Jae-Ick Choi

A Compact Wideband Modified Planar Inverted

A compact wideband modified planar inverted F antenna (PIFA) with two shorting strips for 2.4/5.2-GHz wireless local area network (WLAN) operations is presented. As a starting point, two-branch strip lines derived from the dipole antenna structure are used to achieve the desired resonant frequency. One of them is connected to two shorting strips with the different length and width, and those strips generate additional resonant modes. A wideband characteristic can be optimized by tuning the parts of two shorted patches and size of each strip line segment. The proposed antenna has a low profile and can easily be fed by a 50-Omega coaxial cable. In addition to covering 2.4- and 5.2-GHz band, a wide impedance bandwidth from 2.94 to 5.82 GHz (|S11|<-10 dB, about 69% centered at 4.14 GHz) is obtained. The measured maximum radiation gains at the frequencies of 2.44, 4.14, and 5.2 GHz are about 1.6, 3.8, and 2.5 dBi, respectively. The proposed antenna is suitable for the multiband operations, covering 2.4/5.2-GHz WLAN operation

F

Four head models with the outer shapes of different ages were established using the specific anthropomorphic mannequin (SAM) model of IEEE Standard 1528. The criteria of head height, face length, head length, and head breadth by age were applied to build the models. We assumed that the shells of all the head models have the same dielectric properties with the head-equivalent tissue in order to simulate a real pressed ear. The cheek and tilt positions of three bar-type phone models were used, and the positioning processes against each head model were described in detail. Antenna input impedances of the phones under the test positions and specific absorption rate (SAR) distributions in the head models were computed using the finite-difference time-domain (FDTD) technique. Spatial peak SARs averaging over 1 and 10 g were compared for fixed input and radiated powers of all the phones. The effect of the dielectric properties in a younger head model on SAR result was analyzed. First, input resistance of the phone antennas in the cheek position gradually increased when head size grew with age, but those for the tilt position showed a slight decrease. Second, for a fixed input power, the head models by age changed peak 1- and 10-g SARs by approximately 15%. The electromagnetic absorption depths in the head models in the same test position were about the same, but the head-averaged SAR was higher in the younger model because of the smaller head volume. Third, for a fixed radiated power, the peak SARs got relatively lower in the smaller head model and higher in the larger head model, compared with those for the fixed input power since the smaller head model needs lower input power. Fourth, it was shown that simultaneous change in the conductivity and permittivity of head tissue within 20%-30% did not have a significant influence on energy absorption.

Antenna (PIFA) for 2.4/5-GHz WLAN Applications

We proposed a high-gain wideband resonant-type mobile communication base station antenna using a Fabry-Pérot cavity (FPC) technique. To overcome inherent narrow radiation bandwidth of FPC-type antennas while keeping relatively high gain, we introduced a new superstrate structure composed of square patches and loops, which satisfies an FPC resonance condition at a target frequency region. To do that, we optimized the superstrate geometry with the help of a real-value coding hybrid genetic algorithm (RHGA). The optimized superstrate is very thin, and therefore, it can be fabricated with a single dielectric substrate, which is a fairly strong point in practical applications. Moreover, we enclosed four openings of the antenna in lateral directions to increase antenna gain with a limited aperture area. Therefore, a modified prediction method of an FPC resonance is used, which reduced the effort of complicated three-dimensional antenna optimization. Consequently, our antenna is able to operate in a wide band-width with a relatively high realized gain. Furthermore, good agreement between measured results and prediction ones confirms the validity of our design approach.

Study on SARs in Head Models With Different Shapes by Age Using SAM Model for Mobile Phone Exposure at 835 MHz

In this paper, as one of those RFID tags, novel RFID tag antennas mountable on metallic objects using EBG surface for passive UHF/RFID applications. These tags achieve longer read ranges than tags using EBG surface, and can be utilized in various retail store products including metal, motor vehicles, and containers, etc. Details of the serial design and analysis of the proposed tag are described and the experimental results of the constructed prototype are presented.

A Mobile Communication Base Station Antenna Using a Genetic Algorithm Based Fabry-Pérot Resonance Optimization

A circularly polarized antenna with low cost foam substrate and film is proposed to obtain wide bandwidth and high performance. The proposed antenna is composed of stacked corner-truncated patches with sequential rotation feed. Having above 20% return loss and axial ratio bandwidths, the designed antenna can be used for application of a broadband system using circular polarization. And, as low cost foam and film is used for the substrate, a low cost antenna can be designed.

Design of novel dipole-type tag antennas using electromagnetic bandgap (EBG) surface for passive RFID applications

Recently, the demand for wireless service is highly increased because of many smart devices. Many people want to access the internet by using 802.11 WLAN network as of free service. So, a lot of APs are deployed in many places such as home, office and store. Because anyone can install the AP in any place, APs or STAs are suffered the interference between them. This interference makes whole WLAN network performance to be poor quality. The main reason existing the interference is that a huge number of AP and STA is deployed. To solve this situation, 802.11 standard has established a new study group (SG), high efficiency wireless (HEW) local area network. This SG want to enhance the area throughput which is the average throughput in a specific area. We think average throughput is mainly effected by the inter cell interference which is the interference from other APs or STAs. And average throughput is proportional to the sum rate of each node in a specific region. In this paper, we develop three different downlink interference management approach which is so called distributed interference alignment algorithms. To apply these algorithms in the 802.11 WLAN, we think there are some key points which are distributed processing between nodes, only local channel state information usage, linear processing and IA adaptation possibility for the number of general users. Our algorithms displayed in this paper are followed by above assumptions. And we show the performance comparison between our algorithms.

Broadband circularly polarized corner-truncated square patch array antenna

In this paper, the gain of the single patch with the superstrate is compared to that of the single patch without the superstrate and the experimental results of 2/spl times/8 array antenna with the superstrate, and 4/spl times/8 array antenna without the superstrate are shown. Details of the proposed antenna design are presented.

Distributed implicit interference alignment in 802.11ac WLAN network

A wireless power transmission system for 1.78MHz, 60W docent robot using coupled magnetic resonances is presented. The proposed wireless power transmission system consists of a 130W class-F power transmitter, two magnetic resonance couplers and 60W full bridge RF rectifier receiver. The transmitter is composed of DDS (Direct Digital Synthesizer) block, class-F power amplifier and VSWR measurement block to implement the frequency searching and power tracking function. Two magnetic resonance couplers are designed with a small spiral resonator. The diameter size of the spiral coil is 30 cm (1.8λ/1000). The receiver is composed of RF rectifier, overvoltage protection (OVP) with active dummy load and DC to DC converter. The charging power of the docent robot is about 48W and the entire DC to DC system efficiency of this WPT system is 54%.

High gain and broadband microstrip patch antenna using a superstrate layer

A compact wideband modified planar inverted antenna (PIFA) with two shorting strips for 2.4/5.2-GHz wireless local area network (WLAN) operations is presented. As a starting point, two-branch strip lines derived from the dipole antenna structure are used to achieve the desired resonant frequency. One of them is connected to two shorting strips with the different length and width, and those strips generate additional resonant modes. A wideband characteristic can be optimized by tuning the parts of two shorted patches and size of each strip line segment. The proposed antenna has a low profile and can easily be fed by a 50- coaxial cable. In addition to covering 2.4- and 5.2-GHz band, a wide impedance bandwidth from 2.94 to 5.82 GHz ( 10 dB, about 69% centered at 4.14 GHz) is obtained. The measured maximum radiation gains at the frequencies of 2.44, 4.14, and 5.2 GHz are about 1.6, 3.8, and 2.5 dBi, respectively. The pro- posed antenna is suitable for the multiband operations, covering 2.4/5.2-GHz WLAN operation.

Wireless power transfer system for docent robot by using magnetic resonant coils

In this paper, a 1.9MHz and 60W wireless power transmission system for a fishing port using coupled magnetic resonances is presented. The proposed wireless power transmission system consists of the 130W class-F power transmitter, two magnetic resonance couplers and 30W full bridge diode rectifier receiver. The transmitter is composed of DDS(Direct Digital Synthesizer) block, class-F power amplifier and communication block to implement the frequency searching and power control function. Two magnetic resonance couplers are designed with a small spiral resonator. The diameter size of the spiral coil is 30cm(1.8 λ /1000). The receiver is composed of full bridge diode rectifier, overvoltage protection (OVP) with active dummy load, DC to DC converter and communication block. For the power control scheme, a communication block is embedded in the transmitter and the receiver. Using the communication block, the message about the error value of the received power is sent by the receiver to transmitter and the transmit power is controlled by transmitter using the received message. The power consumption of the fishing port is about 30W and the total power efficiency of this system is about 40%.