Interdigital Bandpass Filter, based on work of Jerry Hinshaw,
Shahrokh Monemzadeh (1985) and Dale Heatherington (1996).
www.changpuak.ch/electronics/interdigital_bandpass_filter_designer.php
Javascript Version : 09. Jan 2014
Design data for a 3 section interdigital bandpass filter.
Center Frequency : 869.5 MHz
Passband Ripple : 0 dB
System Impedance : 50 Ohm
Cutoff Frequency : 864.5 MHz and 874.5 MHz
Bandwidth (3dB) : 10 MHz
Fractional Bandwidth : 0.0115
Filter Q : 86.95
Estimated Qu : 2422.95
Loss, based on this Qu : 0.623 dB
Passband Delay : 63.662 ns
Quarter Wavelength : 86.2 mm or 3.394 inch
Length interior Element : 78.48 mm or 3.090 inch
Length of end Element : 78.86 mm or 3.105 inch
Ground plane space : 30 mm or 1.181 inch
Rod Diameter : 8 mm or 0.315 inch
End plate to center of Rod : 15 mm or 0.591 inch
Tap to shorted End : 3.92 mm or 0.154 inch
Impedance end Rod : 88.549 Ohm
Impedance inner Rod : 93.734 Ohm
Impedance ext. line : 50.000 Ohm
**** Dimensions, mm (inch) ****
End to Center Center-Center G[k] Q/Coup
0 0.00 (0.000)
1 15.00 (0.591) 50.25 (1.978) 1.000 0.707
2 65.25 (2.569) 50.25 (1.978) 2.000 0.707
3 115.50 (4.547) 0.00 (0.000) 1.000 1.000
4 130.50 (5.138)
**** Box inside dimensions ****
Height : 86.20 mm or 3.394 inch
Length : 130.50 mm or 5.138 inch
Depth : 30.00 mm or 1.181 inch
Esattamente, a 15mm dal lato della scatola va il centro del primo risonatore a 65.25 sempre dal bordo il risonatore centrale e così via. A 3.92mm dalla base del risonatore va iniettata la rf io ho utilizzato i conn sma con un pezzettino di filo leggermente curvo che fa da stress durante le dilatazioni termiche. Se riesci ad argentare internamente tanto meglio
