Serial Number 0973.62 Filing Date 3 Octber 998 Inventr Michael J. Jsvpenk NOTICE The abve identified patent applicatin is available fr licensing. Requests fr infrmatin shuld be addressed t: OFFICE OF NAVAL RESEARCH DEPARTMENT OF THE NAVY CODE 00CC ARLINGTON VA 2227-5660 DISTRIBUTION STATEMENT A Apprved fr Public Release Distributin Unlimited 999072 05
Attrney Dcket N. 78559 2 3 QUADRIFILAR HELIX ANTENNA 4 5 STATEMENT OF GOVERNMENT INTEREST 6 The inventin described herein may be manufactured and 7 used by r fr the Gvernment f the United States f America 8 fr gvernmental purpses withut the payment f any ryalties 9 theren r therefr. 0 BACKGROUND OF THE INVENTION 2 () Field f the Inventin 3 This inventin generally relates t antennas and mre 4 specifically t quadrifilar antennas. 5 (2) Descriptin f the Prir Art 6 Numerus cmmunicatin netwrks utilize mnidirectinal 7 antenna systems t establish cmmunicatins between varius 8 statins in the netwrk. In sme netwrks ne r mre statins 9 may be mbile while thers may be fixed land based r satellite 20 statins. Omnidirectinal antenna systems are preferred in 2 such applicatins because alternative highly directinal 22 antenna systems becme difficult t apply, particularly at a 23 mbile statin that may cmmunicate with bth fixed land based 24 and satellite statins. In satellite cmmunicatin 25 applicatins it is desirable t prvide a unidirectinal 26 antenna system that is cmpact yet characterized by a wideband 27 width and a gd frnt-t-back rati, i.e., the rati f 28 verhead pwer t backside pwer, such that its pattern ideally 29 nly ccupies the upper hemisphere.
Sme prir art mnidirectinal antenna systems use an end 2 fed quadrifilar helix antenna fr satellite cmmunicatin and a 3 c-munted diple antenna fr land based cmmunicatins. 4 Hwever, each antenna has a limited bandwidth and cllectively 5 their perfrmance can be dependent upn antenna psitin 6 relative t a grund plane. The diple antenna tends t have 7 n frnt-t-back rati which can cause ttal pattern 8 cancellatin when the antenna is munted n a ship, 9 particularly ver lw elevatin angles. These c-munted 0 antennas als have spatial requirements that can limit their use in cnfined areas abard ships r similar mbile statins. 2 The fllwing patents disclse helical antennas that 3 exhibit sme, but nt all, the previusly described desirable 4 characteristics: 5 3,599,220 (97) Demsey 6 3,623,3 (97) Faigen et al. 7 4,243,993 (98) Lamberly et al. 8 4,644,366 (987) Schlz 9 5,053,786 (99) Silverman et al. 20 5,34,422 (992) Auril 2 5,70,76 (992) Yasunaga et al.
5,343,73 (994) Baldis et al. 2 5,594,46 (997) O'Neil, Jr. 3 5,635,945 (997) McCnnell 4 5 United States Letters Patent N. 3,599,220 t Dempsey 6 disclses a cnical, spiral lp antenna cmprising a plurality 7 f pairs f spirally wund radiating arms. The radiating arms 8 are wund in the shape f a cne and terminate at ne end in a 9 truncated prtin. Impedance matching is prvided between each 0 f the pairs f radiating arms at the truncated end. A grund plane is prvided fr each frequency f peratin; multiple 2 grund planes are required fr multiple frequencies. The 3 primary purpse f this patent is t prvide a cmpact antenna 4 that is tunable. Hwever, it appears that the antenna is 5 generally tuned fr a specific frequency. 6 United States Letters Patent N. 3,623,3 t Faigen et 7 al. disclses a balanced, tunable, helical mn-ple antenna 8 that perates independently f a grund plane. This antenna 9 utilizes a centrally fed, multiple-turn, helical antenna with a 20 single element. End winding shrting means in the frm f "tp 2 hat"- r "can"-type husings tune the antenna by changing the 22 active electrical length f the antenna. A feed lp is 23 centrally dispsed t the helical mn-ple antenna winding t 24 prvide a balanced input t the antenna. Althugh this antenna 25 is cmpact and can be tuned thrugh a wide bandwidth, it des 26 nt prvide an mnidirectinal radiatin pattern.
United States Letters Patent N. 4,243,993 t Lamberty et 2 al disclses a brad band antenna cmprising center fed, spiral 3 antenna arms arranged n planar and cnical surfaces. Each 4 antenna arm includes ne r mre chke elements that resnate 5 at a predetermined perating frequency t eliminate r minimize 6 undesired radiatin and receptin characteristics and prvide 7 sum and difference mde peratins with bth right-hand and 8 left-hand circularly plarized radiatin characteristics. 9 Feeding an antenna as disclsed in the Lamberty et al patent 0 with a phased sequence f signals prduces a radiatin pattern that exhibits a null alng an antenna bre sight axis and a 2 maximum field alng a cne f revlutin abut the bre sight 3 axis. Althugh this antenna has a brad bandwidth and prvides 4 circular plarizatin, it des nt prvide an mnidirectinal 5 radiatin pattern. 6 United States Letters Patent N. 4,644,3 66 t Schlz 7 disclses a miniature radi transceiver antenna frmed as an 8 inductr wrapped abut a printed circuit card. A peripheral 9 cnductr n ne side f the card prvides distributed 20 capacitance t the end f the antenna that cancels inductive 2 effects and bradens bandwidth. A peripheral cnductr n the 22 ppsite side f the card prvides a capacitance t grund t 23 tune the antenna t frequency. An unbalanced transmissin line 24 cnnects between ne end f the antenna and a tap r feed pint 25 t prvide impedance matching and tuning. This antenna has a
limited bandwidth fr a given cnnectin pint. Mrever it 2 des nt prduce an mnidirectinal radiatin pattern. 3 United States Letters Patent N. 5,053,786 t Silverman et 4 al. disclses a brad band directinal antenna in which tw 5 cntiguus cnductive planar spirals are fed at their center. 6 The antenna is psitined near a cavity t absrb rear lbes in 7 rder t imprve the frnt-t-back rati. Even with this 8 imprvement in the frnt-t-back rati, the antenna prvides a 9 relatively narrw beam pattern having bth hrizntal and 0 vertical plarizatin. Apparently, this antenna is designed t perate with a linearly plarized, high gain, narrw beam. 2 Thus the antenna des nt prvide an mnidirectinal radiatin 3 pattern r circular plarizatin. Mrever, by absrbing the 4 rear lbes, the pwer transmitted int the reserve lbes is 5 lst making the antenna less efficient in radiating during a 6 transmitting mde. 7 United States Letters Patent N. 5,34,422 t Auril 8 disclses an antenna with helically wund, equally spaced, 9 radiating elements dispsed n a cylindrical surface. Antennas 20 identified as prir art antennas in this reference include 2 helically wund, end driven antenna elements. The ther ends 22 f the elements terminate as pen circuits. These antennas 23 prvide circular plarizatin, an mnidirectinal radiatin 24 pattern and a gd frnt-t-back rati. The Auril patent is 25 particularly directed t a structure that uses a cnductive, 26 meandering strip t cnnect the driven ends and establish 27 varius phase relatinships and tuning. This antenna is 5
designed t prduce high quality circular plarizatin, an 2 mnidirectinal radiatin pattern and a gd frnt-t-back 3 rati, but nly ver a narrw frequency band. 4 In United States Letters Patent N. 5,70,76 (992) t 5 Yasunaga et al. a quadrifilar helix antenna includes fur helix 6 cnductrs wund arund an axis in the same winding directin. 7 Each helix cnductr has a linear cnductr which is parallel 8 t its axis at either end r bth ends f the helix cnductr. 9 The purpse f this structure is t reduce the effect f 0 multipath fading due t sea-surface reflectin in mbile satellite cmmunicatins. Althugh this patent disclses an 2 antenna that prvides gd frnt-t- back rati, the 3 transmissin pattern frm the antenna is als characterized by 4 essentially frming tw majr lbes abut 60 frm the frward 5 directin s it is nt truly mni-directinal ver a 6 hemisphere. 7 United States Letters Patent N. 5,343,73 (994) t 8 Baldis et al. disclses a phase shifting netwrk and antenna 9 including a series f helical antenna elements with a phase 20 shifting netwrk defining transmissin paths between a radi 2 cnnectin terminal and the antenna elements. Each 22 transmissin path phase shifts the signal relative t an 23 adjacent path pairs that are prgressively jined at cmbiner 24 ndes f equal pwer divisin by shunt cnnectin line 25 segments.
United States Letters Patent N. 5,594,46 (997) t 2 O'Neill, Jr. disclses a lw lss quadrature matching netwrk 3 fr a quadrifilar helix antenna. As in the abve-identified 4 Baldis et al. patent, the O'Neill, Jr. patent utilizes 5 micrstrip techniques t prvide impedance matching in an 6 antenna system. 7 United States Letters Patent N. 5,635,945 (997) t 8 McCnnell et al. disclses a quadrifilar helix antenna with 9 fur cnductive elements arranged t define tw separate 0 helically twisted lps, ne differing slightly in electrical length frm the ther. The tw separate helically twisted 2 lps are cnnected t each ther in a way as t prvide 3 impedance matching, electrical phasing, cupling and pwer 4 distributin fr the antenna. The antenna is fed at a tap 5 pint n ne f the cnductive elements determined by an 6 impedance matching netwrk which cnnects the antenna t a 7 transmissin line. Like t freging Baldis et al. and 8 O'Neill, Jr. patents, this patent als utilizes micrstrip 9 techniques t feed and match thrugh a partly balanced 20 transmissin line. As a result the resultant band width is 2 narrw. 22 The fllwing patent disclses a bradband antenna system: 23 5,257,032 (993) Diamnd et al. 24 This bradband antenna system includes a frequency- 25 independent antenna cupled t the frequency-dependent antenna, 26 specifically, a spiral antenna and a diple antenna. In ne 27 embdiment the antenna system cmprises a diple r mnple 7
cupled t the inner r uter terminatin pints f a spiral 2 antenna. The spiral antenna acts as a bradband transmissin 3 line matching sectin and adds electrical length t the 4 mnple antenna. Thus, the spiral antenna is stated t 5 minimize the negative effects typically assciated with the 6 remval f ne f the elements f a stand alne diple antenna 7 t create a mnple antenna. It is believed that when the 8 diple antenna is added t the terminatin pints f the spiral 9 antenna, the resulting antenna system extends the lw frequency 0 capability f the spiral antenna fr linear plarizatin. It is als felt that the spiral antenna adds electrical length t 2 the diple antenna and acts as a bradband transmissin line 3 matching sectin s that the spiral antenna enhances receiving 4 capability by prducing a maximum signal at the transmissin 5 lines. This patent, disclses the cmbinatin f tw types f 6 antennas. Hwever, the cmbinatin includes a spiral antenna 7 and either a mnple r diple antenna. It als appears that 8 the antenna system is directinal and nt mni-directinal ver 9 bth a brad frequency band and ver a hemispherical vlume. 20 Thus there exists a family f quadrifilar helixes that are 2 bradband impedance wise abve a certain "cut-in" frequency, 22 and thus are useful fr wideband satellite cmmunicatin (DAMA 23 functin f 240 t 320 MHz, ther functins at 320 t 40 MHz). 24 Typically these antennas have: 25. a pitch angle f the elements n the helix cylindrical 26 surface frm 50 dwn t rughly 20 ;
2. elements that are at least rughly % wavelengths lng; 2 and 3 3. a "cut-in" frequency rughly crrespnding t when a 4 turn f an element n the helix cylinder is M wavelength 5 lng. (This dependence changes sme with pitch angle. 6 Abve the "cut-in" frequency, the helix has an 7 apprximately flat VSWR, arund 2: r less abut the Z 0 8 value f the antenna, and thus the antenna is bradband 9 impedancewise abve "cut-in".) 0 The previus three dimensins translate int a helix diameter f. t.2 wavelengths at "cut-in". 2 Fr pitch angles f apprximately 30 t 50, gd cardid 3 shaped patterns exist fr satellite cmmunicatins. Gd 4 circular plarizatin exists dwn t the hrizn since the 5 antenna is greater than.5 wavelengths lng (2 elements 6 cnstitute ne array f the dual array, quadrifilar antenna) 7 and is at least ne turn. At the "cut-in" frequency, the lwer 8 angled helixes have sharper patterns. As frequency increases, 9 patterns start t flatten verhead and spread ut near the 20 hrizn. Fr a given satellite band t be cvered, a tradeff 2 can be chsen n hw sharp the pattern is allwed t be at the 22 bttm f the band and hw much it can be spread ut by the 23 time the tp f the band is reached. This tradeff is made by 24 chsing where the band shuld start relative t the "cut-in" 25 frequency and by chsing the pitch angle.
Fr ptimum frnt-t-back rati perfrmance, the bttm f 2 the band shuld start at the "cut-in" frequency. This is 3 because fr a given element thickness, backside radiatin 4 increases with frequency (the frnt-t-back rati decreases 5 with frequency). This decrease f frnt-t-back rati with 6 frequency limits the antenna immunity t multipath nulling 7 effects. 8 9 SUMMARY OF THE INVENTION 0 Therefre it is an bject f this inventin t prvide a 2 brad band unidirectinal hemispherical cverage antenna. 3 Anther bject f this inventin is t prvide a brad 4 band unidirectinal hemispherical cverage antenna with gd 5 frnt-t-back rati. 6 Yet anther bject f this inventin is t prvide a brad 7 band unidirectinal hemispherical cverage antenna that 8 perates with circular plarizatin. 9 Yet still anther bject f this inventin is t prvide a 20 brad band unidirectinal hemispherical cverage antenna that 2 perates with a circular plarizatin and that exhibits a gd 22 frnt-t-back rati. 23 Yet still anther bject f this inventin is t prvide a 24 brad band unidirectinal hemispherical cverage antenna that 25 is simple t cnstruct. 0
In accrdance with this inventin, a helical antenna 2 includes a plurality f antenna elements supprted as spaced 3 helices alng an antenna axis. Antenna feed pints are lcated 4 prximate the antenna axis at a first end f the helices. A 5 spiral cnnectr between each antenna element and ne f the 6 antenna feed pints is lcated between each antenna element and 7 ne f the antenna feed pints. These spiral cnnectrs lie in 8 a transverse plane at ne end f the helices. 9 In accrdance with anther bject f this inventin a 0 quadrifilar helical antenna perates ver a frequency bandwidth defined by a minimum perating frequency and includes a 2 cylindrical supprt extending alng an antenna axis between 3 first and secnd ends theref. The cylindrical supprt carries 4 fur equiangularly spaced helical antenna elements each having 5 a length f at least 34 wavelength f the antenna minimum 6 perating frequency. A planar feed end supprt is lcated at 7 the first end f the antenna and transverse t the cylindrical 8 supprt fr defining a feed pint fr each antenna element. 9 Fur cnductrs are arranged in spiral paths that are 20 ppsitely wund frm the helical antenna elements. Each 2 cnductr cnnects between a feed pint and a crrespnding 22 antenna element. A pair f radially ppsite cnductrs 23 cnstitutes a transmissin line, thus fur cnductrs, r tw 24 pairs cnstitute tw transmissin lines. The tw transmissin 25 lines are fed in phase quadrature at the antenna feed pint.
BRIEF DESCRIPTION OF THE DRAWINGS 2 The appended claims particularly pint ut and distinctly 3 claim the subject matter f this inventin. The varius 4 bjects, advantages and nvel features f this inventin will 5 be mre fully apparent frm a reading f the fllwing detailed 6 descriptin in cnjunctin with the accmpanying drawings in 7 which like reference numerals refer t like parts, and in 8 which: 9 FIG. depicts an antenna system cnstructed in accrdance 0 with this inventin fr perating in an pen mde; FIG. 2 depicts an antenna system cnstructed in accrdance 2 with this inventin fr perating in a shrted mde; 3 FIG. 3 depicts a transverse sectin f a particular 4 embdiment f spiral feed pint cnnectrs shwn in FIG ; 5 FIG. 4 depicts anther embdiment f a spiral cnductr 6 useful in the cnnectr f FIG. ; 7 FIGS. 5 thrugh 8 prvide cmparisns f the frntback 8 ratis f a prir art antenna and an antenna cnstructed in 9 accrdance with this inventin in hrizntal and vertical 20 plarizatin and in pen and shrted perating mdes; 2 FIG. 9 depicts the vltage standing wave rati (VSWR) f 22 an antenna cnstructed in accrdance with this inventin 23 perating in the pen and shrted mdes; and 24 FIGS. 0 and depict the radiatin patterns fr 25 hrizntally and vertically plarized signals, respectively, t 26 cmpare the patterns frm an antenna embdying this inventin. 27 and the crrespnding prir art antenna. 2
DESCRIPTION OF THE PREFERRED EMBODIMENT 2 FIG. depicts, in schematic frm, an antenna 20 3 cnstructed in accrdance with this inventin. A cylindrical 4 supprt 2 extends alng a lngitudinal antenna axis 22 between 5 a first r feed end 23 and a secnd r distal end 24. The 6 cylindrical supprt 2 is cmpsed f an insulating material 7 that exhibits lw lsses at the RF frequencies invlved, namely 8 between 200 and 500 MHz. 9 The supprt additinally includes a planar supprt 25 at a 0 feed end 23 that is transverse t the cylindrical supprt 2 and the antenna axis 22. The planar supprt 25 is als made f 2 a lw lss insulating material. The planar supprt 25 includes 3 an antenna feed pint shwn generally at 26, fr receiving 4 signals frm a transmitter r transferring received signals t 5 a receiver (nt shwn) in quadrature phase and an array 27 f 6 spiral cnductrs. 7 In accrdance with this inventin, the antenna supprt 2 8 carries an even number f equiangularly spaced helically 9 wrapped antenna elements 30, 3, 32 and 33, respectively. 20 Typically the plurality will be cnstituted by fur such 2 cnductrs. Each f the equiangularly spaced elements 30 22 thrugh 33 will have a length exceeding three-quarters f a 23 wave length (i.e., 34 X min) at a minimum perating frequency. 24 In FIG., each f the antenna elements 3 0 thrugh 33 25 terminates in an pen circuit at the distal end 24. FIG. 2 26 depicts the antenna f FIG. with the additin f shrting 3
cnductrs at the distal end. That is, a diametrically 2 dispsed cnductr 35 intercnnects the distal ends f the 3 antenna elements 3 and 33 and a crrespnding diametrically 4 dispsed cnductr 3 6 intercnnects the distal ends f the 5 antenna elements 30 and 32. As knwn, but nt specifically 6 shwn in FIG. 2, the cnductrs 35 and 36 will be insulated 7 frm each ther. 8 Referring t FIGS., 2 and 3, the array 27 at the feed 9 end 23 depicts fur spiral cnductr paths between the feed 0 pint 26 and the cnductrs. In the embdiment f FIG. 3 a spiral cnnectr 37 extends between an antenna feed pint 38 2 fr abut tw and ne-half turns t an antenna element 3 cnnectin 3 9 with an verall length f at least ne-half 4 wavelength at the minimum perating frequency (i.e.,.5x. min) 5 Other spiral cnnectrs are shwn in partial detail. The 6 result is that each spiral cnductr, such as cnductr 37, 7 cnnects between an antenna feed pint and a cnnectin at an 8 antenna element. Each pair f radially ppsite spiral 9 cnductrs, i.e., (37;43) and (40,46), cnstitutes a 20 transmissin line, designated Tl and T2, respectively. Thus, 2 the fur spiral cnductrs cnstitute tw transmissin lines 22 that are crssed. Fr the antenna f FIG. 3, the cnnectins 23 are as fllws: 4
2 3 4 5 6 7 8 9 0 2 3 4 5 6 7 8 9 20 2 Feed Pint Phase Transmissin Line Spiral Cnductr Antenna Feed Pint Antenna Element Antenna Element Cnnectin 0 Tl 37 38 30 39 270 T2 40 4 3 42 80 Tl 43 44 32 45 90 T2 46 47 33 48 Each f the spiral cnductrs lies alng an Archimedean r equiangular spiral path. As is als particularly evident frm cnductr 3 7 in FIG. 3, the vlume f the cnductr increases frm the antenna element cnnectin 3 9 t the antenna feed pint 38. Each f the ther spiral cnductrs 40, 43 and 46 have the same characteristic. That is, the vlume increases frm the utside f the spiral where the cnnectins are made t the antenna elements t the inside f the spiral where each f the cnductrs attaches as an antenna feed pint. The increase in vlume may be cnstituted merely by an increase in width r by an increase in thickness r bth. Cnsequently the input impedance at the antenna element cnnectins (39, 45) and (42, 48) f the spiral transmissin lines Tl and T2 will match the input impedance t the antenna elements (3 0, 32) and (3, 33) while the input impedance at the antenna feed pints (38, 44,) and (4, 47) will match the impedance f the tw transmissin lines (nt shwn) feeding the RF energy t the antenna. Prcesses fr perfrming this matching peratin by micrstrip technlgy are well knwn in the art. 5
The variatin in vlume is depicted as a linear functin 2 in FIG. 3. The variatin culd be expnential r fllw ther 3 mathematical rules. Mrever, in FIG. 3, the cnductrs culd 4 have a variable width and cnstant thickness. 5 At the antenna feed pint 26, the structure shwn in FIG. 6 3 has a practical lwest input impedance f abut 00 hms, 7 which feeds nicely int the balanced 00 hm prt f a 50 t 8 00 hm, 80 pwer splitter (nt shwn). Tw such splitters 9 cnnected t a 90 pwer splitter will allw a 50 hm line t 0 cnnect t the antenna in phase quadrature. An alternative spiral that can btain exactly 00 hms r much lwer values f 2 input impedance is shwn in FIG. 4. The spiral is cnverted t 3 three dimensins having cnductrs that have a variable depth 4 alng the helix axis 22. In such a structure an air fam 5 spacer wuld separate the cnductrs. The cnductr 50 wuld 6 have a high impedance at an end 5 and a lw impedance at an 7 end 52. This is believed t prvide mre evenly spaced current 8 distributins acrss the element surface, thereby reducing 9 hmic lss in the signal and cnsequently prducing lwer 20 antenna lsses. 2 As shwn in FIGS. and 2, the current path thrugh the 22 spiral cnnectr array 27 and the current path thrugh the 23 antenna elements 3 0 thrugh 33 are in reverse directins when 24 viewed alng the antenna axis 22. That is, viewed frm the 25 feed end 23, the current paths fr the array are clckwise 26 abut the axis while the current paths fr the antenna elements 27 30 thrugh 33 are cunterclckwise. This reverse directin is 6
imprtant in that backside radiatin increases as the elements 2 are changed frm reverse spiral arms t radial arms t same 3 directin spiral arms. It is believed that the small amunt f 4 circular plarized radiatin prduced n the backside f the 5 antenna pattern by the helical elements is canceled t a large 6 extent by circular plarized radiatin in the ppsite 7 directin prduced by cnnectr array 27. 8 The perfrmance and imprvements ver prir art antennas 9 can be better appreciated by referring t the fllwing 0 example: An antenna accrding t this inventin has the cylindrical supprt f a 9" diameter and 39.25" length. The 2 diameter f the antenna elements 3 0 thrugh 33 is 0.5 inches 3 and the pitch angle fr these elements is 42.5. Each spiral 4 element, such as element 3, is frmed f a 0.003" cpper tape 5 laid n a 0.003" mylar substrate. The prir art example has 6 the same cnstructin except fr the spiral cnductrs. In the 7 prir art example the intercnnectin frm the feed pint 26 t 8 each antenna element is a radial feed path, such as shwn in 9 United States Letters Patent N. 5,635,945. Fr the abve 20 example, the RF frequencies invlved are between 200 and 500 2 MHz. Changing the size f the antenna will allw ther 22 frequency ranges. 23 FIG. 5 cmpares the hrizntal plarizatin frnt-t-back 24 ratis f the spiral fed, pen-ended antenna shwn in FIG. 25 fed in backfire mde, i.e., the main pattern beam cmes ff f 7
the feed and f the antenna, t the perfrmance f a prir art 2 system wherein the spiral feed is replaced by radial feeds. 3 Specifically, Graph 60 in FIG. 5 depicts the radially-fed prir 4 art antenna t the perfrmance f the spiral fed pen-ended 5 antenna represented by Graph 6. It will be apparent that the 6 frnt-t-back rati is imprved ver the entire frequency band 7 represented in FIG. 4 frm 200-400 MHz. 8 FIG. 6 prvides a similar cmparisn with vertical 9 plarizatin. In FIG. 6 Graph 62 represents the radial-fed 0 antenna and Graph 63 represents the frnt-t-back ratis fr the spiral fed antenna f FIG.. With the exceptin f a 2 prtin f the lw end f the frequency range (i.e, 200-230 3 MHz) frnt-t-back ratis are imprved ver the entire range f 4 the frequencies. 5 FIG. 7 cmpares the spiral fed, shrted antenna f FIG. 2 6 with a cmparable prir art antenna in which the spiral feeds 7 are replaced with radial feeds. Mre particularly, FIG. 7 8 depicts the frnt-t-back ratis fr hrizntally plarized 9 signals and FIG. 8 fr vertically plarized signals. In FIG. 7 20 graph 64 represents frnt-t-back ratis fr the prir art 2 antenna; graph 65 fr the antenna f FIG. 2. In FIG. 8, graph 22 66 represents frnt-t-back ratis fr the prir art antenna; 23 graph 67 fr the antenna f FIG. 2. Bth these graphs 24 demnstrate that frnt-t-back ratis are imprved ver the 25 entire spectrum by the applicatin f this inventin. 26 FIG. 9 depicts the VSWR f the antenna as shwn in FIGS. 27 and 2. Graph 70 depicts the VSWR f the antenna in FIG. ; 8
Graph 7, the antenna in FIG. 2. The VSWR reaches an 2 acceptable level at abut 200 MHz and remains at acceptable 3 levels t at least 500 MHz. In additin, it will be apparent 4 that whether the antennas are perated in the pen r shrted 5 frms f FIGS. and 2 the VSWR's have abut the same values. 6 Therefre, antenna perfrmance frm this aspect seems 7 unaffected by being in the pen r shrted versins. 8 FIGS. 0 and cmpare sample radiatin patterns fr the 9 antennas in FIGS. and 2 fr bth hrizntal and vertical 0 plarizatins at 270 MHz. Mre specifically, FIG. 0 depicts the patterns fr hrizntal plarizatin, Graph 72 depicting 2 the radiatin pattern fr the prir art antenna and Graph 73 3 the antenna f FIG.. In FIG., Graph 74 depicts the 4 radiatin pattern fr vertically plarized signals fr the 5 prir art antenna and Graph 75 fr the antenna in FIG.. 6 These cmparisns shw that mst f the radiatin frm the 7 antenna is in the frward directin. Mrever, the cmparisns 8 shw that at this particular frequency the frnt-t-back 9 ratis, i.e., the rati f gain at 0 t gain at 80, are 20 imprved thrughut. Further, analyses fr ther frequencies 2 depict that this characteristic cntinues thrughut the 22 spectrum. 23 In summary, the antennas depicted schematically in FIGS. 24 and 2 perate as d prir art antennas ver a wide frequency 25 range with acceptable levels f VSWR in bth an pen mde and 26 shrted mde. Hwever, the antennas f the present inventin 27 imprve frnt-t-back ratis are imprved essentially ver the 9
entire frequency range in all mdes and in bth hrizntal and 2 vertical plarizatins. Mrever, the radiatin patterns frm 3 these are imprved. It will be apparent that this antenna has 4 been described with respect t tw particular embdiments and 5 again in schematic frm. This specific implementatin f this 6 inventin may take different frms. Particularly, several 7 alternative methds fr feeding the antenna elements thrugh 8 the spiral path have been disclsed. It is the bject 9 7" t cver all such variatins and mdificatins 0 as cme under the true spirit and scpe f this inventin. 20
Attrney Dcket N. 78559 2 3 QUADRIFIAL HELIX ANTENNA 4 5 ABSTRACT OF THE DISCLOSURE 6 A quadrifilar helical antenna is prvided having feed pints 7 cnnected t the individual helical antenna elements thrugh a 8 spiral cupling path. The spiral cupling path additinally is 9 wund cntrarily t the winding f the helix. Mrever, each 0 path has variable dimensins t prvide impedance matching. av
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