Metamaterial with polarization and direction insensitive resonant transmission response mimicking electromagnetically induced transparency

We report on a planar metamaterial, the resonant transmission frequency of which does not depend on the polarization and angle of incidence of electromagnetic waves. The resonance results from the excitation of high-Q antisymmetric trapped current mode and shows sharp phase dispersion characteristic to Fano-type resonances of the electromagnetically induced transparency phenomenon

Analog Least Mean Square Loop for Self-Interference Cancellation in Generalized Continuous Wave SAR

© 2018 IEEE. Generalized continuous wave synthetic aperture radar (GCW-SAR) is a promising new imaging radar system since it applies the full-duplex (FD) transmission technique to achieve continuous signaling in order to overcome several fundamental limitations of the conventional pulsed SARs. As in any FD wireless communication system, self-interference (SI) is also a key problem which can impact on the GCW-SAR system. In this paper, the analog least mean square (ALMS) loop in the radio frequency domain is adopted to cancel the SI for a GCW-SAR system with periodic chirp signaling. The average residual SI power after the ALMS loop is analyzed theoretically by a stationary analysis. It is found that the ALMS loop not only works with random signals in general FD communication systems, but also works well with the periodic signal in GCW-SAR systems. Simulation results show that over 45 dB SI cancellation can be achieved by the ALMS loop which ensures the proper operation of the GCW-SAR system

Frequency-domain characterization and performance bounds of ALMS loop for RF self-interference cancellation

© 1972-2012 IEEE. Analog least mean square (ALMS) loop is a promising method to cancel self-interference (SI) in in-band full-duplex (IBFD) systems. In this paper, the steady state analyses of the residual SI powers in both analog and digital domains are firstly derived. The eigenvalue decomposition is then utilized to investigate the frequency domain characteristics of the ALMS loop. Our frequency domain analyses prove that the ALMS loop has an effect of amplifying the frequency components of the residual SI at the edges of the signal spectrum in the analog domain. However, the matched filter in the receiver chain will reduce this effect, resulting in a significant improvement of the interference suppression ratio (ISR). It means that the SI will be significantly suppressed in the digital domain before information data detection. This paper also derives the lower bounds of ISRs given by the ALMS loop in both analog and digital domains. These lower bounds are joint effects of the loop gain, tap delay, number of taps, and transmitted signal properties. The discovered relationship among these parameters allows the flexibility in choosing appropriate parameters when designing the IBFD systems under given constraints

Cold-sintered temperature stable Na0.5Bi0.5MoO4–Li2MoO4 microwave composite ceramics

© 2017 American Chemical Society. A cold sintering process (150 °C, 30 min and 200 MPa) was employed to fabricate Na 0.5 Bi 0.5 MoO 4 -Li 2 MoO 4 (NBMO-LMO) composites with up to 96.4% relative density. X-ray diffraction traces, backscattered electron images and Raman spectra indicated the coexistence of NBMO and LMO phases in all composites with no detectable secondary phases. The pemittivity (ϵ r ) and temperature coefficient of resonant frequency (TCF) decreased, whereas microwave quality factor (Q × f) increased, with increasing weight % LMO. Near-zero TCF was obtained for NBMO-20 wt %LMO with ϵ r ∼ 17.4 and Q × f ∼ 7470 GHz. Functionally graded ceramics were also fabricated with 5 ≤ ϵ r ≤ 24. To illustrate the potential of these cold sintered composites to create new substrates and device architecture, a dielectric graded radial index lens was designed and simulated based on the range of ϵ r facilitated by the NBMO-LMO system, which suggested a 78% aperture efficiency at 34 GHz

Fully fabric knitted antennas for wearable electronics

The worldwide wearable technology market is expected to exceed $6B by 2016 and wearable antennas will be used by the emergency services, fashion designers, military, athletes and patients. Exploring different methods of fabricating antennas is important especially as user comfort and aesthetics are key considerations in ensuring mainstream acceptance. Previously the authors have examined embroidered antennas using highly conductive threads [Chauraya et al. EuCAP 2012]. Please see this paper for a detailed literature review of wearable antennas. In this paper, we examine knitting as a technique of fabricating antennas. These antennas were fully fabric with a knitted ground plane, a knitted substrate and a knitted patch element. They were fabricated using industrial knitting machinery and hence could potentially be scaled up to mass-manufacture. Four different versions were considered (all had a knitted ground plane and substrate): i) a conducting coated nylon fabric (Nora Dell); ii) a knitted patch with a high fiber density (Sample 1); iii) a knitted patch with a medium fiber density (Sample 2) and iv) a knitted patch with a coarse fiber density (Sample 3). The resulting antennas were extremely flexible and soft to the touch. The return loss results are shown in the figure. All the antennas were fed with a probe feed positioned the same distance from the edge of the patch - the magnitude of the return loss could be improved by finding the optimal feeding point. The S11 and associated bandwidth results of the antennas suggests that the Nora Dell antenna exhibits the smallest losses. The results also indicate that the losses of the knitted antennas improve as the knitted patches became denser. The presentation will include measured radiation patterns, efficiency results and an in-depth analysis of the strengths and weaknesses of this manufacturing technique

Analog Least Mean Square Loop for Self-Interference Cancellation in Generalized Continuous Wave SAR

Generalized continuous wave synthetic aperture radar (GCW-SAR) is a promising new imaging radar system since it applies the full-duplex (FD) transmission technique to achieve continuous signaling in order to overcome several fundamental limitations of the conventional pulsed SARs. As in any FD wireless communication system, self-interference (SI) is also a key problem which can impact on the GCW-SAR system. In this paper, the analog least mean square (ALMS) loop in the radio frequency domain is adopted to cancel the SI for a GCW-SAR system with periodic chirp signaling. The average residual SI power after the ALMS loop is analyzed theoretically by a stationary analysis. It is found that the ALMS loop not only works with random signals in general FD communication systems, but also works well with the periodic signal in GCW-SAR systems. Simulation results show that over 45 dB SI cancellation can be achieved by the ALMS loop which ensures the proper operation of the GCW-SAR system

High quality factor cold sintered Li2MoO4BaFe12O19 composites for microwave applications

Ceramics-ceramic composites in series (1-x)Li2MoO4-xBaFe12O19 (LMO-BF12, 0.00 ≤ x ≤ 0.15) have been cold sintered at 120 °C and their structure and properties characterized. X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed that compositions were dual phase and had a dense microstructure. Composites in the xBF12-(1-x)LMO (0.0 ≤ x ≤ 0.15) series resonated at MW frequencies (∼6 GHz) with 5.6≤εr ≤ 5.8 and Qf = 16,000–22,000 GHz, despite the black colour of compositions with x > 0. The permeability of the composites was measured in the X band (∼8 GHz) and showed an increase from 0.94 (x = 0.05) to 1.02 (x = 0.15). Finite element modelling revealed that the volume fraction of BF12 dictates the conductivity of the material, with a percolation threshold at 10 vol% BF12 but changes in εr as a function of x were readily explained using a series mixing model. In summary, these composites are considered suitable for the fabrication of dual mode or enhanced bandwidth microstrip patch antennas

Frequency-domain characterization and performance bounds of ALMS loop for RF self-interference cancellation

Analog Least Mean Square (ALMS) loop is a promising method to cancel self-interference (SI) in in-band fullduplex (IBFD) systems. In this paper, the steady state analyses of the residual SI powers in both analog and digital domains are firstly derived. Eigenvalue decomposition is then utilized to investigate the frequency domain characteristics of the ALMS loop. Our frequency domain analyses prove that the ALMS loop has an effect of amplifying the frequency components of the residual SI at the edges of the signal spectrum in the analog domain. However, the matched filter in the receiver chain will reduce this effect, resulting in a significant improvement of the interference suppression ratio (ISR). It means that the SI will be significantly suppressed in the digital domain before information data detection. This paper also derives the lower bounds of ISRs given by the ALMS loop in both analog and digital domains. These lower bounds are joint effects of the loop gain, tap delay, number of taps, and transmitted signal properties. The discovered relationship among these parameters allows the flexibility in choosing appropriate parameters when designing the IBFD systems under given constraints

Low-Cost Ultrawideband High-Gain Compact Resonant Cavity Antenna

© 2002-2011 IEEE. A 3-D printed planar permittivity-gradient superstrate (PGS) is used to improve the directive radiation characteristics of a waveguide-fed compact resonant cavity antenna (CRCA). Far-field directivity of classical uniform superstrate-based RCAs is limited due to nonuniform aperture phase distribution caused by even transmission through the superstrate. Transverse PGS has been used here to remarkably improve aperture phase distribution and hence directive radiation performance of RCAs. Furthermore, the PGS was rapidly prototyped in one hour and 43 min using a low-cost acrylo-butadiene styrene (ABS) filament without using traditional multistep milling and machining. Single step fabrication was performed and effective dielectric constant of the ABS was varied through controlled infill percentage in different regions of the PGS. Measurements of a prototype indicate unrivaled results, from a smaller footprint, which includes peak directivity of 16.048 dB, 3 dB directivity bandwidth of 49.65% and sidelobe levels lower than -10.4 dB throughout the operating frequency band. The 3-D printed PGS thus outperforms all previously reported superstrates, for RCAs, by demonstrating similar radiation performance with an equivalent material cost of only 0.41 USD

Printed frequency selective surfaces on textiles

This article is closed access.A novel technique for inkjet printing frequency selective surfaces (FSSs) on textiles is introduced. The challenge of printing an inkjet layer of 3 μm thickness on polyester cotton with a surface roughness of the order of 150 μm is achieved with a screen-printed interface layer. The conducting inkjet layer is then printed directly on top of the interface layer. A screen mask was used so that the interface layer was only printed directly below the conducting ink. A square FSS structure has been fabricated and the measured shielding has been compared to simulation