Abstract-The paper sheds light on the beamforming (BF) performance of large (potentially unconstrained in size) as well as dense (but physically constrained in size) antenna arrays when equipped with arbitrarily many elements. Two operational modes are investigated: Single-layer BF and multi-layer BF. In the first mode, a realistic BF criterion namely the average BF gain is revisited and employed to understand the far-field and the near-field effects on the BF performance of large-scale antennas above a clutter. The diminishing throughput returns in a single-layer BF mode versus the number of antennas necessitate multi-layering. In the multi-layer BF mode, the RF coverage is divided into a number of directive non-overlapping sectorbeams in a deterministic manner within a multi-user multi-input multi-output (MIMO) system. The optimal number of layers that maximizes the user's sum-rate given a constrained antenna array is found as a compromise between the multiplexing gain (associated with the number of sector-beams) and the inter-beam interference, represented by the side lobe level (SLL).

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The performance of an antenna cancellation technique for a multipleinput-multiple-output (MIMO) full-duplex system that is based on null-steering beamforming and antenna polarisation diversity is investigated. A practical implementation of a symmetric antenna topology comprising three dual-polarised patch antennas operating at 2.4 GHz is described. The measurement results show an average of 60 dB self-interference cancellation over 200 MHz bandwidth. Moreover, a decoupling level of up to 22 dB is achieved for MIMO multiplexing using antenna polarisation diversity. The performance evaluation of the proposed technique was performed by simulation and measurement and the results have good agreement.

The paper studies deterministic beamforming for advanced base station antenna technologies including vertical sectorization and array pattern compensation. First, an optimized vertical sectorization beamforming design in terms of low inter-vertical sector interference is proposed. The performance gains in terms of the users' sum rate of the proposed technique against unoptimized vertical sectorization in a simple multi-user system scenario are shown. The work also investigates certain novel beampattern recovery approaches studying the capabilities of advanced base station antenna systems to partially compensate for the distortion caused to the array diagram upon transmit branch failure. The schemes are applied to a speci¿c active antenna product architecture suitable for base stations with advanced beamforming capabilities yet with low hardware complexity and cost footprint.