# Hardware Design of a High Dynamic Range Radio Frequency (RF) Harmonic Measurement System
## 5 System Test Results  
The high dynamic range measurement system described in Section 4 was used to measure the second harmonic response from a variety of circuit elements. The passive devices tested are shown in Figure 12.  
The two port devices were tested for their input and output harmonic generation while the one-port devices could only be tested for their reflected harmonic generation. Test setups for the harmonic through and harmonic reflection measurements are shown in Figures 13 and 14, respectively. Since the spectrum analyzer only has one input port, the fundamental and second harmonic at the output of the DUT need to be measured via two separate measurements. Therefore, the loading conditions of the two measurements are slightly different. The spectrum analyzer is matched to 50 \(\Omega\) throughout the bands of interest with an input reflection coefficient \(|S_{11}|\) of less than 20 dB,  
Figure 11: Photograph of the diplexers and 10-W power amplifier. Figure 12: Devices tested for second harmonic characterization. Figure 13: Test setup for harmonic through measurement. which provides a 99% power transfer. The differences between the loading conditions for the fundamental and second harmonic measurements is therefore expected to be negligible compared to using a 50 \(\Omega\) termination. Thus, we believe that any mismatches between the two measurement setups would result in an insignificant difference in nonlinear distortion generated. The test results are summarized in Table 3. The values are shown for \(D_{2}\) in Equation (3), the units for which are dBm\({}^{-1}\). A lower value, i.e., more negative, indicates better harmonic suppression. The results from the open circuit and new N(m)-N(m) adaptor show the minimum detectable \(D_{2}\) coefficient the setup can measure. The open circuit and new adaptor test cases are the baseline measurements used for monitoring the spurs created at the second harmonic and the noise floor, which determines the system dynamic range. Any significant contributions from the higher-order harmonics to the second harmonic would be indicated in this measurement. The observations from this measurement indicated that distortion created from these higher order harmonics are below the noise floor. Since a mixer, by design, is a nonlinear component whose nonlinearity is essential for frequency conversion [52], it shows much higher \(D_{2}\) values. Attenuators typically consist of resistors connected in T- or \(\Pi\)-configurations with dissimilar metal contacts, which results in \(D_{2}\) values of about 60 dB higher than the detection floor. The intense RF magnetic field across the ferrite disk excites nonlinear behavior in a circulator [53], which explains its higher values. The old, i.e., well-used, adaptor shows about 20-dB increase in \(D_{2}\) compared to the new adaptor, which may be ascribed to possible corrosion caused by wear and tear and environmental effects. Connectors terminated in solder and steel show higher \(D_{2}\) values compared to the unterminated connector due to the effect of the dissimilar metal contacts, with steel adding about a 20-dB higher value, consistent with the results reported in [54; 55]. The mixer serves as a reference for traditionally nonlinear devices. Table 3 shows that the nonlinear response from the mixer is about 90 dB over the circulator, about 120 dB over the attenuator, and about 145-170 dB over the adaptors, at an input of 0 dBm. Figure 14: Test setup for harmonic reflection measurement.