In this paper, we show that the orbital angular momentum (OAM) communication performance with a circular loop antenna array can be drastically improved by exploiting the port azimuth effect at the 5-GHz band. The received signal and interference powers are analytically derived with generalized Z-matrices and the perturbation method for short-range OAM communication. The resulting formulas show that the interference power can be drastically suppressed by selecting the proper combination of port azimuths. We also explain the mechanism behind the reduction in interference power. For the obtained port azimuth combination, the simulated and measured transmission isolations at 1cm are better than 24.0 and 23.6dB at 5.3GHz, respectively. Furthermore, to estimate performance in 2×2 MIMO communication, constellations for 64-QAM are estimated. Measured EVMs are less than 3% where signals are clearly discriminated without any signal processing. For long-range OAM communication using paraboloids, the optimum port azimuth combination is estimated by monitoring the current distribution. For the obtained combination of the port azimuths, simulated and measured transmission isolations at 125cm are better than 15.7 and 12.0dB at 5.3GHz, respectively. The measured isolation for short and long ranges are improved by 9.2 and 4.5dB, respectively, compared with the data for the combination of the identical port azimuth.

To design antennas for ingestible capsule endoscope systems, the transmission factors of dipole and loop antennas placed in the torso-shaped phantom filled with deionized water or human body equivalent liquid (HBEL) are investigated by numerical and experimental study. The S-parameter method is used to evaluate transmission characteristics through a torso-shaped phantom in a broadband frequency range. Good agreement of S-parameters between measured results and numerical analysis is observed and the transmission factors for both cases are obtained. Comparison of the transmission factors between HBEL and deionized water is presented to explain the relation between conductivity and the transmission characteristics. Two types of antennas, dipole antenna and loop antenna are compared. In the case of a dipole antenna placed in deionized water, it is observed that the transmission factor decreases as conductivity increases. On the other hand, there is a local maximum in the transmission factor at 675 MHz in the case of HBEL. This phenomenon is not observed in the case of a loop antenna. The transmission factor of capsule dipole antenna and capsule loop antenna are compared and the guideline in designing capsule antennas by using transmission factor is also proposed.

A novel circularly and linearly polarized loop antenna is presented. A simple loop configuration, twisted like a cross shape, has achieved radiating wide beam circular polarization simultaneously with linear polarization in two close bands. This cross configuration brings good circular polarization to a loop antenna because it uses the transmission line mode of a folded dipole antenna. For these reasons, the antenna is named the Cross Spiral Antenna (CSA). In this paper, a basic structure and the principle of the CSA radiating circular polarization with one port feeding is explained. The prototype CSA, which is tuned to around 1.57GHz and 1.6GHz, is tested for verifying the effectiveness of the suggested antenna configuration.

Invention and development of the Yagi-Uda antenna in Tohoku University, Japan are described. Communication experiments in VHF and UHF frequency bands using transmitter and receiver developed in the same university as well as the Yagi-Uda antenna are also presented. Then, self-complementary antennas, which is the frequency independent antenna invented in Tohoku University are described. Analysis methods of large loop antennas is also presented.

This paper presents a DC output voltage-boosting antenna with high input impedance in wide frequency band for RF (radio frequency) energy harvesting of FM broadcasting signals. Target input power level of -20dBm is used to design a loop antenna for DC output voltage-boosting. The RF energy harvesting on YNU campus provides 924mV DC output for a single rectenna and 1.72V DC output for twin rectennas by receiving several FM broadcasting wave simultaneously.

This paper presents a new type of electromagnetic interference (EMI) measurement system. An EMI Camera LSI (EMcam) with a 124 on-chip 25050 µm2 loop antenna matrix in 65 nm CMOS is developed. EMcam achieves both the 2D electric scanning and 60 µm-level spatial precision. The down-conversion architecture increases the bandwidth of EMcam and enables the measurement of EMI spectrum up to 3.3 GHz. The shared IF-block scheme is proposed to relax both the increase of power and area penalty, which are inherent issues of the matrix measurement. The power and the area are reduced by 74% and 73%, respectively. EMI measurement with the smallest 3212 µm2 antenna to date is also demonstrated.

A novel dual-band magnetic loop antenna is proposed using slot-loaded composite right/left-handed (SL-CRLH) structures. Since each radiating element consists of a symmetrically-array of unit-cells, a dual-band magnetic loop source is obtained with unchanged beam patterns. Simulations and measurements show its good radiation performance with monopole-like radiation patterns in both operating bands.

This paper presents a 100–120-GHz pulse transmitter chip with a 5424 on-chip loop antenna array for the purpose of beam-formability in portable millimeter-wave (mm-wave) active imaging applications. We present a new idea for silicon-based mm-wave pulse beam-forming by using voltage-varied CMOS inverter chain. This 4-mm4-mm transmitter chip is designed and fabricated in a 2.5-V 0.25-µm 4-metal-layer Si-Ge Bi-CMOS process. The 30-µm30-µm loop antenna located on the top-metal layer operates as an coil in an integrated mm-wave pulse generator. Each of on-chip pulse generators employing under-damped/over-damped conditions to produce mm-wave pulses includes an R-L-C circuit, a bipolar junction transistor (BJT) operated as a switch and a CMOS inverter chain circuit for shaping the rising edge of the input clock. Simulation results by ADS 2009 and HSPICE show that loop antenna' inductance and resistance at 80–120-GHz are 51 pH and 3 Ω, respectively. A simulation performance of an integrated 136 loop antenna array illustrates the variation of maximum radiation angles depending on different phase values between array's elements. By using an mm-wave power meter, a 90–140-GHz standard horn antenna and a Schottky diode detector, several measured radiation patterns of this loop antenna array chip are achieved. From the measurement result, we demonstrate the possibility of an integrated mm-wave pulse generator for the purpose of beam-forming by changing power supplies of inverter chains.

A sensor network consisting of a number of palm-sized nodes with small electric and magnetic sensors has been proposed to monitor local electromagnetic activities in space plasmas. In the present study, a compact loop antenna system is designed and fabricated for use in sensor nodes that can capture magnetic vector fields from ELF to MF frequencies. The performance of the developed system is shown to be sufficient to allow measurement of the magnetic field activity around artificial structures in addition to intense natural plasma waves in geospace.

This paper proposes a head-local-exposure system using a figure-8 loop antenna for 2-GHz band operation. This system allows us to observe biological effects through microcirculation of the rat brain simultaneously with exposure through a cranial window, i.e., the window made by transparent glass and implanted on the surface of the rat brain. The specific absorption rate (SAR) in a rat exposed to microwaves due to the new exposure system is estimated numerically and experimentally. The ratio of averaged SAR between the target area, which is the brain's surface just under the cranial window, and the whole body is about 59 for the 8-week rat model and 13 for the 2-week rat model. This antenna achieves local exposure for the rat brain for 2-GHz band operation.

This paper presents a wideband technique for a mobile handset antenna. The proposed method inserts a distributed LC resonator into a loop antenna in order to provide non-uniform resonance shifts; without the use of a multi-radiator the bandwidth can be increased from 320 MHz (1900-2220 MHz) to 880 MHz (1750-2630 MHz). As a result of the wide bandwidth and good radiation efficiency, the proposed antenna can be employed in DCS/PCS/WDCMA/Bluetooth mobile handsets.

A new scheme to avoid null zone for HF-band RFID without expanding antenna size is proposed. At first, we demonstrate by FDTD simulation that the null zone occurs because of cancellation of magnetic fields over the loop surface. To prevent cancellation of magnetic fields, the loop antenna is split into four parts, which work as a planar array antenna. The outputs of antennas are gathered by using combining circuit. We have validated by FDTD simulation that the proposed scheme enlarges the worst received power by 13.1 dB.

This paper describes a method for evaluating the performance of a small magnetic core loop antenna used for radio controlled watches. Recently, amorphous metal core loop antennas are used as built-in small antennas inside a metal case. It is difficult to perform electromagnetic simulation for amorphous core loop antennas because of the complicated laminate structure. Therefore, we modeled the amorphous metal core loop antenna as an equivalent bulk structure having anisotropic permeability property that we can simulate. We analyzed the receiving sensitivity of the amorphous antenna by calculating the antenna factor. The receiving sensitivity degrades remarkably when an antenna is inside a metal case. We performed further simulation to investigate eddy current losses that cause deterioration.

In this paper, we evaluated the characteristics of the magnetic core loop antenna that is used to receive long wave radio signals for time standards. To evaluate the receiving sensitivity of the antenna, we calculated the antenna factor of the magnetic core loop antenna by combining a magnetic field simulation and a circuit simulation. The simulation results are in good agreement with the results obtained from the experiments. We then investigated the optimization of the antenna shape, and showed the relation between the shape of the magnetic core and the receiving sensitivity.

Electromagnetic field probes inevitably disturb the original distribution of the field when they are positioned close to a device. This disturbance in turn affects measurement accuracy and device operation. We developed an optical magnetic field probe, comprising a loop antenna element and an electro-optic crystal, for highly accurate magnetic near-field measurement in the GHz frequency range. We analyzed the invasiveness of the optical magnetic field probe quantitatively both experimentally and using finite difference time domain simulation. We found that eliminating the metal cable reduced the disturbance of the surrounding field that was to be measured. In addition, we investigated the magnetic field detection characteristics of the probe and its influence on the operation of a microstrip line. The optical magnetic field probe was less invasive and provided more accurate measurement.

Digital Terrestrial Television (DTV) services began in Japan in December 2003. This paper proposes a novel on-glass antenna for mobile reception of terrestrial television. The gain of the proposed antenna is 4.7 dB higher than commercial monopole antennas when installed on a vehicle. Other merits of this antenna are a broad input impedance bandwidth across the UHF band (470-710 MHz), and the fact that it does not spoil vehicle appearance. Field experiments have confirmed that a diversity system using four of the proposed antennas is capable of mobile DTV reception.

A numerical technique for improving the accuracy of a rectangular loop antenna based on the Finite Difference Time Domain (FDTD) method is proposed. In this technique, a quasi-static field behaviour is incorporated into the FDTD update equations, and the more accurate numerical technique can be obtained without the need of using fine cells. The simulation results of this proposed technique are compared with the Method of Moment to confirm the effectiveness of the technique.

This paper presents a new type of optical probe designed to detect magnetic near-fields with high accuracy in the gigahertz range. Its probe head consists of a loop antenna element doubly loaded with LiNbO3 electro-optic crystals. Through an optical technique, it can work as a conventional double-loaded loop probe without metallic cables or an electrical hybrid junction. We examined probe characteristics for magnetic field detection up to 20 GHz. We confirmed that the probe can measure magnetic fields near a microstrip line in the gigahertz range and can suppress influence of electric fields.

Invention and development of the Yagi-Uda antenna, and the self-complementary antenna are described. Analysis methods of large loop antennas and the improved circuit theory (ICT) for design of linear antennas are presented. Recent developments of axial mode helical antennas and spiral antennas for radiating circularly polarized waves are also described.

A new antenna for a wristwatch phone is proposed. The proposed antenna is a one-wavelength rectangular loop along the cap of the wristwatch phone. The loop is fitted at the periphery of the openable cap connected to the wristwatch case by a hinge. In order to discuss the antenna gain, we define the two different conditions as follows. When the user opens the cap and talks over the wristwatch phone, his wrist is held in front of his face, which is called the "talk position" in this paper. When the user closes the cap and waits for a call, his wrist rests down at the side, which is called the "stand-by position. " We measured the radiation patterns and calculated the pattern averaging gain (PAG) of the proposed antenna for the two positions. In addition, we compared the proposed antenna with the other antennas: a planar inverted F antenna (PIFA) fixed on the strap and a normal mode helical antenna (NMHA) installed on the case. As a result, the PAG of the proposed antenna was about -5.5 dBd, which was the same as the PAG of the other antennas for the talk position. In the case of the stand-by position, the PAG of the proposed antenna was about -3 dBd, which was 7 dB higher than that of the other antennas. The gains of the proposed antenna reached the goal, which was the PAG of a whip antenna of a handy phone held near the head. The results demonstrate that the proposed antenna is suited to a wristwatch phone.