Dual-Band Dual-Mode Filter-Enhanced Linearity Measurement

This letter presents, for the first time, a new filter-enhanced linearity measurement technique using a dual-band and dual-mode filter. While traditional two-tone linearity tests are simple and effective, their ultimate performance is determined by the quality (dynamic range and noise floor) and cost of the employed equipment. On the other hand, the proposed method consists of a simple conventional single-tone test facilitated by a low-cost appropriately designed bandstop filter (BSF). In particular, the employed dual-band/dual-mode absorptive BSF suppresses the fundamental frequency by over 35 dB (absorptive notch) and the second harmonic by over 25 dB (reflective notch), allowing for accurate measurement of the third harmonic, and hence, IP3. The proof-of-concept system is demonstrated at 2 GHz. The filter absorbs with better than 20 dB of reflection the excitation signal at
$f_{0}=2$
GHz and reflects the signal at
$2f_{0}=4$
GHz. With just the insertion of the presented filter and without improving the measurement equipment, we demonstrate an improvement of over 12.7 dB in the IP3 characterization to a maximum of 81 dBm. We also demonstrate the ability to conduct this test with just a low-cost power detector in lieu of a spectrum analyzer leading to a simple scalable measurement technique.