We report here the field and modal characteristics in photonic crystal (PC) Fano reflectors. Due to the tight field confinement and the compact reflector size, the cavity modes are highly localized and confined inside the single layer Fano reflectors, with the energy penetration depth of only 100nm for a 340 nm thick Fano reflector with a design wavelength of 1550 nm. On the other hand, the phase penetration depths, associated with the phase discontinuity and dispersion properties of the reflectors, vary from 2000 nm to 4000 nm, over the spectral range of 1500 nm to 1580 nm. This unique feature offers us another design freedom of the dispersion engineering for the cavity resonant mode tuning. Additionally, the field distributions are also investigated and compared for the Fabry-Perot cavities formed with PC Fano reflectors, as well conventional DBR reflectors and 1D sub-wavelength grating reflectors. All these characteristics associated with the PC Fano reflectors enable a new type of resonant cavity design for a large range of photonic applications.