Multiconductor Tx Line Models

Multiconductor transmission line models for Hairpin, Interdigital, and Combline filters are supported and made available for selection in the distributed selection list.  Multiconductor transmission lines may be modeled with RLGC lines, striplines,  microstrips, and suspended substrates.

 

RLGC:

RLGC filters consist of standard RLGC transmission line models in array of coupled vertical transmission lines. Each vertical line and each coupling between the lines has a specific impedance and effective dielectric constant, or a specific inductance and capacitance, all of which are echoed out on the Nuhertz schematics. Losses are modeled with known resistance and conductance for each line. Hairpin resonators are modeled with equal impedance legs.

 

Striplines:

Stripline models include actual conductor and dielectric geometries required to realize the RLGC lines. Dielectric geometries and conductor width are supplied by the dielectric definitions, and conductor width and length geometries are calculated. Losses are calculated based upon conductor and dielectric geometries, conductor resistivity (with respect to copper), and dielectric loss tangent. Hairpin resonators are modeled with equal width legs and will result in unequal impedances due to the differing gap widths on each side of the hairpin.

 

Microstrips and Suspended Substrates:

Microstrip models are similar to stripline models, except that the dielectric constant (Er) is no longer a constant, due to the existence of air (Er=1) above the conductor. Each vertical line and coupling line has a different effective Er which must be factored into the geometry calculations. The differing effective Er's also produce some error in the filter response in the form of frequency distortion and spurious passbands. Hairpin resonators may be modeled with equal width legs and will result in unequal impedances due to the differing gap widths on each side of the hairpin.

 

Optimization:

The accuracy of the design may be increased by checking the "Quick Optimize" CheckBox.  However, this will be at the expense of  more computer time.  It is good design practice the synthesize the filter without optimization first, then optimize it after an acceptable design is found.  

 

Analysis Calculations:

FilterSolutions produces generally accurate frequency and time response (Advanced Panel required for time response simulations) of the multiconductor filters it synthesizes. This permits a quick inspection to see if the synthesized filter performance is acceptable.