Construction of BPF.
The sides were cut from Aluminium bar 20x6mm (
Aluminium Trade Centre).
Rods are from ebay, brass hex 50x5mm spacers, cut to required length (47.5mm)
The internal surface of the resonator cavity will be covered by copper sticky tape, to ensure the best possible conductivity (according to design, losses should be no more than 0.4dB)
The filter on the image is not tuned yet, it is only test assembly.
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Interdigital Bandpass Filter, based on work of Jerry Hinshaw,
Shahrokh Monemzadeh (1985) and Dale Heatherington (1996).
http://www.changpuak.ch/electronics/...r_designer.php
Javascript Version : 09. Jan 2014
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Design data for a 3 section interdigital bandpass filter.
Center Frequency : 1420 MHz
Passband Ripple : 0 dB
System Impedance : 50 Ohm
Cutoff Frequency : 1410 MHz and 1430 MHz
Bandwidth (3dB) : 20 MHz
Fractional Bandwidth : 14.1 MHz
Filter Q : 71
Estimated Qu : 2064.25
Loss, based on this Qu : 0.597 dB
Passband Delay : 31.831 ns
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Quarter Wavelength : 52.78 mm or 2.078 inch
Length interior Element : 47.59 mm or 1.873 inch
Length of end Element : 47.71 mm or 1.878 inch
Ground plane space : 20 mm or 0.787 inch
Rod Diameter : 5.5 mm or 0.217 inch
End plate to center of Rod : 13 mm or 0.512 inch
Tap to shorted End : 2.64 mm or 0.104 inch
Impedance end Rod : 89.870 Ohm
Impedance inner Rod : 91.889 Ohm
Impedance ext. line : 50.000 Ohm
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**** Dimensions, mm (inch) ****
# End to Center Center-Center G[k] Q/Coup
0 0.00 (0.000)
1 13.00 (0.512) 32.44 (1.277) 1.000 0.707
2 45.44 (1.789) 32.44 (1.277) 2.000 0.707
3 77.88 (3.066) 0.00 (0.000) 1.000 1.000
4 90.88 (3.578)
**** Box inside dimensions ****
Height : 52.78 mm or 2.078 inch
Length : 90.88 mm or 3.578 inch
Depth : 20.00 mm or 0.787 inch