Wireless InSite® Propagation Software
REMCOM 
Wireless InSite is a suite of ray-tracing models and high-fidelity EM solvers for the analysis of site-specific radio wave propagation and wireless communication systems. The RF propagation software provides efficient and accurate predictions of EM propagation and communication channel characteristics in complex urban, indoor, rural and mixed path environments.
License Required
CST Studio Suite
SIMULA, Dassault Systèmes
CST Studio Suite is an industry-leading EM simulation tool, with multiple solvers suitable for a wide range of applications. Engineers can use these solvers to simulate antenna radiation patterns and coupling, both in isolation and as installed in realistic environments. The Hybrid Solver Task, combining FIT and MLFMM methods and the Asymptotic Solver offer an efficient way to calculate 3D propagation around large structures such as buildings and aircraft.
WRAP
Altair HyperWorks
WRAP streamlines the complex task of managing valuable radio spectrum assets to provide maximum utilization and optimal performance. With support for large national and international frequency databases, WRAP's propagation models ensure comprehensive coverage across the entire radio spectrum. And with International Telecommunication Union (ITU)-compliant calculation and coordination methods, WRAP ensures compatibility with spectrum regulations while quickly identifying and resolving interference issues in remote and densely collocated scenarios (license required).
EIRP Calculator 
Pasternack
Pasternack's EIRP Calculator determines the radiated power given the transmitter power, the cable loss to the antenna and the gain of the antenna.
Free Online
Free-Space Path Loss Calculator
Pasternack 
Pasternack's Free Space Path Loss Calculator calculates the loss (in dB) between two antennas where the gain, distance and frequency are known.
Free Online
Friis Path Loss Calculator 
Pasternack
Pasternack's Friis Transmission Equation Calculator will calculate the received power from an antenna at some distance given a transmission frequency and antenna gains.
Free Online
Link Budget Calculator 
Pasternack
Pasternack's Link Budget Calculator determines the received signal strength (in dBm) given a systems amplifier gains, antenna gains and space loss.
Free Online
Maximum Field Strength Calculator
Daycounter, Inc.
This calculator calculates the maximum field strength that a dipole antenna could produce at 3M assuming 100 percent antenna efficiency. This provides an upper bound for transmitter power.
Free Online
P2P Signal Propagation Calculator 
AlphiMAX
Determine whether a wireless link will work given the specific locations you are trying to connect, prior to purchasing equipment or climbing a tower. The Point-To-Point Estimator is a free web based tool with a very nice graphical interface tools that enables you to compare manufacturers, while taking into account the terrain of your area, terrain type, climate, antenna type, define fade margin and more. Use of a GPS database produces a very accurate elevation profile between antenna locations.
Free (Registration Required)
Power Density Calculator
Pasternack
Pasternack's Power Density Calculator is designed to give the power density, in Watts per square meter, at a given distance, output power and antenna gain. Please note that this calculator is only valid for far-field calculations.
Free Online
Radar Maximum Range Calculator 
Pasternack
Pasternack's Radar Maximum Range Calculator produces an ideal maximum range of a radar antenna using the properties of the antenna.
Free
Frequency to Wavelength to Energy Calculator
BYU
To convert wavelength to frequency or energy, use this BYU calculator with formulas and unit noted.