How to design a diplexer having wide differance in BW of TX and RX filter

I want to design a diplexer having wide differance in BW of TX and RX filter.
For example RX filter BW=32 MHz and TX filter BW=450MHz. and separation band=20MHz.
One problem I am getting is the F0 of diplexer, i.e., it is falling in band of TX filter. If this is the case then how to synthesis such diplexer?

For which frequencies do you design? Anyway a separation of 20MHz, i guess only cavity diplexer can handle and if these a case probably easier to buy customized one.

You do not mention the carrier frequency, which is critical for filter Q reasons. But if the carrier frequency is low enough, I might do a lowpass/highpass elliptical diplexer, and follow up with bandpass filtering stages if more rejection is needed.

Referring to your last question:

"One problem I am getting is the F0 of diplexer, i.e., it is falling in band of TX filter. If this is the case then how to synthesis such diplexer?"

...this is not a diplexer anymore...

I guess what you need is a switched filter bank instead of a diplexer.