A radiation generator may include a generator housing, a target electrode carried by the generator housing, a charged particle source carried by the generator housing to direct charged particles at the target electrode based upon an accelerating potential, and a suppressor electrode carried by the generator housing having an opening therein to permit passage of charged particles to the target electrode. A target extender electrode may be between the suppressor electrode and the target electrode and have an opening therein to permit passage of charged particles to the target. At least one voltage source may be coupled to the target electrode, the suppressor electrode, and the target extender electrode to cause the target electrode to have a voltage greater than a voltage of the suppressor electrode and to cause the target extender electrode to have a voltage greater than the voltage of the suppressor electrode.