Which type of filter would be best to use in a 2-metre repeater duplexer?

A repeater duplexer must isolate a highly sensitive receiver from a high-power transmitter operating simultaneously on closely spaced frequencies (typically just 600 kHz apart on the 2-metre band). This requires a filter with an extremely high 'Q' factor, providing sharp tuning and deep rejection notches. Cavity filters are large, rigid, resonant metallic chambers that offer this exceptionally high Q, along with the ability to handle high transmitter RF power with very minimal insertion loss. They are the standard choice for VHF and UHF repeaters. Other filter types are unsuitable for this specific task: crystal or DSP filters cannot handle the high RF transmit power, while standard L-C (inductor-capacitor) filters simply do not have sharp enough tuning to provide the necessary isolation.