Mid-infrared (mid-IR) detection and imaging over atmospheric transparent 3-5 μm and 8-12 μm bands are increasingly becoming important for various space, defense and civilian applications. Various kinds of microbolometers offer uncooled detection of IR radiation. However, broadband absorption of microbolometers makes them less sensitive to spectrally resolved detection of infrared radiation and the fabrication is also very tedious involving multiple complex lithography steps. In this study, we designed an optical nano-antenna array based detector with narrow frequency band of operation. The structure consists of a two-element antenna array comprised of a perforated metallic hole array coupled with an underneath disk array which trap incident radiation as dipole currents. The energy is dissipated as electron plasma loss on the hole-disk system inducing close to ~100% absorption of the incident radiation. This near perfect absorption originates from simultaneous zero crossing of real component of permittivity and permeability due to the geometrical arrangement of the two antenna elements which nullifies overall charge and current distributions, prohibiting existence of any propagating electromagnetic modes at resonance. Moreover, the continuous perforated film allows probing of the induced "micro-current" plasma loss on each nano hole-disk pair via a weak bias current. Such optical antenna design enables flexible scaling of detector response over the entire mid-infrared regime by change in the antenna dimensions. Furthermore, the development of simple nanoimprint lithography based large area optical antenna array fabrication technique facilitates formation of low cost frequency selective infrared detectors.

Yes / This paper presents the results of a study on developing an effective technique to increase the performance characteristics of antenna arrays for sub-THz integrated circuit applications. This is essential to compensate the limited power available from sub-THz sources. Although conventional array structures can provide a solution to enhance the radiation-gain performance however in the case of small-sized array structures the radiation properties can be adversely affected by mutual coupling that exists between the radiating elements. It is demonstrated here the effectiveness of using SIW technology to suppress surface wave propagations and near field mutual coupling effects. Prototype of 2 × 3 antenna arrays were designed and constructed on a polyimide dielectric substrate with thickness of 125 μm for operation across 0.19-0.20 THz. The dimensions of the array were 20 × 13.5 × 0.125 mm3. Metallization of the antenna was coated with 500 nm layer of Graphene. With the proposed technique the isolation between the radiating elements was improved on average by 22.5 dB compared to a reference array antenna with no SIW isolation. The performance of the array was enhanced by transforming the patch to exhibit metamaterial characteristics. This was achieved by embedding the patch antennas in the array with sub-wavelength slots. Compared to the reference array the metamaterial inspired structure exhibits improvement in isolation, radiation gain and efficiency on average by 28 dB, 6.3 dBi, and 34%, respectively. These results show the viability of proposed approach in developing antenna arrays for application in sub-THz integrated circuits. / Ministerio de Ciencia, Innovación y Universidades, Gobierno de España (MCIU/AEI/FEDER, UE) under Grant RTI2018-095499-B-C31, in part by the Innovation Programme under Grant H2020-MSCA-ITN-2016 SECRET-722424, and in part by the U.K. Engineering and Physical Sciences Research Council (EPSRC) under Grant EP/E022936/1.

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A prototype of a bias-switched active sensor is developed and measured to establish the achievable dynamic range in a new generation of active arrays for microwave tissue imaging. The sensor integrates a printed slot antenna, a low-noise amplifier (LNA) and an active mixer in a single unit, which enables inter-sensor separation distance as small as 12 mm. The sensor's input covers the bandwidth from 3 GHz to 7.5 GHz. Its output intermediate frequency (IF) is 30 MHz. The sensor is controlled by a simple bias-switching circuit, which switches ON and OFF the bias of the LNA and the mixer simultaneously. It is demonstrated experimentally that the dynamic range of the sensor, as determined by its ON and OFF states, is 109 dB and 118 dB at resolution bandwidths of 1 kHz and 100 Hz, respectively. The integration of an LNA on the same board with each antenna element is also studied. The LNA circuit dimensions have been reduced from 18.2 mm by 44.6 mm (the size of the evaluation board) to 6 mm by 8 mm in width and length, respectively. Simulations show promising results. Thus, fabrication and measurements can be carried out in the near future. / Thesis / Master of Applied Science (MASc)

Yes / In this paper, a set of singular integral formulations are derived to calculate the surface impedance matrix on the antenna array elements. The proposed mathematical model enables electrodynamic analysis of antenna arrays designed using metamaterial-inspired structures. The formulations allow the determination of the array’s impedance, spatial and polarization characteristics at significantly low computational cost compared to conventional electromagnetic solvers based on method-of-moments (MoM) numerical technique. The accuracy of the surface impedance results obtained from the theoretical formulations are verified using the full wave EM software. It is shown that there is excellent agreement between the proposed formulations and EM software. The accuracy of the theoretical model presented is valid for single layer structures. / RTI2018-095499-B-C31, Funded by Ministerio de Ciencia, Innovación y Universidades, Gobierno de España (MCIU/AEI/FEDER,UE), and innovation programme under grant agreement H2020-MSCA-ITN-2016 SECRET-722424 and the financial support from the UK Engineering and Physical Sciences Research Council (EPSRC) under grant EP/E022936/1

Yes / This paper presents a new optimization algorithm based on the behavior of the fungi kingdom expansion (FKE) to optimize the radiation pattern of the array antenna. The immobile mass ex-pansion of the fungi is mimicked in this work as a chaotic behavior with a sinusoidal map func-tion, while the mobile mass expansion is realized by a linear function. In addition, the random germination of the spores is utilized for randomly distributing the variables that are far away from the best solution. The proposed FKE algorithm is applied to optimize the radiation pattern of the antenna array, and then its performance is compared with that of some well-known algo-rithms. The MATLAB simulation results verify the superiority of the proposed algorithm in solving 20-element antenna array problems such as sidelobe reduction with sidelobe ratio (SLR = 25.6 dB), flat-top pattern with SLR = 23.5 dB, rectangular pattern with SLR = 19 dB, and an-ti-jamming systems. The algorithm also results in a 100% success rate for all of the mentioned antenna array problems

In airborne communication systems such as airborne cell-extender repeaters the receiver faces the challenge of demodulating the signal of interest (SOI) in the presence of excessive amounts of Co-Channel Interference (CCI) from a large number of sources. This results in the overloaded environment where the number of near-equal power co-channel interferers exceeds the number of antenna array elements. This thesis first analyzes the interference environment experienced by an airborne cellular repeater flying at high altitudes. Link budget analysis using a two-ray propagation model shows that the antenna array mounted on an airborne receiver has to recover the SOI out of hundreds of co-channel interfering signals. This necessitates use of complex overloaded array signal processing techniques. An extensive literature survey on narrowband signal extraction algorithms shows that joint detection schemes, coupled with antenna arrays, provide a solution for narrowband overloaded array problem where as traditional beamforming techniques fail. Simulation results in this thesis investigates three "promising" overloaded array processing algorithms, Multi-User Decision Feedback Equalizer (MU-DFE), Iterative Least Squares with Projection (ILSP), and Iterative Least Squares with Enumeration (ILSE). ILSE is a non-linear joint maximum-likelihood detector, is shown to demodulate many more signals than elements even when the users are closely spaced and the channel is blindly estimated. Multi-user time delay estimation is one of the most important aspects of channel estimation for overloaded array processing. The final chapter of the thesis proposes a low-complexity data-aided time-delay estimation structure for embedding in a Per Survivor Processing (PSP) trellis for overloaded array processing. An extensive analysis proves that the multi-user delay estimation is separable, which leads to the proposed multi-user algorithm that estimates the user delays with a bank of simple data-aided synchronization loops to reduce the complexity. This thesis shows simulation results for the single-user case where the low-complexity Delay Locked Loop (DLL) structure, working at a low oversampling rate of 2 samples per symbol, estimates and compensates for any integer or non-integer sample delay within ±Tsym(symbol period). Two extensions to this technique are proposed to provide efficient multi-user delay estimation. The first multi-user structure employs a bank of DLLs, which compensate for the timing offset of each user simultaneously. This multi-user algorithm is suitable for CDMA-type applications, where each user has a distinct PN-code with good auto- and cross-correlation properties. We show that for spreading gain of 31, the presence of an interpolator enables us to reduce the oversampling factor from 4 to 2 samples per chip. Thus, the requirements of the A/D converter are relaxed without sacrificing system performance. Furthermore, we show that the proposed scheme meets the requirements of multi-user interference cancellation techniques for residual worst-case timing errors, i.e., residual timing error < 0.2 Tc, as reported in [200]. Finally, the thesis recommends a similar multi-user structure for narrowband TDMA-type system, which is based on bank of DLLs with whitening pre-filters at the front end of each branch. / Master of Science