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Electromagnetic analysis for microstrip antenna and packaging structures is formulated by volume-surface integral equations (VSIEs). The conducting microstrip and ground are described with SIEs, while the dielectric substrate is governed by volume integral equations (VIEs), and they are coupled to each other to form VSIEs. Using VIEs instead of SIEs for dielectric substrate can improve the conditioning of system matrix related to the multiscale property of antenna and packaging structures. The VSIEs are usually solved by the method of moments (MoM) with well-designed basis functions defined over conforming meshes, resulting in much inconvenience of implementation. We propose a mixed approach to solve the VSIEs by combining the traditional MoM for the conducting part and a point-matching scheme for the dielectric part together. The approach uses cuboids to discretize the dielectric substrate and does not require conforming meshes between the conducting and dielectric parts. Also, the approach considers the thickness of metallic microstrip and ground, which is usually neglected. Typical numerical examples are presented to demonstrate the proposed approach, and its effectiveness has been verified.

In this paper, the well-known high frequency structure simulator (HFSS)is used to design an ultra-high-frequency (UHF)radio-frequency-identification (RFID)tag antenna with a paper substrate. With the continuous development of RFID technology, various factors of designing RFID tags have been investigated such as the substrate material, tag shape, working frequency band, and impedance matching. In the design of passive tag antenna, the impedance matching, broadband, and miniaturization are the main difficulties. We use a special structure to improve the performance of passive tag antenna and an UHF RFID tag antenna with a paper substrate is proposed for near-field applications. The tag antenna uses a matching network to achieve the impedance matching and employs a first-order Hilbert fractal structure to reduce the size. The overall size of the antenna is 63.6mm⨯25mm and the operation band is from 881.9 MHz to 962.2 MHz which can cover the UHF RFID bands of many countries. Its good performance is verified by HFSS simulation and measurement.

Volume integral equations (VIEs) are indispensable to formulate inhomogeneous or anisotropic electromagnetic (EM) problems and cuboid meshes are preferred to discretize volume domains in some applications. In solving the VIEs, accurate evaluation for singular integrals is very essential but there is no direct method to evaluate hypersingular integrals over a cuboid domain so far. In this work, we propose some closed-form formulas for calculating those hypersingular volume integrals and they are simpler and more efficient to implement. A numerical example is presented to demonstrate the formulas and their effectiveness has been verified.

Electromagnetic (EM) scattering by bi-isotropic objects is formulated through volume integral equations (VIEs). The VIEs are usually solved by the method of moments (MoM) in which unknown flux densities are expanded with the Schaubert-Wilton-Glisson (SWG) or other divergence-conforming basis functions, but the approach may not be convenient in implementation because material parameters are involved in integrands. We propose a point-matching scheme to solve the VIEs in which current densities are selected as unknown functions to be solved and integral kernels are free of material parameters, resulting in a facilitation of implementation for bi-isotropic media. A typical numerical example is presented to demonstrate the scheme and its robustness has been verified.

Biological tissues like breasts are dispersive inhomogeneous dielectric objects and microwave imaging for them can be formulated by volume integral equations (VIEs). The distorted Born iterative method (DBIM) is used to reconstruct the objects in recent years, but it requires to update the dyadic Green's function in each iteration and is also sensitive to the initial guess of object property. We use the contrast source inversion method (CSIM) to image the objects by updating the contrast source and contrast simultaneously. The CSIM can avoid the direct solution of dyadic Green's function and does not need an initial guess for the object property. A numerical example is presented to demonstrate the approach and good results have been obtained.

In this paper, a low-profile microstrip monopole antenna with an ultrawide bandwidth (UWB) is proposed. Via holes, rectangular patches, and a tune stub connecting ground plate are employed to improve the gain and impedance bandwidth of the antenna. Meanwhile, the antenna is etched on a single-layer substrate lowering the cost and complexity of manufacturing process. HFSS software is used to design and optimize the antenna's parameters. The novel antenna with the size of 45 mmx50 mm has the resonant frequency of 2.45 GHz, bandwidth of 1.6 GHz. The peak gain of the antenna is from −1.8 dBi to 0.75 dBi against frequency from 1.4 GHz to 3.0 GHz.