A 1D Halbach array looks like the below:
What would it look like in 2D, in order to make a square array?
A 1D Halbach array looks like the below:
What would it look like in 2D, in order to make a square array?
Indeed, the Wikipedia page on Halback arrays presents an image of "a planar Halbach array", which is unique in the sense that this arrangement never reveals itself in web search results with keywords 'Halbach array' (with various modifiers like planar, 2D, square etc.), 'magnetic levitation', 'wiggler magnets' and the like. So I cannot recommend nor dismiss this find, if you are going to research it with practical purpose in mind.
(C) CC BY-SA 4.0, Wikipedia, Uploaded: 5 April 2017
When analyzing field distribution in this arrangement, be careful with intuitive methods: the magnetic field and magnetic dipole are axial vectors, and the axial vector transformation properties can appear counter-intuitive. Even if your spatial imagination is an extraodinary asset, verify your consideration with simulators like COMSOL.
If your only goal is to have an arrangement extended in the transverse direction, you can use rectangular magnets elongated in this direction, like those shown in the schematic diagram of a free-electron laser:
(C) CC BY-SA 3.0, Wikipedia, 11 November 2010