Beamforming technology is essential in modern wireless communication and radar systems. Among the various methods available for designing beamforming networks, such as Rotman lens and Butler matrix, the Nolen matrix with flexible topology has recently drawn significant attention. However, the problem of limited bandwidth persists in Nolen matrix designs. In addition, traditional two-dimensional beamforming networks require an interlocking structure, which inevitably brings disadvantages such as bulky size, complicated assembly processes, and narrow operating bandwidth. Moreover, existing works show that broadband performance and flexible port numbering are hard to realize simultaneously in Butler and Nolen matrix topologies. Furthermore, radiation beams that rely on these networks require highly flexible patterns that are urgently needed for various application scenarios. This thesis proposes several beamforming networks that have flexible topology, broadband characteristics, flexible port numbers, and flexible radiation patterns for use in radar and wireless communication systems.

An analytical design method is proposed to solve the bandwidth limitations of the Nolen matrix structure. It is based on complex exponential signal and signal flow graphs that provide numerical calculations for its fundamental building blocks. A 4×4 Nolen matrix topology is rigorously used by the signal flow graphs, and the phase relationships between internal components are obtained based on complex exponential signals. Based on this, a novel topology based on differential phase shifters and couplers is proposed. A broadband prototype is designed, built, and measured for verification purposes. Measured bandwidths range from 40% to 48.24% for ports 1–4, exhibiting the broadest bandwidth among previously published designs.

A dimension expansion method is proposed to solve the interlocking structure problem in two-dimensional beamforming network topologies. The vertical and horizontal sub-layers can be rotated and orderly arranged, leading to effectively planarized two-dimensional topology. To validate the effectiveness of the proposed method, a broadband planar two-dimensional 3×3 Nolen matrix is designed. It is constructed using a novel 9×9 crossed phase-shift network and 3×3 Nolen matrix. The 9×9 crossed phase-shift network consists of nine crossovers, providing parallel signal transfers in different paths between the expanded sub-layers. For verification, a prototype is designed, built, and measured. Measured bandwidths range from 65.31% to 87.32% for the input ports, validating the proposed dimension expansion method.

To eliminate limited beam resolution and narrow bandwidth in traditional switched-beam systems, a broadband beamforming network with flexible port numbers is proposed. It adopts the Butler matrix as a main frame, and the Nolen matrix is used as a building block. The 2^N order Butler matrix port numbers can be extended to P×M input port numbers and N×Q output port numbers. They are connected via two power distribution groups and two crossed phase-shift networks to form a highly flexible phase coherence beamforming network. Rigorous signal flow analysis is performed to ascertain the amplitude and phase relationships of the internal components and are verified with 3×3 Nolen matrix and 9×9 beamforming network structures. The measured performance reveals a beam-switching capability with a matched bandwidth greater than 62.3%. When integrated with ME dipoles, a bandwidth from 4.2 GHz to 6.4 GHz is obtained.

To provide radiation beams with high pattern diversity, two flexible switched-beam systems are proposed based on reconfigurable beamforming networks. Array factor calculation is performed with a 3-element antenna array. The excitation requirements for radiation zeros, single/dual-lobe, and isotropic array factors are provided and further examined by vector analysis using two 3×3 Nolen matrix topologies. The first is a flexible switched-beam system A, which achieves three single-beam and two dual-beam radiation patterns. It is constructed using a 3-element patch antenna array and a compact 3×3 Nolen matrix integrated with one reconfigurable phase shifter. The second is system B, which achieves five single-beam, one dual-beam, and one wide-beam radiation pattern. It utilizes a 3-bit reconfigurable power divider to provide single/dual/tri-feeds to a 3×3 Nolen matrix. This is validated by both simulations and measurements. This simple and compact structure with less control bias makes them good candidates for complex beamforming application scenarios.