Improved antenna design embodies the principles of turnstiling, broadbanding, and delta dipole matching. Antenna is useful in commercial broadcast applications

Lemson, P. H.

English

NASA Technical Reports Server

August 1970	 Brief 70-10482 
NASA TECH BRIEF H 
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 subscription basis from the Clearinghouse for Federal Scientific and Technical 
Information, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Improved Modified Turnstile Antenna 
3	 4
6 
O.145X 
0.21 AX	 0.145X 
\A /
' 0:21 x
2 
(No Connection of 
Dipole Elements. 
One Feeder Connected 
to Each Dipole.)
EXPLODED VIEW OF FEED AND PHASING SYSTEM 
Coaxial Cable 
HALF-WAVE DIPOLE ELEMENTS-LEMEN
tor 
This improved antenna design embodies the princi-
ples of turnstiiing, broadbanding, and delta dipole 
matching for its operation. It combines the best fea-
tures, with none of the limitations, of the conventional 
turnstile, modified (pretuned) turnstile, and super 
turnstile (broadband) antennas. The conventional 
turnstile and modified turnstile are comparatively 
narrow-band antennas, are difficult to match, and in 
some cases require complicated feed systems. The 
super turnstile (a more-broadband antenna) has a 
complicated feed sysfrni and is susceptible to damage
from sleet in frigid zones. Its numerous connections 
are subject to failure from mechanical stress. Addi-
tionally, super turnstiles cannot be used in highly 
directional arrays. When, as required, two super 
turnstiles are used to develop circular polarization, 
they take up quite a large volume and are not aero-
dynamically suitable for aircraft. 
As shown in the illustration, two pairs of delta 
matched dipoles are fed in phase quadrature to de-
velop circular polarization. The antenna is broad-
banded by making the sum of the lengths of two pairs 
(continued overleaf) 
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 owned.rights.
https://ntrs.nasa.gov/search.jsp?R=19700000465 2020-03-17T00:31:38+00:00Z
of dipole feeders and the dipole segments cut off by 
the feeders equal to one wavelength, thereby making 
use of four half-wave dipoles and two full-wave slots. 
The delta match also contributes to the antenna's 
broad bandwidth characteristics. The four dipole ele-
ments are dc-insulated from one another, even though 
they appear to intersect in the illustration. Since the 
dipoles are fed in pairs, feeders from A and B are 
connected to dipoles 3 and 4 and feeders from C and D 
are connected to dipoles 1 and 2. The phasing lines 
are connected from A and B to C and D. Wires 5 and 
6 are in one phasing line, and 7 and 8 are in the second 
one. The use of more than one phasing line does not 
appreciably change the VSWR and widens the fre-
quency range in which circularity can be obtained. 
The transmission lines used to put the dipole currents 
in proper phase are quarter-wavelengths of balanced 
lines. In a fully tested engineering model, 300-ohm 
TV-type twinlead proved to be very successful. The 
propagation factor of the line used must be taken into 
account in measuring resonant lengths. The resonant 
frequencies of the two lines are those for which a high 
degree of circular polarization can be realized. These 
two frequencies should not differ by more than 25%. 
The engineering model of the improvedturnstile 
antenna was tested with the dipoles and slots resonant 
at 330 MHz and with phasing lines resonant at 320 
MHz and 360 MHz. The VSWR was less than 2:1 
across the entire range of frequencies from 225 MHz 
to 380 MHz. Thus this antenna covered a frequency 
range of 1.7 to I for a VSWR of less-than 2:1 without 
the use of special matching devices. The antenna 
transmission line was an approximately 50-ohm coaxial 
feedline. The gain of this antenna over an isotropic 
source was the same as or slightly more than that of a 
conventional turnstile. Gain measurements, taken 
with the model at 300 MHz, show that circular polari-
zation is obtained over a 1.3 to I frequency range. 
Here circular polarization is defined for an axial ratio 
of less than 3 dB. In the plane of the antenna, radiation 
is omnidirectional and linearly polarized. The radiation 
patterns are the same as those of a conventional 
turnstile.
The antenna could be utilized in a highly directive 
array by mounting a driven element (constructed with 
half-wave dipoles as in the illustration) on a horizontal 
boom, with a parasitic reflector and a number of 
parasitic directors all properly spaced. Such an array 
can be constructed very simply at moderate cost. 
Broadband modified turnstile elements spaced a full 
wavelength apart, fed in parallel and mounted on a 
vertical mast in either the vertical or horizohtal plane, 
would provide excellent results for communications 
where omnidirectional coverage in the horizontal 
plane is desired. Still another application would be in 
printed circuit board mounted arrays. Stripline arrays 
could be connected directly to a receiver front end or, 
because of its low impedance, to a transmitter output 
circuit. Since the use of coaxial feedline at UHF and 
SHF is prohibitive in many cases, this antenna would 
fill a definite need in stripline technology. 
This antenna array also has the advantage of being 
entirely at dc ground potential, thus minimizing 
damage by lightning and static discharge. In frigid 
zones, sleet- and snow-melting equipment can be 
built into the antenna elements themselves rather 
easily. These advantages would make the antenna 
particularly useful in commercial broadcast applica-
tions. 
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
Manned Spacecraft Center, Code BM7 
Houston, Texas 77058 
Reference: TSP70- 10482 
Patent status: 
This invention is owned by NASA, and a patent ap-
plication has been filed. Royalty-free, nonexclusive 
licenses for its commercial use will be granted by 
NASA. Inquiries concerning license rights should be 
made to NASA, Code GP, Washington, D.C. 20546. 
-	 Source: P. H. Lemson 
Manned Spacecraft Center 
(MSC-12209)
. 
Brief 70-10482	 Category 01


Improved modified turnstile antenna

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