Antennas and Front-End in GNSS

Abstract

Antenna and front-end play a key role in global navigation satellite system (GNSS) receivers where multi-frequency and multi-constellation services are used simultaneously to produce high-precision position, navigation, and timing information. Being the first element on the receiver system, specifications on the antenna for multi-constellation GNSS applications can be challenging. Especially, integration of the antenna into the target platform, either mobile or stationary, may severely affect antenna performance. This is usually an issue for small-size antennas where measured stand-alone antenna performance in ideal conditions is usually not descriptive of actual performance on the platform. Furthermore, carrier phase tracking has become popular among algorithm developers to obtain high accuracy and anti-spoofing at the same time which demand minimal phase centre variation of the antenna within the intended GNSS band. Spoofing and jamming of GNSS receivers is a growing concern especially for aerial vehicles with ever-increasing applications of drones. These requirements demand different characteristics on the antenna and front-end than traditional applications. One of the most utilized forms of GNSS antenna is ceramic patch, due to its low height, low cost, and relatively good narrow band performance. Simulations of this particular antenna in terms of axial ratio and impedance bandwidths, axial ratio variation over elevation, and half-power beam width are carried out and discussed with comparison to its counterparts. Another critical part of the receiver is its front-end where huge amount of signal amplification with minimal distortion takes place. Long integration times (>1 ms) in GNSS signal processing also puts severe requirements on the software and temperature-compensated crystal oscillator. For mass production, the front-end should be implemented in the form of an integrated circuit. Front-end architectures from traditional superheterodyne to zero/low-intermediate frequency configurations are presented. Advantages and disadvantages of each configuration are outlined in view of multi-band and multi-standard GNSS receivers.