This paper presents the results from a field measurement campaign that was conducted to provide an understanding of Multiple-Input Multiple-Output (MIMO) performance relative to that of a Single-Input Single-Output (SISO) system in military-type environments. The Space & Terrestrial Communications Directorate (STCD) MIMO system was used to conduct these experiments. The system has two antennas and operates at transmit frequencies of 430 and 1380MHz, which fall within military frequency bands. A variety of operational environments with many scenarios were considered. The experiments were conducted at C4ISR OTM testing facility, Fort Dix, New Jersey for transmissions along a wide road, a narrow road and through heavy foliage. These experiments measured the throughput gain of MIMO over SISO given the same transmit power and channel usage. The gain in throughput was corroborated by information-theoretic capacity calculations using channel estimates collected during the experimental campaign. In addition, the impact of the antenna spacing on throughput gain was also studied. Depending on the multipath-richness of the environment, the experimental results show that the 2-antenna system provides a throughput of 1.3 to 2.0 times that of a SISO system. On average, a range extension of 1.5 times could be realized for all the considered scenarios and transmit frequencies. The results suggest that antennas in MIMO systems should be placed at least a half of carrier wavelength apart, as indicated in open literature.

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