DIY easy to build high gain antennas with 4nec2 models.

Very useful article to understand Stacking distance and gains for antenna array

• https://www.w8ji.com/stacking_broadside_collinear.htm
• https://www.w8ji.com/transmitting%20antennas.htm

Several very useful RF calculators :

• https://www.mantaro.com/resources/impedance-calculator.htm
• https://www.ahsystems.com/EMC-formulas-equations/index.php
• http://dg7ybn.de/index.htm

Impedance matching using coax stub :

• https://www.antenna-theory.com/tutorial/smith/chart.php

Beamwith to coverage at specific disance calculator :

• https://www.ahsystems.com/EMC-formulas-equations/Antenna-beamwidth-coverage-calculation.php

Filters

• https://www.youtube.com/watch?v=xsbRrNJnmgA
• https://charleslabs.fr/en/project-Hairpin+filter+desig

RF probe

• https://charleslabs.fr/en/project-RF+Passive+Differential+Probe