A microstrip antenna structure is provided, which includes a substrate, a ring microstrip line and a signal transmission port. The substrate has opposite first and second surfaces. The ring microstrip line is disposed on the first surface of the substrate. The ring microstrip line has a short coupling gap ranged between 0.004λg and 0.06λg for forming a radiation bandwidth with high selectivity, where λg represents a guided wavelength of an electromagnetic wave in the ring microstrip line corresponding to a center frequency of the radiation bandwidth. The signal transmission port is disposed on the second surface of the substrate. The signal transmission port penetrates through the substrate and is electrically connected to the ring microstrip line.一種微帶天線結構,包含基板、環狀微帶線和訊號傳輸埠。基板具有相對的第一表面和第二表面。環狀微帶線設置於基板的第一表面上。環狀微帶線具有介於0.004λg與0.06λg之間的短耦合間距,用以形成高選擇性的輻射頻帶,其中λg為在環狀微帶線中對應輻射頻帶之中心頻率的波導波長。訊號傳輸埠設置於基板的第二表面上。訊號傳輸埠貫穿基板且電性連接至環狀微帶線。100‧‧‧微帶天線結構110‧‧‧基板111‧‧‧第一表面112‧‧‧第二表面120‧‧‧環狀微帶線130‧‧‧訊號傳輸埠140‧‧‧接地導體
