Tegan Webster

Antenna beam patterns in MIMO radar

This paper deals with the development of an appropriate multistatic or multiple-input-multiple-output (MIMO) radar ambiguity function. Earlier work analyzed the case of isotropic antennas; in this work, we show how to include antenna beam patterns into the model. We consider the case of fixed sensors and a general distribution of objects, each undergoing linear motion; thus the theory deals with imaging distributions in phase space. We outline the derivation for a model for the data that is appropriate for narrowband waveforms in the case when the targets are moving slowly relative to the speed of light. From this model, we develop a phase-space imaging formula that can be interpreted in terms of filtered backprojection or matched filtering. For this imaging approach, we derive the corresponding phase-space ambiguity function or point-spread function. We show plots of the phase-space ambiguity function for various geometries.

Multistatic polarimetric radar data modeling and imaging of moving targets

This paper advances the theory for multistatic imaging of non-interacting moving targets through the development of a vector radar data model for multiple transmitters and receivers and accompanying imaging operations for visualizing multistatic radar data in a common reference frame. The electromagnetic data model incorporates polarization and antenna effects, and the transmit waveform and scattering behavior of the target are left arbitrary for greater flexibility to model multiple scenarios. Two imaging operations are derived that combine the data collected at each receiver, first assuming that the contributions from all transmitters in the scene are separable and then assuming that the contributions from all transmitting antennas cannot be separated. The data model and imaging operations are used to simulate multiple antenna geometries and transmission schemes. Images produced from simulated data exhibit angle- and polarization-dependent scattering behavior consistent with the antenna geometry, transmit waveforms, and target specific to each scenario.

Deterministic and statistical models for multistatic ambiguity functions

This paper gives a comparison between two different approaches for developing a multistatic radar ambiguity function. One of these approaches is deterministic, and the other is statistical. The paper briefly summarizes both approaches and includes side-by-side simulation results for several cases. Although the two approaches are different in some fundamental aspects, the simulation results are quite similar.

Multistatic Velocity Backprojection for visualizing simulated and experimental multistatic radar data

Multistatic Velocity Backprojection (MVBP) is a technique for visualizing multistatic radar data using bistatic range and Doppler information and facilitates the localization of moving targets in a common reference frame. In this paper simulated and experimental passive multistatic radar data are processed using either traditional range-Doppler processing or, in the case of velocity ambiguous targets and high duty cycle and low PRF waveforms, Quasi Fast-Time Matched Filtering (QFTMF). The processed simulated and experimental data are then combined and visualized using MVBP.

Mitigating interference via spatial and spectral nulling: Open air experimental results

Phase only transmit nulling may help the next generation of radar systems operate in an over-crowded RF spectrum. Open air experimental results from an eight-channel X-band radar test bed are presented that demonstrate an approach for generating constant modulus waveforms that possess spatial nulls when transmitted from an antenna array. The Re-iterative Uniform Weight Optimization (RUWO) algorithm is utilized to generate phase only weights using both a deterministic and adaptive approach. The two strategies are compared. The results demonstrate that RUWO can be used to create spatial nulls and highlight the need for careful calibration of both the transmitter and receiver.

Detection Aided Multistatic Velocity Backprojection for passive radar

This paper extends previous work to process and combine data from multiple bistatic pairs in a passive multistatic radar system. The previously presented Multistatic Velocity Backprojection (MVBP) combines and visualizes multistatic radar data. MVBP generates a six-dimensional data cube in position and velocity but does not provide a mechanism for detecting targets within the space. This paper discusses Detection Aided Multistatic Velocity Backprojection (DA-MVBP), a method for seeding MVBP with detections from individual bistatic pairs. DA-MVBP reduces the space through which it is necessary to search for targets in backprojected multistatic radar data and may result in enhanced parameter estimation and detection performance over traditional multilateration of detections. In this work DA-MVBP is applied to experimental passive multistatic radar data.

Phase-only adaptive spatial transmit nulling

Adaptive phase-only transmit nulling was previously demonstrated using an eight-channel radar test bed. An error in the calibration software that left one of the transmit elements uncalibrated has since been corrected. New experimental results are presented that demonstrate improved performance relative to previous experiments. In this paper the Reiterative Uniform Weight Optimization (RUWO) algorithm, which utilizes the maximum signal-to-interference plus noise ratio (SINR) framework in a reiterative fashion, is used to generate adaptive phase-only weights from received interference data. Additionally, this work investigates the impact of the bandwidth of the interference signal on the ability to adaptively produce spatial nulls using RUWO.

Modeling of transmission, scattering, and reception for multistatic polarimetric radar

This paper develops a data model and corresponding imaging operation for multistatic polarimetric radar. The mathematical model describes the processes of radiation from a transmitting antenna, scattering from a moving target, and reception at a receiving antenna. A bistatic scattering matrix based on physical optics and the fast-time Doppler effects of a moving target are incorporated. Simulations are presented that consider a moving target in multiple transmitter and receiver configurations with multiple transmit waveforms and polarization schemes.

Airborne multistatic polarimetric radar modeling

Previous work developed a data model and corresponding imaging operation for multistatic polarimetric radar with stationary transmitters and receivers and moving targets. This paper extends the model to an airborne multistatic polarimetric radar scenario and considers multiple moving transmitting and receiving platforms in addition to moving targets. The formulation results in an expression for the received data that may be coherently combined across receivers, represented in a global coordinate system.

Interference mitigation via phase only transmit nulling: Preliminary experimental results

The increasingly crowded RF spectrum necessitates development of techniques that foster coexistence between multiple RF users. Radar systems can typically mitigate received interference using sidelobe cancellation and adaptive beamforming. In the future, radar systems could possibly use similar techniques to produce nulls in the transmit beampattern further reducing RF fratricide. However, transmit nulling is difficult due to the constant modulus constraint associated with the waveforms transmitted by high power radar systems. Several algorithms have been developed that attempt to determine phase only (PO) weights capable of inducing a transmit null. In this talk, the re-iterative uniform weight optimization (RUWO) algorithm is used as a means to produce PO weights from a measured interference covariance matrix.