New 133 - 190 GHz IRAM doubler

Efficiency Improvement and Fixed Tuned Mode between 130-180 GHz using IFHT Darmstadt University Diodes

 

Abstract

The IRAM 133-180 GHz doubler efficiency and frequency bandwidth was improved by 10% using a WV1312 GaAs diode built by C.I. Lin at the Institut für Hochfrequenztechnik der Technischen Universität Darmstadt (IFHTUD). In the fixed tuned mode, we obtain an efficiency between 3-10% in the frequency band 133-180 GHz.

Introduction

Recent research activities have been focused on planar Schottky diodes, but whisker contacted multipliers give more instantaneous efficiency and frequency bandwidth with lower input power. For many years, IRAM 130-180 GHz doublers (Mattiocco, Halleguen) working in the 1.5 mm SIS receiver local oscillator (LO) at Pico Veleta were built with varactor diodes from UVA [1]. The efficiencies of most doublers are between 2 and 9% in the 133-183 GHz band, using two backshorts and bias tuning.

Recently a cooperation with the IFHTHD was engaged to define the specifications of custom-built varactors for the IRAM doublers and triplers, based on the high level doping profile IFHTUD technology. The first varactor has been whisker-contacted in a doubler block built for the new 1.5 mm SIS receiver generation. Measurements of its performance are presented in the following.

Doubler

The doubler uses a waveguide input associated to a suspended substrate input filter and reduced waveguide output transformer circuits. For tuning, two backshorts and the bias voltage can be adjusted. The fixed tuned backshort mode was also studied.

Whisker contacted GaAs diodes data

The whisker length was 110 $\mu$m in both cases.

	Cjo [fF]	vb [V]	Rs [$\Omega$]
UVA 4T3	13	11	6
IFHT WV1312	13	16	12

Results

Efficiency curves are shown in Fig. 1 over the frequency range between 130-190 GHz with 10 mW and 20 mW input power using the WV1312 diode, and with 10 mW input power using a typical doubler contacted with the 4T3 diode. The voltage bias and the two backshorts are matched at each frequency.

The efficiency for the WV1312 varactor is between 7-10% over 133-185 GHz with 20 mW input power, and 6-10% in the 133-188 GHz band with 10 mW input power. Especially above 155 GHz, the improvement relative to the 4T3 diode is significant.

Figure 2 gives the efficiency and output power for the fixed tuned case using 10 mW and 20 mW at the doubler input. The bias voltage matches the diode at each frequency, but the backshorts stay fixed. The efficiency is between 3-10% over 133-180 GHz at 20 mW input power.

Conclusions

These results are very promising for the concept of large band fixed tuned LO sources. The diodes have a good efficiency at low input power, which is essential for high efficiency multipliers at sub-millimeter wavelengths where the available input power is poor. The doubler could be associated with a multiplied and amplified YIG oscillator to make a 133-180 GHz fixed tuned LO.

Future improvements of the WV1312 diode by IFHTHD aim at a reduction of the substrate losses by applying the substrate-less technology [2], which requires a thinning of the substrate from 80 $\mu$m to 15 $\mu$m.

References

[1]

Semiconductor Device Laboratory, Department of Electrical Engineering, Thornton Hall University of Virginia.

[2]

C.I. Lin et al. "Substrateless Schottky Diodes for THz Applications ", 8th International Symposium on Space Terahertz Technology, Harvard University, March 1997.

François MATTIOCCO and Sylvie HALLEGUEN