Measured Radiation Patterns Research Articles

Asynchronous electric field visualization using an integrated multichannel electro-optic probe

The higher the frequency, the more complex the scattering, diffraction, multiple reflection, and interference that occur in practical applications such as radar-installed vehicles and transmitter-installed mobile modules, etc. Near-field measurement in “real situations” is important for not only investigating the origin of unpredictable field distortions but also maximizing the system performance by optimal placement of antennas, modules, etc. Here, as an alternative to the previous vector-network-analyzer-based measurement, we propose a new asynchronous approach that visualizes the amplitude and phase distributions of electric near-fields three-dimensionally without placing a reference probe at a fixed point or plugging a cable to the RF source to be measured. We demonstrate the visualization of a frequency-modulated continuous wave (FMCW) signal (24 GHz ± 40 MHz, modulation cycle: 2.5 ms), and show that the measured radiation patterns of a standard horn antenna agree well with the simulation results. We also demonstrate a proof-of-concept experiment that imitates a realistic situation of a bumper installed vehicle to show how the bumper alters the radiation patterns of the FMCW radar signal. The technique is based on photonics and enables measuring in the microwave to millimeter-wave range.

Periodic Microstrip Leaky Wave Antenna with Double-Sided Shorting Pins and Pairs of Slots

A backward to forward scanning periodic microstrip leaky wave antenna (MLWA) is presented. The proposed antenna consists of a long rectangular patch with alternating shorting pin on each side, which connects the antenna patch and the ground plane to form periodic shorting circuits. There are two pairs of slots alternately spaced on the long patch to suppress the open stop band (OSB). The OSB problem was initially reduced by optimizing the structural parameters, and the slotting on the patch further improved it. The measured radiation pattern in the y-z plane shows that the antenna can scan electronically from 142° to 39° toward the end-fire (+z direction) when the operating frequency changes from 6 GHz to 12.9 GHz. The measured gain is greater than 5 dBi over the entire operating band.

A Portable Cost-Effective Amplitude and Phase Antenna Measurement System

This article presents a simple, cost-effective system for complex measurements of the field radiated by an antenna. In particular, the proposed architecture is based on an array of antenna probes connected to a set of phase difference detectors and a power detector. Phase difference measurements are processed to recover the phase of the antenna under test. The main novelty of the proposed system is that it does not require regular sampling, making it suitable for in situ antenna measurements. The influence of parameters, such as the number of antennas composing the array (and hence the number of phase difference detectors) and the positioning errors, is analyzed. The proposed architecture, implemented with off-the-shelf hardware, has been assessed for antenna measurement and diagnostics. A discussion of the issues related to the implementation of the system has been included, as well as the proposed solutions to improve its accuracy. Finally, diagnostics and radiation pattern measurement results are compared with those calculated with other phaseless techniques.

The Traveling Wave Loop Antenna: A Terminated Wire Loop Aerial for Directional High-Frequency Ocean RADAR Transmission

In this paper we document the design, development, results, performance and field applications of a compact directive transmit antenna for the long-range High Frequency ocean RADAR (HFR) systems operating in the International Telecommunication Union (ITU) designated 4MHz and 5MHz radiodetermination bands. The antenna design is based on the combination of the concepts of an electrically small loop with that of travelling wave antenna. This has the effect of inducing a radiated wave predominantly in a direction opposed to that of energy flow on the antenna structures. We demonstrate here that travelling wave design allows for a more compact antenna than other directive options, it has straightforward feed-point matching arrangements, and a flat frequency and phase response over an entire radiodetermination band. In situ measurements of the antenna radiation pattern, obtained with the aid of a drone, correlate well with those obtained from simulations, and show between 8dB and 30dB front-to-back suppression, with a 3dB beam width in the forward lobe of 100∘ or more. The broad-beam radiation pattern ensures proper illumination over the ocean and the significant front-to-back suppression guarantees reduced interference to terrestrial services. The proposed antenna design is compact and straight forward and can be easily deployed by minimal modifications of an existing transmission antenna. The design may be readily adapted to different environments due to the relative insensitivity of its radiation pattern and frequency response to geometric detail. The only downside to these antennas is their relatively low radiation efficiency which, however, may easily be compensated for by the available power output of a typical HFR transmitter. Antennas based on this design are currently deployed at the SeaSonde HFR sites in New South Wales, Australia, with operational ranges up to 200 km offshore despite their low radiating efficiency and the extremely low output power in use at these installations. Due to their directional pattern, it is also planned to test these antennas in phased-array Wellen RADAR (WERA) systems in both the standard receive arrays: where in-band radio frequency noise of terrestrial origin is impacting on data quality, and in the transmit array: to possibly simplify splitting, phasing and tuning requirements.

A 20-Element Cavity-Backed Slot Electronically Steerable Parasitic Array Radiator (ESPAR) With 2-D Beamsteering and Minimized Beam Squint

A 20-element cavity-backed slot antenna array is presented herein based on an electronically steerable parasitic array radiator (ESPAR) cross subarray. This ESPAR array is able to steer the main beam within ±45° in the E-plane and ±40° in the H-plane without grating lobes. Inside each subarray, the beamsteering is realized by tuning the reactance of the loads at the four parasitic elements. Therefore, only four phase shifters are needed for this 20-element array to achieve 2-D beamsteering, corresponding to an 80% reduction on the number of phase shifters compared to a classic phased array. The measured impedance matching is maintained below -10 dB from 6.0 to 6.4 GHz (6.4% fractional bandwidth) at all scan angles. The radiation patterns are measured at five different scan angles in E- and H-planes. At each scan angle, the measured radiation patterns at five frequencies across the impedance-matching bandwidth exhibit very small beam squint. The measured peak gain is found to be 14.0 dBi at the boresight direction.

Reconstruction of Antenna Radiation Pattern Based on Compressed Sensing

The measurement of the far-field radiation pattern is an important factor in describing the characteristics of the antenna. The measurement process is time consuming and expensive. Therefore, this paper proposes a novel method to reduce the number of samples required for radiation pattern measurement by adopting compressed sensing theory. This method reconstructs the radiation pattern from data measured by a few sensors, and the positions of these sensors are generated via the m-sequence. Simulation results demonstrate that the proposed algorithm can effectively reconstruct the complete radiation pattern by using the 50% samples.

S-Parameter Analysis for Balanced and Unbalanced Modes Corresponding Dissipated Power of a Small Antenna

In this paper, an analysis method for calculating balanced and unbalanced modes of a small antenna is summarized. Modal condactances which relate dissipated power of the antenna are directly obtained from standard S-parameters that we can measure by a 2-port network analyzer. We demonstrate the validity and effectiveness of the proposed method by simulation and measurement for a dipole antenna with unbalaned feed. The ratio of unbalanced-mode power to the total power (unbalanced-mode power ratio) calculated by the proposed method agrees precisely with that yielded by the conventional method using measured radiation patterns. Furthermore, we analyze a small loop antenna with unbalanced feed by the proposed method and show that the self-balancing characteristic appears when the loop is set in resonant state by loading capacitances or the whole length of the loop is less than 1/20th the wavelength.

GPS용 초소형 1/4파장 마이크로스트립 안테나

In this study, a miniaturized GPS band(L1: 1.575 GHz) antenna that can be mounted on a small device is proposed. The miniaturized antenna was manufactured such that it could be attached to the surface of styrofoam(ϵr=1.06, t=10 mm) having a size of 12×11×10 mm(0.06×0.06×0.05 λ). The thickness and length of the feeding line and the spacing between short stubs were adjusted for impedance matching. S11was found to be −38.6 dB at the center frequency of the fabricated antenna, 1.575 GHz. The radiation pattern measurement results show that the maximum gain of Eθ is −2.3 dBi in 0 directions in the xz-plane, and that Eθ is an omnidirectional characteristic with an average gain of −3.2 dBi in the yz-plane. Under these circumstances, it was found that the antenna can be used as an ultra-small microstrip antenna, which can be mounted on a small device, and is capable of preserving a reduction ratio of 87 % as compared to a λ/2 microstrip patch antenna.

A Novel High Gain Wideband MIMO Antenna for 5G Millimeter Wave Applications

A compact tree shape planar quad element Multiple Input Multiple Output (MIMO) antenna bearing a wide bandwidth for 5G communication operating in the millimeter-wave spectrum is proposed. The radiating element of the proposed design contains four different arcs to achieve the wide bandwidth response. Each radiating element is backed by a 1.57 mm thicker Rogers-5880 substrate material, having a loss tangent and relative dielectric constant of 0.0009 and 2.2, respectively. The measured impedance bandwidth of the proposed quad element MIMO antenna system based on 10 dB criterion is from 23 GHz to 40 GHz with a port isolation of greater than 20 dB. The measured radiation patterns are presented at 28 GHz, 33 GHz and 38 GHz with a maximum total gain of 10.58, 8.87 and 11.45 dB, respectively. The high gain of the proposed antenna further helps to overcome the atmospheric attenuations faced by the higher frequencies. In addition, the measured total efficiency of the proposed MIMO antenna is observed above 70% for the millimeter wave frequencies. Furthermore, the MIMO key performance metrics such as Mean Effective Gain (MEG) and Envelope Correlation Coefficient (ECC) are analyzed and found to conform to the required standard of MEG < 3 dB and ECC < 0.5. A prototype of the proposed quad element MIMO antenna system is fabricated and measured. The experimental results validate the simulation design process conducted with Computer Simulation Technology (CST) software.

Higher Order Mode Attenuation in Microstrip Patch Antenna with DGS H Filter Specification from 5 to 10 GHz Range

Abstract This work proposes the application of a slot in the ground plane, Defected Ground Structure (DGS), of a microstrip patch antenna. The application of this technique aims to attenuate higher-order excited modes without deteriorating the antenna parameters in the fundamental mode. The methodology for the design of the slot in H-format is presented, based on the physical dimensions of the microstrip patch antenna. The positioning of the DGS concerning the feed line was determined from a detailed parametric analysis. The antenna was designed for the fundamental mode at 2.45 GHz frequency. Two antenna prototypes were built, with and without DGS, and measurements of reflection coefficient, gain, and radiation pattern were performed. The measured results show that the application of DGS considerably attenuated higher-order excited modes. A good agreement between simulated and measured results is achieved.

28 GHz metal cavity‐backed twin arc slot antenna for high efficiency and thermal management

AbstractThis article presents a metal cavity‐backed antenna array with high gain and high radiation efficiency. The proposed antenna can be used for the purpose of thermal management. A 28 GHz linear polarized antenna is implemented on a low cost substrate with an aluminum structure that functions as a heat sink. Each antenna element is connected to integrated circuits with a stripline embedded in the printed circuit board. Each element is fed by a slot‐coupled feeding structure and radiated through twin arc slots fabricated in circular metal cavity. The simulated antenna efficiency is over 80% including feeding structures. The simulated and measured radiation patterns show 17.2 dBi of peak gain. From the thermal simulation, temperature reduction can be expected.

A Linear-Array of 300-GHz Antenna Integrated GFET Detectors on a Flexible Substrate

Terahertz imaging has potential in a variety of applications, such as noninvasive inspection, medical examination, and security. Many of these applications call for flexible focal-plane arrays with large fields of view. Here, we demonstrate the implementation of a flexible, 300 GHz, 1 × 6 linear detector array based on graphene field-effect transistors and integrated bow-tie antennas. Conservative estimates based on room temperature measurements at 300 GHz show element voltage responsivities in the range from 20 to 70 V/W, and noise equivalent powers in the range from 0.06 to 0.2 nW/ √Hz. Measured radiation patterns, showing good agreement with simulations, reveal half-power beamwidths of 45° and 60° for H-and E-planes, respectively. Characterization of the antenna array in a curved configuration shows that the voltage response is reduced up to 3 dB compared to the flat configuration due to a decrease of the antenna directivity. We believe that our preliminary results could serve as an enabling platform for the future development of flexible antenna arrays based on graphene field-effect transistors for curved focal plane imaging, important for wearable sensors and many other applications.

Orthogonal Code-Based Transmitted Radiation Pattern Measurement Method for 5G Massive MIMO Antenna Systems

This article presents a novel method to measure the transmitted radiation pattern by using orthogonal encoded signals during the process of hybrid analog-digital (HAD) beamformer development. One of the most important indicators in evaluating the performance of HAD beamforming systems is the measurement of the sub-array radiation patterns. However, as the number of elements increases, the number of combinations that can create sub-arrays increases significantly, and the conventional radiation pattern measurement process becomes exhaustive. However, when an orthogonal coded signal is used for the HAD beamforming system measurement, the magnitude and phase information of each element of the HAD beamforming system, including mutual coupling, can be simultaneously obtained from a single scan. Hence, it is possible to measure all feasible sub-array patterns very efficiently. Therefore, we propose an orthogonal code-based time-domain measurement technique and validate it with full-wave time-domain simulations. The results show that it is possible to receive element pattern information independently and that any sub-array pattern can be reconstructed with an accuracy greater than 99.99%.

Study on Impedance Matching of 2.4 GHz Dipole Antenna

Understanding on matching impedance between feedline and load is important in many aplication. Theoritically, matching impedance can be calculated easily if charateristic impedances both load and line is known. Practically, when we do impedance matching at certain frequency we face a problem if the impedance of the feedline and antenna are unknown. by using vector network analyzer and anechoic chamber we tried to study and to approach the impedance match through measurement of return loss, VSWR, and antenna radiation pattern. The results of studies have shown that adjusting dipole antennas to lines can be done by optimizing antenna and lines length and subsequently optimizing the use of balun. In this reasearch we optimized 2.4 GHz dipole antenna and matched it to feedline by using bazooka and balun 1 : 1. To achieve good matching, the antenna length is 0.35 λ and the feedline length multiplies 0.5 λ. The length of the bazooka and balun for the best impedance adjustment are 0.25 λ and 0.2λ.

Wideband circularly polarized, slot antenna array loaded with metasurface

AbstractThis article presents the design and measurement results of a novel wideband circularly polarized 2 × 2 slot antenna array loaded with a metasurface layer. The proposed array exploits circularly polarized elements. Each element is sequentially rotated and fed with an appropriate phase difference to ensure the generation of a circularly polarized wave. The use of metasurface enlarges the impedance bandwidth of the antenna by creating an additional resonance. The metasurface layer also improves the axial ratio bandwidth of the array. Its other major benefit is mitigating the beam squint in the higher frequency band without sacrificing the axial ratio (AR). A prototype of the antenna is built and measured in an anechoic chamber. The measured impedance bandwidth (|S11| < −10 dB) of the array is 66.7% (from 1.6 to 3.2 GHz) and its axial ratio bandwidth (AR < 3 dB) is 63.8% (from 1.6 to 3.1 GHz) which are outstanding numbers compared to the current state of the art. The measured radiation patterns of the antenna array are stable across the band of interest with a gain of >4 dBi. The overall size of the antenna is 170 mm × 170 mm.

A coplanar waveguide‐fed flexible antenna for ultra‐wideband applications

This paper presents a novel ultra-wideband (UWB) antenna printed on a 70 μm thick flexible substrate. The proposed antenna consists of a hybrid-shaped patch fed by coplanar waveguide (CPW). The ground planes on opposite sides of the feeding line have different height to improve antenna bandwidth. Simulation shows that the proposed antenna maintain wide bandwidth when changing its substrate's thickness and dielectric constant, as well as bending the antenna on a cylindrical foam. The proposed antenna is fabricated in laboratory with a simple and low-cost wet printed circuit board (PCB) etching technique. Measured bandwidths cover 3.06 to 13.58, 2.8 to 13.55, and 3.1 to 12.8 GHz in cases of flat state and bent with radii of 20 and 10 mm, respectively. Measured radiation patterns show the antenna is omnidirectional in flat and bent cases.

A Low-Cost, High-Efficiency and Full-Metal Reflectarray Antenna With Mechanically 2-D Beam-Steerable Capabilities for 5G Applications

This article presents a low-cost, high-efficiency, and full-metal reflectarray (RA) antenna with mechanical beam-steerable capabilities. A unit cell (UC) implemented by a metal cylinder with a cuboid-shaped notch is proposed to achieve a 1 bit reflection phase (0 and $\pi $ ) for the transverse electric (TE) and transverse magnetic (TM) normal incidence waves. The proposed UCs can be employed to construct an RA antenna with 2-D beam-steerable abilities. For demonstration, the RA antennas with six different beam directions are presented as examples, by simply adjusting the rotations of the UCs. The impedance matches of the RA antenna are all below −10 dB from 22 to 33 GHz, and the measured radiation patterns of the RA antenna are all highly consistent with the simulated counterparts for the six different beam direction scenarios. A 1.5 dB gain drop bandwidth of approximately 20% from 24.7 to 30 GHz and a peak realized gain of 18.9 dBi at 26 GHz are experimentally obtained for the RA antenna with radiation patterns at broadside. Compared to the substrate-based UCs loaded with p-i-n diodes, the proposed UCs have full-metal structures without using any active RF components and dielectric substrates, leading to the high total efficiency of the proposed RA antenna. Due to the low-cost, high-efficiency, and high-power handling properties, the proposed RA antenna can provide a fixed or scanning beam and is a good candidate for 5G millimeter-wave communication applications.

Gridded parasitic patch stacked microstrip array antenna for 60 GHz band

An array antenna design based on a gridded parasitic patch stacked microstrip antenna element is presented. The radiating part in the top layer of one antenna element has nine rectangular metal patches placed in a grid with three rows and three columns with a separation of 0.1 mm between the patches. Two means of realising the array are investigated. In a regular 2 × 2 concept, the parasitic patches of individual elements are placed next to each other, forming on the top layer a uniform grid of parasitic patches with six rows and six columns. In an alternative concept named as shared array, neighbouring antenna elements share one row and one column of parasitic patches, forming on the top layer a uniform grid of parasitic patches with five rows and five columns. The antenna arrays are designed for the 60 GHz band. The measured bandwidth is 13.8 GHz for the single antenna, 15.3 GHz for the 2 × 2 array, and 12.4 GHz for the shared array. The measured realised gain at 60 GHz is 6 dBi for the single antenna, 11 dBi for the 2 × 2 array, and 10.5 dBi for the shared array. The measured radiation patterns have good agreement with simulations.

Design and analysis of a quad‐band substrate‐integrated‐waveguide cavity backed slot antenna for 5G applications

A planar and compact substrate integrated waveguide (SIW) cavity backed antenna and a 2 × 2 multi-input multi-output (MIMO) antenna are presented in this study. The proposed antenna is fed by a grounded coplanar waveguide (GCPW) to SIW type transition and planned to be used for millimeter-wave (mm-wave) fifth generation (5G) wireless communications that operates at 28, 38, 45, and 60 GHz frequency bands. Moreover, the measured impedance bandwidth (|S11| ≤ − 10 dB) of the antenna covers 27.55 to 29.36, 37.41 to 38.5, 44.14 to 46.19, and 57.57 to 62.32 GHz bands and confirms the quad-band characteristic. Omni-directional radiation characteristics are observed in the far-field radiation pattern measurements of the antenna over the entire operating frequency. The reported antenna is compact in size (9.7 × 13.3 × 0.6 mm3) and the gain values at each resonance frequency are measured as 3.26, 3.28, 3.34, and 4.51 dBi, respectively. Furthermore, the MIMO antenna performance is evaluated in terms of isolation, envelope correlation coefficient and diversity gain.

Quad‐mode radial uniform circular array antenna for OAM multiplexing

This study presents a novel radial uniform circular array (UCA) antenna for quad-mode orbital angular momentum (OAM) multiplexing in the 5.2 GHz band. The antenna can simultaneously generate four OAM modes (±1, ±2) using two radial UCAs printed concentrically on a single substrate. Each UCA is connected to an individual dual-mode feeding network, and generates a pair of complementary OAM modes. The feeding network for each UCA consists of one quadrature hybrid coupler and two circular feedlines, and they can be integrated onto a single substrate. The measured radiation patterns and helical phase wavefronts show the successful generation of four OAM modes by the proposed antenna. The quad-mode OAM transmission test was performed using two prototypes of the proposed antenna, and good isolations >13.7 dB were obtained between four OAM mode channels, which demonstrates that the antenna can be successfully used for OAM multiplexing.