Exploration of mimo radar techniques with a software-defined radar

The application of multiple-input multiple-output (MIMO) techniques to radar has been an active research topic recently due to their successful implementation in modern wireless communications systems. Looking to further leverage this success, many researchers have studied the applicability of spatial diversity and waveform diversity to radar. It has been shown that a MIMO radar system with spatially diverse transmitters and receivers utilizing orthogonal waveforms can provide benefits in target detection and parameter estimation when compared to a traditional phased array system. The current research typically attempts to apply the Swerling-I model when analyzing the performance of the multistatic MIMO system. However, this model was originally developed for monostatic systems and may not accurately describe the bistatic scattering behavior of targets. Other research has shown that MIMO arrays with co-located transmitters and receivers could be used in imaging applications by forming virtual arrays of elements. It has been suggested that time diversity be used to unambiguously separate the transmitted waveforms at the receivers. The application of suitable transmit waveforms which could be measured simultaneously and then separated by matched filtering could extend the usefulness of the virtual array idea. This dissertation explores MIMO concepts using both co-located and spatially diverse transmitters and receivers. A new target scattering model is presented which extends the Swerling-I model to include a new correlation parameter. This parameter allows the bistatic scattering behavior of the model to be tuned to more accurately represent some classes of real-world targets. It is shown through simulation that increasing the amount of correlation in the target effectively decreases the target detection performance of the MIMO system, so validation of these target models is necessary. A MIMO array with co-located antennas is also explored to study the effects of using orthogonal waveforms (or waveforms with low cross-correlations) on imaging quality. The approximation of a MIMO array by a virtual array whose elements are located at the center of mass of each transmitter/receiver pair is verified through simulation. Then images of both a point target and distributed scatterer are compared to test whether or not waveforms with small cross-correlations can be separated sufficiently in the receivers. It is shown that the separation is sufficient in both cases. The design and development of a flexible software-defined radar system (SDR) is outlined. Utilizing a powerful digital baseband transceiver with a 1 GSPS dual-channel ADC and DAC, the system is capable of generating, receiving, and coherently processing waveforms with up to 500 MHz of bandwidth. Two independent transmit channels and two independent receive channels are available, with a center frequency which can be tuned from 2–18 GHz. This system is used to measure the scattered fields from a complex target using spatially diverse transmitters and receivers. These results are used to evaluate the correlated scatterers model presented here. Furthermore, the SDR is used to measure a sphere using co-located transmitters and receivers to experimentally verify the imaging simulations.