Abstract: An electronic counter countermeasure (ECCM) circuit for Automatic Gain Cool (AGC) electronic countermeasure (ECM) deception of conical scanning tracking radar receivers having a two position limiter in circuit with the AGC circuit to eliminate signal information enhancing the amplitude modulation of the error modulate signal to provide selectable values of dynamic range in a signal processor to render the ECM ineffective in target evaluation.

Abstract: In multiple frequency estimation, the bandwidth and resolution of Fast Fourier Transform (FFT) based frequency estimators are limited by A/D converter sampling rate constraints and also by real-time computational requirements. The disclosed configuration uses a Modified Chinese Remainder Theorem of a paper entitled, "A Noise Insensitive Solution to an Ambiguity Problem in Spectra Estimation" by McCormick et al and a subsampling approach of U.S. Pat. No. 5,099,194 entitled, "Digital Frequency Measurement Receiver With Bandwidth Improvement Through Multiple Sampling of Real Signals" to resolve the frequency ambiguity problem. The configuration extends these ideas to the multiple frequency case. It significantly extends system bandwidth by operating I FFT units in parallel at specific sampling rates chosen to maximize system bandwidth for a fixed level of noise protection.

Abstract: An IFM (Instantaneous Frequency Measurement) receiver is disclosed that can process two simultaneous signals for electronic warfare application. Three IFM receivers are employed (cooperating in the 2 to 4 GHZ range) and have three filters in front of them. Filter 1 is a 2-4 GHz band pass receiver in front of the first receiver. In front of the second receiver is a low pass filter with a band edge at 2 GHz. In front of the third receiver is a high pass filter with the band edge at 4 GHz. In filters 2 and 3, the skirts of the filters are used rather than their pass bands. Details on the signal conditions, calculations for the frequencies, and the equations are disclosed.

Abstract: In a noise radar a pseudo-random sequence is generated repeatedly and used to phase modulate a transmitted signal. The transmission is interrupted during a number of periods during each pseudo-random sequence which allows returns from targets to be received from the same antenna as is used for transmission during those periods of interruption. Each transmitted pulse, between successive periods of interruption, contains a different selection of successive digits of the code thus increasing the apparent randomness of the transmitted code and making detection more difficult.

Abstract: A complementary threat sensor data fusion capability for an aircraft survivability equipment system. A set of aircraft survivability sensors provides a threat sensor data fusion control process with status data. The control process controls whether or not a threat ambiguity detector receives radar warning receiver data or a radar emitter ID conversion apparatus receives pulsed radar jammer data or continuous wave radar jammer data. The threat sensor data fusion control process also determines whether missile approach detector data is sent to a countermeasures analyzing apparatus. The threat ambiguity detector provides ambiguity data to a threat ambiguity resolving apparatus. The radar emitter ID conversion apparatus provides converted jammer data to a functional sensor back-up apparatus. The radar emitter ID conversion process receives a common radar emitter ID data base. The threat sensor data fusion process controller also provides fusion process control to the complementary threat data apparatus.

Abstract: Method and apparatus for reducing the effects of noise jamming on coherent frequency or phase modulated signals employs a two channel radio signal processing system (15, 20) which accepts an input signal containing a desired signal (S) and a jamming signal (J) from a receiver input circuit (10). In the first channel (15), a hetrodyne mixer (30) and wideband filter (35) select the difference frequency component between the jamming signal and the desired signal [X(t)] while in the second channel (20), a local oscillator (45), mixer (50) and filter (55) function to select the difference frequency between the jamming signal and the local oscillator [Y(t)]. A third mixer (90) and bandpass filter (95) combines the outputs X(t) and Y(t) to provide the desired signal, including its original phase and frequency modulation components substantially independent and free of the jamming signal, to the receiver output circuit (12).

Abstract: An interference signal suppression system and method that suppresses coherent jamming signals. The system comprises first and second receiving antennas that are physically separated from each other to generate non-coherent received signals of interest. The antennas are positioned to receive communication signals that are jammed with coherent energy. The separation distance is typically 40 to 50 wavelengths of the non-coherent scattered wave radio frequency signals. Phase and amplitude adjustment circuitry is provided that alters the phase and amplitude of the received signals such that the coherent received signals are balanced and out-of-phase. These signal are then summed in a summing circuit and the output of this circuit generates signals wherein the coherent signals are nulled and the non-coherent signals are detectable. The signal suppression system and method is independent of the direction of arrival of the coherent signals, which overcomes limitations of conventional techniques.

Abstract: A method and apparatus for communicating radio frequency signals that may reduce the susceptibility of the signals to jamming. A digital voice signal may be interleaved and transmitted with error correction signals related to the voice signal. The transmission may use frequency hopping with each hop including appropriate synchronization signals, data signals and error correction signals. The received signal at the receiver portion of the signal may contain means for removing both nonexcisable and excisable interference. The nonexcisable interference may be identified and removed by (1) assuming different jamming patterns, (2) decoding to resolve the received signals for each of the assumed jamming patterns, and (3) voting all of the resolved signals to determine which assumed jamming pattern produces the best results. An adaptive filter for removing excisable jamming may applied when such jamming is detected.

Abstract: A method is disclosed for encoding signals for transmission to provide signals which simultaneously have specifiable autocorrelation properties and low predictability. To enhance the accuracy of time of arrival measurements in the presence of either noise or multipath due to skywaves in systems such as LORAN, the coding method provides for low autocorrelation function values at time offsets approximately equal to the expected delay between direct waves and skywaves. This is accomplished by constructing the codeword which is used to encode the signal, from an Nth difference constant ratio codeword, where the expected time delay is equal to N-bits. The constant ratio codewords and the transmitted codewords are both pseudo-randomly generated, resulting in a transmitted signal having very low predictability to an unintended recipient, thereby considerably reducing the effectiveness of attempts at jamming or other electronic countermeasures attacks.

Abstract: This invention concerns a system to protect active or passive electronic equipment from radar detection. In other words equipment which transmits or receives microwave radiation, for example a radar or telecommunications transmitter or receiver.For this purpose, the transmitting surface of the equipment is covered by a device which can be controlled to apply a phase shift of approximately .pi./2 to the incident wave; this enables a microwave incident on the equipment to be modulated in phase. The frequency spectrum of the wave reflected by the equipment is modified and spread thus making it more difficult to detect the equipment. To avoid any perturbation of the operation of the equipment, an inverse modulation is applied to signals transmitted and/or received by the equipment itself.

Abstract: Parallel architectures preprocesses large matrices from sampled coherent time apertures receiving signals from distant sources to produce lower order matrices, derived from pseudo coherent time apertures, which are computationally less burdensome. The large matrices are processed by frequency shifting, low pass filtering with an FIR filter, and executing front-end decimation to create the pseudo coherent time apertures, each corresponding to different subbands of the temporal frequency spectrum. The signals representing the pseudo coherent time apertures are processed using matrix based superresolution spectral estimation algorithms such as the Tufts-Kumaresan (T-K) reduced rank modified covariance algorithm and the Linear Minimum Free Energy algorithms to produce an image of the sources.

Abstract: This proposed approach to extending the frequency range uses non-uniform sampling to gain the advantages of a high sampling rate with only a modest increase in the number of samples. The basic idea is to use two sets of uniform samples with slightly different sampling frequency. Each set of samples is Fourier transformed independently and the frequency of the lowest aliases determined. It is shown that knowledge of these two alias frequencies permits unambiguous determination of the signal frequency over a range far exceeding the Nyquist frequency, except at a discrete set of points. It is further shown that one additional set of samples is sufficient to resolve all these discrete degeneracies.

Abstract: This is a technique for extending the frequency range which employs in-phase and quadrature components of the signal coupled with non-uniform sampling to gain the advantages of a high sampling rate with only a small increase in the number of samples. By shifting the phase of the local oscillator by 90 degrees, a quadrature IF signal can be generated. Both in-phase and quadrature components are sampled and the samples are combined to form a complex signal. When this signal is transformed, only one alias is obtained per periodic repetition and the effective Nyquist frequency is doubled. Two sets of complex samples are then used with the slightly different sampling frequency. Each set is independently Fourier transformed and the frequency of the lowest aliases permits unambiguous determination of the signal frequency over a range far exceeding the Nyquist frequency.

Abstract: There is disclosed a video processor, for use in a counter-countermeasure stem, to convert radar video signals into binary information, consisting of four parallel channels, the outputs of which are ORed to obtain a combined synthetic video signal. Two channels operate on video from a logarithmic detector to optimize sensitivity in the presence of jamming and to extract real target information. The third and fourth channels operate from the output of a wide band detector and can distinguish between swept noise pulses and true target signals.

Abstract: A system and method for pulse interval modulating signals in accordance with a code wherein the code resides in the spacing between adjacent pulses. The invention has particular utility in connection with laser designators and laser seekers and, while clearly not limited to this application, is disclosed hereinafter mainly in connection with laser designators and seekers. In connection with this laser environment, the invention may include a pulse interval modulation encoder for encoding the laser designator output signal and a pulse interval modulation decoder for decoding by the laser seeker of the encoded designator signal. The encoder preferably employs an ordered arrangement of unique pulse interval pairs which cyclically repeats after a relatively long time period. Because of the length of the time period and the apparent randomness of the intervals forming the unique interval pairs, the code appears to enemy countermeasures to be random.

Abstract: A device for rejecting pulse repeater deception jamming and post dispensed haff jamming in pulse type tracking radars. By use of a very narrow sampling gate with appropriate thresholding delay and timing, a narrow portion of the target pulse which is in minimum coincidence with the jamming pulse is selected. This selected portion is used to construct a restored duplicate of the target pulse for tracking and display purposes.

Abstract: Sidelobe jamming in dual diversity troposcatter link receivers is effectively suppressed by providing an auxilliary low power antenna, the output of which is differenced from the high power main antenna signals prior to processing in the receivers's dual diversity demodulator. The auxilliary antenna power is substantially equal to the sidelobe power of the main antennas. The auxilliary antenna receives jamming power that is comparable to the jamming power received by the main antennas. However, it receives much lower desired signal power. Differencing of the signals therefore, cancels jamming power with minimal effect on the desired signals.

Abstract: A method and a device for reducing the power of jamming signals received by the secondary lobes of the main antenna AP of a radar transmitting at a random frequency f.sub.E (n), with which is associated a number of secondary antennas ASl, . . . ASN. The signals used for the calculation in circuit (10) of the weighting coefficients (Wl to WN) to be applied to obtain a signal resulting from the weighted linear combination of the secondary signals Dl, . . . DN to be subtracted from the signal Do in the main channel (VPD) relative to the transmission frequency f.sub.E (N+1) are those (V.sub.0, V.sub.1, . . . V.sub.N) processed in the main and secondary auxiliary channels (VPA, AsAl, . . . ASAN) relative to the transmission frequency f.sub.E (n+1) of the next recurrence train during the period of radar reception of the recurrence train corresponding to the transmission frequency f.sub.E (n) for the jammed range slots selected by circuit (15).

Abstract: The invention provides an apparatus and method to confirm or deny the presence of an object within the scan area of an ultrasonic sensing system by requiring that any object be identified on at least two consecutive scans of the sensing system and using scan energy patterns which occur at irregular repetition times to selectively reject spurious direct or reflected signals present in the area. A generator of predetermined pattern burst of ultrasonic energy is arranged to produce one such burst of ultrasonic energy and a timing signal is coupled thereto so as to apply timing signals to cause production of the bursts. The timing signal source produces timing signals only according to a varying pattern whereby separation between adjacent signals meet certain present parameters. The energy patterns are applied to a transmitter which applies them to a scan area whereby the echo or returned energy from an object in the scan area is received and stored.

Abstract: A radar detector capable of discriminating a prescribed radar signal from other undesired radar or interference signals by mixing an incoming electromagnetic wave radar signal with a local signal whose frequency varies with time within a fixed range of frequency repeatedly at regular periods, thus providing a beat signal; temporarily stopping the frequency sweep in response to appearance of dc components alone in the beat signal when the incoming radar signal matches the local signal in frequency; and watching the length of time for which the incoming radar signal matches the local signal in frequency. The reception of the prescribed radar signal is indicated using a sound-generating unit such as a speaker or a light-emitting unit.

Abstract: In side-lobe cancelling equipment direct jammer signals appearing in an auxiliary antenna channel are better correlated with reflected jammer signals in a main antenna channel by splitting the signal in the auxiliary channel into two parts, one of which is directly correlated with direct jammer signals in the main channel and the other is passed through a delay line to alter its timing to match the timing of the reflected jammer signals in the main channel.

Abstract: A technique and apparatus are disclosed for determining the performance of a pulse doppler radar system every integration period. The test is accomplished by injecting into the front end of the radar a highly calibrated signal during initialization or during a periodic test and measuring the signal at the Fast Fourier Transform (FFT) output. This measured signal is used by the radar signal processor as a reference signal which is adjusted for internally induced changes by the radar's signal processing system then summed with the in-phase amplitude of the selected range gate filter cell. The sumed signal and the cell quadrature amplitude are then envelope detected, and a detection counter is incremented when the envelope detection compares favorably with the cell's constant false alarm rate. Each integration period, the process is repeated for all range gate filter cells to obtain a detection count. Then the probability of detection is estimated using the equation: ##EQU1## where N.sub.

Abstract: A radar detector is disclosed which comprises a radar wave signal receiver for producing a detection output when the incident radar signal is synchronized with a local oscillation frequency at a certain sweeping time, first and second pulse train signal generators for producing pulses with different cycles, and a cycle alteration circuit for altering the cycle of the second pulse train signal generator in accordance with a logic output corresponding to the detection output from said receiver, thereby synchronizing such cycle with the cycle of the first pulse train signal generator. The regular radar wave signal is discerned by the detection of coincidence between the output pulses from the first and second pulse train signal generators at certain time intervals. Consequently, the radar system is prevented from responding to interference noise or extraneous radar waves.

Abstract: A radar ECCM system for degrading the effect that a standoff noise jammer has on a radar receiving site that is tracking an incoming aerial target. The system effectively removes from the mainlobe of the beam emanating from the site the component of random noise contained in the jamming signal.