Low-loss microstrip filters developed by frequency scaling

Low-pass and band-pass microstrip filters up to 30 GHz have been built on silica substrates by photolithographic reduction of optimized low-frequency models. Scaling accuracies of 1.8 percent or better have been achieved. An insertion loss of 0.28 dB has been measured for a five-section low-pass filter with a cutoff frequency of 5.7 GHz. The insertion loss of a 12-percent band-pass filter at 8.18 GHz is 0.16 dB. Good agreement between measured and calculated losses has been obtained. Circuit dimensions are given to facilitate scaling of the low-pass and band-pass microstrip filters to other frequencies.