RF and Microwave Filter Design with EM Simulation - CEI-Europe
Course #10

RF and Microwave Filter Design with EM Simulation

Since 2014 this course is replaced by courses #30 PCB Filters and Multiplexers using Standard SMT Components, #31 Cavity Filters and Multiplexers for Wireless Applications and #32 Filters and Multiplexers for Military Systems.


Filters are one of the fundamental building blocks of RF and microwave systems, along with amplifiers, oscillators, mixers, and switches. Filter design and realization can be challenging for several reasons. No one technology or filter topology is suitable for all applications. There is also a fundamental limitation imposed by the relationship between unloaded Q and volume. 
Many of the simpler design procedures can sometimes arrive at geometries that are unrealizable, and the available literature is generally focused on theory rather than practical information on realization. However, with a few basic concepts in hand, even the non-specialist can achieve useful results. 

Electro-Magnetic (EM) simulation is also an essential component of modern filter design.We now have the ability to model and optimize complete filter structures in the EM domain. Current developments in cluster computing and multi-threading promise to enhance those capabilities as well. 

This course is devoted to the fundamentals of practical filter design for RF and microwave systems.The core material is a universal procedure for narrow band filter design that can be applied to virtually any filter technology or topology. The procedure is rooted in Dishal's method with powerful extensions that include the port tuning concept, equal ripple optimization techniques, and efficient EM simulation. All the techniques presented can be implemented using commercially available CAD tools. 

Practical procedures for extracting unloaded Q, external Q, and coupling coefficients are quite important in the design process and in evaluating prototypes. These techniques will include extracting data from hardware and from EM simulations. Some tutorial material on field-solvers will also be presented. The EM simulation examples relate specifically to filter design and include tips and techniques for more accurate and efficient simulation. 

Example filter designs that cover a broad range of commercial and military applications will be presented with measured data and error analysis.The instructor will choose examples to develop based on the interests of the class. The course material is suitable for filter designers, designers of other components, systems engineers, and technical managers. 

Filter Design, Optimization, and Port Tuning 
We will present the briefest possible introduction to basic filter design concepts. Starting with lowpass prototypes, we will touch on Chebyshev and elliptic prototypes and finding prototype element values. Next we will turn to a brief overview of the most common filter design techniques. Topics will include synthesis from an insertion or return loss function, the coupling matrix approach, and synthesis by optimization. The use of general purpose linear simulators for equalripple optimization will also be discussed. Finally, we will introduce the port tuning concept.

  • Basic Filter Concepts
  • Chebyshev and Elliptic Prototypes
  • Synthesis From Insertion Loss Functions
  • Coupling Matrix Approach
  • Synthesis by Optimization
  • Equal-ripple Optimization
  • The Port Tuning Concept

Narrow Band Filter Design and EM Simulation 
Our approach to narrow band filter design starts with Dishal's method and moves a step beyond with port tuning of a full EM model. The port tuned model is a virtual prototype that can be diagnosed and optimized before any hardware is built. Modern TEM filters often employ cascade triplets and quads to realize transmission zeros in the stopband or flatten group delay in the passband. These filters can also be designed using our approach. At some point, practical 
procedures are needed to measure unloaded Q, external Q, and coupling coefficients. Systematic methods for tuning filters are also needed. All of these methods and procedures can be applied to actual hardware or to an EM simulation of the hardware.

  • Narrow Band Filter Design
  • EM Filter Prototypes
  • Cascade Triplets and Quads
  • Unloaded Q
  • External Q
  • Coupling Coefficients
  • Filter Tuning

Designing Combline, Waveguide, DR Filters, and Diplexers 
When higher unloaded Q is required, designers often turn to cavity combline, waveguide, or dielectric resonator (DR) filters. Combline and DR filters are now used in high volumes in cell phone base stations. Meeting customer requirements often requires additional transmission zeros in the stopbands, which are realized using various types of cross-couplings. Both narrow band and broadband combline filters can be found in many military systems. Some applications also call for these high performance filters to be diplexed or multiplexed. Again, strategies for efficient design and EM simulation will be discussed for all the topologies presented.

  • Cavity Combline
  • Waveguide
  • Dielectric Resonator
  • Base Station Filters
  • Diplexers and Multiplexers
  • Strategies for Design and EM Simulation

Designing Planar Filters 
Filters in planar form can be built using several different topologies and technologies. Various single and multilayer ceramic and soft substrate (PCB) technologies are available to the filter designer. We will cover the more common distributed topologies including edge-coupled, hairpin, and interdigital. More recent coupled and cross-coupled loop topologies will also be presented. At lower microwave frequencies a pseudo-lumped approach using printed inductors and capacitors is more space efficient. Lowpass, elliptic lowpass, and bandpass filters using this approach will be presented. Strategies for efficient design and EM simulation will be discussed for all the topologies presented.

  • Planar Filters
  • Single and Multilayer
  • Ceramic and PCB
  • Edge-coupled, Hairpin, and Interdigital
  • Coupled and Cross-coupled Loops
  • Pseudo-lumped Lowpass and Bandpass
  • Strategies for Design and EM Simulation 


Said about the course from previous participants:
"The course has an engineering approach and the teacher gives many examples and explains mistakes also."
"Broad coverage of filter designs and different technologies."
"Pointers on how to dig deeper into certain aspect."
"Lots of measurement results."
"A good coaching of all aspects. Industry relevant and practical experienced teacher."
"Fits my work very well, working as a filter designer. Best course I have been to!!!"
"Very related to real problems. Touch different technologies with a good approach to actual designs."
"State-of-the-art lecture material."
"Practical hints and tricks."

CEI-Europe AB, Teknikringen 1F, SE-583 30 Linköping, Sweden Phone +46-13-100 730 Fax +46-13-100 731 cei@cei.se