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I am not aware of any radar uses. Xband is pretty high frequency, and gets absorbed quickly. It might be usable for seeing just underneath the skin, maybe to detect skin cancers. Unfortunately, the wavelength is pretty large, so it will not image anything very precisely. You would need it to be << 1 Watt transmit power to be safe for medical use, and you might still have trouble with implanted devices, like pacemakers.
Much higher frequencies, like 77 GHz, are used in passive imaging--might be useful for scanning human skin.
Thanks for the reply... actually my project is to design a radar for sleep apnea detection... So i need to design a radar to detect the movement of the human chest while asleep.. which band of frequency would be suitable for this?