Design of Reconfigurable Rim Scattering Reflectarrays for Null Steering in Reflector Antennas

Reflector antennas are susceptible to interference arriving through its sidelobes. The design of a reconfigurable rim scattering reflectarray which can be retrofitted to existing high gain reflector antennas giving the reflector adaptive null steering capabilities is presented thereby giving the reflector interference mitigation capabilities. The conformal reflectarray, placed along the outer rim of the reflector antenna, contains reconfigurable unit cells (RUC). The states of the RUCs allow the reflectarray to place a null in any direction within the first few sidelobes of the reflector pattern. A 1-bit RUC containing two pin diodes with less than 0.44dB loss at the operating frequency is presented. It is found that the dielectric and switch losses do not significantly affect the overall efficiency of the reflector as they are placed only along the outer rim of the reflector which is weakly illuminated. Two reflectarrays are designed. First, a L-band non-reconfigurable reflectarray based on variable patch size for an 18m prime focus fed parabola is presented. A full-wave simulation of this design serves to validate the design approach. Subsequently, a reflectarray design using RUCs is presented. All necessary formulations for complete reproducibility of results are provided in appendices allowing for follow-on work

Advisory Councils For Business Colleges: Composition And Utilization

A major challenge facing business colleges is keeping up with the rapid changes in the business world.  Business advisory councils provide an important link between business colleges and the business world.  This study was conducted to gather data on the composition and utilization of these councils.  The results reveal that there is widespread use of advisory councils by business colleges.  The most commonly discussed issues by advisory councils were those dealing with administrative issues and student concerns while faculty issues were the least discussed.  Advisory councils were also perceived as being most effective in addressing administrative and student-related issues

A Low-Cost L-Band Line Amplifier (Rev. 1)

This report documents the design of a low-cost L-band line amplifier. The description presented here is complete, although the design is a minor revision to a design previous reported in [1]. The change is a reduction in size and a modification to the enclosure to reduce cost. The cost of the new design is about $44 each in small quantities. Although this unit is intended to be used in conjunction with the LNA described in [2], it may also be useful in other applications. Specifically, this unit provides a 9 VDC bias through the RF input jack which can be used to power the LNA described in [2]. The intended configuration is for the line amplifier to be located within a few feet of the LNA, and used to drive a long section (e.g., 100 ft.) of coaxial cable. The completed line amplifier is shown in Figure 1 and its specifications are summarized in Figures 2, 3, and 4. Figure 5 shows a schematic of the line amplifier, with a parts list given in Figure 6. Components L1 and C1 form a bias-tee, setting the DC voltage at the input jack to 9 VDC, thereby powering the connected LNA. This part of the circuit also forms a high-pass filter with cutoff at about 200 MHz, which contibutes to the suppression of strong VHF-band interference, such as FM broadcast radio. MMIC amplifiers U1 and U2 provide gain and also serve to buffer the stripline bandpass filter, FL1. Figure 7 shows the assembled circuit on its printed circuit board (PCB). FL1 is a 3-finger interdigital bandpass filter which was designed through a process of trial-and-error using the “Sonnet ” electromagnetic modeling software by Sonne

Digital Receiver for Microwave Radiometry

A receiver proposed for use in L-band microwave radiometry (for measuring soil moisture and sea salinity) would utilize digital signal processing to suppress interfering signals. Heretofore, radio frequency interference has made it necessary to limit such radiometry to a frequency band about 20 MHz wide, centered at .1,413 MHz. The suppression of interference in the proposed receiver would make it possible to expand the frequency band to a width of 100 MHz, thereby making it possible to obtain greater sensitivity and accuracy in measuring moisture and salinit

GBTrans: A commensal search for radio pulses with the Green Bank twenty metre telescope

We describe GBTrans, a real-time search system designed to find fast radio bursts (FRBs) using the 20-m radio telescope at the Green Bank Observatory. The telescope has been part of the Skynet educational program since 2015. We give details of the observing system and report on the non-detection of FRBs from a total observing time of 503 days. Single pulses from four known pulsars were detected as part of the commensal observing. The system is sensitive enough to detect approximately half of all currently known FRBs and we estimate that our survey probed redshifts out to about 0.3 corresponding to an effective survey volume of around 124,000~Mpc$^3$. Modeling the FRB rate as a function of fluence, $F$, as a power law with $F^{-\alpha}$, we constrain the index $\alpha < 2.5$ at the 90% confidence level. We discuss the implications of this result in the context of constraints from other FRB surveys.Comment: 7 pages, 6 figure

Spectroscopy of Luminous Compact Blue Galaxies in Distant Clusters I. Spectroscopic Data

We used the DEIMOS spectrograph on the Keck II Telescope to obtain spectra of galaxies in the fields of five distant, rich galaxy clusters over the redshift range 0.5 < z < 0.9 in a search for luminous, compact, blue galaxies (LCBGs). Unlike traditional studies of galaxy clusters, we preferentially targeted blue cluster members identified via multi-band photometric pre-selection based on imaging data from the WIYN telescope. Of the 1288 sources that we targeted, we determined secure spectroscopic redshifts for 848 sources, yielding a total success rate of 66%. Our redshift measurements are in good agreement with those previously reported in the literature, except for 11 targets which we believe were previously in error. Within our sample, we confirm the presence of 53 LCBGs in the five galaxy clusters. The clusters all stand out as distinct peaks in the redshift distribution of LCBGs with the average number density of LCBGs ranging from 1.65+-0.25 Mpc^-3 at z=0.55 to 3.13+-0.65 Mpc^-3 at z=0.8. The number density of LCBGs in clustes exceeds the field desnity by a factor of 749+-116 at z=0.55; at z=0.8, the corresponding ratio is E=416+-95. At z=0.55, this enhancement is well above that seen for blue galaxies or the overall cluster population, indicating that LCBGs are preferentially triggered in high-density environments at intermediate redshifts.Comment: 45 pages, 19 figures, accepted to ApJ. For Full resolution figure and data tables, see http://www.salt.ac.za/~crawford/projects/deimos

The Radio Sky at Meter Wavelengths: m-Mode Analysis Imaging with the Owens Valley Long Wavelength Array

A host of new low-frequency radio telescopes seek to measure the 21-cm transition of neutral hydrogen from the early universe. These telescopes have the potential to directly probe star and galaxy formation at redshifts $20 \gtrsim z \gtrsim 7$, but are limited by the dynamic range they can achieve against foreground sources of low-frequency radio emission. Consequently, there is a growing demand for modern, high-fidelity maps of the sky at frequencies below 200 MHz for use in foreground modeling and removal. We describe a new widefield imaging technique for drift-scanning interferometers, Tikhonov-regularized $m$-mode analysis imaging. This technique constructs images of the entire sky in a single synthesis imaging step with exact treatment of widefield effects. We describe how the CLEAN algorithm can be adapted to deconvolve maps generated by $m$-mode analysis imaging. We demonstrate Tikhonov-regularized $m$-mode analysis imaging using the Owens Valley Long Wavelength Array (OVRO-LWA) by generating 8 new maps of the sky north of $\delta=-30^\circ$ with 15 arcmin angular resolution, at frequencies evenly spaced between 36.528 MHz and 73.152 MHz, and $\sim$800 mJy/beam thermal noise. These maps are a 10-fold improvement in angular resolution over existing full-sky maps at comparable frequencies, which have angular resolutions $\ge 2^\circ$. Each map is constructed exclusively from interferometric observations and does not represent the globally averaged sky brightness. Future improvements will incorporate total power radiometry, improved thermal noise, and improved angular resolution -- due to the planned expansion of the OVRO-LWA to 2.6 km baselines. These maps serve as a first step on the path to the use of more sophisticated foreground filters in 21-cm cosmology incorporating the measured angular and frequency structure of all foreground contaminants.Comment: 27 pages, 18 figure