Why are insulators used at the ends of a suspended wire antenna?

Insulators are placed at the ends of a suspended wire antenna to stop the flow of radio frequency (RF) current at exact points. By physically isolating the wire from its support lines, the insulators strictly limit and define the electrical length of the antenna. If insulators were not used, the RF energy could couple into the support ropes (especially if they are wet or conductive), effectively making them part of the antenna. This would unpredictably lengthen the antenna and alter its resonant frequency. Insulators are not used to increase bandwidth or reduce ground capacitance; their primary RF purpose is simply to establish the precise endpoints of the resonating element.