I am looking for a formula for near field power density from a dipole antenna antenna. Is cylindrical model is sufficient? Do I have to consider ground reflection too? Please share your ideas?
It is accepted that an EM wave doesn't properly form in the near field because the E and H fields are not properly aligned. Therefore you cannot consider a near field signal as a power. Here's a simple illustration: -
As for trying to understand or predict the E and H fields closeby, this is quite difficult. Here is an article from wiki that might help you understand. Here is an extract concerning the near field: -
In contrast to the far-field, the diffraction pattern in the near-field typically differs significantly from that observed at infinity and varies with distance from the source. In the near-field, the relationship between E and H becomes very complex. Also, unlike the far-field where electromagnetic waves are usually characterized by a single polarization type (horizontal, vertical, circular, or elliptical), all four polarization types can be present in the near-field. The "near-field" is a region in which there are strong inductive and capacitive effects from the currents and charges in the antenna that cause electromagnetic components that do not behave like far-field radiation. These effects decrease in power far more quickly with distance than do the far-field radiation effects. Non-propagating (or evanescent) fields extinguish very rapidly with distance, which makes their effects almost exclusively felt in the near-field region. Also, in the part of the near-field closest to the antenna (called the "reactive near-field", see below), absorption of electromagnetic power in the region by a second device has effects that feed-back to the transmitter, increasing the load on the transmitter that feeds the antenna by decreasing the antenna impedance that the transmitter "sees". Thus, the transmitter can sense when power is being absorbed in the closest near-field zone (by a second antenna or some other object) and is forced to supply extra power to its antenna, and to draw extra power from its own power supply, whereas if no power is being absorbed there, the transmitter does not have to supply extra power.