I am trying to make a LTE signal repeater and trying to filter all other signals except the band 3 (869 - 894 MHz)

This is what I am getting:

enter image description here This is the circuit:

enter image description here Any suggestions on improving the filter and how can I use standard value components instead of exact values?

Edit: The test signal is 1Vpp

Edit: Made modifications as per The Photon's comment. Still the voltage in the pass band is quite low!

  • 4
    \$\begingroup\$ Will your filter really be driven by an ideal voltage source in the actual application? And will its load really have infinite impedance? Notice that in your model the initial shunt arm (L1 and C1) has no effect because of the ideality of the source. \$\endgroup\$
    – The Photon
    Commented Aug 19, 2020 at 14:12
  • 1
    \$\begingroup\$ Sag between the peaks implies too loose (too little) coupling between the tuned circuits. But before fiddling with the coupling. simulate with the correct terminations per the Photon't comment. \$\endgroup\$
    – user16324
    Commented Aug 19, 2020 at 14:31
  • \$\begingroup\$ You haven't said what your design expectations are so how can you expect help. Ditto the previous. \$\endgroup\$
    – Andy aka
    Commented Aug 19, 2020 at 14:33
  • \$\begingroup\$ The previous comments are on point, I'll just add that you should avoid nets with more than two labels: IN2 and OUT2 are both connected to ground (they can be removed). \$\endgroup\$ Commented Aug 19, 2020 at 15:47
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    \$\begingroup\$ @Prabodh did you use \$Z_0 = 50 ohm\$ to calculate the L and C values (as mentioned in the link) ? Can you update the question with the detailed calculations you made ? \$\endgroup\$
    – AJN
    Commented Aug 20, 2020 at 16:15

1 Answer 1


I applied the formulae given in the reference link posted in the comments to the question. I used the frequency values 860MHz and 900.5 MHz for f1 and f2 (no particular reason).

filter design equations

From the values of components obtained, I made the filter in SPICE.

filter circuit

Then plotted the response to get the desired bandpass response.

frequency response of the band pass filter

I also noticed that the filter pass band flatness is quite sensitive to the number of decimal places used for the simulation. Hence my circuit above has up to 4 significant digits for the component values.


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