We present a new method to achieve an optical vector network analyzer (OVNA) based on a polarization multi-plexing electro-optic modulator (PM-EOM) without an optical bandpass filter.Optical single sideband (OSSB) modulated signals with a tunable optical carrier-sideband ratio (OCSR) are obtained at the output of the PM-EOM.The OCSR can be flexibly tuned by controlling bias voltages of the PM-EOM.The dynamic range of the OVNA is expanded by taking the improvement of the OCSR into account.The transmission response of an optical device under test (ODUT) is measured based on one-to-one mapping from optical domain to electrical domain.By optimizing the OCSR of the OSSB modulated signals,the dynamic range of the OVNA can be effectively improved with 3.7 dB.An analytical model is derived to describe the transfer function of the ODUT.The magnitude and phase responses of a fiber Bragg grating are characterized with a large dynamic range.