Abstract:Frequency diverse array (FDA) radar applies a small frequency offset between the adjacent elements to synthesize a range-angle-dependent beampattern. It is difficult to control the beam steering for the coupled time-variant beampattern. For this problem, the time-variant characteristic and point beam forming of FDA radar were mainly studied in the paper. Firstly, the characteristic of transmit beampattern of FDA using linearly increasing frequency increment was analyzed. Secondly, two signal models of FDA using logarithmically frequency increments (log–FDA) and multicarrier frequency increments (multi-FDA) were constructed, where the multi-FDA transmit beampattern has lower sidelobes. Then, the relationship between the time variable of the frequency increase term and the time variable of the propagation term in the two time modulated signal models was studied in detail. If both of them are the same, the time-varying characteristics of the transmit beampattern can be eliminated by the two time variables offset. However, they have different physical meanings. When the electromagnetic signal is generated and propagated in space, the time variable in the frequency increase term will not change, whereas the time variable of the propagation term in the propagation process is related to the propagation characteristics of the electromagnetic wave, which is a variable quantity, so the two time variables cannot offset each other. Finally, the simulation results verify the correctness of the transmit beampattern analysis of time modulated FDA radar, and demonstrate that the spot transmit beampattern with dynamic forward propagation can be synthesized using log–FDA and multi-FDA, where the beampattern of the multi-FDA has lower sidelobes.