Large Fractional Bandwidth Research Articles

Super-Resolution Doppler Velocity Estimation by Kernel-Based Range–$\tau$ Point Conversions for UWB Short-Range Radars

Lower band ultrawideband (UWB) Doppler radar is promising for through-wall imaging, e.g., human body detection in rescue scenarios. The inherent problem with pulse-Doppler radar is the tradeoff between the Doppler velocity resolution and the resulting temporal resolution that makes it difficult to conduct real-time target tracking, because the separation of micro-Doppler velocities of the human body requires a higher Doppler velocity resolution. This problem is particularly severe for lower band UWB radar systems, which are required to attain a sufficient penetration depth in concrete material in the through-the-wall imaging scenario. Because UWB signals generally have large fractional bandwidths, the reflected pulse is located over a range gate along the slow-time direction; this is well known as the range walk problem. As a promising solution to this problem, this article newly introduces a technique for a super-resolution Doppler velocity estimation algorithm based on Gaussian kernel density estimation, which converts observed range– $\tau $ points to Doppler-associated ranges. In addition, this approach makes an important contribution for super-resolution range extraction with a compressed sensing (CS) filter, which is combined with the range-point migration (RPM) method for human body imaging associated with micro-Doppler components. 2-D or 3-D numerical simulations, including human body imaging scenario, demonstrate that the proposed method allows both accurate Doppler velocity estimation and human body imaging, which can be updated at the pulse-repetition interval.

A 39-GHz Frequency Tripler With >40-dBc Harmonic Rejection for 5G Communication Systems in 28-nm Bulk CMOS

The generation of the carrier signal with a very low spur level is a key challenge in all the communication systems, especially those operating at mm-waves, where a frequency multiplier is typically used to break the tradeoff between high frequency of operation and low phase noise. This letter describes a frequency tripler tailored to cover the fifth generation new radio 39-GHz frequency range. By embracing the edge-combining concept, together with the combination of a single-stage polyphase filter and a multipoint injection-locked ring oscillator, the proposed frequency multiplier is able to offer robust and consistent high harmonic rejection ratio over a large fractional bandwidth. Fabricated in 28-nm bulk CMOS technology, the measured frequency multiplier features >40-dBc harmonic rejection over an outstanding 35% fractional bandwidth, while consuming 25 mW only from 0.9-V supply. To the best of our knowledge, the proposed multiplier achieves the highest harmonic rejection among the state-of-the-art multipliers in CMOS and BiCMOS technologies, while having 60% smaller area.

3-D Printed Antenna for Snowpack Monitoring

Microwave radars represent a viable solution to perform rapid and nondestructive snowpack analyses. Depending on the working frequency, they are required to provide a suitable compromise between the penetration depth and the spatial resolution. For these reasons, antennas able to cover relatively large fractional bandwidths at a few gigahertz are fundamental, while minimizing the antenna mass and volume to do not jeopardize the portability often required to these systems. This letter presents the development and the experimental results of a novel antenna realized by three-dimensional printing, based on a double-ridge waveguide configuration and on the use of different infill percentages. The operation bandwidth is from 2.3 to 6 GHz, with a gain at the central frequency of around 5 dBi. The antenna is fabricated using low-loss filaments, with a relatively high dielectric constant (4.5); thus, maintaining the mass in the order of 100 g, with an encumbrance of 5.16 × 2.40 × 6.78 cm 3.

Systematic study of the cross polarization introduced by broadband antireflection layers at microwave frequencies.

Implementation of antireflection layers using structured materials is of common use in millimeter- and submillimeter-wave refractive optic systems. In this work we have systematically studied the effect of such structures in the optical propagation with special emphasis on the cross polarization they introduce. We have performed extensive simulations and experimental verification of several commonly used structures: concentric grooves, parallel grooves, an array of boxes, an array of cylinders, and rectangular- versus triangular-shaped grooves. As a result, we propose optimal structures for demanding applications in terms of polarization and return losses over large fractional bandwidths.

A Cross-Stacked Radiating Antenna With Enhanced Scanning Performance for Digital Beamforming Multifunction Phased-Array Radars

This contribution presents the results of a dual-polarized radiating element designed to achieve low cross-polarization (lower than −40 dB measured for the E-and H-plane, at least −30 dB in the D-plane based on simulations) and large fractional bandwidth (18%) over wide scanning angles (±60°). The proposed design includes multiple features that enable high isolation between ports, reduction of spurious radiation, highly symmetrical radiated fields, and suppression of diffracted fields between contiguous subarray gaps. To verify the polarimetric requirements for a weather radar, simulated and measured results, including electronic scanning of the array and embedded element patterns of the antenna, are shown.

A High-Fractional-Bandwidth, Millimeter-Wave Bidirectional Image-Selection Architecture With Narrowband LO Tuning Requirements

An image-selection, two-element transceiver is presented that operates over a large fractional bandwidth (FBW) covering both 71–76 and 81–86 GHz while requiring only 3 GHz of local oscillator (LO) tuning range at the RF mixer. A bidirectional sliding-intermediate frequency (IF) Weaver architecture allows operation in either transmit (TX) or receive (RX) modes. The sliding IF and narrow LO tuning range allow wideband image rejection using only a single-stage polyphase filter. The circuit is implemented in a 90-nm SiGe BiCMOS process and the RF and LO circuitry consume at most 150 and 250 mW, respectively. Measurements show less than ±0.75-dB gain variation over 10 GHz in the TX mode and less than ±1-dB variation over 10-GHz bandwidth in the RX mode. With 16- and 64-quadrature-amplitude modulation (QAM), the error vector magnitude is below −22 and −28.5 dB at the data rates of 12 and 9 Gb/s, respectively.

3.5 GHz longitudinal leaky surface acoustic wave resonator using a multilayered waveguide structure for high acoustic energy confinement

In this paper, the use of a structure comprising a thin LiNbO3 plate and a multilayered acoustic mirror composed of SiO2 and Pt for high-performance longitudinal leaky surface acoustic wave (LLSAW) device is proposed. The mirror is expected to offer a much higher reflectivity than that composed of SiO2 and AlN, which the authors proposed previously. The field distribution of these structures is calculated by using a finite element method. It is shown that the acoustic wave energy of the proposed structure is well confined in the vicinity of the top surface, and that leakage to the substrate is reduced. A one-port resonator is fabricated on the structure and its performance characteristics are evaluated. Owing to a high phase velocity of 6,035 m/s, which is about 1.5 times higher than that of conventional SAWs, a large impedance ratio of 71 dB was achieved at 3.5 GHz in addition to a large fractional bandwidth of 9.5%.

A Broadband Class-AB Power Amplifier With Instantaneous Supply-Switching Efficiency Enhancement for Cable TV Application

A broadband power amplifier is presented, combining a Class-AB core with a novel supply-modulation technique, instantaneous supply switching. High- $f_{{t}}$ NPN cascodes switch the amplifier signal current to high supply or low supply rails depending on instantaneous signal magnitude. Current-mode switching at gigahertz rates enhances efficiency for bandwidths well beyond existing envelope trackers. The 1.35-W peak power and efficiency of 13.6% at 14-dB peak-to-average-power ratio (PAPR) are observed. The combination of $P_{\mathrm {{out}}}$ , large fractional bandwidth, and high-PAPR efficiency exceeds prior art.

Faceting for direction-dependent spectral deconvolution

The new generation of radio interferometers is characterized by high sensitivity, wide fields of view and large fractional bandwidth. To synthesize the deepest images enabled by the high dynamic range of these instruments requires us to take into account the direction-dependent Jones matrices, while estimating the spectral properties of the sky in the imaging and deconvolution algorithms. In this paper we discuss and implement a wideband wide-field spectral deconvolution framework (ddfacet) based on image plane faceting, that takes into account generic direction-dependent effects. Specifically, we present a wide-field co-planar faceting scheme, and discuss the various effects that need to be taken into account to solve for the deconvolution problem (image plane normalization, position-dependent Point Spread Function, etc). We discuss two wideband spectral deconvolution algorithms based on hybrid matching pursuit and sub-space optimisation respectively. A few interesting technical features incorporated in our imager are discussed, including baseline dependent averaging, which has the effect of improving computing efficiency. The version of ddfacet presented here can account for any externally defined Jones matrices and/or beam patterns.

Attenuation limits in longitudinal phononic crystals

The acoustic attenuation inside the bandgaps is, together with the bandgap width, a fundamental design parameter for phononic-crystal-based systems. We discuss approximate expressions for the maximum attenuation inside the bandgaps of one-dimensional longitudinal phononic crystals and its dependence on the acoustic contrast and the fractional bandwidth. We provide different approximations at small and large fractional bandwidths, computed from the trace of the transmission matrix of the crystal elementary cell. We show that, for relatively small gaps, the attenuation is roughly proportional to the fractional bandwidth, in analogy with the flexural case. For larger gaps, a large attenuation can be obtained only for high (and possibly impractical) acoustic contrasts. Approximate expressions are validated through comparison with FEM results. We also derive asymptotic upper limits for the bandgap borders and show that high contrasts do not necessarily lead to wide bandgaps, a fact connected to geometrical phase inversion for the acoustic wave in the crystal. We finally compare the attenuation of flexural and longitudinal waves at a fixed fractional bandwidth and derive regions of optimum attenuation for the two propagation modes.

Lithium Niobate MEMS Chirp Compressors for Near Zero Power Wake-Up Radios

This paper presents the first demonstration of chirp compressors based on laterally vibrating modes in suspended lithium niobate thin films. Both shear-horizontal and length-extensional modes have been explored and demonstrated with the electromechanical coupling coefficients of 30% and 39%, respectively, in a double-dispersive delay line structure. The high electromechanical coupling, along with the low propagation loss in the suspended thin film, produces a low insertion loss of 10 dB over a large fractional bandwidth of 50%. The best fabricated device demonstrates a delay-bandwidth product of 100, and provides a voltage gain of 5 to the corresponding chirp signals. Moreover, significant signal-to-noise ratio enhancements (>100), collectively enabled by the processing gain and filtering characteristics of the chirp compressors, have been demonstrated. The measured devices, in this paper, greatly outperform state-of-the-art chirp compressors based on surface acoustic waves in insertion loss for a comparable TB . As a result, signal-to-noise ratio enhancement and voltage gain have been simultaneously demonstrated for the first time in a passive device and the analog domain. The high performance can be harnessed to greatly enhance the sensitivity of near zero power wake-up radio receivers and enable low-power wireless connectivity for Internet of Things applications. [2017–0126]

Using low-frequency pulsar observations to study the 3-D structure of the Galactic magnetic field

AbstractThe Galactic magnetic field (GMF) plays a role in many astrophysical processes and is a significant foreground to cosmological signals, such as the Epoch of Reionization (EoR), but is not yet well understood. Dispersion and Faraday rotation measurements (DMs and RMs, respectively) towards a large number of pulsars provide an efficient method to probe the three-dimensional structure of the GMF. Low-frequency polarisation observations with large fractional bandwidth can be used to measure precise DMs and RMs. This is demonstrated by a catalogue of RMs (corrected for ionospheric Faraday rotation) from the Low Frequency Array (LOFAR), with a growing complementary catalogue in the southern hemisphere from the Murchison Widefield Array (MWA). These data further our knowledge of the three-dimensional GMF, particularly towards the Galactic halo. Recently constructed or upgraded pathfinder and precursor telescopes, such as LOFAR and the MWA, have reinvigorated low-frequency science and represent progress towards the construction of the Square Kilometre Array (SKA), which will make significant advancements in studies of astrophysical magnetic fields in the future. A key science driver for the SKA-Low is to study the EoR, for which pulsar and polarisation data can provide valuable insights in terms of Galactic foreground conditions.

High‐gain printed monopole arrays with low‐complexity corporate‐feed network

Printed monopole antennas fed by microstrip lines can provide a wide bandwidth and can be employed as terminal antennas in RF circuits. In the same perspective, the authors propose a novel planar array in which N + 1 parasitic monopoles, properly placed in a linear array where only N directly-fed monopoles are used, allow a broadside radiation and a gain value close to that of a standard printed array composed of 2N + 1 directly-fed elements. To verify the validity of the proposed design, prototype arrays for the S and C bands, composed of five- and nine-monopoles, are simulated, fabricated and tested. In addition, it is demonstrated that a flat metal sheet placed at 0.25 λ 0 from the array board can further increase the directivity of about 3 dB; as a result, the measured gain is ∼10 dB for the five-monopole array and 14 dB for the nine-monopole array. Owing to their large fractional bandwidth (30%) and high gain, these monopole arrays may work as external antennas for high-data-rate point-to-point transmissions or for C-band radar sensors.

Cavity-backed metasurface antennas and their application to frequency diversity imaging.

Frequency diversity antennas with spatially structured radiation patterns reduce the reliance on actively switched elements for beamforming which become increasingly expensive and impractical as frequency increases. As the quality factor Q of a frequency diverse antenna increases, the antenna samples more spatial structure as the number of unique radiated coded spatial patterns correspondingly increases. Antennas that combine hollow cavities and metamaterial apertures achieve both large fractional bandwidth, in excess of 40%, and a high Q of 1600, so that each antenna radiates over 640 unique coded patterns. As compared to switched active antennas, such a passive antenna replaces the 50 antennas and switches that would produce at most (50/2)2=625 unique patterns. Furthermore, the engineered metamaterial apertures enable a radiation efficiency exceeding 60% to be achieved in a single desired polarization. The theory of cavity-backed metasurface antennas is explained, and frequency diverse imaging is demonstrated with a pair of these antennas.

Wideband RF Filters Using Medium-Scale Integration of Lithium Niobate Laterally Vibrating Resonators

This letter presents wideband spurious-free microelectromechanical systems (MEMSs) filters based on shear horizontal (SH0) mode Lithium Niobate (LiNbO3) laterally vibrating resonators. The filters, monolithically fabricated on the same chip, have center frequencies at 400 and 750 MHz. The measured performance exhibits in-band ripple-free response, a low insertion loss (IL) of 1.7 dB, a 30-dB shape factor of 1.41, and a 3-dB fractional bandwidth (FBW) of 9.6 %-the largest reported for MEMS-resonator-based filters. The high performance was collaboratively enabled by the LiNbO3 material and filter design. The excellent piezoelectric coupling and low acoustic loss in LiNbO3 thin film ensure the low IL and large FBW, while the medium-scale integration of 200 spurious mode-free resonators fully harnesses the potential of LiNbO3 material without introducing spurious response. The filters have a device footprint less than $360 \times 350\,\,\mu \text{m}^{2}$ , thus suitable for RF frontends in handheld wireless devices.

A Wideband Dual-Polarized L-Probe Antenna Array with Hollow Structure and Modified Ground Plane for Isolation Enhancement

A two-element wideband dual-polarized L-probe antenna array with hollow structure is presented in this letter. The hollow structure is applied to offer space for hosting other antennas (e.g., the concept of shared-aperture antenna). Each radiating element is designed with a compact size of 51 mm × 51 mm × 24.5 mm (0.374λ 0 × 0.374λ 0 × 0.18λ 0 at 2.2 GHz) and has a hollow volume of 31 mm × 31 mm × 24.5 mm. With a slotted square ring patch and unique L-probes, the antenna element exhibits a fairly large fractional bandwidth of 45%, ranging from 1.71 to 2.69 GHz. Moreover, a narrow slot and T-shaped metallic structures on the ground plane are introduced to increase the input-port isolation of the proposed antenna array to 26 dB across the entire operating bandwidth. The experimental results indicate that the antenna array has an average realized gain of 10.5 dBi, which correlates well with the simulations.

High Efficiency Wideband Refractive Optics for ALMA Band-1 (35-52 GHz)

We present the design, implementation, and characterization of the optics of ALMA Band 1, the lowest frequency band in the most advanced radio astronomical telescope. Band 1 covers the broad frequency range from 35 to 50 GHz, with the goal of minor degradation up to 52 GHz. This is, up to now, the largest fractional bandwidth of all ALMA bands. Since the optics is the first subsystem of any receiver, low noise figure and maximum aperture efficiency are fundamental for best sensitivity. However, a conjunction of several factors (small cryostat apertures, mechanical constraints, and cost limitations) makes extremely challenging to achieve these goals. To overcome these problems, the optics presented here includes two innovative solutions, a compact optimized-profile corrugated horn and a modified Fresnel lens. The horn profile was optimized for optimum performance and easy fabrication by a single-piece manufacturing process in a lathe. In this way, manufacturability is eased when compared with traditional fabrication methods. To minimize the noise contribution of the optics, a one-step zoned lens was designed. Its parameters were carefully optimized to maximize the frequency coverage and reduce losses. The optical assembly reported here fully complies with ALMA specifications.

Absolute phase determination for low‐frequency ultra‐wideband synthetic aperture radar interferometry

Absolute phase determination plays a key role in the synthetic aperture radar interferometry (InSAR). In this study, the authors focus on the low-frequency ultra-wideband (UWB) InSAR with large fractional bandwidth. They refer to the reference phase derived from the registration offsets as the registration phase (RP), and the subtraction of RP from the interferometric phase as the misregistration phase (MRP). Theoretical analysis shows that the MRP is inversely proportional to the fractional bandwidth of the synthetic aperture radar system and proportional to the misregistration. Therefore, for the UWB InSAR data, the MRP image is unambiguous in most of the area with high coherence, and phase unwrapping (PU) is even unnecessary for the MRP image when the fractional bandwidth is very large. Even though PU is required for the MRP image, it can be unwrapped efficiently by the classic minimum discontinuity PU algorithm since there are only a few discontinuities in it. Moreover, the residual ambiguity of the unwrapped MRP image can be estimated from the distribution of the unwrapped MRP. The proposed method is based on the above idea, and determines the absolute interferometric phase by adding RP and the obtained absolute MRP. The experimental results of the P-band UWB InSAR data with fractional bandwidth of 0.25 demonstrate that the method is effective and more efficient than the traditional method.

Spatial resolution analysis of low frequency ultrawidebeam–ultrawideband synthetic aperture radar based on wavenumber domain support of echo data

Compared with the traditional narrowbeam–narrowband (NB) synthetic aperture radar (SAR), the large fractional signal bandwidth and wide azimuth beamwidth of the low frequency (LF) ultrawidebeam–ultrawideband (UWB) SAR induce serious coupling between the azimuth and range wave numbers of the echo data, which might influence the behavior of the spatial resolution in the SAR imaging. The spatial resolution considering the system wave number coupling and radar squint angle for the LF UWB SAR system is proposed based on the wave number domain support (WDS) of the echo data. First, the SAR imaging geometry is built and then the spatial wave number of the echo data for the LF UWB SAR is analyzed. Second, based on the WDS of the echo data, the spatial resolution of the LF UWB SAR is derived. Moreover, the narrowing/broadening factor defined as the ratio of the proposed spatial resolution to the traditional spatial resolution is presented, which indicates the effects of the fractional bandwidth and associated integration angle as well as the squint angle on the spatial resolution. Finally, simulation results are given to prove the correctness of the theory analysis and validity of the proposed spatial resolution.

Phase Unwrapping for Large-Scale P-Band UWB SAR Interferometry

Phase unwrapping (PU) for large-scale images is a new challenging problem in reconstructing a digital elevation model from synthetic aperture radar interferometry (InSAR) data. In this letter, we proposed a region-partition-based PU method that could improve the efficiency and decrease the processing memory of the large-scale PU problem for P-band ultrawideband (UWB) InSAR. The interferometric phase is flattened by the reference phase, which is generated from the shift estimation in the registration step. We refer to the residual phase as the misregistration phase (MRP), which corresponds to the error of the shift estimation. The MRP is unambiguous in most of the area with high coherence because of the large fractional bandwidth; thus, the regions that assuredly have the unambiguous MRP are partitioned out from the MRP image and referred to as the high-quality area. Meanwhile, the remaining low-quality areas are separated by the high-quality areas and are considered irregular tiles. After unwrapping the tiles by a minimum discontinuity PU algorithm either in parallel or in series, the full-size unwrapped result is obtained. The test performed on real P-band UWB InSAR data confirms the effectiveness and efficiency of our method.