Receiver front-end circuits and components for millimetre and submillimetre wavelengths

This dissertation focuses on the development of millimetre- and submillimetre-wave receiver front-end circuits and components. Seven scientific articles, written by the author, present this development work. A short introduction to the technology related to the designs of the thesis precedes the articles. The articles comprise several novel structures and techniques intended to further improve the performance of receivers or to provide new ways for receiver circuit implementation, summarised as follows. 1) Novel rectangular waveguide-to-CPW waveguide transition using a probe structure. The measured insertion and return loss of an X-band (8.2-12.4 GHz) back-to-back structure are less than 0.5 dB and more than 17 dB, respectively, over the entire frequency band (fractional bandwidth of > 40 %). The transition is used in a submm-wave mixer. 2) Novel rectangular waveguide-to-CPW transition using a fin-line taper. The measured insertion and return loss of an X-band (8.2-12.4 GHz) back-to-back structure are less than 0.4 dB and more than 16 dB, respectively, over the entire frequency band. 3) Novel tunable waveguide backshort based on a fixed waveguide short and movable dielectric slab. The measured return loss for a W-band backshort is less than 0.21 dB (VSWR > 82) over the entire frequency band of 75-110 GHz. 4) New coaxial bias T. The insertion loss is less than 0.5 dB at 3-16 GHz (fractional bandwidth of 137 %) and 0.1 dB at 5.2-14.1 GHz. In the latter range, the return loss is more than 30 dB. The RF isolation is greater than 30 dB at 1-17 GHz. 5) First millimetre-wave subharmonic waveguide mixer using European quasi-vertical Schottky diodes. The mixer utilises a single diode chip with quartz filters in a four-tuner waveguide housing. A single-sideband noise temperature of 3500 K and conversion loss of 9.2 dB (antenna loss included) have been measured at 215 GHz with an LO power of 3.5 mW. 6) Balanced-type fifth-harmonic submillimetre-wave mixer. It uses two planar Schottky diodes, quartz filters, and a tuner-less in-line waveguide housing with an integrated diagonal horn antenna and new LO transition structure. The designed RF range is 500-700 GHz enabling the use of an LO source at 100-140 GHz. A conversion loss of about 27 dB has been measured at 650 GHz with an LO power of 10 mW. The mixer has been in use in phase locking of a submm-wave signal source. 7) Characterisation procedure of planar Schottky diodes with extensive dc, capacitance, and wide-band (up to 220 GHz) S-parameter measurements and parameter extraction. Parameters of a simple diode equivalent circuit and results of extensive measurements are available for designers and diode manufacturers for further use.reviewe

Non-Abelian magnetic monopole in a Bose-Einstein condensate

Recently, an effective non-Abelian magnetic field with a topology of a monopole was shown to emerge from the adiabatic motion of multilevel atoms in spatially varying laser fields [J. Ruseckas et al., Phys. Rev. Lett. 95, 010404 (2005)]. We study this monopole in a Bose-Einstein condensate (BEC) of degenerate dressed states and find that the topological charge of the pseudospin cancels the monopole charge resulting in a vanishing gauge invariant charge. As a function of the laser wavelength, different stationary states are classified in terms of their effect to the monopole part of the magnetic field and a cross-over to vortex ground state is observed.Comment: 5 pages, 1 color figure; v2 modified according to referees' suggestions, some typos corrected; v3 minor modifications, published versio

Pediatric traumatic brain injury and early age multiple sclerosis in Finland : A nationwide register-based cohort study

Objective: Examine the link between pediatric traumatic brain injury (pTBI) and early-onset multiple sclerosis in Finland. Methods: Conducted nationwide register study (1998−2018) with 28,750 pTBI patients (< 18) and 38,399 pediatric references with extremity fractures. Multiple sclerosis diagnoses from Finnish Social Insurance Institution. Employed Kaplan−Meier and multivariable Cox regression for probability assessment, results presented with 95% CI. Results: Of 66 post-traumatic multiple sclerosis cases, 30 (0.10%) had pTBI, and 36 (0.09%) were in the reference group. Cumulative incidence rates (CIR) in the first 10 years were 46.5 per 100,000 (pTBI) and 33.1 per 100,000 (reference). Hazard ratio (HR) for pTBI was 1.10 (95% CI: 0.56−1.48).Stratified by gender, women's CIR was 197.9 per 100,000 (pTBI) and 167.0 per 100,000 (reference) after 15 years. For men, CIR was 44.6 per 100,000 (pTBI) and 34.7 per 100,000 (reference). In the initial 3 years, HR for female pTBI was 1.75 (95% CI: 0.05−6.32), and between years 3 and 20, it was 1.08 (95% CI: 0.51−1.67). For male patients, HR was 1.74 (95% CI: 0.69−4.39). Significance: We did not find evidence of an association between pTBI and early-onset multiple sclerosis 20 years post-initial trauma.Peer reviewe

Association between pediatric traumatic brain injury and epilepsy at later ages in Finland : A nationwide register-based cohort study

Objective: This study was undertaken to examine how pediatric traumatic brain injury (pTBI) correlates with incidence of epilepsy at later ages in Finland. Methods: This nationwide retrospective register-based cohort study extended from 1998 to 2018. The study group consisted of 71 969 pediatric (<18 years old) patients hospitalized with TBI and a control group consisting of 64 856 pediatric patients with distal extremity fracture. Epilepsy diagnoses were gathered from the Finnish Social Insurance Institution. Kaplan–Meier and multivariable Cox regression models were conducted to analyze the probability of epilepsy with 95% confidence intervals (CIs). Results: Cumulative incidence rates (CIRs) for the first 2 years were.5% in the pTBI group and.1% in the control group. The corresponding rates after 15 years of follow-up were 1.5% in the pTBI group and.7% in the control group. Due to proportional hazard violations, the study population was split to the first 2 years and in subgroup analysis 4 years. During the first 2 years of surveillance, the hazard ratio (HR) for the pTBI group was 4.38 (95% CI = 3.39–5.66). However, between years 2 and 20, the HR for the pTBI group was 2.02 (95% CI = 1.71–2.38). A total of 337 patients (.47%) underwent neurosurgery, and 36 (10.7%) patients subsequently developed epilepsy. The CIR for the first year after TBI was 4.5% (95% CI = 2.3–6.7) in operatively managed patients and.3% (95% CI =.3–.4) in nonoperatively managed patients. Corresponding figures after 15 years were 12.0% (95% CI = 8.2–15.8) and 1.5% (95% CI = 1.4–1.6). During the first 4 years of surveillance, the HR for the operative pTBI group was 14.37 (95% CI = 9.29–20.80) and 3.67 (95% CI = 1.63–8.22) between years 4 and 20. Significance: pTBI exposes patients to a higher risk for posttraumatic epilepsy for many years after initial trauma. Children who undergo operative management for TBI have a high risk for epilepsy, and this risk was highest during the first 4 years after injury.Peer reviewe

Quantum circuits with uniformly controlled one-qubit gates

Uniformly controlled one-qubit gates are quantum gates which can be represented as direct sums of two-dimensional unitary operators acting on a single qubit. We present a quantum gate array which implements any n-qubit gate of this type using at most 2^{n-1} - 1 controlled-NOT gates, 2^{n-1} one-qubit gates and a single diagonal n-qubit gate. The circuit is based on the so-called quantum multiplexor, for which we provide a modified construction. We illustrate the versatility of these gates by applying them to the decomposition of a general n-qubit gate and a local state preparation procedure. Moreover, we study their implementation using only nearest-neighbor gates. We give upper bounds for the one-qubit and controlled-NOT gate counts for all the aforementioned applications. In all four cases, the proposed circuit topologies either improve on or achieve the previously reported upper bounds for the gate counts. Thus, they provide the most efficient method for general gate decompositions currently known.Comment: 8 pages, 10 figures. v2 has simpler notation and sharpens some result