Various filter design aids.
(in early/rough form, beware, read my notes!)
1) Edge coupled microstrip/stripline bandpass design (includes folded/hairpin variety)
2) lumped chebychev lowpass and highpass synthesis
3) stepped impedance transmission line lowpass filter (usable for microstrip, stripline, or even
coaxial implementation)
Note: Discontinuities such as end effect capacitances, Steps (stepped impedance lowpass), Tee
junctions, and bends (hairpin case) are not accounted for. For the bandpass designs you should
expect to adjust the length and possibly the tap point slightly to compensate for these effects.
See included PDF drawings for implementation hints and physical references.
ref: Microwave Filters, Impedance-Matching Networks, and Coupling Structures, from Matthaei,
Young, and Jones, PG 473, etc.
another good reference is Randy Rhea's HF Filter Design and Computer Simulation
Lance Lascari 6/20/2000 (personal work)
http://tools.rfdude.com
LL 6/20/2000, 6/27/2000,7/1/2000
LL 7/3/2000 -adding resonator and system impedance
LL 7/14/2000 -finally got wong reference from MTT CD's (Tap angle for hairpins)
LL 7/17/2000 -included the Tchebyscheff polynomials..... Ref: Matthei, Young, Jones Pg 99
LL 7/18-19/2000 - put generalized lumped filter design and stepped-impedance transmission line
filter design at the bottom
LL 11/24-25/2001 -- adding plots for ideal response, etc. Note: for specific filter types, better
approximations can be found in M, Y, J. I elected to only show the ideal responses for now until
I have a better grasp of the other approximations/mappings from LPF to BPF. In the future
I would like to add the additional design equations and frequency mappings from section 10 of
M, Y, J... but that will depend on the time I have available...
Main user input area:
mil 10
3−
in⋅:=
nH 10
9−
henry⋅:=
L
ar_db
0.5:=
passband ripple in dB
N 5:=
order of the filter (for now this is only valid for N ODD, since that forces input
and output load resistances to be equal, which is generally desirable)
f
low
5.5 GHz⋅:= f
high
6.02 GHz⋅:=
bandpass cutoff frequencies (these are the
equiripple band edge frequencies, not
necessarily the 3 dB cutoff frequencies)
(LPF design later in this document)
Z
r
50 Ω⋅:=
resonator characteristic impedance (coupled line char. impedance used in
calcs). It may be a good idea to change this to minimize losses in some
cases, depending on the substrate to be used. 70 ohms is often used as a
resonator or "internal" impedance of many filters.
Z
o
50 Ω⋅:=
System impedance (mainly used for deriving tap-point -- wong reference)
