Antenna In Free Space Research Articles

Magnetodielectric Nanocomposite Polymer-Based Dual-Band Flexible Antenna for Wearable Applications

One of the major challenges in wireless communication technologies is the antenna design. In this paper, a wideband flexible antenna made by covering a Kapton substrate with a flexible magnetodielectric polymer-based nanocomposite layer is proposed. This novel magnetodielectric polymer-based nanocomposite relies on carbon-coated cobalt (CCo) and is coated with a conjugated polymer, polyaniline (PANI). The nanocomposite (PANI/CCo) fabrication, whose morphology was studied via scanning electron microscopy, demonstrates a relative permeability, a dielectric permittivity, and a conductivity of 5.5, 4.3, and 7500 S/m, respectively. In this paper, two frequency bands are of interest [1.8–2.45 GHz (personal communication service and wireless local area network) and 5.15–5.825 GHz (wireless networks)]. The functioning of the antenna in free space and on body is numerically and experimentally investigated. The average specific absorption rate is also discussed. Thanks to its performance this magnetodielectric nanocomposite polymer (PANI/CCo) antenna has been found to be a good candidate for wearable applications where complex bending situations are encountered.

Radiation Blockage Reduction in Antennas Using Radio-Frequency Cloaks [Antenna Applications Corner

This article presents an experimental demonstration of antenna blockage reduction based on the concept of radio-frequency (RF) cloaking. The proposed cloaking configuration is validated by studying the antenna characteristics in the presence of obstacles that are covered with and without the cloaking surface. The known concept of thin cloaks used for reducing the scattering width is extended in this article to mitigate the blockage in antennas. An attempt is made to improve the degraded radiation characteristics of the antenna due to the presence of metal obstacles loaded in front of the aperture. This is accomplished by covering the obstacles with a cloaking surface made up of a periodic arrangement of interconnected patches and microstrip lines. The optimizations are carried out for various scenarios by varying the thickness of the substrate and the length of the interconnecting microstrip line to achieve an optimum cloaking performance. It is demonstrated through measurements that the RF cloaking could be achieved between the frequencies 3 and 3.3 GHz. At 3.2 GHz, the gain of the horn antenna in free space is measured to be 17.2 dBi, and the gain of the horn antenna with uncloaked obstacles at the aperture is 3.73 dBi. The same configuration with cloaked obstacles exhibits a gain of 12.13 dBi.

A Fast Way to Accurately Calibrate Tunable Dipole Antennas at VHF

A fast method is proposed and verified experimentally to calibrate tunable dipole antennas. An adapter is introduced to convert a commercially available balun for dipoles into a three-port network; this allows its S-parameter to be accurately measured. Using this process, the antenna factor, site attenuation (SA), as well as balance, can be calculated with the method of moments (MoM). The calculated SA is verified by precise measurements on a high-performance open-area test site, and the differences are less than 0.3 dB from 30 to 282 MHz. As an application, the mutual impedance correction factors are calculated with the MoM for tunable dipole antennas. Furthermore, the three balun method is proposed to measure the loss of a balun with two simple adapters, which provides a faster method to calculate the free-space antenna factor ( F a). The new method will reduce the time from several days to several hours to calibrate a pair of tunable dipole antennas. A clearer traceability chain for measuring F a is illustrated, too.

Outdoor-to-Indoor Empirical Path Loss Models: Analysis for Pico and Femto Cells in Street Canyons

The applicability of COST231, WINNER+, ITU-R, and 3GPP urban microcell outdoor-to-indoor path loss prediction models is empirically tested in 100 m radius urban femtocells. The analysis is based on more than 500 link measurements. Considerations not specified in the models such as the inclusion of antenna gains and the effect of base station location on the street are evaluated. We find that for our scenarios, discrepancies among the models can reach up to 10 dB at the median. Using the WINNER+ model path loss with free-space antenna gains yields the best match to our measurements.

Effect of External Antenna Patterns for a GMR-1 3G Handset on Satellite Forward Link Radio Channels

Based on the measurements for a GEO-mobile radio-1 third generation (GMR-1 3G) handset with different external antennas in free space as well as with the head and hand setups, effects of the antenna patterns on a satellite forward link radio channel are studied in this paper. When merging the antenna gain patterns into Rayleigh and Ricean channels proposed in GMR-1 3G standard, it’s found that the received power in satellite forward link has big deviation from original Rayleigh and Ricean distributions. At the same time, the performances for different external antennas are evaluated, it’s found that helix octafilar with 16 mm diameter is much better than other external antennas which are aimed to be directed to a specific angular range in the elevation plane for a geo-satellite mobile system.

A dielectric rod antenna driven by a pulsed power system

A dielectric rod antenna was constructed for stimulating biological tissues. The antenna consists of three sections (a conical wave launcher, a cylindrical waveguide, and a conical emitting section). The simulation of the antenna in free space was confirmed with measurements of the return loss (S11) and the transient electric field. To reach the electric field threshold for tissue stimulation, a high voltage pulsed power system was designed and constructed to drive the antenna. Central to the pulsed power system is a transformer and an oil peaking switch. The transformer is an ultrafast, dual resonance pulse transformer with a linearly integrated primary (LIP) stage. It is capable of generating pulses with rise time <50 ns. The load for the transformer was an oil-filled transmission line that was connected to the antenna. An oil peaking switch was used to switch the line to produce high voltage picosecond transients. The electric field was measured in the near field at a distance of 4 cm. A 500 ps pulse with an amplitude of 600 V/cm was recorded for a 25 kV input from the pulse transformer. These results demonstrate the feasibility of the system and so future work will be focused on increasing the voltage and the electric field in order to stimulate biological tissues.

금속 원통 케이스를 방사소자로 활용한 펜타입 무선 프리젠터용 비대칭 다이폴 안테나

본 논문에서는 금속 케이스를 접지 방사체로 활용한 비대칭 다이폴 안테나를 제안하고, 이를 ISM 대역(2.4~2.48 GHz)에서 동작하는 펜타입 무선 프리젠터에 적용하였다. 제안한 비대칭 다이폴 안테나는 긴 원통 모양의 금속 케이스 상단에 수직모드 헬리컬 코일이 장착된 구조로, 접지면인 금속 케이스를 방사소자로 동작하게 하여 헬리컬 안테나의 좁은 대역폭과 낮은 이득을 증가시켰다. 또한, 특수 제작된 인체 팬텀을 사용하여 사람이 무선 프리젠터의 금속 케이스를 손으로 잡을 때 안테나의 성능에 미치는 영향을 분석하였다. 측정 결과, 제안한 안테나는 자유공간에서 반사손실 -10 dB를 기준으로 2.3~2.5 GHz까지 200 MHz의 대역폭을 가지며, 5 dBi의 최대이득을 나타내었다. 사람 손이 금속 케이스에 접촉한 경우에는 2.24~2.72 GHz까지 480 MHz의 대역폭이 측정되었고, 최대이득은 3 dB만큼 낮아진 2 dBi로 측정되었다. In this paper, we propose an asymmetric dipole antenna utilizing the metal case as a ground radiator for a pen-type wireless presenter which operates in the ISM frequency band(2.4~2.48 GHz). A normal mode helix mounted on the top end of the long metallic cylinder case which acts as the ground plane takes the form of the asymmetric dipole structure in the proposed antenna. The metallic cylinder case which performs as a radiating element increases the inherent narrow bandwidth and low gain of the helix. The effects of the hand contacts with the metal case on the antenna performance are measured and analyzed with a specially designed human phantom. Experimental results show that the -10 dB return loss bandwidth of the proposed antenna in free space(no hand contact) is 200 MHz that ranges from 2.3 to 2.5 GHz and the maximum gain is measured to be 5 dBi. Under the normal operating condition where the metal case is contacted with a human hand, the bandwidth is 480 MHz from 2.24 to 2.72 GHz. The maximum gain is 2 dBi, lowered by 3 dB due to the hand contact.

Results of an intercomparison for free space antenna factor measurements within the German Calibration Service (DKD)

Abstract. In this paper we discuss the results of an intercomparison for free space antenna factor measurements performed within the German Calibration Service (DKD). Three different types of antennas covering the frequency range from 30 MHz to 26.5 GHz have been calibrated in five different laboratories using different methods and calibration sites to obtain the free space antenna factor. The results agree well within the uncertainties specified by the laboratories suggesting that different approaches and different measurement sites to obtain the free space antenna factor are well compatible.

Effect of Complementary Split Ring Resonator Structure on PIFA Antenna

This paper proposes a new design of Planar Inverted-F Antenna with complementary split ring resonators (CSRRs). The operating frequency of this antenna is 2.425 GHz for Wireless Local Area Network (WLAN) application. The method is to incorporate a single CSRR cell and a periodic array CSRRs on the radiating patch. We studied the effect of this method on the characteristics of antenna in free space and in the presence of the user. We used a homogeneous model of a human head near our antenna. The parameters that considered in these works are gain, electric field, magnetic field, return loss, radiation pattern, power loss density and Specific Absorption Rate. The addition of CSRRs on to PIFA antenna will improve the gain from 4.76 dB to 4.81 dB and will reduce the Specific Absorption Rate from 3.57 W/kg to 2.95 W/kg.

Study on Interface Scheme for Non-Uniform Rational B-Spline Uniform Geometrical Theory of Diffraction Method

ABSTRACTAn interface scheme is presented to analyze radiation pattern of complex antennas for non-uniform rational B-spline-uniform geometrical theory of diffraction method. Antennas are represented as the distribution of vectorial fields around antennas in free space which can be achieved either from electromagnetic algorithms, software simulations, or practical measurements. The given scheme can be applied on common PC to analyze the radiation pattern of large-scale antenna mounted around electrically large targets efficiently especially when the structure of the antenna is unknown.

A PRACTICAL THEOREM ON USING INTERFEROMETRY TO MEASURE THE GLOBAL 21 cm SIGNAL

ABSTRACT The sky-averaged, or global, background of redshifted 21 cm radiation is expected to be a rich source of information on cosmological reheating and reionization. However, measuring the signal is technically challenging: one must extract a small, frequency-dependent signal from under much brighter spectrally smooth foregrounds. Traditional approaches to study the global signal have used single antennas, which require one to calibrate out the frequency-dependent structure in the overall system gain (due to internal reflections, for example) as well as remove the noise bias from auto-correlating a single amplifier output. This has motivated proposals to measure the signal using cross-correlations in interferometric setups, where additional calibration techniques are available. In this paper we focus on the general principles driving the sensitivity of the interferometric setups to the global signal. We prove that this sensitivity is directly related to two characteristics of the setup: the cross-talk between readout channels (i.e., the signal picked up at one antenna when the other one is driven) and the correlated noise due to thermal fluctuations of lossy elements (e.g., absorbers or the ground) radiating into both channels. Thus in an interferometric setup, one cannot suppress cross-talk and correlated thermal noise without reducing sensitivity to the global signal by the same factor—instead, the challenge is to characterize these effects and their frequency dependence. We illustrate our general theorem by explicit calculations within toy setups consisting of two short-dipole antennas in free space and above a perfectly reflecting ground surface, as well as two well-separated identical lossless antennas arranged to achieve zero cross-talk.

Free-Space Antenna Pattern Retrieval in Nonideal Reverberation Chambers

Free-space antenna radiation pattern estimation from intensity measurements made in reverberating environments has been investigated by several authors. We extend our previous analysis of a simple directivity estimator appropriate to the case where the antenna under test (and the measuring probe) is located in an ideal reverberation chamber, where the reverberation-field components are Gaussian distributed and uncorrelated to a more realistic reverberation chamber model, where the field statistics deviate from the ideal ones.

Simulation of Planar Inverted F Antenna for On-Body and free space Communication

The expansion of recent wireless communications devices has put significant Compression on the antenna performance, as the size of the device has decreased in parallel to the increase in the number of communications systems supported by a single terminal. The Body Area Network (BAN) helps constant monitoring of Human health with updates of medical records through Internet. In this paper, we propose an on-body and free space performance of Planar Inverted F antenna which operates in Industrial scientific and Medical (ISM) frequency band at 2.45 GHz. The planar inverted –F antenna is popular for portable wireless devices because of its low profile, small size, and built-in structure This antenna is designed to achieve better Specific absorption rate. Other field parameters like Gain, Directivity, Return loss and Radiation have been evaluated on the body and on free space antenna with FEM based software HFSS ver. 13.0.

A Modular Textile Antenna Design Using Snap-on Buttons for Wearable Applications

An antenna design concept with detachable radiation elements offering modular geometry reconfigurabilities for wearable applications is presented. By utilizing snap-on buttons, both as the radio-frequency (RF) connection and mechanical holding mechanism, different modularly interchangeable microstrip patches are employed to demonstrate geometry reconfigurabilities in terms of polarization and resonance frequency. The uniqueness of the design arises from the fact that all configurations share one common feed structure which consists of a two-layered substrate including snap-on buttons, a ground plane, and a proximity coupled feed. To show the concept, modular realizations with different functionalities in terms of polarization or resonance frequency are demonstrated in this paper. First, a detachable patch offering interchangeable right-hand circular polarization (RHCP) and left-hand circular polarization (LHCP) at 5 GHz is proposed. Second, a demonstration of a planar inverted-F antenna (PIFA) concept offering interchangeable resonance frequencies for the 2.4- and 5.3-GHz bands of wireless local area networks (WLAN) is given. Finally, a patch module designed for 8-GHz operation is presented to show the versatility in frequency modularity. Experimental results of the fabricated antennas in free space, worn by a torso phantom and in bending conditions, validate the concept and prove that this type of modular design offers convenient, passive, low cost, and versatile system reconfigurabilities, which can benefit wearable applications.

3D printing technique for the development of non‐planar electromagnetic bandgap structures for antenna applications

The use of 3D printing for the development of non-planar electromagnetic bandgap (EBG) structures for antenna applications is proposed. A coplanar waveguide (CPW) fed antenna is tested on a non-planar EBG substrate, fabricated using additive manufacturing techniques. Inexpensive fuse filament fabrication is used as the fabrication process. Silver-loaded conducting ink is employed for the metallic components of the EBG. The CPW antenna on the non-planar EBG structure has a satisfactory reflection coefficient at 2.45 GHz, which is suitable for Bluetooth/WLAN communications. The radiation patterns have reduced back lobes and improved gain compared with the antenna in free space.

1~3 GHz 대역용 계산가능 다이폴안테나의 접지판 위 안테나 인자 특성

본 논문은 하이브리드 발룬을 갖는 계산가능 다이폴안테나가 접지판 위에 수평 및 수직으로 놓여 있을 경우의 안테나 인자 특성을 모멘트법으로 검토하고 있다. 안테나 인자의 표현식은 전력부정합손실의 개념을 적용하여 도출한 식을 사용하였으며, 안테나 인자의 계산에서 나타나는 안테나의 입력 임피던스 및 유효길이는 모멘트법을 적용하여 계산하고 있다. 그 결과, 접지판 위에서의 안테나 인자 특성은 안테나의 편파상태에 따라 달라지며 자유공간 안테나 인자와는 최대 ± 0.14 dB 의 차이가 발생함을 알 수 있었다. 또한, 수평편파인 경우의 안테나 인자 변동폭이 수직편파인 경우보다 0.2 dB 정도 더 크다는 것도 확인할 수 있었다.

A compact dual‐band frequency‐reconfigurable textile antenna for wearable applications

ABSTRACTThis communication presents a flexible, low‐profile, frequency‐tunable textile antenna for body area wireless communication. The antenna operates in both instrument, scientific and measurment (ISM), 2.45 GHz and wireless local area network (WLAN), 5 GHz bands. It features with an overall 5 × 23.5 mm2 compact planar geometry consisting of a well‐optimized slotted radiating patch fabricated using conductive copper tape on Denim material as a very common flexible textile substrate. The antenna radiates unidirectionally, and the ground plane made up with copper tape avoids radiation coupling to the users’ body. A single PIN diode with simple biasing circuitry is used to tune the antenna between the two operating bands. The performance of the antenna in free space as well as under bending conditions and when placed on the body is presented. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2251–2257, 2015

Tri‐band HIS backed spiral antenna for wireless LAN applications

ABSTRACTThis study reports the performance of an Archimedean spiral antenna, which exhibits unidirectional circularly polarized radiation patterns with a peak gain &gt;8 dBic in the lower (2.4–2.485 GHz) and upper (5.15–5.35 and 5.725–5.875 GHz) Wireless local area network frequency bands. The required backlobe suppression and impedance match are obtained by placing a multiresonant high impedance surface (HIS) in close proximity to the radiating aperture. Simulated and measured radiation patterns are shown at the center frequency of all three channels and a comparison of the key performance metrics is made with free space and metal backed antenna arrangements to demonstrate the enhancements which are attributed to the HIS reflector. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1116–1121, 2015

Differential site attenuation without using free space antenna factor

Differential site attenuation (DSA) to verify the performance of electromagnetic compatibility (EMC) facilities, open area test site and semi-anechoic chamber, without using a calibrated free space antenna factor (AFFS) is proposed. In the evaluation of EMC facilities, the AFFS is one of the main uncertainty contributions. The measured results are reported and compared with the current site attenuations. It is shown that the proposed DSA has good discrimination capability in verifying the performance of EMC facilities.

An Approximate Method for Calculating the Near-Field Mutual Coupling Between Line-of-Sight Antennas on Vehicles

Calculating the mutual coupling between antennas on vehicles using full-wave simulations requires a vast amount of computer resources due to the electrical size of the structures. We therefore propose an alternative and approximate method to determine mutual coupling between antennas on vehicles for the case where there is line-of-sight (LOS) between the antennas. The proposed method is based on approximating the mutual coupling between LOS antennas on vehicles as near-field transmission between antennas in free space. We begin the analysis with a brief review of four methods for calculating the near-field free-space transmission. Of the investigated methods, we demonstrate that a nonsingular form of the near-field transmission integral originally proposed by Yaghjian (1982) is the most suitable for LOS antennas on vehicles. We introduce a modification to this method, in order to only use the antenna far-fields and geometrical separation to determine the mutual coupling. The comparison with full-wave simulations indicates that the proposed method has a good accuracy for LOS antennas. This paper ends with a full-scale mutual coupling calculation for two monopoles on an aircraft under LOS conditions, demonstrating a root mean square (rms) accuracy of 6 dB for frequencies up to 5 GHz, as compared with full-wave simulations.