Antenna Downtilt and Coverage Calculator 
Pasternack
The Antenna Downtilt and Coverage Calculator (aka Antenna Tilt Angle Calculator) is used to determine the approximate downward angle, measured in degrees, which the transmitting antenna is to be positioned for optimal signal strength and coverage. It also provides, given a beamwidth, the inner and outer radii of beam's coverage.
Free Online
Dassault Systemes: CST Studio Suite
CST
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 simulate antenna radiation patterns, installed performance and coupling in realistic environments. CST STUDIO SUITE is suitable for designing a wide range of antenna types, including horns, reflectors, wire antennas, printed antennas and arrays.
Antenna Magus is a software tool to help accelerate the antenna design and modelling process. It increases efficiency by helping the engineer to make a more informed choice of antenna element, providing a good starting design tuned to the specifications of the application. Engineers can then export their antenna design to CST STUDIO SUITE for 3D simulation and integration into full system simulation.
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
Helical Antenna Design Calculator
Daycounter, Inc.
Helical antennas, invented by John Kraus, give a circular polarized wave. They are one of the easiest to design. Find a tube with a circumference equal to one wavelength, and wrap wire in a helix spaced a quarter wavelength. The conductor width is not of great importance in the design. The greater the number of turns the greater the directivity or antenna gain. Receiving and transmitting antennas must be wound in the same direction, since the wave is polarized.
Free Online
Microstrip Patch Antenna Calculator 
Pasternack
Pasternack's Microstrip Patch Antenna Calculator determines the length and width (in millimeters) of a rectangular patch antenna.
Free Online
Whip Antenna Design Calculator
Daycounter, Inc.
A whip antenna also known as a monopole antenna looks capacitive if it is shorter than a quarter wavelength, and is tuned to resonance with a series inductor. PCB antennas are often shorter than a quarter wavelength due to board size restrictions and often fit into this category.
Free Online
AWR for Antenna and Phased Array Design
Cadence/AWR
Cadence AWR software helps engineers design, optimize, and integrate antennas/arrays, providing powerful electromagnetic (EM) technologies to simulate antenna metrics such as gain, return loss, radiation efficiency, and currents, and to visualize 2D/3D far-field antenna patterns. Configure individual antenna elements into phased array systems and feed network with a comprehensive workflow that extends from synthesis through physical implementation.
MATLAB and Simulink Antenna Toolbox™
Mathworks
Mathworks design, analysis and simulation software includes an antenna design toolbox. Antenna Toolbox™ provides functions and apps for the design, analysis and visualization of antenna elements and arrays using either predefined elements with parameterized geometry or arbitrary planar elements.
Trial Download
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. The software includes application libraries featuring a variety of antenna examples such as a microstrip patch antenna array used as transceivers of radar and RF signals. The libraries also include: dipole, biconical, and log periodic antenna, parabolic reflector, slot antenna and PIFA, state-of-the-art models such as fractal, substrate integrated waveguide, two-arm helical antenna, double ridged horn, corrugated circular horn antenna and so on. The RF module allows for the computation of antenna impedance matching, far-field radiation pattern, gain and directivity, and can be extended to include other physics phenomena, such as structural deformation induced by temperature change.
For more information visit: www.comsol.com/rf-module
XFdtd®
REMCOM 
XFdtd® 3D EM Simulation Software provides engineers with powerful tools to shorten development time and release products to market sooner. A full-featured electromagnetic simulation solver, XF outpaces other methods in efficiency as the number of unknowns increases. XF includes full-wave, static, bio-thermal, optimization, and circuit solvers to tackle a wide variety of applications, including antenna design, microwave, mobile device, automotive radar, and more. It also works with Remcom’s ray-tracing products to provide thorough simulation capability at the low-, middle-, and high-end of the electromagnetic spectrum.
Wireless InSite®
REMCOM 
Wireless InSite® 3D Wireless Prediction Software 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 software provides efficient and accurate predictions of EM propagation and communication channel characteristics in complex urban, indoor, rural and mixed path environments. Wireless InSite's unique MIMO capability simulates the detailed multipath of large numbers of MIMO channels while overcoming the limitations of traditional methods. With optimizations that minimize runtime and memory constraints, Wireless InSite efficiently simulates even the large arrays present in Massive MIMO systems.
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 intended for rapid development and analysis of Rotman Lenses given several physical and electrical input parameters. RLD generates the proper lens contours, transmission line geometry, absorptive port (dummy port) geometry, provides an approximate analysis of performance, and generates geometry files for import into Remcom's XFdtd® for further analysis and fabrication.
XGtd®
REMCOM 
XGtd® is a general-purpose ray-based electromagnetic analysis tool for far zone radiation, RCS, and EMI/EMC for electrically large platforms. XGtd uses Geometric Optics and the Uniform Geometrical Theory of Diffraction (GTD/UTD) to assess the effects of a vehicle or vessel on antenna radiation, estimate radar cross section (RCS), and predict radiated fields, scattering, and coupling between antennas. XGtd includes a number of capabilities that extend well beyond standard ray-tracing codes to provide high-fidelity output products.
Empire XPU
IMST
EMPIRE XPU is a high performance 3D EM-field solver based on the powerful FDTD method. It is especially suited for the analysis and design of antennas including interaction with the direct surroundings as well as complete antenna front ends including complex RF feeding networks and interfaces. The IMST proprietary & innovative XPU technology significantly speeds up the FDTD algorithm so that complex EM-simulation problems can be solved in no time on standard PCs. Time signals, scattering parameters, near- and far fields are generated for a broad frequency range within only one simulation run. Monitoring and animation capabilities give physical insight into electromagnetic wave phenomena.
Optenni Lab™
Optenni
Optenni’s main product Optenni Lab™ is a worldwide leading solution for automated antenna system optimization. It features bi-directional links with leading EM tools, and provides synergy by assessing design candidates’ post-matched performance, regarding bandwidth, isolation and total efficiency. Optenni Lab relaxes EM design challenge, because many adjustments in the EM model or physical prototype can be done with circuit design techniques. Being a radiation pattern -aware circuit synthesis tool, Optenni Lab is suitable also for aperture tuner design, coupled multi-antenna system optimization and phased array assessment and optimization.