Broadband modified turnstile antenna for use in space tracking and communication

Lemson, P. H.

English

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https://ntrs.nasa.gov/search.jsp?R=19710015366 2020-03-17T02:59:44+00:00Z
Dec. \F4, 1970 P. H. LEMSON 3,546,r05 
BROADBAND MODIFIED TURNSTILE ANTENNA 
Filed Dec. 1, 1969 
3,546,785 United States Patent Office Deca ,9 ,, 
3,546,705 
BROADBAND MODHFED TUIPNSTI[EE ANTENNA 
Paul W. Lernson, Houston, %ex., assignor to the United 
States of America as represented by the Admninisirator 
of the National Aeronau~cs and Space Adminiskatic~ln 
Filed Dec. 1, 1969, Ser. No. 881,039 
Int. CI. HOlq 21/26 
1 J.S. @I. 343-797 7 Claims 
to be employed together as is rcquired for circrrlar polani- 
zation. 
SUMMARY O F  T I E  INVENTION 
The present invention incorporates the desiiable fea'ur es 
of a turnstile, modified turnstile and supcrl~ir~~sl~;e  a: tcra- 
nas, while avoiding or eliminating most of the s:?o;icorn- 
ings of these antennas. The structure of the az??enni! eie- 
ment of the present invention is extremely simeile, occu- 
. . pies relativel; little space, is durable and resists Sreakage. 
A B S m C T  OP THE DISCLOSURE The antenna element is an essentially planar structixre hav- ing a series of interconnected rod-like com~onents ~vhicl~ 
-
An antenna element is provided with two resonant half- include two resonant half-wave dipole elements and four 
wave dipoles energized through feeders connected to the delta matching feeder elements. The feeder elemealls co- 
dipoles with a delta match. The feeders to each dipole cO- operate with the dipole elements in the antenna slrrcture 
operate with the dipoles and each other to form a half-wave l5 to form a half-wave wire slot which combines the rcact~v-, 
wire slot. TWO antenna elements may be combined and fed components of the slot and dipole to increase the hr osd- 
in phase quadrature to develop circular polarization. band characteristic of the antenna element The viiie slot 
may be dimensioned to establish a desired inpi11 ril~pcdm:i. 
20 to the antenna element which permits the use of economl- 
The invention described herein was made by an em- cal, high impedance, low loss lines. 
ployee of the United Stales Government and may he man- Where circular polarization is desired, two antenna eIe- 
ufactured and used by or  for the Government for govern- merits of the invention are employed. 
mental purposes without the payment of any royalties The two elements are positioned In overlapping !-on- 
thereon or therefor. 25 touching relationship and since each is essentially pianar, 
BACKGROUND O F  THE INVENTION the total space occupied by the com,posiie antenna ns ieXa- 
Field of the invention tively small. Quarter-wavelength, balanced phasing lines 
connect the two elements to place the four dipole cr i3 enis 
The present invention relates to antenna elements and of the composite antenna in proper phase. 19-1 ths preferred 
configurations which may be employed in broadcasting form of the circularly polarized antenna, two phasing lines 
telemetry transmissions, experimentation, tracking, radar 30 zre employed to increase the frequency range o m  whrc!? 
and other applications. More specificaliy, the present in- circular may be obtained. 
vention relates to a broadband modified, turnstile antenna By means of the antenna element of the present inven- 
which may be employed in space tracking and communica- tion, broadband antenna characteristics are achieved Twitll- 
tions. 35 out any loss of gain. Two elements n ~ a y  be co1115rncd Brief description of the prior art whereby circular wave polarization is acbievcd w,thout 
Original forms of turnstile antennas generally included the use of complex coaxial phasing Iilles O r  networks. In 
two half-wave dipoles fed in phase quadrature. While the addition, the antenna element of the plesent mventlcn may 
first turnstile antenna desim had many desirable features be employed in highly directive configurations men at the 
alld exhibited many improved operating characteristics, 40 lower frequencies where other antenna forills a:e nor USC- 
tuning of the antenna generally required the cutting of able. 
matched transmission lines to a predetermined length while These and other features and advantages of the ptcseni 
the antenna was mounted in an operative position. Tun- invention will be more fully evident from the t"o!iowinz 
ing after the antenna has been mounted is often difficult specification, drawings and related claims. 
or impossible especially where the antenna is positioned 45 BRIEF DESCRIPTION OF THE. 
atop a high structure such as a tall office build in^ or tower. 
The original turnstile design was subsequently improved FIG. 1 is a front view of a broadband modified turn- 
by pretuning it during its fabrication so that no tuning stile antenna constructed in accordance wit11 the teachings 
was required after the antenna had been mounted in its of the present invention designed for circular polariza*im; 
operative position. 50 FIG. 2 is a side view of the antenna of the present ingen- 
Further modification of the basic turnstile antenna in- tion taken along the line 2-2 of FIG. 4; 
cluded the addition of radiating elements constructed from FIG. 3 is an elevation illustrati~~p the antenna element 
metal sheets and rod-like dipole elements connected to- of the present invention; 
gether to form a wire slot. The latter antenna is generally FIG. 4 is a schematic diagram iIkuslraling ih? phas:?g 
referred to as a "Superturnstile" while the pretuned anten- 55 and feed coxnections of the antenna ~liusti ate6 iil FIGS 
na described earlier is referred to as a modified turnstile 1 and 2; 
antenna. FIG. 5 is a schematic representatior~ of a airective an- 
In general the turnstile and modified turnstile are rela- tenna array constructed in accordance with teachings of 
tively narrow band width antennas. Complex feed systems the present invention for providing unidirecblona"iover- 
are often required for use with the turnstile and modified 60 age in a single plane; and 
turnstile and both of the antenna configurations are diffi- FIG. 6 is a schematic represeritation of a di eclive an- 
cult to match. The superturnstile exhibits broader band tenna array for omnidirectional coverage in t i ~ ~  horizon- 
width characteristics than the turnstile or modified turn- tal plane. 
stile but required a complicated feed system and cannot 
be used in highly directional parasitic arrays. In addition, 65 PREFERRED EMBODIMENTS OF THE 
the broad surface areas of the superturnstile and the in- INVENTION 
herent structural weaknesses imposed by its large number With reference to FIG. 1 of the drawings, a bioadbaqci 
of connections and elements also make the superturnstile modified turnstile antenna of the present invention de- 
undesirable for use where ice, snow and sleet may form. signed for circular polarization is indicated ge~cralii/ at 
The large volume occupied by the superturnstile prevents 70 HQ. The antenna 11) which may be lnounted on any suit- 
it from being suitable for use in aircraft and spacecraft able means such as a mast IVI includes two Pntenna eic- 
particularly in applications where two superturnstiles are ments 11 and 12 each of which has a pair of rod-like 
3,546,705 
3 4 
&pole segnlcnts Ila, Plb, and 12a, 12b respectively. The struction illustrated in FIGS. 1 and 2 was built with the 
dipole sezmenls $!id and 1Pb of element 11 are fed by dipoles of elements 11 and 12 designed to be resonant at 
tour rod Jlhe Cccder elements 1lc ,  Bid, 11e and 1 I f  which 330 mRz., the slots S designed to be resonant at 440 
form a cizlia match with their respective dipoles. Similar- mHz., the two   ha sing lines being 300 ohm lines with one 
15,  thz dipoles of the secoild antenna element 12 are fed line being resonant at 320 mHz. and the other being 
by iccdcr ci?ments 13c, I2d,  12e and 121 which also resonant at 360 mPk. In this test model, the voItage 
iolm a Jzlta rnatcil "vkth their respective clipole radiating standing wave ratio (VSWR) was less than 2:l across 
eleixcnts. the entire range from 225 to 380 mHz. and the resultant 
? h e  eles~enls 11 and 12 of the antenna 10 are electri- characteristic impedance of the transmission line 13 was 
cally coi:accted lo a coaxial feed cable 13 having inner approximately 150 ohms. The antenna covered a fre- 
anc' outen conductors 13n and 130 respectiveiy. The con- quency range of 1.7 to 1 for a VSWR of less than 2: 1 
ncct on of tlhe ccs:lductors B3a and 13b to the antenna. without the use of special matching devices. 71he gain of 
elcinents is zcpleseilted schematically in FIG. 4. The in- the antenna wfer an isotropic source was found to be 
rrer cord~lc to~  13a is connected to the junction of feeder equivalent to or slightly g~eater than that of a conven- 
elements E l c  and Blie and the outer conductor 13b is I j tional turnstila antenna and circular polarization was 
c o ~ n e c ~ e d  to the junction of feeder elements B1d and achieved over a 1.3 to 1 frequency range. 
I If FIG. 5 o l  the drawings illustrates the antenna element 
For c;1cular polarization, the antenna element 12 is of the present invention employed in a highly directive 
rot,ibed ~;j~~roxirncitePy 93" with respect to element 11 and array. Two driven antenna elements 111 and 112 which 
is heid li? this position by any suilable means such as the 20 are rotated 90" with respect to each other are illustrated 
rnoilnls F which sectire the elements to the mast M. in coaxial alignment with two parasitic arrays of direc- 
9% ismg IAlies 14 a?d 15 are then employed to appropri- tors and reflectors indicated generally at 113 and 114, 
alely co:lncct the two elements 11 and 12 to provide the with the driven antenna elements 111 and 112 being 
desir ecl elccirical pllasing relationship for the antenna sig- axially spaced from the two parasitic arrays 113 and 114. 
n,\l Each o f  the lines 14 and 15 is a quarter-wave length 2.5 The parasitic elements in each array may be formed of 
baldnccd tiansmission line. Each of the lines 14 and 15 four crossed, connected dipoles having the illustrated 
albo Inc,~,de "Ivo conductors 14a, 14b and 15a, 1Sb re- configuration. The driven elements 111 and 112 have 
\pec:avely C3nduitors 14a and 15a are connected to the same form as illustrated in FIG. 3. By means of the 
fern a Si st phasing line and conductors 14b and 1% are i!lustrated antenna construction, a highly directional sig- 
connecteil l o  Form a second phasing line. If desired, single 30 nal of the type required for space communications and 
c o i ~ c i ~ ~ t o l s  may bc employed for the phasing lines, how- tracking may be obtained. It  wiil also be understood that 
ever plural lines of slightly varied length increase the other configurations may also be employed with the an- 
flequeficv range within which circular polarization may tcnna element of the present invention for achieving a 
h-, elcrectrd directive or an omnidirectional array. Thus, by way of 
Wilh reference :o FIG. 3, the antenna element 11 of ::3 example rather than limitation, a conical horn reflector 
the preiei?l invention is illustrated in greater detail and is or pa~abolic dish reflector located approximately a quar- 
seen to include a first dipole 11a extending between the ter-wave length behind the driven antenna elements 
pomts de;ign ited as A and B and a second, parallel dipole could be employed for producing a highly directive array. 
91b exiei~dlng between the points C and D. The dipole Where omnidirectional coverage is desired, two antenna 
clcmcnt,s I l n  and I l b  are fed using a delta match by 40 elements such as the element illustrated in FIG. 3 may be 
feeder eleiments I lc ,  I l d ,  11e and I l f  which extend spaced a full wave length apart, fed in parallel and 
~espectively between &e points EF, HI, F G  and 19. The mounted on a vertical mast in either the vertical or 
cocstriictvon rllustl-ated in FIG. 3 also forms a half-wave horizontal plane. 
wlxe slot 5; defined by the "keyhole" configuration With reference to FIG. 6, a modified form of the 
EFGJP1.P. By this construction, the reactive components 4j invention is illustrated for prodacing omnidirectional 
of llie visre slot S are combined with the reactive com- coverage in the horizontal plane. In the form of the inven- 
ponents of the dipoles 11a and 1Ib  to provide broadband tion illustrated in FIG. 6, two sets of antenna elements 
antenna characteristics for the composite antenna ele- 211, 212 and 214, 215 are horizontally mounted on a 
men:. In designing the slot S, it is dimensioned to be a vertical mast M' and are interconnected by one or more 
resonant half-wave slot and lo provide the desired input transmission lines 213 of approximately one wavelength. 
impedance of the element 11 which should be approxi- The two antenna elements in each set are rotated 90" 
malely equal to this impedance of the transmission line to with respect to  each other in the manner previously de- 
be employed with the element. scribed with reference to FIG. 1. It should be noted that 
length of the intercepted segmnts EH and GJ if desired, more than two antenna elements of the PreS- 
largely determine the input impedance of the element 11, 55 ent invention may be included in any group- 
with impeclancc increasing as the length of the intercepted While the antenna of the present invention has been 
-egments In constructing the antenna element described as having rod-like dipoles and feeders, it will 
11, it is desirable to maintain the length of the intercepted be understood that the antenna elements may be formed 
segments EH and GJ in the range between 0.1 and 0.25 by printcd circuit technique or may take on any other 
wave length. With smaller lengths, inproper matching 60 physical configuration which provides the desired results. 
occurs which causes loss of s o a e  of the antenna's broad- The foregoing disclosure and description of the inven- 
band characteristics, while larger lengths prevent the wire tion is illustrative and explanatory thereof, and various 
S fronl operaling as a slot and cause the element to changes in the size, shape and materials as well as in the 
operate .Is two folded dipoles.  he separation between details of the illustrated construction may be made with- 
the two dipoles Pln and 116 is dependent upon the de- 05 in the scope of the appended claims without departing 
siied resonant slot frequency and the element input im- from the spirit of the invention. 
pedance. For optimum performance characteristics, it is I claim: 
preferable that the resonant frequency of the slot and 1. An antenna comprising: 
dipole be within approximately 2.5% of each other. a filst antenna element having first and second dipole 
In thc preferled form of the invention, the lengths EH 70 elements fed in a delta match by a ~ l ~ l r a l i t ~  of first 
a r J  GJ ~~teicepted by the feeders I l c ,  Bld and I l e ,  111 feeder elements with said first feeder elements and 
xes@ectively plus the sum of the lengths of the feeder said first and second dipoles cooperating to form 
elenenls themselves is equal to approximately one wave a first half-wave wire slot; 
I-~igth. a second antenna element having third and fourth di- 
In the way of example, an antenna having the con- 75 pole elements fed in a delta match by a plurality of 
3,546,705 
5 6 
second feedel elcil~enls with said second feeder cle- with the total lengths of said second fcedcr clin~silt\ I ~ L I ~ I S  
ments and said thlrd and fourth dipoles coopelating approximately equal to one wave length. 
to form a second half-nave wire slot, said first and 5. The antenna as defined in claim 4 further inclnding 
second antenna elements being disposed with the di- directive means associated wlth said first Lind recond av- 
pole elements of the first antenna element in spaced tenna elements for forming a direct~ve antenna arrav 
orthogonal relationship to the dipole elements of the 6 .  The antenna as defined in claim 1 wiiere~n s a d  first 
second antenna element; and and second dipole elements are spaced from each oibei 
a plurality of quarter-wa\e length phasing lines con- in an approximately para!lel disposition and he in approx- 
necting said first and second antenna elements for imately the same plane. 
developing circular wave polarization. 7. The antenna as defined in claim 1 wl~ercin said thiid 
2. l-he antenna as defined in 1 further including lo and fourlh dipole elen~ents ale spaced from each 0th;~ 1.1 
directive means associated with said first and second an- an approximately parallel disposition and 11e i n  the same 
tenna elements for form~ng a directive antenna array. plane. 
3. The antenna as defined in claim 1 wherein said References Cited 
filst feeder elements intersect and connect to said first l5 UNITED STATES PATENTS 
and second dipole elements to intercept first and second 2,364,084 12/1944 Marlin ---------__-- 347-79- 
lengths along each of said dipole elements respectively 3,036,302 5/ 1962 Hudock ----------.  743-767 
with the sum of said first and second lengths combined 
with the total lengths of said first feeder elements being 20 OTHER REFERENCES 
approximately equal to one wave lengtth. Wireless World; Oct. 1954; p. 499, 
4. The antenna as defined In claim 1 wherein said Wolfe: Electronics; July 1947, pp 88, 89 90 
second feeder elements intersect and connect to said third ELI LIEBERMAN, primary ~~~~i~~~ 
and fourth dipole elements to intercept third and fourth 
lengths along each of said dipole elements respectively 25 U.S. C1. X.R. 
with the sum of said third and fourth lengths combined 343-767, 817 


Broadband modified turnstile antenna Patent

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