Overcoming Antenna-Induced Bias in GPS Measurements

  • Published
  • By Maria Callier
  • Air Force Office of Scientific Research
ARLINGTON, Va. --  An Ohio State University research team led by AFRL-funded scientist Dr. Inder J. Gupta developed very efficient approaches vital to the growth of global navigation satellite systems. The team conducted both the theoretical work and the practical work, the outcome of which are key techniques for estimating and mitigating antenna-caused biases in Global Positioning System (GPS) receivers equipped with antijam, or adaptive, antennas.

Military GPS receivers use adaptive antennas to operate in hostile electromagnetic environments, frequently referred to as jamming environments. An adaptive antenna will adjust its pattern in real time in order to minimize the effects of jamming on the GPS receiver. The device accomplishes this mitigation activity by steering the radiation pattern in the jammer direction while maintaining the desired response in the GPS satellite direction.

GPS is the most widely used source for obtaining precision navigation and timing information. A GPS receiver determines its locations by measuring the distance from multiple GPS satellites in view. The newfound approaches are extremely valuable because they address several known system deficiencies, including the previous tendency of the receiver antenna and associated electronics to introduce distortion into the satellite signals (a situation that produced distance measurement biases and thereby affected position and time solution accuracy).

In addition to devising the bias estimation and mitigation capability, the researchers designed and built a new ground plane for testing the antennas and also investigated the effects of antenna elements on the performance of GPS antijam antennas. In addition to earning a number of notable awards and substantial recognition for his efforts, Dr. Gupta most recently received an Institute of Navigation Fellowship for his contributions to the theory and development of adaptive antennas for satellite navigation.