A study is made of the scattering of a plane wave incident obliquely upon an infinite plane grid of parallel equidistant circular wires. A simple means is described of picturing the mechanism by which side waves are produced as the angle of incidence is varied. Exact formulae and curves for the shunt reactance of the grid are given for the most useful case in which the spacing is less than a wavelength. Thus the reactance of the grid referred to the component of the wave impedance of the incident plane wave which is normal to the grid, viz. 376.5 sec θ ohms, isXg = 376.5d/λ[logε (d/2πa)+F(d/λ,θ)] ≃ 376.5d/λ[logε (d/2πa) for a ≪ b ≪ λ,where d = spacing of wires, a = radius of each wire, θ = angle of incidence. The correction term is plotted in Fig. 6. The reflection coefficient is r = − 1/(1 + 2Xg/Zsec θ), Z0 = 376.5 ohms