Interference Tests at Room Temperature Applied to Deployed Low-Noise Receivers
Daniel G. Kuester, Duncan A. McGillivray, Adam J. Wunderlich, William F. Young
Wireless interference tests are often performed in shielded anechoic and semi-anechoic chambers near room temperature. The corresponding test condition experienced by a receiver DUT is antenna noise temperature equal to physical room temperature (barring EMI in the test zone). This technical note considers a simple analytical model for adjusting interference response from these room temperature tests for use in deployment antenna noise environments. The method we propose is focused toward applications in which the total receiver system noise is less sensitive to potential variability in antenna noise temperature than receiver noise performance (like noise figure and dissipative losses inside the antenna). Example applications include ground-based satellite receivers (for which antenna noise temperature is likely the averaged sky temperature) or cellular handsets (for which noise may originate primarily within the receiver electronics and antenna). As a case study, we analyze test results published in NIST Technical Note 1952. The DUTs under study are GPS L1 receivers exposed to antenna ("sky") noise temperatures of 90 K to 340 K. For practical combinations of receiver noise figure and receive antenna efficiency performance, we develop an regression correction model that transforms interference power levels from the room temperature test environment into estimated equivalents in deployment. The regression is a function of antenna noise temperature, leaving receiver performance variability as a fit error. The worst-case error across the receiver performance parameter space was +/- 1.6 dB, which is tighter than the +/- 2.4 dB uncertainty in the measurement of interference power level.