UHF AND MICROWAVE PROPAGATION - What happens between the transmit and receive antennas dictates a lot of design decisions

摘要

Many of today's popular communications technologies including Wi-Fi, Bluetooth, ZigBee, WiMAX, cell phones and their data services (HSPDA, GPRS, KV-DO and EDGE) all use either the top end of the UHV1' range or the lower microwave hands. Because signals on these frequencies are not reflected by the atmosphere they pass right on out into space when directed upward - their use is pretty much limited to line of sight, whether or not you can actually see the transmitting antenna from the receiving one. These short wavelengths have propagation issues that are unique to them, issues that designers of portable communications devices must understand and grapple with if their products are to work reliably under real-world conditions Assumptions about propagation conditions dictate the choice of frequencies, modulation techniques, coding schemes, antenna strategy and design, and power levels, to name a few.