The signal statistics of a WCDMA signal reveal high crest factors (peak-to-average power ratios). Therefore, amplifiers with a wide linear range are required to ensure distortion-free transmission not only of average transmit power but also of high power peaks. The requirements on base station power amplifiers become even more stringent since the amplifiers also transmit multicarrier signals within the 60 MHz downlink band. In addition to single-carrier power amplifiers (SCPAs), multicarrier power amplifiers (MCPAs) are increasingly used. Signal sources featuring wide dynamic range and high accuracy, such as the Â¸SMIQ03HD, are required for the development and production testing of the amplifiers. WCDMA specifications allow base stations only a very low adjacent-channel power (ACP). The new model SMIQ03HD features hardware improvements providing previously unheard of performance for Alternate Channel Leakage Ratio (ACLR) measurements, a critical property for the correct functioning of WCDMA systems. For a single carrier WCDMA signal in the downlink frequency range (2110 MHz to 2170 MHz) R&S SMIQ03HD, with the additional new option R&S SMIQB57, generates a signal with an ACLR of 77 dB for the adjacent and an ACLR of 82 dB for the alternate channel, compared to previous bests of around 70 dB. A leap in performance of at least 7 dB. For multi-carrier signals with up to four carriers the appropriate I/Q filter with 2.5, 5, 7.5, or 10 MHz bandwidth can be selected to optimize ACLR performance. Typical results for a four carrier scenario are an ACLR of 62 dB for the adjacent and an ACLR of 64 dB for the alternate channel.