We study the Deligne interpolation categories $$\underline{\textrm{Rep}}(GL_{t}({\mathbb F}_q))$$
Rep
̲
(
G
L
t
(
F
q
)
)
for $$t\in \mathbb {C}$$
t
∈
C
, first introduced by F. Knop. These categories interpolate the categories of finite-dimensional complex representations of the finite general linear group $$GL_n(\mathbb {F}_q)$$
G
L
n
(
F
q
)
. We describe the morphism spaces in this category via generators and relations. We show that the generating object of this category (an analogue of the representation $${\mathbb C}{\mathbb F}_q^n$$
C
F
q
n
of $$GL_n(\mathbb {F}_q)$$
G
L
n
(
F
q
)
) carries the structure of a Frobenius algebra with a compatible $${\mathbb F}_q$$
F
q
-linear structure; we call such objects $$\mathbb {F}_q$$
F
q
-linear Frobenius spaces and show that $$\underline{\textrm{Rep}}(GL_{t}({\mathbb F}_q))$$
Rep
̲
(
G
L
t
(
F
q
)
)
is the universal symmetric monoidal category generated by such an $$\mathbb {F}_q$$
F
q
-linear Frobenius space of categorical dimension t. In the second part of the paper, we prove a similar universal property for a category of representations of $$GL_{\infty }(\mathbb {F}_q)$$
G
L
∞
(
F
q
)
.