Optimized amplitude taper for a linear array of multiple true-time-delay beams

This paper proposes a systematic approach of determining the optimal amplitude taper for a shared aperture linear array that possesses true-time-delay (TTD) multiple beam functionality. Conventionally, uniform taper is used to achieve maximum gain, while Taylor taper is widely used in low side lobe applications. However, when multiple beams are generated across ultra-wideband frequencies, they seem cumbersome to maintain a good balance between the side lobe level (SLL) and peak gain (or beam width). In this paper, an optimal amplitude taper is characterized as the one that meets a prerequisite average side lobe level (SLL) and at the mean time maintains a reasonable peak gain for all scanning beams in the array pattern across frequency band. To achieve so, an objective function is derived using the classical array theory, and then numerical optimization is used to obtain the optimal solution. As an example, an 8-element spiral antenna array is demonstrated. The optimal taper achieves SLL of 18.3 dB for scanning range of ±22 degrees across 6~18 GHz. The merit of the optimized taper is demonstrated by comparison with the uniform and Taylor tapers.