Efficient analysis, design, and filter applications of EBG waveguide with periodic resonant loads

An efficient analysis and design of an electromagnetic-bandgap (EBG) waveguide with resonant loads is presented. Equivalent-circuit analysis is employed to demonstrate the differences between EBG waveguides with resonant and nonresonant loadings. As a result of the resonance, transmission zeros at finite frequencies emerge. The concept is demonstrated in E-plane waveguides. A generic fast and efficient formulation is presented, which starts from the generalized scattering matrix of the unit cell and derives the dispersion properties of the infinite structure. Both real and imaginary parts of the propagation constant are derived and discussed. The Floquet wavelength and impedance are also presented. The theoretical results are validated by comparison with simulations of a finite structure and experimental results. The application of the proposed EBG waveguide in the suppression of the spurious passband of a conventional E-plane filter is presented by experiment.

Periodically loaded dipole array supporting left-handed propagation

Periodically loaded dipole arrays printed on grounded dielectric substrate are shown to exhibit left-handed propagation properties. In an equivalent transmission line representation, lefthandedness emerges due to the excess series capacitance and shunt inductance. Based on this concept, the authors study the distribution of the modal fields and the variation of series capacitance and shunt inductance as the dipoles are loaded with stubs. Full wave dispersion curves that show the gradual transition from a right-handed to a left-handed medium upon periodically loading the dipoles with stubs are presented. An equivalent circuit is derived that matches to a very good extent the full wave result. The cell dimensions are a small fraction of the wavelength (),15), so the structure can be considered as an equivalent homogeneous surface. The structure is simple, readily scalable to higher frequencies and compatible with low-cost fabrication techniques.

Uniplanar left-handed artificial metamaterials

Planar periodic arrays of metallic elements printed on grounded dielectric substrates are presented to exhibit left-handed properties for surface wave propagation. The proposed structures dispense with the need for grounding vias and ease the implementation of uniplanar left-handed metamaterials at higher frequencies. A transmission line description is used for the initial design and interpretation of the left-handed property. A thorough study based on full wave simulations is carried out with regards to the effect of the element geometrical characteristics and the array periodicity to the properties of the artificial material. Dispersion curves are presented and studied. The distribution of the modal fields in the unit cell is also studied in order to provide an explanation of the material properties. The scalability of the proposed structures to infrared frequencies is demonstrated.

Periodically loaded 1-D metallodielectric electromagnetic bandgap structures for miniaturisation and bandwidth enhancement

Periodic loading of 1-D metallodielectric electromagnetic bandgap (MEBG) structures has been rigorously investigated. Miniaturised and broadband MEBG structures have been produced by means of periodically loading a dipole array. A study has been carried out with regard to the loading mechanism, the number of stubs, the topology of the structure and the order of loading. Simulations have been carried out using a method of moments based software. First order uniform loading stubs have yielded a significant size reduction of the MEBG array and the bandwidth has doubled. Good agreement between simulations and measurements has been achieved. The current distribution on the proposed structure has been studied, yielding valuable insight. An interdigital topology has resulted in further miniaturisation and bandwidth enhancement. Fractal-type arrays have been produced after applying second order loading. A maximum miniaturisation of 2.5:1 has been achieved.

An array-based study of reactivity under solvent-free mechanochemical conditions-insights and trends

An array-based approach is put forward to obtain insight into reactivity under mechanochemical solvent-free conditions. We describe a survey of sixty potential reactions between twelve metal salts MX2 {(M = Cu, X-2 = (OAc)(2), (HCO2)(2), (F3CCO2)(2), (acac)(2), (F(6)acac)(2), (NO3)(2), SO4; M = Ni, X-2 = (OAc)(2), (NO3)(2), SO4; M = Zn, X-2 (OAc)(2), (NO3)(2)} and five bridging organic ligands {isonicotinic acid (HINA), 1,4-benzenedicarboxylic acid (H2BDC), acetylenedicarboxylic acid (H(2)ADC), 1,3,5-benzenetricarboxylic acid (H3BTC), 4,4'-bipyridyl (BIPY). Reaction conditions involved a ball mill, applied for 15 min at 30 Hz, without external heating. When examined by XRPD, forty of the combinations gave detectable reactions, thirty-eight with crystalline products. Of these, twenty-nine reactions were quantitative (consuming all of at least one reactant). Comparison of XRPD patterns with patterns simulated from single crystal X-ray diffraction data in the Cambridge Structural Database allowed structural identification of six products. Of particular interest are the microporous framework materials [Cu(INA)(2)] and [Cu-3(BTC)(2)] (HKUST-1) obtained by reaction of the corresponding carboxylic acids with copper acetate. Other non-porous polymers with 3-dimensional connectivity, [Ni(ADC)(H2O)(4)], or 1-dimensional connectivity, [Cu(acac)(2)(BIPY)] and [Cu(F6acac)(BIPY)] were also obtained. Reaction between zinc acetate and H2ADC gave a new product which had not previously been characterised by single-crystal X-ray crystallography, but whose XRPD pattern suggests that it is isostructural with the known nickel polymer [Ni(ADC)(H2O)(4)]. Two further isostructural nickel and zinc products were obtained in reactions between HINA and nickel nitrate and zinc nitrate. Trends observed within the array are discussed. Copper acetate and copper formate were the most effective starting materials for reaction with carboxylic acids, potentially related to the basicity of their anions and the solvating effects of the formic and acetic acid byproducts. Amongst the ligands there was a general negative corelation between melting point and reactivity. The issue of pore templating in microporous phases and the generation of new structures is also discussed in relation to the Cu(INA)(2), Cu-3(BTC)(2) and nickel nitrate-BIPY systems. Overall, the study suggests that mechanochemical reactivity between metal salts and organic ligands under solvent free conditions is remarkably general. Use of array-based approaches as demonstrated here is advocated a useful way to reveal underlying trends in reactivity under solvent free mechanochemical conditions and to highlight particular cases for more detailed study.

Dual-mode retrodirective/phased array

A method for producing a retrodirective (self-tracking) antenna, which can also be operated as a phased (selectively pointed) array through the addition of a simple switching circuit and DC bias offset adjustment, is presented. Phase adjustment to individual antenna elements is shown to be readily carried out by a simple frequency pushing technique, applied to a PLL circuit, thus replacing the requirement for additional phase shifters. Practical results when applied to a ten-element array operating at 2.4 GHz are shown for both modes of operation.

High-performance IQ modulator-based phase conjugator for modular retrodirective antenna array implementation

In this paper, we verify a new phase conjugating architecture suitable for deployment as (lie core building block in retrodirective antenna arrays, which can be scaled to any number of elements in a modular way without impacting on complexity. Our solution is based on a modified in-phase and quadrature modulator architecture, which completely resolves four major shortcomings of the conventional mixer-based approach currently used for the synthesis of phase conjugated energy derived from a sampled incoming wavefront. 1) The architecture presented removes the need for a local oscillator running at twice the RF signal frequency to be conjugated. 2) It maintains a constant transmit power even if receive power goes as low as -120 dBm. 3) All unwanted re-transmit signal products are suppressed by at least 40 dB. 4) The issue of poor RF-IF leakage prevalent in mixer-based phase-conjugation solutions is completely mitigated. The circuit has also been shown to have high conjugation accuracy (better than +/-1 degrees at -60-dBm input). Near theoretically perfect experimental monostatic and bistatic results are presented for a ten-element retrodirective array constructed using the new phase conjugation architecture.