The main objective of this chapter is to provide the reader who is not a radar specialist, with a tutorial on the main aspects of radar design architectures and techniques, which support conventional radar modes. It is aimed to provide the reader with a general understanding of how current radars are designed and how they function by presenting some typical designs, without covering all the detailed techniques available. Radars which employ mechanically scanning antennas such as parabolic reflectors and phased array radars which utilise electronic scanning techniques are presented. The main functional components employed and the basic principles of radar signal processing are also discussed.

In this chapter, techniques for providing high cross-range resolution are presented, which correspond to the direction perpendicular to the radar's radial vector.

The high-resolution techniques presented in this chapter can be considered to be extensions of the main target recognition methods discussed earlier in the book. The super resolution and monopulse techniques effectively improve the resolution of radar measurements by utilising relatively high signal-to-noise ratios. However, for the practical implementation of these methods, the radar must operate at higher than normal sensitivities, which means that the target range is short or there is time available for long integration periods. The polarisation techniques are directly compatible with, and would be used in conjunction with, other high-resolution methods. Relatively high signal-to-noise ratios are required to extract all the polarisation matrix components. The impulse and ultra-wideband techniques are extensions of high-range resolution methods and tend to have niche applications. The combined high-range resolution and high-frequency resolution techniques are based on the respective individual techniques and can be applied to targets with mechanical propulsion systems. Components such as rotors, rotor blades and jet engines can be detected, recognised and localise in range, to supplement range profile data.

The detailed requirements for the radar components needed to support target recognition functions are dependent upon several factors. The key ones are the type of high-resolution mode being employed, the range and the type of target, the level and the reliability of the target recognition capability required and the clutter environment. Although requirements for individual applications vary considerably from recognising ships with ISAR at short range, to discriminating the warhead at a range of several hundred or even thousands of kilometres in ballistic missile defence, general guidelines can be provided.

From the operational viewpoint tracking radars are considered to be well suited for incorporating high-performance target recognition modes, while maintaining the main tracking function. Active-phased array radars can also support high-resolution modes, but are more constrained by design architecture issues than the trackers. Active arrays with fixed faces have more time available than the rotating designs, so can support modes with longer dwell periods. The passive-phased array radars are the most difficult for incorporating a target recognition function, while maintaining the key operating functions of the radar. However, passive array designs, which include an azimuthal squint capability, provide potential for increasing the dwell period for implementing stepped frequency high-range resolution modes. Phased array radars have surveillance and tracking functions to perform, so target recognition modes have to be implemented within already tight resourcing budgets. For environments with large numbers of targets to be recognised, radars are under development that are to be specifically used for target recognition. For systems, such as tracker radars, that can operate with very short engagement timelines, the target identity decisions would be made automatically. For longer range surveillance and multi-function radars, there would normally be sufficient time for the operator to study the signature data and the computer's recommendations and make the final decision on the target's identity and the appropriate response to the threat.

Within this chapter the various processes which are required to provide a radar target recognition function are brought together and build on the concepts that have been discussed earlier in the book. Key radar measurements issues, which were extensively presented earlier, are reviewed and include a discussion on target signature distortion in Section 12.2.

Radar is the key sensor for providing a long-range, all weather, day and night, non-cooperative target recognition capability. In this final chapter, the main radar techniques employed for recognising targets and the key technical and implementation issues are summarised.