Angle-Dependent Synthesis Method for Holographic Multi-Feed Antennas

A novel synthesis method for holographic multi-feed antennas is presented to combine all sub-holograms into an angle-dependent shared holographic aperture. In order to find the global error minimum between the shared holographic aperture and all ideal sub-holograms, a non-pixel-based genetic optimization is used. For a more accurately implementation of the analytical impedance tensor an eigenvector approach taking all tensor components into account is introduced. The optimized holographic antenna has four feeds for an exemplary integration into a 2D-monopulse radar system and is realized on a fused silica wafer due to its lower loss at millimeter-wave frequencies compared to Teflon-based materials. The antenna prototype provides a measured gain of 23dBi, a polarization purity of
$\mathrm {26 \ \text {dB}}$
and a side-lobe level of
$\mathrm {20 \ \text {dB}}$
for feed 1, 2 and 4 is reached across 76GHz−81GHz. The S-parameters are measured from
$\mathrm {60 \ \text {GHz}}$
to
$\mathrm {90 \ \text {GHz}}$
, and a reflection coefficient of
$-\,\,\mathrm {14\,\, \text {dB}}$
and an inter-port coupling
$< -\,\,\mathrm {38\,\, \text {dB}}$
are achieved. The measured 2D-monopulse patterns provide a FOV of ang 10, the sum beam has a gain of 26dBi leading to an aperture efficiency of 45% and the differential beams show a null depth of
$\mathrm {30 \ \text {dB}}$
.