Lumped-element unit cell for designing beam forming networks

A lumped-element unit cell that can be used as a building block for beam-forming networks is presented. In particular, the network is used to implement a directional coupler with arbitrary output amplitude and phase distributions. The proposed structure provides an attractive solution for applications that require size reduction, especially at low frequencies. Design equations and simulation results are presented for a design at f₀ = 1 GHz. During the presentation, the use of the coupler as a building block of a 4 × 4 Butler matrix will be discussed.