Anti-jam RF front-end and antenna design for global navigation satellite system receivers

Global navigation satellite system (GNSS) covers wide range of applications, and has become an integral part of many systems. GNSS signals on earth are very weak, and are below noise floor in the GNSS application bandwidth. This feature of GNSS presents itself as a major drawback on the user as GNSS signals are vulnerable to intentional or unintentional jamming very easily. Jamming may result in loss of GNSS service or incorrect/false positioning, which is also called spoofing. The loss of GNSS signal under jamming conditions has resulted in serious system failures in the past. Considerable research has been devoted to circumvent jamming effects ranging from complex receiver architectures to redesign of satellite services that incorporate additional satellites and frequency bands coupled with multitude of modulation and encryption techniques. In this study, we propose front-end solutions for GNSS jamming without changing the legacy or existing GNSS receiver. Most anti-jam solutions require substantial hardware and/or software change on the receiver side which renders them useless for existing receivers. Most GNSS applications on the user side are terrestrail based and jamming signal can be assumed to be originated from low-elevation angles. Proposed solution offers jamming resistance to low-elevation originated signals by electronically changing antenna from wide beamwidth to narrow beamwidth using single and array antenna as two modes of operation. The selection between these modes is accomplished electronically at the RF front-end. First ,a new-class of antennas has been designed to cover entire GNSS bandwidth with a single feed and without using a hybrid coupler. Among eight possible antenna designs, one of them is chosen for the intended application and utilized in field trials. RF front-end which consists of low-noise amplifiers, filters, couplers, attenuators, and signal-detection loop are designed, prototyped and tested. Signal envelope detection and processing are performed partly with the help of a microcontroller, which enables a more precise measurement of signal power and electronic switch control. Field trials for GPS have been carried out, and the proposed system has been verified for superior performance under jamming conditions.