03/01/11: Come see us at ISSTT 2011!

2011 March Newsletter    Adobe PDF icon

VDI President Tom Crowe and VDI CTO Jeffrey Hesler will be giving talks at the 22nd Annual International Symposium on Space Terahertz Technology in Tucson Arizona, April 26-28 2011.  Please see the abstracts of their talks below:


VNA Measurements in the 0.75-1.1 THz Band

J.L. Hesler*, K. Hui, B. Foley, S. Durant, and T.W. Crowe

 ( Hesler@vadiodes.com)

 Abstract—The design, development and testing of a state-of-the-art 0.75-1.1 THz Vector Network Analyzer Extender will be presented. The extender consists of a series of multipliers and mixers that are used to extend the frequency of Microwave Vector Network Analyzers (with operating frequency typically below 50 GHz). The transmitter consists of a x27 multiplier chain generating an average output power of -24 dBm over the 0.75-1.1 THz band. This power is then fed into a bi-directional coupler that is used to sample the outgoing wave (reference mixer) and the test signal (measurement mixer). The coupler has an insertion loss of ~ 6 dB, yielding a test port power of -30 dBm typical. The receivers have a harmonic factor of 36, and consist of a multiplier chain driving a harmonic mixer. The conversion loss of these mixers is in the range of 20-25 dB. Transceiver measurements of the VNA system yielded a dynamic range of 60-70 dB over ¾ of the frequency band, with reduced performance at the band edges. The dynamic range measurements were performed with a 10 Hz measurement bandwidth.


The VNA Extender was used to perform calibrated measurements of a variety of one-port and two-port test pieces, using a Short-Open-Load-Thru calibration method. The open circuit was implemented using a ¼-wave delayed short circuit, and the load was a precision load with expected return loss better than 50 dB. Measurements of a 1” straight waveguide piece indicated a return loss of 25-30 dB typical, with the reflections generated by mechanical misalignments at the waveguide interfaces. The measured insertion loss of the 1” straight waveguide piece matched the theoretical loss with a “roughness” factor of 1.4, which is consistent with losses measured at other bands. Additional measurements will be presented at the symposium.


Development and Characterization of a 2.7THz LO Source

 T.W. Crowe, J.L. Hesler, C. Pouzou, W.L. Bishop, G.S. Schoenthal

 ( Crowe@vadiodes.com)

 Abstract— Over the last several years VDI has been developing THz sources based on microwave frequency amplifiers and a cascaded series of frequency multipliers. These are intended to be used as local oscillator sources for astronomical receivers, such as those on the Sofia airborne observatory. In 2010 a 1.9 THz source with greater than ten microwatts output at room temperature was presented at this conference.  VDI has now completed the initial testing of a similar source at 2.7 THz. The measured output power is about 1.5 microwatts (at RT, measured with Erickson PM4).


This effort has required the development of improved millimeter-wave varactor multipliers with better thermal grounding for greater power handling, the optimization of the THz multipliers for operation at low power levels and the development of improved assembly and testing techniques. This paper will discuss the many challenges of achieving useful sources at such high frequency and review the results that have been achieved to date, with emphasis on the new 2.7THz source.