discrete bowtie; plasmonic nanoantenna; scanning-scattering near-field optical microscopy Electric fields; Metamaterial antennas; Nanoantennas; Plasmonics; Scanning antennas; Bow tie; Electric field enhancement; Low sidelobe level; Near field analysis; Near field optical microscopy; Near-field measurement; Plasmonic nanoantenna; Scanning microscopy; Near field scanning optical microscopy