Low-Sidelobe-Level Series-Fed Microstrip Antenna Array of Unequal Interelement Spacing

Using the differential evolution algorithm (DEA), low-sidelobe-level (SLL) series-fed microstrip antenna arrays of unequal interelement spacing (IES) are investigated. The proposed design method can achieve conversion between the SLL and half-power beamwidth (HPBW). The constraint conditions for the IES and amplitude are set up, and the element size is also taken into account in the pattern function. Based on the solutions from the DEA, two types of series-fed antenna arrays of unequal IES, i.e., uniform amplitude and nonuniform amplitude arrays, are designed, fabricated, and measured. Measurement results show that 8- and 10-element series-fed antenna arrays of unequal IES and nonuniform amplitude can achieve the SLL of -23.7 dB with HPBW of 9.7. and the SLL of -25.3 dB with HPBW of 8.3., respectively. Compared to the traditional design methods, the proposed one can achieve the series-fed antenna array with a lower SLL and more narrow HPBW.