A model for tuning microstrip patch antennas with a controllable impedance “black box” is presented. These tunable impedance elements can be placed along the mid-line of the patch antenna to alter the impact of the tuning range on the antenna field pattern. Simulation results demonstrate the impact of this level of physical design control. Also highlighted is the improved ability to design beyond tunability with additional impedance matching and antenna area margins. Finally, the unique capability of the IMPATT diode for achieving these tunable impedance properties is discussed.