ComNav Engineering has some neat software for Engineers that need to specify or design filters. And the best part is that it’s FREE.

Download it here.

Designs include:
Lowpass Filters, Highpass Filters,  Bandpass Filters, Notch Filters,  Diplexers, Multiplexers, Delay Equalizers, Amplitude Equalizers, Attenuators, Coax Resonators, Puck Resonators, Microstrip, Stripline, Round and Square Rod Coupled and Transmission Lines.

Many Analysis options are available, including:
S Parameter, Return Loss, Attenuation,  Phase Linearity, Delay, Smith Chart.

Write Industry Standard *.S2P files for further simulation.
Fourier Pulse: Define Pulse Train,  Set Noise Level, View Pulse Distortion,  Power, Rotate source and load impedances, Set Impedance Mismatch, Identify max Voltage, Current, and Power dissipation etc.