Makoto Higaki

Novel small structure for low profile antenna by analogy with EBG structure

By using the image theorem, the relation between the reflection phase of an infinite plane and the input impedance of the dipole antenna just above the plane has been discussed. It has been confirmed that the dipole antenna matches with 50 Omega when the reflection phase is around pi/2, and it is similar to the dipole antenna above an EBG structure. We have proposed the novel small structure which enables the dipole antenna to lay in low profile to the ground plane. The proposed structure rotates the reflection phase through a frequency band and the dipole antenna just above the structure matches with 50 Omega when the reflection phase is around pi/2. It is concluded that the periodicity of an EBG structure is NOT indispensable to realize a low profile antenna.

Novel multiband autonomous impedance restoration antenna system by using a probe

Recently the number of operating frequency bands for a single mobile terminal has been increasing, while the size reduction for a built-in antenna is required. Therefore, it has become more difficult for the antennas built-in mobile terminal to cover all frequency bands with high efficiency. Moreover, the body of the user and the other objects in the vicinity of the mobile terminal usually detune the antennas. In this paper, a novel multiband autonomous impedance restoration antenna system by using a tiny probe has been proposed. The antenna is a 60mm×10mm sized planar monopole on the same plane with the 60mm×90mm ground plane and covers the following wireless communication system bands: LTE (704-746MHz and 2500-2690MHz), GSM850 (824-894MHz), EGSM (880-960MHz), DCS (1710-1880MHz), PCS (1850-1990MHz) and UMTS (1920-2170MHz). It has been shown that the VSWR and total efficiency ηtot(transmission coefficient T×radiation efficiency ηrad) of the antenna are optimized as the received power of a probe is maximized regardless of frequencies.

Automatic tunable antenna system using MEMS variable capacitors and a probe triggered by TPC

Built-in antennas in mobile equipment are often subject to changes in input impedance due to the proximity of objects, e.g. a users hand/head, a desk, etc. To compensate this mismatch, an automatic tunable antenna system using Micro-Electro-Mechanical System (MEMS) variable capacitors and a probe is proposed in this paper. The system controls MEMS variable capacitors based on the received power of the probe and triggered by the Transmission Power Control (TPC). A prototype using a square-law detector, an Analog-to-Digital Converter (ADC), a Field Programmable Gate Array (FPGA) and a matching circuit containing MEMS variable capacitors is also demonstrated.

Automatic tunable antenna controlling varactors based on the received power of a probe

Built-in antennas in mobile equipments are often subject to changes in input impedance due to the proximity of objects, e.g. a users hand/head, a desk, etc. The resulting mismatch can lower the efficiency of the RF power amplifiers (PAs), will reduce battery life, cause low communications quality, etc. To mitigate these problems, a novel automatic tunable antenna system using a probe is proposed in this paper. The system controls two varactor diodes (VDs) in the matching circuit (MC) according to the received power of the probe. When the power is less than -20dB relative to the input power to the MC for all VD conditions, this corresponds to only -0.01dB loss which is considerably less than the insertion loss of a directional coupler. Moreover, the system is frequency independent, consequently significantly wideband, and can operate from 700MHz to 2.7GHz. A prototype using a programmable logic device (PLD) is also demonstrated.

Wideband Characteristic of Dipole Antenna on Mushroom-like EBG Substrate with Narrow Gap

In this paper, we adopted the EBG structure for the antenna substrate to achieve low profile antennas. The thin mushroom-like EBG substrates with narrow gaps were fabricated to limit the area size of the substrate to apply small equipments. The impedance and radiation pattern of a dipole antenna were measured when the antenna was closely located above the EBG substrate. It was confirmed that a dipole antenna located 80 mum above the EBG substrate worked well through wideband. It has been observed that the EBG substrate with the area similar with the footprint of the antenna is enough to obtain a good VSWR. The verification of the operation mechanism and the application to wireless small terminals are future works.

Radiation characteristics of modified H-shaped antenna with robustness against the environment around the antenna

In order to realize an antenna capable of operating without depending on the environment around the antenna, we have proposed a modified H-shaped antenna which has a unidirectional radiation pattern like a Yagi-Uda array. The antenna characteristics in the vicinity of the metal plate are calculated using the moment method, and the proposed antenna has little degradation of VSWR compared with a two-element Yagi-Uda array

A study on the variable radiation pattern antenna using a parasitic slot

It is advantageous for cellular phones or WLAN-APs (wireless LAN access points) that their antennas have variable radiation patterns in certain cases, such when they are mounted on a wall or for the purpose of avoiding interference. Most conventional antennas, such as reactively controlled directive arrays, are composed of multiple elements of identical shape to resolve the above-mentioned issues. This work proposes a novel variable radiation pattern antenna consisting of an inverted-F antenna and a parasitic slot with an electrical switch, and shows its fundamental characteristics and the appropriateness of its parameter optimization with GA.

Design of an electrically small antenna using a broadside-coupled split ring resonator

An electrically small planar antenna using a broadside-coupled split ring resonator (BC-SRR) with a simple structure is presented. Due to the capacitance between the two SRRs in the BC-SRR, the resonant frequency of the antenna is lowered without increasing the size of the antenna. The proposed antenna resonates at 2.45 GHz and 7.31 GHz. At 2.45 GHz, the dimension of the SRR in the proposed antenna is as small as 0.012λ<inf>0</inf>× 0.082λ<inf>0</inf>, where λ<inf>0</inf> is the wavelength in vacuum. The radiation efficiency is 24% at 2.45 GHz.

Radiation mechanism of H-shaped antenna using parallel resonance mode

It is required to work in various surrounding environments in order that the small antennas used for mobile terminal and RFID tag are located in the vicinity of various objects including the human body and the metal. H-shaped antenna has been proposed to obtain the characteristics not to be changed by circumference environment. The H-shaped antenna has been designed by adjusting offset position and the ratio between the lengths of parallel elements. As a result of examination about the antenna height (h), the shift of input impedance near the metal was the smallest when h=0.04ε.

Radiation efficiency improvement of low profile antenna with metamaterial structure using LCP substrate with low profile copper foil

EBG (Electromagnetic BandGap) structures have lately attracted considerable attention both for the surface wave suppression and low profile antennas [1] [2]. To achieve low profile antennas by using an EBG structure for the antenna substrate, the thinner EBG substrate as well as the smaller gap to the antenna above the EBG substrate is important [3]. Furthermore, a smaller EBG substrate area is required to accommodate the antenna into small wireless equipments. We have proposed a small metamaterial structure by analogy with a mushroom-like EBG structure, which enables a dipole antenna just above the structure to match with 50Ω as well as EBG structures [4] [5].