Recently, sub- and super-synchronous oscillation (SSO) associated with converter-based wind turbine generators (WTGs) has been attracting wide attentions. To investigate such SSO incidents, impedance or admittance-based modeling and analysis were widely used. It was discovered that coupling effects exist between impedances or admittances at complementary (i.e., sub and super-synchronous) frequencies. However, there is a lack of experimental validation on the coupling effects of different WTGs. In this paper, the frequency-coupling admittance models (FCAMs) of two types of widely adopted WTGs, i.e., direct-drive and doubly-fed WTGs, are presented at first. Secondly, a perturbation based identification method is proposed to obtain the FCAMs. Next, the method is implemented in a control-hardware-in-the-loop (CHIL) platform based on RTDS. Then with extensive CHIL tests, the FCAMs of both types of WTGs are obtained, and the impacts of frequency-coupling effects on SSO are validated. Finally, the characteristics of frequency-coupling effects and the root causes are further examined. This study is of important reference value to select appropriate models for oscillatory stability analysis.