| Applications:
Millimeter wave
reflectometers are used to measure reflection characteristics of various objects,
plasma, materials and scenes to obtain some of their specific features or properties at
millimeter wavelengths. Reflectometers are somewhat similar to radars and interferometers
in their architecture and function, but are often treated as an independent class of
instruments or equipment. Millimeter wave reflectometers find applications in many diverse
fields, such as:
|
- Plasma diagnostics
- Dielectric and other material properties measurement
- Imaging
- Process Monitoring/Control
- Radar Signature Characterization and Data collection
|
Reflectometers are used in
specific applications as diverse as plasma density measurement, determination of thickness
of ash and carbon build-up and modeling of aircraft and military vehicles.
Description:
Many possible configurations and
architectures are used to realize millimeter wave reflectometers for specific
applications. A generic reflectometer arrangement is shown in Figure 1. The equipment or
instrument consists of a millimeter wave transmitter as the illumination source for the
object or scene under study. Suitable antenna(s) and optical arrangements are employed to
optimally illuminate the scene or item being characterized. A quasi-optical realization of
millimeter wave and submillimeter wave reflectometers is also practical for
characterization of specific materials or objects. One or more receivers may be used to
collect the reflected signal from the object/scene using appropriate optics or antenna
configuration. The angular location and/or physical distance to the scene/object can be
varied, if desired. Depending on the type of reflectometer and the purpose of the
measurement, the local oscillator for the receiver is either derived from the same master
oscillator that produces the transmitter/illumination signal or created independently. The
received signal may be obtained either as a scalar (amplitude of the return signal) or
vector (amplitude and phase using I-Q detector/mixers).
Figure 1
Most typical applications use a
fixed frequency CW signal for illumination. However, a multi-frequency or swept signal is
also employed in some cases. Dual frequency reflectometry is useful in obtaining material
properties and related information. Generally, for most applications and measurement
scenarios, the transmitter is a stable (but not phase-locked) source.
Operation and Typical Performance Characteristics:
Typical Examples and Case Histories
Table and Figure
| Frequency |
Application |
Subsystem
description |
| 35, 60 GHz, 140
GHz |
Plasma diagnostics
and characterization. Monitoring instrument for plasma etching process |
Real-time
measurement of reflection properties of plasma using a stable phase-amplitude measurement
subsystem. |
| 70 GHz (any
suitable millimeter wave frequency) |
Liquid
characterization by measuring its loss and dielectric properties |
Characterization
of loss in liquids at millimeter wavelengths. |
| 47 and 94 GHz |
Moisture content
measurement in paper and other materials |
Measurement of
transmission and reflection coefficient at two frequencies to determine moisture content
and other properties |
| 94, 140 GHz |
Measurement of
deposits of carbon and ashes in chimneys |
Measures
reflection from deposits. |
QuinStar Components and Products Used
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