LPF gives 2 different simulations

deki · Aug 25, 2015

I've designed a 3rd order BPF. I tuned it in AWR Design Environment (Microwave Office), and got the response I wanted:

Graph 1 plots DB(|S(2,1)|) and DB(|S(1,1)|) for a BandPassFilter against frequency from 900 to 3000 MHz, with dB on the vertical axis from -80 to 0.

However using the same component values with LT Spice gives me a different response:

LTspice schematic of a third-order bandpass filter between Input and Output, with L1 44.2n, C1 0.1645p, L2 0.328n, C2 22.18p, L3 60.25n, C3 0.105p and R2 50, above a plot of output/input voltage gain in dB from 0.9 GHz to 3 GHz.

The other thing I've noted in the plot is the input voltage. I'm not that familiar with AC analysis in LT Spice, but why does the input voltage look like that? That's what is contributing to my uneven response.

meBigGuy · Aug 26, 2015

I'm just guessing, but one program may include the source impedance in the AC source, and the other not.

LPF gives 2 different simulations

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