Field operational waveguide noise standard with nominal noise temperature of 78.09 plus/minus 0.12 deg K is calibrated more precisely than before. Calibration technique applies to various disciplines such as microwave radiometry, antenna temperature and loss measurement, and low-noise amplifier performance evaluation

Stelzried, C. T.

English

NASA Technical Reports Server

May 1971	 Brief 71-10139 
NASA TECH BRIEF 
NASA Pasadena OJjke	
-4 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a aubscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the. Tech Brief program may 
be directed to the Technology. Utilization Office, NASA, Code KT, Washington, D. f. 20546. 
Microwave Cryogenic Thermal-Noise Standards 
A field operational, liquid nitrogen cooled, wave- relatively conventional techni 
guide noise standard with a nominal noise tempera- set up for use in the feed ur 
ture of 78.09 ± 0.12 K has been calibrated with parabolic antenna. The ir/ 
Fill 
1: 
Termination 
t	 Mounting Plate 
/(Temperature 
Antenna
	 Control led) 
Zenith 
Direction
	 Stainless Steel 
-	 Waveguide 
Polystyrene 
-	 Insulation 
-	
Copper 
- -
	 Waveguide 
95.25 cm
	
,--. .--	
Liquid Nitrogen 
•	 Tuning Screws 
Termination 
Section 
rad (30°) Dewar Mounting
Plate 
greater precision than had previously been achieved. 
Originally intended for calibrating maser-ampli-
fier units used in large diameter, Cassegrain-feed, 
deep-space communications antennas, the calibration 
technique may also be applied to various dis-
ciplines such as microwave radiometry, antenna tem-
perature and loss measurement, low-noise amplifier 
performance evaluation, and low-level CW signal 
amplitude calibration. 
The noise standard (see fig.), constructed using
ues, is shown as it is 
lit of a large-diameter, 
rad (30°) mounting 
inclination prevents loss of the liquid nitrogen as the 
antenna sweeps from the zenith to the horizon. 
The heavy-wall copper waveguide, the straight sec- 
tion of which is filled with a polystyrene foam 
block, is used to assure a constant waveguide tem- 
perature, independent of liquid nitrogen level. The 
15.24 cm (6 in.) section of thin-wall (0.0626 cm) 
stainless steel waveguide, plated with approximately 
330 m of copper with a 25 jim gold flash, is 
sealed with polystyrene and foamed in place. The 
7r/6 cad (30°) waveguide bend is sealed with a 
10.6 cm (3 in., or approximately 1/2 wavelength) 
section of polystyrene, foamed in place. This foam 
plastic window serves as both a gas and a thermal 
barrier. The complete waveguide section is filled with 
polystyrene foam to eliminate gas convection and 
radiation heating of the termination. 
Voltage standing-wave ratio (VSWR) matching is 
done directly at the termination section with tuning 
screws. This eliminates the standing waves that 
occur in the transmission line if the matching is 
done in the upper waveguide sections. Standing 
waves in a standard operational thermal noise trans- 
mission line invalidate the transmission line calibra- 
tions performed under matched conditions. 
The top mounting plate is heated with thermostat- 
ically controlled power resistors to prevent moisture 
from condensing around the waveguide during opera- 
tion. 
The temperature distribution along the stainless 
steel section is measured with chromel-constantan 
thermocouples referenced to liquid nitrogen. Dissipa- 
tive and transmission line losses of the various 
(continued 0' uncut) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately ownedrights.
https://ntrs.nasa.gov/search.jsp?R=19710000138 2020-03-17T02:24:08+00:00Z
sections of waveguide are measured using both trans-
mission and cavity resonance techniques. The tempera -
ture and loss measurements are used with a computer 
program (see Note 1) to define the nominal noise 
temperature at the output of the steel section. 
Use of the computer is necessary because the as-
sumptions, such as linear temperature and loss dis-
tributions, that must be made in analytical solu-
tions are not precisely satisfied. The calibration 
error that results from such assumptions is greater 
than 0.1 K. The program, employing iterative tech-
niques, uses higher-order terms in the expansion of 
the loss and temperature distribution functions, or an 
exact expression for losses greater than 0.02 dB. 
Notes: 
1. The computer program 15 written in FORTRAN 
IV and is available from COSMIC, Barrow Hall, 
University of Georgia, Athens, Georgia 30601 
(Ref. N PO- 10610).
2. Requests for further information may be directed 
to:
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: B71-10139 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of the invention may be made to: 
Patent Counsel 
Mail Code 1 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Source: C. T. Stel'zried

Caltech /JPL

under contract to

NASA Pasadena Office

(N PO- 1 1424)
. 
Brief 71-10139	 Category 03,09, & 01


Microwave cryogenic thermal-noise standards

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server