How to prove the existence of the spectral expander with the given parameteres?
There are also expanders with the following parameters: $(3, 2, 1/2)$ — complete graph on 3 vertices and $(8,8, 0)$ — complete graph on 8 vertices with the loop in each vertex. So we have the following tensor product:
$$
(1944, 144, 0.5) = (9^2, 9, 1/3) \otimes (3, 2, 1/2) \otimes (8,8, 0)
$$