US Government As Represented by the Secretary of the Army

Other

Frank S Gutleber

Interference signal cancelling is provided by a multiplexed interference celling system that utilizes a primary high gain antenna and an auxiliary antenna pair including a low gain notch antenna in conjunction with a low gain omnidirectional antenna. The output of the two low gain auxiliary antennas are subtracted from each other to provide an output that is substantially free of all input signals except for the interfering signal received in the narrow notch of the notch antenna. This signal is then subtracted from the composite output signal of the primary antenna. One of these auxiliary antenna pairs is employed for each separate jamming signal source to be cancelled, thus enabling each jamming signal to be orthogonally isolated, whereupon its magnitude and phase is then adjusted to be equal to and 180.degree. out of phase with the same component contained in the composite signal from the primary antenna. Each interfering signal is then separately subtracted from the composite signal, leaving only the desired signal.

Antenna sidelobe interference canceller

A high gain, primary receiving antenna and a single scannable auxiliary lar antenna array are utilized. The auxiliary linear array is coupled to means for forming multiple directive narrow receiving beams simultaneously on the auxiliary array, each of which are scanned over an assigned segment of space to locate and isolate a respective one of a plurality of interfering or jamming signals which are also contained in the signal received by the primary antenna. The interfering signals are cancelled by separately adjusting the phase and amplitude of each one of the interfering signals received and then feeding them to a respective signal subtractor coupled to the output of a receiver connected to the primary antenna.

Auxiliary antenna interference canceller

An interference cancelling transmitter is configured which provides electagnetic compatibility (EMC) among different communications apparatus in the same area as well as providing a low probability of intercept (LPI) in a dense communications environment where secure communications is required between users. This is accomplished by means of a communications transmitter coupled to a transmitting antenna configuration comprised of an omnidirectional antenna and a notch antenna having a single deep null over a small angular beamwidth. RF power is fed equally thereto so that the radiated power from each antenna is the same but the phase is mutually inverted (180.degree.) so that a cancellation of the radiated power occurs in all directions of space except over the angular region where the null of the notch antenna is located. The null can be varied in direction and results in a relatively narrow pencil-like radiation pattern being radiated to a predetermined receiver.

Interference cancelling transmitter

A relatively narrow beamwidth (10.degree. or less) receiving antenna patt is formed at the receiver end of a radio frequency transmission link where a plurality of radiating sources are operating in a dense communications environment. The antenna pattern comprises the difference between two antenna receiving patterns where the beamwidth of one pattern is wider by a predetermined angular amount than the other pattern. In the preferred embodiment, a phased linear array of antenna elements is operated as two sets of elements wherein one set of elements comprising a number of elements less than the total number of elements provides a beamwidth that is broadened by a predetermined angular sector greater than the beamwidth formed by the entire array. The antenna elements are progressively phase shifted to provide overlapping beam patterns and the pattern of one set of elements is scanned so that one side of both patterns are substantially coincident. The received signals from the elements developing the two antenna patterns are respectively combined and linearly subtracted to provide cancellation of all the received radiation except over the small angular sector defined by the difference between the two patterns.

Small angular beamwidth antenna system

A notch antenna for the elimination of external interference sources such jamming, self-interference, atmospheric noise and man made noise is provided by a grounded electrically conductive shield placed in the front of an omnidirectional antenna coupled to radio communications apparatus, such as a receiver, whereby the shield blocks electromagnetic waves arriving within an angular arc defined by the position and size of the shielding element.

Notch antenna for a radio communications system

A swept interference canceller including a multiplexed interference cancelling receiver coupled to a scanned notch antenna and an omni-directional antenna as well as an estimator type of angular beam splitting system for accurately measuring angular bearing of a plurality of sequentially received radiating sources in a dense communication environment. A difference signal between the signals received by the two antennas is developed which is then split into a plurality of equal time samples which are then simultaneously fed into two synchronous multi-stage shift registers. The output stages of one of the shift registers operate so that they all have the same output states. The output stages of the other shift register, however, operate so that the first half have the same output state as the first shift register while the second half are of the opposite output state. The outputs from the two shift registers are summed and fed to a logic gate which operates to generate an output signal following the occurrence of the middle time sample which is a time corresponding to the position of the boresight axis of the signal received from a radiating source.

Interference cancelling receiver having high angular resolution

Noise codes are generated of a type termed 'code mates' having correlation unctions which, upon detection in a matched filter, provide an impulse autocorrelation function. More particularly, code mate pairs of at least two code bits each are generated and shown, for purposes of illustration, utilized in a communications system and wherein one code mate is comprised of two signal bits of first and second or opposite polarity, one bit of which has a larger amplitude than the other bit and wherein the other code mate is comprised of two signal bits of said second polarity, one bit of which has a like larger amplitude than the other bit.

Multilevel noise code mate pair generation and utilization of such codes

A coded linear array antenna comprised of a plurality of multiple element barrays, each providing sin mx/sin x patterns which are combined, i.e. summed into a composite pattern by having the subarrays commonly connected to a signal summation means. Each subarray is comprised of multiple elements which are respectively spaced equidistantly apart and positioned symmetrically on either side of a common array axis center or axis of symmetry and wherein the individual antenna elements of each subarray are positioned at an i.sub.th location according to the normalized equation ##EQU1## where i=1, 2, 3, . . . h, n.sub.m defines the maximum number of elements in the length or aperture of the composite array, h is the number of elements in the respective subarray, and n is proportional to the element spacing of the respective subarray.

Linear array antenna employing the summation of subarrays

Expanded multilevel noise codes are generated of a type termed 'code mates' aving autocorrelation functions which, upon detection in a matched filter, provide an impulse autocorrelation function. More particularly, expanded multilevel code mate pairs are generated by interleaving two multi-bit codes comprising a mate pair wherein one of the codes in each expanded mate pair comprises a code having a larger amplitude than the other code and whose position is mutually transposed in the expanded mate pairs and further wherein one of the interleaved codes is the complement or negative of one of the original or basic code mates.

Code generator for multilevel interleaved multiplexed noise codes

Expanded multilevel noise codes are generated of a type termed 'code mates' aving autocorrelation functions which, upon detection in a matched filter, provide an impulse autocorrelation function. More particularly, expanded multilevel code mate pairs are generated by butting two multi-bit codes comprising a mate pair wherein one of the codes in each expanded mate pair comprises a code having a larger amplitude than the other code and whose position is mutually transposed in the expanded mate pairs and further wherein one of the butted codes is the complement or negative of one of the original or base code mates.

Expanded multilevel noise code generator employing butting

A multichannel time division multiplexed (TDM) bit stream has specific channels selected by gating selected channel bits out of a composite group of channels. The selected channel bits are spread spectrum coded as multiplexed noise codes which are then used to modulate a transmitter for communicating the codes over a transmission link. The noise codes are then automatically compressed back to original channel bits at a receiver to provide output signals which are totally non-interfering with each other.

Multichannel time division multiplexed trunk transmission link

Multilevel code mates A and B expanded in accordance with the expression , b.sup.K and B=a.sup.K, b are compressed to a lobeless basic mate pair by repeatedly compressing corresponding code mate pairs in successive stages to provide diminishing codes of half the code length by amplifying the code mates by a predetermined amplification factor and then adding and subtracting the code mates in accordance with the expressions A.sub.i-1 =A.sub.i +B.sub.i.sup.K.sbsp.i and B.sub.i-1 =A.sub.i.sup.K.sbsp.i -B.sub.i where i is the i.sub.th compression stage and K.sub.i is the amplification factor applied to the codes A.sub.i and B.sub.i.

Multilevel mate pair code compressor for codes expanded by the process

Method and apparatus for generating and utilizing a pair of expanded multiplexed noise codes from multi-bit code mate pairs having code bits of equal pulse width by first reducing the pulse width of each of the original code bits of both code mates by one half to form a pair of intermediate code mates having code bits of one half the pulse width of the original code bits. One of the intermediate codes is delayed by a time equal to at least three times the pulse width of the intermediate code bits after which it is added to the other intermediate code mate to form a first partially interleaved code mate, while a second partially interleaved code mate is generated by subtracting the delayed intermediate code mate from the other intermediate code mate and effected, for example, by forming the negative of the delayed intermediate code mate and adding it to the other intermediate code mate. The resulting partially interleaved code mates compress to an impulse when they are detected with their respective matched filters and linearly added.

Code expansion generator

A digital pulse position modulation (PPM) communications system with threld extension including a radio receiver for achieving optimum coherent detection of a pulse position modulated communication signal including a coherent video detector coupled to the IF output of the radio receiver and a pulse repetition frequency loop locked to the detected video signals containing position modulation. The pulse repetition frequency loop includes a time discriminator, a filter, a voltage controlled oscillator, and a split gate generator providing a split gate no greater than the width of the applied video signal. The split gate is applied to the time discriminator resulting in the detected video signal being multiplied by itself or coherently detected. A low pass filter is connected to the output of the discriminator to provide a demodulated communications analog or quasi-analog output signal such as a voice signal, transmitted to the receiver from a digitally coded PPM communications transmitter.

Digital pulse position modulation communications system with threshold

Expanded multiplexed noise codes including code mate pairs having autocoration functions which upon detectionprovides an impulse autocorrelation function are generated by delaying the inverse of one of the code mate pairs (code b) by a value .tau. and adding it to the other code mate pair (code a) to form a first expanded code mate (code A) while a second expanded code mate (code B) is generated by delaying the inverse of said other code (code a) also by a value .tau., forming the complement thereof and adding it to said one code mate (code b). Such an expansion enables each expanded code to begin with each different code of a mate pair.

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Little Silver, NJ, United States of America

Frank S Gutleber