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A novel composite phase-shifting transmission line (TL) with designable characteristics is presented, which can be used to achieve arbitrary phase of the transmission coefficient at any required frequency with a certain length of the TL. An empirical formula is given of the relationship between the phase and physical length of the composite TL at a required frequency. A sample of 0?? phase-shifting TL is designed in detail, and is verified by the full-wave simulation. At the required frequency of 5 GHz, the amplitude of S21 is equal to -0.23 dB with a phase of -0.467??. The electric length is only 0.212??0, which has been decreased by 68.5% compared to the conventional microstrip line. Using the proposed composite TL, an antenna array is designed with two radiation patches excited by the novel series feed-line. The detailed procedure of such design is presented. The lowest reflection coefficient is exactly achieved at the required frequency of 5 GHz. The maximum radiation is obtained at ??0=0??, which indicates that the 0?? phase-shifting TL works very well. The sample is also fabricated and good agreements between simulation and measurement results are obtained.