Ultra-wide Frequency Bandwidth Research Articles

Design and Development of Ultra-Wideband 3-D Monopole Antennas Based on Supercurves

This article deals with the design and development of supershaped monocone and rotationally symmetric monopole antennas with omnidirectional radiations to cover an ultra-wide frequency bandwidth. The attractive feature of supercurves is their ability to generate various complex and nonintuitive curves, and shapes through a simple mathematical equation called superformula. In the proposed designs, the surface profiles of monocone and rotationally symmetric monopole antennas are expressed using supercurves and the six unknown parameters of superformula are optimized to fulfill the bandwidth and radiation pattern requirements. The use of supercurves is extremely effective in reducing computational complexity and saving a lot of computation time. The electromagnetic performances of the proposed antennas are investigated by the simulations and experiments. The measured results reveal that the proposed monopoles satisfactory radiation characteristics over the 26:1 and 43:1 impedance bandwidths. The findings are valuable for the design and evaluation of ultra-wideband antennas and the proposed monopoles can be used as good candidates at various communication applications.

Compact Ultra-Wideband Phase Inverter Using Microstrip-CPW-Slotline Transitions

A planar ultra-wideband phase inverter, which consists of a series of transitions between microstrip, coplanar waveguide, and slotline, is designed and implemented. This compact-sized phase inverter can be used to generate wideband 180° phase differential signals, especially at high microwave frequencies up to millimeter-waves. The design is based on the impedance matching and smooth field transformation between the transitional stages. The fabricated transition has dimensions of 7.36 mm × 5.08 mm, and provides ultra-wide frequency bandwidth from 13 GHz to 38 GHz with low insertion loss of better than 2 dB within ±5° phase deviation and with return loss of greater than 10 dB.

Integration of Rotation Estimation and High-Order Compensation for Ultrahigh-Resolution Microwave Photonic ISAR Imagery

The microwave photonic (MWP) radar technique is capable of providing ultrawide frequency bandwidth waveforms to generate ultrahigh-resolution (UHR) inverse synthetic aperture radar (ISAR) imagery. Nevertheless, conventional ISAR imaging algorithms have limitations in focusing UHR MWP-ISAR imagery, where high-precision high-order range cell migration (RCM) and phase correction are crucially necessary. In this article, a UHR MWP-ISAR imaging algorithm integrating rotation estimation and high-order motion terms compensation is proposed. By establishing the relationship between parametric ISAR rotation model and high-order motion terms, an average range profile sharpness maximization (ARPSM) is developed to obtain rotation velocity by using nonuniform fast Fourier transform (NUFFT). Second-order range-dependent RCM is corrected with parametric compensation model by using the rotation velocity estimation. Furthermore, the spatial-variant high-order phase error is extracted to compensation by the entire image sharpness maximization (EISM). A new imaging framework is established with two one-dimensional (1-D) parameter estimations: ARPSM and EISM. Extensive experiments demonstrate that the proposed algorithm outperforms traditional ISAR imaging strategies in high-order RCM correction and azimuth focusing performance.

An Isolation Enhanced, Printed, Low-Profile UWB-MIMO Antenna with Unique Dual Band-Notching Features for WLAN and WiMAX

Here, a low-profile, printed, ultra-wideband (UWB), multiple-input–multiple-output (MIMO) antenna with unique dual band-notching feature for selective elimination of the interferences from the existing WLAN and WiMAX bands has been investigated. The antenna proposed here consists of two fractal radiators and a defected ground structure. The designed antenna shows an ultra-wide frequency bandwidth of 8.6 GHz (2.0–10.6 GHz). A slot having the shape of the English Letter “U” has been finely etched from the surface of the fractal radiators in order to realize a frequency band-notch, centered at 3.5 GHz (WiMAX). A second band-notch, centered at 5.2 GHz (WLAN) has been obtained by adding horizontal stubs. The prevailing issue of mutual isolation between the adjacent radiating elements has been significantly enhanced by incorporating a vertical decoupling strip at the rear side of the proposed two-port diversity MIMO antenna. The antenna proposed here is compact in shape, having a dimension of 26 × 35 mm2. Simulated and measured results show a good match, justifying its applicability in the modern communication era.

Optical imaging of post-embryonic zebrafish using multi orientation raster scan optoacoustic mesoscopy

Whole-body optical imaging of post-embryonic stage model organisms is a challenging and long sought-after goal. It requires a combination of high-resolution performance and high-penetration depth. Optoacoustic (photoacoustic) mesoscopy holds great promise, as it penetrates deeper than optical and optoacoustic microscopy while providing high-spatial resolution. However, optoacoustic mesoscopic techniques only offer partial visibility of oriented structures, such as blood vessels, due to a limited angular detection aperture or the use of ultrasound frequencies that yield insufficient resolution. We introduce 360° multi orientation (multi-projection) raster scan optoacoustic mesoscopy (MORSOM) based on detecting an ultra-wide frequency bandwidth (up to 160 MHz) and weighted deconvolution to synthetically enlarge the angular aperture. We report unprecedented isotropic in-plane resolution at the 9–17 μm range and improved signal to noise ratio in phantoms and opaque 21-day-old Zebrafish. We find that MORSOM performance defines a new operational specification for optoacoustic mesoscopy of adult organisms, with possible applications in the developmental biology of adulthood and aging.

Micromachined piezoelectric ultrasonic transducer with ultra-wide frequency bandwidth

An ultrasonic transducer with a wide frequency bandwidth is always preferred for diagnostic ultrasound imaging, because a wide frequency bandwidth can reduce the duration of an ultrasonic pulse and enhance the axial imaging resolution. However, the frequency bandwidth of both conventional ultrasonic transducer and normal piezoelectric micromachined ultrasonic transducer (pMUT) is quite limited. To overcome this limitation, the mode-merging pMUT is presented in this letter. By using the rectangular membrane with large length/width aspect ratio, several resonant modes are excited within a narrow frequency range. When this pMUT works in a largely damped medium, excited modes are merged together and result in an ultra-wide bandwidth. A −6 dB bandwidth of 95% is measured in water for the proposed pMUT without matching layer, which is much broader than that of conventional pMUTs. Benefited from such ultra-wide frequency bandwidth, the pulse duration of 1 μs is achieved at a central frequency of 1.24 MHz. If this ultra-wide bandwidth pMUT is utilized to replace the conventional transducer for diagnostic ultrasound imaging, the axial resolution can be significantly enhanced without compromising imaging depth.

SAW tags for the 6-GHz range.

The possibility of using 6-GHz frequencies for passive SAW tags is discussed. An example of an inline 6-GHz SAW tag design is presented. Supposing that an ultrawide frequency bandwidth B = 775 MHz can be used, the tag dimensions can be significantly reduced and the loss of reflected response remains at an acceptable level of around 50 dB. The devices were manufactured using E-beam lithography and, probed on wafer, show performance close to predicted, including the loss level of approximately 55 dB. The possibility of high-throughput manufacturing by combining nano-imprint and e-beam lithography is discussed.