Xuan Hui Wu

Considerations for source pulses and antennas in UWB radio systems

This paper addresses two vital design considerations in ultrawide-band radio systems. One is that radiated power density spectrum shaping must comply with certain emission limit mask for coexistence with other electronic systems. Another is that the design of source pulses and transmitting/receiving antennas should be optimal for the performance of overall systems. The design of source pulses and transmitting/receiving antennas under the two considerations is discussed. First, the characteristics of transmitting/receiving antenna systems are described by a system transfer function. Then, the design of source pulses and transmitting antennas are studied based on the considerations for emission limits. Finally, the design of transmitting and receiving antennas are investigated in terms of pulse fidelity and system transmission efficiency. In the studies, thin wire dipoles with narrow bandwidths and planar dipoles with broad bandwidths are exemplified.

Comparison of planar dipoles in UWB applications

The characteristics of four planar dipoles are studied and compared based on the design considerations of ultrawide-band (UWB) antennas. Their impedance matching, realized gain, and polarization over the UWB band are investigated. The current distributions on the dipoles are illustrated to interpret their different radiation characteristics. Furthermore, pulses radiated in different directions are presented for both single-band and multiband schemes in UWB applications.

Wide-slot antenna for UWB applications

A wide-slot antenna with a fork-shaped microstrip line feed structure is investigated and optimized for UWB applications. The prototype shows good UWB behavior. The bandwidth for 10 dB return loss is more than 2 octaves (f/sub h//f/sub 1/=4.52, or (f/sub h/-f/sub 1/)/f/sub 0/=127%); it also shows a good gain flatness and phase linearity. The proposed antenna is easy to fabricate, low cost and presents stable characteristic over 3.1 GHz to 10.6 GHz, and it is suitable for future UWB applications.

A Transmission Line Method to Compute the Far-Field Radiation of Arbitrarily Directed Hertzian Dipoles in a Multilayer Dielectric Structure: Theory and Applications

A transmission line method is proposed to compute the far-field radiation patterns of arbitrarily directed Hertzian dipoles that are embedded in a multilayer dielectric structure. The evaluation of the field in the far-zone region is transformed into the evaluation of the field inside the multilayer structure by applying the reciprocity theorem. The horizontal field component inside the structure is derived by analyzing a transmission line circuit, and the vertical component is obtained from the horizontal component by separating the forward and backward waves. This method is implemented and verified by IE3D for the case of a three-layer structure excited by either electric Hertzian dipoles, magnetic Hertzian dipoles, or their combination. The radiation patterns of any antenna embedded in a multilayer dielectric structure can be computed with this method after replacing the physical antenna with a set of Hertzian dipoles. As examples, a quarter wavelength thin wire monopole antenna and a dielectric resonator antenna, both embedded in a multilayer structure, are investigated. Furthermore, the arrangement of the structure is optimized to maximize the antenna directivity. The results are also verified by the simulation of the entire structure with IE3D

Signal optimization for UWB radio systems

This paper presents and studies three frequency-domain models for optimizing source pulses and detection templates in ultrawide-band (UWB) radio systems. The optimization aims mainly at maximizing the equivalent isotropically radiated power band efficiency in the free space and the output of correlation detection at a receiver. These models are based on the differential evolution, an improved version of the genetic algorithm, and carried out on a set of UWB signals with given mathematical forms. As examples, these models are used to optimize the UWB signals for both narrow-band thin-wire and wide-band planar antenna systems. In addition, the optimized results are validated by nonoptimization simulation.

Hybrid of Method of Moments and Cylindrical Eigenfunction Expansion to Study Substrate Integrated Waveguide Circuits

A hybrid method that combines method of moments (MOM) and cylindrical eigenfunction expansion is presented to study a substrate integrated waveguide circuit that consists of metallic and dielectric circular cylinders. The problem is considered as a 2-D electromagnetic problem assuming no field variation normal to the dielectric substrate. The scattered field from each circular cylinder is expanded by cylindrical eigenfunctions, and the equivalent current densities at a waveguide port are expanded using the MOM. After enforcing boundary conditions and applying the additional theorem of Bessel and Hankel functions, a set of linear equations are constructed using the orthogonality of the exponential function. With matrix manipulation and sub-ports combination, the S matrix can then be obtained. Four examples are analyzed by using the hybrid method and verified by using Ansoft Corporations commercial High Frequency Structure Simulator (HFSS) software package. It is shown that the hybrid method runs faster than HFSS and requires less memory. It is also pointed out that the method can be used to study a circuit with noncircular cylinders.

Study of an Ultrawideband Omnidirectional Rolled Monopole Antenna With Trapezoidal Cuts

An ultrawideband (UWB) omnidirectional monopole antenna is presented. It is shaped by symmetrically wrapping a PEC sheet that has two trapezoidal cuts at the bottom corners. The antenna features about 132% impedance bandwidth and a stable as well as omnidirectional gain versus frequency response over the UWB band. The monopole antenna is investigated both experimentally and numerically by using an FDTD method. A parametric study is carried out for the monopole above an infinite ground plane to obtain an optimal design. The effects of a finite ground plane on both the impedance matching and gain of the antenna are discussed. Particularly, a simple expression is derived based on ground plane size to estimate the ripples appearing in the gain versus frequency response. Furthermore, ground plane edge loading with resistive sheet is proposed to eliminate the edge diffraction effects on the antenna gain, and thus improves the antenna performance.

Design and optimization of UWB antennas by a powerful CAD tool: PULSE KIT

In this paper, we discuss the assessment and optimization of UWB antennas for two proposed schemes, based on their unique requirements. One is impulse radio that adopts impulses with transient bandwidths covering the entire UWB band, and the other is multi-band OFDM where the UWB band is divided into several OFDM sub-bands. Firstly, some special requirements for the design of UWB antennas are briefly reviewed. Next, the assessment and optimization of a UWB antenna system is presented. Then, a CAD tool, PULSE KIT, is introduced to conduct the optimization. Lastly, as an example, a planar diamond antenna is optimized, and its performance in a UWB radio system are investigated.

A linear antenna array for UWB applications

A uniformly spaced linear antenna array was investigated for UWB applications. A planar UWB dipole antenna was selected as an array element, and simulated with both FDTD and MoM. A source pulse was optimized to make full use of the FCC allocated UWB bandwidth. It was proven that the pulse optimized for a single antenna element could also be applied to all of the array in the sense of complying with emission limits. Three different radiation patterns were examined for arrays with different numbers of elements and different element spacings. For all three patterns, a narrow main lobe beam width was achieved by increasing the array size, either by increasing the number of elements or the element spacing. However, the latter raises the sidelobe level. Among all the patterns for a given array configuration, the peak value pattern gave the narrowest beam width of the main lobe, and the lowest sidelobe level.

Design considerations for antennas in UWB wireless communication systems

General design considerations for the transmit/receive antennas in ultra-wideband wireless communication systems are discussed. The considerations include radiated power density lower than the required emission limits and maximum energy at the output of receive antennas. As an example, a pair of center-fed thin wire dipoles is investigated by using an FDTD method. The effects of the parameters of transmit/receive antennas and source pulses on the overall system performance are studied.