A method and an apparatus for frequency synthesizing are provided for a wireless communication system. In a frequency synthesizer, a phase lock loop (PLL) circuit generates a first elemental frequency based on a reference frequency and a unity frequency. A first division module then divides the first elemental frequency to generate a second elemental frequency. A second division module divides the second elemental frequency a multiple of times to generate the unity frequency and a plurality of intermediate frequencies each having an exponential ratio to the unity frequency by a power of two. A second mixer is provided to mix one of the intermediate frequencies with the unity frequency to generate a step frequency, and a first mixer mixes the step frequency with one of the first and second elemental frequencies to generate an output frequency having a variety covering all frequency bands in an Ultra-Wide-Band (UWB) spectrum.