Ihaga may have been based in Liége. As far as I know they produced two basic designs:

• The single pulley S.A.G. in this collection.
• A double pulley 'touring' model that clamped onto the chainstay.

Their, very modest, claim to fame was a Quixotic, but highly rational, commitment to the idea that derailleurs should be ‘top normal’ (in an era dominated by ‘low normal’ Simplex designs). Ihaga considered that it was better to get the rider to do the ‘hard work’ of shifting the chain ‘up the hill’ onto larger cogs, allowing the spring mechanism to perform the ‘easier’ task of shifting the chain ‘down the hill’ onto smaller cogs.

I would, personally, still choose a top normal design in preference to a low normal mechanism. And it is notable that, although Shimano claim to love their low normal ‘rapid rise’ designs, every Dura-Ace derailleur ever made has been top normal.

The only Ihaga patent, that I have been able to find, lists the inventor as Jules Hendrick of Liège, Belgium. We could guess that Ihaga was Mr Hendrick's brand. I might also note that JH (his initials) and IH (the first two letters of Ihaga) are sometimes interchangeable in Northern Europe - but this is all a spuriously speculative.