# PSSFSS - analysis of polarization and frequency selective surfaces in Julia

PSSFSS is a Julia package for analyzing polarization selective surfaces (PSSs), frequency selective surfaces (FSSs), reflectarray elements, radomes, and similar structures. It is intended to be useful to antenna design engineers and others who work in applied electromagnetic engineering.

The user specifies the geometry to be analyzed as a `Vector`

containing two or more dielectric `Layer`

s and zero or more `RWGSheet`

objects that define the PSS/FSS surfaces. Due to the included plot recipes, the surfaces and their associated triangulations can be conveniently visualized using Julia's standard `Plots`

package. After also specifying the scan angles or unit cell incremental phasings, frequencies to be analyzed, and optionally selecting performance parameters to be written to CSV file(s), the user then invokes the `analyze`

function to perform the analysis. Post-processing and plotting of results can be performed in the same analysis script using the immensely powerful Julia programming language.

## Features

- Designed to be useful and accessible to working engineers.
- Accommodates planar FSS/PSS surfaces with no limits to number of dielectric layers or FSS/PSS sheets.
- Simple specification of geometry to be analyzed.
- Automatically chooses number of modes needed for rigorously cascading multiple FSS/PSS sheets of identical periodicities using generalized scattering matrices (GSMs).
- Supports (approximate) cascading multiple sheets of different periodicities, as in a multilayer meanderline polarizer.
- Solution of mixed-potential integral equation using Rao-Wilton-Glisson triangle subdomain basis functions and multi-threaded method of moments.
- Fast analysis for frequency sweeps using an extremely robust rational function interpolation algorithm.
- Automatic triangulation of sheet geometries to user-specified number of triangles.
- Exploits redundancies inherent in structured meshes for greater numerical efficiency.
- Easy extraction of useful engineering performance parameters, including
- Reflection and transmission coefficient magnitudes and/or phases or complex coefficients for the field components of
- TE/TM
- Vertical/horizontal (Ludwig 3)
- LHCP/RHCP (circular polarization)

- Delta insertion phase delay (ΔIPD)
- Delta insertion loss (ΔIL)
- Axial ratio

- Reflection and transmission coefficient magnitudes and/or phases or complex coefficients for the field components of

## Limitations

- Only zero-thickness, planar FSS/PSS sheets are currently supported.
- Frequency sweeps are fastest for normal incidence or for the case where unit cell incremental phase shifts ψ₁ and ψ₂ are constant with frequency (as in a waveguide). This is due to the use of a wide-band expansion of the potential Green's functions for a stratified medium with quasi-periodic excitation. Frequency sweeps for non-normal angle of incidence are typically slower. However, as of PSSFSS version 1.1, all frequency sweeps are now much faster, often by more than an order of magnitude, compared to previous versions. The speedup is due to the use of a fast interpolated sweep by default.

## Installation

You can obtain PSSFSS using Julia's Pkg REPL-mode (hitting `]`

as the first character of the command prompt):

`(v1.8) pkg> add PSSFSS`

or with `using Pkg; Pkg.add("PSSFSS")`

.

## Documentation

- The theory documentation is here
- The user manual is here
- If you prefer to explore the documentation more interactively, Jupyter notebooks containing documentation can be found here

## Community

Help from the community is actively sought and greatly appreciated! There are several open issues which you might want to tackle, and the documentation could always be improved. Pull requests are welcome. Feel free to open more issues, whether for basic capability, performance, examples, documentation, etc.