If it is property, tax it like property, at 1% of value per year. All of a sudden, every trivial patent will be assigned 0 value by its owner, and then convincing a court the violation is worth $100M is hard.
Real estate, essentially everywhere in the western world. The range I have observed in multiple countries is 0.5%-1.5%, and it isn't always called "property tax" (e.g., in the UK it breaks between "council tax", and various other taxes, none of which is specifically named "property tax"; in the neighborhoods of CA I'm familiar with, it's 1.2% in the last few years)
Car licenses in many places are also essentially a property tax of 1% of the car value, or so.
Also puts old and new patents on equal footing.