Networks of small ground sensors and other near earth devices deployed in the battlefield are postulated to be of considerable value to the future warfighter. The radio frequency (RF) link between devices will dictate the resilience of the network in communicating critical information in the battlespace. A prior knowledge of the RF environment inches above the ground is required to properly design the sensor network. Signal strength was measured with antennas at 4, 7, and 120 inches above the ground over a range of 10 to 400 feet. The source consisted of a 1780 MHz, 1/4 watt transmitter feeding a quarter wave vertical monopole. The receive equipment consisted of a corner reflector monopole, spectrum analyzer and data logger program. Data points were taken at 10-foot increments over the 400-foot range. The received signal, at heights of 4 and 7 inches, were compared to the measurements taken at a height of 120 inches (close to “free space”). It was found that there is a significant increase in path loss as the antenna approached the ground. There was a 15 dB increase in path loss from when the antennas were at 120 inches to 7 inches off the ground and 18 dB increase in path loss with the antenna 4 inches off the ground. Variations in path loss (10 dB) over time (seconds) were also noted.
The Global Positioning System (GPS) has become a mature technology and is continually being applied in new and more demanding applications. A current effort in this area is the development of compact, durable but lightweight GPS antennas on conformal surfaces for handheld devices. Because modeling the electromagnetic performance of these antennas is often difficult, prototypes are typically built, measured and redesigned in an iterative process. We demonstrate the fabrication of a GPS conformal antenna under ambient-temperature conditions using a combination of laser micromachining and/or laser direct-write processes. The electromagnetic behavior of the antennas is then characterized and the design of the antenna structures is further optimized. Pattern simulations and input impedance measurements of the antenna are presented that demonstrate the usefulness and success of the iterative process made possible with this fabrication technique
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