Broadside Mode Research Articles

Multifunctional Reconfigurable Wearable Textile Antennas Using Coplanar Reconfiguration Modules

A concept to realize multi-functional reconfigurable antennas for wearable applications is proposed. The general structure simply consists of a textile circular patch with three varactor-loaded reconfigurable modules evenly distributed around its edge. Based on the proposed concept, a frequency-and pattern- reconfigurable, and a frequency- and polarization-reconfigurable wearable textile antenna are demonstrated. The first design is able to switch between broadside and omnidirectional radiation modes with frequency fractional tuning ranges of 57.3% and 27.2%, respectively. The second design radiates in broadside mode with the ability to switch its linear polarization between 0°, 120° or 240°, with a frequency tuning range of 31.9% at each of states. The antennas are fabricated and measured which successfully validate the operation concept.

A high gain reduced side‐lobe miniaturized frequency and pattern reconfigurable planar array operating in higher‐order mode

In this work a low profile (˂0.01λ0), single layered, high gain reduced side-lobe miniaturized microstrip planar array operating at higher-order broadside mode (HOM) with frequency tuning and 2-D beam scanning ability is proposed. The gain is enhanced significantly by array configuration using elements operating at TM03 mode. A rectangular slot is etched in the middle of the patch to reduce the side-lobe level (SLL) below −15 dB in both principal planes. λ/2 parabolic shaped current linkages are connected between the outer λ/2 patch strips supporting TM03 mode to reduce the non-resonant length from 1.5λ to 1.167λ; hence minimizes the patch area by 22%. A 2 × 2 miniaturized planar array is designed at 2.45GHz using these elements; hence reducing the array footprint. Frequency tuning mechanism is incorporated by placing varactor diodes on the radiating edges of the array elements. Also 360° beam switching at azimuth plane and ± 40° (including 3 dB beam width) at elevation plane is achieved by suitably detuning the varactor capacitances. The simulated and measured results are found to be consistent throughout the 10% frequency tuning range. Maximum 17.1 dBi realized gain is measured which remains consistent within 2 dBi variation for entire frequency tuning and beam scanning range.

2-D Frequency Autofocus for Squint Spotlight SAR Imaging With Extended Omega-K

In the existing time-domain autofocus algorithms, the azimuth deramping operation will change the azimuth-independent phase into the azimuth-dependent phase, which may greatly reduce the accuracy of autofocus processing in squint spotlight synthetic aperture radar (SAR). In contrast, the frequency-domain autofocus algorithms can avoid this problem because it does not involve the azimuth deramping operation. However, the existing frequency-domain autofocus algorithms are proposed based on the assumption of broadside mode, which cannot be directly applied to the squint mode. Therefore, this article extends the existing frequency-domain autofocus algorithm to the squint mode combined with the extended Omega-K (EOK) algorithm. Furthermore, a space division (SD) algorithm is embedded into the proposed algorithm as preprocessing, which can effectively compensate for the azimuth-dependent motion error. The simulation and real data are processed to verify the effectiveness of the algorithm.

A Conformal, Dynamic Pattern-Reconfigurable Antenna Using Conductive Textile-Polymer Composite

A conformal antenna with electronically tuning capability of its radiation pattern between broadside and monopole-like patterns is proposed. The antenna is based on a proximity-fed circular patch, loaded with a ring patch and four rectangular slots. The design is planar without any use of rigid shorting posts or a complex feeding network. The reconfigurability is achieved by activating and deactivating the slots using p-i-n diodes to switch between TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> (monopole-like mode) and perturbed TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> distributions (broadside mode) of the antenna. For conformability, the antenna is fabricated using a highly flexible PDMS-conductive fabric composite. All the antenna parts, including the RF switches, wires, and dc biasing circuit, are fully encapsulated by PDMS to provide resilience against deformation and harsh environment. Investigations on the RF performance and mechanical stability of the antenna were conducted. Under various bendings, it was demonstrated that all the antenna components, including those for electronic switching, remained intact and in working order even under the radius bending of 40 mm, thus maintaining good pattern reconfigurability and overall performance. When bent, the measured results at 5.2 GHz show a stable radiation performance relative to those of the flat case (i.e., the maximum gain of 2.9 dBi and the efficiency of 64% in the broadside mode, corresponding to 1.75 dBi and 52% in the monopole-like mode). To the best of our knowledge, all these features have never been demonstrated in previously published pattern reconfigurable antennas.

Design of a Metasurface Antenna With Pattern Diversity

A dual-port metasurface (MS) antenna for pattern-diversity applications is proposed. The planar MS, consisting of 4 × 4 square patches, is excited by a driven patch. A pair of differential probe feed is used to drive the patch with broadside mode, while a stepped probe feed is employed in the center of the patch to generate conical mode. The capacitive-loaded stepped probe of the center feed is able to adjust the operating frequency of the conical mode and provide the two different modes with a wide overlapped frequency range. A prototype of the antenna was fabricated and measured for demonstration. The measured overlapped bandwidth (| S 11| < −10 dB) is 11.2% ranging from 5.11 to 5.72 GHz. Within the band, the measured peak gain is 11.5 dBi for the broadside mode and 6.8 dBi for the conical mode. High isolation of greater than 32 dB between the two ports is achieved over the band. Benefiting from the gain and bandwidth improvement brought by the MS, the proposed pattern diversity antenna is attractive for many wireless communication systems.

Mechanically reconfigurable array with pattern and polarization diversity

AbstractA 2 × 2 array with reconfigurable pattern and polarization is presented. The element of the array is a circularly polarized (CP) antenna, which is mainly composed of a monopole slot, a dipole, and a cylindrical copper tube. By manually moving the dipole arms, the element can be operated at right‐handed and left‐handed circular polarization states; besides, each CP element can be electrically rotated with a servo motor, whereby the phase of its radiated fields is varied with rotation angle. Based on such a mechanically reconfigurable element, the resultant array at each CP state can be operated in different radiation modes, including broadside mode, conical mode, and steerable beam mode. In addition, the array operated in the broadside mode can also provide a linearly polarized radiation with 360° polarization scanning. Simulations for typical radiation modes of the proposed array are performed, and they are validated with experiments.

High gain broadside mode operation of a cylindrical dielectric resonator antenna using simple slot excitation

AbstractIn this work, the authors report the operation of a cylindrical dielectric resonator antenna (CDRA) in the high gain HEM13δ mode, for the first time. This mode, excited with a standard microstrip slot, radiates in the broadside direction with gain in the range of 8−10 dBi. It is shown that through feed optimization, the HEM13δ mode can be excited dominantly by suppressing the fundamental HEM11δ mode of the CDRA. Detailed simulation studies show that the HEM13δ mode is supported by cylindrical dielectric resonators with an aspect ratio (radius to height ratio or a/d) &gt;1, and it resonates at a frequency approximately 2.2 times that of the fundamental HEM11δ mode. The above features of the HEM13δ mode CDRA can be used as approximate design rules. For a CDRA with dielectric constant ɛr = 24, diameter 2a = 19.43 mm, and height d = 7.3 mm (a/d = 1.3), the HEM13δ mode is excited at 6.125 GHz with a peak gain of 10.14 dBi in simulation. Corresponding values from prototype measurement are 5.981 GHz and 9.62 dBi, respectively for the resonant frequency and the gain, verifying the simulation.

A Low-Profile and Stacked Patch Antenna for Pattern-Reconfigurable Applications

A low-profile stacked patch antenna is proposed for pattern-reconfigurable (PR) applications. A referential circular radiation patch with desired conical beams and broadside beams operation is analyzed. However, due to bad port isolation, slant radiation patterns with high cross-polarization levels occur. Suspended pin loading and gap-coupled feeding techniques are introduced to achieve better port isolation, which leads to stable radiation patterns and low cross-polarization levels. Meanwhile, in order to broaden the operation bandwidth, two stacked square patches integrated with a T-shaped feeding branch are utilized and analyzed for exciting low-frequency resonances at the broadside mode. By controlling the p-i-n diodes implanted in the feeding network, reconfigurable conical and broadside beams are obtained. The measured results show that the proposed antenna yields a 10 dB operation impedance bandwidth of 11%, ranging from 2.41 to 2.69 GHz. The peak gains operating at the conical state and broadside state are 4.5 and 7.7 dBi, respectively. The overall profile of the proposed antenna is only 0.07λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the free space wavelength at 2.55 GHz.

Single Slot Antenna With Multiple Radiation Modes Using a Parasitic Loop Pair

In order to increase radiation modes for slot antennas, a new method of loading a parasitic loop pair is proposed. By adding switches to control the open- or closed-state of each loop, the loop pair works at four states, generating multiple radiation modes. Consequently, besides the original bidirectional broadside mode, two additional directional radiation modes are generated, radiating to endfire. As a result, a simple slot antenna could work in multiple radiation modes with the proposed method; meanwhile, no much-increased size or complicated structure is needed. Thus, a single slot antenna can be employed to meet the requirement for multifunction and multienvironment applications. To demonstrate this design concept of using the parasitic loop pair, an antenna structure is designed and fabricated. One parasitic loop is formed by connecting two printed metallic strips with copper shorting pins; p-i-n diode switches and bias circuits are inserted to control the state of the two loops with dc signals. Both measured and simulated results indicate that the proposed parasitic loop pair is effective in providing multiple radiation modes for slot antennas.

Improving estimates of buried pipe diameter and infilling material from ground-penetrating radar profiles with full-waveform inversion

Ground-penetrating radar (GPR) is a widely used tool for the detection and location of buried utilities. Buried pipes generate characteristic diffraction hyperbolas in raw GPR data. Current methods for analyzing the shapes and timing of the diffraction hyperbolas are very effective for locating pipes, but they are less effective for determining the diameter of the pipes, particularly when the pipes are smaller than the radar wavelengths, typically a few tens of centimeters. A full-waveform inversion (FWI) method is described for improving estimates of the diameter of a pipe and confirming the infilling material (air/water/etc.) for the simple case of an isolated diffraction hyperbola on a profile run perpendicular to a pipe with antennas in broadside mode (parallel to the pipe). The technique described here can improve a good initial guess of the pipe diameter (within 30%–50% of the true value) to a better estimate (less than approximately 8% misfit). This method is developed by combining two freely available software packages with a deconvolution method for GPR effective source wavelet estimation. The FWI process is run with the PEST algorithm (model-independent parameter estimation and uncertainty analysis). PEST iteratively calls the gprMax software package for forward modeling of the GPR signal as the model for the pipe and surrounding soil is refined.

A reconfigurable parasitic antenna with continuous beam scanning capability in H-plane

A reconfigurable microstrip Yagi antenna is proposed to realize continuous and improved beam scanning from −40° to 40° in the H-plane. The antenna is designed using a square shaped driven patch and two hexagonal slotted tunable parasitic elements placed in the H-plane. The mutual coupling between the driven and tunable parasitic elements is controlled by changing the capacitance of varactor diodes loaded in the hexagonal slot. The relative lead and lag of current due to change in the dimension of tunable parasitic patch causes phase distribution across the elements resulting in continuous scanning of the main beam. The performance of the antenna is measured in three operating modes namely Reflector-Director (RD), Director-Reflector (DR) and broadside. In RD and DR mode, the main beam is continuously scanned from 14.4° to 40° and −14.4° to −40° respectively. The main beam is directed to 0° in the broadside mode with a gain of 3.36 dBi. The antenna achieves overall bandwidth from 2.43 to 2.47 GHz in all the operating modes without any impedance matching network. The reflection and radiation performance of the fabricated antenna shows good agreement with the simulation results.

Coherent Auto-Calibration of APE and NsRCM under Fast Back-Projection Image Formation for Airborne SAR Imaging in Highly-Squint Angle

Synthetic Aperture Radar (SAR) imaging with a non-zero (forward) squint angle is capable of providing a longer time for reaction than that of the broadside mode. However, due to the large squint angle, there will be severe coupling between range and azimuth samples in the echoed data, which is known as the problematic Range Cell Migration (RCM) in the SAR community. Especially when the SAR sensor mounted on an airborne platform encounters unexpected motion deviations/errors, the coupling becomes more complicated, and it is difficult to differentiate the systematic RCM for the SAR Image Formation Processing (IFP) and the non-systematic RCM error to be compensated. To this end, a novel and accurate SAR imaging algorithm is proposed in this paper to facilitate the processing of airborne SAR data collected at a high-squint angle. Firstly, the proposed algorithm is established under a Fast Time-Domain Back-Projection (FTDBP) framework for the SAR IFP. FTDBP paves the way to avoid the complicated processing for the systematic RCM as for the conventional SAR IFP in the Doppler processing manner. It is capable of generating a high-resolution SAR image efficiently under more general geometries and configurations. Secondly, regarding the non-systematic RCM errors, the proposed algorithm realizes the compensation by correcting both the Non-systematic Range Cell Migration (NsRCM), as well as Azimuthal Phase Error (APE) in a coherent manner. It is consequently capable of auto-calibrating the effects of the motion error completely without being dependent on the airborne navigation unit. Finally, both simulated and raw data collected by the airborne squinted SAR are applied to evaluate the proposed algorithm. Comparisons with conventional algorithms are carried out to reveal the superiority of the proposed algorithm.

Broadband Pattern Diversity Patch Antenna With Switchable Feeding Network

A single-feed wideband pattern diversity antenna is presented in this paper. The pattern reconfigurability is realized by a p-i-n-diodes-intergrated switchable feeding network with the ability of providing 0° in-phase or 180° out-of-phase antenna excitation. The radiating patch is excited by the feeding network through a pair of symmetric stepped probes. When the two stepped probes are with in-phase excitation, a conical mode can be generated on the patch. On the other hand, the antenna can operate at a broadside mode if the excitation is out-of-phase. A meticulous prototype is developed, manufactured, and measured. The measured impedance bandwidths of the 10-dB return loss are 60.7% from 1.95 to 3.65 GHz for the broadside mode and 72.7% from 1.65 to 3.65 GHz for the conical mode. Meanwhile, measured peak gains of up to 10.2 and 7.7 dBi and measured radiation efficiencies of higher than 80% and 76% are obtained for the broadside mode and conical mode, respectively.

Extension of Map-Drift Algorithm for Highly Squinted SAR Autofocus

For highly squinted synthetic aperture radar (SAR) imaging, the Omega-k algorithm is generally accepted as an effective focusing processor. However, the performance of the Omega-k algorithm may be degraded by the trajectory deviations due to the precision limitation of the navigation system in airborne SAR. In this paper, we focus on the autofocusing approach, which is compatible with the Omega-k imaging for highly squinted SAR. This new autofocusing approach can be viewed as an extension version of the conventional map-drift (MD) algorithm, which has been widely used in the broadside mode. Two-step process is performed in the proposed autofocusing method: 1) the range-independent phase-error is first retrieved by a squinted MD (SMD) estimator; and 2) a squinted range-dependent MD (SRDMD) estimator is proposed to derive the residual range-variant phase-error. By correcting the phase-errors obtained from SMD and SRDMD, the highly squinted SAR data can be finally focused. The effectiveness of the proposed algorithm has been demonstrated by both simulated and real-measured SAR data in highly squinted mode.

Wideband Pattern-Reconfigurable Antenna With Switchable Broadside and Conical Beams

A wideband, pattern-reconfigurable antenna is reported that is, for example, a good candidate for ceiling-mounted indoor wireless systems. Switchable linearly polarized broadside and conical radiation patterns are achieved by systematically integrating a wideband low-profile monopolar patch antenna with a wideband L-probe fed patch antenna. The monopolar patch acts as the ground for the L-probe fed patch, which is fed with a coaxial cable that replaces one shorting via of the monopolar patch to avoid deterioration of the conical-beam pattern. A simple switching feed network facilitates the pattern reconfigurability. A prototype was fabricated and tested. The measured results confirm the predicted wideband radiation performance. The operational impedance bandwidth, i.e., |S 11 | ≤ -10 dB, is obtained as the overlap of the bands associated with both pattern modalities. It is wide, from 2.25 to 2.85 GHz (23.5%). Switchable broadside and conical radiation patterns are observed across this entire operating bandwidth. The peak measured gain was 8.2 dBi for the broadside mode and 6.9 dBi for the conical mode. The overall profile of this antenna is 0.13λ 0 at its lowest operating frequency.

Optimal Data Acquisition and Height Retrieval in Repeat-Track Geosynchronous SAR Interferometry

Geosynchronous synthetic aperture radar (GEO SAR) will move in a high orbit of ~36,000 km with a long integration time of hundreds of seconds. It is obviously impacted by orbital perturbations and the Earth’s rotation, which can give rise to un-parallel repeated tracks and induce a squint-looking angle in the repeat-track SAR interferometry (InSAR). Thus, the traditional data acquisition method using in the zero-Doppler centroid (ZDC) configuration to generate the GEO InSAR pair will bring about the obvious rotation-induced decorrelation. Moreover, the conventional height retrieval model with the broadside mode imaging geometry and the approximate expression of the interferometric baseline will induce large height and localization errors in the GEO InSAR processing. In this paper, a novel data acquisition method is firstly presented based on a criterion of optimal minimal rotational-induced decorrelation (OMRD). It can significantly improve the coherence of the InSAR pair. Then, considering the localization equations in the squint-looking mode and the accurate expression of the interferometric baseline, a modified GEO InSAR height retrieval model is proposed to mitigate the height and localization errors induced by the conventional model. Finally, computer simulations are carried out for the verification of the proposed methods. In a typical inclined GEO InSAR configuration, the averaged total correlation coefficient increases more than 0.4, and height errors of hundreds of meters and localization errors of more than 10 degrees are removed.

Geo‐location error analysis in geosynchronous SAR

The Doppler rate of geosynchronous synthetic aperture radar (GEO SAR) is zero at some orbital positions due to their high altitude. Also, the Doppler frequency varies along the range direction in the squint mode which is widely used in GEO SAR. The above-mentioned Doppler characteristics have serious effects on the calculation of geo-location error, which are not considered in the conventional model. To solve the problem, an accurate model of the geo-location error is derived based on the range-Doppler equations and the geometry of the squint GEO SAR. The proposed model perfectly matches the simulation results, and can be widely used in both the broadside mode and the squint mode of the spaceborne SAR. Furthermore, the sensitivity of the geo-location error to error sources is analysed based on the simulation for GEO SAR. It is found that the satellite velocity error is the main error source of the geo-location error in GEO SAR.

A Compact Dual-Band Dual-Pattern Mode Antenna Design

A compact dual-band dual-pattern mode antenna is proposed in this article. A microstrip rectangular semi-ring antenna that has the feature of compact size is first employed as the driven element. Then by placing a parasitic element next to the driven element, a novel dual-band dual-pattern mode antenna is designed. In the first band, the beam peak of the proposed antenna steers from the broadside, called the microstrip Yagi mode. In the second band, the beam peak of the proposed antenna changes to the broadside direction, which can be regarded as the broadside mode. A prototype operated at C-band is designed, fabricated, and measured to verify the proposed design methodology.

Pattern Purity of Coiled-Arm Spiral Antennas

The consequences of the coil-type arm treatment on the far-field characteristics of spiral antennas excited in the broadside mode (also referred to as Mode 1) are discussed. Computational analysis of the coiled-arm spiral antenna with two and four arms is performed using the moment method, and the effects on modal content, 3-dB beamwidth, azimuthal gain uniformity, off-axis axial ratio, and co-polarized broadside gain are reported. Predictions of the numerical calculations are verified experimentally through far-field measurements. It is found that the coil-type arm treatment produces significant modal contamination of the far-field pattern when compared to a conventional smooth spiral (with no arm coiling). It is shown that these effects can be mitigated by employing an antenna design that uses four spiral arms. For instance, the measured cross-polarization discrimination of the four-armed spiral at 47 degrees from broadside is improved by up to 15 dB with respect to a comparable two-armed spiral.

Design and Time-Domain Analysis for a Novel Pattern Reconfigurable Antenna

This letter presents a novel wideband pattern reconfigurable antenna. The antenna consists of a pair of Vivaldi-shaped slots, two switches, and a rectangular slot for impedance matching. By switching between the on and off status, the proposed antenna is able to provide three different radiation patterns over a bandwidth from 4.96 to 8.3 GHz: one broadside mode and two oppositely directed endfire modes. We investigate the antenna's impedance bandwidth, its radiation characteristics, and time-domain characteristics. Experimental and simulated results are presented and discussed.