HF SKYWAVE SPATIALLY DIVERSE WAVEFORM RADAR: TRANSMITTERSUBSYSTEM IMPLEMENTATION ISSUES

摘要

Transmission of spatially diverse orthogonal waveforms inradar to support enhanced illumination control and surveil-lance timeline management has been recently discussed inthe radar literature. Such use of orthogonal waveformsin radar (sometimes referred to as MIMO radar) is poten-tially attractive in modern HF over-the-horizon (skywave)radar systems. However, HF radar implementation of or-thogonal waveforms present some special challenges towaveform design. HF radars operate over several octavesof RF frequency, have array inter-element spacing whichdeviates significantly from one half-wavelength, use non-linear power amplifiers, and have stringent spectral occu-pancy requirements. Implementation of specific orthogonalwaveform types present their own particular design require-ments, but some issues are generic and span a wide rangeof waveform classes. In particular, operation with over-sampled arrays can give rise to excessive reactive power.This can be mitigated by the use of a unitary transforminto a separate orthonormal beamspace, but this also trans-forms constant modulus waveforms favored in HF skywaveradar into waveforms with significant peak to mean varia-tion. Such amplitude variation results in loss in high-poweramplifier efficiency. The impact of operation with thosewaveforms with HF skywave radars is examined.