1. Different uses:
A. Duplexers are generally used at the output and input ends of equipment to isolate signals of different frequency bands. For example: uplink and downlink signals of mobile communications.

B. Combiners are generally used for power synthesis in hardware circuits. For example: to get a 40dbm signal, two power amplifiers with an output power of 20dbm can be used for combining.

2. Different structures: The inside of the duplexer should be a filter cavity, and the inside of the combiner is a coupling circuit.

3. Different signal processing methods: The duplexer only processes heterofrequency signals, while the combiner can process both homofrequency and heterofrequency signals.