Radio frequency attenuator, having negligible insertion loss at minimum attenuation, can be used for making precise antenna gain measurements. It is small in size compared to a rotary-vane attenuator

Dickinson, R. M.

Hardy, J. C.

English

NASA Technical Reports Server

October 1969	 Brief 69-10502 
NASA TECH BRIEF 
.
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Rotary Antenna Attenuator 
0 Indicator Dielectric Cylinder 
Package	 Resistive Termination 
Gears	 jj Coaxial Connector 
Slotted Balun 
6)	 Antenna B	
Antenna A Fixed Antenna 
Slotted Balun 
RF Rotary Joint 
Connector 
This innovation is an accurate radio frequency 
attenuator having negligible insertion loss at minimum 
attenuation. It can be used for making precise antenna 
gain measurements. 
The apparatus consists of an input dipole antenna 
electrically coupled to an output dipole antenna within 
a circular waveguide. The antennas are rotatable with 
respect to each other. The attenuation is proportional 
to the angle of rotation 20 log 10 sec e; thus the 
electrical drive/readout can be calibrated in dB atten-
uation. The advantages of this configuration are: (I) 
negligible insertion loss at minimum attenuation com-
pared to a conventional piston waveguide-beyond-
cutoff attenuators (which has 20 db minimum); and 
(2) small size compared to a rotary-vane attenuator. 
The innovation is currently in use as a transfer 
standard in making precise antenna gain measure-
ments. An S-band version (2297 MHz) has a circular 
wave guide 4" dia x 20" long. 
The advantages of the innovation are: (1) greatly 
reduced size relative to competitive devices; (2)
low initial insertion loss; (3) low variation of 
attenuation with angle: 20 log 10 sec 0 vs 20 log10 
sec 2 0 variation for rotary-vane attenuators; (4) input 
and output dipole antennas mounted coaxially in a 
circular waveguide section and rotatable relative to 
each other; and (5) calibrated drive/readouts 
measuring the angle between the planes of the two 
dipoles accurately, whereby the attenuation may be 
read directly. 
Note the figure. An RF signal injected in the RF 
rotary joint, which allows the angular rotation of 
antenna B, will be attenuated by polarization mis-
match upon excitation through the fixed antenna. This 
attenuation varies with the angular difference between 
the planes of the two antennas in accordance with the 
relation 20 log 10 sec 0. 
The gears, synchro package and indicator allow 
the precise reading of angle 0. Antenna A, which is 
oriented 90 degrees with respect to the fixed antenna' 
and coaxial therewith, is provided with a resistive 
termination in order to match out the cross polarized 
(continued overleafl 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19690000482 2020-03-16T18:06:51+00:00Z
component between the antennas as antenna B is 
rotated relative to the fixed antenna. All antennas are 
housed in the circular waveguide and terminate in the 
coaxial connectors. 
The excited dipoles are fed by use of slotted baluns. 
The terminated dipole is supported by a dielectric 
cylinder that needs no balun. 
Note: 
This Tech Brief is complete in itself. No additional 
information is available.
Patent status: 
No patent action is contemplated by NASA. 
Source: R. M. Dickinson and J. C. Hardy of 
Caltech/ JPL 
under contract to 
NASA Pasadena Office 
(NPO-10648)
is 
Brief 69-10502
	 Category 01


Rotary antenna attenuator

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