  We have studied the quantum transmission properties of serial stub and loop
structures. Throughout we have considered free electron networks and the
scattering arises solely due to the geometric nature of the problem. The band
formation in these geometric structures is analyzed and compared with the
conventional periodic potential scatterers. Some essential differences are
pointed out. We show that a single defect in an otherwise periodic structure
modifies band properties non trivially. By a proper choice of a single defect
one can produce positive energy bound states in continuum in the sense of von
Neumann and Wigner. We also discuss some magnetic properties of loop structures
in the presence of Aharonov-Bohm flux.
