Omnidirectional Mode Research Articles

A dual‐band dual‐polarized omnidirectional patch antenna for on‐body application

AbstractAiming at the 3.5 GHz world interoperability for microwave access band and 5.8 GHz industrial scientific medical band, a dual‐band antenna operating in omnidirectional mode is proposed. The antenna uses a single‐layer dielectric substrate made of FR‐4, which is cheap and easy to process. It uses circular patches and metal branches to generate orthogonal electric fields to achieve circular polarization. At the same time, the upper patch is symmetrically slotted in a T shape, so that the patch produces two resonance frequencies. The measured impedance bandwidth of the antenna in circular polarization on‐body mode and linear polarization on‐body mode is 110 MHz (3.41–3.52 GHz) and 460 MHz (5.42–5.88 GHz), respectively. In addition, the antenna shows good performance under bending conditions and close to human tissue. At the same time, the low specific absorption rate value proves that the antenna is safe to wear on the human body.

Ultra-broadband directional thermal emission

Abstract Directional control of thermal emission over its broad wavelength range is a fundamental challenge. Gradient epsilon-near-zero (ENZ) material supporting Berreman mode has been proposed as a promising approach. However, the bandwidth is still inherently limited due to the availability of ENZ materials covering a broad bandwidth and additional undesired omnidirectional modes in multilayer stacking with increased thickness. Here, we show that broadband directional thermal emission can be realized beyond the previously considered epsilon-near-zero and Berreman mode region. We then establish a universal approach based on effective medium theory to realizing ultra-broadband directional thermal emitter. We numerically demonstrate strong (emissivity >0.8) directional (80 ± 5°) thermal emission covering the entire thermal emission wavelength range (5–30 μm) by using only two materials. This approach offers a new capability for manipulating thermal emission with potential applications in high-efficiency information encryption, energy collection and utilization, thermal camouflaging, and infrared detection.

Location Aware Beamforming in Millimeter-Wave Band Ultra-Dense Radio Access Networks. Part 2. Model of a Set of Radio Links

The second part of the study of beamforming issues, based on positioning in ultra-dense millimeter wave radio access networks, is devoted to the formalization and software implementation of a complex simulation model of the functioning of a set of directional radio links. Each directional radio link between a base station (gNodeB – gNB), equipped with an antenna array, and a user equipment (UE), operating in omnidirectional mode, is formed according to the location of the UE, known at the gNB. The set of gNB→UE directional radio links, simultaneously operating in a common frequency range, is studied as a set of traffic beams, that implement space division multiple access (SDMA). Spatial multiplexing is implemented through three-dimensional beamforming at the gNB and makes it possible to compensate for propagation losses and high levels of interference. In the first part of the study, it was shown that the problem of practical implementation of SDMA in ultra-dense radio access networks is a significant (tens of dB) spread in the signal to interference plus noise ratio (SINR), depending on the arrangement of two devices. The purpose of this study is to establish the dependence of SINR on 1) the beamwidth of the gNB sector in the direction of the user equipment in the radio link of the signal of interest (SOI); 2) uncertainty of the UE location; 3) interference from radio links of signal not of interest (SNOI): a) within its sector, b) other sectors of its cell and c) other cells in the network. The simulation model developed and implemented in software in this work for the first time made it possible to establish the interdependence of the UE positioning error factors and the required width of the traffic beam for its service. In particular, it was found, that as the positioning error decreases from 10 to 1 m, the required beam width in the horizontal and vertical planes narrows to 3 °, which makes it possible to increase the SINR to 25 dB. A simultaneous transmission multiplexing study showed that for 64 spatially multiplexed UEs, as the cell size increases from 20 to 300 m, the SINR increases by approximately 30 dB, subject to a beamwidth constraint of 3°. Unlike similar studies, in this model, the contribution from interference from simultaneously operating traffic beams within its sector, other sectors of its cell and other cells in the network is shown separately for the first time, which allows to differentiate the origin of interference and use scientifically based beamwidth control for their compensation.

A Pattern Reconfigurable Antenna Using Eight-Dipole Configuration for Energy Harvesting Applications.

A pattern reconfigurable antenna, composed of eight elements, is proposed for energy harvesting applications. Pattern reconfigurable antennas are a promising technique for harvesting from different wireless sources. The radiation pattern of the proposed antenna can be steered electronically using an RF switch matrix, covering an angle range from 0 to 360 degrees with a step size of 45 degrees. The proposed antenna primarily consists of an eight-dipole configuration that shares the same excitation. Each dipole is excited using a balun comprising a quarter-wavelength grounded stub and a quarter-wavelength open-circuit stub. The proposed antenna operates in the frequency range of 4.17 to 4.5 GHz, with an impedance bandwidth of 7.6%. By switching between the different switches, the antenna can be steered with a narrower rotational angle. In addition, the antenna can work in an omnidirectional mode when all switches are in the ON state simultaneously. The results demonstrate a good agreement between the numerical and experimental findings for the reflection coefficient and radiation characteristics of the proposed reconfigurable antenna.

Design of a transparent and flexible broadband omnidirectional antenna using characteristic mode analysis

An optically-transparent, mechanically flexible, monopole-radiation-characteristic, broadband omnidirectional antenna is proposed in this work. The radiator layer of the sandwich-structured antenna consists of a circular central patch with 16 circular satellite patches, and the characteristic mode analysis (CMA) was used to guide the detailed design process. We first analyzed the different modes of the 3×3 circular patch array, further reduced the size of the surrounding patch to increase the required omnidirectional mode bandwidth, further reduced the cross-polarization by adjusting the distance between the four corner patch and the central patch, and finally increased the number of surrounding patches to increase the bandwidth and gain. The entire analysis and optimization process uses the CMA. The antenna was excited by a single probe, with good omnidirectionality, low cross-polarization, and broad operating bandwidth in (5-12.7) GHz, achieving 87% relative bandwidth and peak gain of 4.1 dBi. The antenna has a radius of 27 mm and a thickness of 4.5 mm. A transparent and flexible antenna sample was fabricated on a flexible polydimethylsiloxane (PDMS) substrate using electrohydrodynamic (EHD) printing technology. The optical transmittance of the horseshoe-structured metal grids fabricated by EHD was investigated, as well as the equivalent surface resistance evaluation method. The theoretical optical transmittance of the horseshoe-structured single-layer silver grid on the PDMS substrate was 81.2%, versus 80.8% measured value, with an equivalent surface resistance of roughly 5 Ω/◻. The proposed antenna was bent on a 50 mm-radius cylinder surface and retained excellent omnidirectionality.

A compact four states radiation-pattern reconfigurable monopole antenna for Sub-6 GHz IoT applications

A simple design of a compact radiation-pattern reconfigurable monopole antenna with different states is proposed. The antenna switches between four radiation patterns by introducing two parasitic elements, which can be controlled by activating or deactivating two p-i-n diodes. The antenna presents two opposite-direction unidirectional modes, one bidirectional mode, and one omnidirectional mode. Few lumped components are used in the DC bias network, reducing the fabrication cost and antenna complexity. An antenna prototype is fabricated and tested to validate the proposed approach. The common operating frequency band measured realized gain and realized efficiency ranging from 3.36 GHz to 3.6 GHz, 2.13 dBi to 4.93 dBi, and 62% to 82%, respectively. The antenna presents the benefits of a low profile, simple DC bias, and the ability to suppress radiations in unwanted directions. Therefore, the antenna can be easily integrated and used in different wireless systems requiring pattern diversity, for instance, in Sub-6 GHz Internet of Things (IoT) Applications.

A Highly Pattern-Reconfigurable Planar Antenna With 360° Single- and Multi-Beam Steering

A novel single-fed horizontally polarized pattern-reconfigurable antenna is proposed with the key feature that is highly pattern-reconfigurable. The antenna is able to generate a large variety of radiation patterns, including omnidirectional, single-directive, and multi-beam patterns without using phase shifters. The antenna is based on a planar geometry, which consists of an Alford loop and four compact parasitic pixel rings with 60 integrated controlling units utilizing p-i-n diodes. Experimental and simulation results are provided for the proposed antenna design operating at 5 GHz. The results show that the single-beam steering with 7.3 dBi gain through 360° in the azimuth plane is achieved. Moreover, flexible dual-beam steering with one beam fixed and the other beam scanning independently among 360° in the azimuth plane is also demonstrated where each beam has 5 dBi gain. Other radiation modes, such as the omnidirectional mode, the tri-beam-steering mode, and the elevation plane steering mode, are also verified. The features of high pattern reconfigurability, 360° single-beam- and multi-beam-steering ability, full 3-D space scanning, planar geometry, and compatibility with a digital controller make it useful in various sub-6 GHz wireless applications, such as wireless power transfer, RF sensing, and analog precoding.

A Planar Pattern-Reconfigurable Antenna With Stable Radiation Performance

In this letter, a planar antenna withreconfigurable radiation pattern is investigated for smart Wi-Fi systems. The design incorporates one pair of folded dipoles, a microstrip-to-via feeding balun and two reconfigurable parasitic strips which are near-field excited by the dipole pair. By controlling the states of two Pin diodes embedded in two reconfigurable printed lines, the proposed antenna can switch between one omnidirectional mode and two unidirectional endfire radiation modes. This optimized antenna exhibits a decent size of 0.5 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.38 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ×0.004 λ <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 free space wavelength at 2.45 GHz). Good agreement is observed between the simulated and measured results. The overlapped impedance bandwidth with | <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | < −10 dB for the three pattern modes is from 2.34 to 2.6 GHz in the measurement. Throughout the overlapping bandwidth, the front-to-back ratios are higher than 15 dB for the two unidirectional radiation modes and out-of-roundness is less than 1.2 dB for omnidirectional radiation mode. The measured peak realized gain of the proposed pattern-reconfigurable antenna is 6 dBi. This proposed Wi-Fi antenna is well poised for intelligent Wi-Fi communication systems.

Speech perception in noise and sound localization using different microphone modes in pediatric bilateral cochlear implant users

ObjectiveThe aim of the study was to investigate if a directional microphone mode improves speech perception in noise and sound localization in experienced pediatric bilateral cochlear implant users. Methods15 bilaterally implanted children were included in the analysis. Speech perception in 4 noise conditions (S0N0, S0N90, S0N-90, S0N180) and sound localization were measured when using the OPUS 2 audio processor (omnidirectional mode) and the SONNET audio processor (omnidirectional and natural mode). ResultsSpeech perception in all 4 noise conditions was better with the SONNET natural mode than with the omnidirectional mode of either SONNET or OPUS 2. The root-mean-square error of the sound localization test was smaller with the natural mode of SONNET than with the omnidirectional mode of either SONNET or OPUS 2. The performance of the audio processors in the omnidirectional mode did not differ significantly except in the S0N0 condition of the speech perception test. ConclusionThe natural microphone mode of the SONNET audio processor improved speech perception in noise and sound localization in bilaterally implanted children.

Pinna-Imitating Microphone Directionality Improves Sound Localization and Discrimination in Bilateral Cochlear Implant Users

To compare the sound-source localization, discrimination, and tracking performance of bilateral cochlear implant users with omnidirectional (OMNI) and pinna-imitating (PI) microphone directionality modes. Twelve experienced bilateral cochlear implant users participated in the study. Their audio processors were fitted with two different programs featuring either the OMNI or PI mode. Each subject performed static and dynamic sound field spatial hearing tests in the horizontal plane. The static tests consisted of an absolute sound localization test and a minimum audible angle test, which was measured at eight azimuth directions. Dynamic sound tracking ability was evaluated by the subject correctly indicating the direction of a moving stimulus along two circular paths around the subject. PI mode led to statistically significant sound localization and discrimination improvements. For static sound localization, the greatest benefit was a reduction in the number of front-back confusions. The front-back confusion rate was reduced from 47% with OMNI mode to 35% with PI mode (p = 0.03). The ability to discriminate sound sources straight to the sides (90° and 270° angle) was only possible with PI mode. The averaged minimum audible angle value for the 90° and 270° angle positions decreased from a 75.5° to a 37.7° angle when PI mode was used (p < 0.001). Furthermore, a non-significant trend towards an improvement in the ability to track moving sound sources was observed for both trajectories tested (p = 0.34 and p = 0.27). Our results demonstrate that PI mode can lead to improved spatial hearing performance in bilateral cochlear implant users, mainly as a consequence of improved front-back discrimination with PI mode.

The efficacy of microphone directionality in improving speech recognition in noise for three commercial cochlear-implant systems

Objectives: To investigate the effect of fixed and adaptive microphone directionality on speech reception threshold (SRT) in noise when compared to omnidirectional mode in unilateral cochlear-implant (CI) use for three different CI systems.Methods: Twenty-four CI recipients with bilateral severe-to-profound hearing loss participated in the study. Eight recipients of each CI system were enrolled, and their SRT in noise was measured when the speech and noise signals were co-located in the front to serve as a baseline. The acute effect of different microphone directionalities on SRT in noise was measured with the noise emanating at 90° in the horizontal plane from the side of the CI sound processor (S0NCI).Results: When compared to the baseline condition, the individual data revealed fairly similar patterns within each CI system. In the S0NCI condition, the average improvement in SRT in noise for fixed and adaptive directionalities over the omnidirectional mode was statistically significant and ranged from 1.2 to 6.0 dB SNR and from 3.7 to 12.7 dB SNR depending on the CI system, respectively.Discussion: Directional microphones significantly improve SRT in noise for all three CI systems. However, relatively large differences were observed in the directional microphone efficacy between CI systems.

Audiological Results with the SAMBA Audio Processor in Comparison to the Amadé for the Vibrant Soundbridge

Background: Since its introduction in 1996, the Vibrant Soundbridge (VSB) has been upgraded with several improved generations of processors. As all systems are compatible, implanted patients can benefit from new technologies by upgrading to the newest processor type available. Objectives: The aim of this study was to compare the performance of the new (current) SAMBA processor with the previous Amadé processor. Methods: Twenty subjects monaurally implanted with a VSB and the Amadé processor tested the new SAMBA processor for a trial period of 4 weeks. We measured air conduction and bone conduction thresholds, unaided thresholds, and aided free field thresholds with both devices. Speech performance in quiet using the Freiburg monosyllabic test at 65 dB SPL (S₀) was compared. The speech intelligibility in noise was determined using the Oldenburg sentence test measured in different listening conditions (S₀N_VSB/S₀N_contra) and microphone settings (omni/directional vs. adaptive directivity). Results: Word recognition scores in quiet with the SAMBA were still significantly lower than with the Amadé after the 4 weeks trial period but improved over the following year. Speech intelligibility with the SAMBA was significantly better than with the Amadé in omnidirectional mode and comparable with the Amadé in directional mode. Hence, the adaptive directionality provides an advantage in difficult hearing situations such as noisy environments. The subjective benefit was evaluated using the Abbreviated Profile of Hearing Aid Benefit and the Speech, Spatial and Qualities-C questionnaire. Results of the questionnaires demonstrate an overall higher level of satisfaction with the new SAMBA speech processor than with the older processor. Conclusion: The SAMBA enables similar speech perception in quiet but more flexible adaptation in acoustically challenging environments compared to the previous Amadé processor.

Improving Cochlear Implant Performance in the Wind Through Spectral Masking Release: A Multi-microphone and Multichannel Strategy.

Adopting the omnidirectional microphone (OMNI) mode and reducing low-frequency gain are the two most commonly used wind noise reduction strategies in hearing devices. The objective of this study was to compare the effectiveness of these two strategies on cochlear implant users' speech-understanding abilities and perceived sound quality in wind noise. We also examined the effectiveness of a new strategy that adopts the microphone mode with lower wind noise level in each frequency channel. A behind-the-ear digital hearing aid with multiple microphone modes was used to record testing materials for cochlear implant participants. It was adjusted to have linear amplification, flat frequency response when worn on a Knowles Electronic Manikin for Acoustic Research to remove the head-related transfer function of the manikin and to mimic typical microphone characteristics of hearing devices. Recordings of wind noise samples and hearing-in-noise test sentences were made when the hearing aid was programmed to four microphone modes, namely (1) OMNI; (2) adaptive directional microphone (ADM); (3) ADM with low-frequency roll-off; and (4) a combination of omnidirectional and directional microphone (COMBO). Wind noise samples were recorded in an acoustically treated wind tunnel from 0° to 360° in 10° increment at a wind velocity of 4.5, 9.0, and 13.5 m/s when the hearing aid was worn on the manikin. Two wind noise samples recorded at 90° and 300° head angles at the wind velocity of 9.0 m/s were chosen to take advantage of the spectral masking release effects of COMBO. The samples were then mixed with the sentences recorded using identical settings. Cochlear implant participants listened to the speech-in-wind testing materials and they repeated the sentences and compared overall sound quality preferences of different microphone modes using a paired-comparison categorical rating paradigm. The participants also rated their preferences of wind-only samples. COMBO yielded the highest speech recognition scores among the four microphone modes, and it was also preferred the most often, likely due to the reduction of spectral masking. The speech recognition scores generated using ADM with low-frequency roll-off were either equal to or lower than those obtained using ADM because gain reduction decreased not only the level of wind noise but also the low-frequency energy of speech. OMNI consistently yielded speech recognition scores lower than COMBO, and it was often rated as less preferable than other microphone modes, suggesting the conventional strategy to switch to the omnidirectional mode in the wind was undesirable. Neither adopting an OMNI nor reducing low-frequency gain generated higher speech recognition scores or higher sound quality ratings than COMBO. Adopting the microphone with lower wind noise level in different frequency channels can provide spectral masking release, and it is a more effective wind noise reduction strategy. The natural 6 dB/octave low-frequency roll-off of first-order directional microphones should be compensated when speech is present. Signal detection and decision rules for wind noise reduction applications are discussed in hearing devices with and without binaural transmission capability.

Pattern Reconfigurable Rectenna With Omni-Directional/Directional Radiation Modes for MPT With Multiple Transmitting Antennas

A pattern reconfigurable rectenna, consisting of a pattern reconfigurable receiving antenna and a low-/medium-power rectifying circuit, is proposed for microwave power transmission with multiple transmitting antennas. By controlling the states of p-i-n switch groups, the receiving antenna can work at one omni-directional mode and eight directional modes with flattened wide main beams for the arbitrary direction of incoming waves. In order to achieve good impedance matching at different modes, where the received power fluctuates severely, a complex impedance compression network (CICN) is introduced to the rectifying circuit. Since the proposed rectenna has a versatile structure, it can be used for multiple transmitting antennas in conformity with the incoming waves’ direction.

Speech understanding and listening effort in cochlear implant users – microphone beamformers lead to significant improvements in noisy environments

Objectives: To evaluate the effect of microphone directionality, i.e. beamforming, on speech understanding in noise with the SONNET audio processor.Methods: Speech reception thresholds (SRTs) were tested in three different microphone settings (omnidirectional, adaptive, and fixed beamformer (natural)) and assessed via the Oldenburg Sentence Test and the Just Understanding Speech Test. Subjects rated the listening effort needed to understand speech in different signal-to-noise ratios (−10, −5, 0, 5, 10, 15 dB SNR) via a Visual Analogue Scale. For all test methods, speech was presented at 0° azimuth while fixed and uncorrelated masking noise was presented simultaneously from five loudspeakers positioned at ±70°, ±135°, and 180° azimuth.Results: Compared to the omnidirectional mode, significant improvements (p<0.001) were shown in mean SRTs for both the natural (3.3 dB SNR) and adaptive (5.2 dB SNR) settings. Using the natural or the adaptive setting required significantly less listening effort than using the omnidirectional setting for the SNR conditions −5 dB SNR (p=0.002) and 0 dB SNR (p<0.001).Discussion: The beamformer settings significantly improved speech understanding in noise over the omnidirectional setting. Due our multi-speaker test setup, we conclude that beamforming should yield significantly better and less stressful speech understanding in demanding real-life listening situations.

AutoAdaptive: A Noise Level-Sensitive Beamformer for MED EL Cochlear Implant Patients.

When cochlear implant (CI) listeners use a directional microphone or beamformer system to improve speech understanding in noise, the gain in understanding for speech presented from the front of the listener coexists with a decrease in speech understanding from the back. One way to maximize the usefulness of these systems is to keep a microphone in the omnidirectional mode in low noise and then switch to directional mode in high noise. The purpose of this experiment was to assess the levels of speech understanding in noise allowed by a new signal processing algorithm for MED EL CIs, AutoAdaptive, which operates in the manner described previously. Seven listeners fit with bilateral CIs were tested in a simulation of a crowded restaurant with speech presented from the front and from the back at three noise levels, 45, 55, and 65 dB SPL. The listeners were seated in the middle of an array of eight loudspeakers. Sentences from the AzBio sentence lists were presented from loudspeakers at 0 or 180° azimuth. Restaurant noise at 45, 55, and 65 dB SPL was presented from all eight loudspeakers. The speech understanding scores (words correct) were subjected to a two-factor (speaker location and noise level), repeated measures, analysis of variance with posttests. The analysis of variance showed a main effect for level and location and a significant interaction. Posttests showed that speech understanding scores from front and back loudspeakers did not differ significantly at the 45- and 55-dB noise levels but did differ significantly at the 65-dB noise level-with increased scores for signals from the front and decreased scores for signals from the back. The AutoAdaptive feature provides omnidirectional benefit at low noise levels, i.e., similar levels of speech understanding for talkers in front of, and in back of, a listener and beamformer benefit at higher noise levels, i.e., increased speech understanding for signals from in front. The automatic switching feature will be of value to the many patients who prefer not to manually switch programs on their CIs.

Speech polar plots for different directionality settings of SONNET cochlear implant processor

Objectives: The newest CI processor from MED-EL company, the SONNET, has two new directional microphone settings. Besides the Omnidirectional microphone mode, it has the possibility to switch to Natural or Adaptive directionality. Both new modes favour perception of sound coming from a front-facing direction compared to sounds from sources at alternate azimuths. Natural directionality mimics the pinna effect of the normal external ear.Design: We undertook to verify the effect of these options in vivo by means of clinical audiological tests. Speech reception thresholds were successively measured for a variety of speech presentation azimuths while keeping the noise azimuths constant. Complete ‘Speech Reception Threshold (SRT)-Polar-Plots’ were obtained from these data for the Omnidirectional and Natural directionality modes of the SONNET. In addition, one ‘SRT-point’ was also measured in the ‘Adaptive’ mode for speech coming from 45° azimuth.Study sample: A group of 13 adult CI recipients participated. Only one of these subjects had previous experience with the SONNET processor.Results: Complete ‘SRT-Polar-Plots’ could be measured in Natural and Omnidirectional modes in CI recipients within an acceptable timeframe. The pinna-following directionality for Natural mode could be confirmed. Median SRT in noise for speech coming from the 45° azimuth speaker was −5.6 dB SNR for Omnidirectional, −9.1 dB SNR for Natural and −12.8 dB SNR for Adaptive microphone. Natural and Adaptive significantly improved performance compared to Omnidirectional mode at this optimal azimuth of 45° with a median improvement in SRT of 3.5 and 7.2 dB respectively.Conclusions: A novel audiological method, ‘SRT-Polar-Plot’, was developed and described. Significant directionality benefits for Natural and Adaptive mode were confirmed in vivo using this technique.

A Clustering Approach for Multiband Neighbor Discovery on 60 GHz WLAN

The 60 GHz mmWave unlicensed band has a very large spectrum available, divided into four orthogonal channels, which allows up to 7 Gbps data rate. On the other side, the propagation in the 60 GHz band is subject to severe path loss attenuation, which can be mitigated using highly directional antennas. This high directionality brings a new challenge to neighbor discovery; the devices now need to know the exact neighbors’ physical location to successfully communicate with them. In order to expedite the neighbor discovery process, multiband protocols have been proposed in the literature in which a separate band is used for the exchange of control messages in an omnidirectional mode. Nonetheless, these proposals suffer from the control channel bottleneck problem due to the numerous messages that need to be exchanged in this channel. In this work, we propose a scheme that divides the network nodes in clusters and for each cluster we allocate one separate control channel and also a separate mmWave channel for beamforming only. The former separation allows decreasing the number of control messages exchanged in each control channel, and the latter allows the simultaneously execution of multiple beamforming. In conjunction to this clustering scheme, we propose a multiband protocol in which only the cluster leader performs beamforming and uses the control channel to propagate the information obtained during this process. We compare the existing protocols with our proposed clustering protocol in terms of average transmission time, overhead, and accuracy of neighbor discovery information.

Design of Dual-Mode Arc-Shaped Dipole Arrays for Indoor Base-Station Applications

In this letter, two novel designs of dual-mode beam-steerable antenna arrays using arc-shaped dipoles are proposed for indoor base-station applications. To obtain the optimal distribution of excitations for each array, its gain and front-to-back ratio are optimized by using the method of maximum power transmission efficiency. The first design operates at 2.45 GHz and consists of a circular ring reflector and four arc-shaped dipoles, with the electrical length of one dipole arm being 1/4 wavelength. It can switch between omnidirectional mode and directional mode, and has 360° beam scanning capability in azimuth when operating in the directional mode. The realized omnidirectional gain of the first design is 1.5 dBi, and its peak gain and front-to-back ratio in the directional mode are 7.4 dBi and 15.5 dB, respectively. The second design also operates at 2.45 GHz, composed of two circular ring reflectors and eight arc-shaped dipoles distributed in two substrates, separated by a foam layer. Compared with the first design, it has a higher omnidirectional gain of 2.9 dBi and more uniform gain distribution in azimuth in the directional mode, with a peak gain of 8.4 dBi and a front-to-back ratio of 12.5 dB.

Bandwidth enhanced dual‐band patch‐coupling microstrip antenna with omnidirectional CP and unidirectional CP characteristics

Patch-coupling method is adopted to broaden the bandwidth of one dual-band dual-mode dual-circular polarisation (DBDMDCP) circular microstrip antenna in this paper. The function of dual-band dual-mode (DBDM) is excited by simplified metamaterial structure. Curved branches loaded on the ground plane and slots perturbation of radiating patches are used to excite the circular polarisation (CP) property for both n = 0 omnidirectional mode and n = 1 mode unidirectional mode, respectively. By loading four parasitical coplanar coupling patches on the top surface, the impedance of the patch mode is obviously broadened. Furthermore, methods of coplanar coupling and cascade coupling with circular patches are both adopted to broaden the axial ratio (AR) bandwidth maintaining the impedance matching condition. Considering the processing precision, the cascade coupling type is finally fabricated and compared with the probe-fed type for verification. Measurement results show that impedance bandwidths of 4% (centered at 4.52 GHz) and 17% (centered at 5.89 GHz) with maximum gain of 1.0 dBic and 7.1 dBic are realised for the dipole mode and patch mode, respectively. Furthermore, the 3 dB axial ratio (AR) bandwidth of the patch mode is 9.2% (520 MHz centered at 5.66 GHz). Compared with the former designs, this one owns simpler structure, considerable bandwidth besides of pattern and polarisation diversity.