This work focuses on the implementation of dynamic spectrum access in a scenario where the existing wireless infrastructure is shared by a secondary cellular system. We study the optimization of the physical antenna configuration of the secondary-system base stations, assuming that these antennas are deployed at the transmitter sites of a primary broadcast network. Specifically, we maximize the throughput of a secondary network (SN) operating within a primary network (PN) by finding the optimal antenna height and vertical tilt for the SN base stations. This optimization is constrained by the physical restrictions in the deployment site and by the maximum allowed interference to the PN. We show that this optimization provides significant gain in the cell throughput of the SN while reducing interference toward users of the primary system. As a case study, we design an optimized configuration for the SN antenna when the SN operates as a dedicated communication link for a regional transport system. To this end, field measurement data gathered in collaboration with a regional transport authority are used to calibrate the presented modeling method.