous wave at the instant of transmission of an outgoing pulse, these values being used thereafter to establish coherence with an incoming echo pulse at a time when the power oscillator is no longer able to do so on account of unavoidable frequency drifts or because of intervention of a new recurrence period. Thus, the stored values permit the correct detection of targets at the far end of the range and/or the cancellation of second-time-around clutter echoes. The continuous wave may be generated by a coherent oscillator, phase-locked during each recurrence period by the outgoing pulse, or a separate crystal-controlled oscillator of highly stable frequency.

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Rome, Italy

Ennio Giaccari