Pulse Repetition Frequency Mode Research Articles

Detection of hypersonic weak targets by high pulse repetition frequency radar based on multi‐hypothesis fuzzy‐matching radon transform

AbstractFor the integration detection of near space hypersonic weak targets by high pulse repetition frequency (PRF) radar, a novel method named Multi‐Hypothesis Fuzzy‐Matching Radon transform (MHFM‐RT) is proposed for the near space hypersonic target detection and tracking. For remote hypersonic target detection, to avoid range ambiguity, current radars always use a low PRF mode, which limit the number of pulse accumulations. Using the high PRF mode, the fuzzy folding will appear in the target range measurements when target trajectory crosses range fuzzy intervals. Therefore, there is a contradiction between range ambiguity and energy accumulation. The proposed method is used to match the fuzzy measurements, so as to realise the correct integration in the condition of range ambiguity. Firstly, considering the need of range ambiguity resolution, the mode of staggered PRF is used. Secondly, the first frame measurements are periodically extended for multiple‐fuzzy hypothesis. Finally, the weak target track is accumulated in MHFM‐RT domain, and the signal integration and ambiguity resolution can be realised simultaneously. The proposed method expands the Variable‐Diameter‐Arc‐Helix Radon transform (VDAH‐RT) method to fuzzy folding conditions. Compared with the existing methods, for 7‐scan measurements non‐coherent integration, the detection sensitivity of the proposed method is about 0.5–1 dB higher than that of the IMM hybrid filter algorithm, and about 1 dB higher than that of the RHT‐TBD approach, and it needs less storage space and has higher detection probability.

White noise jammer mathematical modelling and simulation

The radar equation is the fundamental mathematical model of the basic function of a radar system. Moreover, there are many versions of the radar equation, which correspond to particular radar operations, like low pulse repetition frequency (PRF), high PRF, or surveillance mode. In many cases, all these expressions of the radar equation exist in their combined forms, giving little information to the actual physics and signal geometry between the radar and the target involved in the process. In this case study, we divide the radar equation into its major steps and present a descriptive mathematical modelling of the radar and other related equations utilizing the free space loss and target gain concepts to simulate the effect of a white noise jammer on an adversary radar. We believe that this work will be particularly beneficial to instructors of radar courses and to radar simulation engineers because of its analytical block approach to the main equations related to the fields of radar and electronic warfare. Finally, this work falls under the field of predictive dynamics for radar systems using mathematical modelling techniques.

Clutter suppression approach for non‐sidelooking airborne radar with medium pulse repetition frequency

For non-sidelooking airborne radar operating in medium pulse repetition frequency mode, the space–time adaptive processing (STAP) technique suffers from a significant performance loss due to the range dependence of clutter. Here, an efficient clutter suppression approach is presented to improve STAP performance. Utilising the characteristics of clutter, the near-range clutter, the major reason for the performance degradation, is extracted from raw returns using a specially designed oblique projector firstly, and then is mitigated by an adaptive beamformer estimated from the extracted components. Subsequently, an azimuth-Doppler STAP beamformer is employed to further suppress the residual clutter. To enhance the robustness of the approach, a simple steering vector calibration technique is taken into account. The proposed approach can eliminate the near-range clutter effectively, and therefore alleviate the clutter range dependence greatly. The STAP performance can be improved significantly. Simulation results demonstrate the effectiveness of the presented method.

Adaptive attenuation of clutter and jamming for array radar

Minimising clutter breakthrough while adaptively cancelling jamming is a recognised problem for radar, especially for airborne radar where ground clutter is distributed widely in direction and Doppler frequency. By adapting the angular gain of an array independently for each range bin and by adapting both the small and the large scale order of its weight function, it is shown that clutter can be reduced to levels well below what is possible for a conventional antenna and that the advantage remains when jamming is cancelled at the same time. Separating the spatial adaption into processes for different spatial scales enables the weights for an array of several thousand elements to be calculated with a numerical workload similar to that for a sub-arrayed radar, but with improved clutter suppression ultimately deriving from access to signals from individual array elements. The arguments are illustrated by simulations for an airborne radar operating in a high pulse repetition frequency mode.

Medium PRF for the AN/APG-66 radar

This paper discusses the medium pulse repetition frequency (PRF) pulse doppler mode of the AN/APG-66, the multimode fire control radar for the F-16A/B aircraft. This radar is currently in production and as of January 1984 over 1700 have been delivered. Included is a discussion of the three PRF types: high, low, and medium PRF, leading to the conclusion that for an airborne, look-down application the medium PRF waveform is the best choice. System tradeoffs between a high peak power and a low peak power transmitter are discussed which show that when only a medium PRF waveform is required, the high peak power transmitter yields better performance. Some system design considerations concerning the PRF selection and sidelobe clutter are also included. Finally, the radar mechanization is presented. The AN/APG-66 radar in general, and its medium PRF mode in particular, have undergone extensive operational evaluation and the results have been excellent. The radar has met or exceeded its performance design specifications and the field reliability has been outstanding. For example, for the year 1983 the MTBF was 102.9 h based on 64 204 operating hours from two operational air bases.