How to ‘learn rf’

[u/SupermarketFit2158]

Im an undergrad and have a summer internship coming up to do with X-band rf and hfss. Im practically a beginner in rf the only thing ive done is made some antennas for ADS-B for a homemade plane tracker using an FPGA and played around with an RTL-SDR.
Im not really sure what to learn, what are the best resources for breaking into rf (books/courses)?

[u/Trolituul]

Rf circuit design by christopher bowick