Nonuniform aperture synthesis radiometers (NASRs) have the advantage of flexibility in practical applications. However, the main limitation of NASRs for Earth observation is the poor reconstruction quality. In this letter, the array factor of 1-D NASR is analyzed. Array factor forming (AFF) is introduced to improve the reconstruction quality of 1-D NASRs. The limitations of the AFF on array configurations are given. The NASR that meets the given limitations is called the optimizable NASR (ONASR). The numerical results and experimental results demonstrate that the AFF is able to improve the reconstruction quality of 1-D ONASRs. To assess the performance of the AFF thoroughly, the comparisons are made against the linear interpolation and the regularized G-matrix method. Meanwhile, the comparisons between the AFF-based 1-D ONASRs and the 1-D uniform ASRs are also made. The comparison results demonstrate that the AFF can obtain better reconstruction quality than the linear interpolation and the regularized G-matrix method. Additionally, the comparison results also demonstrate that the reconstruction quality of AFF-based 1-D ONASRs can approach that of 1-D uniform ASRs.