What happens to SWR bandwidth when one or more loading coils are used to resonate an electrically short antenna?

Any time an antenna is made physically shorter than its natural resonant length, its performance involves a series of compromises. An electrically short antenna has high capacitive reactance and low radiation resistance. Adding a loading coil introduces inductive reactance to cancel the capacitance, creating resonance. This combination of high reactance and low resistance turns the antenna system into a high-Q (high quality factor) tuned circuit. A fundamental property of high-Q circuits is that they are very sharply tuned. They resonate perfectly at one specific frequency but detune very quickly as you move away from that center frequency. Consequently, the SWR rises sharply as you change frequency, meaning the SWR bandwidth is significantly decreased compared to a full-sized, naturally resonant antenna. No matter where the coil is placed, this narrowing of bandwidth is an unavoidable tradeoff of physically shortening the antenna.