What is narrow band and broad band in low and high frequency range

Dear Sir ,
When we are calling as narrow band and broad band in low frequency ( in terms of MHz or KHz)range. Suppose we design a low pass filter of 10MHz or 10KHz, at what frequency range we can say narrow band low filter and what frequency range we can say broad band.

Similarly when we are calling as narrow band and broad band in high frequency range (in terms of GHz or THz). Suppose we design an amplifier at 2 GHz or 100GHz, at what frequency range we can say narrow band amplifier and what frequency range we can say broad band amplifier.
Can you clear the above doubts.

I believe narrow and broad refer to the filter topologies.

Narrow band suggests a filter which resonates at a particular center frequency. Example, LC tank.

Broadband suggests a combination of a low-pass circuit and a high-pass circuit. The cutoff frequencies are independent and adjustable.

There is some overlap of terms. An LC tank can have very high Q (a narrowband characteristic), although the bandwidth can be broadened by adding resistance in the loop.

Dear Sir,
O.k, in terms of amplifier itself, you can differentiate it narrow and broad band amplifier with low (KHz) and high (GHz) range of frequencies. Can you clarify it.

Broadband amplifier:
I have an amplifier hooked up to my TV antenna, so I can get better reception on my air-broadcast TV. I do not tune it to any particular channel. It is designed to act on a wide range of frequencies, simultaneously.

Narrowband amplifier:
A radio receiver tunes to a particular frequency. It amplifies that frequency so we do not hear other broadcasts. In this case we want a narrowband amplifier.

There is no generally accepted definition for broad band or narrow band.

In my opinion when BW/Fcenter ratio << 1, it is narrow band, from a filter or amplifier design point of view. So a 9 kHz BW at 455 kHz is narrow band in my opinion.

A 10..20 MHz amplifier (BW/Fcenter = 0.67) I classify as broad band.

When you need to design an audio filter that passes. 300...3400 kHz (BW/fc = 1.67) , I would classify as broad band, but a 390...410 Hz filter (BW/fc = 0.05) I would classify as narrow band.

You will sure find people that would classify 10 kHz at 150 MHz a narrowband channel , but 100 kHz at 150 MHz a wide band channel.

From a signal perspective one could look to Fup/Flow ratio (BW = Fup - Flow). If this is << 1, output wave forms generally have a sinusoidal envelope, so you can use steady state analysis to design the circuit. You may classify that as narrow band, as you use design rules applicable to tuned amplifiers/filters. When Fup/Flow > 1, the output waveform can be anything and then a transient approach would be preferred.

I agree that there's no general definition for the terms.

If I had to choose, I'd say that when referring to filters, narrowband means that filter response peaks at one frequency but is never locally flat, while a broadband filter would be a cascade of HP/LP stages to get a flat passband.

Sir,
Can you make out differentiate in terms of amplifier narrow and broadband with low and high frequency ranges