Real-time imaging and wavevector analyses of radio waves incident to electromagnetic absorbers
Radio waves incident to electromagnetic absorbers have been experimentally visualized for the first time, which has been accomplished by the real-time visualization method for high-frequency electric field distributions: the live electrooptic imaging technique. Imaged have been electromagnetic reflections, refractions, and standing wave formations at sheet absorbers as well as gradual variations of wave fronts at a ravine plane of pyramidal absorber. Their wave properties have been clarified qualitatively as well as quantitatively by experimental mapped wave vectors.
Wavevector mapping for antenna emission by Fourier transform of complex electrooptic images
A unique approach has been proposed and demonstrated for experimental analyses of electromagnetic emission from planar antennas; their emission wavevectors are mapped in a wavenumber space. The proposed method consists of (a) the live electrooptic imaging technique visualizing their near fields in real time and (b) the two-dimensional Fourier transform of complex electrooptic images providing power spectra of emission. A proof-of-principle demonstration has been performed successfully for an 18-GHz wave emitted from a 2×2 patch array and its manipulation by dielectric loading.
VLA stereoscopy of solar active regions. 2: Altitude, relative motion, and center-to-limb darkening of 20 centimeter emission
A newly developed method of stereoscopic correlation is applied to solar radio maps at a wavelength of 20 cm. On the basis of stereoscopic correlations between radio maps obtained on 6 different days we establish the presence of 66 radio source components associated with 22 active regions. We find the following statistical results for active region source structures at 20 cm: 1. The observed lifetime is consistent with an exponential distribution having an e-folding time scale of greater than 18 days. 2. The average altitude of 20 cm sources is 25 +/- 15 Mm; 90% of the sources are found in heights less than 40 Mm. 3. The average diameter of discrete source structures is 48 +/- 15 Mm, implying a vertical/horizontal aspect ratio of q(sub A) approx. = 0.5. 4. No significant source motion has been found with respect to the standard differential rotation rate of Omega = 13.45 deg - ((3 deg (sin(exp 2)B)). 5. We find a statistical limb darkening, which can be described by the relation (T(sub B)(alpha))/T(sub B)(0)) = 0.4 + ((0.6(cos(exp 2) alpha)) for sources with T(sub B) greater than 0.5 MK. 6. The degree of source polarization is 15% +/- 10% and is independent of source location. 7. Bright sources (greater than or approximately equal to 0.5 MK), or equivalently, long-lived sources (greater than or approximately equal to 5 days) show a systematic variation of their altitude as function of the center-limb distance.