Simultaneous-Multi-Beam Transmit Antenna Arrays - A General Study
Anton Atanasov is a PhD student in the Department of Integrated Circuit Design. (Co)Promotors are prof.dr.ir. F.E. van Vliet and dr.ir. M.S. Oude Alink from the Faculty of Electrical Engineering, Mathematics and Computer Science.
Simultaneous-multi-beam (SMB) antenna array transmitters (TX) offer significant advantages in terms of form factor and operational flexibility. The ability to simultaneously transmit multiple independent beams from a single compact unit is especially beneficial in scenarios where space and weight are at a premium, such as in mobile devices, maritime vessels, satellites, and autonomous land, aerial or marine vehicles. This capability can be realized through various methods, including the use of highly linear and efficient power amplifiers (PAs), dividing the aperture into smaller array sections, or closely interweaving two or more arrays. As is often the case in engineering, each of these approaches involves trade-offs, affecting either the performance of the amplifiers or the characteristics of the antenna array.
This dissertation presents a general study on achieving SMB TX functionality. First, it introduces a simple and useful figure of merit (FoM) to evaluate the performance of SMB TX antenna arrays. The FoM builds upon the power-aperture product and effective isotropic radiated power (EIRP) for single-beam arrays and extends it to SMB arrays. The FoM is the product of radiated power, antenna aperture efficiency and the amplifiers power added efficiency and enables systematic comparison of current and future multi-beam radar and communications arrays.
We use the FoM to compare three representative two-beam SMB array designs consisting of identical antennas and PAs. The first one relies on efficient and linear PAs, the second is an array whose aperture is divided into independent subarrays, and the final consists of two arrays, which are densely interleaved with one another. The FoM score indicates that using very efficient and linear PAs can be just as effective as densely interleaving two arrays together, encouraging further development in both directions. The subarray design, on the other hand, achieved the lowest FoM score.
An efficient feed-forward linearisation architecture for saturated PAs is developed based on the SMB performance opportunities suggested by the FoM. The architecture, which we have named the load-modulated lineariser (LML), utilizes active load-modulation to absorb individual out-of-band AM-AM intermodulation distortion (IMD) components at the output of a power amplifier. When properly designed, the proposed PA architecture requires only slightly more additional power than the IMD power it absorbs, making it very efficient. It retains the power conservation properties of the load-modulated balanced amplifier (LMBA) and achieves better linearization than an equivalent digital predistortion (DPD) system, at a very low power and complexity penalty. As the LML operates at the output of the nonlinear PA, it can independently target IMD without affecting the desired signal.
