Cosecant-Squared Pattern Synthesis for Compact Antenna Arrays Based on Regional Root Allocation

To meet the communication and sensing demands of unmanned aerial vehicles in urban low-altitude airspace, this letter proposes a low-sidelobe, cosecant-squared pattern synthesis method based on a compact antenna array. By employing a 0.25-wavelength element spacing, the array provides increased degrees of freedom for radiation pattern synthesis. A root-moving method with complex-plane, regional root allocation is introduced and combined with the cuckoo search (CS) algorithm to synthesize low-sidelobe, cosecant-squared radiation patterns. A compact 32-element magnetic dipole antenna array is designed and fabricated for the U6G band, capable of switching between a wide-angle scanning beam and a cosecant-squared shaped beam. Results show that the array achieves a scanning range greater than 130° and a peak gain of 19.5 dBi for the scanning beam pattern. For the cosecant-squared pattern, it achieves a maximum sidelobe level (SLL) of −27.5 dB and a main lobe gain of 17.0 dBi.