The space charge effect inside the beam of charged particles causes serious problems in high-intensity linear particle accelerators. At the present time there is only the Alvarez-Biewett accelerating structure which uses continuous strong focusing to keep the beam confined to the axis. The most serious problem is at the injection end of the accelerator where the particle velocities are low and the drift tube structure has decreased efficiency. It is suggested here that some new or less well known accelerating structures using rf quadrupole focusing and H-type mode resonators may solve this problem.The disk-and-washer structure with very high coupling coefficient can be used successfully for the high-energy part of the accelerator. A newly developed coaxial coupler solves the problem of the intertank rf coupling.