Joshua Le-Wei Li

Wide-angle and polarization-independent metamaterial absorber based on snowflake-shaped configuration

A metamaterial absorber (MA) based on snowflake-shaped resonators is designed and experimentally demonstrated in this paper. Such an MA possesses a nearly perfect absorption with wide angle of incidence and polarization independence. The measurement in a rectangular waveguide system shows the absorptivity as high as 99.5% at 11.28 GHz. Furthermore, the operating frequency can be flexibly controlled by adjusting the lengths of the snowflakes branches, while keep the peak absorptivities nearly uniform (>97.5%). The proposed MA is sure to find wide applications in, for instance, stealth technology, thermal detector and imaging.

Compact coupled-fed wideband antenna for internal eight-band LTE/WWAN tablet computer applications

In this article, a compact coupled-fed antenna for eight-band LTE/WWAN tablet computer applications is proposed. The designed antenna consists of an L-shaped monopole, a long meandered strip, a long radiation strip, and a short shorted strip. The long meandered strip and long radiation strip can generate a dual-resonance characteristic for the antenna’s lower band, making it capable of a wideband operation to cover the desired LTE700/GSM850/900 (698–960 MHz) bands. Furthermore, the notch in the long radiation strip can also influence the bandwidth of the antenna’s lower band. The long radiation strip can generate an additional higher order resonant mode at the upper band, combining the two resonant modes contributed by the L-shaped monopole and the short shorted strip to form a wide upper band, covering GSM1800/1900/UMTS2100/LTE2300/2500 (1710–2690 MHz) bands. With the proposed scheme, the antenna only occupies a small volume of 60 12 4 mm3 and can mainly be disposed on a 0.8-mm thick FR4 substrate. The antenna is mounted at the top edge of the display ground which supports a 150 200 mm2 display for the tablet computer. Reasonably good radiating efficiency and antenna gain are also achieved for the practical tablet computer.

A Novel Ultra-Wideband Antenna with Distributed Inductance for Wireless Usb Dongle Attached to Laptop Computer

A novel printed ultra-wideband wireless USB dongle antenna designed utilizing a long meandered strip as a distributed inductance to enhance input impedance matching over the desired lower bands of 698–960 MHz has been proposed in the paper. The antenna is a PIFA of uniplanar configuration, which comprises a big radiating plate with a long meandered strip and a lump chip capacitance in order to improve operating band impedance matching. Therefore, it covers entire eight bands of LTE700/GSM850/900/DCS1800/PCS1900/UMTS2100/LTE2300/2500WWAN in operation. A 50-Ω microstrip feed line printed on the other side along the antennas system ground plane is applied to excite the antenna. By incorporating the scheme, two very wide operating bandwidths (3:1 VSWR or 6-dB return loss) of about 400 MHz (from 600 to 1000 MHz) and 1750 MHz (from 1250 to 3000 MHz) are obtained, although the radiating PIFA patch is of size 20 × 20 mm2, and a simple structure above the top of the antennas system circuit board is used to support the design. In addition, the antenna (as a surface-mountable antenna) can be printed on a thin FR4 substrate of size 70 × 20 × 0.8 mm3, making it promising for USB dongle applications. Finally, details of the proposed antenna are illustrated and discussed, where perfect return loss is measured and simulated. Reasonably good radiating efficiency and antenna gain are also achieved for practical laptop computers.

Non-invasive breast cancer thermotherapy studies using conformal microstrip antennas

In this paper, a circular and a toroidal conformal microstrip antenna are proposed for a simplified non-invasive microwave breast cancer therapy and the Specific Absorption Rate (SAR) in the breast and heart model is analyzed based on the simulated results by HFSS using Finite Element Method (FEM). Different schemes of antenna ground plane are considered in the simulation to find the best focusing effects in the tumor region. By comparing the simulation results, the conclusion can be drawn that the focusing effect in tumor region is enhanced when the size of antenna ground decreases. Moreover, the toroidal antenna with inner radius of 15mm has a better focusing effect when antenna shape changes from circular to toroidal. In the meantime, the SAR value in heart region is much smaller than that in breast region, i.e. heart is in good condition.

Forward-looking bistatic SAR imaging based on high-order range equation and high-order phase compensation

Synthetic aperture radar (SAR) techniques are typically used to achieve a high azimuth resolution, but conventional monostatic SAR is not applicable in forward direction because of azimuth ambiguities and poor Doppler resolution. This paper focuses on SAR imaging processing in a novel forward-looking bistatic configuration that a pilotless plane transmits signals and a guided missile receives echo which can avoid image ambiguities and to improve the azimuth resolution. A fourth-order range equation and a fourth-order phase term are adopted to improve the accuracy in the approximation of the range history and two-dimensional spectrum for forward-looking bistatic SAR, respectively. The spectrum is used for high-order phase compensation, range compression, secondary range compression, range cell migration correction, and azimuth compression. Especially, the proposed algorithm is able to focus the translational variant bistatic configuration where the transmitter and receiver platforms are moving in parallel tracks with different velocities and high squints. Finally, simulations validate the effectiveness of the algorithm.

Tunable triple-band negative permeability metamaterial consisting of single-loop resonators and ferrite

We numerically propose a novel tunable metamaterial with triple bands of negative permeabilities. This metamaterial is composed of an array of single-loop resonators (SLRs) and ferrite slabs, where the SLRs provide two magnetic resonances while the ferrite slabs under an applied dc magnetic bias give rise to the third magnetic resonance. By adjusting the intensity of the dc magnetic bias, it is able to tune all the three magnetic resonances. The -negative features of these resonant bands are investigated by retrieving the constitutive parameters from simulated -parameters. The results in this paper open a new approach for designing tunable multiband metamaterials, which is sure to find extensive applications in fields such as tunable multiband notched ultra-wideband (UWB) antennas, tunable multiband perfect lens, and tunable multiband absorbers.

Printed multi-resonant antenna embedding two inductors in radiating strips for internal mobile phone LTE/WWAN operation

In this article, a planar printed antenna for eight-band LTE/WWAN operation applied in the internal mobile phone has been proposed and studied. The presented antenna consists of a feeding strip and a coupling strip, where two chip inductors with different inductances are loaded in place. The desired lower bands of LTE700/GSM850/900 operation can be achieved by the coupling strip loading an inductor of 12 nH and a longer branch loading another inductor of 24 nH in the feeding strip, which provide a quarter-wavelength dual-resonance mode at 720 and 900 MHz. While a quarter-wavelength resonant mode at around 2.95 GHz can be generated by the shorter branch of the feeding strip, and other resonant modes at 1.92 and 2.23 GHz are contributed by the higher-order resonant modes of the long feeding strip and coupling strip, covering the desired upper bands of DCS1800/PCS1900/UMTS2100/LTE2300/2500 operation. In fact, the desired resonant lengths in the lower frequencies can be decreased, and impedance matching can be properly adjusted with the help of the two embedded inductors. Besides, a chip inductor of 2.2 nH is helpful for improving all the bands’ impedance matching. Detailed considerations of the antenna design and main parameters are studied and measured.

Gain enhancement of axial-mode helical antenna with a cylindrical ring

This paper proposed a helical antenna with a cylindrical ring above the antenna along the axial direction. Compared with the traditional helical antenna gain boosting techniques, without adding coil number, the gain of the proposed antenna is enhanced by a maximum of 3.8dB in the working bandwidth by adding a cylindrical ring, while the impedance matching bandwidth and other antenna characteristics remain.

Printed slot antenna for seven-band GSM/UMTS/LTE operation in the internal mobile phone

In this paper, a promising internal printed slot antenna for seven-band operation applied to the mobile phone has been proposed, covering all the five WWAN (namely, Wireless Wide Area Network) bands of GSM850/900/DCS1800/PCS1900/UMTS2100 and two LTE (namely, Long Term Evolution) bands of LTE2300/2500. With the use of slot elements, the presented antenna can be easily printed on an inexpensive FR4 substrate and shows a planar structure for low-profile mobile handsets. The antenna comprises an inverted L-shaped slot and three open-ended monopole slots, and these slot elements are integrated into a compact configuration to occupy a small area of 15 mm  40 mm in the back side of the system circuit board. A 50- microstrip feed line is employed to excite the designed antenna, which is printed on the top side of the PCB (Printed Circuit Board). Details of the antenna design, simulated and measured results on the return loss and radiation characteristics of the proposed antenna are presented and discussed.

A multiple-grid p-FFT with IE-DDM for analyzing scattering from structures above a half space

In this paper, a multiple-grid precorrected fast Fourier transform (MG-pFFT) based on the integral equation domain decomposition method (IE-DDM) is presented for multi-scale, dynamic electromagnetic scattering problems in half space. In the framework of the IE-DDM, the proposed method employs multiple auxiliary FFT grids in each domain. Numerical experiments validate the reduced complexity and accuracy of this method. It is also shown that the proposed method is an efficient and robust preconditioner for the original IE system in half space.