Manju Henry

Double Corrugated Waveguide for G-Band Traveling Wave Tubes

A novel wide-band traveling wave tube (TWT) based on the double-corrugated waveguide (DCW) is proposed for operating in IEEE G-band (110-300 GHz). The DCW has been conceived for relaxing critical technological issues in terahertz vacuum tube realization, such as assembly, and to support a cylindrical electron beam. The study of the properties of the DCW in the forward wave regime demonstrates wide band performance suitable for TWTs fabrication at millimeter wave-terahertz frequencies. A traveling wave tube with 18-dB gain and up to 3.7 W output power over a bandwidth of about 30 GHz at 225 GHz as central frequency is demonstrated, assuming 13-kV beam voltage and 30-mA beam current.

Schottky diode technology at Rutherford Appleton Laboratory

Most parts of the electromagnetic spectrum are well understood and exploited, but the terahertz region between the microwave and infrared is still relatively under developed. Potential receiver applications are wide-ranging and cross-disciplinary, spanning the physical, biological, and medical sciences. In this spectral region, Schottky diode technology is uniquely important. InP MMIC amplifiers are generally limited to frequencies less than ∼200 GHz, above which their noise performance rapidly deteriorates. Superconducting circuits, which require cooling, may not always be practical. Either as varistor diodes (heterodyne mixing), or varactor diodes (sub-millimetre power generation), Schottky technology underpins terahertz receiver development. Two important developments have occurred in recent years. First, the underpinning technology base has demonstrably matured. Planar Schottky diode technology has been shown to be practical at frequencies as high as 2,500 GHz, and frequency multipliers have been shown to be capable of generating 100s of mW at frequencies around W-band. Secondly, circuit designs can now be optimised theoretically with CAD electromagnetic structure simulators and non-linear analysis programs. New high-speed computer controlled mills, improved lithographic capabilities and micro-machining techniques also offer exciting new options for cavity and circuit manufacture. This paper describes the Schottky diode technology currently being developed at the Rutherford Appleton Laboratory. Discrete diode components are described as well as integrated diode/filter circuits. Frequency multiplier diode structures are reported which include novel substrate transfer techniques to reduce the effects of dielectric loading and self-heating.

Inter-laboratory comparison of reflection and transmission measurements in WR-06 waveguide (110 GHz to 170 GHz)

This paper describes an exercise that was undertaken recently to compare reflection and transmission measurements in rectangular metallic waveguide from 110 GHz to 170 GHz (i.e. in the WR-06 waveguide size). The comparison involved making measurements on four devices fitted with ‘precision’ MIL-DTL-3922-67D style flanges. These devices were circulated amongst the nine organizations that chose to participate in the exercise. The comparison took place between August 2008 and September 2009. Results from the exercise are presented in graphical form along with a statistical summary showing average variability for the measurements. The authors believe this is the first time that such a comparison of measurements has been made at these frequencies. These results therefore provide a benchmark for the current state-of-the-art for measurements made in waveguide at these frequencies.

Multi-octave metamaterial reflective half-wave plate for millimeter and sub-millimeter wave applications

The quasi-optical modulation of linear polarization at millimeter and sub-millimeter wavelengths can be achieved by using rotating half-wave plates (HWPs) in front of polarization-sensitive detectors. Large operational bandwidths are required when the same device is meant to work simultaneously across different frequency bands. Previous realizations of half-wave plates, ranging from birefringent multi-plates to mesh-based devices, have achieved bandwidths of the order of 100%. Here we present the design and experimental characterization of a reflective HWP able to work across bandwidths of the order of 150%. The working principle of the novel device is completely different from any previous realization, and it is based on the different phase-shift experienced by two orthogonal polarizations reflecting, respectively, off an electric conductor and an artificial magnetic conductor.

WR-3 Waveguide Bandpass Filters Fabricated Using High Precision CNC Machining and SU-8 Photoresist Technology

This paper presents two WR-3 band (220–325 GHz) filters, one fabricated in metal using high precision computer numerically controlled milling and the other made with metallized SU-8 photoresist technology. Both are based on three coupled resonators, and are designed for a 287.3–295.9-GHz passband, and a 30-dB rejection between 317.7 and 325.9 GHz. The first filter is an extracted pole filter coupled by irises, and is precision milled using the split-block approach. The second filter is composed of three silver-coated SU-8 layers, each 432 μm thick. The filter structures are specially chosen to take advantage of the fabrication processes. When fabrication tolerances are accounted for, very good agreement between measurements and simulations are obtained, with median passband insertion losses of 0.41 and 0.45 dB for the metal and SU-8 devices, respectively. These two filters are potential replacements of frequency selective surface filters used in heterodyne radiometers for unwanted sideband rejection.

Low-Pass FSS for 50–230 GHz Quasi-Optical Demultiplexing for the MetOp Second-Generation Microwave Sounder Instrument

This paper reports the design, manufacture, and characterization of a new frequency selective surface (FSS) structure which meets the demanding requirements for transmission of 50.2–57.7 GHz radiation simultaneously for TE and TM polarizations at 45° incidence, and reflection of signals in four discrete higher frequency bands centered at 89, 165.5, 183.3, and 229 GHz. The FSS is required for a quasi-optical network, which was developed during the preparatory breadboarding of the microwave sounder instrument. The 100 mm diameter ultrawideband FSS must exhibit ≤0.25 dB loss for all signals in the above bands, and has to satisfy the requirements of the space environment. The FSS is formed by a periodic metal film array sandwiched between two 0.83 mm thick, optically flat, fused quartz substrates. It has 19 000 unit cells composed of two compact resonant slot elements, a meandering elliptical annulus and a folded dipole. Spectral transmission and reflection measurements in the 50–230 GHz frequency range yielded results that are in excellent agreement with numerical predictions.

Design and fabrication of double corrugated waveguide for a Ka-band traveling wave tube

The double corrugated waveguide is demonstrated to be a slow wave structure which is straightforward to manufacture and assemble. The design and fabrication of a Ka-band prototype is presented. The ability of the double corrugated waveguide to be bent through 90° has permitted the build of a compact slow wave structure with very good electrical behavior which is suitable for millimeter wave travelling wave tubes.

Recent progress in the Elegant Breadboard supra-THz activities for LOCUS and a view to an astronomy application

We report on ongoing technology activities on the Elegant Breadboard for the LOCUS telescope and its 1.15THz receiver. LOCUS is a Low-Earth orbit small satellite (150kg category) with the objective of linking observations of climate, the upper atmosphere and space weather by performing simultaneous high spectral resolution measurements of molecular signatures of molecules which drive the thermal exchange in the highest layers of our atmosphere. These measurements are performed both in the THz frequency region and in a photometric narrow-band near and mid-IR channels allowing to decouple molecular abundances from temperature and pressure profiles. The elegant breadboard under development will reproduce representative optics and explore the thermal implications of a compact optical-bench with a small cryo-cooler and radiator stage for a small LEO satellite. An extensive test programme will be undertaken to raise the payload and receiver system and we will seek opportunities to test the system in an observational campaign. Technology developments will benefit future technology activities related to both a future Earth-Orbit mission and potential astronomy missions.

The LOw Cost Upper atmosphere Sounder: The "elegant breadboard" programme

The LOw Cost Upper atmosphere Sounder (LOCUS) mission has a core objective of probing the Earths meso-sphere and low thermosphere (MLT) region using THz receivers combined with an infrared (IR) filter radiometer. This will give the first comprehensive data on the energy balance and chemical processes in the MLT from direct detection, including the important atomic oxygen which until now has never been mapped by remote sensing measurements. The payload and mission design concept has very recently, and very successfully, concluded an ESA sponsored phase A0 study, led by SSTL. It is essential to build upon this success and to maintain the mission momentum towards achieving a high readiness level (TRL) and eventual flight. A key step in this process is the demonstration and proof of operation of the THz payload in a representative environment (towards TRL 6). We therefore have begun working on a hi-fidelity breadboard of the LOCUS payload suitable for both extensive laboratory and environmental testing, and with a potential for deployment on a high-altitude platform, such as NASAs Global Hawk. The latter will prove the system technical operation in a closely representative environment, and will return valuable and useful scientific data. The breadboard will consist of the system primary antenna; optical bench; one or more THz receivers; back-end electronics, and a physical realisation of the spacecraft payload bay. An extensive test programme will be undertaken to raise the payload and receiver system towards level 6, and we will seek opportunities to test the system in an observational campaign.

Local oscillator development for focal plane array and supra-THz astronomy receivers

Ultra-sensitive superconducting tunnel junction heterodyne receivers used for astronomy research require relatively low levels of local oscillator (LO) power. When configured as an imaging array, however, the LO power required substantially increases and the provision and distribution of a harmonically generated LO signal to multiple pixel elements becomes a technically challenging task. Furthermore, the difficulty of generating LO power is compounded as the operational frequency is increased into the supra-THz region (<1 THz). We will present our programme of research directed towards the provision of future THz astronomy receivers, in which we have been pursuing the development of enhanced harmonic up-conversion LO technology.