I'm no "antenna guru", but have enough antenna theory to throw out a couple of observations:
-- The UHF band allocation is pretty wide. But a receiving antenna has less of a concern of matching the resonant frequency of the received signal than a transmitting antenna. It is more about collecting the electrons, and getting them to the receiver. (On transmit, there are matching concerns to protect the equipment's output, and not radiating from your feed line).
-- Speaking of feed line - before CATV became the prevalent method of receiving TV, most antenna systems used 300ohm twin lead. Much less loss between the antenna and the TV. Since CATV and satellite have become the norm, many newer TVs no longer even have a 300ohm input. We may soon see a return of the 300ohm-75ohm transformer on the back of TV sets, to reduce the amount of feed line loss.
-- UHF stations have always been the red-headed stepchild to the bigger VHF stations. Most people accepted the fact that, unless the station was nearby, they wouldn't receive a big signal. Now people want to maximize their OTA choices, to offset not having the 300+ channels that CATV/SAT have to offer.
-- Until now, not much had changed in OTA television reception technology since the 1930s. First people had rabbit ears on their TV. They moved to the outdoor antenna (log periodic, most with UHF as an afterthought in the design). As CATV, then SAT, came to became more popular, the demand for improved designs dropped. As more people will again look at digital OTA as an option, some new designs are starting to appear (most common, the pre-amp panel design). I think more will eventually appear, as people finally lose their analog OTA and look for improvement.
To answer some of your questions: I believe the initial television signal is horizontally polarized, given the traditional VHF log periodic antenna is also horizontal. Of course, as the signal bounces off of obstructions, it develops multipath and changes polarization. that might suggest the "corkscrew" design you saw.
The grid is a reflector. It will increase the gain of the antenna in front of it. Without a particular antenna to evaluate, figure the grid will add 2-3db in the desired direction (and drop the same in the direction behind it). A benefit (with analog anyway, I don't know if it helps at all with digital) is that it also helped reduce multipath reception, especially when mounted to the side of a house. Multipath is what causes "ghosting" of TV images.--
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