Qorvo
Trace Width Calculator
Calculating an accurate trace width is important in RF PC board design. Proper trace width is necessary to guarantee the desired DC current can be transported without overheating or damaging your PC board. By providing input values such as current, board thickness, temperature rise, ambient temperature and trace length your able to calculate an estimate of the internal and external trace width layers for a given current and copper weight. The trace width design tool is based on the charts in IPC-2221 (A) equations.
PAD Attenuator Calculator
This calculator is helps calculate the value of the resistors R1, R2 and R3 in a T-pad and Pi-pad attenuator. The user only needs to enter the attenuation in decibels (dB) and the given input and output characteristic impedance of the transmission lines to be matched.
Bandpass Filter Response Calculator
This tool helps you analyze a Butterworth and Chebysheve filter response using frequency inputs. To use this calculator, you simply change the upper, lower frequencies as well as the order. For Chebyshev filter designs input the ripple in dB. As you move to another input field, the output values and graph will automatically update showing you the response of the filter.
Analog Filter Wizard 
Analog Devices
Use the Analog Filter Wizard to design low-pass, high-pass or band-pass filters with actual op amps in minutes. As you progress through the design process, you can observe the characteristics of your filter design from ideal specifications to real world circuit behavior. Quickly evaluate the tradeoffs in op amp specifications-including gain-bandwidth, noise and supply current–to determine the best filter design for your requirements.
Free Online
Attenuator Calculators
Pasternack
Allows the determination of resistor values for the following:
Free Online
CRA Calculator 
Pasternack
Pasternack's CRA Calculator finds capacitance, reactance and admittance given the operating frequency and either the capacitance or the reactance.
Free Online
CST Studio Suite
SIMULA, Dassault Systèmes
CST Studio Suite is an industry-leading EM simulation tool, with multiple solvers for suitable for a wide range of applications. These can be used to design and optimize RF components both in isolation and as part of systems. The tools Filter Designer 2D and Filter Designer 3D can be used to synthesise and tune circuit, planar and cavity filters, including cross-coupled filters.
FEST3D is a software tool capable of analysing complex passive microwave components based on waveguide technology (such as multiplexers, couplers, filters…) in very short computational times with high accuracy. FEST3D achieves this by the use of the most advanced algorithms based on full-wave electromagnetic analysis methods.
Filter Wizard: Filter Synthesis & Selection Tool 
K&L Microwave
The Filter Wizard® filter synthesis tool streamlines identification of filter products meeting customer specifications across K&L's standard product offerings accelerating progress from specification to RFQ for RF & microwave filters. Enter your desired specifications, and the software returns a list of matching products, response graphs, outline drawings, and downloadable s-parameters. Click here to start designing your filter now.
QuEST: Design Your Own Filter 
BSC Filters
The QuEST tool allows you to design low pass, high pass, narrow and wide band pass filters in a variety of technologies based on your required configuration. Choose your desired technology type, add insertion and return loss limit lines, then adjust the filter complexity to realize your desired filter response. The s-parameter file can be downloaded for use in your own modelling, or you can submit your design to the factory for a quick proposal. Click here to start designing your filter now.
Free Online (registration required)
SynMatrix Filter Design Platform
SynMatrix is a microwave filter design platform for 5G and mmWave requirements. It features a comprehensive set of tools that can help engineers accelerate their design workflows with a greater amount of accuracy.
SynMatrix users are given a complete set of tools, some of which include coupling matrix synthesis with arbitrary topology and coupling matrix extraction. Advanced computer aided tuning features include dispersive effects and spurious prediction.
With direct integration into Ansys HFSS, SynMatrix also offers one of the world’s first AI-based tuning optimization systems and an advanced space mapping workflow. The AI-based tuning function was designed to converge to a solution automatically. With a near-final design, users benefit not only from more accurate and faster design outputs, but also avoid the need for costly physical sample productions.
IRA Calculator
Pasternack 
Pasternack's IRA Calculator finds inductance, reactance and admittance given the operating frequency and either the inductance or the reactance.
Free Online
Marki Spur Calculator
Marki Microwave
Marki Microwave’s spur calculator has two modes: the spur web and spectrum analyzer. Like most similar calculators, spur web will show what spurious products to expect in a basic conversion (up or down) from a given input and output band. The unique spectrum analyzer view shows what the theoretical output of a mixer displayed on a spectrum analyzer if two given single frequencies were input to a mixer. In this case there are two discrete input frequencies and the graph shows the location of different spurs at each output frequency, along with their power level. The standard spur power calculation performed by the spur calculator is based on Bert Henderson's spur model for double balanced mixers ("Predicting Intermodulation Suppression in Double-Balanced Mixers", The Communications Edge, Vol. 10, No. 4, August 1983). Marki Microwave’s Spur Calculator is available online here.
Free Online
Mixer Spurs Calculator
José Luis Flores, AT4 Wireless
A new method for mixer spurs calculation has been developed which is easier and more straightforward to use than the traditional spurs chart approach when dealing with the frequency plan optimization in broadband double conversion transceivers suitable for applications as multi-band, multi-standard and Software Defined Radio. A full technical article describing this new method can be found here.
Free Download
N-Way Power Divider Calculator 
Pasternack
Pasternack's N-Way Power Divider Calculator allows you to calculate the total path loss (in dB) you can expect based on the number of output ports on an RF power splitter device (up to 16 ports).
Free Online
RF Inductor Comparison Tool
Coilcraft 
This interactive online comparison tool for RF inductors replaces manual methods and helps prevent false starts in the design of new microwave and RF circuits. The user enters his/her operating frequency between 1 MHz and 3 GHz, then selects up to four inductors to compare using pull-down lists to pick the product series and inductance value. The results screen provides a table showing specifications for each part at the user’s own operating frequency: inductance, Q factor, impedance and equivalent series resistance (ESR). Below that, these same parameters are graphed to show performance over the 1 MHz to 3 GHz frequency range. Each part is plotted in a different color to make it easy to distinguish. And because they all appear side-by side on the same grid, it’s easy to quickly spot the best performer at any frequency.
Free Online
RF Passive Design Calculators
Chemandy Electronics 
These calculators, courtesy of Chemandy Electronics, are designed to be easy to use and follow a common theme and layout where possible.
Free Online
RF Passive Design Calculators
Daycounter, Inc.
The following is a collection of passive electronic design calculators from Daycounter, Inc., a rapid product development services company.
Free Online
Tank Circuit Resonance Calculator 
Pasternack
Pasternack's Tank Circuit Resonance Calculator calculates a system's resonant frequency.
Free Online
Rotman Lens Designer®
REMCOM
Rotman Lens Designer (RLD) is a software tool for the design, synthesis and analysis of Rotman Lenses and their variants. It is based on geometrical optics combined with classical Rotman Lens design equations. It generates the proper lens contours, transmission line geometry, absorptive port (dummy port) geometry, provides an approximate analysis of performance and produces geometry files for import into Remcom's XFdtd® for further analysis and fabrication.
License Required
COMSOL Multiphysics®
COMSOL 
The RF Module, an add-on product to the COMSOL Multiphysics® simulation software, enables engineers to analyze RF, microwave, mmWave and THz designs in multiphysics scenarios. Multiphysics modeling allows the analysis of both traditional electromagnetic wave propagation and resonant behavior of circuits and temperature-dependent material properties and structural deformation. The RF Module also allows for the extraction of parameters that are difficult or impossible to measure in a lab setting. The software features a number of examples for the modeling of filters, power dividers, cavities, lumped elements and couplers based on a microstrip line and a coplanar waveguide (CPW).
For more information visit: www.comsol.com/rf-module
Modelithics CLR Library™
Modelithics
Modelithics CLR Library™ contains Microwave Global Models™ for passive components and is a subset of the Modelithics COMPLETE Library. It includes simulation models for various component body-sizes and part values for capacitors, inductors, and resistors from many popular vendors. Eliminate bench tuning and concentrate on your next design with accurate parasitic simulation. The versatility and accuracy of these substrate and part value-scalable models help to ensure proper component selection at the simulation stage. Our Model Library software product is available for use with Keysight Technologies’ PathWave Advanced Design System (ADS), AWR Design Environment/ Microwave Office™, Keysight Technologies’ PathWave RF Synthesis (Genesys), ANSYS® HFSS™, Sonnet® Suites™ and Cadence Spectre RF.