Deconvolution of target signature for a scene with bistatic impulse radiating antennas and a sphere
A model for an impulse radiating antenna (IRA) has been developed in WIPL-D. A scene using a bistatic pair of these IRAs is modeled with a sphere target and is simulated in the frequency domain. The input to the antenna is a Gaussian pulse, and the current on the receive antenna is plotted vs. frequency. This receiver response is proportional to the scattered field from the sphere. The frequency domain data are processed to give the time domain response. The objective of this work is to deconvolve the signature of the scatterer from the receiver transient response. Additional separate simulations for each scene component and electromagnetic interaction were needed and were performed using WIPL-D. The process is successful for this scene, which does not include a ground plane. The analysis of the simulated data and deconvolution of the target signature are done in Matlab.
WIPL-D model and simulation results for a 46cm diameter impulse radiating antenna (IRA)
WIPL-D was used to model and simulate an impulse radiating antenna (IRA) with a 46cm diameter paraboloidal reflector and 45 degree feed arms. Model views are shown and the results of frequency domain simulation up to 20GHz are shown to agree with results from published measurements. Beam patterns at three frequencies show the highly directional behavior of this antenna. The simulated frequency domain data is inverse Fourier transformed to obtain the time domain response to a Gaussian pulse input. This response is integrated to obtain the response to a step input, which compares well with the theorized step input response of the IRA.
Observations of nearshore infragravity waves: Seaward and shoreward propagating components
[1] The variation of seaward and shoreward infragravity energy fluxes across the shoaling and surf zones of a gently sloping sandy beach is estimated from field observations and related to forcing by groups of sea and swell, dissipation, and shoreline reflection. Data from collocated pressure and velocity sensors deployed between 1 and 6 m water depth are combined, using the assumption of cross-shore propagation, to decompose the infragravity wave field into shoreward and seaward propagating components. Seaward of the surf zone, shoreward propagating infragravity waves are amplified by nonlinear interactions with groups of sea and swell, and the shoreward infragravity energy flux increases in the onshore direction. In the surf zone, nonlinear phase coupling between infragravity waves and groups of sea and swell decreases, as does the shoreward infragravity energy flux, consistent with the cessation of nonlinear forcing and the increased importance of infragravity wave dissipation. Seaward propagating infragravity waves are not phase coupled to incident wave groups, and their energy levels suggest strong infragravity wave reflection near the shoreline. The cross-shore variation of the seaward energy flux is weaker than that of the shoreward flux, resulting in cross-shore variation of the squared infragravity reflection coefficient (ratio of seaward to shoreward energy flux) between about 0.4 and 1.5.