Nannan Wang

Design of a Near-Field Focused Reflectarray Antenna for 2.4 GHz RFID Reader Applications

The design of a reflectarray antenna is presented when the radiated field is focused in the near-zone of the array aperture. In particular, the reflectarray antenna is implemented for RFID reader applications at 2.4 GHz. Numerical investigations on the radiation characteristics of this reflectarray, as well as an experimental validation, are presented to demonstrate its feasibility.

An Effective Synthesis of Planar Array Antennas for Producing Near-Field Contoured Patterns

We present an efficient procedure for the synthesis of planar array antennas to radiate contoured patterns in the near zone of array aperture, as desired in RFID applications. It first grids the target area, and then utilizes a global basis set to span the arrays excitations. Each basiss excitation of the array radiates a focused spot beam in the near zone and serves as a local basis function for representing the radiation field. The unknown coefficients of the arrays basis set are then found via a minimum least square error (MLSE) technique. It is found that only a small number of basis functions are sufficient to synthesize the radiation pattern, and make the present approach very fast.

Synthesis of array antennas to produce near-field contoured patterns for RFID reader applications

An efficient procedure is developed to synthesize the radiation pattern of a planar antenna array in the near zone of array aperture, which can be used for the applications of RFID reader as illustrated in Fig. 1 [1,2]. In this case, the objects under detection may locate in the near zone of antenna. The presented work appears to be more effective than a conventional near-field focused array antenna [3] because the field distribution in the target zone can be optimized, and can help to reduce the interferences. In this synthesis scheme, we utilize a global basis set to span the array excitation as previously proposed in [4], where each basiss excitation will radiate a near-field focused spot beam in the target area, and serves as local basis functions to synthesize the contoured pattern in the target area. The unknown coefficients of arrays basis set are then found via a MLSE technique. It is found that only a small number of basis functions are sufficient to resemble the radiation pattern, and make the present approach very fast.

Numerical synthesis of reflectarray antenna for Optimum Near-Field Radiation at 2.4GHz

This paper develops a procedure of steepest decent method (SDM) to synthesize the impressed phases of reflectarray array antennas, which will radiate an optimum field pattern in the near-zone of array aperture. For the purpose of validation, a reflectarray of microstrip patch elements is investigated with a feed antenna operated at 2.4 GHz band and can be used for RFID applications.

Characteristic comparisons between array, reflectarray and elliptic reflector antennas in RFID near-field focused communications

This paper presents characteristic comparisons between array, reflectarray and elliptic reflector antennas which can be implemented to radiate fields focused in the near zone of antenna aperture. A potential application, as to be demonstrated later in this paper, is for RFID reader applications at 2.4 GHz. The comparisons include beamwidth, field strength and contoured patterns, which allows one to justify the selection of a proper antenna type for practical applications.

Passive Millimeter-Wave Imaging Technology for Concealed Contraband Detection

In this chapter, we firstly introduce the fundamental radiation detection theory of the passive millimeter-wave imaging technique for human-body security inspections. A radiation temperature transfer model for the passive millimeter-wave near-field imaging is then proposed. The method to analyze the temperature contrast between the human body and the concealed objects under indoor and outdoor environments is presented accordingly. Furthermore, several key technologies involved in the passive millimeter-wave imaging systems are discussed in detail, including the millimeter-wave radiometer, the millimeter-wave feed antenna, the focusing antenna, and the quasi-optical theory. Finally, a prototype of a Ka-band passive millimeter-wave imaging system based on the focal plane array is manufactured. The system design process and the measurement results for some typical scenarios are elucidated.

Improved design of balanced antipodal Vivaldi for MMW applications

A novel balanced antipodal Vivaldi antenna (BAVA) featured with substrate cut-out (CUT), additional substrates (ADS) and mixed slot edge (MSE) is designed to operate from 10GHz to 40GHz. Without increasing the total dimensions, beam squint in E-plane which is considered to be the major defect of conventional BAVA is effectively negated by the asymmetric structure. Besides, the antenna has better than −10dB S11 and much lower side lobe level (SLL) over the entire operating band-width benefiting from MSE. And gain of the antenna is respectively elevated by substrate cut-out up to 15 dB at higher frequencies and by MSE to 10 dB at lower frequencies.

A frequency beam scanning substrate integrated waveguide slot array antenna for 94GHz band

Millimeter-wave imaging technology has been the hotspot in microwave area recently. The special antennas are needed in order to acquire the information of the view rapidly. A 16 element slot array antenna using substrate integrated waveguide and snaky slow wave line technology is proposed in this paper. It can achieve -15°-+40° frequency beam scanning from 92GHz to 99.5GHz.

Research of Klopfenstein taper UWB monopole antenna

The tapered line theory in circuit can be applied to the design of the special-shaped monopole antenna in order to obtain better electrical characteristics. So the circular disc monopole antenna is optimum designed and a novel Klopfenstein taper monopole antenna is proposed. The impedance matching characteristic of the Klopfenstein tapered line is the best, and the Klopfenstein taper monopole antenna is designed based on it. The antennas electrical characteristic is similar to the circular disc monopole. On this basis, the coplanar waveguide-fed and microstrip line-fed planar Klopfenstein taper monopole antennas are designed. The simulation and measurement results prove that the Klopfenstein taper monopole antennas have small size and good performance. And the planar printed antenna can be convenient integrated with other radio frequency circuits. The idea to design antenna by using of tapered line theory directly can be used in practical operations.

A new method towards traffic flow control by millimeter wave radiometers

In order to release the increasing pressure of traffic flow in metropolises, this paper introduced a method of using high sensitivity microwave radiometric systems to monitor the traffic flow in all-weather conditions. In this method, radiometers were employed to detect and recognize the automobiles on the roads based on different behaviors of the automobile roofs and road surface in the millimeter microwave bands. The traffic control can be flexible according to the quantity of moving automobiles detected by the radiometers. Radiometers of 8 mm wavelength were constructed and used for detecting the traffic flow. This proposed method was proven to be low-cost, high accurate and fully capable in all-weather conditions in contrast with other competitors.