Since this is in Hawaii, could it be part of a seismic (earthquake or tsunami) measurement/prediction system?
Since they have been seen on top of numerous utility poles, my guess is that it’s part of a municipal network. This sort of network is used by fire, police, ambulance, etc. and may also be used by local utilities like the power company and water company. The power company can use networks like this to better monitor their systems, and water and other utilities can use these types of networks for automatic meter reading and billing.
If you have a CPAP machine or some other type of medical device that requires monitoring and data collection, these will often also use these types of networks.
This isn’t anything to do with cellular, 5G or any other public telecom use. It isn’t a public safety repeater though there’s an unlikely possibility it’s a receive site for a system. Like @Napier says, it’s some sort of boring telemetry system, probably public utility or municipal.
Part of a seismic measurement or prediction system? Sounds like a reasonable guess. That’s a nice example of a real time need.
Though, I guess I might also have observed that the need for the data in real time isn’t the only possible motivation. It might also be less expensive to use cellular or other radio than it would be to send somebody around to download data, even if they’re not in a rush.
O.P. here. FYI: I live in New England. My screen name was given to me by a Jan & Dean fan after I returned from a trip to Hawaii. The antenna has nothing to do with seismic activity.
I have noticed four telephone poles within five miles of my house that have that weird antenna on top. I now notice that each of them also had two boxes below, One of them was the size of a large suitcase and the other was probably a control box about 10 feet off the ground.
My current guess is that they have something to do with electric power distribution.