The Continuous Transverse Stub (CTS) antenna is implemented with an array of continuous transverse radiating stubs extending from the upper conductive plate of an open parallel-plate transmission-line structure, and internally excited by a TEM mode linear source. It is an important topic for high gain antennas due to its high radiation efficiency and aperture efficiency. CTS array is also convenient for beam-controlling and dual-polarizations application and has the advantages of ease fabrication and low cost, which promise its broad application prospects. In this dissertation, design on planar CTS arrays and low-loss TEM mode linear sources are investigated as follows. First, the radiation mechanism of CTS element i...