Jiangniu Wu

Bandwidth Enhancement of a Planar Printed Quasi-Yagi Antenna With Size Reduction

A compact planar printed quasi-Yagi antenna is presented. The proposed antenna consists of a microstrip line to slotline transition structure, a driver dipole and two parasitic strips. The driver dipole is connected to the slotline through coplanar stripline (CPS). The ground plane is modified by symmetrically adding two extended stubs to reduce the lateral size. Experimental and simulated results show that the proposed quasi-Yagi antenna has a wide bandwidth and good unidirectional radiation characteristics. Compared with conventional printed quasi-Yagi antennas, the width of the proposed quasi-Yagi antenna is reduced by approximately 16.7%. The proposed antenna presents an excellent end-fire radiation with a front-to-back ratio greater than 10 dB. Its measured bandwidth is from 3.6-11.6 GHz with a ratio of about 3.22: 1. A moderate gain, which is better than 4 dBi, is obtained.

A Printed UWB Vivaldi Antenna Using Stepped Connection Structure Between Slotline and Tapered Patches

In this letter, a new stepped connection structure between slotline and tapered patches is adopted in a planar printed Vivaldi antenna. By using the stepped connection structure, the impedance matching is significantly improved and a wide bandwidth is achieved. In order to illustrate the effectiveness of this design, a prototype of the modified Vivaldi antenna is fabricated and tested. Experimental results show that the impedance matching is significantly improved in the band from 3 to 15.1 GHz. In addition, a measured gain, which is better than 5 dBi, is obtained with a compact size. Compared to other techniques, the presented technique effectively improves the impedance matching and enlarges the bandwidth without changing the overall dimensions. Moreover, a relatively flat group time delay response is achieved within the band of 3-15.1 GHz.

A Broadband Unidirectional Antenna Based on Closely Spaced Loading Method

In order to achieve broadband and unidirectional radiation, a planar printed antenna based on closely spaced loading method is proposed and fabricated. This antenna consists of a printed rectangular loop with two gaps and a metallic strip. The rectangular loop has a good direction but has a drawback of narrow band. According to the closely spaced loading theory, the impedance at the upper frequency will decrease when a metallic strip is placed at the maximum radiation direction of the rectangular loop. This improves the impedance matching. A new resonant frequency point is induced. Meanwhile, the resonant frequency point can be changed by modifying the length of the metallic strip. The impedance matching between the two resonant peaks (One peak is determined by the rectangular loop, the other is determined by the metallic strip) is improved by changing the length and the position of the metallic strip. Thus the impedance bandwidth is greatly expanded. Experimental results show good performance of the proposed antenna. It has a 40.7% measured bandwidth, ranging from 2.29 to 3.46 GHz. The measured front-to-back (F/B) ratio of the proposed antenna is larger than 10 dB in the whole frequency band.

Design of a Wideband Planar Printed Quasi-Yagi Antenna Using Stepped Connection Structure

Although conventional Yagi antenna has the advantage of unidirectional radiation patterns, it is not suitable for wideband applications due to its drawback of narrow bandwidth. In this communication, a compact wideband planar printed quasi-Yagi antenna is presented. The proposed quasi-Yagi antenna consists of a microstrip line to slotline transition structure, a driver dipole, and a parasitic strip element. The driver dipole is connected to the slotline through a coplanar stripline (CPS). The proposed antenna uses a stepped connection structure between the CPS and the slotline to improve the impedance matching. Two apertures are symmetrically etched in the ground plane to improve the unidirectional radiation characteristics. Simulation and experimental results show that the unidirectional radiation patterns of the proposed antenna are good. A 92.2% measured bandwidth with from 3.8 to 10.3 GHz is achieved. A moderate gain, which is better than 4 dBi, is also obtained.

A Novel Simple and Compact Microstrip-Fed Circularly Polarized Wide Slot Antenna With Wide Axial Ratio Bandwidth for C-Band Applications

This communication presents a design of a new compact circularly polarized (CP) slot antenna fed by a microstrip feedline. The 3-dB axial ratio band can be achieved by simply protruding a horizontal stub from the ground plane toward the center of the wide slot (WS) and then feeding the WS with a microstrip feedline positioned to the side of the WS, underneath the protruded stub. The feedline and metallic stub are perpendicular to each other, and they resemble a T shape when viewed from the top. The proposed antenna is fabricated with an area of 25 × 25 mm2. Measurement results show that the antenna attains an S11 ≤ -10 dB impedance matching bandwidth of 90.2%, from 3.5 to 9.25 GHz, and a broadband 3 dB-AR bandwidth of 40%, ranging from 4.6 to 6.9 GHz. A peak gain of 0.8-4.5 dBi is achieved within the AR band. The proposed antenna is suitable for circular polarization applications in C band.

Evaluation of Contrast Enhancement by Carbon Nanotubes for Microwave-Induced Thermoacoustic Tomography

Microwave-induced thermoacoustic tomography (MITAT) is a hybrid method which constructs images with ultrasound spatial resolution while exploiting dielectric contrast at microwave frequency. It has great potential in biomedical imaging especially in early breast cancer detection. The detection of early stage breast tumor in MITAT is challenged by the moderate endogenous dielectric contrast between malignant and healthy glandular tissues. In order to overcome this limitation, the performance of using carbon nanotubes (CNTs) as an imaging contrast enhancement agent is evaluated. First, the influences in dielectric and acoustic properties caused by CNTs are measured. Second, based on the measurements and the published data, numerical breast phantom is created and then used to explore the contrast enhancing effect of CNTs for MITAT, by an integrated simulation approach in both electromagnetic and acoustic field. With an experimental MITAT system, the thermoacoustic responses of tissue mimicking materials with different CNTs concentrations are also quantitatively investigated. Finally, the effectiveness of the contrast agent is also validated experimentally by using a MITAT system. The results show that the using of the dielectric contrast agent can effectively enhance the contrast of the MITAT image.

System Development of Microwave Induced Thermo-Acoustic Tomography and Experiments on Breast Tumor

Microwave induced thermo-acoustic tomography (MI- TAT) has become a keen research topic in recent years due to its great potential in early breast cancer detection. A secure and accurate MI- TAT system has been established. Some experiments have been made to demonstrate the performance of the MITAT system. Based on an experiment using phantom, some quantitative features of the system have been obtained. Some imaging experiments with real human breast cancer tissues are performed to demonstrate its efiectiveness and the potential in clinical diagnosis. Images with both high contrast and flne spatial resolution are achieved by using time reversal mirror (TRM) technique in the imaging processing. Moreover, comparisons between the MITAT system result and an ultrasound imaging system result are made. From the comparison, the MITAT system shows its advantages of better contrast over the ultrasound imaging system. The system and the experiments in this paper verify the mechanism of MITAT for breast cancer detection and provide a prototype basis for clinical practice.

A Compact Printed Dipole Antenna for Wideband Wireless Applications

A compact printed dipole antenna with wide impedance bandwidth is proposed in this paper. This antenna consists of a pair of radiation metal arms and a microstrip-to-slotline transition structure. At the end of the feeding slotted line, a beveled slot with stepped connection structure is designed to realize an ofiset feeding structure for feeding the dipole antenna. By using the beveled ofiset feeding structure, the bandwidth of the dipole antenna is signiflcantly improved. The microstrip-to- slotline transition is used as an integrated balun to realize a balanced feeding for the dipole antenna. To demonstrate the efiectiveness of the proposed design, a prototype of the designed antenna is fabricated and measured. The measured results show that the designed dipole antenna achieves a gain of 2.2{4.4dBi across a wide impedance bandwidth from 2.65GHz to 17.5GHz with a compact size (33mm£16mm). The performance of the proposed dipole antenna is also compared with some similar printed dipole antennas with respect to overall size, substrate dielectric constant, impedance bandwidth and antenna gain.

Electromagnetic inverse scattering series (ISS) method for sensing 2-D objects buried in layered media with unknown dielectric properties

To reconstruct objects buried in layered media, most of current imaging methods are based on a common assumption that the dielectric properties of layered media are given. However, this assumption is unrealistic in practice. To study a more realistic electromagnetic inverse scattering problem in which the dielectric properties of layered media are not given, an inverse scattering series (ISS) method which has been used in seismic exploration is extended into electromagnetic field. By using the developed ISS method, objects buried in layered media can be imaged without knowing the dielectric properties of layered media a prior. The feasibility of the improved ISS method has been demonstrated by some numerical simulations.

Design of Anti-Phase Feeding Network for W8JK Array Based on In-Phase Power Divider

Double-dipole antennas driven by anti-phase signals (W8JK array) are often used to achieve broadband and good unidirectional radiation patterns. The two dipole elements need a pair of anti-phase signals equal in magnitude. However, realization of anti-phase signals with equal magnitude for the W8JK array is difficult in a planar structure. In this communication, an equivalent feed mechanism of W8JK array is presented. An in-phase power divider is used to realize an anti-phase feeding network for feeding the W8JK array. In order to demonstrate the effectiveness of the designed anti-phase feeding network, an antenna prototype has been designed, fabricated and tested. Experimental results show that the designed anti-phase feeding structure for the W8JK array is effective. The designed antenna provides a 64% measured bandwidth ranging from 6.9 to 13.4 GHz. An excellent endfire radiation characteristic with an F/B ratio better than 17 dB is achieved. The measured gain is better than 4 dBi.