Wee Sang Park

Design of a frequency selective surface (FSS) type superstrate for dual-band directivity enhancement of microstrip patch antennas

A novel design of a high-directivity resonator antenna that utilizes a two-layered frequency selective surface (FSS) superstrate - as an alternative to a dielectric electromagnetic band gap (EBG) superstrate - for dual band directivity enhancement and reduction in height is presented in this paper.

Sectoral Conical Beam Former for a 2

We propose a switched feed network for a 2 times 2 array antenna to form a sectoral conical beam. The proposed feed network, which is a symmetrical structure, consists of four 90deg hybrids, a crossover, and four 90deg delay lines. The prototype feed network and a 2 times 2 array antenna were fabricated on microstrip structures. The performance of the feed network was verified by measuring the radiation patterns at the center frequency of 2.57 GHz. The maximum radiation was measured at the 45deg elevation and at the 45deg, 135deg, 225deg, and 315deg azimuth angles, depending on the choice of the input port of the feed network.

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A windmill-shaped loop antenna is designed for polarization diversity. Its circumference is almost 10 times that of a conventional small loop antenna whose circumference is less than but its the radiation pattern is omni-directional. An identical parasitic element is placed over the radiator to match the antenna input impedance. An equivalent transmission line and RLC circuit models are shown to fully describe for the windmill-shaped loop antenna. The proposed antenna has a bandwidth of 6 % with input VSWR less than 2:1 and a polarization purity of 15 dB at 2.6 GHz, and the gain of 1.5 dBi. The simulated and measured results show fairly good agreement.

2 Array Antenna

In this paper, we present some applications of metamaterial superstrates for directivity enhancement of printed antennas. Three different types of superstrates, viz., multilayer dielectric slabs, electromagnetic band gap (EBG) materials, and frequency selective surfaces (FSSs) are discussed. We first present the design of a multilayer dielectric slab, consisting of high and low permittivity dielectric layers and air-gap tuners for suppressing the grating lobes of patch array antennas. Next, a dielectric-rod EBG-type superstrate with two defect frequencies is proposed for dual-band directivity enhancement of a patch antenna at a boresight. With this design we can increase the degrees of freedom that adjust the level of directivity enhancement and operating frequency location, relative to those of the multilayer dielectric slab type. Finally, an FSS superstrate consisting of two-layered FSS screens for dual-band directivity enhancement is introduced as an alternative to an EBG type of dielectric superstrate to reduce its height and facilitate the fabrication process.

Design of a Windmill-Shaped Loop Antenna for Polarization Diversity

A Phase Inverter (PI) is a device that changes the phase of a signal by 180°. It has been applied many microwave components such as rat-race hybrids [1–2], branch line couplers [3], and bandpass filters [4] to reduce size by changing the 3/4 wavelength line to a 1/4 wavelength PI integrated line, or to widen the bandwidth of the components by using the flat phase properties of the PI. A parallel strip PI [1] and a coplanar stripline (CPS) PI [5] have been used to implement these applications. However, a large proportion of microwave components are implemented on a microstrip line and these PIs are generally not applicable to the conventional components. A PI that is integrated on the microstrip hybrid requires a transition between the microstrip line and CPW [2] that requires complicated structures. This paper proposes a simple microstrip PI using a slotted ground without any complicated transitions.

Directivity enhancement of printed antennas using a class of metamaterial superstrates

This paper presents a system that supplies power to a rotating spindles diagnostic sensor using wireless power transfer technology based on electromagnetic coupled resonance and gauges strain experienced by the spindle. In order to transfer power to the spindles sensor through the wireless power system, we attached power receiving coils to the spindle at 120 degree intervals and fixed the power transmitting coils to the ground at 60 degree intervals. We used a resonance frequency of 14.32MHz for wireless power transfer; and an interval of 30cm was maintained between the transmitting and receiving coils. The wireless power transfer system to diagnose a rotating spindle was applied at an industrial site, and demonstrated its applicability.

Microstrip phase inverter using slotted ground

A general theory to analyze an inclined microstrip-slot-line transition with the use of the spectral-domain immittance approach with a finite Fourier transform is proposed with a view to developing an equivalent circuit of the transition. The theory is shown to yield more accurate circuit parameters than other previous theories.

Wireless power transfer system for diagnostic sensor on rotating spindle

The authors propose techniques for controlling the defect frequencies of an electromagnetic bandgap (EBG) superstrate with the objective of enhancing the directivity of a patch antenna at two frequencies.

ANALYSIS OF AN INCLINED MICROSTRIP- SLOT-LINE TRANSITION WITH THE USE OF THE SPECTRAL-DOMAIN IMMITTANCE APPROACH

A composite-antenna-structure covering three bands of global positioning system (1.575u2009GHz), digital multimedia broadcasting (2.62u2009GHz) and direct broadcast satellite (11.7–13.5u2009GHz) was designed and fabricated as a part of the structure surfaces. A new concept of antennas integrated into a composite sandwich structure provides a design that is an electrically and structurally effective multi-functional antenna structure. We designed two types of antennas. One is an annular ring patch antenna for global positioning system and digital multimedia broadcasting. The other is a microstrip patch antenna for direct broadcast satellite. In the design process, the effects of the composites and adhesive films are considered for in the design processes, because structural materials affect the antenna performance. Additionally, the composite-antenna-structure was designed by considering the coupling effect in a strict substrate. The measured results of buckling tests have provided useful information regarding not only the compression behavioral characteristics but also its degradation in electrical performance before and after the test. The experimental results have shown good results for compressive tolerance, though the specimens after compression loading returns to their original shape before failure. Additionally, an acoustic emission system is implemented in the buckling test system to study the inner behavior of the composite-antenna-structure for the reliability of secure mechanical performance. The antenna performance, as measured by the return loss and radiation pattern, remained excellent after the compression tests. These electrical performance results suggest that antennas with composite laminates will function well despite damage.

Techniques for controlling the defect frequencies of electromagnetic bandgap (EBG) superstrates for dual-band directivity enhancement of a patch antenna

The critical point analysis(CA) and impedance matching analysis(IA) are performed and compared for a 4-coil magnetic resonance wireless power transfer system. Because the operating frequency splits at short distance while the efficiency drops drastically at long distance in this system, the optimization technique is needed for either a specific distance or efficiency at the fixed frequency. CA uses the critical point where shows maximum efficiency in the entire range and IA uses the impedance matching technique to achieve maximum efficiency at the specific distance. Comparison result shows that IA is more efficient than CA. Also, it shows one side matching has a tradeoff relationship comparing to both side matching. By using four spiral resonant coils, the analysis was experimentally verified. The measured data agreed well with the calculated data.