Ken-Huang Lin

Implementation of Broadband Isolator Using Metamaterial-Inspired Resonators and a T-Shaped Branch for MIMO Antennas

We develop a novel MIMO antenna with excellent broadband isolation performance in this communication. Metamaterial (MTM)-inspired resonators can function as insulators and are placed periodically into a compact MIMO antenna system for portable applications. These insulators only need a 0.18 wavelength. The broadband insulators can efficiently reduce the coupling of MIMO antennas. Isolation bandwidth under 20 dB can reach 8% with relative to the center frequency. Adding a T-shaped branch behind the insulators markedly improves the isolation bandwidth. An isolation bandwidth under 20 dB can achieve 19.3% relative to the center frequency. The effectiveness of the proposed insulators is validated by measurements.

Design of MIMO antennas with strong isolation for portable applications

Single negative metamaterial designed in MIMO antenna is suitable for portable applications. Metamaterials reduce the coupling at a separation distance of 0.18-wavelength for the MIMO system. Multi-layer metamaterials with different spiral length can improve the isolation bandwidth. In our design, it can cover whole WiMAX bands. And Ω-shape arrangement is also proposed; the isolation has 6dB improvement at 2.6GHz. This paper successfully shows that metamaterials can be used in MIMO antennas system to reduce correlation and size. And it is suitable for portable applications.

A Looped-Bowtie RFID Tag Antenna Design for Metallic Objects

Design of a long read-range, reconfigurable operating frequency radio frequency identification (RFID) metal tag is proposed in this paper. The antenna structure consists of two nonconnected load bars and two bowtie patches electrically connected through four pairs of vias to a conducting backplane to form a looped-bowtie RFID tag antenna that is suitable for mounting on metallic objects. The design offers more degrees of freedom to tune the input impedance of the proposed antenna. The load bars, which have a cutoff point on each bar, can be used to reconfigure the operating frequency of the tag by exciting any one of the three possible frequency modes; hence, this tag can be used worldwide for the UHF RFID frequency band. Experimental tests show that the maximum read range of the prototype, placed on a metallic object, are found to be 3.0, 3.2, and 3.3 m, respectively, for the three operating modes, which has been tested for an RFID reader with only 0.4 W error interrupt pending register (EIPR). The paper shows that the simulated and measured results are in good agreement with each other.

Characterization of RFID Strap Using Single-Ended Probe

Radio frequency identification (RFID) strap attachment modality is more reliable, low cost, and easy to assemble, and therefore, it becomes increasingly more popular in RFID tag designs. This paper presents a single-ended probe method with power transmission coefficient compensation for the characterization of RFID straps. Approximate identification of the read/write threshold power and impedance is based on the charge status of voltage multipliers and charge pumps instead of on the read/write-modulated commands. For comparison purposes, the conventional source-pull system is also briefly reviewed and applied to verify the measurement results of absorbing power and impedance of RFID straps using the presented method. An enhanced source-pull system, named RFID source-pull system, for an RFID strap that can accurately measure the threshold power and impedance for read/write-modulated commands is also constructed for verifying the presented method. Alien and Texas Instruments (TI) straps are used for measurement examples in this paper. It is found that the measurement results of both RFID straps obtained by the presented method agree well with those by the conventional source-pull system and the RFID source-pull system. The single-ended probe method can measure the approximate read/write threshold power and impedance of the RFID strap with minimum operating procedures; furthermore, the complicated radio frequency (RF) facilities are not required. Obtaining the read/write threshold power and impedance of RFID straps allows designers to estimate the maximum read range of the designed RFID tag in advance. Therefore, the implemented cost and design cycle times can substantially be reduced.

A Measurement Technique for Verifying the Match Condition of Assembled RFID Tags

In radio frequency identification (RFID) tag design, many measurement methods are available for individually characterizing either the RFID chip or the antenna; however, to the best of the knowledge of the authors, no direct method has been developed for the assembled RFID tag. In this paper, a measurement method for verifying the match condition of the assembled RFID tag is proposed. The proposed method can not only verify the final impedance match condition of the assembled RFID tags but also be used to identify the resistance and reactance mismatch condition between the RFID chip and the antenna. Furthermore, the measurement data obtained from the verification method can be used to estimate the assembly error introduced by different mounting methods. The use of the corrected circuit model of the RFID chip impedance, which includes the assembly error, helps improve the accuracy of the RFID tag design. Five RFID tag antennas, each with a different complex impedance, are used to verify the proposed method. This paper compares the simulated and measured results to illustrate the application of the proposed verification method to the aforementioned RFID tag antennas. It is shown that the experimental tests for the maximum read range agree well with the measured data generated by using the proposed verification method.

Design of dual-polarized high-gain antenna radome by using Jerusalem cross metamaterial structure

We find that using metamaterial antenna radome made by 90 degree rotational symmetric unit cell structure can enhance the gain of dual-polarized antenna. The Jerusalem cross structure is proposed for dual-polarized antenna radome and its refraction index is designed to be near zero. This radome is designed for the WiMAX applications. Simulation results show that this antenna radome can improve the gain of dual-polarized patch antenna.

Microstrip antenna gain enhancement by metamaterial radome with more subwavelength holes

A high gain patch antenna using more subwavelength hole metamaterial as radome operating at 3.5 GHz band is proposed in this work. We use a metamaterial superstrate, which is constructed by stacking three layers of Jerusalem cross structure. The structure can be applied to modify the radiation pattern and increase antenna gain. The proposed structure is made by three layers FR4 and the Jerusalem cross structure is printed on the front slab at each layer. This radomes refraction index approximately equals zero and increases the antenna gain at a frequency close to 3.5 GHz. In addition, we change the number of subwavelength holes in metamaterial radome to further enhance antenna gain. A patch antenna which is covered by the proposed metamaterial radome can achieve a maximum gain of 7.8 dBi.

A low profile RFID tag designed for metallic objects

This paper proposed a low profile RFID tag antenna design for metallic objects application. The antenna structure consists of two non-connected capacitance loads and two rectangular patches electrically connected through vias to the ground plane to form an RFID tag antenna that is suitable for mounting on metallic objects. The experimental tests show that the maximum read range of RFID tag placed on a metallic object and in the air are approximately 2.5 and 2.3 m, respectively. Hence, it is suitable for RFID applications when the tag needs to be mounted directly on a metallic object, and the thickness of the tag is of major concern. Simulation and measurement results of the proposed RFID metal tag antenna are also presented in this paper.

Broadband MIMO antennas for MIMO radar systems

Methods of reducing both electric and magnetic field coupling for enhancing the isolation in broadband MIMO antenna system is presented. The proposed MIMO antenna consists of two coplanar waveguide (CPW) fed self-complementary antennas (SCAs) and a U-shaped slot is etched on the ground plane. The protruding structure from the ground plane behaves as both the part of the SCA and an isolator when two SCA protruding structures are connected to each other. Furthermore, the U-shaped slot is introduced for isolation enhancement. The proposed MIMO antenna covers the impedance bandwidth of 4-8 GHz (|S11| ≤ -10 dB) and reaches the good isolation (|S21| ≤ -18 dB) in the band of interest to radar systems.

Gain-enhanced metamaterial radome for circularly-polarized antenna

In the fix-point wireless communications, the high gain antennas are preferred for the reason of high receiving power and signal to interference ratio. Nowadays, the most common methods to enhance the gain of antennas are using antenna array and reflector. However, using antenna array will increase the complexity and the loss of feeding network and both methods will increase the dimensions and costs of antennas. Metamaterial-based radome is another solution for gain-enhancement. The radome has some attractive properties such as light-weighted and low cost.