Abstract: A monitor for an electronic TACAN (ELTA) includes a 16-way switch whereby samples of the r.f. signal fed to each TACAN antenna element are fed via a common lead 30 to (a) means for r.f. phase correlating the samples with the transmitter generated signals, and (b) means for determining the relative phse and amplitude of the low frequency modulations in the sampled signals.

Abstract: A steered adaptive antenna arrangement including an adaptive beamforming network 10 to which the output signals of an array of antenna elements are applied, the network having a feedback wherein the summed output of the network is correlated with each element signal, applied to a limiter and added to the steering component whereby the derived value is used to drive the associated weight coefficient, characterized in that the summed output of the beamformer network 10 is further applied to a desired signal estimator 11 the output of which is subtracted from the summed output to provide the feedback input 12 to be correlated with each element signal.

Abstract: An electronic navigation beacon, particularly for coastal navigation, in which an unmodulated carrier f.sub.c is transmitted from the first antenna of a pair of antennas, and a periodically modulated sideband f.sub.c .+-.f.sub.a is transmitted from both antennas, where f.sub.a is in the audio frequency domain. A cyclical RF phase variation is imposed on the sideband signal transmitted from the second antenna. The effect in space is that of a rotating radial having an audio frequency null, the periodic modulation providing the listener at a remote point with timing information enabling determination bearing as a function of the time of passage of the radial through the remote point relative to the start of rotation of the radial.

Abstract: 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.

Abstract: A received signal processor in a remote receiving (airborne) station including amplitude modulation elimination means for improving the determined value of Doppler beat, angle representing signal, generated from reception of the transmissions of a Doppler Scanning (ground) Beacon station, for enhancing the accuracy of air derived angle data in the presence of near-angle multipath signal.

Abstract: A simulated Doppler navigation beacon system providing second order spatial diversity with respect to excitation of its commutated 2-dimensional main (coordinate) array and a linear reference array. For elevation measurement, the main array excitation is advanced in elevation, one element at a time during each scan cycle, but the lateral (horizontal) excitation is varied pseudo-randomly in both main and reference arrays while maintaining the same lateral spatial relationship between the main and reference array element pair excited at any time. The reference array comprises a larger number of elements than the horizontal elements in said array and the adjacent group of reference elements excited during any scan cycle of the main array is shifted laterally for each succeeding main array scan cycle.

Abstract: A Doppler Navigation ground beacon antenna commutating arrangement in which the primary scan program radio frequency and reference radio frequency signals are both applied to the antenna elements in mutually opposite commutation directions. The two signals are separated in frequency, as they are in the prior art fixed reference antenna arrangement; accordingly, a fixed reference antenna is no longer required. The novel system greatly reduces the effect of multipath reference signals, especially in situations where there is one or more inopportunely located reflecting object.

Abstract: 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.

Abstract: 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.

Abstract: A Doppler navigation system with tracking filter for reducing suceptibility to multipath signals. For acquisition of a Doppler ILS angle representing a signal within a spectrum also containing multipath signals, a self-tracking variable-Q filter arrangement is used, with wide band acquisition (low Q) followed by progressive steering of the filter center frequency to the desired signal frequency, together with decrease of the filter bandwidth to an equivalent of 2 beamwidths (high Q) at final balance.

Abstract: A method of determining, at the site of a radio beacon, the location of any beacon signal reflecting objects, in which method the beacon is caused to transmit a directionally coded signal over a given service sector, in which during said signal transmission a radio receiver is moved towards said beacon along a predetermined path in said sector, in which during said movement all beacon-derived signals received by the receiver are recorded in a form such as to be coded at least in respect of beacon related bearings and in which said recorded signals are individually isolated in such a manner as to permit identification and location of any of said reflecting objects.