Showing papers presented at "International Workshop on Antenna Technology in 2011"

Terahertz photoconductive antenna efficiency

Abstract: Terahertz (THz) photoconductive antennas are the most common device for the generation and detection of THz waves and are very different from conventional RF/microwave antennas. One of the major problems of the current photoconductive antennas is that the antenna efficiency is very low, thus it is difficult to obtain high power THz waves. In this paper a comparison of the conventional and photoconductive antennas is made and various parameters and aspects of photoconductive antennas are examined with the aim to maximise its efficiency factor. A new antenna efficiency expression is derived which clearly shows how the efficiency is linked to various parameters. An example is used to demonstrate why the total efficiency is very low and what the major limiting factors are. Recommendations for how to increase the efficiency are presented.

Small circularly polarized patch antenna

Abstract: This paper presents a novel size reduced circularly polarized (CP) patch antenna by introducing a substrate integrated metallic wall structure to provide capacitive and inductive loading to the patch. Pairs of metallic walls are formed by conducting vias and assigned at four corners underneath the patch. To generate circular polarization, a square patch with unbalanced tails is applied. The antenna works at 3.24GHz. With the presents of the proposed metallic wall structure, the antenna has a considerable size reduction by the capacitive and inductive loading effect. Comparing with a traditional half-wavelength square patch antenna, the proposed CP antenna has achieved 86% size reduction experimentally.

Inductive wireless power transmission for implantable devices

Abstract: Inductive coupling is considered as one of the main stream techniques in wireless power transmission for implantable devices. In this paper, we present a generic analysis of the different topologies for wireless power transfer and arrive at boundary frequencies that separate various topologies, thereby allowing users to identify the topology that best suits the application requirements. In the meantime, we present a method of how to characterize and optimize rectangular coils used in inductive links for more general applications. Finally, preliminary results for retinal prosthesis applications are presented.

Miniature transparent UWB antenna with tunable notch for green wireless applications

Abstract: In this paper, the design of a UWB antenna using a transparent AgHT-8 material is proposed for green wireless applications. Computer simulation is used for studies. For verification of the design, the proposed antenna is fabricated on an AgHT-8 film and measured. Results show that the antenna has better radiation efficiency relative to its size than the previous designs, good omni-directional radiation patterns throughout the FCC bandwidth of 3.1–10.6 GHz and a comparable gain. To filter out the unwanted signals in the WLAN band, two vertical slots are introduced to produce a tuning notch in the 5 GHz frequency band. For demonstration of green wireless applications, the transparent antenna is incorporated with a solar panel for harnessing solar energy. Results show that the transparency of the antenna makes it a good candidate for future green wireless applications.

Silicon based THz antenna and filter with MEMS process

Abstract: A silicon based THz substrate integrated waveguide (SIW) bandpass filter with a pair of antipodal linearly tapered slot Antennas (ALTSA) is designed and fabricated with MEMS process A prototype with passband range 350GHz∼370GHz is measured by using a quasi-optic measurement system The measured data are in agreement with the simulated results, which show the filter has good selection performance and verified the wideband characteristic of the ALTSAs

Antenna design challenges and solutions for compact MIMO terminals

Abstract: The design of antennas for compact multiple-input multiple-output (MIMO) terminals is a challenging feat, due to the space constraint and the physical structure of the terminal. The space constraint forces the antennas to be closely spaced, which degrades MIMO performance due to high signal correlation and low antenna efficiency. Moreover, the terminals are equipped with ground planes which further complicate the implementation of antennas for good MIMO performance. This paper elaborates on the two aforementioned challenges in MIMO antenna design and surveys recent techniques that are developed to address these challenges.

A concept for MIMO antennas on small terminals based on characteristic modes

Abstract: In this paper, we present a concept for a MIMO antenna system on a small terminal platform. The concept is based on the selective excitation of different orthogonal characteristic modes on the chassis of the small terminal. Thereby the chassis of the mobile terminal itself can be effectively used as the MIMO antenna similar to the concept commonly applied to single port (single mode) antennas on mobile terminals. The different modes generate orthogonal radiation patters and are therefore suited to radiate de-correlated signals fed to the different antenna ports. Such modes can be excited selectively by certain sets of couplers distributed around the outer edges of the chassis. First stage numerical investigations show that coupling between the modes is low.

A zoned two-layer flat lens design

Abstract: In this paper we present a flat lens based on a zoned two-layer design, which provides us the freedom to simultaneously control the magnitude and phase of the transmitted wave passing through the lens. A transmission line approach is used to analyze the reflection and transmission coefficients of the proposed two-layer slab, and a two-step method is introduced to determine the distribution of the dielectric constants of the zones. The performance of the developed flat lens has been investigated, and the simulated results are shown to validate the design methodology. They also serve to demonstrate that the focal region of the lens exhibit a sub-wavelength characteristic in the transverse direction, even though it does not utilize a double-negative (DNG) material.

Researches on pattern reconfigurable antenna and its application in phased array

Abstract: This paper introduces the achievement and progress in the research on pattern reconfigurable antenna and its application in phased array, in Computational Electromagnetic Laboratory (CEMLAB) at UESTC. Several typical pattern reconfigurable antennas are introduced. A phased array composed of one kind of pattern reconfigurable elements is simulated on plane platform and conformal platform, and the array realize excellent scanning characteristics such as wide scanning coverage, less gain fluctuation and low cross-polarization. At last, the development trend of reconfigurable antenna is predicted in the conclusions.

Compact arc-shaped slotted circularly polarized microstrip antenna for RFID readers

Abstract: A compact arc-shaped slotted circularly polarized (CP) microstrip antenna is presented for ultra high frequency (UHF) radio frequency identification (RFID) handheld reader applications. Four unequal arc-shaped slots are cut diagonally onto the square patch radiator for CP radiation and compact size. The antenna prototype is with an overall antenna size of 90 × 90 × 4.572 mm3 (0.277λ 0 × 0.277λ 0 × 0.0141λ 0 at 924 MHz). The measured 3-dB axialratio (AR) bandwidth of around 8.0 MHz with and 10-dB return loss bandwidth of 24.0 MHz are achieved. The gain is up to 3.7 dBic.

Design of a MIMO antenna with improved isolation using meta-material

Abstract: In this paper, a Multi-Input Multi-Output (MIMO) antenna is proposed. The isolation characteristic of proposed MIMO antenna between two radiating elements is improved by using a Split Ring Resonator (SRR) array structure. The fabricated antenna satisfied the 10 dB return loss requirement and the isolation between the two radiating elements was higher than 15 dB in the Mobile-WiMAX frequency band. The measured peak gains of the two elements were 2.3 dBi and 2.4 dBi.

Mobile phone antenna impedance variations with real users and phantoms

Abstract: This paper shows the differences between mobile phone antenna impedance measurements with real users and phantoms. Three typical mobile phone antennas are measured with 63 volunteers and with phantoms. The results with phantoms are consistent with those obtained with real users, but do not represent the full extent of the changes (when compared to the impedances in free-space). As such, current phantoms are not appropriate for the design of reconfigurable antenna systems that seek to compensate as much of the range of values encountered in practice as possible.

Enhanced gain UWB slot antenna with multilayer Frequency-Selective Surface reflector

Abstract: Adequately design Frequency Selective Surfaces (FSSs) allow significant control of the phase of reflection and transmission characteristics over a wide frequency band. This property is used here to develop a multilayer FSS reflector enhancing the gain and radiation properties of antennas for ultra wideband applications. These kinds of reflectors make structures low profile by providing the flexibility in mounting them closer to antenna without disturbing the impedance bandwidth and providing a good gain control in the main beam direction. In order to design a suitable reflector dual layer FSS have been designed and employed with a slot antenna. FSS layer works from 4 GHz to 12 GHz, providing a linear transmission phase in the 133% bandwidth. Performance of the FSS is tested with UWB slot antenna and predicted results show significant gain enhancement while maintain the bandwidth of 140%.

Optimal multiple antenna design for compact MIMO terminals with ground plane excitation

Abstract: The compactness of mobile terminals complicates the design of multiple antennas, since coupling among the antennas increases when they are placed in proximity of one another. While it is possible to mitigate coupling between closely spaced antennas, a tradeoff in bandwidth is required. In this paper, we highlight ground plane excitation as an additional dimension to consider in the design of multiple antenna terminals. This is because a compact ground plane, especially in mobile application, can interact with the antenna elements and contribute significantly to their radiation characteristics. Our results show that several design parameters, namely element locations, spacing between elements, and radiation characteristics of individual elements, must be jointly considered in order to achieve the optimal MIMO performance tradeoff for compact multiple antenna terminals.

A discussion on electrically small antennas loaded with high permittivity and permeability materials

Abstract: Electrically small antennas have remained a significant topic of interest for a number of applications, particularly low frequency systems and wireless networks requiring small devices. As is well-known, there are a number of techniques whereby an electrically small antenna can be efficiently matched to a 50Ω system impedance. Ultimately, the primary design challenge is achieving as wide an efficient operating bandwidth as possible, within the constraints of manufacturing tolerance issues and de-tuning effects resulting from the surrounding operating environment. One common size reduction technique is the utilization of dielectric materials to capacitively load the antenna structure. In this paper, which is intended to be mostly a tutorial discussion, we focus on loss and bandwidth issues associated with material loading an antenna using high permittivity and/or high permeability materials. We particularly focus on how these materials impact overall efficiency and discuss the relationship between conductor and material losses within an impedance matched electrically small antenna.

Simple printed monopole slot antenna for WWAN mobile handset

Abstract: A simple printed monopole slot antenna for penta-band WWAN operation (824∼960/ 1710∼2170 MHz) in the mobile handset is presented. The monopole slot has a length of 50 mm only and is embedded close to the bottom edge of the system ground plane of the handset with a small distance of 11 mm. By adding a small-size C-shaped strip connected orthogonal to the bottom edge of the system ground plane, good excitation of the monopole slot antenna at its fundamental (0.25-wavelength) and higher-order resonant modes can be obtained. The excited resonant modes form two wide operating bands to respectively cover the GSM850/900 operation (824∼960 MHz) and GSM1800/1900/UMTS operation (1710∼2170 MHz). Operating principle and radiation characteristics including the SAR (specific absorption rate) results of the proposed monopole slot antenna are described. Measured results of the fabricated antenna are also presented.

Bandwidth enhancement of substrate integrated waveguide (SIW) slot antenna with center-fed techniques

Abstract: Owing to many advantages of rectangular waveguide and microstrip lines, substrate integrated waveguide (SIW) can be used for the design of planar waveguide-like slot antenna. However, the bandwidth of this kind of antenna structure is limited because of its low profile and dielectric filling effect. In this work, center-feding technique is proposed to enhance the bandwidth of the slot antenna. To demonstrate the validity of the bandwidth enhancement technique, a linear slot antenna array with center-fed technique is proposed and implemented. The measured bandwidth of the fabricated antenna prototype is 9.8%, indicating about 145% bandwidth enhancement.

Interference suppression using parasitic reconfigurable aperture (RECAP) antennas

Abstract: Most of today's practical wireless systems are interference limited, meaning that the degree of spectral reuse possible is dictated by the size of the coverage area (or cell) and the degree of tolerable interference experienced at the cell edges. Much higher spectral reuse is possible with nodes that can control their radiation patterns to suppress and avoid interference, which is also the basis of spatial division multiple access (SDMA) techniques. A typical goal in interference-limited systems is to maximize the signal-to-interference ratio (SIR) of the nodes in the network. Although SIR minimization is possible with array signal processing, a drawback is the need for additional radio-frequency (RF) chains and digital signal processing (DSP) resources.

Design of a flexible Minkowski-like pre-fractal (MLPF) antenna with different ground planes for VHF LMR

Abstract: This work investigates the suitability of a flexible Minkowski-like pre-fractal antenna (MLPF) for application in the Very High Frequency (VHF) Land and Mobile Radio (LMR) frequency bands (136–174 MHz) The proposed center-fed, third iteration antenna has been manufactured using both copper tape and Shield It Super, a conductive textile It has been tested on four types of ground plane, ie rectangular, fractal Minkowski, meander line and L-shaped It is observed that an L-shaped ground plane performs the best, and provides an additional frequency tuning parameter to the overall structure Simulated and measured S 11 show a good agreement and the proposed antenna is working within the desired frequency range A simulated gain and efficiency of more than 19 dB and 76 %, respectively, are obtained The measurement in a Satimo SG64 anechoic chamber provided 0 dB gain and about 48 % efficiency

Offset-fed UWB antenna with multi-slotted ground plane

Abstract: This paper presents the design and results of an offset feed Ultrawideband(UWB) antenna with a multiple-slotted ground plane. The antenna consists of a square shaped radiator, a feed slightly offset from the middle along the radiator side and a ground plane with multiple rectangular slots. Simulation results show that the antenna can achieve a wide bandwidth from 3.3 to 18 GHz.

Reconfigurable Vivaldi antenna with tunable stop bands

Abstract: A novel Vivaldi antenna is presented with tunable stop bands. A microstrip line resonator is coupled to the tapered slot, with three varactors used for tuning. The stop band can be tuned between 2 GHz and 7 GHz, to give a very wide tuning ratio, of 3.5:1. Good agreements between simulated and measured results are observed, which verify the design concepts.

Two-dimensional beam steering based on the principle of holographic antennas

Abstract: This paper presents a novel concept for two-dimensional (2-D) beam steering using a planar printed antenna. The concept is based on the theory of holographic antennas and is using frequency scanning in one dimension and phase scanning in the second dimension. A short review on the principle of holography and holographic antennas is given, as well as measurements and simulations of a 20 GHz printed holographic antenna. Finally, the novel beam-scanning concept is explained and verified by electromagnetic simulations of a 90 GHz unidirectional 2D beam steering antenna.

Capacity maximizing MIMO antenna design for Car-to-car communication

Abstract: The handling of the radio channel is an important aspect that determines the working capability of a mobile communication system. Since the channel behavior is influenced by the environment, which leads to a different behavior in different environment, the antenna design (synthesis) becomes environment dependent (time-variant) as well. In this paper, a capacity maximizing approach to design antenna systems for time-variant channels is presented. Real world constraints such a space, transmit power, the number and arrangement of the antennas are taken into account. The theory of this approach and an optimization of a 2×2 MIMO system for Car-to-car (C2C) communication using measured antennas patter and simulated in typical C2C scenarios are shown.

Time-domain pulse-matched synthesis of ultra-wide band antennas

Abstract: Antenna synthesis can yield optimal radiating structures in terms of pattern diagram, gain, bandwidth or other figures of merit. Although the synthesis might be more difficult for continuous sources than for antenna arrays the resulting radiating structures are cheaper and easy to manufacture. In this paper, we propose a time-domain synthesis approach for ultra-wide band antennas. The method is based on a finite expansion of the antenna time-domain response. The synthesis is performed with regard to the resemblance between the time-domain radiated waveform and the waveform at the antenna input. The approach is validated by synthesizing a planar, ultra-wide band antenna designed for a particular waveform of excitation.

Characterization and modelling of Ultra Wideband radio links for optimum performance of body area network in health care applications

Abstract: Ultra Wide band (UWB) is an appealing technology for health care applications. The paper aims to investigate the optimum location for putting sensors on the body for remote patient monitoring. The on-body measurements are performed in both anechoic chamber and in an indoor environment for more than 100 receiver locations for both line of sight (LOS) and non-line of sight (NLOS) scenarios. The on-body path loss model has been extracted from the measured data. Bit Error Rate (BER) for different receiver locations is calculated by incorporating channel impulse responses for each link in Multiband-OFDM based UWB system. The conducted system analysis shows that for LOS case best location for putting sensor are legs and for NLOS case both legs and arms perform equally well.

Design of a U-shaped RFID tag antenna with an isotropic radiation characteristic

Abstract: In this paper, we propose a simple U-shaped radio-frequency identification (RFID) tag antenna with an isotropic radiation characteristic for stable operation of an RFID system. The antenna is composed of a U-shaped half-wavelength dipole and a rectangular-shaped feed. The feed is connected at the bottom of the dipole for conjugate impedance matching with a commercial tag chip. The gain deviation of the antenna can be further improved by inserting a rectangular slit in the lower central portion of the antenna body. For VSWR ≤ 2, both designs comply with the Korea ultra-high frequency RFID bandwidth. Within the operational frequency range, the gain deviation of the tag with a slit was less than 0.71 dB, while the gain deviation of the tag without a slit was less than 1.62 dB.

Planar antenna for RFID tags on metal platform

Abstract: In this paper, a planar RFID tag antenna in the UHF band that can be stuck to metallic objects is designed. The proposed tag antenna consists of a slotted radiating patch and a grounded microstrip line, which serves as an impedance matching stub between the radiator and a tag chip. The fractional return loss bandwidth for S11<−10dB is about 9%. When the antenna is placed on the large metal platforms, the impedance matching remains almost unchanged while the reading range is increasing as the size of the metal platform is increasing.

Electromagnetic human phantoms for the purpose of antenna design

Abstract: To determine the effective performance of handheld cellular radio antenna, it is essential to evaluate the electromagnetic (EM) interaction between the antenna and the human body. EM evaluation using the real human bodies has drawbacks such as poor repeatability and traceability. This is because the different ways of holding the terminal give a variety of geometric relationship between the terminal and the human head and hand. To develop antennas that are less affected by the human body, the mechanisms for the variations in the characteristics with respect to the antenna structure, caused by absorption in each region of the human body, must be considered. However, measurements made with the respective parts of real human bodies are difficult. Thus, human phantoms are widely used in the various fields of antenna engineering to solve these problems. In realizing human phantoms for the purpose of antenna design, there are two points that have to be considered; (1) What kind of antenna to be estimated? (2) What kind of characteristic to be measured? This paper presents recent status and some technological issues for the development of human phantoms used for antenna designs from the above-mentioned two perspectives. Furthermore, as a new trend of phantom applications towards future wireless radios, MIMO over-the-air testing (MIMO-OTA) using a phantom and an arm-waving dynamic phantom for the assessment of body area network (BAN) systems are briefly introduced.

Design and development of a multiband loop antenna for cellular mobile handsets

Abstract: This paper presents the results of the design and characterization of a loop antenna for mobile cellular handsets. Based on a typical smart phone antenna geometry, a bottom mounted off-ground meanderline loop antenna has been designed, which has the potential to cover the required bands of Long Term Evolution (LTE) US 700MHz, Global System for Mobile communications (GSM) 824–960MHz, Digital Communication System (DCS) 1710–1880 MHz, Personal Communication Services PCS 1850–1990 MHz, Universal Mobile Telecommunications System (UMTS) 1920–2170MHz and LTE EU 2500. The carrier volume of 50∗10∗5mm3 and ground plane of length 100mm is used. The carrier permittivity e r is 2.66 and loss tangent tanδ is 0.00629 @2.44GHz. Copper is used as a metal part of the antenna having conductivity of 5.8e7 S/m and thickness of 0.1mm. The antenna supports balanced and unbalanced modes for certain frequencies. It is highly efficient in terms of small volumetric size for a given bandwidth of operations. The antenna generates weak near field electric and magnetic fields complying with the standards for the Specific Absorption Rate (SAR) and Hearing Aid Compability (HAC). The impact of body effects on the radiation efficiency has been quantified. The measured results of the prototype are in good agreement with the simulated results.

Application of antenna in strain measurement

Abstract: A multi-band antenna which can be used as a passive strain measurement device is presented. The dimensions of the antenna will change when different strains are applied, resulting in changes in the resonant frequencies. The proposed antenna resonates at multiple frequencies. By creating slots on the patch of the antenna, these resonant frequencies shift to a higher or a lower value for different strain orientation along the length or width. By measuring the resonant frequencies of the antenna, the corresponding strain applied to the antenna is identified, leading to the strain measurement. To verify our design concept, a prototype antenna was fabricated using Rogers RT/duroid substrate with a thickness of 0.254mm. The total length and width of the antenna is 19.8mm and 17.9mm, respectively. The simulated and measured results along with the mechanical testing procedure have been presented, which are consistent with each other.