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Dielectric superlayers can be used to reduce the grating lobe levels in thinned phased arrays, i.e., arrays with large periodicities. In this contribution we show how the mutual coupling impacts the active impedance and the roll-off of the embedded patterns necessary to achieve the grating lobe angular filtering in this type of arrays. The reduction of the grating lobes in the thinned array radiation pattern depends on the dielectric superlayer constant. The larger the dielectric constant the higher the attenuation of the grating lobe will be. However, this can only be obtained at the cost of an increased mutual coupling. This mutual coupling will impact on the embedded patterns reducing the actual roll-off that can be achieved. Several 11 x 11 phased arrays with different dielectric superlayers are studied in order to establish the maximum useful permittivity as a function of the mutual coupling level. We show that antenna elements based on dielectric superlayers leading to mutual coupling levels larger than -20 dB suffer from a loss of directivity in the embedded pattern and a loss of gain in the phased array because of the highly resonant active impedance. As a reference we also compare the performances of the 11 x 11 leaky wave phased array with an 11 x 11 phased array of standard conical horns. We show that an increase in the gain of more than 2.2 dB over all the frequency and scanning ranges is obtained in the leaky wave array with respect to the reference horn array. The leaky wave array leads to a reduction of the grating lobe of more than 10 dB.
frequency selective surface; leaky wave antennas (lwas); phased array antennas; thinned arrays; reflector antennas; improvement; filters; cavity; gain