Frequency Diverse Array Antenna Using Time-Modulated Optimized Frequency Offset to Obtain Time-Invariant Spatial Fine Focusing Beampattern

For a frequency diverse array (FDA) antenna, the combination of time-modulated and nonlinear distributed frequency offset is proposed to realize time-invariant spatial fine focusing beampatterns. The distribution of the nonlinear function is optimized by using artificial bee colony algorithm, and the resultant frequency offset is termed as time-modulated optimized frequency offset (TMOFO). In addition to design a TMOFOFDA in realistic situations, the interval-based tolerance analysis is introduced to predict the impact of frequency-offset uncertainties or errors on the time-invariant spatial focusing beampattern. The spatial focusing performance of the TMOFO-FDA is compared with an analytical FDA scheme based on a time-modulated logarithmically increasing frequency offset (TMLFO). Numerical examples of a ten-element linear FDA with λ
₀
/2 element spacing in the presence of mutual coupling effects based on the TMOFO and the TMLFO are reported and compared. The comparative results between the ideal TMLFO and TMOFO show that, in range-angle plane the size of the focal spot for TMOFO-FDA is reduced by about 70% compared to that for TMLFO-FDA. The side lobe level is reduced about 49%. The comparative results from IA-based beampattern tolerance analysis also reveal the superiority of the TMOFO-FDA scheme.