[en] A conventional RFQ uses a constant beam aperture and a constant intervane voltage. The mean accelerating gradient can be increased by using a beam aperture varying along the length proportional to ion velocity, and adjusting the intervane voltage to maintain a constant transverse electric field. The 4-vane configuration was studied both theoretically using RFQ3D and by cold model measurements to determine if the required voltage tilts could be achieved within practical mechanical design limitations. Results indicate that a voltage tilt of 2.5 is possible with a 1.5 m long four-vane RFQ having a 14% longitudinal variation in individual quadrant cross-sectional area. The four-rod configuration can also achieve similar voltage tilts with a factor of two longitudinal variation in inductor dimensions. (author)