We theoretically investigate waveguide structures in three-dimensional meta
llic photonic band-gap (MPBG) materials. The MPBG materials used in this st
udy consist of a three-dimensional mesh of metallic wires embedded in a die
lectric. An L-shaped waveguide is created by removing part of the metallic
wires. Using finite difference time domain simulations, we found that an 85
% transmission efficiency can be achieved through the 90 degrees bend with
just three unit cell thickness MPBG structures. [S0163-1829(99)13831-1].