| RF modulated backscatter (RFMB), which is used for long-range passive and semi-passive RF tags in the UHF/microwave bands, makes a two-way link that consists of an unmodulated segment and a modulated segment. The two-way nature of this link means that the path loss for a symmetric geometry follows 1/d4 in free space, where d is distance of one segment. Another consequence of the two-way nature is that the small-scale fading observed on the backscattered signal has deeper fades than a signal received over a traditional one-way link of the same range in the same environment. This happens because the fading on the backscattered signal is a product of the fades on the two segments.; One objective of this dissertation is to measure the small-scale fading statistics and median path loss of the two-way links for the indoor environment at 2.4 GHz considering the continuous wave type of RFMB, in which the interrogator transmitter and receiver antennas are at different locations. One goal of these measurements is to determine the theoretical distributions that best fit the measured data in different environments. Others are to verify that the small-scale fading for the modulated backscatter channel can be modeled by the product of two uncorrelated one-way fades and the path loss exponent of the two-way propagation is double that of the one-way path loss.; The range of conventional long-range RF tags is only up to tens of meters. However, with the combination of directional antennas and multi-element array techniques, the range may be extended to the point that interrogators on aircraft or ground vehicles are being considered for communication with ground sensors that employ RFMB. For mobile and especially airborne interrogators, the effects of clutter or unmodulated backscatter in a dynamic environment become important.; Another objective of this dissertation is to address certain interrogator receiver impairments that are associated with aerial interrogation of ground sensors. To do this, many factors are jointly considered, including modulation technique and clutter motion. Signal to clutter ratios are evaluated to determine appropriate receiver filters for the airborne interrogation. |
