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Milligan T.,8204 W Polk Pl | Jones T.O.,System Center Pacific
IEEE Antennas and Propagation Magazine | Year: 2014

Arrays of two and four horizontal dipoles were used to achieve higher efficiency and vertical gain for several conductivities. These designs were compared to a single horizontal dipole. The four-horizontal-dipole array could be pointed 34° away from the vertical. The efficiency was reduced by only 1 dB. The groundwave was computed for all of the designs. The peak magnitude of the groundwave did explain the improved antenna efficiency. The antenna efficiency could be dramatically improved by increasing the antenna's height or operating frequency. © 1990-2011 IEEE.

Ontiveros M.,System Center Pacific | Arceo D.,System Center Pacific | Allen J.,System Center Pacific
IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) | Year: 2015

This work presents a comparison of RCS and Doppler spectrograms of a 10 m tall Vertical Axis Wind Turbine using the Physical Optics and Multilevel Fast Multipole Method numerical techniques. The MLFMM results are then compared with measurements. Simulations and measurements were performed at 1.5GHz, 3.6GHz, 5.8GHz, and 9.7GHz corresponding to electrical dimensions of 50λ-323λ. The average RCS using PO and MLFMM over the entire rotation period has good agreements for all frequencies; however, the PO RCS produces irregular Doppler spectrograms. The measured VAWT results have close agreement with the simulations. © 2015 IEEE.

Quimby J.T.,System Center Pacific | Thompson R.,System Center Pacific | Marhefka R.J.,Ohio State University | Rockway J.D.,System Center Pacific
Applied Computational Electromagnetics Society Journal | Year: 2015

A spherical harmonic expansion is proposed to provide a more efficient interface between a reflector antenna simulation code and an Uniform Geometrical Theory of Diffraction (UTD) ray tracing code. The principal bottleneck is a large number of dipole sources. As a consequence, a large number of dipole sources lead to a large number of ray traces, which increases the computational times in the UTD code. We propose to use a spherical harmonic expansion of the reflector fields as an efficient interface. This method saves significant computational times in the UTD code provided that the number of dipole sources per cell is large. © 2015, The Applied Computational Electromagnetics Society.

Reinhardt C.N.,System Center Pacific | Kuga Y.,University of Washington | Ritcey J.A.,University of Washington | Ishimaru A.,University of Washington | And 2 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2011

The performance of terrestrial free-space optical communications systems is severely impaired by atmospheric aerosol particle distributions where the particle size is on the order of the operating wavelength. For optical and near-infrared wavelengths, fog droplets cause multiple-scattering and absorption effects which rapidly degrade received symbol detection performance as the optical depth parameter increases (visibility decreases). Using a custom free-space optical communications system we measured field data in fog within the optical multiple-scattering regime. We investigate the behavior of the estimated channel transfer function using both real field-test data and simulated propagation data based on field-test conditions. We then compare the channel transfer function estimates against the predictions computed using a radiative-transfer theory model-based approach which we also developed previously for the free-space optical atmospheric channel. © 2011 SPIE.

Church J.,System Center Pacific | Chieh J.-C.S.,System Center Pacific | Xu L.,System Center Pacific | Rockway J.D.,System Center Pacific | Arceo D.,System Center Pacific
IEEE Antennas and Wireless Propagation Letters | Year: 2014

Traditional impedance-matching methods typically employ matching networks at the antenna input terminals. Alternatively, the antenna may be embedded with a non-Foster load to enhance the radiation bandwidth. This method is demonstrated here with the design of an electrically small box cage loop antenna (ka ~ 0.37). Simulated results using ideal non-Foster components are compared against a negative impedance converter (NIC) circuit realization. These results show that the VSWR bandwidth is improved 8× by using the NIC circuit. Simulated radiation efficiencies are also presented for the first time. © 2002-2011 IEEE.

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