A new design of dual-band series-fed array (SFA) using coupled line sections with one series-fed network (SFN) and one port is proposed in this article. Compared with the conventional array, the proposed design provides one more degree of freedom in antenna array synthesis. It can realize equal beam angles at two operational frequencies and reduce element spacing to eliminate the grating lobe by virtue of nonlinear phase properties. The parameters have been extensively studied and considered in the analytical analysis. An assessment method of achievable beam angles for dual-band SFAs is proposed and conducted in the entire upper hemisphere. Compared with the conventional array, the proposed dual-band SFA can expand the achievable radiation range with regard to $\theta {\mathrm {d1}}$ and $\theta {\mathrm {d2}}$. Its limitations are also analyzed and discussed. Furthermore, in order to realize specified sidelobe level (SLL) at two operational frequencies, the closed-form design formulas are deduced for the proposed dual-band SFA with arbitrary N elements and amplitude distributions. To verify the proposed design concept and synthesis method, a prototype of proposed six-element dual-band SFA with specified $\theta{\mathrm {d1}}\,\,= 90^{\circ }$ , $\theta{\mathrm {d2}}\,\,= 110^{\circ }$ , and SLL = -20 dB centered at $f_{1}\,\,=2.1$ GHz and $f_{2}\,\,=3.5$ GHz is designed, fabricated, and tested. The simulated and measured results match well with the theoretical predictions.