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2) substrate integrated waveguides
for filters, slot antennas, and even making some 20GHz waveguides in FR4 substrate =)
There are others, maybe not so hot:
3) different microstrip resonators, for example split ring resonators
4) active integrated antennas. Maybe not very hot topic, but still: making distributed cellular tower antenna based on small active integrated antennas. There can be malfunction of small part of antenna, but whole antenna still works. Something like that
5) beam steering in WiFi / cellular. Making multiple narrower beams for higher gain, higher speed, less interference.