Creating Step frequencies

Hi,

I need a sinusoidal frequency input where the frequency can be increased in step.

For example, 250MHz, then 251MHz, then 252MHz, and the list goes on until 450MHz.

How can I do it?

E.g. using a programmable frequency generator. The question isn't very clear, I fear.

Use the Analog Devices AD9835 Direct Digital Synthesis (DDS) Generator chip.

It has a clock frequency of 50 MHz...

FvM is correct you can use similar Analogue Devices products that support higher frequencies for example the AD9912

What if using voltage controlled oscillator? anyone got any idea with that?

The frequency does not change linear with tuning voltage. If your frequency does not need to be exact, you could measure the VCO tuning curve and use a non-linear tuning voltage to obtain a linear frequency sweep. If you need accurate frequency, use some PLL to lock the VCO frequency (reference frequency = 1MHz, VCO output frequency = N * 1MHz)