An Accurate and Efficient Gain Pattern Analysis Method for Transmitarray Antennas

This letter presents an accurate and efficient method for analyzing the gain pattern of transmitarray antennas (TAA). This method is derived by following the definition of antenna gain and considering the entire electromagnetic propagation process of a TAA. That is starting from the vectorial far-field pattern of a feed source, calculating the illuminated field on the incident side of the TAA, and then incorporating the scattering matrix of each TAA unit cell to obtain the aperture field distribution, and the power density of far-field can be obtained by utilizing near-to-far-field transformation. As a result, the gain pattern of TAA can be obtained according to the gain definition. The proposed method differs much from the existing gain calculation methods which multiply the pattern directivity, the spillover efficiency of TAA aperture and the average loss of unit cells, avoiding some errors such as inaccurate sidelobe distribution included into the pattern directivity calculation. In addition, an expanded virtual aperture is introduced in the analysis to reduce the effect of spillover radiation on the gain pattern. Two examples of calculating the gain pattern of TAA are conducted to demonstrate the effectiveness and advantages of the proposed analysis method.