Interdigital Filters

Interdigital Filter may be produced by selecting a band pass filter with Interdigital selected in the distributed selection list.

 

Wideband Interdigital Filters

Wide band Interdigital filters are synthesized with open end on the input and out couplers.  This option works much better for wideband filters, or for application that require open end couplers.

 

Tapped Interdigital Filters.

Interdigital filters (without the "Wideband" selection) are prone to having narrow gaps at the input and output couplers, or not synthesizing at all due to unrealizable geometries.  This situation may be corrected with the use of taps by selecting the Tapped check box.  This option removes the outer couples and taps the remaining outer couplers.

 

Pinned Interdigital Filters

Interdigital filters with the "Wideband" selection prone to having narrow gaps at the input and output couplers, or not synthesizing at all due to unrealizable geometries.  This situation may be corrected with the use of taps by selecting the Pinned check box.  The pinned option replaces the outer couplers with hairpin resonators..

 

Equal Width Approximation

It is frequently advantageous to maintain the same width for all conductors.  When this is the case, selecting the Equal Width Approx option accomplishes this.  The resulting increased error is usually negligible.

 

Interdigital Options

Interdigital line impedance may be user selectable, of the default value is not desired.  Standard Interdigital filters use via terminated resonators., and offer relatively high spurious frequencies (3X center frequency).

 

Open End Interdigital

Open end  Interdigital termination are selectable as an option.   Open end Interdigital offers the advantage of not using vias, but have the disadvantage in requiring larger geometries and lower spurious frequencies (2Xcenter frequency).

 

 

Manufacturing Geometry Limitations

To meet manufacturing geometry requirements, geometry limits under the "Geometry tab are enforced.

 

Tuning

Interdigital filters may be tuned by adjusting their tap position, end ring gaps, overall length, and resonator separations.  Clicking on the ring resonator schematic or the "Edit" button brings up the Change Control Panel, where values may be easily edited and scrolled to different values while the analysis graphs update in real time.  The Change control panel maintains physical symmetry or not as desired.  

 

AEDT Tuning and Optimizing

AEDT tuners and optimizers may tune or optimize the exported filter, and the tuned filter may be imported back into Nuhertz.  

Change Control Panel for Tuning the Interdigital Filter Geometry.