  The concept of capacitive-sharing readout, described in detail in a previous
study, offers the possibility for the development of high-performance
three-coordinates (X-Y-U)-strip readout for Micro Pattern Gaseous Detectors
(MPGDs) using simple standard PCB fabrication techniques. Capacitive-sharing
(X-Y-U)-strip readout allows simultaneous measurement of the Cartesian
coordinates x and y of the position of the particles together with a third
coordinate u along the diagonal axis in a single readout PCB. This provides a
powerful tool to address multiple-hit ambiguity and enable pattern recognition
capabilities in moderate particle flux environment of collider or fixed target
experiments in high energy physics HEP) and nuclear physics (NP). We present in
this paper the performance of a 10 cm {\times} 10 cm triple-GEM detector with
capacitive-sharing (X-Y-U)-strip anode readout. Spatial resolutions of the
order of {\sigma}^res_x = 71.6 {\pm} 0.8 {\mu}m for X-strips, {\sigma}^res_y =
56.2 {\pm} 0.9 {\mu}m for Y-strips and {\sigma}^res_u = 75.2 {\pm} 0.9 {\mu}m
for U-strips have been obtained at a beam test at Thomas Jefferson National
Accelerator Facility (Jefferson Lab). Modifications of the readout design of
future prototypes to improve the spatial resolution and challenges in scaling
to large-area MPGDs are discussed.
