Miniaturizing and optimizing the design of miniaturized hairpin resonator filters

April 12, 2012 // By Jeff Kahler, Nuhertz Technologies
Nuhertz Technologies’ FilterSolutions™ and QuickFilter™ programs enhance the design techniques for standard and miniaturized hairpin resonator or ring resonator filters.

Using circuit and electromagnetic simulation tools from AWR Corporation and Sonnet Software, the synthesized design of optimized cross-coupled circuits assist in the minimizing the use of circuit board space. The techniques offered by Nuhertz allowing the filter’s resonators to be folded down or inside the Hairpin structure, solving for electromagnetic interaction of the resonators.

Cross-coupling enhances space efficiency as well by narrowing the passband. (See Figures 1 and 2).

Hairpin resonator designs can meet manufacturing geometry limitations without the need for vias between layers. The design synthesis programs available from Nuhertz Technologies are valuable in allowing these considerations to be realized and optimized.

Figure 1: Narrow passband bandpass filter design centered at 1 GHz. Design uses hairpin resonators with legs folded inside the hairpins:
(Approximate size: 650 mm 2).

Figure 2: Narrowed passband produced by cross coupled resonator filter.

Nuhertz filter synthesis tools support the design of miniaturized hairpin and ring resonator filters, including cross-coupled designs, within manufacturing geometry limitations. Internal circuit tuning may be used to finetune to the desired response. Optimization may be accomplished by exporting the Nuhertz synthesized design into a robust transmission line circuit optimization program, such as AWRCorp’s Microwave Office™. (Direct export into AWR’s circuit simulators is a standard feature of FilterSolutions and QuickFilter). The Nuhertz programs set up the AWR tuning equations to enforce geometry limitations. The Microwave Office optimized filter may then be re-imported into the Nuhertz program, if needed.

In consideration of manufacturing and electrical performance requirements, electromagnetic optimization is usually necessary to account for the interaction between the various conductor segments of the Hairpin. These interactions cannot be easily modeled in a circuit analysis program. The electromagnetic optimization of the design may be accomplished with the use of Sonnet Software’s em® Port Tuning optimization technique, AWR’s Axiem™ extraction, or other third party extraction optimization.

The Nuhertz program sets up the electromagnetic optimization equations in the AWR optimization schematic. When completed,

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