214 research outputs found
Analysis of the Effect of EBG on the Mutual Coupling for a two-PIFA Assembly.
yesSize constraints and mutual coupling on the
performance of a two-element PIFA assembly are investigated
for a design frequency of 2.4 GHz. A benchmark antenna
assembly, employing a normal metallic ground plane is
compared with an EBG modified ground plane. The height of the
antenna elements over the EBG is optimised, and an isolation
factor of 9.12 dB is achieved for a gap of 2.5 mm. Prototype
structures have been constructed and measured for both cases
Compact Microstrip Antenna Design for Microwave Imaging
YesAn ultra-wideband microstrip antenna design is
considered with respect to applications in breast cancer
detection. The underlying design concept is based on ground
penetrating radar (GPR). Simulated and measured prototype
performance show excellent performance in the input impedance
and radiation pattern over the target range from 4 GHz to 8
GHz. The 4 GHz to 8GHz frequency band for microwave
imaging perform better in comparison with other microwave
frequencies. The antenna also shows a reasonable uniform
radiation performance in the broadside direction which
contributes to the reduction of clutter levels, thus aiding the reconstruction quality of the final image
A Capacitively loaded Antenna for use in Mobile Handsets
YesA tuneable slotted patch antenna design is presented and verified for use in the DCS, PCS and UMTS bands. The tuning circuit consists of two varactor diodes with some passive components, and is integrated fully with the r radiator patch, with the varactors occupying different locations over the slot. The tuning does not require any further modification to the patch or feed geometry. Good agreement is observed between the predicted and observed impedance bandwidth, return loss, gain and radiation pattern, throughout the range 1.70 GHz-2.05 GHz
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Optimum Design of Doherty RFPA for Mobile WiMAX Base Stations
YesRF power amplifiers in mobile WiMAX transceivers operate in an inherently nonlinear manner. It is possible to amplify the signal in the linear region, and avoid distortion, using output power back-off; however, this approach may suffer significant reduction in efficiency and power output. This paper investigates the use of Doherty techniques instead of back-off, to simultaneously achieve good efficiency and acceptable linearity. A 3.5 GHz Doherty RFPA has been designed and optimized using a large signal model simulation of the active device, and performance analysis under different drive levels. However, the Doherty EVM is generally poor for mobile WiMAX. Linearity may be improved by further digital pre-distortion, and a simple pre-distortion method using forward and reverse AM-AM and AM-PM modeling. Measurements on the realized amplifier show that this approach satisfies the EVM requirements for WiMAX base stations. It exhibits a PAE over 60%, and increases the maximum linear output power to 43 dBm, whilst improving the EVM
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Calculation of the Spatial Envelope Correlation Between Two Antennas in Terms of the System Scattering Parameters Including Conducting Losses.
yesThe envelope correlation for a two-element antenna
array may be calculated using the antenna radiation fields, or
more simply from the scattering parameters of the system. The
use of scattering parameters provides a major simplification over
the direct use of field data. In this paper we propose a
modification of the scattering parameter method which also
includes the antenna losses. This approach has the advantage of
simplifying the antenna design process, especially when low
envelope correlations are needed. It also offers a better
prediction of the spatial envelope correlation, and a good
framework for understanding the effects of the mutual coupling.
The accuracy of this proposed method is illustrated by two
examples
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Improvements in Multicarrier Modulation Systems using a Wavelet OFDM Scheme
yesThis paper investigates the performance of wavelet OFDM signals
over a wireless communications link. The scheme is shown to be generally
similar to Fourier based OFDM, but with some additional features, and
improved characteristics. The sensitivity of both schemes to the nonlinear
amplification in the transmitter is compared by monitoring the time domain
output data and the adjacent channel power ratio (ACPR) performance
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Explanation of DC/RF Loci for Active Patch Antennas
YesA characteristic loop locus of dc power versus RF output power was observed as the frequency was varied around the optimum point of an operational active antenna. A new technique was introduced into the simulation, plotting the dependence of parameters such as supply current, efficiency or output power on internal impedance as seen by the naked transistor. It is now clear that the loop was formed as a consequence of the interaction of the transistor packaging elements with the patch impedances
Design of a Planar Inverted F-L Antenna (PIFLA) for Lower-band UWB Applications
YesThis paper examines the case for an ultrawideband
planar inverted-F-L-antenna design intended
for use in the lower sub-band. The antenna construction is
based on the conventional inverted F, and inverted L as
its feed element, and parasitic element, respectively. The
optimized antenna size is 30×15×4mm3. The prototype
antenna has a good return loss of -10 dB, and a 66.6%
impedance bandwidth (2.8 GHz ¿ 5.6 GHz), the gain
varies between 3.1 dBi and 4.5 dBi
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A Frequency Tunable PIFA Design for Handset Applications.
yesA frequency tunable planar inverted F antenna (PIFA) is presented for use in the following bands: DCS, PCS, and UMTS. Initially, the tuning was achieved by placing a lumped capacitor, with values in the range of 1.5 to 4 pF, along the slot of the radiator. The final tuning circuit uses a varactor diode, and discrete lumped elements are fully integrated with the antenna. The antenna prototype is tunable over from 1850 MHz to 2200 MHz, with an associated volume of 21×13.5×5 mm3, making it suitable for potential integration in a commercial handset or mobile user terminal
Risk Factors and Outcome of Varicella-Zoster Virus Pneumonia in Pregnant Women
To determine the factors associated with an increased risk of developing varicella-zoster virus (VZV) pneumonia during pregnancy, a case-control analysis was done in which 18 pregnant women with VZV pneumonia were compared with 72 matched control subjects. VZV infection was identified clinically, and VZV pneumonia was diagnosed by dyspnea and findings on chest radiographs. Of 347 pregnant women with VZV infection, 18 (5.2%) had pneumonia treated with acyclovir, and none died. Mean gestational age at rash onset was 25.8 ± 8.8 weeks for patients with pneumonia and 17.7 ± 10.3 weeks for control subjects, which was not significant in the multivariable model. Women with VZV pneumonia were significantly more likely to be current smokers (odds ratio [OR], 5.1; 95% confidence interval [CI], 1.6–16.7) and to have \u3e100 skin lesions (OR, 15.9; 95% CI, 1.9–130.2). Pregnant women with VZV infection may be more likely to develop varicella pneumonia if they are smokers or manifest \u3e100 skin lesions
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