Showing papers presented at "International Workshop on Antenna Technology in 2010"

Progress in the design and realization of an electrically small Huygens source

Abstract: In this paper, we describe our progress to date in the design and realization of an electrically small Huygens source. We begin discussing work by Yaghjian that predicts the maximum directivity achievable with single and dual Huygens sources. Here, we attempt to realize the Huygens source utilizing electrically small electric and magnetic dipoles. Using straight-wire dipole and circular-loop elements, we demonstrate that the directivities predicted by Yaghjian can be achieved with the single and dual Huygens sources. Next, we attempt to realize the Huygens source using recently described, more practical electrically small electric and magnetic dipoles. In free space, these antennas are impedance matched to 50 Ohms and exhibit a quality factor (Q) that approaches the lower bound (the Chu limit). When used in the realization of a Huygens source, these antennas no longer exhibit matched impedances nor low Q's. The limitations that arise in realizing the Huygens source are discussed.

A new FSS design proposal for UWB applications

Abstract: This work presents a new proposal for Frequency Selective Surface (FSS) design for Ultra-Wideband (UWB) applications. The new FSSs consist of an array composed by the association of two patch elements per cell: a square loop and a crossed dipole. These structures are called Crossed Loops and have the objective of increasing the bandwidth of the square loop and the crossed dipole, when analyzed separately. Simulated results of the transmission coefficients are obtained using the Ansoft Designer™ commercial software. Some of the FSSs tested were fabricated in order to make an experimental analysis with the measured results and to validate the new proposal. In particular, the presented results for the transmission coefficient of a built FSS prototype indicate a percent bandwidth 52.4%.

A direct antenna modulation (DAM) transmitter with a switched electrically small antenna

Abstract: The first demonstration of a DAM transmitter with an electrically small antenna is presented in this paper. Traditionally efficiency-bandwidth product of an electrically small radiation system is inversely proportional to radiation Q of the antenna, which is high in nature according to radiation wave properties. However, a DAM transmitter operates in time-variant mode so that its efficiency-bandwidth product is not limited by Q. The key to improve the efficiency-bandwidth product is to decouple far-field radiation energy from near-field reactive energy. In DAM scheme, far field radiation is directly turned on and off to represent information, while a maximum reactive energy is circulated within system to enhance efficiency-bandwidth performance. To prove the concept, a traditional and a DAM transmitter have been tested and compared under the same condition. Results show that information tone received from the DAM transmitter is significantly higher in magnitude when signal bandwidth exceeds bandwidth of the traditional transmitter.

Wideband antenna efficiency measurements

Abstract: Over the past 10 years or so, many broadband and ultra-wideband antennas have been developed for broadband high data rate mobile communications. It is realized how to make efficient and accurate measurements for such antennas could be a challenging issue. In this paper, we examine the antenna efficiency measurement techniques which have been used up to now, and identify their advantages and disadvantages for broadband measurements. It is shown that the classic Wheeler cap method, which is the best for electrically small antennas, has a lot of attractive features even for broadband antenna measurements in terms of the cost and efficiency although the newly proposed reverberation chamber method may become a good alternative method. A “source stirred” method is proposed as a new approach for the broadband antenna efficiency measurement and its major advantages are cheap, convenient, and efficient. Both the experimental and numerical results are provided. It is shown that the loss due to the imperfection of the cavity can cause a serious problem for obtaining an accurate result. How to eliminate the effects of the cavity loss and improve the measurement accuracy for this method is an issue to be resolved.

Compact dual-band (2.4/5.2GHz) monopole antenna for WLAN applications

Abstract: A compact and optimized design of a rectangular printed monopole antenna with slits and truncated ground plane on FR-4 substrate is presented. The proposed antenna is designed for dual-band operation at 2.4 GHz and 5.2 GHz for Wireless Local Area Network (WLAN) applications with S 11 ≪ −10 dB. This antenna has good return loss and radiation characteristics in required frequency band. The proposed antenna gives omni-directional radiation pattern in the E Plane and H plane over the frequency range of 2.4 GHz and 5.2 GHz. The calculated and measured results in terms of return loss show good agreement and the results also show good wideband characteristics.

Fractal negative-epsilon metamaterial

Abstract: In this paper, a novel fractal metamaterial with negative permittivity is presented. It consists of two pairs of fractal Hilbert curves with antisymmetric current distribution at resonance. The resonant current distribution shows that the structure behaves as an electrically small dipole. This approach, which is different from the conventional Complementary Split Ring Resonator (CSRR) based approaches, is described and the electric resonance is illustrated. The negative permittivity is derived from the numerically calculated Z-parameters for one unit cell-thick sample under plane wave excitation. The unit cell size is only eo/21.80 × eo/21.80 at resonance. The proposed electrically small structure presents therefore a more homogeneous negative-epsilon material for “Left-handed Metamaterial” applications than the standard CSRR based solutions.

Highly-efficient multiple antenna-systems for small MIMO devices

Abstract: In this paper, we focus on highly-efficient multiple antenna-systems for small MIMO communicating devices. First, we perform a state-of-the art review of the best solutions developed by various researchers. Then we consider some fundamental aspects involved when integrating multiple antennas in a small terminal. Thereafter, we present several multiple antenna-systems designed at the LEAT of the University of Nice-Sophia Antipolis since 2004. We especially describe our neutralization technique dedicated to enhance the total efficiency of several radiators when they are closely placed over the same small ground plane. Last, we try to identify promising solutions and future trends.

Dual-band low profile antennas for body-centric communications

Abstract: Dual-band operation is highly desirable for wearable devices that need to connect with a range of wireless systems. We present a series of microstrip-line fed, dual-band compact patch antennas designed to operate in the common 2.45 GHz and 5.8 GHz bands for body-centric communications. All of the designs are low-profile and, with further study, may be suitably implemented in flexible or fabric materials. Our best performance was obtained with a shorted parasitic patch element close to a rectangular patch operating at the TM 10 mode. This design, with an overall height of less than λ/24, had a radiation efficiency of 91% at 2.45 GHz and 95% at 5.8 GHz in free space. When placed 2 mm above a muscle tissue phantom at 2.45 GHz, an efficiency of 52% and a 2∶1 impedance bandwidth of 95 MHz was obtained. The bandwidth at the 5.8 GHz band was 400 MHz in free space.

Effects of ground plane size on a square microstrip patch antenna designed on a low-permittivity substrate with an air gap

Abstract: The effects of ground plane size on the characteristics of a square microstrip patch antenna designed on a low-permittivity substrate with an air gap were investigated. The characteristics studied include return loss, gain, halfpower beamwidth (HPBW), and radiation pattern. The gain and HPBW varied periodically with increasing ground plane size, and were out of phase with each other. The relationship of the above parameters with the height of the antenna was also considered. Decreasing the antenna height changed the smallest ground plane size for impedance matching, and also reduced back radiation, which improved the front-to-back level of the microstrip patch antenna.

Effects of substrate on the performance of photoconductive THz antennas

Abstract: Photoconductive antennas have been widely used to generate and detect THz waves in recent years Because the thickness of the substrate is usually larger than the wavelength of THz waves, surface/substrate modes may be generated and the effect of the substrate cannot be ignored - this has not been properly investigated This paper is therefore to investigate this problem using a numerical simulation tool The radiation pattern and power of photoconductive antennas with different sizes of substrates are obtained The results show that the radiated power is sensitive to the dimensions of the substrate: most of the radiated power is radiated towards the substrate side rather than the free space, and a thin substrate is preferred to maximise the radiated power and control the radiation direction

A Reconfigurable Planar Antenna Array (RPAA) with back lobe reduction

Abstract: A novel structure of Reconfigurable Planar Antenna Array (RPAA) added with a microwave absorber is designed. This antenna is consists of two elements structure, which are the 16-element microstrip rectangular patch antenna structures (top structure) and the separated feed line structure (bottom structure). The unique property of this antenna design is that instead of fabricating all together in the same plane, the antenna's feeding network is separated from the antenna radiating elements (the patches) by an air gap distance. This allows reducing spurious effects from the feed line. This antenna is integrated with RF switches to produce the scanning beam pattern to desired direction. This can be done by controlling the switch state to either on or off mode. The additional material was proposed involves placing a microwave absorber material such as ECCOSORB@ (Emersion & Cuming Microwave Products, Inc., Randolph, and Mass) at the back of the top substrate. The ECCOSORB is useful for suppression of unwanted radiated field and thus improved the back lobe pattern at an average of 10 dB. The simulated results are presented to demonstrate the excellent performance of this antenna.

A printed LPDA with UWB capability

Abstract: This work deals with the design of a wideband microstrip log periodic array operating between 4 and 18 GHz (thus working in C,X and Ku bands). A few studies, since now, have been proposed but they are significantly less performing and usually quite complicated. Our solution is remarkably simple and shows both SWR and gain better than likely structures proposed in the literature. The same antenna can also be used as an UWB antenna. The design has been developed using CST MICROWAVE STUDIO 2009, a general purpose and specialist tool for the 3D electromagnetic simulation of microwave high frequency components.

UHF near-field RFID antennas

Abstract: Near-field radio frequency identification (RFID) technology has been traditionally used at low frequency (LF) and high frequency (HF) bands; now developing this technology at ultra high frequency (UHF) band is of increasingly interest. Designing a UHF near-field RFID reader antenna is one of the most challenging tasks. Traditional loop antennas cannot operate properly at the UHF band when the antennas tend electrically large so that they are unable to generate strong and uniform magnetic field in an adequate interrogation zone. A number of techniques have been presented to design UHF near-field RFID reader antennas, which enables the electrically large loop-type antenna generating desired magnetic field distribution. In this paper, the challenges of the UHF near-field antenna design are addressed. The state-of-art UHF near-field antenna techniques are reviewed and discussed.

Channel model for on body communication along and around the human torso at 2.4GHz and 5.8GHz

Abstract: A new trend in developing wireless sensors consists in using wearable wireless sensors to monitor human vital parameters, activities and movements. Characterizing the radio channel is an important issue to design a suitable communication system, especially when the propagating medium is the human body. To address this problem, on body measurements along and around the torso were performed. Two path loss models were analyzed considering the propagation channel characterization between two wearable devices placed on a human body, and operating at 2.4GHz and 5.8GHz. Wearable wireless low-cost commercial modules and low profile annular ring slot antennas were used as transceivers Measurement results were compared with CST Microwave Studio simulations using simplified body models like spherical and ellipsoidal geometries.

OTA measurements of wireless stations in reverberation chamber versus anechoic chamber: from accuracy models to testing of MIMO systems

Abstract: The paper will describe the fundamental characteristics of different wave propagation environments (such as Rayleigh fading, Rice fading, and polarization balance; coherence bandwidth and time delay spread; and fading speed, coherence time and Doppler spread), and relate these characteristics to the Line-Of-Sight (LOS) emulated by good anechoic chambers, and the rich isotropic multipath environment emulated by good reverberation chambers. The conclusion is that the reverberation chambers mean the same to Over-The-Air (OTA) testing of antennas for use in multipath environments as anechoic chambers do to antennas for free-space-like environments. They enable a unique, objective and repeatable antenna characterization that cannot be achieved in other environments. Thereby, the reverberation chambers and anechoic chambers complement each other perfectly.

Passive real-time submillimetre-wave imaging system utilizing antenna-coupled microbolometers for stand-off security screening applications

Abstract: At present, the imaging of concealed weapons and contraband is primarily carried out at a relatively short stand-off range of a few meters mainly because of spatial resolution considerations. In order to maintain a reasonable aperture size, there is a desire to extend the operating frequency towards 1 THz. In this paper we report the progress on a video-rate THz camera demonstrator which utilizes broadband antenna-coupled microbolometers as detectors, operated within a turn-key commercial closed-cycle cryocooler. A full system has been integrated consisting of 64 parallel sensors and readout electronics, and reflective Schmidt camera optics incorporating a conical scanner for real time imaging. At present, the system provides near real time submillimetre-wave video imagery at 6 frames per second.

Dual UHF RFID band miniaturized multipurpose planar antenna for compact wireless systems

Abstract: In this paper, we will discuss the design and development of a miniaturized dual UHF band antenna, resonating on the RFID bands. The antenna resonates on 433MHz and on the European RFID band (865MHz–868MHz). This antenna design is an updated version of the miniaturized 433MHz antenna model [1], with an improved performance and dual band characteristic. This type of planar antenna can be used in different type of small compact wireless systems, such as small RFID reader units, wireless sensor network nodes, and different indoor/outdoor wireless devices. The biggest challenge in designing such an antenna was the size of the antenna, for which different miniaturization techniques [2] have been used. Miniaturization techniques like shorting the radiating part of the antenna with the ground plane, similar to PIFA (Planar Inverted F Antenna) [3], and using closely coupled parallel meander line approach greatly helped in reducing the size of the antenna. The design and structure of the planar [4] antenna makes it very stable and less vulnerable to the external environmental factors, like different type of hand and walls effects. The reduced size of the antenna, with an ability to resonate on multiple most commonly used frequencies with a good gain and omni-directional radiation pattern makes it a good competitor for replacing the old antenna model with the new multipurpose small, low cost antenna model.

Antennas for RFID applications

Abstract: Antenna is one of the key factors in RFID systems. The performance of the reader / tag antennas shows significant effect on the reading range and detection accuracy of an RFID system. Since RFID systems operate at frequencies varying from low frequency (LF) to microwave frequencies (MWF), the RFID antenna designs are with distinct requirements. In this paper, we address the antenna design considerations for the latest RFID applications. Several antennas are exemplified to show the recently developed technologies for RFID antenna designs in specific RFID applications.

Multiple antenna systems for increasing on-body channel capacity and reducing BAN-to-BAN interference

Abstract: The application of multiple-input multiple-output (MIMO) in body-area networks (BAN) is considered in the paper. The correlations between MIMO sub-channels and the MIMO channel capacity are investigated for three on-body channels when random movements are performed in an indoor environment. Some of the MIMO sub-channels were found to be correlated. Nevertheless, a significant capacity increase due to use of MIMO was still observed thus demonstrating the feasibility of using MIMO in BAN communications. A simple BAN-to-BAN interference rejection method which makes use of interrupted transmission is also proposed in the paper, and is shown to produce interference rejection gains significantly higher than those produced by two conventional interference rejection methods.

A simple planar high-directivity Yagi-Uda antenna with a concave parabolic reflector

Abstract: A simple planar Yagi-Uda antenna with a single director and a concave parabolic reflector on a thin dielectric substrate is proposed. Through the innovative design, the simple Yagi-Uda antenna can achieve the high directivity of 9.0 dBi, front-to-back ratio of 14.5 dB, cross-polarization level of −38.7 dB, bandwidth of 6.0%, and the radiation efficiency of 85.1%, i.e., better than −1 dBi in terms of the 3D average gain. This proposed antenna is especially suitable for the mobile devices with GPS functions.

An elliptical UWB monopole antenna with reduced ground plane effects

Abstract: Many monopole UWB antennas have been developed over the years. One common problem is that their performance is heavily affected by the ground plane. In this paper, a new approach on how to reduce the ground plane effects on such antennas is proposed: L-shape cuts on the edge of the ground plane are introduced and it is shown that this method changes the current distribution on the ground plane without sacrificing the frequency and time domain performance, which makes such antennas more suitable for real applications with different sizes of the ground plane.

Link budget analysis and characterization for ingestible capsule antenna

Abstract: This paper characterizes and analyses the link budget requirements for the conformal capsule antenna in the medical capsule imager system. A link budget is developed for the capsule system based on certain parameters (frequency, SAR, power limitations) and it is shown that using the present antenna system; a reliable communication link can be developed for indoor communication for bio-telemetry applications. The polarization diversity exhibited by the conformal capsule antenna is tested and compared to simple dipole design. Due to diverse polarization, a reliable link is obtained irrespective of the capsule location and orientation and this study is discussed in detail.

A dual feed PIFA diversity antenna for MIMO systems

Abstract: This paper presents a novel dual-feed Planar Inverted-F Antenna (PIFA) for MIMO radio communication systems at 2.45 GHz. This antenna contains only one radiating plate with two matched and isolated ports. To reduce the mutual coupling and to achieve a good isolation, ground plane under the top radiating plate is etched. The calculated envelope cross-correlation is less than 0.02 and the ratio of the mean effective gain between the two ports is close to unity. It is shown that a single PIFA antenna can be used instead of two antennas for diversity gain which is an excellent solution for saving the space and cost. Simulated and measured results are provided to verify the conclusion.

60-GHz broadband folded dipole array

Abstract: Nowadays antennas operated in V-band receive more and more attention as communication technology develops. Progress in material engineering opens a wide window for high frequency applications. In this paper, a broadband folded dipole antenna array is first presented, which has a magnitude of S11 lower than −10 dB over the range between 48 GHz and 64 GHz, an efficiency of 90 percent and a gain of 10 dBi. A novel configuration with a superstrate and two separate grounds is taken for improving the performance. Flip-chip connection is used between the integrated circuit carrier and the antenna.attached to the superstrate.

Electrically-small TE 01 mode spherical wire antennas employing lossy magneto-dielectric materials

Abstract: It well-known that a spherical wire antenna designed to radiate solely the TE 01 mode exhibits higher radiation Q than does one designed to radiate solely the TM 01 spherical mode, when both are unfilled and of the same size. Introduction of a magnetic core into a TE 01 mode spherical wire antenna is known to reduce the radiation Q by reducing the magnetic energy stored in the interior of the sphere, although only to a certain extent depending on the electrical size of the sphere. Here we examine the case of a lossy magneto-dielectric core. We show that even when the magnetic material exhibits significant loss, the performance of the antenna in terms of its gain including radiation efficiency is still greatly improved. Even in the hypothetical case in which the loss tangent tends to infinity, the efficiency of the antenna can still be quite large. In fact, the use of a ferrite which is predominantly lossy avoids the detrimental effect of internal modes in the spherical volume. However, the dielectric behavior of a magneto-dielectric core has a detrimental effect of on both radiation efficiency and radiation Q. We examine specific cases involving commercially available ferrite materials. The detrimental effect of the dielectric polarizability essentially precludes the use of so-called broadband, high impedance Mn-Zn ferrites.

Printed fractal monopole antenna array for WLAN

Abstract: This paper presents the design of a single feed multiband printed monopole antenna array using the 2nd generation of the Minkowski fractal geometry. The multiband operation is achieved by a suitable chosen of the size and iteration of the fractal geometry, which is optimized using the EM simulation tool Ansoft HFSS. During this work, it is found that adding a rectangular stub on the ground plane, the impedance match of the antenna can be improved with little influence on the original resonant frequencies. This finding has been confirmed by both simulation and measurement results. Meanwhile, the antenna array on a PDA size substrate was also designed and fabricated. The experimental results show that it can operate from 2.32 to 2.49 and from 5.1 to 5.88 GHz, which covers the required bands for IEEE 802.11a/b/g (2.41–2.48 GHz, 5.15–5.35 GHz and 5.725–5.875 GHz) applications. Measurements indicate that the maximum gain of this printed monopole array can reach 2.3 dBi at lower band and 5.6 dBi at upper band. The simulation results show that the radiation efficiency of this antenna array is 86% at 2.4 GHz, 82% at 5.2 GHz and 89% at 5.8 GHz.

Novel electrically small spherical electric dipole antenna

Abstract: This paper introduces a novel electrically small spherical meander antenna. The horizontal sections of the meander are composed of wire loops, the radii of which are chosen so that the whole structure is conformal to a sphere of radius a. To form the meander the loops are connected by wires at a meridian plane. The antenna operates as an electric dipole, i.e. it radiates the TM 10 spherical mode. The antenna is self-resonant and can be matched to a wide range of input feed lines without an external matching network. In this paper, a spherical meander antenna of the size ka = 0.27 and the input impedance of 72 ohms is numerically investigated and its performance is compared to that of the multiarm spherical helix antenna of the same size. Both antennas yield equal quality factors, which are about 1.5 times the Chu lower bound, but quite different cross-polarization characteristics.

New size reduction for patch antenna by parasitic shorting elements

Abstract: This paper presents a new size reduction technique for a microstrip antenna by adding parasitic L-shaped shorting strips which are equivalent to provide capacitive and inductive loading effects to the patch. With the use of these parasitic elements, the antenna finds an obvious size reduction while maintaining a good broadside radiation characteristic. Because of this attractive radiation feature, the antenna is suitable for circularly polarized (CP) antennas. A new small CP patch antenna operating at 2.492GHz is therefore proposed using a microwave substrate of dielectric constant, e r =10, with a coaxial probe feed. The total area of reduction is about 82% in comparison with the conventional half-wave patch antenna.

Development of an implanted helical folded dipole antenna for 2.45 GHz applications

Abstract: Small implanted devices have been investigated with great interest for wireless medical applications due to the promise of different clinical usages in order to promote patient's independence. In these implanted device systems, an antenna plays an important role as a part of transmitting and receiving power. Therefore, the research on the antenna for implantable device (implanted antenna) is important. In this study, we propose an implanted helical folded dipole antenna for short-range wireless communications. The antenna is designed to operate at 2.45 GHz, one of the industrial-scientific-medical (ISM) bands, and it is investigated by use of the finite-difference time-domain (FDTD) calculation. We have analyzed some performances of the proposed antenna and the results show that the proposed antenna can be a candidate as an implanted antenna.

Improving stop-band properties of frequency selective surfaces with Koch fractal elements

Abstract: Design and experimental investigations are presented for a cascaded frequency selective surface (FSS) with perfectly conducting Koch fractal patch elements The work was developed in two steps In the first step two Koch fractal FSS screens were designed using the software Ansoft Design™ and several prototypes were built In the second step these FSS screens were cascaded and separated by an air gap layer to improve the bandwidth behaviour The structures are cascaded using Teflon spacers and screws to obtain the air gap The FSSs were built on a RT-Duroid 3010 substrate Good agreement was observed between simulated and measured results