Hi,
If my memory isn't failing the nport component supports TOUCHSTONE file format, the first line of that text file has the following description:
# <frequency unit> <parameter> <format> R <n>
in parameter you can specify what kind of data you are introducing(S,Y,Z,H,G).
Hope it helps,

I don't check Cadence Spectre. But Cadence Spectre should treat Y/Z parameter same as Agilent ADS.

Agilent ADS treats Y/Z parameter in Touchstone and Citi file like followings.

(1) Y/Z parameter in Touchstone
“test_touchstone1.y2p”
! Touchstone for Two-port Y-parameter Data in a single line format
# GHZ  Y  RI  R 50
1.0      11 0  21 0  12 0  22 0

Y/Z parameter in touchstone format are assumed to be normalized by reference resistnace R0.
So actual Yij will be (1/R0)*yij, here R0=Reference Resistance, yij is normalized admittance parameter.
The actual Y- (Z-) parameter value is obtained by dividing (multiplying)
the file entry with the reference resistance.
For example, actual Y11 will be (1/50)*y11=(1/50)*11=0.22, etc…

(2) Y/Z parameter in Citi file
“test_y2p.citi”
CITIFILE A.01.00
NAME SP1.SP
VAR freq MAG 1
DATA Y[1,1] RI
DATA Y[1,2] RI
DATA Y[2,1] RI
DATA Y[2,2] RI
DATA PortZ[1] RI
DATA PortZ[2] RI

VAR_LIST_BEGIN
       4e9
VAR_LIST_END
BEGIN
11, 0
END
BEGIN
12, 0
END
BEGIN
21, 0
END
BEGIN
22, 0
END

BEGIN
100, 0
END
BEGIN
200, 0
END

Y/Z parameter in Citi File format file are assumed to be unnormalized.