Company Profi leBased in Santa Rosa, California, Phil Jobson Consulting provides RF/microwave system

and component design solutions, including linear, nonlinear, EM, system modeling and

simulation, system/component characterization and measurement, and prototyping.

The Design ChallengePhil Jobson Consulting was asked to design a family of low-cost, ultra high-frequency

cavity-based helical resonator bandpass fi lters for the CATV test market that could be

combined into a switched fi lter bank. Cavity-based fi lter performance is determined entirely

by geometry. Even though the devices are tuned, it can be challenging to size all the

components such that the tuning elements are effective to meet desired synthesized

response. 3D EM geometry creation and simulation for cavity-based fi lters is generally very

time intensive. The designer wanted to create a complete “synthesis to implementation”

process for helical cavity-based bandpass fi lters in a single, integrated project that could be

quickly applied to new designs by changing a small number of key global parameters. He

also wanted to be able to leverage reusable parameterized 3D EM building blocks for

cavities and resonators in the fi lter synthesis and design stages to simplify design capture

and re-use. Finally, he wanted to leverage layout parameterization to automatically create

fabrication fi les for cavities for each new design based on a few key global parameters.

The SolutionThe designer used NI AWR Design Environment™ Microwave Offi ce circuit design

software and Analyst™ 3D electromagnetic (EM) simulator to capture and automate

the entire fi lter design process within a single Microwave Offi ce project. The tightly

integrated environment enabled a single, simple fl ow from synthesis to design to

verifi cation and then to implementation.

Success Story

Phil Jobson Consulting Designs Family of UHF Cavity-Based Helical Resonator Bandpass Filters with NI AWR Software

Application:

Helical Resonator Bandpass

Filters

Software:

NI AWR Design Environment

Microwave Office

Analyst

‘‘ Being able to create

tightly integrated, reusable

parameterized 3D EM building

blocks in the Microwave Office

simulation environment has

changed the way I design high-

performance RF/microwave

circuitry. I am able to solve

problems and create solutions

for new challenges with a

confidence, efficiency, and

effectiveness that I had only

dreamed of in the past.’’– Phil Jobson

Design Engineer

Phil Jobson Consulting

linkedin.com/pub/phillip-jobson/18/780/208/

First prototype.

ni.com/awr

The design and manufacture of the fi lter presented a number of challenges, as is typical of this type of fi lter design. First, the fi lter was

designed using ideal elements and traditional fi lter theory. Optimizations were carried out to get the required response. The fi rst challenge

was to get the ideal fi lter response into an actual, physical cascaded, cavity fi lter topology. Analyst was used for the EM simulation because

of its ability to create 3D parts as PCells that can be repeatedly used in the fi nal layout. This made model creation easier, as the steps from

individual cavity design to the fi nal fi ve cascaded sections essentially involved connected similar shapes. The shapes were created using

parameters so that the actual geometries could be quickly changed without having to redraw the structures in a 3D layout editor. The fi nal

fi lter was created using only three basic 3D components: the cavity with the coil, the end plates with the coaxial feeds, and the interior

separation walls with the coupling slots. Figure 1 shows the fi nal geometry in Analyst.

The actual manufacture of the fi lter was carried out quickly and inexpensively by fi rst creating

the basic parts without the coils, and then winding the coils to the predetermined

specifi cations. As noted above, the actual layout was done in Microwave Offi ce and exported.

The resulting board was then cut, and the fi lter assembled. The coil was wound on a plastic

cable former that was created using a 3D printer. Final assembly was then carried out by

positioning the coils and tuning screws. A wooden dowel was used for mechanically

supporting the coils. Figure 2 shows the fi lters combined into a switched fi lter bank.

The designer achieved fi rst pass success on three fi lter designs, despite never having

designed cavity-based fi lters before. His success also yielded at least a 5x reduction in time for 3D EM structure creation of the fi lter

family due to the cascadable building block nature of Analyst 3D fi nite element method (FEM) EM PCells. He noted that the

innovative integration of Analyst is an exceptional feature within NI AWR Design Environment that differentiates it from the

competition. Measured results are shown in Figure 3. Agreement between simulated and measured results was considered excellent.

First pass design, construction, and verifi cation of the fi lters was achieved.

Why NI AWR Design EnvironmentPhil Jobson Consulting chose NI AWR Design Environment

because he was an early adopter and expected that the

integrated environment would fulfi ll his needs. He has always

enjoyed the ease of use, customer care and constant innovation

of AWR (now National Instruments).

©2015 National Instruments. All rights reserved. A National Instruments Company, AWR, Microwave Offi ce, National Instruments, NI, and ni.com are trademarks of National Instruments. Other product and company names listed are trademarks or trade names of their respective companies. SS-JBSN-2015.4.14

Figure 2: Filters combined into a switched filter bank.

Figure 3: Measured results.

Figure 1: The filter as modeled in Analyst.