Directivity Beamwidth Research Articles

Diffused Sensing for Sharp Directive Beamforming

We generalized our previously proposed diffused sensing for a microphone array design to achieve sharp directive beamforming to enable various filter design methods to be applied. In the conventional microphone array, various filter design methods have been studied to narrow the directivity beam width. However, it is difficult to minimize the power of interference sources in the beamforming output (output interference power) over a broad frequency range since the cross-correlation between transfer functions from sound sources to microphones increases in some frequencies. With the diffused sensing, the cross-correlation is minimized by physically varying the transfer functions. We investigated how a microphone array should be designed in order to minimize the cross-correlation between transfer functions and found that placing the array in a diffuse acoustic field produces optimum results. Because the transfer functions are known a priori, this finding makes it possible to narrow the directivity beam width over a broad frequency range. This observation can be practically achieved by placing microphones inside a reflective enclosure, part of which is open to let sound waves enter. We conducted experiments using 24 microphones and confirmed that the output interference power was reduced over a broad frequency range and the beam width was narrowed by using the diffused sensing.

Emission and Transmission Properties of a Doubly Resonant 3D Nanodisk Yagi–Uda Antenna for Wireless Optical Communications

In this paper, a novel doubly resonant three-dimensional (3D) nanodisk Yagi–Uda antenna, conceived for realizing wireless optical links within electronic circuits, is proposed. The prominent emitting properties of this nanoantenna have been deeply investigated both in the near and far field through a useful comparison with a more traditional 3D nanorod Yagi–Uda antenna. The behavior of the nanodisk antenna, both configured as a single nanoantenna and arranged in planar arrays, have been illustrated, emphasizing its improved performances with relation to crucial aspects as directional features, wavelength bands of operation, frequency tuning, and polarization influence on radiation. In particular, the single nanodisk antenna has been accurately designed to enhance the transmission feature in the near field at the wavelengths λ = 1.3 and λ = 1.55 μm. Also, the emission pattern of the array of nanodisk antennas has been properly tailored to ensure high peaks of directivity and narrow beam width in those ranges. Hence, efficient unidirectional angle patterns have been shaped for any operation wavelength and dimensions of the array, reaching extremely effective outcomes for a 3 × 3 array, which exhibits a maximum of directivity of 19 and 17.6 and −3 dB points at 18° and 21° for λ = 1.3 and λ = 1.55 μm, respectively.

Empirical mode decomposition-based monopulse processor for enhanced radar tracking in the presence of high-power interference

Monopulse radars are used to track targets that appear in the look direction beam width. The distortion of the tracking information produced when high power interference signals (jamming) are introduced through the radar antenna can cause severe erroneous outcomes from the monopulse tracking processor. This leads to errors in the target tracking angles that may cause target mistracking. New monopulse radar structures that utilizes an empirical mode decomposition (EMD) based denoising processor are presented in this paper. EMD filtering is carried out for the complex radar chirp signal with subsequent detrending, thresholding, and denoising processes. These processes are used to decrease the noise level in the radar processed data to improve the signal to noise ratio. The performance enhancement using the monopulse radar tracking system with EMD based filtering is included using the standard deviation angle estimation error (STDAE) for different jamming scenarios and different target SNRs. STDAE shows that the new EMD based system works well in the case of main beam interference and side lobe interference for the conventional processor and, in the case of the spatial adaptive processor, is effective in the case of main lobe interference.

Fast neighbor positioning and medium access in wireless networks with directional antennas

We study the problem of fast neighbor positioning and medium access in wireless networks with directional antennas. In this problem, the cross-layer dimension inherently comes into stage through the impact of PHY-layer antenna directionality on medium access. Fast neighbor positioning reduces the network initialization overhead and leaves more time for executing other protocols. Fast medium access leads to larger volume of transmitted data per unit of time. The two problems are studied in a unified manner in a system with one Access Point (AP) and multiple users around it. The AP sequentially scans the space by forming directional beams and applies contention-free or contention-based user polling within each beam. In the former method, polling messages are addressed to a specific user. In the latter, users in a beam contend to have their message received by the AP.We explore the impact of the contention resolution protocol and the directional beam width on user positioning and medium access delay. A large beam width incurs large expected delay for contention resolution due to the larger expected amount of contention in the beam, but on the other hand, it implies that fewer beams, and hence smaller delay is needed to scan the entire space. We obtain analytic expressions for the total average user positioning and the medium access delay, and we present an optimization method for minimizing it by appropriately selecting the beam width and the persistence probability of the collision resolution protocol. Our method uses accumulated knowledge from previous scans to estimate the anticipated amount of contention in upcoming scans and to adjust the beam width and persistence probability accordingly. Our numerical results demonstrate the efficiency of our techniques in terms of fast neighbor positioning.

Wireless communication capability of a reconfigurable plasma antenna

A 30 cm long plasma column is excited by a surface wave, which acts as a plasma antenna. Using plasma properties (pattern formation/striations in plasmas) single plasma antenna can be transformed into array, helical, and spiral plasma antenna. Experiments are carried out to study the power patterns, directivity, and half power beam width of such different plasma antennas. Moreover, field properties of plasma and copper antenna are studied. Further, wireless communication and jamming capability of plasma antenna are tested. Findings of this study suggest that directivity and communication range can be increased by converting single plasma antenna in to array/helical/spiral plasma antenna. Field frequencies of plasma antenna determine the communication and jamming of radio frequency waves. Therefore, this study invokes applications of pattern formation or striations of plasmas in plasma antenna technology.

Enhanced monopulse tracking radar using optimum fractional Fourier transform

Conventional monopulse radar processors are used to track a target that appears in the look direction beam width. The distortion produced when additional targets appear in the look direction beam width can cause severe erroneous outcomes from the monopulse processor. This leads to errors in the target tracking angles that may cause target mistracking. A new signal processing algorithm is presented in this study which offers a solution to this problem. The technique is based on the use of optimal fractional Fourier transform (FrFT) filtering. The relative performance of the new filtering method over traditional-based methods is assessed using standard deviation angle estimation error (STDAE) for a range of simulated environments. The proposed system configuration succeeds in significantly cancelling additional target signals appearing in the look direction beam width even if these targets have the same Doppler frequency.

The TOA-distribution of multipaths between an omni-directional transceiver and a mis-oriented directional transceiver

For a directional (a.k.a. directive) transceiver misaligned towards an omni-directional transceiver, the multipaths' time-of-arrival (TOA) distribution is herein derived in closed form explicitly in terms of the "geometric modeling" parameters. This derivation allows the directional beamwidth to mis-point to any arbitrary azimuth-direction, even if entirely away from the intended omni-directional transceiver.

Mutual Impedance Extraction and Varactor Calibration Technique for ESPAR Antenna Characterization

An extraction and calibration technique is proposed that allows electronically steerable parasitic array radiator (ESPAR) antennas to achieve high efficiency and precision in performance characterization. The proposed technique is based on a reactive-near-field measurement or direct acquisition of RF current. We present a simple formulation that requires minimal current measurements to successfully extract the mutual impedance. Currents are predicted for an arbitrary combination of bias voltages that are used to control the reactance of varactor diodes integrated with the antenna's parasitic elements. These predicted currents are compared by conducting an experiment with a seven-element ESPAR. For the bias voltage combinations that have reasonably good symmetry, the differences in relative gain, beam direction and half power beam width (HPBW) actually fall within 0.5 dB, 4deg and 9deg, respectively. Directivity patterns obtained by calculating the predicted currents are verified with those obtained by calculating the directly measured currents. Furthermore, the calculated patterns are verified through comparison with far-field measurements in a conventional anechoic chamber. The differences in beam direction and HPBW are also found to be acceptable. Using the proposed technique, the required number of measurements is reduced from 85,766,121 to just 149 for a seven-element array

HIGH PERFORMANCE CONICAL HORN ANTENNAS (PART I)

This is the first of a series of papers concerned with improving the radiation characteristics of conical horn antennas by means of dielectric loading, edge modification, edge diffraction compensation, wall corrugation and impedance loading schemes. A conical dielectric shell attached to the inner wall of the horn is examined in this paper and found to improve the axial directivity and half power beamwidth of the antenna at the expense of minor deterioration in the side lobes. An exact formulation of the boundary value problem is presented leading to analytical results which are in good agreement with experiment.

A synoptic study of different superdirective endfire array concepts

Under a synoptic viewpoint end-fire array concepts are presented by using Chebyshev and Legendre polynomials. The arrays are designed by different combinations of their coefficients. Directivity and half power beamwidth (HPBW) versus the array spacing as well as versus the side lobe level are given. Finally several examples for the Chebyshev and Legendre arrays and arrays based on products of Chebyshev as well as Legendre polynomials are presented.

Finding the approximate angular probability density function of wave arrival by using a directional antenna

The first-order approximate angular probability density function of wave arrival can be obtained by plotting the mean-square value of signal level versus the pointing angle of a mobile radio directional antenna during an entire test run. The accuracy of this first-order approximation is dependent on the beamwidth of the antenna. As the beamwidth of the antenna becomes narrower, the approximate density function becomes more accurate. There are also higher order approximations for obtaining a more accurate angular probability density function without narrowing the directional antenna beamwidth. These higher order approximations are related to the moments of the signal strength received by the same directional antenna used in obtaining the first-order approximation. All of these are theoretical predictions. An experimental verification using a first-order approximate angular probability density function in finding theoretical level crossing rates of a mobile radio signal is given. The theoretical level crossing rates are in fairly good agreement with the experimental ones as long as the angular probability density function is not far from a uniform distribution.

Radiation characteristics of dielectric-loaded horn antennas

The radiation characteristics of electromagnetic horns loaded with curved transverse dielectric slabs and radial dielectric strips are investigated experimentally. It is shown that the axial directivity and halfpower beamwidth of horn antennas may be significantly improved with such schemes of dielectric loading.