Effect of internal reflections on the radiation properties and input admittance of integrated lens antennas

This paper begins with the modeling of the reflected waves within integrate d lens antennas, which consist of a dielectric lens on which a planar anten na is mounted. It is demonstrated that if the relative dielectric constant of the lens is small (epsilon(r) less than or equal to 4), the single- and double-reflected waves are sufficient to analyze the effect of the internal reflections. For small angles around boresight, these unwanted reflected f ields mainly affect the cross-polar far-held pattern, while for large obser vation angles, both the co-polar and cross-polar patterns are significantly disturbed. It appears that by neglecting the internally reflected field co ntributions, the beam efficiency may be overestimated more than 10%, In thi s paper, two types of matching layers are analyzed in order to reduce these unwanted reflections. It is demonstrated that the radiation performances o f the integrated lens antennas with optimum-thickness and quarter-wavelengt h matching layer are almost equal. Even for low dielectric-constant lenses, the beam efficiency can be increased by over 10%, Finally, it is demonstra ted that the internal reflections may also have a strong effect on the ante nna admittance, which can only be reduced partly by the use of a matching l ayer.