zplane z or z-1

Hello, does anyone know if this graph of zplane corresponds to the z or z-1 plane?

Fs = 4400;  
Fn = Fs/2;    
 
n = 3; Rp = 0.5;
Wn = [250 2000]/Fn;
 
[b a]=cheby1(n,Rp,Wn,'bandpass')
[h,w]=zplane(b,a)

Answer 1

[Chunru]

It's z-plane. See the following example, where all poles are inside the unit circle.

[b,a] = cheby2(8/2,20,[1 5]/8);
zplane(b,a)

[Juan Chehin]

Thanks!