Novel formulation of coefficients of low-pass prototype filter for the design of four-element planar filtering antenna array

The paper is focused on a formulation of a new coefficient of the low-pass prototype filter for the design of a four-element filtering antenna array. Due to the new g_i coefficients, we can comfortably and easily control a shape of the frequency responses of the reflection coefficient and normalized realized gain. The described process of the design methodology and new g_i coefficients were verified over the frequency band from 4.8 GHz to 6.8 GHz; for fractional bandwidth from 8 % to 12 % and for level of the reflection coefficient from -10 dB to -20 dB. The whole design methodology was supported by comparison of three samples of filtering antenna arrays with different configuration.