The most flexible and powerful Microwave and RF Filter and Multiplexer Design Software

Prof. Dr. Nevzat Yildirim, E-Mail:

(Presented at the workshop "State of the Art Filter Design using EM and Circuit Simulation Techniques" in MTT-S'97, Denver, Colorado, USA)

FILPRO at the MTT-S'97, Denver

Filpro Team

Two of the FILPRO creators, Dr. Nevzat Yildirim (right)and his assistant Mehmet Karaaslan (left) with Dr. Richard Snyder (sitting) of RS MICROWAVE COMPANY at MTT-S'97 Symposium, Denver, Colorado where FILPRO is also presented in the workshop entitled "State of the Art Filter Design Using EM and Circuit Simulation Techniques

FILPRO at the MTT-S'99, Los Angeles

Filpro Team at MTT-S'99

Four of the FILPRO creators (left-to-right), Yakup Sen, Nevzat Yildirim, Ozlem Sen and Mehmet Karaaslan at MTT-S'99 Symposium, Los Angeles, California where some CQ-CT applications of FILPRO are presented as a paper

FILPRO at the MTT-S 2000, Boston

with Dieter

With Dieter Pelz of RFS Australia, a distant contributor of Filpro

FILPRO at the MTT-S 2004, Forth Worth, Texas

with Mustafa

With Mustafa Akkul of Filtronics-England, another contributor of Filpro

FILPRO at the MTT-S 2004, Forth Worth

Turkish Team

Turkish Team at MTT-S 2004

Filpro is an extremely flexible software package developed in a novel approach for fast synthesis, circuit transformation and analysis of lumped and distributed element filtering, multiplexing, matching and coupling structures. The distinguishing characteristics of the approach is modularity of all design steps. Almost all the synthesis and circuit transformation techniques available in literature are programmed as independent modules and placed in different toolboxes (menus). A typical design procedure is formed simply by selecting the necessary techniques from the toolboxes and linking them. This approach provides great flexibility in reaching almost any filter seen in literature in a fast and easy way using a single software. All the steps are under the control of designer, giving the opportunity to observe effects of various circuit transformations and approximations on response instantly. It is aimed at the most complex lumped and distributed filters. The well known, classical filters can be designed just as side products.


A targeted filter is designed by selecting a proper technique from the synthesis menu containing diverse filter design techniques like Exact Synthesis, Synthesis from Built in LC Prototypes, Synthesis using Prototypes with Inverters, Synthesis from User Defined Prototypes, Cross-Coupled filters, Diplexers, Dual Band Filters, etc.


  • Synthesis of Cascaded Triplet (CT), Cascaded Quadruplet (CQ) and Generalized Cascaded Quadruplet (GCQ) (Quadruplets with diagonal cross-coupling) filters by pole placement using the classical cascade synthesis approach are now available, including linear phase options.
  • Design of higher order N-tuplet filters (Quintuplet, Sixtuplet, Seventuplet, eighttuplet, ninetuplet and tentuplet) are available including linear phase options with inverter type coupling elements.


    Synthesized filters usually have undesirable topologies with unrealizable element values. In Filpro these circuits are transformed into desired toplogies with realizable element values by applying a set of circuit transformations selected from the Circuit Transformations toolboxes (menus). Macro programming feature speeds up the design if the number of circuit transformations are excessive. A huge number of circuit transformations are have been developed and placed into Filpro for designing almost all the classical and novel filters seen in literature. The circuit appears on the screen automatically after the synthesis stage with a textbook type schematics. Elements of circuits are pointed by a moving cursor. Parameters of pointed elements are displayed automatically. The whole circuit can also be moved to right or left if the number of elements is large. The transformations are applied by pointing the element(s) with the circuit cursor and clicking the circuit transformation command selected from the menu. Some of the circuit transformations available in Filpro are as follows:

  • Cascaded Triplet (CT) filters are used to place finite transmission zeros in lower and upper stopbands independently of each other. Such filters were designed using Cross-coupled filter synthesis approach.With Filpro, it is now possible to synthesize them by the classical cascade synthesis approach with pole placement and using a single command to transform it to a cascaded triplet form.
  • Cascaded Quadruplet (CQ) filters are formed by cascading sections termed as Quadruplets (four coupled resonators). Such sections place finite transmission zeros on both sides of the passband in a geometrically symmetric manner. Till now, they were designed using cross-coupled filter synthesis approach and "Rotations". With Filpro, it is now possible to synthesize them using the classical cascade synthesis approach and a simple circuit transformation command, "Convert to CQ". If necessary, one or more of the quadruplets can be made to create a SIGMA AXIS TRANSMISSION ZERO to approximate constant delay about passband center.
  • Generalized Cascaded Quadruplet (GCQ) filters are formed by cascading sections termed as Generalized Quadruplets (four coupled resonators including a diagonal cross-coupling). Such sections can place finite transmission zeros on both sides of the passband in asymmetric manner.
  • Cascaded Quadruplet elements may also be used to create a single finite transmission zero on any side of the passband. This approach avoids the diagonal cross-couplings of GCQ and CT sections.
  • Arbitrary CT, CQ and GCQ sections may be cascaded(CQ) to form diverse topologies to get different filter characteristics, avoiding the practical difficulties of Canonical Cross-coupled filters (filters with input-output on the same side and having many vertical and diagonal cross-couplings).
    With these tools, the unbearably tedious circuit transformations are transformed into a one or several push button manipulations, easing the life of designer a lot. With these barriers eliminated, it is now much easier and faster to search for the alternative equivalent circuits. It is left to the imagination of the designer to discover new solutions. The design process is splitted into a large number of command steps, each step being under the control of the designer. Thus, the effect of each transformation or approximation on response is instantly observed.

    The state of the art in filter synthesis, design and implementation are tracked closely simply by adding new modules into Filpro. It is an open ended, extremely adaptive software, undergoing continuous modifications after each academic or industrial applicaton.



    The software is capable of designing most of the practical filtering, multiplexing, matching and coupling circuits, from old classical filters to modern, miniature circuits. Owing to modularity, new filter types can also be handled by adding the necessary modules. Some of the filter types that the present version of Filpro can handle are listed as follows:

    LUMPED ELEMENT LP, HP, BS and BP FILTERS (singly or doubly terminated):

    DISTRIBUTED ELEMENT LP, HP, BS and BP FILTERS (singly or doubly terminated):