Abstract:  

Global Navigation Satellite Systems (GNSS) play an important part in applications such as aviation, maritime navigation, Unmanned Aerial Vehicles (UAVs) and global transportation. Major GNSS services include GPS, Galileo, BeiDou and GLONASS satellite systems. These services are divided into different frequency sub-bands ranging from 1.17642 GHz to 1.610 GHz. In this thesis, we will be focusing on the upper L- band which consists of GPS L1 (1.575 GHz), Galileo E1 (1.57542 GHz), BeiDou B1 (1.561098 GHz) and GLONASS G1 (1.602 GHz) bands covering a wide frequency spectrum from 1.561098 – 1.610 GHz. This frequency band is used for Aviation Radio Navigation Service (ARNS) and Radio Navigation Satellite Service (RNSS). 

GNSS satellites are located hundreds of kilometers away from the earth. Due to such a large distance, GNSS signals become very weak when they reach the earth and are vulnerable to jamming and interference. As a result, the satellite signals are masked with noise resulting in signal loss. This can be mitigated by designing multi-element antenna arrays capable of creating nulls in the direction of potential jammers. In addition to this technique, designing an antenna array which is wideband and covers multiple GNSS bands will minimize the effect of jamming as if one frequency band is jammed then the array will still be able to receive the signal in the other GNSS frequency bands. Designing such antenna arrays is a challenging task as the mutual coupling between antenna elements and compactness must be taken into account.  

In this seminar, we address the problem of mutual coupling by presenting new techniques to increase the inter-element isolation in a compact four element antenna array. Our proposed design is wideband and covers all the four major GNSS services in the entire GNSS upper L-band (1.561 – 1.610 GHz) with an isolation of more than 20 dB. The initial design is fabricated on a low-cost FR4 substrate and high isolation is achieved by incorporating a defected ground structure (DGS). After that a high epsilon material and a microwave absorber is used to achieve compactness and high isolation respectively. In the next step, the microwave absorber thickness is reduced as it degrades the radiation efficiency and a DGS is added to achieve high isolation. In the third phase, the microwave absorber is replaced by a fractal load and a defected ground structure to simultaneously achieve high isolation, high gain and high efficiency. Finally in the fourth step another high epsilon material is utilized to fabricated the DGS/fractal load based four element array to achieve further miniaturization. All four designs have been fabricated and measured results are presented. 

Thesis Committee Members:  

1- Dr. Ijaz Haider Naqvi 

2- Dr. Imran Cheema