LAB EXPERIMENT: 7 EE-3407 Remote Sensing ELECTROMAGNETICS

Department of Electrical Engineering Arlington, Texas
Objective
The purpose of this lab will familiarize us with a few basic ideas in the application of electromagnetics to remote sensing. Remote sensing refer to many types of noncontact applications, from sensing of the environment from space and remote sensing of the cosmos from Earth, to noncontact sensing of physiological parameters and remote infrared measurements to assess temperature in industrial settings.
Equipment and Components Used
Vector Network Analyzer (VNA) (Brand:HP, Model: 8753D)
Measuring tape Large Object of reflection wave Dual polarization antennas Theory
Remote sensing also can be characterized as passive if the instrument consists only of a receiver, or active if both receiver and transmitter (illuminator) are included in the instrument. Recall that all objects emit energy due to thermal excitation of molecules and atoms. For objects characterized as
“blackbodies” emission is predicted according to Planck’s Law, i.e.,, where E is energy per unit wavelength, k is Boltzmann’s constant, h is Planck’s constant, and T is absolute temperature (oK). Objects other than blackbodies, referred as “gray bodies,” demonstrate similar temperature dependence but with lower emission strength. Note that the peak emission at body temperature occurs in the thermal infrared range, i.e., at a wavelength of approximately 10 m. Passive remote sensing instruments, also oftentimes referred to as radiometers, may operate in the microwave range up through the visible light range.
For this lab emphasis is on active remote sensing systems, in particular on radar and related proximity/field disturbance techniques. The Vector Network Analyzer (VNA) will once again be used, but this time as a probing transmitter and receiver that assesses interaction of electromagnetic waves with objects in the environment. Two modes of instrument operation are used in this lab; the instrument is operated in a step-frequency mode in which the instrument sequentially collects phase and amplitude data over a bandwidth of frequencies, and a single frequency mode of operation is used in which phase variations over time correspond to object motion in the environment. In the former the amplitude and phase data collected over frequency is converted to a synthesized time domain mode, via use of an inverse Fourier Transform; this operating mode of the instrument is often referred to as the Time domain Reflectivity (TDR) mode. For our case TDR will be applied through 1 and 2 antenna setups so as to emulate radar. Note that when applied through cables the TDR mode is useful for locating damage or breakage in cables.
The basic ideas of the VNA in TDR mode can be compared to the operating principle of simple pulse radar. In this case distance to the object (also known as the target) is determined based on the total time delay of the pulse from the radar transmitter to the object and back to the radar receiver. Since the pulse propagates through air, which is electrically equivalent to free space at microwave frequencies, the time delay associated with an object at distance R is t=2R/c, where c is the speed of light. The ability of the radar to discriminate between two closely spaced objects depends on the width of the pulses that are transmitted. The radar can only discriminate between two objects if the return (at the receiver) from the closer object is completed before the return from the farther object begins. That is, for a pulse of width the relationship with inter object distance is =2r/c, where r is the inter object spacing, implying that to ensure that the objects can be identified as separate objects.
The basic instrument setup for lab 6 is