Low-profile fully-metallic Luneburg lens antenna

Abstract: Modern communication systems face new technological challenges, such as the narrowness and overload of the conventional frequency bands employed for these applications. Nowadays, communication systems are expected to operate at higher frequencies, such as the mm-wave band. In particular, for space applications, specific environmental conditions make it necessary to design low-profile, lightweight and high gain systems with wide-angle scanning capabilities. Traditional solutions are reflectors antennas or planar arrays. Reflectors often end up being bulky, whereas array antennas are lossy and costly. Lens antennas, unpopular at low frequencies due to their large size, offer a better solution in this context, due to their focusing properties, wide-scanning capability, and broadband behaviour. Among lens antennas, geodesic lens antennas have recently increased interest since they are fullymetallic and easy to manufacture. Previous research aiming at reducing the profile of geodesic lens antennas, while preserving high performances, allowed a total height reduction by a factor 4. In this work, I investigate the possibility of reducing the profile even further by following a different approach. Instead of folding by mirroring the curved profile, the lens antenna is built with circular ridge structures, in an attempt to discretize the original profile. Different approaches have been proposed. First, designs with different numbers of squared ridges were proposed. The reflections are reduced by chamfering the corners of the ridges. Moreover, triangle ridges and alternating the ridges orientation have also been investigated. The final design has four squared ridges with the same orientation. This design was chosen due to its radiation performance. This approach reduces the profile by a factor 18. A prototype has been manufactured working on the frequency band [24,34] GHz. The scanning range is ±62◦ , reflections levels are below -15 dB and at 29 GHz the maximum realized gain is equal to 15.75 dBi. This solution offers attractive properties, mainly due to its compactness. The height of the lens antenna is restricted by the flare, which was set at λ/2. This means that this lens antenna can be stacked in a linear array with grating-lobe-free performance in the elevation plane.