Nonlinear behavior of Coupled Resonator Filter at high RF power levels in time and frequency domains

The nonlinear behavior of Coupled Resonator Filters (CRF) is studied in time and frequency domains. 1 dB-compression point and/or Intermodulation Products (IMD) are both frequency-dependent parameters and thus, they can not be used to study simultaneously the nonlinearities in time and frequency domains. The proposed characterization method consists on sending a digitally modulated signal (QPSK) through CRF devices with RF carrier frequency sweeping the filter band-pass at high power levels. Two spectral occupancies of QPSK signal can be used covering whether a narrowband of 8% (WCDMA single channel bandwidth) or a wideband of 40% of the filter bandwidth. The signal received at CRF output provides two response types: a system-parameter as the Error Vector Magnitude (EVM) and transmission S-parameter. Measurements are carried out at CRF´s 1 dB-compression point of 40 dBm Results show EVM variations of 4% and 1% respectively for narrow and wide spectral occupancy. We observe also a transmission phase shifting going to 10° in the band-pass for 1 dB magnitude decrease.