broadband vs frequency band

broadband is not a noun while frequency band is a noun.

Word	Noun	Adjective	Verb	Adverb
broadband	No	Yes	No	No
frequency band	Yes	No	No	No

broadband (noun)	frequency band (noun)
	a band of adjacent radio frequencies (e.g., assigned for transmitting radio or television signals)

broadband (adjective)	frequency band (adjective)
responding to or operating at a wide band of frequencies
of or relating to or being a communications network in which the bandwidth can be divided and shared by multiple simultaneous signals (as for voice or data or video)