Showing papers on "Secondary surveillance radar published in 1983"

Performance Analysis of Monopulse Receivers for Secondary Surveillance Radar

Abstract: In modern secondary surveillance radar (SSR) the monopulse technique is currently introduced for the measurement of the azimuth of the targets. The monopulse technique is based on a suitable processing of signals received by a multiple antenna. In SSR the signals are generated by a transponder on the aircraft as replies to interrogations from ground equipment, and consist of trains of pulses. The monopulse measurements can be carried out on the basis of a single pulse from each train, so that it provides a great number of azimuth estimates. Many monopulse measurement devices exist, corresponding to different processing techniques. From the point of view of accuracy and precision, their behaviors differ with respect to the sources of errors, both internal (noise and imperfect calibrations) and external (interference and propagation effects). The four main types of monopulse receivers are analyzed here with respect to the effects of the internal error sources on the resulting measurement accuracy. After an introductory discussion of the performances of the receivers, a detailed analysis is carried out on the basis of a general mathematical model. The results are given in an analytical form and in some comprehensive diagrams.

VHF/radar transponder collision avoidance aid

Abstract: A radiotelephone and a radar transponder are interconnected in such a manner as to establish a VHF communications link via the radiotelephone in response to interrogation of the radar transponder. The radar transponder will ordinarily be periodically enabled and will transmit a code which partially identifies the transmission source in response to interrogation when enabled. The radiotelephone will also be periodically enabled so as to transmit a more complete identifying code and requests and coded information received via the VHF communications link will be decoded and displayed.

Radar performance studies of adaptive lattice clutter-suppression filters

Abstract: The paper describes the use of a prediction-error filter (realised in the form of an adaptive lattice filter) for enhancing the detection of a moving target (for example aircraft and migrating flocks of birds) in the presence of clutter. This process is well suited for use in a surveillance radar environment (for example air-traffic control). The clutter may arise owing to reflections from ground and weather disturbances. Experimental results are included in the paper, comparing the performance of the processor with that of a conventional moving-target indication (MTI) filter.

System for suppressing unwanted long-range and/or second-time-around radar echoes

Abstract: A receiving section of a surveillance radar equipped with a power oscillator in its transmitting section comprises several registers for the storage of values, perferably in complex digital form, representing the starting phase of a continuous wave at the instant of transmission of an outgoing pulse, these values being used thereafter to establish coherence with an incoming echo pulse at a time when the power oscillator is no longer able to do so on account of unavoidable frequency drifts or because of intervention of a new recurrence period. Thus, the stored values permit the correct detection of targets at the far end of the range and/or the cancellation of second-time-around clutter echoes. The continuous wave may be generated by a coherent oscillator, phase-locked during each recurrence period by the outgoing pulse, or a separate crystal-controlled oscillator of highly stable frequency.

Radar image display

Abstract: PURPOSE:To prohibit the display of a track only for the secondary video without use of any special memory by separating the storage system for the memory of the secondary radar video from that from the primary radar video. CONSTITUTION:A primary radar video (PSR) signal which is converted into a binary value such as 4 bits excluding the highest value with an analog/digital converter 2 is compared with a secondary radar video (SSR) signal which is encorded into the highest value of binary 4 bits or the like by means of a comparison/selection circuit 4 and the larger value is held in a buffer memory 5 until the updating of a video memory 7. This updating is accomplished by reading out the contents of the memory 7 in such a manner that they are outputted as intact through a decoder 9 not applied to a track processing circuit 8 when corresponding to the SSR signal while applied to the circuit 8 to control the trailing when corresponding to the PSR signal. This permits the prohibition of track display only for the SSR signal thereby preventing misrecognition in reading the indication of the SSR signal without use of any special memory.

Optimisation of a generalised square-law detector

Abstract: An interference improvement factor (IIF) is derived for a generalised square-law detector utilised for a radar application. This factor, which is a ratio of two quadratic forms, incorporates the effects of antenna beam shape as the radar beam scans over the target, interference due to receiver noise plus clutter and the target Doppler frequency. The IIF can be maximised to improve target detectability via eigenvalue, eigenvector techniques so that the optimal weights to be applied by a weighted integrator following the square-law device can be determined for an N-pulse batch. Numerical results are presented for a sea surveillance application.

Radar target detector

Abstract: PURPOSE:To reduce the processing time by an efficient sweep correlation processing using only effective information when there is a hit in the SSR target detection with a target detector of a secondary surveillance radar (SSR) made to facilitate sweep correlation. CONSTITUTION:The up-to-date-hit information 1 is stored temporarily in a separate memory table instead of being stored into a memory table corresponding to a range bin R7 immediately and based on the information, a sweep correlation is done for range bins R2 and R5 closer in the distance. The distance of the up- to-date hit 1 is compared with that of a range bin R10 next to the range bin R5 subjected to the final sweep correlation. When they are different, a memory table is acquired a new corresponding to the range bin to shift the hit information but when they are the same, it isn't. Therefore, memory tables are only necessary for the range bins R2, R5, R7 and R10 eliminating the need for providing all range bins with corresponding memory tables. This allows single and simple searching of memory tables enabling a waste-free efficient sweep correlation, hence reducing the processing time.

Comparison of a jump-diffusion tracker with a Kalman tracker: an evaluation with emphasis on air traffic control

Abstract: A sophisticated starting point for a probabilistic approach to the radar tracking problem is a Markov jump-diffusion model for the aircraft dynamics, its control and the radar measurements. From nonlinear filtering theory, a closed form description of the evolution of the conditional distribution of this Markov process can be obtained. This jump-diffusion filter, however, is infinite dimensional and approximations are necessary for algorithmic implementation. The indirect approach of approximating the jump-diffusion by a diffusion leads to a Kalman-like tracker. The recently developed approach of approximating the jump-diffusion filter directly, leads to a bank of interacting Kalman-like trackers. The report is directed to the evaluation of tracking algorithms that are based on these two approaches. Their results are compared in an air traffic control environment. It is concluded that the jump-diffusion' tracker performs considerably better than the Kalman tracker.

Antenna system for a secondary radar transponder

Abstract: 1. A secondary radar transponder with an antenna system having an omni-directional receiving antenna (8) for 45 degrees linear polarisation provided for the reception of an interrogation signal, and an omni-directional narrow-band transmitting antenna (9) designed for the specified polarisation is provided for the emission of response signals having a specified polarisation, in particular vertical linear polarisation, characterised in that the receiving antenna (8) is a wide-band antenna covering a broad frequency band that lies above the narrow frequency band of the transmitting antenna (9), that the transponder is connected by a first, wide-band receiving channel (1) to the wide-band receiving antenna (8), and that the transponder is connected to the narrow-band transmitting antenna (9) by a second, narrow-band receiving channel (2) and by a responder transmitter (7) driven by the two receiving channels via a transmitting/receiving switch (6), e.g. a circulator, as a result of which the narrow-band transmitting antenna (9) of the transponder is used to transmit the response signals and also to receive response signals in this narrow-band frequency, range.