# A Millimeter-Wave 4 th-Harmonic Schottky Diodes Mixer with Integrated Local Oscillator
## 3 Fabrication and Experimental Results  
The manufacturing process combined photolithography for the circuits on a COC substrate and CNC micromachining for the the metallic housing block. The Schottky diodes were fabricated by the United Monolithic Semiconductors (UMS) foundry. Finally, the diodes were fixed onto the circuits with silver loaded epoxy (EPOTEK H20E). The MMICs for the local oscillator were soldered onto a 670 \(\upmu\)m thick Rogers 3210 substrate. Its frequency is controlled by means of a phase-lock loop, which was mounted in a external board and controlled by an Arduino Due. Photographs of all these circuits are shown in Figure 4.  
For characterization, the Y-Factor gain method was used [16]. A schematic of the setup for Y-Factor characterization of the mixers is shown in Figure 5. The hot load is obtained by placing a piece of WAVASORB RAM material in front of the RF antenna. For the cold load measurement, the RAM material is cooled down in a container with liquid nitrogen and then placed in front of the RF antenna. Using the power difference, the Y-Factor is calculated; thus, the DSB equivalent noise temperature of the receiver is obtained. The mixer equivalent noise temperature and conversion loss are then obtained by removing the IF chain contribution. The IF chain consists of two GAMP0100.0600 SM10 LNA amplifiers with 35 dB gain and 1.8 dB NF. Their output was connected directly to a Keysight N9030A spectrum analyzer, where the power at 2 GHz was measured. A 20 dBi standard gain horn antenna was connected to the RF port of the mixer and the Y-Factor technique was applied as described above.  
Figure 4: Photographs of (**a**) top view of the subharmonic mixer and local oscillator in the metallic block; (**b**) measurement setup for the fourth-harmonic mixer characterization.  
A photograph of the fabricated prototype and the measurement setup can be seen in Figure 4.  
The mixer characterization results are shown in Figure 3, where the comparison between the measured and the simulated performance can be observed. The minimum and mean measured conversion losses for the range between 298 and 310 GHz are 14 and 18 dB, respectively. Regarding the DSB equivalent noise temperature, the minimum and mean values are 9600 and 26,000 K, respectively. There is good agreement from 298 to 304 GHz between these results and the predictions using around 6 dBm LO power. For higher frequencies (304-310 GHz) the measured performance shows a difference of around 3 dB with respect to the simulated performance using \(\sim\)6 dBm LO power. According to the datasheets of the COTS components of the LO, the output power should be \(\sim\)10 dBm. However, the similar performance to the simulated case using \(\sim\)6 dBm indicates that the amount of LO power pumping the diodes might be lower than this LO source expected output power. This can be ascribed to losses in the circuits and to the output power being lower than the nominal level. This behavior is similar to that reported in [8], where a similar integrated LO was used. Unfortunately, with the current configuration the LO power cannot be measured to confirm this hypothesis. In addition to this, tolerance errors in fabrication and the manual positioning of the diodes can also contribute to the losses.