Timothy Brockett

A novel portable bipolar near-field measurement system for millimeter-wave antennas: construction, development, and verification

As new antenna designs require higher frequencies and smaller sizes, traditional large-scale antenna measurement systems become ill-suited for such measurements. External mixing, room-sized chambers, and expensive test equipment add large costs and burdens to antenna measurement systems. A smaller and more cost-effective system is presented in this paper. Using the bipolar planar scanning technique developed at UCLA, a portable millimeter-wave antenna measurement system has recently been constructed. The system was designed to fit on the end of a standard optical table, and enjoys the spacesaving and accuracy inherent to the bipolar planar configuration. Simple construction of the chamber allows for relatively easy assembly and disassembly, and allows movement of the system from one table to another, if needed. Antennas of diameters up to 24 in can be accommodated, and scan planes of up to a diameter of 60 in can be measured. Millimeter-wave frequencies from around 30 GHz to 67 GHz can be measured, with potential extension to higher frequencies. Planar nearfield-to-far-field techniques are used to construct the antennas far-field patterns from the measured near field. In particular, the post processing follows the OSI/EFT method for pattern reconstruction and diagnostics. The design of the scanner configuration allows the incorporation of the phase-retrieval techniques developed for the bipolar configuration. These phaseless measurements allow the use of scalar millimeter-wave test equipment, with much lower cost than comparable vector test equipment.

Subarray Design Diagnostics for the Suppression of Undesirable Grating Lobes

This paper investigates various subarray pattern distortions that can cause the appearance of grating lobes with the aim to provide an insightful and valuable first-order diagnostic tool for antenna array designers. In typical subarray configurations, the emergence of undesirable grating lobes is a possibility due to distortions in the subarray array factor which can be caused by feeding errors, mutual coupling between elements and/or feed lines, or other discrepancies. This paper will focus on systematic errors that can arise in subarray designs that feature common element excitation schemes. Distortions will be categorized by amplitude and phase errors separately, demonstrating their distinct manifestations in each excitation scheme. Recognition of these manifestations can lead to better subarray designs and save significant time in the development of large array antennas. The concepts introduced here will be supported by analytical array factor calculations for 1 × N linear subarrays, full-wave simulations of a 1 × 4 subarray and 1 × 16 array, and representative measurements of two 1 × 16 arrays at Ku-band.

Investigation of semiconductor nanostructures photovoltaic for next generation solar cells

The purpose of this paper is to investigate the electromagnetic performance of various potential semiconductor nanostructures photovoltaic for future solar cells. GaAs is used as the semiconductor for this particular study. Nanostructures such as nanocones, nanopillars, and nanoprisms are compared systematically for their reflection and absorbance properties. The presence of nanostructures reduces the optical reflection and increases absorption as compared to conventional flat cell geometries. Initial studies show that nanocones and nanoprisms have the very good electromagnetic performance in terms of reflection and absorption over the solar spectrum. It is also shown that the nanocone arrays have robust performance for different polarizations and angles of incidence making them an attractive solution for solar cell designs.

Electromagnetic Characterization of High Absorption Sub-Wavelength Optical Nanostructure Photovoltaics for Solar Energy Harvesting

This paper presents a detailed numerical electromagnetic characterization of GaAs photovoltaic (PV) nanopillar array solar cells recently developed for solar energy harvesting. Through electromagnetic theory, full-wave simulations, and an optical measurement, a deeper understanding of the electromagnetic operation of these nanostructure arrays is achieved by revealing the mechanisms that allow for its inherent improvement of optical absorption over conventional PV solar cells. Initial investigations include incorporating and verifying material optical properties through measurements of bulk GaAs samples, simulating the effects of nanopillar geometry and configuration, and an analysis of the optical absorption mechanism of the nanopillar arrays through the graphical visualization of the electric fields in the vicinity of the nanopillars. These investigations will offer critical insights into the effects of pillar dimensions and configuration that can significantly increase optical solar energy absorption approximately 1.5 times that of conventional solar cells spanning the entire visible spectrum and for angles of incidence up to 60

The Spillover Effect on the Directivity Calculation of Reflector Antennas in Planar Near-field Measurements [Measurements Corner]

^{\circ}

GaAs nano-pillars for solar power absorption: Electromagnetic characterization

. Furthermore, comparisons between nanopillar arrays with and without substrates will demonstrate the mechanism that drives the efficient optical absorption. In addition, the importance of the nanopillar structure (i.e., dimensions) and reflecting substrate in providing energy coupling and improving the air-to-array interface will be discussed.

Sub-array design diagnostics for the development of large uniform arrays

The knowledge of an antennas directivity (or gain) performance is sometimes the most important information in designing a communication link. Depending on the application, one might be interested in a very accurate measure of the directivity value. This paper focuses on the accurate estimation of antenna directivity in planar near-field measurements. Planar near-field chambers are the most natural systems for the measurement of highly directive antennas such as reflectors, the weight and bulkiness of which may prevent one from using any other system. The main drawback of these systems is that only the forward-directed wave emanating from the antenna will be measured. The spillover energy cannot be captured, and therefore the value calculated for the directivity will be higher than the actual value. This paper develops a systematic approach for the accurate measurement of the spillover losses to compensate for the inaccuracies of the directivity calculation.

On the importance of sub-array design in the suppression of undesirable grating lobes

Semiconductor nano-pillars have been a recent development in solar cell technology [1–2]. Nano-pillar structures were devised with the potential to overcome the limitations of conventional flat cells. Specifically, the nano-pillar increases the total surface area of the cell without changing the footprint, has a shorter diffusion length, and less carrier recombination. The first step in the development of an efficient solar cell is to maximize the amount of absorbed energy and minimize the reflection off the cell (Fig. 1). Thus, the electromagnetic performance of the cell is an essential component in developing these structures for efficient solar power applications.

Superquadric nanostructures for enhanced absorption in solar cells

The use of sub-arrays has been a popular approach in the design of large array antennas. Using sub-arrays simplifies the array design by allowing the designer to concentrate on the smaller sub-array and repeating it throughout the rest of the array. Anomalous grating lobes have been shown to appear in large uniform arrays caused by systematic errors in the design of sub-array. Thus, it is important for the sub-array designer to be able to diagnose errors in the sub-array design before incorporating it into the larger array. This paper will categorize and demonstrate specific sub-array pattern distortions that can cause grating lobes to appear in uniform arrays. In addition, a design example will present how recognition of the aforementioned distortions can be used to diagnose and prevent the appearance of grating lobes. This will be done by showing the design process of a 1×16 linear array design that uses four 1×4 sub-arrays. Its design progress will include analytical, full-wave simulation, and measurement parts.

A novel approach for testing antennas with internal sources: Phaseless near-field measurements

A useful strategy in simplifying the development of large antenna arrays is to use sub-arrays as a building-block. When employing this strategy, care must be taken in designing and implementing the sub-arrays because they can be considered array elements that are more than one wavelength apart resulting in array factor grating lobes. In ideal situations, the grating lobes that one would expect are cancelled out by the individual sub-array pattern nulls. However, if care is not taken in the design of the sub-array, errors in that design can distort the sub-array pattern and cause it to no longer properly cancel the grating lobes and ultimately degrade the overall array pattern. Thus, it is essential to understand the mechanism that can cause unwanted distortion in the sub-array pattern. Here, we investigate a number of situations that can cause unwanted distortions in the sub-array pattern and their effects on the final overall pattern. We will focus on 1×4 sub-arrays, which are one of the more common sub-array designs that are implemented in large arrays. Analysis of the array factor and simple simulations will demonstrate the possible mechanisms of these distortions and illustrate the importance of the sub-array design.