International Standard Electric Corporation

International Telephone and Telegraph Corporation

Paul Barton

Francis G Overbury

William D Waddoup

Peter Kenneth Blair

Kevin M Kelly

A phased array radar system, such as may be used in a low-angle tracking radar or direction finding equipment, includes a multi-channel digital filter to remove unwanted multipath signals. The R.F. signals from the array are first converted to zero I.F. and digitized. After n-channel Doppler filtering (13) the digital signals are subjected to filtering (14) either to effect band-pass spatial filtering, thereby attenuating generally all signals arriving outside preset angular limits, or notch filtering which heavily attenuates signals arriving from one particular angle. In one embodiment spatial filtering is followed by notch filtering. The filtered signals are then beam-formed (15) before being applied to further digital processing, such as beam peak tracking (16).

Phased array signal processing

An array (aperture) signal processor using surface acoustic wave delay lines for reordering of the received signals according to the prime number transform algorithm. The output of the processor is a radar response equivalent to forming a multiplicity of narrow beams essentially simultaneously. Reordering of the received signals is simply a matter of rearranging the hardwired connections to a first SAW delay line, and convolution of the reordered signals is achieved by phase weighting the taps in a second SAW delay line which forms part of a transversal filter.

Multiple beam receiving array signal processor

A height finding arrangement for a range/azimuth surveillance radar using a mechanically rotated planar antenna array. The received outputs from the array are combined with suitable weighting functions to give two sectorial pattern signals whose effective phase centers are respectively above and below the center of the array aperture. The phase difference between these two signals is measured to provide the elevation angle of the target.

Height finding radar

A radio navigation system of the simulated Doppler type, including a ground beacon having a multi-element linear antenna array, the elements of which are energized discretely and, in turn, to provide digitized scanning. A remote receiver, in an aircraft on landing approach, for example, derives a beat signal relating to a navigational angle. The remote receiver has a bandpass filter covering the range of Doppler beat frequencies of directly received signals and also detects the start of each ground beacon commutation cycle. A unique combination of inhibiting circuits for eliminating filter transients during at least part of its transient response time and filter cut-off characteristics affords discrimination between direct and multi-path signals when the angular separation of the paths of those signals is at a minimum.

Doppler navigation system with enhanced multi-path discrimination

A scanning beam navigational beacon for transmission to a remote station (aircraft, for example) which measures a navigational angle therefrom. A thinned, two-dimensional main antenna array and linear reference array are provided. A single antenna element is provided at each vertical level of the array. Reference radiations are based on main array phase to allow coherent signal processing at the remote station. Azimuth frequency diversity is provided by grouping of the excited main elements and reference array elements at different frequencies, all features cooperating to minimize the effects of azimuthally displaced multipath signals which may fall inside the far-beam of elevation guidance. Thus, the effective array aperture exhibits a distributed frequency pattern in the azimuth plane.

Scanning beam navigational beacon with transmitted coherence reference

A scanning beam radio guidance system in which a ground beacon equipment transmits a single frequency collimated beam which sweeps a space sector of interest, and also transmits a frequency offset reference signal. An airborne remote receiver is responsive to both transmissions and includes post-detection signal processing means in the form of a time gate for inhibiting those parts of the main beam signal corresponding to angles outside the sector. A filter is also included for reducing the total spectrum contribution of the residual side-lobes of any out-of-sector beam signal.

Scanning beam receiver

A receiving system for a time-reference, scanning beam radio guidance system in which the scanning beam, an offset frequency reference signal and a time reference signal are provided from the ground beacon location. The receiving system includes a first detector responsive to the scanning beam and offset reference signals to provide a spectrum centered about the offset signal. A bandpass filter with sloping skirts on both sides of the center (offset) frequency provides tapering, with decreasing amplitude response on each side of the center frequency, the width of the spectrum being a function of the aperture of the beam transmitting antenna at the ground beacon. Angular information is determined by thresholding the beam signal to find two points on either side of beam center, averaging these times and comparing with the time-reference signal to air-derive angular navigational data, especially for aircraft landing approach systems.

Scanning beam receiver system with coherent post-detection signal

A Doppler Radio Navigation beacon with multi-element reference and main commutated arrays. The reference signal is programmed among the reference array elements irregularly to provide spatial diversity to the reference signal to eliminate or substantially reduce reference masking effects in certain multi-path situations (as observed at a remote receiving station such as on an aircraft on landing approach deriving angle information from said beacon). A similar irregular element excitation program is imposed on the normal array preserving coherence in the relative radiator movement (during commutation) between reference and main arrays.

Doppler navigation system with reference signal source diversity

A receiving arrangement for a pulse radar tracker facilitating low elevation angle tracking. The received signals are sampled along the focal plane of the receiving antenna system aperture. Range gating at IF and delay line serialization are provided to generate a simulated (synthetic) scan of the aforementioned aperture plane in the form of a coherent signal waveform. The main lobe of a multipath (ground reflection in the elevation case) is substantially eliminated by the time gating and filtering is provided to greatly reduce the corresponding sidebands. Desired (direct) received signals are substantially unaffected.

Low angle radar

A radio navigational device for determining the angle of a mobile craft by analyzing the signals arriving at each element of a linear array of n equally spaced elements. A series of received R.F. pulses emanating from the mobile craft by transmission or reflection provide contemporaneous signals at the antenna elements with a phase difference .psi. between successive elements in accordance with the angle of arrival of the R.F. pulses. Using 'zero' IF techniques, each signal of the series is processed to provide signal outputs in I and Q form. Sequential or parallel sampling of these I and Q signals provides a synthesized scanning beam signal from which .psi. is determined.

Radio direction finder with array element signal processing

A Doppler type radio navigation system in which each element of a linear array is energized discretely and sequentially to produce a simulated Doppler effect at a remote location such as an aircraft on landing approach. A reference signal is also transmitted, and a receiver at the remote location 'sees' a Doppler frequency shift proportional to the sine of the angle subtended by the receiver normal to the axis of the array by processing of the commutated data against the received reference signal to obtain a beat. A sum and difference transversal tracking filter arrangement is included for tracking the desired beat signal to exclude multi-path spurious beat signals. The tracking arrangement includes a voltage controlled oscillator, the detected beat signal being taken therefrom. Low noise bandwidth is obtained and performance under severe multipath conditions is improved.

Tracking filter for frequency measurement in a Doppler type navigation

A navigation guidance receiving system for use with a Doppler navigation beacon of the type comprising a commutated linear array for producing a simulated Doppler effect. The receiving system includes a wideband Doppler beat waveform information filter and measurement circuits. Means are also provided to gate the filter output synchronously to allow dissipation of the filter transient response. The result is reduced filter frequency 'pulling' and reduced measurement error due to the effect of multipath signals having beat frequencies in the filter rejection band.

Navigation receiver with doppler filter gating

A signal processing arrangement, particularly for Doppler ILS, giving complete scanning verification and tracking filter operation. Two commutated filters are driven by two voltage controlled oscillators whose roles are interchangeable. One filter is used solely for information signal tracking and the other solely for scanning. If the true signal is being tracked, the peak output from the scanning filter corresponds in amplitude and frequency to this signal and occurs at the same time as the frequency coincidence of the two oscillators. If the incorrect signal is being tracked, there is non-correspondance between the peak output and the signal being tracked. This is detected and the roles of the oscillators are interchanged, causing the oscillator which was scanning to reside on the correct signal and the other oscillator to adopt the scan program.

Signal processor for doppler type navigation system

Radio navigation receiver apparatus for operation with ground beacon equipment of the simulated Doppler type (having a commutated array). The receiver derives a beat between the received ground beacon (commutated) signals and a reference signal also from the ground beacon. Angular information is extracted from this beat signal. Means are included for determining the commutation times and scan reversals at the receiver location, so that the effect of phase transients can be ameliorated by discriminating against the received signal at these phase transient times.

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Bishop's Stortford, United Kingdom

Paul Barton