Three-way signal divider with tunable ratio for adaptive transmitting antenna arrays

A tunable wideband three-way signal divider that is useful in adaptive transmitting arrays is presented. The design of the proposed device is based on using three stepped-impedance coupled microstrip lines that have controllable coupling factors, and thus a variable signal ratio at the three output ports. The variation in the coupling factors is achieved by using two varactor diodes that are connected between the central coupled line and each of the side lines. The biasing voltages of the varactor diodes are used to control their capacitors and thus to achieve the required output signal ratios. A signal-flow analysis is used to predict the performance of the proposed device, whereas the conformal mapping technique is used to obtain the required dimensions of the coupled structure and the varactors´ capacitors. The validation of the proposed design method is tested by simulations and measurements. The results indicate the possibility of changing the signal ratio across a wide range of values with more than 10 dB return loss at the four input/output ports and isolation between the output ports across more than 85% fractional bandwidth.