Lorenzo Lo Monte’s research while affiliated with Telephonics Corporation and other places

Magnetron based marine radar technology is mature, affordable, reliable, and very effective for maritime safety applications. Commercial systems may be procured at a modest cost as compared to fully coherent solid state systems. Magnetron oscillators inherently generate random phase signals. Phase instability on a pulse-to-pulse basis impedes this class of marine radar from success in applications requiring coherency such as moving target indication (MTI) or in generating target imagery. This limitation may be overcome by incorporating radio frequency (RF) sampling and cross-correlation of the transmit and receive signal technology to augment the current capability of available systems. In this research, the pulse train on transmit and receive is correlated in order to reject interference and detect image targets. Sampling the transmit signal and the target echo on receive permits fully coherent processing. Marine radars traditionally operate non-coherently, and as such, offer limited surveillance in clutter rich environments. In this article, we report on a non-coherent marine radar that has been modified to produce a pseudocoherent or coherent-on-receive sensor system. This is crucial to MTI and target image formation. In laboratory experiments, we employed a magnetron oscillator based system to generate an inverse synthetic aperture radar (ISAR) image. The image was formed using four different algorithms: filtered back-projection (FBP), time domain back-projection (TDBP), an Algebraic reconstruction technique (ART), and frequency domain back-projection (FDBP). In our research, TDBP produces exquisite imagery of steel rods (Figure 16), and it is the standard developed in this paper. FBP performed poorly as compared to all other algorithms (Figure 17).

Non-coherent marine radar technology has matured over the past several decades. Researchers have investigated coherening one or more magnetron oscillator based marine radars by sampling the radar signals on transmit and receive [1]. We leverage this research to contribute to the science and technology of RF Tomography based upon exploitation of marine radar technology and these sampling techniques. This requires many steps. First, selecting and suitably modifying an affordable yet suitable marine radar. In this case, we employ a Furuno DRS25A. Second, by embedding an RF sampling circuit, we capture samples of the various radar waveforms. Third, we digitize these transmit and receive signals using a Signatec ADC model PX1500. Next, we design an experimental geometry to support image formation via RF Tomography. We apply Filtered Back projection (FBP) based upon the Fourier Slice Theorem (FST) in order to the match filtered the data and image targets. We provide both simulation analysis and experimental results in this paper.

We proposed an improved solution to two problems. The first problem is caused by the sidelobe of the dominant scatterer masking a weak scatterer. The proposed solution is to suppress the dominant scatterer by modeling its electromagnetic effects as a secondary source or “extra dependent transmitter” in the measurement domain. The suppression of the domain scatterer reveals the presence of the weak scatterer based on exploitation of multipath effects. The second problem is linearizing the mathematical forward model in the measurement domain. Improving the quantity of the prediction, including multipath scattering effects (neglected under the Born approximation), allows us to solve the inverse problem. The multiple bounce (multipath) scattering effect is the interaction of more than one target in the scene. Modeling reflections from one target towards another as a transmitting dipole will add the multiple scattering effects to the scattering field and permit us to solve a linear inverse problem without sophisticated solutions of a nonlinear matrix in the forward model. Simulation results are presented to validate the concept.

Non-coherent marine radar technology has matured over the past several decades. Researchers have developed coherent magnetron oscillator based marine radars by sampling the signals on transmit and receive [1]. We leverage this research to contribute to the science and technology of RF Tomography based upon exploitation of marine radar technology, and digital sampling / signal processing techniques. This requires many steps. First, selecting and modifying an affordable yet suitable marine radar. In this case, we employed a Furuno DRS25A. Second, by embedding an RF sampling circuit, we captured the various radar waveforms. Third, we digitized transmit and receive signals using a Signatec model PX1500 analog-to-digital converter (ADC). Next, we designed an experimental geometry to support image formation via RF Tomography. We applied Filtered Back Projection based upon the Projection-Slice Theorem, the Algebraic Reconstruction Technique, and classical Inverse Synthetic Aperture Radar imaging algorithms in order to match filter data and image targets. We provide both simulation analysis and experimental results in this paper.

A forward model for diffraction tomography is derived for the case of thin cylindrical objects by introducing a dyadic contrast function that takes into account depolarization phenomena, which were not previously addressed. As a result, polarimetric measurements may be used to distinguish between dielectric or metallic thin-cylindrical objects. In the case of metallic objects, it is also possible to reconstruct their direction.

Increasing congestion of the electromagnetic spectrum has spurred investigation into approaches that provide more efficient spectrum use. While many approaches focus on some type of orthogonality in time, frequency, or coding, another less explored option is mixed modulation of two complementary signals through intentional modulation of pulse. This study discusses intentional modulation of a linear frequency modulated (LFM) chirp radar pulse with a communications signal in order to conduct complementary activities with a combined signal. In order to reduce cross-interference between the signals, the communications message employs spread-spectrum encoding (binary M-sequences) and new modulation scheme with reduced phase change to modulate the LFM waveform. Preferred pair of M-sequences exhibit excellent auto-correlation and low cross-correlation properties that lend themselves to simultaneous transmission of channelised communication signals. The proposed approach is to modulate a radar signal with preferred pair M-sequences using binary reduced phase shift keying modulation that provides a low throughput, communications signal that could be used for administrative or navigation purposes. To measure effect on radar performance, comparison of the radar ambiguity function for the LFM signal is contrasted with combined radar-communication signal.

Multiple input multiple output (MIMO) beamforming is examined both theoretically and experimentally to highlight practical performance aspects that require a careful understanding when deciding if the MIMO concept is appropriate for a given application. Specifically, the time division multiplexing (TDM) and code division multiplexing (CDM) cases are compared. While both TDM and CDM form beams that agree closely with predictions, there are significant differences in system performance due to limits on the orthogonality of waveforms that occur when using CDM. These limits are manifested in the peak-to-mean sidelobe ratios, resulting in significant and extended range sidelobes consistent with a value approximately equal to the time-bandwidth product, and fairly independent from the number of transmitters or receivers used. In many cases, these sidelobes fundamentally limit the dynamic range of the radar. Simulations and experiments using a TDM/CDM MIMO radar validated these observations.