For an Receiver, we want to design an IF Bandpass with the following key data : Center Frequency F = 270 MHz, Bandwidth B = 10 MHz, Ripple R = 0 dB (Butterworth), System Impedance R = 50 Ω, 2 resonators, allow the Calculator to choose inductors from E12 range. As we want to use standard values (capacitors and inductors), we do play a little a sophisticated guess and choose L = 27 nH. (Switch to "use my value"). The Designer finally suggests the following values :

Direct Coupled Resonator Bandpass Filter Designer
https://www.changpuak.ch/electronics/Direct-Coupled-Resonator-Bandpass.php
Javascript Version : 27. Jan 2014
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Design Data for a 2-Resonator Bandpass Filter.
Center Frequency : 270.0 MHz
Bandwidth : 12.0 MHz
Passband Ripple : 0 dB (Butterworth Characteristic)
System Impedance : 50 Ohm
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Coupling Capacitor : 2.22 pF
Resonator #1 C : 10.32 pF // L : 27.00 nH
Coupling Capacitor : 0.40 pF
Resonator #2 C : 10.32 pF // L : 27.00 nH
Coupling Capacitor : 2.22 pF
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Please verify by simulation that attenuation above passband is sufficient.
Negative capacitances indicate an unhappy inductance.

Approach 1    Uses 2.2 pF SQCB low ESR capacitors from ACX RF, TOKO LL2012-FHL Chip Inductors, muRata 3-10 pF Trimmer and a 'wire' capacitor for coupling. Insertion Loss was 5.7 dB.
Approach 2    Uses 2.2 pF SQCB low ESR capacitors from ACX RF, TOKO LLQ2012 Wire Wound Chip Inductors, muRata 3-10 pF Trimmer and a 2 x 1 pF in series to do the coupling, as the 'wired' capacitor was somehow tricky to handle.
Approach 3    Uses 2.2 pF SQCB low ESR capacitors from ACX RF, muRata 3-10 pF Trimmer and a 2 x 1 pF in series to do the coupling. DIY coils (n=4, d=4). Insertion Loss was 1.3 dB.

The insertion loss of the board was not calibrated out to get nicer measurements. The idea was to show, that the calculator delivers useful values :-)

And yes, the bandwidth is larger. This is due to the (slightly) different coupling-capacitor. We therefore introduced the bandwidth-tuning-buttons to adjust for a minimum value of e.g. 1 pF.

The larger bandwidth was also caused by an error in the javascript. We would like to thank Gregory for his valuable feedback on this. MUITO OBRIGADO !!!

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