Microstrip Pseudocombline Bandpass Filter

Model

The first figure shows the geometry of a microstrip pseudocombline filter on a substrate with a relative dielectric constant of 10.8 and a thickness of 1.27 mm. The structure consists of an array of coupled resonators and uses the tapped lines as the input and output. The resonator lines are half-wavelength long at resonance. Edge sources are used to feed the microstrip line at two ports.

Simulation

A template broadband simulation is prepared and then the S-parameter Simulation Setup tool is used to build necessary simulations to extract the two-port S-parameters of the filter. The UPML absorbing boundary conditions are used to truncate the domain.

Results

The S-parameter Evaluation tool is employed to calculate S-parameters of the filter. The simulated frequency response of the filter is illustrated in the second figure. It shows that a transmission zero occurs near the high edge of the passband which improves the performance of the filter with a higher selectiveness on that side. The second passband is centered about 4 GHz which is expected since half-wavelength resonators are used without capacitor loading.

Ref. Jia-Sheng Hong and M.J. Lancaster, Microstrip Filters for RF/Microwave Applications, New York:Wiley-Interscience, 2001.