Y. J. Fan

Compound Diffractive Lens Consisting of Fresnel Zone Plate and Frequency Selective Screen

We describe a new Fresnel zone plate (FZP) and frequency selective screen (FSS) compound lens consisting of a binary FZP and FSS. The FZP has eight circular zones totally, four open and four closed, and the FSS is a square array of 40 × 40 four-leg loaded elements cut in a thin metal sheet. The FZP-FSS lens is designed for a paraxial plane-wave illumination at the frequency of 12 GHz, with a focal length of 15 cm. The compound lens is simulated and analyzed numerically by means of a specially developed hybrid PSTD-FDTD algorithm and software. The PSTD-FDTD results are contrasted with those obtained by lens prototype measurements. As a result, some attractive focusing and spectral properties of the FZP-FSS lens compared to the same-size FZP lens have been found: a frequency filtering property enhancement, about 2 dB increase in the peak focusing intensity, and more than 4 dB reduction of the first off-axis maximum. Both lenses have roughly the same transverse angular resolution.

Compact CPW-to Microstrip transition design for MMIC packaging

In MMIC circuit design, the transitions and interconnects are essential components for integration and packaging [1-3]. However, the conventional distributed type transition circuits will result in great loss owing to their huge size, most especially in medium and low frequency band. In this paper, a new CPW-to-microstrip transition design based on lumped element circuits is proposed. The optimized design can achieve a return loss of less than 10 dB from 3 to 14 GHz and insertion loss of less than ldB from 3 to 14 GHz.

An UWB Multi-frequency transformer

A novel multi-frequency transformer is developed based on dual frequency transformer reported recently. Different from dual frequency transformer, which has two steep poles, the return loss curve of the transformer developed in this paper has one steep pole with two gentle side poles. This transformer can achieve ultra-wideband because it makes use of big separation ratio between center frequencies as employed in dual frequency transformer. At the same time, the gentle side poles avoid sharp jump of peak values between two adjacent poles. The transmission line analysis shows that the three-pole transformer can achieve 120% bandwidth compared to 60% of dual frequency transformer

A Hybrid Fast Multipole Pseudo-Spectral Time Domain Method

The major computation cost of pseudo-spectral method comes from the evaluation of differentiation matrix multiplication. In the past, uniform or Chebyshev collocation points are used for sampling. The differentiation matrix multiplication was evaluated by fast Fourier transform (FFT) or fast cosine transform (FCT), in order to reduce the computation complexity from O(N2) to O(N log(N)). However, the intrinsic properties of FFT or FCT may cause the wraparound effect and Gibbs phenomenon. Moreover, FFT or FCT is not applicable to other collocation points such as Legendre and Hermite. In order to improve the accuracy and applicability of the pseudo-spectral method, the fast multipole method (FMM) is exploited to substitute the FFT or FCT. By making use of the similarity of the N-body problem and the collocation problem, a new FMM-based pseudo-spectral time domain method is developed in this paper.

Element-free method for the computation of cutoff wavenumbers of waveguides partially filled with dielectric

Researchers have shown growing interest in mesh free methods, since they can solve partial differential equations numerically only based on a scattered set of nodes inside the analysis domain. These methods are especially attractive for problems in which re-mesh is needed. Recently, we used a mesh free method, element-free (EF) method, based on the moving least square approximation, for the analysis of homogeneous waveguides (Ooi, B.L. et al., IEE Proc. Microwaves, Antennas and Propag.). The EF method does not require laborious and time consuming mesh generation and can achieve higher accuracy than the FEM with the same number of nodes. Mesh free methods also have features like fast convergence, ease of adaptive refinement, trivial raising of the consistency order and the continuity of derivatives up to the desired order. These advantages stimulate us to expand the method for inhomogeneous waveguides. The element-free method is applied to compute the cutoff wavenumbers of waveguides partially filled with dielectric. Variational forms are used to derive the governing equations. Simulation results show that good agreements can be achieved.