Standardizing Rectangular Metallic Waveguides for Terahertz Applications N M Ridler * , and R A Ginley † * National Physical Laboratory (NPL), Teddington, UK nick.ridler@npl.co.uk † National Institute of Standards and Technology (NIST), Boulder, CO, USA ronald.ginley@nist.gov Abstract — This paper describes an on-going activity to develop an international documentary standard for defining rectangular metallic waveguides for use in the submillimeter- wave to terahertz frequency range. The IEEE’s Microwave Theory & Techniques Society (MTT-S) is sponsoring the development of this standard. The MTT-S Standards Committee has set up a Working Group (P1785) that is tasked with writing the standard. 1 Work completed to date by the Working Group and the future activities that will be necessary to complete the standard are described. Index Terms — millimeter-wave, rectangular waveguides, submillimeter-wave, waveguides, waveguide apertures, waveguide interfaces. I. INTRODUCTION Many applications are presently being researched in the submillimeter-wave to low-terahertz frequency range. These applications are supporting many areas including: astronomy, remote sensing, communications, radar systems, and homeland security. However, no international documentary standards currently exist for defining the rectangular metallic waveguides that are used at these frequencies. 2 The situation has been recognized by the IEEE Standards Association, and has led to the development of an IEEE standard to address this need (started in 2008). The standard will ensure that all applications will have a commonality and can interface easily with other technologies under development. The IEEE standard is being developed in three separate parts: • P1785.1: “Frequency Bands and Waveguide Dimensions”; • P1785.2: “Waveguide Interfaces”; • P1785.3: “Recommendations for Performance and Uncertainty Specification”. This paper describes the progress made to date with each part of the standard. 1 Mr Ridler and Mr Ginley are Chair and Vice Chair, respectively, of the IEEE P1785 Working Group. 2 Existing international standards [1, 2] specify such waveguide only to a maximum frequency of 330 GHz. II. FREQUENCY BANDS AND WAVEGUIDE DIMENSIONS To date, much of the work of the P1785 Working Group has concentrated on establishing the frequency bands and waveguide dimensions (i.e., Part 1 of the standard). It was agreed early on that, for the waveguide aperture, the ratio of the width to height of the waveguide would be 2:1. The waveguide sizes and frequency bands, for submillimeter-wave frequencies, that have been chosen to be included in the standard are shown in Table 1 (see [3], for more details). Note that the waveguide dimensions are specified using metric units (i.e., micrometers, rather than mils, that were used, for example, in [1]). However, these dimensions provide a logical, compatible extension to the series of waveguides used traditionally at millimeter-wave frequencies [1, 2]. The waveguides are also named according to their metric size: the letters WM indicate that the size refers to Waveguide using Metric dimensions, followed by a number indicating the size (in micrometers) of the broad wall dimension of the waveguide. For example, WM-710 refers to waveguide with a broad wall dimension of 710 m. The IEEE standard also uses tighter tolerances (when compared with [1, 2]) for specifying the critical dimensions of the waveguide (i.e., those dimensions that directly affect electrical performance). Table 1. Frequency bands and waveguide dimensions. Waveguide Name Aperture Width (m) Aperture Height (m) Minimum Frequency (THz) Maximum Frequency (THz) WM-710 710 355 0.26 0.40 WM-570 570 285 0.33 0.50 WM-470 470 235 0.40 0.60 WM-380 380 190 0.50 0.75 WM-310 310 155 0.60 0.90 WM-250 250 125 0.75 1.10 WM-200 200 100 0.90 1.40 WM-164 164 82 1.10 1.70 WM-130 130 65 1.40 2.20 WM-106 106 53 1.70 2.60 WM-86 86 43 2.20 3.30