Global Navigation Satellite Systems (GNSS) play an important part in applications such as aviation, maritime navigation, Unmanned Aerial Vehicles (UAVs) and global transportation. These systems are susceptible to jamming and spoofing resulting in signal loss. Therefore, there is a need to develop antenna arrays capable of mitigating these effects by covering multiple frequency bands and with the ability to create nulls in the direction of interference. An important parameter that affects the performance of such arrays is the mutual coupling between the antenna elements. Mutual coupling is the sharing and exchange of energy between multiple antennas when they are placed on the same substrate. High mutual coupling degrades the performance of the antenna array in terms of gain, radiation pattern, radiation efficiency, MIMO performance parameters and null steering capability. Mutual coupling mechanism between multiple antennas in an array is mainly due to the propagation of surface waves and space waves. Surface waves are currents that flow through the shared substrate to the surrounding antennas whereas space waves are the radiation by antenna in the free space which is absorbed by the neighboring antennas due to their close proximity.

In this work, first a comparative study is presented on mutual coupling reduction techniques based on these propagation mechanisms focusing on the antenna arrays covering the GNSS upper L- band (1561 – 1610 MHz). Furthermore, the design of a compact 4 element antenna array with high inter-element isolation (> 20 dB) will also be presented.