United States of America as Represented by the Secretary of the Air Force

David M Lin

James B Y Tsui

Stephen L Hary

James B Tsui

John M Emmert

Keith M Graves

Nicholas A Pequignot

Lihyeh Liou

An imbalance compensation system includes a receiver, a first path and a second path electrically coupled to the receiver, and a 90 degree hybrid coupler electrically connected to the second path, wherein the first path is configured to convey an in-phase (I) signal and the second path is configured to convey a quadrature phase (Q) signal. A processor is configured to perform Finite Impulse Response (FIR) filtering upon the I signal and the Q signal, wherein the processor is configured with an inverse matrix of coefficients corresponding to a frequency-dependent phase imbalance and a frequency-dependent amplitude imbalance between the I signal and the Q signal. The processor is configured to perform FIR filtering to attenuate an image signal down to a system noise floor when the processor simultaneously receives signals in a primary Nyquist region and a conjugate Nyquist region.

Methods and apparatus for wideband imbalance compensation

A new approach for applying the multiple signal classification (MUSIC) method for high spectral resolution signal detection is described. The new approach uses a lower order covariance matrix, or, alternately, an autocorrelation matrix, to calculate only the number of eigenvalues and associated eigenvectors actually needed to solve for the number of signals sought.

Low order multiple signal classification (MUSIC) method for high spectral resolution signal detection

A moderate cost and complexity digital radio receiver system having enhanced instantaneous dynamic range response to the receipt of simultaneous signals and also providing large single signal dynamic range. Multiple signal instantaneous dynamic range improvement is achieved through use of a suppressed zero signal amplitude representation arrangement having a selected number of signal amplitude representing digital bits rather than the larger entire array of digital output bits of the receiver system's analog to digital converter. Digital apparatus for accomplishing the selection of desired high order bits from the analog to digital converter output is also disclosed in detail. Use of a 'Monobit' and related simplified Fourier transformation radio receivers as disclosed in identified previous patents of the recited inventors and colleagues is preferred for embodying the digital radio receiver circuit included in a present system.

Digital receiver instantaneous dynamic range enhancement

A Fourier transformation algorithm implementation in which accommodation is provided for the output attenuation occurring when an input signal falls intermediate two terms of the transformation output series in its frequency. Corrected Fourier transformation terms, achieved by combining the magnitudes of attenuated Fourier transformation terms generated by the input signal at Fourier transformation frequencies distant to the input signal frequency, in either a vectorial or a scalar combination, are substituted for an attenuated Fourier transformation term according to the invention. Noise correction of the substitute Fourier transformation terms is also provided. The invention is disclosed through use of a global position system signal example that is subjected to a double Fourier transformation filtering process to enhance the incoming signal to noise ratio. Normally occurring 3.9 decibel attenuations in each Fourier transformation step are reduced to about 0.9 decibel each through use of the invention.

Accommodating fourier transformation attenuation between transform term frequencies

A Fourier transformation arrangement usable in an electronic warfare radio receiver for analyzing spectral content of multiple transmitter-sourced brief duration incoming signals for their signal characteristics. The disclosed Fourier transformation arrangement includes approximated Kernel function values disposed in a significant plurality of locations about a real-imaginary coordinate axis origin according to disclosed locating principles. The points are displaced from the origin by magnitudes having real and imaginary component lengths of powers of two commencing with zero. Multiplication involving a power of two component length during a Kernel function utilization are preferably achieved by way of an expanded binary shift multiplication algorithm in lieu of a full fledged digital multiplication algorithm. A group of guiding principles for selecting desirable approximation Kernel function locations is included.

Kernel function approximation and receiver

A digital cueing radio receiver system embodied using digital memory in lieu of analog delay lines and thereby avoiding delay line implementation difficulties. The cueing receiver system includes a wideband receiver portion providing an output signal employed for tuning a narrowband receiver portion of the system. Signal delay enabling use of the wideband receiver portion output signals for tuning the narrow band receiver portion selection frequency is provided by a digital memory circuit operating on analog-to-digital converted samples of input signal data of the receiver system. Approximated unity value related mathematical multiplication free Kernel function values are employed in the Fourier transformation. Avoidance of analog delay line-elements in embodying the system is a significant practical advantage of the invention.

Digital cueing receiver

An improved apparatus and method for determining the carrier frequency in a biphase coded signal such as the course acquisition code signal in a global position sensing system. The described system may also be used for other purposes. The described system is based on use of the conventional data signal squaring or frequency doubling step to remove biphase coding but performs a series of frequency reducing steps prior to applying the Fourier transformation sequence. The frequency reducing steps include heterodyne mixing and signal averaging. These frequency-reducing steps diminish the speed and capacity requirements imposed on the Fourier transformation sequence and thereby decrease the cost and complexity of the overall system.

Downconvert and average identification of biphase coded signal carrier

A simplified, weak GPS C/A code coherent acquisition method. When performing GPS signal acquisition, the strength of a signal received at a GPS receiver having an outside antenna is generally sufficiently strong such that only 1 ms of data needs to be used in acquisition to find the signal. However, for weak signals received at a GPS receiver, when the antenna is inside a building or vehicle, for example, a long record of data is needed for acquisition. The present invention reduces the calculation burden for GPS signal acquisition for a weak signal.

Signal folding coherent acquisition for weak global positioning system (GPS) C/A coded signal

A global position system radio receiver achieved through use of an electronic warfare receiver, and particularly one of the electronic warfare receiver output frequency channels, as a front-end signal processor for the global position system receiver. Electronic warfare receiver channel selection for such usage is described and the attenuating effect of electronic warfare receiver channel center frequency and global position system signal frequency differences are considered. A favorable comparison of present invention and conventional global position system receiver-generated results in processing a global position system signal are included along with control of a sampling frequency characteristic within the electronic warfare receiver in order to align global position system signal frequency and electronic warfare receiver channel location to an electable better degree.

GPS receiver with electronic warfare receiver front end

An electronic warfare apparatus for determining the location of for example a ground based source of electromagnetic radiation from a platform such as an aircraft. Location is determined using angle of arrival based vector determinations provided by signal differences detected in the ground based signals arriving at platform antennas. Elimination of angle of arrival errors arising from imprecise knowledge of platform electronic warfare antenna characteristics is a focal point of the invention and is accomplished through precision use of global position system information received via the same electronic warfare antennas. Accurate determination of electronic warfare antenna characteristics prior to consideration of the large distance multiplication factors imposed by aircraft to distant signal source geometry enables accurate distant signal source location using the invention.

Phase center measurement of electronic warfare antennas using GPS signals

An arrangement for calibrating the sample frequency determining clock in a global position system receiver using signals received from a Wide Area Augmentation System satellite or other Wide Area Augmentation System signal source. Such Wide Area Augmentation System based clock calibration is free of the Doppler frequency effects impressed on a global position system signal in view of the geo-stationary orbit of a Wide Area Augmentation System satellite. Use of the calibration invention enables correction of the pseudo range determination accomplished with global position system receiver output data. The invention may be considered a new use of signals available from the Wide Area Augmentation System. A noise-considered arrangement for comparing Wide Area Augmentation System and global position system frequencies is included.

Calibrating the sampling frequency of a GPS receiver

An improved global positioning system satellite signal acquisition method. The method of the invention reduces the number of operations in the block correlation used in determining Doppler frequency and time of the received GPS C/A or P(Y) codes. Reducing the number of operations in block correlation increases acquisition speed making it conducive to commercial and military GPS receivers

Acquisition for GPS C/A code and P(Y) code

An improved global positioning system satellite signal acquisition method and device. The method and device of the invention reduces the number of operations in the block correlation used in determining Doppler frequency and time of the received GPS C/A and P(Y) codes. Reducing the number of operations in block correlation increases acquisition speed and reduces energy requirements, aspects conducive to commercial and military hand held GPS receivers.

Acquisition through circular correlation by partition for GPS C/A code and P(Y) code

An apparatus and method for providing small size, high gain corner reflection of radio frequency signals for use in military and commercial applications. Conventional corner reflector practice is combined with electronic amplifying reflection devices such as the superregenerative amplifier to provide an array of antennas and amplifiers spread over each planar surface of a corner reflector. The specific antenna used may be selected from a plurality of various antenna types depending on the application. As in a conventional corner reflector, the amplified signal is reflected at the same angle and in the opposite direction of the incident signal.

Active corner reflector

This invention is directed to an expendable which includes an electronic circuit for introducing a simulated Doppler frequency shift. When dropped from an aircraft, the expendable is used to confuse hostile radar operations. In the past, the approach has been to use a high frequency electronic switch (PIN diode) and drive oscillator to change the impedance of the expendable antenna. This invention involves a simplification which combines the electronic switch and its drive oscillator into a single semiconductor component. By connecting a feedback circuit from the collector to the base of a high frequency transistor as well as to the two arms of the antenna, the antenna impedance is changed at the transistor oscillating frequency.

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Beavercreek, OH, United States of America

David M Lin