Antenna Feed Point Research Articles

On the uncertainty in numerical modeling of wireless communication devices operating at frequencies of 900 MHz, 1800 MHz, and 28 GHz.

Some of the difficulties in numerical modeling of wireless communication devices for dosimetric evaluations arise from, e.g. incomplete documentation available for the numerical model, such as missing information on dielectric materials or the antenna matching circuitry. This study investigates the impact of these difficulties on the dosimetric results, such as the peak spatial average specific absorption rate at 900 and 1800MHz and the peak spatial average power density at 28GHz. The impact of dielectric losses, detuning, and mesh resolution is quantified using different generic and Computer Aided Design (CAD) based models of wireless transmitters. The findings show that the uncertainties of the numerical results due to detuning and mesh resolution can be reduced by normalization to the antenna feedpoint power instead of the feedpoint current. Uncertainties due to variations in dielectric losses can largely be compensated by normalization to the radiated power.

Examination of Mid-Infrared Photon Detection by Hot Electron Bolometer With Twin Slot Antenna

As a high-speed and sensitive mid-infrared (MIR) photon detector, we developed a MIR superconducting hot electron bolometer (MIR-HEB). The MIR-HEB consists of a twin-slot MIR-wavelength antenna and a small Nb/NbN superconducting strip located at the antenna's feeding point. To prevent the HEB from latching, a parallel shunt resistor was added. For detector evaluation, a continuous-wave quantum cascade laser with a wavelength of 4.57 μm was used as the source of MIR light. A constant bias current was applied near the HEB critical current during the detector operation. Upon illumination with MIR light, numerous voltage pulses with a width of approximately 4 ns were observed. Furthermore, it was demonstrated that the pulse count rates were nearly proportional to the incident power over a two-order magnitude range. We conclude that MIR-HEB achieved MIR photon detection based on this result. Also confirmed were the polarization dependences attributed to the antenna's operation.

Compact dual-band MIMO monopole dual-antenna system for 5G laptops

AbstractThe study aimed to present a dual-band 5G multi-input multi-output monopole dual-antenna system, which was configured on the upper edge of the display ground plane for laptops. The dual-antenna unit is a 29 × 2 × 3 mm3three-dimensional structure with two antennas of the same structure and size, consisting of a fed monopole antenna and a shorted monopole antenna. The antennas are arranged 4 mm apart, side by side in the same direction, to form a dual-antenna unit. Such a configuration allows the feeding points of the two antennas to be separated by the shorting point of the shorted monopole antenna, and the shorting point of the low-frequency resonant path (the shorted monopole antenna) of the two antennas to be larger than a quarter of the wavelength of the low frequency with appropriate bending. The strong current will be concentrated near the shorting point of the shorted monopole antenna when the low-frequency mode is excited, and the current flow from the ground to the feeding point of the other antenna will be reduced, achieving the isolation which is better than 10 dB in measurement between the two antennas without adopting any isolation element. The envelope correlation coefficients calculated from the measured complex E-field radiation patterns are all smaller than 0.12, which can cover the 5G dual-band operations of 3300–3600 and 4800–5000 MHz, and the measured antenna efficiencies can reach more than 40%, which are well suited for multiple antenna applications.

Assessment of incident power density in different shapes of averaging area for radio-frequency exposure above 6 GHz

Objective. The International Commission on Non-Ionizing Radiation Protection guidelines and IEEE C95.1-2019 standard for human protection from local electromagnetic field exposure above 6 GHz state that absorbed (or epithelial) power density (APD) and incident power density (IPD), averaged over a square area, are internal and external physical quantities, respectively, that set the exposure limit. Per exposure standards, the measurement procedure and evaluation of the IPD have been established in technical standards, where a circular averaging area is recommended only for non-planar surfaces in IEC/IEEE 63195-1 and -2. In this study, the effects of two averaging shapes on the APD and IPD are evaluated computationally to provide new insights from the viewpoint of exposure standards. Approach. The relation between the APD, IPD, and the steady-state temperature rise (heating factor) in rectangular and human models for exposure to a single dipole, dipole arrays, and the Gaussian beams is investigated computationally with finite-difference method. Main results. The maximum differences in the heating factor of the APD and IPD for square and circular averaging areas were 4.1% and 4.4% for the antenna–model distance >5 mm, respectively. These differences appear when the beam pattern on the model surface has an elliptical shape. For an antenna–model distance ≤5 mm and at frequencies ≤15 GHz, the heating factors for square averaging areas were not always conservative to those for circular ones (−7.8% for IPD), where only the antenna feed point are visible before beam formation. Significance. The heating factors of the APD and IPD for a circular averaging area are conservative for near-field exposure of canonical sources for frequencies up to 300 GHz, except for a beam with a significant major-to-minor axis ratio and an angle of 30°–60° to a square averaging area. This tendency would help bridge the gap between exposure and product standards.

Remote dynamic actuation of an electrostatically driven microcantilever by a wireless power transfer system

The design, modelling, fabrication and test of a device prototype, based on a microcantilever capacitively connected to a folded-end half-wave dipole antenna, which is remotely actuated by a wireless power transfer (WPT) system are presented here. The microcantilever and the antenna, which are coupled at the antenna feeding point, work as a new device, is able to harness the radiated energy wirelessly transferred from an emitter antenna to directly excite the mechanical vibration modes of the microcantilever. The response to an amplitude-modulated (AM) RF radiated signal excitation produced by a transmitting antenna is experimentally analysed and fit to a simple model when the distance between both antennas varies from the near field to the radiated far field regime. • Folded-end half-wave dipole antena coupled to an electrostatically actuated microcantilever. • Wireless Power Transfer in the near and far field regions. • Direct transduction of microwave radiated power into AC mechanical vibration. • Compact batteryless AM receiver that includes the antenna, the demodulator and the microcantiltver based microspeaker.

Improving power transfer in rectenna via impedance matching at GHz frequencies

A simple and elegant impedance-matching method for rectenna operating in a narrow frequency range is presented. The method used two coplanar strip lines emerging from the antenna feed-point, to correct for the reactive component of the antenna impedance on one side, and to connect the rectifier and transform its impedance on the other side. The experimental results were supported by numerical simulations, which suggest that the same impedance matching technique can be used for mm-waves and terahertz (THz) radiation applications. Microwave characterization of the fabricated devices (impedance-matched and non-matched) showed that the responsivity of the impedance-matched rectenna is approaching an order of magnitude higher at 20 GHz than that of a control device without a matching network.

Electromagnetic Navigation System-Guided Microwave Ablation of Hepatic Tumors: A Matched Cohort Study.

To assess the accuracy and applicability of an electromagnetic navigation system (EMNS) for CT-guided microwave ablation (MWA) of hepatic tumors in comparison with conventional CT-guidance. 34 patients (m = 20/f = 14, mean age 34y) with 34 liver tumors (primary = 22, metastases = 14, mean size 20mm) referred for CT-guided MWA were included in this IRB-approved study. Interventions were performed prospectively using an EMNS in 17 patients (navigation group), and results were compared to a matched historic cohort of 17 patients using conventional CT-guidance (control group, t-test, p < 0.05 deemed significant). Primary outcome measurement: accuracy of antenna placement (deviation). Secondary outcome measurements: setup time, number of control scans, duration and radiation exposure for antenna placement. Ablations were performed using a single or a double-angulated approach. Application of the EMNS was feasible in 14 cases (82%). Mean total deviation of the antenna feed point in the navigation and control group was 2.4mm (range 0.2-4.8mm) and 3.9mm (range 0.4-7.8mm), p < 0.05. Mean setup time for the EMNS was 6.75 ± 3.9min (range 3-12min). Mean number of control scans in the navigation and control group was 3 ± 0.9 (range 1-4) and 6 ± 1.3 (range 4-8), p < 0.0001; mean time for antenna placement was 9 ± 7.3min (range 1.4-25.9min) and 11.45 ± 6.1min (range 3.9-27.4min), p = 0.3164. Radiation exposure was significantly less in the navigation group. Our experience in a limited number of patients suggests that EMNS enables intuitive CT-guided MWA of liver tumors with higher accuracy when compared to ablations performed without navigation and with fewer control scans needed.

Novel Miniaturized Antenna With a Highly Tunable Complex Input Impedance for Capsules

A novel miniaturized antenna with a complex input impedance that can be flexibly tuned is proposed for ingestible capsules in this work. The antenna is circular in shape with a diameter of 10 mm and works in the industrial, scientific, and medical (ISM) 2.45 GHz band. Owing to the use of a novel $\Pi $ -match and the utilization of coupling between the antenna end and feed point, both the real and imaginary parts of the input impedance of the proposed antenna can be tuned flexibly in a wide range. In addition, the input impedance varies smoothly with frequency, which implies a wide bandwidth. Hence, the proposed antenna can be conjugately matched to a transceiver directly without using extra impedance matching network. The operating principle of the proposed antenna is analyzed in-depth through the equivalent circuit and parametric study. To demonstrate the advantages, the proposed antenna is then compared with a widely used miniaturized antenna with T-match. Finally, the prototypes are fabricated and measured to experimentally validate the proposed design.

Design of a low‐cost broadband loaded dipole antenna for VHF/UHF frequency range

This study describes the concept and design of a low-cost super broadband dipole antenna with a passive matching network. The proposed dipole antenna is designed in three steps. First, a simple planar dipole antenna with six different loads and a balanced to unbalanced (Balun) transformer is designed by the genetic algorithm optimisation. The position and value of the loads are optimised to achieve an acceptable radiation pattern and voltage standing wave ratio (VSWR) over the desired frequency bandwidth. In the next step, the shape of the printed strip dipole antenna is optimised to improve the frequency response of the designed antenna. Finally, an LC network is added to the antenna feed point to reduce the antenna VSWR at low frequencies. The final dipole antenna has a length of 1.7 m and can operate over 30-1200 MHz with VSWR -10 dBi. The proposed antenna can easily be fabricated at a low cost via the printed circuit board technology. An industrial prototype of the proposed antenna is fabricated and measured. A good agreement between measurement and simulation results is observed.

A 60 GHz phased array with measurement and de-embedding techniques

We present a 60 GHz phased array system that combines several key technologies to realize 10 GHz bandwidth coverage. Particularly, a tightly coupled dipole array centered at 60 GHz is designed and tested for its wideband performance. The tightly coupled dipole elements offer excellent wideband behavior of 10 GHz with voltage standing wave ratio < 3 with scanning to 45°, as well as low cost printed circuit board fabrication. Additionally, we demonstrate a measurement setup with de-embedding procedure to measure gain at the antenna feed point. A feeding structure was designed and fabricated for de-embedding gain pattern measurements. Recovered measurements are shown to be in agreement with simulation.

SAR Comparison of SAM Phantom and Anatomical Head Models for a Typical Bar-Type Phone Model

The current IEEE 1528 and IEC 62209-1 standards specify a simplified physical model of the human head to provide conservative measurement procedures of the peak spatial-average specific absorption rate (SAR) of a mobile phone. This means that the evaluated SAR in a specific anthropomorphic mannequin (SAM) head model should be higher than in the heads of a significant majority of users under normal operational conditions. In this paper, the conservativeness of the SAM is investigated by numerically comparing the SAR in the SAM with those in four anatomical head models at different ages for exposure from a typical bar-type mobile phone. A numerical bar-type phone model with an internal antenna at the bottom of the phone body was implemented at 835 and 1850 MHz. This model provides an SAR pattern and levels similar with the commercial bar phones released in Korea. For two standard test positions, spatial peak 1- and 10-g SARs were calculated for both the SAM phantom and anatomical head models. The SARs were also calculated when the antenna is located on top of the phone. The results show that the SAM phantom provides a conservative evaluation for a phone model with the antenna on the top. However, when the antenna is located at the bottom, the hotspot in the SAM occurred farther from the antenna feed point, and, thus, produced lower 1- and 10-g SAR results compared with the anatomical models.

Numerical models to evaluate the temperature increase induced by ex vivo microwave thermal ablation

Microwave thermal ablation (MTA) therapies exploit the local absorption of an electromagnetic field at microwave (MW) frequencies to destroy unhealthy tissue, by way of a very high temperature increase (about 60 °C or higher). To develop reliable interventional protocols, numerical tools able to correctly foresee the temperature increase obtained in the tissue would be very useful. In this work, different numerical models of the dielectric and thermal property changes with temperature were investigated, looking at the simulated temperature increments and at the size of the achievable zone of ablation. To assess the numerical data, measurement of the temperature increases close to a MTA antenna were performed in correspondence with the antenna feed-point and the antenna cooling system, for increasing values of the radiated power. Results show that models not including the changes of the dielectric and thermal properties can be used only for very low values of the power radiated by the antenna, whereas a good agreement with the experimental values can be obtained up to 20 W if water vaporization is included in the numerical model. Finally, for higher power values, a simulation that dynamically includes the tissue’s dielectric and thermal property changes with the temperature should be performed.

A Balun-Free Helical Antenna for Minimally Invasive Microwave Ablation

We present a balun-free coax-fed helical antenna for microwave ablation. The proposed antenna produces a localized specific absorption rate pattern at the desired frequency of operation without using a coaxial balun. This reduces the outer diameter of the antenna and, thus, its invasiveness. Balun-free operation of the proposed antenna is achieved by operating the helical antenna at the second resonant frequency of the helix where a current minimum occurs at the feed point, resulting in an intrinsically high feed-point impedance. This efficiently chokes the currents excited on the outer surface of the feeding cable. Using a compact quarter-wavelength impedance transformer or a coaxially implemented pi network of reactive elements at the antenna feed point, we achieve an excellent impedance match between the antenna and the main feeding line. We fabricated a prototype of the proposed helical antenna with an outer diameter of 2.2 mm using the pi matching network. We used this prototype to conduct ablation experiments in ex vivo bovine liver. The dimensions of the resulting ablation zones are similar to those produced by coaxially fed antennas that use coaxial baluns. Our balun-free antenna design offers a promising solution for reducing the invasiveness of interstitial antennas used in microwave ablation.

A Broadband VHF/UHF Double-Whip Antenna

This paper presents a broadband VHF/UHF double-whip antenna with one lossless matching scheme combining two methods, embedded transmission line matching method and lumped-distributed hybrid matching method. By adjusting the length of the embedded transmission line, the combination of double-whip antenna and the transmission line can achieve resonance, thus realize a coarse matching. By adding a lumped-distributed hybrid matching network at the feeding point of the double-whip antenna, we can further improve the matching for the double-whip antenna. Moreover, based on the two-step matching scheme, a double-whip antenna has been designed and fabricated. Measured results show that, the VSWRs of the double-whip antenna, with the electrical lengths of 0.16 λ and 0.03 λ at the minimum operation frequency respectively, are less than 2 over a 17:1 octave bandwidth, and the horizontal gains of the antenna are between 4.2 dB and 6.8 dB. Thanks to its high gain, broadband and low reflection, the proposed double-whip antenna in this paper is ideal for application in vehicle wireless communication.

Bandwidth enhancement of WWAN/LTE tablet computer antenna using embedded parallel resonant circuit

AbstractBy embedding a printed parallel resonant circuit, the lower‐band bandwidth of the proposed internal tablet computer antenna is greatly enhanced.This bandwidth‐enhancement technique allows the proposed antenna to cover the eight‐band wireless wide area network/long term evolution operation in the 704–960 and 1710–2690 MHz bands with a small size of 12 × 60 × 3.8 mm3 in the tablet computer. The main radiator of the antenna comprises a patch monopole, a longer shorted strip, and a shorter shorted strip. The latter two shorted strips form the outer boundary of the antenna and are parasitically excited by the patch monopole. The parallel resonant circuit is formed by embedding a chip‐inductor‐loaded narrow strip in‐between the longer shorted strip and the patch monopole, with the narrow strip whose front terminal connected to the patch monopole and end section gap‐coupled to the longer shorted strip. This embedded circuit can lead to the generation of a parallel resonance seen at the antenna's feeding point. By controlling the parallel resonance to be at the high‐frequency tail of the resonant mode at about 800 MHz contributed by the longer shorted strip, an additional resonance can be generated, which can result in dual‐resonance excitation of the original single‐resonance mode. Thus, a wide antenna's lower band is obtained. Further, the patch monopole can contribute a resonant mode to combine additional resonant modes contributed by the two shorted strips to form a wide antenna's upper band. Details of the proposed antenna with the embedded parallel resonant circuit are described in the article. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:305–309, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26580

Design of a Planar Slotted Waveguide Array Antenna for X-band Radar Applications

A planar slotted waveguide array antenna has been designed at 9.37 GHz for X-band radar applications. The antenna consists of multiple branchline waveguides with broadwall radiating shunt slots and a main waveguide to feed the branch waveguides through a series of inclined coupling slots. The antenna feed point is located at the center of the main waveguide. Element weights in the array have been calculated bysampling a continuous circular Taylor aperture distribution at the 25 dB sidelobe level in both the E and Hplanes. A commercially available electromagnetic (EM) simulation tool has been used to characterize the individual isolated slot and that data hassubsequently been used to design the planar array. The array is finally analyzed in a CST Microwave studio and the measured and simulated results have been found to be in good agreement.

A Modified Bow-Tie Antenna for Improved Pulse Radiation

The analysis, design, and realization of a modified bow-tie antenna optimized for impulse ground penetrating radar (GPR) applications is described. The proposed antenna shows improved properties important for GPR, which include its compact size (in comparison with a conventional bow-tie antenna) and ability to radiate UWB pulses with increased amplitude and very small late-time ringing. A substantial increase in the amplitude of the transmitted pulse is achieved by utilizing radiation from discontinuities introduced by the resistive loading employed in the antenna to suppress late-time ringing. By choosing an optimal distance between the antenna's feed point and the location of the resistive loading, radiations that occur from the antenna's feed point and the mentioned discontinuities at the resistive loading will combine constructively in the boreside direction of the antenna. As a result, one will observe a substantial increase of the amplitude of the transmitted pulse in the boreside direction. Furthermore, an analytical expression describing approximate time-harmonic current distribution is derived to indicate an optimal resistive loading profile for the proposed antenna. Additionally, the traveling-wave current distribution of the antenna is theoretically analyzed to examine the applicability of the obtained time-harmonic expression for pulse excitation. It has been found that when the antenna is resistively loaded both the time-harmonic and traveling-wave currents decay to approach nearly the same value at the end section of the antenna. As the amount of current at the antenna ends corresponds to the level of reflection which occurs there, the derived expression is found to be useful to indicate an optimal loading profile for the proposed antenna. A theoretical model of the proposed antenna has been developed to perform numerical analysis using a modified NEC-2 code. In addition, an experimental verification has been carried out and both the simulation and experiment confirmed the improved properties of the proposed antenna.

Design, Analysis and Optimization of A Slotted Microstrip Patch Antenna Array at Frequency 5.25 GHz for WLAN-SDMA System

The design of array antenna is vital study for today's Wireless communication system to achieve higher gain, highly directional beam and also to counteract the effect of fading while signal propagates through various corrupted environments. In this study, the design and analysis of a (2x2) microstrip patch antenna array is introduced. It is designed to function in the 5.25 GHz which corresponds to IEEE 802.11a (VSWR -9.5dB) and antenna gain of 13.88 dBi have been achieved. Both numerical and experimental studies have been carried out to optimize the distance between the antenna elements. The measured results have a good agreement with that of simulated results. The numerical study has been done by using Zeland make IE3D electromagnetic simulator and measurements have been done with the help of Agilent make N5230A, network analyzer. Index Terms: Antenna array, Antenna gain, Slotted microstrip patch, Fringing field, Wireless LAN, IE3D electromagnetic simulator, antenna feed point, Array optimization.

Ultra‐wideband loop antenna coupled‐FED by a monopole feed for penta‐band folder‐type mobile phone

AbstractAn ultra‐wideband coupled‐fed loop antenna for penta‐band operation in the folder‐type mobile phone is presented. The antenna comprises a loop strip and a monopole feed; the latter not only serves as a coupling feed for the loop strip to generate a 0.5‐wavelength loop resonant mode, but also provides a 0.25‐wavelength monopole resonant mode for enhancing the operating bandwidth of the antenna. Hence, with an occupied volume of 2.6 cm3 only, the antenna can provide a very wide operating band of larger than 100% or about 1.7 GHz (from 790 to 2480 MHz), allowing the antenna to cover GSM850/900/DCS/PCS/UMTS penta‐band operation with radiation efficiencies larger than 70% for the folder‐type mobile phone in the open state (talk condition). For the antenna in the close state (idle condition), it can still provide a very wide operating band just by including a matching circuit of a series chip capacitor at the antenna's feeding point, and the radiation efficiencies over the five operating bands are still better than 53%. Details of the proposed antenna are studied. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2706–2712, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23753

Broadband planar dipole antenna for DTV/GSM operation

AbstractThis article presents a new broadband planar dipole antenna for DTV signal reception in the UHF band (470 ∼ 862 MHz) and mobile communications in the GSM850/900 band (824 ∼ 894/890 ∼ 960 MHz), which requires an operating bandwidth (3:1 VSWR) of 490 MHz or about 69% centered at 715 MHz. The antenna has two radiating arms (arm 1 and arm 2) with a total length 230 mm and a width 14 mm, which are easily printed on an FR4 substrate. Broadband operation is obtained from successful excitation of the half‐ and one‐wavelength modes of the antenna, which is achieved by shifting the antenna's feeding point away from the dipole center through adding a tuning strip to arm 1 and embedding a tuning slot to arm 2. The tuning strip is extended across the tuning slot, and both are also formed as an internal matching circuit for achieving good impedance matching of the excited half‐ and one‐wavelength modes of the antenna. The proposed antenna is presented and studied. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1900–1905, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23500