Synthetic bandwidth radar for ultra-wideband microwave imaging systems

A synthetic bandwidth radar as an approach to build ultra-wideband (UWB) imaging systems is presented. The method provides an effective solution to mitigate the challenges of UWB antenna's implementation with ideal performance. The proposed method is implemented by dividing the utilized UWB into several channels, or sub-bands, and designing an antenna array that includes a number of antennas equal to the number of channels. Each of those antennas is designed to have excellent properties across its corresponding channel. As part of the proposed approach, a two-stage calibration procedure is used to accurately estimate the effective permittivity of a heterogeneous imaged object at different angles and the phase center of each antenna for accurate delay time estimation. When imaging an object, each of the antennas transmits and captures signals only at its channel. Those captured signals are properly combined and processed to form an image of the target that is better than the current systems that use array of UWB antennas. The presented method is tested on breast imaging using the band 3-10 GHz via simulations and measurements on a realistic heterogeneous phantom

Effects of hospital facilities on patient outcomes after cancer surgery: an international, prospective, observational study

Background Early death after cancer surgery is higher in low-income and middle-income countries (LMICs) compared with in high-income countries, yet the impact of facility characteristics on early postoperative outcomes is unknown. The aim of this study was to examine the association between hospital infrastructure, resource availability, and processes on early outcomes after cancer surgery worldwide.Methods A multimethods analysis was performed as part of the GlobalSurg 3 study-a multicentre, international, prospective cohort study of patients who had surgery for breast, colorectal, or gastric cancer. The primary outcomes were 30-day mortality and 30-day major complication rates. Potentially beneficial hospital facilities were identified by variable selection to select those associated with 30-day mortality. Adjusted outcomes were determined using generalised estimating equations to account for patient characteristics and country-income group, with population stratification by hospital.Findings Between April 1, 2018, and April 23, 2019, facility-level data were collected for 9685 patients across 238 hospitals in 66 countries (91 hospitals in 20 high-income countries; 57 hospitals in 19 upper-middle-income countries; and 90 hospitals in 27 low-income to lower-middle-income countries). The availability of five hospital facilities was inversely associated with mortality: ultrasound, CT scanner, critical care unit, opioid analgesia, and oncologist. After adjustment for case-mix and country income group, hospitals with three or fewer of these facilities (62 hospitals, 1294 patients) had higher mortality compared with those with four or five (adjusted odds ratio [OR] 3.85 [95% CI 2.58-5.75]; p<0.0001), with excess mortality predominantly explained by a limited capacity to rescue following the development of major complications (63.0% vs 82.7%; OR 0.35 [0.23-0.53]; p<0.0001). Across LMICs, improvements in hospital facilities would prevent one to three deaths for every 100 patients undergoing surgery for cancer.Interpretation Hospitals with higher levels of infrastructure and resources have better outcomes after cancer surgery, independent of country income. Without urgent strengthening of hospital infrastructure and resources, the reductions in cancer-associated mortality associated with improved access will not be realised

Planar ultra wideband antennas with rejected sub-bands

A simple method for the design of a coplanar waveguide-fed ultra wideband antenna is presented. The proposed antenna has a rejection capability for a certain undesired sub-band used by other communication systems. The proposed antenna has a uniplanar configuration. The radiating element and the ground plane of the antenna are in a shape of half a circle. Two methods for rejecting the undesired sub-band are presented. In one method, a tuning strip is used at the bottom layer of the antenna facing the radiator at the feeding point, whereas in the other method a tuning slot is made at the radiator. The length of the tuning element can be used to control centre of the rejected sub-band. Results of simulations for the two methods show that the designed antennas have a bandwidth from 3.1 GHz to more than 10.6 GHz with near omnidirectional characteristics. The designed antennas have a radiation efficiency which is higher than 90% over the whole passband. The gain of the antenna at the rejected sub-band is as low as -5 dB proving the filtering characteristics of the antenna at that band

Design of a CPW-fed band-notched UWB antenna using a feederembedded slotline resonator

A complete design method for a compact uniplanar ultra-wideband antenna with subband rejection capability is presented. A slotline resonator is incorporated in the coplanar waveguide feeder of the antenna to act as a bandstop filter, hence enabling the rejection of any undesired band within the passband of the antenna. Two samples of the proposed antenna were designed and manufactured. One of the developed antennas does not contain a resonator, whereas the other contains a slotline resonator. The designed antennas feature a compact size of 27 mm × 27 mm. Results of the simulation and measurement show that the designed antennas have a bandwidth from 3 GHz to more than 11 GHz. The results also reveal that the use of the resonator in the feeder of the antenna efficiently rejects any undesired subband, such as the 4.9–5.9 GHz band assigned for IEEE802.11a and HIPERLAN/2. The gain of the antennas with the resonator is about 2.2 dBi at the passband, while it is less than −8 dBi at the rejected subband

Analytical closed-form solutions for different configurations of parallel-coupled microstrip lines (vol 3, pg 137, 2009)

The author noticed that three of the equations that are published in the paper [1] include typos that cause significant confusion to the researchers and engineers who try to use the derived closed-form model. This letter includes the corrected equations. All the results included in the published paper are correct as they are based on the correct form of the equations

Compact tunable reflection phase shifters using short section of coupled lines

In the design of reflection-type phase shifters, the coupler that represents the shifter's backbone is usually assumed to be a quarter-wavelength 3-dB coupler. In this paper, a derived theoretical model shows that, for certain values for the odd- and even-mode impedances, a coupled structure with a length that is less than one tenth of a wavelength is sufficient to build a high-performance reflection phase shifter. The presented analysis indicates that reflection phase shifters can be designed with a more compact size and larger phase range compared with the conventional method of using a quarter-wavelength 3-dB coupler. However, the required odd-mode impedance in the proposed design is low (≈10 Ω) , whereas the required even-mode impedance is high (≈200 Ω). To realize those impedances when using parallel-coupled lines, slotted ground and shunt chip capacitor are used. The proposed design is supported by full-wave electromagnetic simulations and measurements. The simulated results show that 0.085λ coupled structure achieves 255° phase range across 36% fractional bandwidth with less than 1-dB insertion loss and more than 10-dB return loss. In another design, a full-cycle phase range is obtained with less than 1.5-dB insertion loss across the same band by using two 0.076λ coupled sections. A manufactured prototype for a full-cycle phase range validates the simulation results and, thus, the proposed method