Helmken, Henry

For radiowave propagation on earth-space communication links at high frequencies such as Ka-band, the effect of atmospheric gaseous absorption (mainly due to oxygen and water vapor) is the primary cause of attenuation. This thesis examines the applicability of the surface based Crane's model currently employed by the Advanced Communications Technology Satellite (ACTS) propagation experiment for estimation of attenuation due to atmospheric gaseous absorption (AGA), developed for Oklahoma, to sub-tropical climate regions such as Florida. The Microwave Propagation Model is used as a basis of comparison since it uses the direct atmospheric measurements (temperature, relative humidity, and pressure) made at different levels of the atmosphere with radiosonde instrumentation. The AGA was individually examined for oxygen and water vapor. Finally, accuracy of the Crane's model was verified by computing the attenuation results using real acquired data for both models and comparing their results in various ways for several months.

The rapid growth of satellite services using higher frequency bands such as the Ka-band has highlighted need for analyzing effects of different propagation phenomena. Since the wavelength of radiowaves is comparable with the size of rain drops, rain attenuation is the dominant propagation impairment at Ka frequencies. In addition, other impairments such as gaseous absorption, cloud and fog attenuation, tropospheric refractive effects, as well as depolarization become increasingly important with increasing operating frequency. Theoretical background of radiowave propagation principles, rain systems and gases in the atmosphere are presented to insure comprehension of propagation effects on space communication in Ka-band. Models for predicting rain attenuation and other propagation impairments along Earth-satellite path are provided in order to simplify design of communication systems. Propagation phenomena are explained on example of three propagation experiments performed in U.S., Europe and Japan. Whenever possible, mitigation techniques to overcome severe attenuations are introduced.

To observe the effects of satellite transmission on video compression technology designed at FAU's Imaging Systems Lab; an interface was designed to accept data directly from a video encoder or a 16 GByte RAID storage device. The design uses a Xilinx XC4005E field programmable gate array. The interface connects to a high speed enhanced parallel port at the computer backplane. Data stored via the interface on the computer; is transferred at a T1 rate through the ACTS T1-VSAT satellite link. In loop-back mode the data is stored, then evaluated.

The Advanced Communications Technology Satellite propagation experiment was designed by NASA to study the effects of precipitation, primarily rain, on Ka frequency band signals. Two beacon signals, transmitted from the satellite, provide attenuation data that is recorded by a propagation terminal located in Tampa, Florida. The received beacon data contains a DC bias and diurnal effects and is therefore uncalibrated. Radiometers, centered at each beacon carrier frequency, are used to set the 0 dB reference level for the beacon data, using constants determined through radiometer calibration techniques. The details of this process are examined using actual propagation data.

For certain wavelength size objects, the frequency range between 100 MHz and 1000 MHz spans a transition region when using low frequency electromagnetic scattering codes based on Method of Moments (MoM) to high frequency codes based on Physical Theory of Diffraction (PTD) and ray tracing techniques. As the wavelength size of the object increased, MoM codes can require prohibitively long computational times and hence the more approximate high frequency codes become more attractive. The Ohio State Material Wire code (MATWRS) was selected as a representative MoM code for characterizing the transition region. XPATCH was selected as a representative high frequency code with ACAD used as the general modeling program. To evaluate these codes, a comparison of Radar Cross Section (RCS) predictions for simple PEC canonical shapes was made. Comparisons were made to both measured data where available and predictions generated by the McDonnell Douglas Body of Revolution (BOR) code.

A test system was designed to determine the performance a QPSK satellite burst modem when using the Ka band link of the Advanced Communications Technology Satellite. Interface circuitry, largely based on the 22V10 programmable logic device, was designed to allow the modem to be controlled by a personal computer. Communication between the interface and the computer was accomplished through the computer's parallel port. TDMA frame timing was automatically controlled by the interface. A C language program provided operator control of the interface itself. Tests using this system showed that a severe night-time fading problem is experienced at the FAU receiver site. Very low error rates were recorded by this system in a loop-back transmission at the NASA satellite control terminal.

This thesis is concerned with adapting a sequential code that calculates the Radar Cross Section (RCS) of an open-ended rectangular waveguide cavity to a massively parallel computational platform. The primary motivation for doing this is to obtain wideband data over a large range of incident angles in order to generate a two-dimensional radar cross section image. Images generated from measured and computed data will be compared to evaluate program performance. The computer used in this implementation is a MasPar MP-1 single instruction, multiple data massively parallel computer consisting of 4,096 processors arranged in a two-dimensional mesh. The algorithm uses the mode matching method of analysis to match fields over the cavity aperture to obtain an expression for the scattered far field.

Rain attenuation is the most dominant cause of signal degradation in satellite links operating at Ka-band. A review of rain measurements and effects of rain attenuation on satellite links will be discussed and will be followed by the latest developments in prediction and modeling of rain attenuation. Then an adaptive rain fade countermeasure based on the effective utilization of the channel capacity will be presented. In order to determine the outage rates both in terms of channel capacity and bit error rate (BER), Manning's rain attenuation prediction model, based on the rain history of the transmitting and receiving stations, will be employed. Finally, a comprehensive statistical model for Land-Mobile Satellite Systems (LMSS) in the presence of rain attenuation will be proposed.

It has been proposed that the use of a small number of ground radials elevated above the surface of the earth can yield similar or actually better radiated performance than a larger number (typically 120) of buried ground radials in the case of a monopole element used in the standard AM broadcast band. This proposal is based on the results of numerous computer modelling. The author knows of no A-B field tests compared to the computed data. A case study is performed at 1 MHz (the center of the standard AM broadcast band) using the NEC-81 computer program modelling both the elevated and buried ground radial scenarios and comparing the findings to the identical measured data. Tower impedances, currents in both the tower legs and along the elevated radials, and radiated fields along one radial and in between two radials at 1 km are presented.

In this research project the objective is to realize a software - hardware design implementation of a real time digital signal processing (DSP) radiometer - receiver for atmospheric noise temperature detection using the digital cross correlation technique. Atmospheric noise in the band of 20-30 GHz band is down-converted to 10.7
MHz IF and 3 MHz bandwidth in the form of statistical additive white gaussian noise
which is used as the received signal by a digital signal processing broadband microwave
radiometer based on the digital cross correlation technique.
Living in a technological era, which is characterized as the era of data
transmission and reception for RF-wireless communication systems, the theory of RF
digital signal processing detection has applied to radar, ultrasound, and digital
communications. Due to the need of high speed of data detection, much effort has gone into the
design and development of sophisticated equipment to obtain such DSP detectors.
Detection can also apply in seismic and big earthquake measurements by using
geophones, nuclear testing, sonar and acoustic localizations, and even for oil excavations.
Based on a statistical model and proposed design implementation, a basic DSP
atmospheric noise temperature radiometer system is introduced and developed. The
realization of the DSP Radiometer examines the noise characteristics (parameters) and
their corresponding parameter values at the received input at the Antenna. It is essential
to introduce the fundamental and statistical properties of the additive white gaussian
noise, as well as the key-parameters which are used for the development of this real time
design implementation. A design implementation of the proposed DSP atmospheric noise
radiometer is discussed and developed via a statistical analysis. The statistical analysis
utilizes the standard deviation, intermediate frequency, bandwidth, number of samples,
and the temperature of the noise received signal at the antenna. Measurements and real
time simulations in order to evaluate the noise temperature’s detectability in terms of
system’s accuracy and performance of the noise random variable are also presented in
this research work. The advantage of the digital cross correlation technique is examined
and investigated.