  To overcome the limited payload of lightweight vehicles such as unmanned
aerial vehicle (UAV) and the aerodynamic constraints on the onboard radar, a
compact nonuniform conformal array is proposed in order to achieve a wide
beamscanning range and to reduce the sidelobes of the planar array. The
non-uniform array consists of 7x4 elements where the inner two rows follow a
geometric sequence while the outer two rows follow an arithmetic sequence along
the x axis. The element spacing along the y axis is gradient from the center as
well. This geometry not only provides more degrees of freedom to optimize the
array radiation, but also reduces the computation cost when synthesizing the
excitation and the configuration of the array for a specific beam pattern. As
field cancellation may happen due to the convex and concave features of the
non-canonical UAV surface, a fast and low-cost in-house code to calculate the
radiation pattern of a large scale conformal array for an arbitrary surface and
element pattern is employed to optimize the array structure. As a proof of
concept, the proposed array with a total volume of 142x93x40 mm3 is implemented
at ISM band (5.8 GHz) using a miniature widebeam single-layer patch antenna
with a dimension of 0.12lambdax0.12lambdax0.025lambda. By using the beamforming
technique, an active onboard system is measured, which achieves the maximum
gain of 21.8 dBi and a scanning range of >50deg and -28deg~28deg with a small
scan loss of 2.2 and 0.5 dB in elevation and azimuth, respectively. Therefore,
our design has high potential for wireless communication and sensing on UAV.
