Abstract: Sky-wave radar works on the high frequency band, the working bandwidth of which is often limited by interference of ionosphere characteristics and artificial signals. The bandwidth of engineering signal is generally around ten thousands Hertz. This paper proposes a technique of improving the signal bandwidth of this kind of radar system. The technique sends a group of orthogonal multicarrier(MC) modulated linear frequency modulated(LFM) signals with ten thousands Hertz bandwidth each to illuminated targets, and then composites matched filtering signal group to a broadband signal at the receiver. Without the consideration of multimode and multipath circumstances of a HF radar, sending N orthogonal MC modulated LFM signals and synthesizing them after matched filtering and space time processing at a receiver will improve signal bandwidth approximately by N times. Simulations by using Watterson sky-wave channel model are given to demonstrate the theoretical analysis. In conclusion, this technique can improve the distance resolution of a HF radar when the HF radar multipath environment is not serious.