A novel planar E-plane waveguide power divider with extra 180° phase difference and full bandwidth is proposed. It is basically an E-plane waveguide T-junction power divider with its input port rotated around its axis by 90° and arranged symmetrically to form a planar structure. A sample power divider is then designed, fabricated and tested. The test results indicate that, in a relative bandwidth of 40%, the reflection coefficient is lower than −20 dB and the extra phase difference between the two output ports is 180° within an error of ±1.5°.