This paper presents a new method for single-layer broadband phase shifter without needing any coupling structure. The phase shifter consists of a multimode resonator and two shunt lambda/4 stubs. Meanwhile, the bandwidth of proposed phase shifters can be achieved more than 100%. For prescribed return loss, phase shift value, and phase error, this paper develops a synthesis approach to determine all parameters of designed phase shifter. In addition, both the return-loss bandwidth and phase-error bandwidths can be considered simultaneously so as to determine the return loss and phase error for a desired bandwidth. The 45 degrees, 90 degrees, 135 degrees, and 180 degrees phase shifter are theoretically designed and presented. To validate the design method, a broadband 90 degrees phase shifter is designed, fabricated, and measured. The synthesized, simulated, and measured results are found in good agreement with each other, and the experimental results show that the phase shifter achieves 90 degrees +/- 5 degrees, vertical bar S11 vertical bar < - 14 dB, and insertion loss < 0.7 dB over the bandwidth from 1.43 to 4.45 GHz (102.7%).