Threat sector indicating warning device

Abstract: A threat sector indicating warner having a separate alarm channel (1) for each threat sector. The alarm channel (1) comprises in series an integrator (9) and a comparator (10). An antenna covering a threat sector is connected to the input of the alarm channel via an intermediate amplifier and threat sector indicating means (11) is connected to the output of the alarm channel. In particular the warner is suitable for use for indicating threat from equipment working with a relatively high pulse frequency of the light.

Description: The present invention relates to a warner indicating a threat sector for electromagnetic radiation, preferably laser light, incident towards the warner, the warner comprising a receiver antenna for the electromagnetic radiation of each sector, means for amplifying the antenna signals generated in the antennas by the electromagnetic radiation and means indicating in which sector a threat may be present after signal processing in signal processing means of the amplified antenna signals. Such a warner is, for example, known from NO, B 144 500. In the described embodiments there is a co-use of signals from more than one threat sector before a threat sector indicating means is activated. It is an object of the present invention to obtain a non-complicated warner provided with separate channels for each threat sector. Hence, the channels are able to work quite independent of each other. The invention is characterized in that the warner for each threat sector is allotted an alarm channel connected via said amplifier means to the output of the receiver antenna and comprising a sequence of an integrator and a comparator, arranged in order of said sequence, the alarm channels of which have their outputs coupled to the threat sector indicating means to activate a threat sector indicating means when the comparator determines that the output signal of the integrator exceeds a reference level, whereby the alarm channel first activating a threat sector indicating means indicates the sector threatened. The alarm channels are built up from a very limited number of components of standard type. The introduction in each channel of a high pass filter and a rectifier prior to the integrator eliminates a great deal of the 1/f-noise introduced in the signal by the amplifier means during processing. Accordingly, a favourable embodiment of the invention is characterized in that each alarm channel comprises a high pass filter and a rectifier arranged in series between the input of the alarm channel and its integrator. The warner is intended for relatively high pulse frequencies of the order of magnitude of tens of kilohertz, in the frequency range of which the building up of the alarm channel has been found appropriate. More complicated warners and intended to cover other, preferably lower pulse frequency ranges are easy to complete with a warner according to the invention. For example, a warner according to our patent application EP-A-506641 is suitable for such an complementary addition. The invention will be described in more detail below with reference to the accompanying drawings in which figure 1 schematically shows how the warner according to the invention may be realized and figure 2 illustrates the appearance of the noise arising in amplifiers. The warner according to the invention shown in figure 1 controls four threat sections and for that purpose it is built up by means of four separate parallel alarm channels 1-4, one channel,channel 1, being shown in more detail. Each threat sector is equipped with an antenna 5 for receiving electromagnetic radiation, preferably as laser light, incident within the threat sector. The antenna 5 is coupled to the input of an alarm channel 1, possibly via an amplifier 6 and possibly some further, not shown, means. The amplifier and said further means may be included in a warner system in which the warner according to the invention is intended to complete for certain pulse frequency ranges. A high pass filter 7, a rectifier 8, an integrator 9 and a comparator are included in the alarm channel 1. The input of the high pass filter 7 is the input of the alarm channel and the output of the comparator 10 is the output of the alarm channel, the output being coupled to threat sector indicating means 11. A pulse 12 emitted within a threat sector of an antenna 5 is received by the antenna 5 and applied to the alarm channel 1 after amplifying and possibly further signal processing. On the entrance or input of the alarm channel, i. e. the input of the high pass filter 7, a pulse 13 and added disturbances 14 added to the pulse 12 due to noise in the amplifier are found. After high pass filtering the input signal on the high pass filter 7 assumes a signal indicated by the reference numeral 15. The signal is rectified in the rectifier 8 and may for a plurality of pulses in series received within the threat sector assume the signal shape 16. The signal shape 16 is applied to one of the inputs of the integrator 9 and a fixed negative signal value 5 is applied to the other input of the integrator. On the output of the integrator a signal is received which almost step-wise increase as long as the antenna receives pulses having a sufficient pulse frequency, pulse duration and signal level. The output signal of the integrator has got reference numeral 17. This output signal from the integrator is compared with a reference level T in a comparator and when the reference level T is exceeded the threat sector indicating means 11 is activated thereby indicating a threat within the threat sector referred to. An activated threat sector indicating means constitutes the basis for an evasive maneuver that the craft on which the warner is fixed should carry out. The negative signal value S has for its object to prevent that noise and other disturbances are integrated, so that the output signal of the integrator reaches the reference level T even in absence of emitted pulses 12. In order to prevent that the output signal of the integrator 9 in absence of emitted pulses 12 assumes an increasingly more negative value, a diode 18 is connected between the output of the integrator 9 and a negative tension V. The diode ensures that the level of the output signal of the integrator does not fall below the tension V. In figure 2 the noise arising in the amplifier within the frequency range of interest for warners according to the invention is schematically shown. More precisely the density B of the noise is shown as a function of the frequency f. The noise may be divided into two pieces, namely 1/f-noise 19 and noise 20 having a constant density. A break point 21 is defined as the point in which the the level of the l/f-noise intersects the level of the noise having a constant density. The introduction of a high pass filter 7 having a lower limiting frequency in the vicinity of the break point, enables an essential reduction of the influence of the difficult to handle 1/f-noise. In case of a break point 21 occuring at relatively low frequencies due to well-operating amplifying means the high pass filter and the rectifier may be omitted.

Claims: A warner indicating a threat sector for electromagnetic radiation, preferably laser light, incident towards the warner, the warner comprising a receiver antenna (5) for the electromagnetic radiation for each sector, means (6) for amplifying the antenna signals generated in the antennas by the electromagnetic radiation and means (11) indicating in which sector a threat may be present after signal processing in signal processing means of the amplified antenna signals, characterized in that the warner for each threat sector is allotted an alarm channel (1-4) connected via said amplifier means (6) to the output of the receiver antenna (5) and comprising a sequence of an integrator (9) and a comparator (10), arranged in order of said sequence, the alarm channels (1-4) of which have their outputs coupled to the threat sector indicating means (11) to activate a threat sector indicating means when the comparator (10) determines that the output signal of the integrator (9) exceeds a reference level. whereby the alarm channel (1-4) which activates a threat sector indicating means (11) indicates the sector threatened. A warner as claimed in claim 1, characterized in that each alarm channel (1-4) comprises a high pass filter (7) and a rectifier (8) in series between the input of the alarm channel (1-4) and its integrator (9). A warner as claimed in claim 1 or 2, characterized in that a diode (8) is connected between the output of the integrator (9) and a negative tension (V) and is conducting in a direction towards the output of the integrator.

Inventors: BJOERKMAN BENGT, BJOERKMAN, BENGT, Björkman, Bengt
Applicants: CELSIUSTECH ELECTRONICS AB
Application year: 1992
Main classification: G08B21
IPC codes: G08B21, G01S3