High-overtone　bulk　acoustic　waves　driven　magnetoelectric　(ME)　antennas　operate　in　the　acoustic　resonant　frequency　range,　exhibiting　continuous　narrowband　electromagnetic　radiation.　ME　antennas　based　on　cooperative　excitation　of　multiple　high-overtone　bulk　acoustic　waves　are　expected　to　achieve　broadband　performance　and　are　worthy　of　in-depth　exploration.　High-overtone　bulk　acoustic　resonator　(HBAR)　antennas　with　polished　and　rough　acoustic　reflection　interfaces　were　fabricated　and　tested　to　investigate　the　influence　mechanisms　of　acoustic　modes　in　the　HBAR　on　the　radiation　bandwidth,　as　well　as　the　relationship　between　antenna　impedance　and　radiation　response.　Far-field　radiation　characteristics　indicate　that　the　antenna　with　rough　acoustic　reflection　interfaces　featuring　more　high-overtone　bulk　acoustic　wave　modes　suppress　radiation　dips　of　up　to　5　dB　at　anti-resonant　frequencies　without　sacrificing　radiation　gain.　The　radiation　gain　of　the　antenna　was　calculated　using　the　gain-comparison　method　to　be　-35　dBi,　with　a　-3　dB　bandwidth　of　120　MHz　and　a　fractional　bandwidth　of　up　to　11.4%.　Finally,　a　comparison　of　the　radiation　characteristics　of　the　HBAR　piezoelectric　antenna　without　the　magnetic　film　demonstrates　that　the　broadband　radiation　of　the　HBAR　ME　antenna　originates　from　dynamic　magnetic　flux　driven　by　high-overtone　bulk　acoustic　waves.