Filter Products

Custom Solutions

The filters shape factor is primarily determined by the transfer function, or mathematical function, used to realize the circuit. Chebychev transfer functions are typically used in applica­tions requiring higher performance in the frequency domain (i.e., a sharp cutoff between passband and rejec­tion bands).

The filter's topology is typically selected based upon the frequency of operation, relative bandwidth, shape factor, and insertion loss, and rejection requirements: 

1. Operating Frequency. The following plot provides the approximate frequency capability of various topologies available at Q Microwave.
   
2. Relative Bandwidth. The passbands relative size as defined by the 3 dBc band­width divided by the center frequency. As noted in the below plot, this can restrict the available filter topologies.
   
3. Passband Shape Factor. The relative rolloff or shape of the filter's passband, as defined by the loss characteristics be­tween the 1 dBc and 3 dBc bandwidths, is provided below for comparison of available topologies. Customers should note that this relationship is an approximation using typical perform­ance requirements and does vary based upon other specifica­tion issues. A more detailed estimate of rejection performance is available at our website.
   
4. Insertion Loss Requirements. Passband loss will limit the available topologies as illustrated in the figure below. Typically, larger topologies provide lower loss solutions. Customers should note that this relationship is an approximation using typi­cal performance requirements and does vary based upon other specification issues. A more detailed estimate of insertion loss is available by following this link. These capabilities also do vary from manufacturer to manufacturer. 
   
5. Rejection Performance. With all other factors being equal,  each topology provides the same rejection performance outside of the 3 dBc bandwidth. Some exceptions include the following:
   • Ultimate Rejection. Combline/cavity topology can provide up to 100 dBc of rejection while other topologies will consis­tently provide no more than 50 dBc. 
   • Resonances. Circuit re-resonances will limit rejection per­formance at higher frequencies. This will limit the upper re­jection band frequency range. 
     
6. Physical Topology Issues. Physical concerns may dictate the  selection of one topology over another. Most of these con­cerns relate to size limitations. A rough tradeoff analysis with size verses electrical performance can be done using the above plots and discussions.
   

Considerations for packaging op­tions are provided at our website. Variables considered include topology, size constraints, installation method, and desired in­put/output interface. 

Probably the single most important issue not addressed here is cost. Cost tradeoffs are not easily quantified without a specific requirement for evaluation and tradeoff comparisons. Q Microwave's sales and engi­neering staff will gladly provide the necessary review of our customer's requirements to ensure that the opti­mal solution is proposed.