Metasurfaces: From microwaves to visible

Introduction to Electromagnetic Compatibility

A novel triple-frequency microstrip-fed planar monopole antenna for multiband operation is proposed and investigated. Defected ground structure (DGS) is used in this antenna, which has a rectangular patch with dual inverted L-shaped strips and is fed by a cross-shaped stripline, for achieving additional resonances and bandwidth enhancements. The designed antenna has a small overall size of 20 × 30 mm2, and operates over the frequency ranges, 2.14-2.52 GHz, 2.82-3.74 GHz, and 5.15-6.02 GHz suitable for WLAN 2.4/5.2/5.8 GHz and WiMAX 3.5/5.5 GHz applications. There is good agreement between the measured and simulated results. Experimental results show that the antenna gives monopole-like radiation patterns and good antenna gains over the operating bands. In addition, effects of both the length of the protrudent strips and the dimensions of the DGS for this design on the electromagnetic performance are examined and discussed in detail.

Design of Triple-Frequency Microstrip-Fed Monopole Antenna Using Defected Ground Structure

We present a comprehensive synthesis procedure for designing low-profile, band-pass frequency selective surfaces composed of non-resonant constituting elements. The proposed FSSs use arrays of sub-wavelength periodic structures with non-resonant constituting unit cells with unit cell dimensions and periodicities in the range of , where is the free space wavelength. The main advantages of this type of FSS, compared to traditional ones, are that they allow for the design of low-profile and ultra-thin FSSs that can provide sharp frequency selectivity and stable frequency responses as functions of angle and polarization of incidence of the EM wave. An order FSS designed using this technique typically has an electrical thickness in the order of which is significantly smaller than the overall thickness of a traditionally designed order FSS . The proposed synthesis procedure is validated for two FSS prototypes having third- and fourth-order band-pass responses. Principles of operation, detailed synthesis procedure, measurement results of a fabricated prototype, and implementation guidelines for this type of FSS are presented and discussed in this paper.

A Generalized Method for Synthesizing Low-Profile, Band-Pass Frequency Selective Surfaces With Non-Resonant Constituting Elements

A coplanar waveguide (CPW)-fed planar monopole antenna with triple-band operation for WiMAX and WLAN applications is presented. The antenna, which occupies a small size of 25(L) × 25(W) × 0.8(H) mm3, is simply composed of a pentagonal radiating patch with two bent slots. By carefully selecting the positions and lengths of these slots, good dual stopband rejection characteristic of the antenna can be obtained so that three operating bands covering 2.14-2.85, 3.29-4.08, and 5.02-6.09 GHz can be achieved. The measured results also demonstrate that the proposed antenna has good omnidirectional radiation patterns with appreciable gain across the operating bands and is thus suitable to be integrated within the portable devices for WiMAX/WLAN applications.

Novel CPW-Fed Planar Monopole Antenna for WiMAX/WLAN Applications

In this letter, we propose a miniaturized periodic element for constructing a band-pass frequency selective surface (FSS) that demonstrates an excellent resonance stability performance with respect to different polarizations and incidence angles. In contrast to traditional periodic elements with sizes comparable to a half of the wavelength at the resonant frequency, the size of the proposed element is reduced highly to only a tenth-wavelength. We created and examined a prototype of the miniaturized-element FSS. Both the simulated and measured results obtained demonstrate the claimed performance.

A Novel Miniaturized-Element Frequency Selective Surface Having a Stable Resonance

In this letter, we propose a novel dual-frequency miniaturized periodic element for creating a dual-band frequency selective surface (FSS) having closely spaced bands of operation. Using this element and its complementary structure, the dual-bandstop and dual-bandpass FSSs can be simultaneously created without extra effort. The mechanism responsible for the two element resonances and the new way to make these resonances closer is revealed. Based on this revelation, the newly proposed element can be simply and quickly designed to be compact in size and to have two resonances closely spaced. Furthermore, the dual-band FSS created using this element demonstrates excellent resonance stability with respect to different polarizations and incidence angles. Both the bandstop and bandpass FSS prototypes are fabricated and examined. Their measured and full-wave simulated results validate the performance. The created element size is about 8% of the free-space wavelength at the first resonant frequency, and the ratio of the second resonant frequency to the first one is only 1.4.

A Dual-Frequency Miniaturized-Element FSS With Closely Located Resonances

A compact and wideband common-mode filter is newly proposed to embed in a cable-attached printed circuit board (PCB) or packages for the suppression of the common-mode noise and its resulting electromagnetic interference (EMI) emission from the attached cable. The proposed filter consists of a pair of distributed signal lines on the top of a mushroom-like structure. Owing to its symmetry, an equivalent circuit model is developed and applied efficiently for this filter design. As an example, a filter prototype is designed and fabricated on a multilayer PCB. The filter prototype shows that it can greatly reduce the common-mode noise over 10 dB from 1.65 to 5.2 GHz. In addition, the corresponding fractional bandwidth is over 100% while the electrical size of the prototype is only 0.11 × 0.11 λg, where λg is the wavelength of the central frequency of its stopband. Also in the time domain, this filter prototype can reduce over 60% of the unintended noise. More importantly, the differential-signal integrity, in terms of the insertion loss in the frequency domain and the eye diagram in the time domain, is maintained up to 7 GHz. To the best of our knowledge, it is the first embedded common-mode filter proposed for gigahertz differential signals with such a large bandwidth and the most compact size. To further demonstrate the ability of the filter to suppress the common-mode current on the attached cable and the corresponding EMI emission, a test board design is also introduced and realized. From the experimental results related to this test board, a 10-dB suppression on average is indeed achieved.

Radiation Suppression for Cable-Attached Packages Utilizing a Compact Embedded Common-Mode Filter

A novel circular-ring miniaturized-element (CRME) metasurface is proposed for frequency selective electromagnetic shielding applications in this paper. The proposed structure exhibits good performance in many aspects. The CRME size can be easily reduced to $0.088\, \lambda _r \times 0.088\, \lambda _r$ , where $\lambda _r$ is the wavelength at resonance. Such small size can be useful in applications with limited space. The newly proposed metasurface not only shows the stability to incidence angles and polarizations, but also demonstrate negligible polarization crossing. The metasurface also presents low coupling between elements, which leads to the insensitivity of periodicity fluctuation in fabrication process. Moreover, the frequency responses can be varied through the modification of the element pattern of the metasurface. It provides flexible frequency responses to use in frequency selective shielding applications. Also, this element is suitable for constructing a metasurface aligned in either square or even hexagonal lattice, which owns the best adaptability to a doubly curved surface or a spherical one. Without revising the CRME, both the square- and hexagonal-lattice metasurfaces constructed can perform competently at the same time. Finally, the metasurface prototype is fabricated and tested in a fully anechoic chamber to verify the design. The measured results well agree with the simulated ones.

A Circular-Ring Miniaturized-Element Metasurface With Many Good Features for Frequency Selective Shielding Applications

This paper proposes fabricating a new 2.5-dimensional ultraminiaturized element on a cost-effective printed circuit board to build a frequency selective surface (FSS). The proposed element consists of two main parts: a planar tapered meandering line (PTML) and a vertical via-based meandering line (VVML). Compared with previous published two-dimensional miniaturized elements, the proposed element is smaller (only 3.3% of the free space wavelength at the resonant frequency) and exhibits high resonant stability at various polarizations and incidence angles (only 0.4% deviation at the resonant frequency when the incident angle is as great as 75°). In particular, the introduction of VVML in the element substantially improves the FSS performance. A third-order equivalent circuit model was established to model the FSS performance precisely. This model can be reduced to a simpler first-order model, thus enabling the resonant frequency of the FSS to be predicted quickly. A prototype of the ultraminiaturized-element FSS was created and examined. The results of the proposed models, full-wave simulation, and measurement exhibited satisfactory consistency.

Cheng-Nan Chiu

Papers

A Novel Miniaturized-Element Frequency Selective Surface Having a Stable Resonance

A Dual-Frequency Miniaturized-Element FSS With Closely Located Resonances

Radiation Suppression for Cable-Attached Packages Utilizing a Compact Embedded Common-Mode Filter

A Circular-Ring Miniaturized-Element Metasurface With Many Good Features for Frequency Selective Shielding Applications

A Novel 2.5-Dimensional Ultraminiaturized-Element Frequency Selective Surface