A compact, high performance, semi-lumped, low-pass filter fabricated with a standard air bridge process

A compact, semi-lumped, low-pass filter with a sharp cutoff and a very wide stopband is presented. It is composed of a cascade of elevated low-loss lumped inductors and ultra-low impedance thin film microstrip line (TFMS) sections made using a standard air bridge process. This new type of TFMS is suspended using air bridges providing a small air gap between the signal line and ground metal - "Air TFMS". This results in a wide stopband at high frequency and, when combined with high quality factor suspended inductors, also gives a sharp cutoff response at low frequency. The combined characteristics of these elements make for excellent low-pass filter performance.