Frequency-Selective Feeding Network Based on Directional Filter for Constant-Beamwidth Scalable Antenna Arrays

A concept of scalable antenna arrays with an even number of radiating elements and nonuniform element spacing has been proposed. It has been shown that the proposed arrays can be fed with a frequency-selective network based on a well-known directional filter and with such a network the beamwidth can be kept constant across one frequency octave. The appropriate adjustment of coupled-line sections in such a directional filter allows for flexible selection of transmission coefficients between two outputs, and therefore, can be used for gradual switching of the signals between radiating elements. The proposed frequency-selective feeding network has been applied in a six-element antenna array operating in 1.75-3.5 GHz frequency range in which constant beamwidth around 16° has been achieved.