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We demonstrate experimentally that phase-conjugate techniques can be used to achieve super-resolution focusing of electromagnetic waves in a multipath indoor environment at 2.45 GHz. The focusing phenomena was used to direct independent signals to two locations separated by approximately one-half wavelength, thereby creating two simultaneous channels at the same frequency. An increase in channel capacity is shown to be achievable by an experimental transmission of a 1 Mbps signal over two channels created using a four element phase-conjugate array.

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We report the experimental observation of an inverse Doppler shift from the motion of an ordinary solid object. The experiment used left-handed, or backward, spin waves in a magnetic thin film. As a pickup antenna was moved toward the spin wave source, the measured frequency decreased. In contrast, an increase would be expected in everyday experience as the observer approaches the source. The backward spin wave wavelength in the experiment was 1.83 mm at 3 GHz, resulting in a Doppler shift of 546 Hz sec/ m, or about 50 times larger than would be observed on an ordinary electromagnetic wave at the same frequency. The measured shifts and dispersion relation agree well with the established theory.

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An experimental study of the Doppler coherence time properties of Vehicle-to-Vehicle (V2V) wireless channels at 5.9 GHz in both rural and highway environments is presented. Simultaneous RF and mobility measurements were conducted in environments near Pittsburgh, Pennsylvania. The average Doppler spread was observed to depend linearly on effective speed, defined as the square root of the sum of the squares of the ground speeds of the two vehicles. Sample spectrum is analyzed and comparisons with the double-ring models are presented. The coherence time was observed to vary inversely with effective speed, as expected. In addition, the coherence time was observed to decrease with vehicle separation out to about 100m, followed by a relative peak at about 200m. A possible interpretation of this peak in terms of a two-ray propagation model is presented. The observed Doppler spread should not be a problem for proposed V2V OFDM signal transmission formats, but the channel coherence time is much shorter than a typical packet suggesting that present equalization schemes may not be adequate.

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