Lecture videos to supplement electromagnetic classes at Cal Poly San Luis Obispo

Electromagnetics and Transmission Lines is a fundamental, yet difficult subject in the Electrical Engineering (EE) field. To help improve information retention, a series of lecture videos was created to supplement traditional lectures, to facilitate in-class discussions, and to improve students’ proficiency and interest in electromagnetics. Engineering electromagnetics classes at California Polytechnic State University, San Luis Obispo cover fundamentals to understand and analyze cell phone communications, radar systems (air traffic control, law enforcement), and biomedical imaging (MRI). However, this subject also requires considerable mathematics preparation in vector calculus, differential equations, linear algebra, and background in both physics and EE. Lecture videos were created on the Camtasia software to produce MP4 audio-visual files. All videos include a topic outline, stationary and animated visual displays of lecture topic applications, and a detailed discussion using outlines and handwritten notes. Example calculations and real-world applications, Smith Chart graphical analysis, and Matlab computations and visual animations (standing and traveling waves, dynamic vector field and scalar contour diagrams) augment theoretical discussions and help visualize course concepts. Real-world applications including the Large Hadron Collider (CERN), RF test equipment (network analyzers), cell phone tower antennas, and radar imaging systems are introduced in the videos and related to course topics. A total of 36 videos were recorded for EE 335 (junior-level electromagnetics); average video length is 20 to 25 minutes for each 50 minute lecture. All lecture videos were stored online (dropbox.com) and made available one week prior to each class session. A student survey was conducted to assess perceived video effectiveness, to compare to traditional lectures, and to estimate video usage (how often watched, how many hours per week). Questions also include overall suggestions for video improvement, favorite (and not so favorite) parts of the class, and overall impressions. Most students appeared to value the new videos: 55% agreed with the statement “the lecture videos helped me learn course concepts.” Video length (20 – 25 minute average) was between too long (43%) and just right (29%). The most common negative comment mentioned the additional time required to view the videos over a traditional lecture class. Future efforts toward a flipped (inverted) classroom format include the development of topic videos and post-video quizzes to encourage pre-lecture viewing, as suggested in [1]. Video production improvements including minimized length and enhanced information organization will be applied to future lecture videos. Practical lab projects [2] will also be explored and added as another method of enhancing student interest in electromagnetics. Finally, information retention between traditional and flipped classroom formats will be compared to determine the relative effectiveness of both approaches

Multi-Technique Broadband Microstrip Patch Antenna Design

Microstrip patch antennas offer low profile and small footprint advantages, but limited operating bandwidth. Substantial research focuses on broadband techniques. This paper presents the design, simulation, fabrication, and characterization of a 30% bandwidth microstrip patch antenna that incorporates multiple broadband techniques while minimizing footprint area. Methods include patch shape, dielectric thickness, and coupling slot optimization, with capacitively-coupled L-probe feeds. The final design incorporates an electrically thick dielectric and circular-E patch geometry. Microstrip L-probe feed and coupling slot dimensions were optimized via HFSS simulations. The final design was fabricated, and then tested in an anechoic chamber. The new design has measured and simulated impedance bandwidths (VSW

Aperture Coupled Patch Antenna Design Methods

Microstrip patch antennas have been used extensively in applications requiring low-profile, mounting structure conforming, and low-cost wireless communications. Feed methods (antenna-transmission line interface) are critical for optimum performance. The aperture coupled technique exhibits reduced transmission line radiation and enhanced antenna radiation and co- to cross-pol performance relative to microstrip and probe fed configurations. Researchers have focused on analytical methods and design improvements without identifying parametric tradeoffs or design methods. Hence, this paper presents theoretically and parametrically identified critical antenna dimensions and performance effects, and a design procedure to convert desired performance requirements into operational prototypes

UHF RFID Antenna impedance matching techniques

The modified T-match network uses planar inductive strips for conjugate matching Radio Frequency Identification (RFID) Integrated Circuits (RFICs). Narrow and broadband matching techniques and electromagnetic simulations are applied in [1] for specific designs. This paper extends these efforts through antenna element parameterization and design trade-off analysis. Narrow and broadband designs are fabricated; antenna input impedance and tag range tests confirm predictions

Organic-Based Microwave Frequency Absorbers Using Corn Stover

Commercial antenna test chambers (anechoic) currently use polyurethane foam absorbers on chamber interiors to eliminate undesired radio-frequency (RF) reflections. While effectively absorbing microwave signals, polyurethane material particulates over time adding contaminants to clean rooms and reducing absorber lifetime. These absorbers also release toxic gas when operating under high temperatures and pose a health risk to direct-contact personnel. This paper presents reflectivity analysis and performance of alternative organic-based (corn stover) microwave frequency absorbers for use in anechoic chambers. These absorbers are composed of renewable materials and eliminate the toxic gas release problem for polyurethane materials under high power test conditions. Preliminary results show that the organic absorbers perform at levels comparable to commercially-available absorber panels

Absorber Foam Characterization for Predicting Overall Anechoic Chamber Performance

A new rectangular anechoic chamber (20’L x 10’W x 9’7”H) has been established at California Polytechnic State University (Cal Poly) through donations and financial support from industry and Cal Poly departments and programs. The chamber was designed and constructed by three graduate students as part of their thesis studies to explore and further their understanding of chamber design and antenna measurements. The chamber project has included RF absorber characterization, overall chamber performance assessment, and software development for the coordination of a positioner with a vector network analyzer. This paper presents absorber characterization as a function of incidence angle and orientation to enable an overall chamber performance analysis. Test data at low incidence angles (\u3c 30o) are compared to manufacturer performance curves at normal incidence. The mean response of the measured data indicates a correlation with manufacturer curves. Through ray tracing analysis, the ripple encountered in the test data is used to identify two effective reflection planes indicative of the foam geometry. The measured data are subsequently used to predict overall anechoic chamber performance to within 1dB for a majority of the actual scan data. Details of this analysis and comparisons to actual chamber performance are presented in a companion paper

Conducted Emissions Testing for Electromagnetic Compatibility

Operating frequencies in the gigahertz range is creating an increased need for electromagnetic compatibility (EMC) testing. In the United States, FCC regulations require conformance to radiated and conducted emissions specifications. An EMC laboratory was established at Cal Poly San Luis Obispo (screen room, test instrumentation, and software) and an experiment was developed to explore conducted emissions effects. This paper will describe the test configuration, explain the calibration procedure needed to acquire accurate measurements, and illustrate measurement techniques applied to two example systems. In addition, the data collection process is illustrated through software donated by CKC Laboratories (EMC specialists). To verify the functionality of the laboratory and to assess measurement accuracy, two 12V/15W switching power supplies are characterized for conducted emissions performance; one as supplied by the vendor (KGCOMP) and a second unit with the EMC filters removed. The noise spectrum for both units are plotted against frequency and compared to FCC specifications. The unaltered unit is shown to be in compliance, thus verifying the accuracy of the test procedure and instrumentation

A Laboratory Course on Antenna Measurement

This paper presents background information and experiment procedures for an antenna measurement laboratory course to be held in a new anechoic chamber at California Polytechnic State University. The lab consists of five experiments and one design project intended to give students practical experience with antenna measurement techniques and to creatively apply analytical skills to design, construct, and test antennas that meet given specifications. The experiments reinforce antenna principles including E-field polarization, antenna gain, radiation patterns, image theory, and frequency response. In addition to the experiment procedures, this paper presents the design and characterization of Helical Beam (RHCP and LHCP) and Discone antennas, a Dipole Antenna near Planar and Corner Reflectors, and Dipoles with and without a balun. These antennas demonstrate polarization, antenna gain, broadband matching characteristics, image theory, and feedline radiation due to unbalanced currents. Measured radiation patterns, gain, and axial ratio (helical only) show excellent correlation to theoretical predictions