ABSTRACT. Photonic Bangap structures are proposed for the design of the coupler of a 346 GHz sheet-beam backward wave oscillator. The design solves for typical issues of THz vacuum electron devices based on large sheet beams.

ABSTRACT. Pseudospark electron beams have been studied recently with their application to millimeter-wave and terahertz radiation generation. To this end, millimeter wave sources which utilise a pseudospark produced electron beam in different beam-wave interaction structures have been designed and modelled using the particle-in-cell code MAGIC. The experimental demonstration of coherent millimeter wave radiation generated from pseudospark sourced electron beams in different beam-wave interaction structures will be presented.

ABSTRACT. Demand for very high speed wireless communication is increasing due to the high computer and fiber speeds. W-band spectrum could support broader bandwidth and higher data transmission rate. In order to cover a long range, high power amplifier is necessary for W-band wireless communication system. In this paper, 50 watts continuous-wave W band TWT is designed. A two-step phase velocity tapering folded waveguide circuit was chosen. A two stage depressed collector is also designed for recycling more energy. For 4GHz bandwidth in W-band, the negative PVT is more suitable for efficiency enhancement. The interaction region of TWT with the negative PVT is divided into a constant phase velocity section followed by an increased phase velocity section and then a negatively tapered one. The constant pitch section establishes a growing electromagnetic wave, and the increased pitch section plays a role in making a high density electron bunch. The final negatively tapered section efficiently extracts the kinetic energy from the electron beam. The dispersion, coupling impedance and attenuation of different pitch circuit was calculated by Microwave Studio. Microwave Tube Simulation Suite (MTSS) is used to optimize the circuit profile which including the uniform circuit length, step position, step circuit length, step amplitude. The optimized pitch profile is shown in figure 1 with positive step circuit pitch 1.02P0 and negative step circuit pitch 0.95P0 respectively. The output power curve is shown in figure2 which indicates over 50 watts could be reached. The electron efficiency is about 6%. 3D PIC simulation software was used to predict the whole tube performance. Figure3 shows the result of RF voltage varying with the time at the output port with a 94GHz signal input. The output power is about 68W. In this paper a W-band folded waveguide CW TWT with two step negative tapering circuit and two-stage depressed collector is designed. The electron efficiency could reach 6%. The maximum overall efficiency of 23.6% could be achieved.

ABSTRACT. A W-band corrugated horn including a broadband vacuum window for use in gyro-devices has been designed, constructed and experimentally measured. The horn and 3 disk vacuum window converts a cylindrical TE11 mode into the free space quasi-optical TEM00 mode over the frequency band of 90–100 GHz with a reflection better than -30 dB and a coupling efficiency of ~99.4%.

ABSTRACT. With the diversified demands of meteorological observation were put forward, millimeter/submillimeter wave sounder on GEO is proposed to improve the temporal resolution. Limited by the spatial resolution, an extremely large aperture reflector antenna is inevitable for rainfall and typhoon detection. This paper mainly introduces the design of the reflector antenna on the payload, the frequency selected and the main beam efficiency calculation. Link between Shape accuracy and radiation pattern is also discussed.

ABSTRACT. Abstract: Graphene, as one of the most widely studied material, has been applied to many fields. With voltage control characteristic and high electron mobility, graphene has been focused on the application of antenna design. In this paper, the electromagnetic property of graphene material has been studied. When the graphene material is used directly as the antenna radiation material, it does not show more excellent performance than the conventional good conductor materials like gold. At the same time, this paper，the surface plasma polaritons of graphene material is simulated by using the electromagnetic computing software. The spreading phenomenon of surface plasma wave is realized in simulation. Graphene can be used as a kind of guided wave material in antenna design. Finally, a reflectarray antenna using graphene is designed in this paper. With the adjustable voltage performance of graphene material, the beam control function of reflectarray antenna is realized. Graphene SPP (surface plasma polaritons) model has been simulated by electromagnetic software CST. The surface plasma wave propagation using graphene material is shown in Figure 1.There are two layers in the structure, silicon dioxide of the substrate and graphene of surface layer. The working frequency is 2 Thz. Figure 2 shows the structure of the graphene reflectarray unit. The resistance of the graphene surface will change by changing the external voltage value. Therefore, the control of the reflected beam is realized by changing the voltage.

ABSTRACT. Well-understood optical test systems are needed for precise characterisation and calibration for all high-performance detectors. A cryogenic variable temperature blackbody load has been developed to test the optical efficiencies of ultra-low-noise Transition Edge Sensors (TESs) for space science. The few-mode, partially coherent illumination conditions of the measurement system are engineered to be precisely the same as those of the telescope. We have used a SPICA/SAFARIlike telescope/detector for demonstration purposes. The essential difference between the test system and an equivalent representation of the telescope’s optics is that the telescope has a lens of effective focal length f, but the test system does not. A key part of our analysis is to describe behaviour in terms of the optical modes of the test system, as distinct from the optical modes of the detector under test. Here we describe the analysis of the test assembly in terms of signal power, background power and photon noise.

ABSTRACT. A novel power combining technique, which combines multi beams into one beam by using quasi optical technique, is proposed and demonstrated by full wave simulation at terahertz band. The principle of the beam power combining is described. Simulation results are given to show the validation of the power combining technique.

ABSTRACT. We present the preliminary measured responses of a planar superconducting on/off switch operating at the 220 GHz range. Our superconducting switch, comprising of several niobium nitride (NbN) nano-bridges, were deposited across the slotline section of a back-to-back unilateral finline transmission line, made of a similar superconducting material. The transmission characteristics of the superconducting switch under the illumination of a sub-millimetre local oscillator (LO) were measured directly using a terahertz power meter or using a superconductor-insulator-superconductor (SIS) chip as a direct detector. The nano-bridges were switched from the superconduct- ing state to the normal state by applying a bias current exceeding the critical current along the nano-bridge. In this paper, we present the measured current-voltage (IV) characteristic curves of the superconducting switches and their transmission responses between the superconducting and the normal states, along with the theoretical analysis done using rigorous electromagnetic simulations in combination with the accurate superconducting surface impedance description.

ABSTRACT. This paper presents the design and performance of a x2x2 frequency multiplier chain from 40 to 160 GHz. The input power at 40 GHz is 500 mW with a final output power of 35 mW at 158 GHz. The 3 dB bandwidth at the output frequency is over 10%. The results demonstrate good agreement between the modeled and measured data. The paper includes extensive thermal modeling of the structure including the circuits, which shows a good performance of power handling for high power applications.

ABSTRACT. A handheld THz probe has been developed by TeraView with the goal to assess tumor resection margins intra-operatively in breast-conserving surgery (BCS) specimens and metastatic status of sentinel lymph nodes (SLNs), with a view to reduce re-operation rates. The utility of this probe for this purpose has already been shown in an ex vivo setting. Further work carried out by Teraview Ltd together with the breast surgical team at King’s College London (KCL)/Guy’s and St Thomas’s NHS Foundation Trust (GSTT) is confirming promise of this technique, with focus on the in vivo application of the handheld THz probe for real-time assessment of tumor resection margins in BCS. In particualr, the probe is designed to acquire THz images during breast cancer surgery to distinguish between normal and malignant breast tissue, thus assisting complete surgical excision of cancers. Findings of this study leading to in-vivo testing are discussed in this paper.

ABSTRACT. The quantum beat (QB) emitter is a multiple quantum well (MQW) structure designed to utilize light hole (lh) and heavy hole (hh) energy states for producing coherent excitation of lh and hh excitons and resulting in radiation in the THz range of frequencies [1]. Energies of states are tunable with applied electric bias, resulting in a tuneability of the radiation frequency. In this work, we aim to produce room temperature tuneable THz radiation by optically exciting the QB sample using CW laser sources. In order to maximize the incident power upon the sample, and simplify the collection of the THz radiation, a structure which has had the substrate removed, and is capillary bonded to diamond is required. The fabrication processes are described here. The sample has been designed to enable excitation by commercially available CW semiconductor laser sources at ~850nm. The e1-hh1 and e1-lh1 transitions are designed to obtain transition energies in this range in addition to a difference in energy which should allow tuneability of the THz radiation from ~3.3 to 4.2 THz. See Figure 1. The QB sample was grown by MBE on a heavily doped n-GaAs substrate to allow biasing of future devices. The layer sequence consists of an (1500nm) n-doped Al0.4Ga0.6As layer, undoped MQW region, (1500nm) p-Al0.4Ga0.6As layer and 200nm p+ GaAs cap layer The MQW region is made up of 30 repeats of 11.9 nm GaAs quantum wells separated by 7.1 nm AlAs barriers. Following growth, an optical access mesa-diode structure was fabricated to assess the structure through photocurrent (PC) spectroscopy. Figure 2 shows at 0V-applied bias. The results are in excellent agreement with simulation. For initial analysis of the sample, we remove both the highly doped p-GaAs contact layer (which absorbs ~20% of the incident pump laser), and the n-GaAs substrate. Absorption coefficients [2] for this material indicate losses in excess of 6db/um, indicating that the complete removal of the substrate is required. Firstly, the p-GaAs cap layer has been etched using citric acid+H2O2. This etches selectively attacks GaAs as opposed to the underlying Al0.4Ga0.6As (selectivity =102). Following this process two routes are possible to obtain substrate removal. One option is to use capillary bonding [3] to attach the sample to the diamond heat spreader, and in order to remove the substrate; a combination of non-selective etching and selective etching [4] has been used. The first 200 microns were etched by NH4OH+H2O2, which has a high etch rate, rough etch profile, and non-selectivity. This is followed by citric acid + H2O2 which has a slower, selective etch. In this case the etch stops once the substrate is entirely removed. This is shown in Figure 3. Alternatively, following selective etching of the p+ GaAs cap, the substrate may be lapped to a thickness of ~150 um, capillary bonded, and selectively etched using citric acid + H2O2. In both cases SEM and surface profiling indicate that the sample thickness was 3.6 um indicating that only the doped Al0.4Ga0.6As and MQW remained. References [1] P. Planken, M. Nuss, I. Brener, K. Gossen, M. Luo and S. Chung (1992). Terahertz emission in single quantum wells after coherent optical excitation of light hole and heavy hole excitation. Phys. Rev. Lett., vol. 69, pp. 3800–3804. [2] U. Kim, S. Oh, Inhee Maeng, C. Kang and J. Son (2007). Terahertz Electrical Characteristics of Heavily Doped n-GaAs Thin Films. J. Korean Phys. Soc. Vol. 50, pp. 789-792 [3] Z. Liau (2000). Semiconductor wafer bonding via liquid capillarity. Appl .Phys. Letters, vol. 77, pp. 651–653. [4] Y. Uenishi Y Uenishi, H Tanaka and H Ukita (1994). Characterization of AlGaAs Microstructure Fabricated by AlGaAs/GaAs Micromachining. IEEE Trans. Electron. Dev, vol. 41, pp. 1778–1783.

ABSTRACT. Cherenkov radiation of terahertz waves by an ultrashort laser pulse propagating as a Gaussian beam in an electro-optic crystal is theoretically studied. By applying the developed theory to a Ti:sapphire laser pulse in an lithium niobate crystal we demonstrate the existence of an optimal size of the laser beam waist which maximizes the terahertz yield. The optimal size depends on the time duration of the laser pulse.

ABSTRACT. This paper analyzes typhoon and rainstorm observation requirements of Geostationary Orbit Millimeter and Sub-millimeter Wave Sounding. The specification of the sounder is put forward. A real aperture radiometer system, which consists of extremely large electrical size antenna, quasi-optical network feed system, millimeter and sub-millimeter receivers and calibration equipments, is designed on system level. Newly progress of technologies on subsystem level are summarized, and techology development and international cooperation are proposed, which will promote the realization of the first Geostationary orbit microwave payload in the world.

ABSTRACT. See PDF

ABSTRACT. The LOw Cost Upper atmosphere Sounder (LOCUS) mission has a core objective of probing the Earth’s mesosphere and low thermosphere (MLT) region using THz receivers combined with an IR filter radiometer. This will give the first comprehensive data on the energy balance and chemical processes in the MLT. 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 NASA’s 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.

ABSTRACT. ICEMuSIC is a new satellite instrument concept for Earth observation applications. The instrument is enabled by the availability of large arrays of kinetic inductance detectors, and will observe the upper atmosphere across a frequency range of 100GHz to ~1.5 THz. Observations in this frequency range are very important to constrain fundamental climatology parameters related to clouds, particularly the ice-water path (IWP) and particle size distribution. With the same instrument, we have the opportunity to make observations of atmospheric temperature and humidity with unprecedented resolution, enabled by the sensitivity and frequency coverage of the KID arrays. These observations are very important to numerical weather prediction agencies. This paper presents the results of a trade-off study, funded by the UK Space Agency, to find the optimal instrument configuration - maximum science return for minimum cost.

ABSTRACT. The Balloon-borne Large-Aperture Submillimeter Telescope for Polarimetry (BLASTPol) is a suborbital mapping experiment designed to study the role played by magnetic fields in the star-formation process. BLASTPol uses a total power instrument and an achromatic half-wave plate to modulate the polarization signal. During two long-duration flights from Antarctica in 2010 and 2012, BLASTPol made degree-scale maps of linearly polarized dust emission from molecular clouds in three wavebands centered at 250, 350, and 500 microns. The next-generation BLASTPol incarnation (BLAST-TNG) will build on the success of the previous experiment and continue its role as a unique instrument and a testbed for new technologies. With a 16-fold increase in mapping speed, BLAST-TNG will make larger and deeper maps. Major improvements include a 2.5 m carbon fiber mirror that has a 40% wider diameter than the BLASTPol mirror and 3000 polarization-sensitive detectors. The telescope will serve as a pathfinder project for microwave kinetic inductance detector (MKID) technology, as applied to feedhorn-coupled submillimeter detector arrays. BLAST-TNG will also be the first balloon-borne telescope to offer shared-risk observing time to the community.

ABSTRACT. Spectral-spatial interferometry pioneered in a narrow band in the near infrared has not enjoyed much exploitation as a technique. Proposed as a promising modulation method for a potential Far-infrared future satellite, a period of study was performed on two testbeds to improve and evolve this technique in the laboratory in order to simplify some of the technical aspects and the data analysis involved. Here we will present an update on the successful upgrade of a previous wideband millimetric (0.3-1.0 THz) testbed to a mid-IR (11-14THz) one, as well as the ongoing progress on a broadband setup for an imaging system with a commercial thermal-IR (8 to 12 micron or 25-35 THz) camera currently working as imaging FTS. Ideal source size, illumination and analysis are discussed.

ABSTRACT. The potential of the Low THz spectrum for high resolution imaging applications such as automotive radar is described. Outdoor experiments require compact and portable equipment which may be achieved by extending the operation of current battery powered vector network analyzers. The development of radars in the 300 and 670 GHz bands is detailed including instrument performance data and preliminary imaging results.

ABSTRACT. A digital communication system operating in the 220GHz atmospheric window is reported. Preliminary demonstration of the wireless data link was conducted in the lab environment at 5m range, which yielded a bit error rate(BER) <10-6 when the data rate of 3Gbit/s was achieved. The system is wholly based on solid-state technology. Schottky subharmonic mixers (SHM) are employed as the frequency up- and down-converters respectively in the transmitter (Tx) and receiver (Rx) ends. In the Tx end, broadband base-band signals are I/Q modulated on an X-band carrier (10.8GHz) before up-converting to the transmission frequency around 218.8GHz by the subharmonic mixer which consumes 4mW local oscillator (LO) power at 104GHz and operates in the single side band mode due to the existence of a band-pass filter between the mixer and the antenna. The Rx end consists of the same components with its Tx counterpart except for the automatic gain control (AGC) amplifier which is designed to ensure an optimum detectable power level by the I/Q demodulator. LO signals for the Tx and Rx ends are generated in the same frequency multiplication configuration based on two 50MHz crystal oscillators (CO) separately for each end. System characterization with higher transmission data rate and longer link distance in the outdoor environment will be presented at the conference.

ABSTRACT. Understanding the mechanics of biological systems such as the energy transfer along long chained polymers is an ongoing challenge. One example of these polymers and an essential part of all living organisms are deoxyribonucleic acids (DNA) which contain complex molecular building blocks. By breaking the DNA down to its vital components including the nucleobases and nucleosides, the Terahertz (THz) spectra can reveal unique characteristic features for different molecular conformation. By using a low intensity THz source, it factors out any possibility of heating or damage to the sample which alleviates the difficulties in multiple measurements. Presented here is the spectra of all four nucleobases and their corresponding nucleosides from 0.6 THz to 18 THz by using a safe and novel technique.

ABSTRACT. A new open cavity is proposed and used to measure the permittivity of dielectric material at millimeter wave band. The transcendental equation from that the dielectric constant can be determined is presented. Experiment is carried out and measured data are presented.

ABSTRACT. Metal mesh technology has been employed for decades to build high performance filters working at millimetre and sub-millimetre wavelengths. They have found a wide range of applications, mainly targeted to astronomical instrumentation. Mesh filters, dichroics, beam dividers and polarisers have been used in tens of ground based, balloon-borne and satellite projects. The technology is well proven and space qualified. The same technology can be used to develop more general quasi-optical devices able to manipulate and transform the electromagnetic field amplitude and phase across their surface. We summarise recent developments in this field discussing devices such as mesh Half Wave Plates, flat mesh lenses, gradient index lenses, integrated mesh lens arrays, polarisation splitting devices and mesh prisms.

ABSTRACT. This paper introduces a new technique for enhancing the selectivity of frequency selective surfaces (FSS) for sensing applications [1], [2]. The proposed FSS functions as a free-space bandpass resonator, designed to sense the changing dielectric properties of minute amount of material loaded on the FSS. The technique is mainly based on two concepts; enhancing the electric field in a given area and introducing transmission zeros in the FSS response. Two designs based on a modified split-ring resonator (SRR) at 300 GHz have been simulated. The first one is composed of triple-split ring resonator as shown in Fig. 1. The splits behave as capacitive elements, obtaining a high electric field concentration and a transmission zero in the pass band, and thus produce a resonance quality factor (Q-factor) of 49. By controlling the orientation of the three splits, a higher Q-factor of 126 is attainable. The second structure is designed using concentric triple-split rings. The concept behind it is the increasing electromagnetic coupling effect between the concentric rings. Therefore, the transmission response becomes steeper as compared with the single triple-split ring, and the quality factor is 99. Further enhancement can be achieved by decreasing the inter-spacing between the two rings. The increased coupling effect is able to push the position of the transmission zero nearer to the resonant frequency to get an even faster roll-off. By reducing the inter-spacing distance by three times, the FSS Q-factor can be increased to 286. The proposed FSS is designed for fabrication using SU8-based micromachining process [3] and the parameter studies of the FSS structures based on full-wave simulations will be presented.

[1] M. Nagel, P. H. Bolivar, M. Brucherseifer, H. Kurz,A.Bosserhoff, and R. Büttner, “Integrated THz technology for label-free genetic diagnostics,” Appl. Phys. Lett., vol. 80, no. 1, pp. 154–156, Jan. 2002. [2] C. Debus, P. H. Bolivar, “Frequency Selective Surfaces for high sensitivity terahertz sensing”, Applied Physics Letters, vol. 91, no. 18, Oct. 2007. [3] Yi Wang, B. Yang, Y. Tian, R. S. Donnan, M. J. Lancaste, “Micromachined Thick Mesh Filters for Millimeter-Wave and Terahertz Applications”, IEEE Trans. Terahertz Sci. Techn., vol. 4, no. 2, pp. 247-253, Mar. 2014.

ABSTRACT. This paper presents the performance of microstrip lines on 50um-thick LCP substrate at the frequency bands (220-330GHz). Characteristic impedance, effective dielectric constants and losses with different widths of Microstrip line are extracted from measured S-parameters.

ABSTRACT. See pdf

ABSTRACT. The output signal of a gyro-multiplier mainly contains two distinguished frequencies. This paper presents our work on the design of a gyro-multiplier output system for the conversion and separation of the two modes. Correspondingly, the key components including the mode converter and the frequency selective surface are simulated and designed.