Disadvantages of two element filter over a single element filter

[Pradeepbp]

Hi all,
I want to know if there is any disadvantages with two element filters over single element.

For a low pass filter, we can have a single capacitor(a shunt connection) OR single inductor(a series connection). These provide a 20dB/decade roll off after the break frequency.
If I use LC together then I get 40dB/decade roll off after break frequency.

Apart from extra cost for another element, is there any disadvantage with two element filter over single one??

Thanks in advance!

 

[barry]

Added poles, zeroes. Phase shift. DC Loss.

 

[LvW]

For a low pass filter, we can have a single capacitor(a shunt connection) OR single inductor(a series connection). These provide a 20dB/decade roll off after the break frequency.
If I use LC together then I get 40dB/decade roll off after break frequency.
Apart from extra cost for another element, is there any disadvantage with two element filter over single one??
Thanks in advance!

There is no "single element filter". In any case, you need at least two passive elements which constitute a frequency-dependent voltage divider.
Here you have two alternatives: RC or LC.
RC is first order with rather poor filtering of the unwanted frequencies.
LC is second order with improved filtering.

Since the task of a filter is to suppress unwanted frequencies as good as possible (or as required) it is clear that a second order circuit is "better" than a first order circuit.