Nearly the answer is Xcircuit viewtopic.php?t=43 but while it's easy to learn, Xcircuit's symbol set has some tedious omissions, like an antenna.
I just blundered upon KiCad -available truly free for Linux, Win and Mac. It does more, including schematics, component lists, PCB layout and project documentation. Yes, it includes an antenna. Download is from the KiCad DL page at https://www.kicad.org/download/, or from your Linux included software. Arch Linux has suitable packages at AUR.
Easy to use? Well, yes, but you do need to RTFM, available here:
The whole package is extensible with extra symbols and all customizable, if a twin-cavity reflex klystron doesn't immediately come to hand...

This is what the control page looks like:
and here is a PCB design, with complexity cl…login to view the rest of this post