A small size and high efficiency HF broadband antenna that use wire sector-conical structure is designed. The Method of Moment is used to compute the VSWR and power gain of the antenna with different wire number, different size of feed-point gap and different sector-conical open angle. A sample antenna is built base on simulation results. The measured VSWR and radiation pattern agree well with those from simulation. The VSWR is within 2:1 over more than 95% of HF band, the average efficiency is 98% and the average gain is greater than 6dBi.