  The behavior of a 2-D model of an extended hemielliptic silicon lens of a
size typical for THz applications is accurately studied for the case of a plane
E-wave illumination. The full-wave analysis of the scattering problem is based
on the Muller boundary integral equations that are uniquely solvable. Galerkin
discretization scheme with a trigonometric basis leads to a very efficient
numerical algorithm. Numerical results related to the focusability of the lens
versus its rear-side extension and the angle of the plane-wave incidence, as
well as near-field profiles, demonstrate strong resonances. Such effects can
change the principles of optimal design of lens-based receivers.
