Network analyzers up to 1.5 THz

https://www.keysight.com/en/pcx-x205186/pna-network-analyzers-300-khz-to-11-thz?cc=US&lc=eng

https://www.vadiodes.com/en/products/vector-network-analyzer-extension-modules

http://www.abmillimetre.com/Introduction.htm

https://www.omlinc.com/

Horn antennas

http://www.elva-1.com/products/a40102

http://vivatech.biz/Joomla/index.php/products-services/components/waveguide-horn-antenna/lens-horn.html

Waveguide at 300 GHz

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