PCFILT sample design

*** Speed and Flexibility ***

To illustrate the power and flexibility of PCFILT, Here's an example.One quick way to design a bandpass filter is to simply scale it from anormalized lowpass filter. This method has been expanded to its logical limitwith the ability to scale any filter topology from any type of lowpass!

A typical PCFILT menu (The filter "type" menu from the DOS version) looks like this:

The rest of the screen shots are the Windows version

Here's the example:

Let's make a 10% bandwidth filter at 100 MHz that has capacitively coupled parallel resonant sections at one end and shunt coupled series sections at the other. Just for good measure, we will stick two stopband "notch" sections in the middle by using the lowpass reference pole placer.

After you have selected the reference to be a pole-placed lowpass, the "Design Parameters" menu comes up automatically. This where you select the specifications for the filter.

Next, Set the 3rd coupling to be the inter-network dual ("D") and the rest as capacitors.

Press the [CALCULATE] button to start the action.

Now you can synthesize the reference lowpass by just pressing [Automatic]. Any network you need can also be selected by pointing to the desired sub-network codes in the right order with your mouse.

Here is the default reference lowpass filter that is synthesized by simply pressing the [Automatic] key (finite zero "notch" sections are placed in the middle of the network):

The narrow-band bandpass dialog box let you force the L/C ratio to realizable values.

The impedance matcher menu appears next

The "Matcher" gives you a list of optional networks to "tack-on" to each end of the filter to transform it from the "design impedance" (624.25 Ohms) to whatever you like, usually 50 Ohms.

Termination end impedance matching options:

Source end impedance matching options:

Each element in the reference lowpass is then scaled to form a single section of the final bandpass filter.

The circuit editor draws the schematic like this:

After a little work with the circuit editor, using the Norton transform and "Cp" functions, the hot nodes around the finite zeros (notch sections) are gone!

Here's a response plot of this example:

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