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Spie Press Book

Passive Millimeter-Wave Radiometry
Author(s): Michael A. Gritz
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Book Description

The millimeter-wave (mmW) portion of the spectrum presents unique technical challenges due to low-thermal-background emissions. The literature often uses simplified system temperature models or basic radiometric calculations, resulting in costly design errors that compound the difficulty of working in the mmW. This Spotlight provides readers with proper derivations of basic radiometric equations and an end-to-end system model for radiometers that use an antenna as the detection element.

Book Details

Date Published: 3 September 2021
Pages: 54
Volume: SL60

Table of Contents
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Chapter One: The Basics
1.1 Diffraction
1.2 Antenna Concepts
1.3 Introduction to Antenna Coupled Detectors

Chapter Two: Basic Radiometry

2.1 Spectral Radiance
     2.1.1 MATLAB lab spectral radiance example
2.2 Integrated Radiance (L)
     2.2.1 MATLAB lab integrated radiance example
2.3 Flux Received
2.4 Approximations and Comparisons
     2.4.1 MATLAB lab power received (PR) example

Chapter Three: System Noise

3.1 mmW Detectors
3.2 Noise Sources
     3.2.1 Thermal noise
     3.2.2 Shot noise
     3.2.3 Flicker or 1/f noise
     3.2.4 Analog-to-Digital conversion noise
     3.2.5 Noise figure or high-frequency noise
     3.2.6 Analog electronics or low-frequency noise
     3.2.7 Total noise analysis

Chapter Four: mmW Receiver System Design

4.1 Figure of Merit-Receiver Sensitivity
4.2 Receiver Types
4.3 Modern Dicke Switch Receiver
4.4 MDSR End-to-End System Model
     4.4.1 PR module
     4.4.2 Front-end receiver module
     4.4.3 Detector responsivity
     4.4.4 Back-end electronics module

Chapter Five: Antenna-Coupled Staring Arrays

5.1 Silicon-based Receivers
5.2 Antenna – Coupled Focal Plane Staring Arrays



This Spotlight is focused on radiometers operating in the millimeter-wave (mmW) portion of the electromagnetic (EM) spectrum. A radiometer is a device for measuring the radiant flux or power of certain portions of the EM spectrum. Often these flux measurements are converted into a temperature to be used for remote sensing or atmospheric modeling. However, a radiometer is also used to generate photographic images.

EM radiation is a wave of alternating electric and magnetic fields. The propagation of light in a medium is defined by the frequency (ν) in which the wave passes a point in one second. The distance from the peak of one wave to the peak of the next is defined by the wavelength (λ). These two parameters are related by (ν = c∕λ), where c is the speed of light.

EM radiation is generally divided into different spectra, as shown in Table 1. Specific bands of the spectrum are used depending on the application or data requirements. In the mmW spectrum, a meteorological satellite, such as the Advanced Technology Microwave Sounder (ATMS), measures the brightness temperature and moisture levels of the atmosphere. ATMS is a multiple channel narrow band system operating from 30 to 200 GHz. These channels are identified by climate scientists to collect essential data for weather tracking, including hurricanes. Another application is imaging through clothing and other obscurants such as fog, clouds, smoke, sand, and dust. Imaging through clothing in real time provides airport screeners the ability to detect contraband such as concealed weapons or other illegal contraband from stand-off distances, which not only eliminates the need for imaging portals requiring a second image capture time but also improves throughput. Security system imaging systems require an operational capability of functioning from a range of greater than 10 meters and at video rates (30 Hz). Therefore, considerable interest exists in developing low-cost wideband passive millimeter-wave imaging (PMMWI) systems operating at video frame rates with no scanning mirrors. During this development process of such a passive mmW imaging (PWWMI) system, it was found that the traditional narrow band design equations used simplified radiometric equations to determine the collected power, which often resulted in costly design errors.

This Spotlight is broken down into five chapters. Chapter 1 covers the basic concepts for systems engineers working on a mmW radiometer. Chapter 2 develops the basic radiometry equations with matrix laboratory (MATLAB) examples. Chapter 3 will define the noise sources and provide examples on determining the system noise. Chapter 4 will develop an end-to-end system model for a modern mmW receiver. Chapter 5 will cover antenna-coupled detectors used to form staring arrays (two-dimensional arrays).

Michael A. Gritz
August 2021

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