[Go to TOC]
MICROWAVE MEASUREMENTS
Measurement Procedures
Calculate your estimated power losses before attempting to perform a
measurement. The ideal input to a measurement device is in the 0 to 10 dBm (1 to 10 mW) range.
Linearity
Check
To verify that a spectrum measurement is accurate and signals are not due to mixing inside the
receiver, a linearity check should be performed, i.e. externally insert a 10 dB attenuator  if measurements are
in the linear region of the receiver, all measurements will decrease by 10 dB. If the measurements decrease by
less than 10 dB , the receiver is saturated. If the measurements disappear, you are at the noise floor.
HalfPower or 3 dB Measurement Point
To verify the half power point of a pulse width measurement on an oscilloscope, externally insert a 3 dB
attenuator in the measurement line, and the level that the peak power decreases to is the 3 dB measurement point
(Note: you cannot just divide the peak voltage by onehalf on the vertical scale of the oscilloscope).
VSWR
Effect on Measurement
Try to measure VSWR (or reflection coefficient) at the antenna terminals. Measuring VSWR of an antenna through
it's transmission line can result in errors. Transmission lines should be measured for insertion loss not VSWR.
High Power Pulsed Transmitter Measurements
When making power measurements on a high power pulsed
transmitter using a typical 40 dB directional coupler, an additional attenuator may be required in the power meter
takeoff line, or the power sensor may be burnt out. For example, assume we have a 1 megawatt transmitter, with PRF
= 430 pps, and PW = 13 Fs. Further assume we use a 40 dB directional coupler to tap off for the power
measurements. The power at the tap would be:
10 log(Pp)  10 log(DC)  Coupler reduction = 10 log(109mW)
 10 log(13x106)(430)  40 dB = 90 dBm  22.5 dB  40 dB = 27.5 dBm (too high for a power meter)
Adding
a 20 dB static attenuator to the power meter input would give us a value of 7.5 dBm or 5.6 mW, a good level for
the power meter.
High Power Measurements With Small Devices
When testing in the presence of a high
power radar, it is normally necessary to measure the actual field intensity. The technique shown in Figure 4, in
Section 67, may not be practical if the measurement device must be small. An alternate approach is the use of a
rectangular waveguide below its cutoff frequency. In this manner, the "antenna" waveguide provides sufficient
attenuation to the frequency being measured so it can be coupled directly to the measurement device or further
attenuated by a low power attenuator. The attenuation of the waveguide must be accurately measured since
attenuation varies significantly with frequency.
Table of Contents for Electronics Warfare and Radar Engineering Handbook
Introduction 
Abbreviations  Decibel  Duty
Cycle  Doppler Shift  Radar Horizon / Line
of Sight  Propagation Time / Resolution  Modulation
 Transforms / Wavelets  Antenna Introduction
/ Basics  Polarization  Radiation Patterns 
Frequency / Phase Effects of Antennas 
Antenna Near Field  Radiation Hazards 
Power Density  OneWay Radar Equation / RF Propagation
 TwoWay Radar Equation (Monostatic) 
Alternate TwoWay Radar Equation 
TwoWay Radar Equation (Bistatic) 
Jamming to Signal (J/S) Ratio  Constant Power [Saturated] Jamming
 Support Jamming  Radar Cross Section (RCS) 
Emission Control (EMCON)  RF Atmospheric
Absorption / Ducting  Receiver Sensitivity / Noise 
Receiver Types and Characteristics 
General Radar Display Types 
IFF  Identification  Friend or Foe  Receiver
Tests  Signal Sorting Methods and Direction Finding 
Voltage Standing Wave Ratio (VSWR) / Reflection Coefficient / Return
Loss / Mismatch Loss  Microwave Coaxial Connectors 
Power Dividers/Combiner and Directional Couplers 
Attenuators / Filters / DC Blocks 
Terminations / Dummy Loads  Circulators
and Diplexers  Mixers and Frequency Discriminators 
Detectors  Microwave Measurements 
Microwave Waveguides and Coaxial Cable 
ElectroOptics  Laser Safety 
Mach Number and Airspeed vs. Altitude Mach Number 
EMP/ Aircraft Dimensions  Data Busses  RS232 Interface
 RS422 Balanced Voltage Interface  RS485 Interface 
IEEE488 Interface Bus (HPIB/GPIB)  MILSTD1553 &
1773 Data Bus  This HTML version may be printed but not reproduced on websites.
