Agilent Measurement Journal - Issue 4 - 2008 - (Page 57)

PCF cross section Air hole After experimental determination of the waveguiding properties (phase propagation constant and loss) of the ﬂexible dielectric guide, work will concentrate on whether the guide can be engineered into a practical ruggedized cable with connectors. For connectors, such high frequencies pose severe challenges on fabrication tolerances and planarity of interface. What’s more, it is essential — but difﬁcult — to design a metrologygrade connector with 60-dB repeatability levels. Applications around future products such as security and medical scanners require cables and connectors that can be replaced by nonspecialist ﬁeld engineers. Connector design issues will be studied in terms of connectability (ease of connect/disconnect, standardization of coupling mechanism, threads/engagement/ latching), repeatability and lifetime, and effect of mechanical tolerances. The longer term goal of the research is to work towards an open standard for terahertz connectors and guiding structures. Diameter Hole pitch Figure 3. Conventional hexagonal photonic crystal ﬁber (PCF), shown in cross section, can be applied to the design of terahertz dielectric waveguide.2 The effective refractive index of the cladding region n clad is frequency dependent. When the frequency is relatively high, the ﬁeld becomes more concentrated in the silica region and away from the air holes, which leads to high n clad. Consequently, the gap between n core and n clad becomes small at high frequency and therefore the frequency range for single-mode operation can be extended. The project is developing full-wave modeling techniques for terahertz PCF dielectric waveguide structures. The modeling will then lead to a study of the optimum design of a dielectric guide cross-section for single-mode behavior and low dispersion. The design of transitions from the dielectric guide to conventional sub-millimeterwave rectangular waveguide will be investigated in order to demonstrate practical measurements in the 140-GHz to 325-GHz range using a sub-millimeterwave Agilent 8510XF system. Stepping backward, then forward Joel Dunsmore, Ph.D. Senior R&D Engineer/Scientist, Agilent Technologies joel_dunsmore@agilent.com It started with an observation of unusual time-domain behavior when tuning a multicavity ﬁlter: The timeresponse changes corresponded to changes in the tuning screws. From this, I found that these ﬁlters could be tuned exactly using only the time-domain response — something that had never before been observed. Taking this beyond mere observation, however, would require a detailed look at the mathematics of ﬁlter responses and Fourier transforms. As it happened, Roger Pollard was visiting for the summer and we discussed a Ph.D. topic focused on a theoretical explanation of the observed behavior. I quickly discovered that this was akin to jumping in at the midpoint of a Ph.D. program. I spent the next two years seemingly going backward until a broad study of the area enabled me to conﬁdently describe the research problem. Outside interests fell by the wayside as some aspect of research, experiment or writing absorbed any free time. Three years later I had answered the problem, and also came to understand that learning the process of research is just as important the research itself. Agilent Measurement Journal 57

Table of Contents Feed for the Digital Edition of Agilent Measurement Journal - Issue 4 - 2008

Agilent Measurement Journal - Issue 4 - 2008 Delivering Confidence through Compliance with Standards Contents Emerging Innovations Trying Early Device Implementations at the IEEE 1588 PlugFest Achieving Greater Confidence in Measurement Accuracy through Consistency in Calibration Services Overcoming the Challenges of RFID Component Testing 3GPP LTE: Introducing Single- Carrier FDMA Ensuring Reliable Operation and Performance in Converged IP Networks Testing Storage Area Networks and Devices at 8.5-Gb/s Fibre Channel Rates Choosing an Appropriate Calibration Method for Vector Network Analysis Making Traceable EVM Measurements with Digital Oscilloscopes Exploring Terahertz Measurement, Imaging and Spectroscopy: The Electromagnetic Spectrum’s Final Frontier Interpreting Quoted Specifications when Selecting Digitizers

Agilent Measurement Journal - Issue 4 - 2008

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