Axially Symmetric Radiation Patterns from Flanged E-Plane Sectoral HornFeeds

P MOHANAN, P A PRAVINKUMAR & K G NAIR*

t)epartmen : of Physics; University of Cochin, Cochin 682022

Received 21 December 1981; revised received 29 March 1982

A simple technique for obtaining identical F and 11-plane patterns from E-plane sectoral feed horn is presented. Half-power beam width and gain of the antenna are also improved considerably. Experimental results for a number of horns withflanges of various parameters are also presented . This system may find practical application in radar and space communicationsystems.

I Introduction .An antenna structure having equal E- and 11-plane

patterns was proposed by Simmons and Kay'.Grooved walls in a horn would present the sameboundary conditions for TM and TE waves and hencegive symmetric radiation patterns. A large amount ofwork has been done on corrugated horns producingidentical radiation patterns -6. It is reported that anE-plane sectoral horn fitted with plane metallic flangescan have a beam with adjustable beam characteristics'.The effects of corrugated metal flanges on H-planesectoral horn antenna have also been explored'. Butthe effect of corrugated flanges on E-plane sectoralhorn has not been a topic of investigation so far. Thework reported in this paper is a study of the effect ofplane and corrugated flanges on both E- and H-planeradiation patterns of E-plane sectoral horns.

Fig. 1 shows the geometry of the flanged E-planesectoral horn. Flange system can be slid back and forthalong he entire length of the horn using a rack andpinion arrangement. A linear potentiometer isattached to this arrangement which gives an analogvoltage reading corresponding to the position (Z) ofthe flange from the aperture of the horn. An X-bandGunn oscillator having i. -- 3.6 cm is used as the sourceof microwaves. The TE,o mode electromagnetic waveswere used to excite the antenna system.

Table I gives the various parameters of different E-

plane sectoral horns used in this study. Theinvestigations are carried out at X-band. Theparameters of various flanges used are given in Table 2.The width, w, of the flange is of the order of 3i.. Theheight, h, of the corrugations is of the order of %/4 <h

<i./2 to prevent surface waves'. The flanges are

`Present address: Department of Electronics & CommunicationSystems, University of Cochin, Cochin 682022.

mounted in such a way that their edges are parallel tothe E-vector.

2 Method of MeasurementsThe experiments were carried out in two steps,

namely, (i) the variation of on-axis power density (Pt)and VSWR with the relative position of the flange, and(ii) plotting of the radiation patterns.

Experimental set-up used to study the variation ofPo and VSWR is shown in Fig. 2. Flanged E-planesectoral horn is treated as the transmitter of CWmicrowave signal . A standard pyramidal horn is usedas the receiver, which is kept along the axis of thetransmitter at a distance greater than (d, + d' )/;+, toensure plane electromagnetic waves, where dl and d2are the apertures of the transmitting and receivinghorns, respectively. The received polder is rectified attdfed to one axis of the X- Y recorder and the do signalfrom the linear potentiometer attached to the flangemount is given to the other axis. Now the flange systemis moved at uniform slow speed along the length of thehorn from its aperture and the variation of on-axispower density is automatically traced, This will givethe variation of Po with Z. The VSWR correspondingto the maximum and minimum power positions*of theflange are now measured separately using the slottedsection and VSWR meter. The experiment is repeatedfor different horns with various flanges of varyingparameters. Values of VSWR and Po corresponding tothe simple horn alone is also noted in each case forcomparison.

The set-up used for plotting the radiation pattern isshown in Fig. 3. Here a standard pyramidal horn is usedas the transmitter and the flanged E-plane sectoralhorn under test is used as the receiver, This part of theexperiment is carried out inside an anechoic chamber

MOHANAN rr cl.: SYMME I RIC RADIATION PATTERNS FROM SECTOR AL HORN FEEDS

1-ig. I Geometry of the hanged E-plane sceteral horn: Si) fl-plane view anti (ii) E- plane view 1w width of the flange, (i

=corrugation width, Ii corrugation height.)

Table I - Parameters of Different E-plane Sectoral HornsUsed

Horn Flare angle Aperture width (cm) inN dego.

L•', 60

fl-Plane

2.3

E-Plane

II

E2 60 2.2 15.345 2.3 8.6

Table 2.-- Parameters of Different Corrugated Flanges Used

FlangeNo.

No. ofcorrugations

(n)

Corrugationwidth ([t)

cm

1 0 (Plane) ---2 6 1.663 1.254 li 0.905 14 0.714

6 19 0,526

Microwave test bench

X-Y Recorder

Fig. 2 - Block diagram irf expenmental set-up used to study the

variation of P„ arid VSW R(A: I Isngrd F plane'.ectoral horn. B

l'yranudaI horn and (': l enninal to the sliding potentiometer.)

Mtcrrw.'cve test bench

IAntenna

Turntable

X-Y RecOrder

Fig. 3---Block diagram of experimental set-up used for plottingthe radiation patterns (A: Flanged F-plane horn and B:

pyramidal horn.)

15f-

5

0l I I L I I

0 1 2 3 4 5

Z, cm

Fig. 4 Variation of Po withZ

( Horn E,. 2(1 60 for

corrugation numbers A, I4, B, 14; C, 11; D, 8; f bandF. natural (horn alone).:(

INDIAN I ItAI)IO & SPACE. PHYS . VOL 11, Jt,N1' 19x'

having facilities for automatic pattern recording. Thereceived microwave signal is rectified and fed to oneaxis of the recorder. The dc signal from the antennapositioner is given to the other axis.

3 Experimental Results and Discussion

31 Variation of P„ with Z

For a particular horn operating at a fixed frequencywith a particular flange and included angle (2/0, Povaries with the position (Z) of the flange'fr-om theaperture. As Z is increased gradually, Po rises to amaximum value and then falls steadily as shown in Fig.4. It is found' from the experimental data thatmaxitnunr on•-axis power density is obtained when theflange system is near the aperture of the horn. Theeffects of increase in the number of flanges on the on-axis power from the natural horn, for differentparameters a re listed in Table 3. here an increase of Poof 19.22 dB from the natural value is achived. It canalso be noted from the VSWR studies that the positionof the flange is not considerably affecting the matching

conditions.

'rabic 3----improvement of On-axis Power (Po) from theNatural Horn in dB

3.2 t)ependence of )'„ on Number of Corrugations (o)

For a particular horn and flange angle (2f), the ort-axis power density varies with the number ofcorrugations. If the operating frequency and horn isfixed, maximum on-axis power is achieved for aparticular corrugation number, n, as shown in Fig. S.

3.3 'Variation of Po, with 213

The on-axis power density also varies with the flangeangle. A typical variation of Po and 2/3 is shown in Fig.

6. The optimum flange angle is a constant only for aparticular flange used on a particular horn.

3A Effect of Radiation Pattern In H-plane

The radiation patterns of natural horn in both E-and H-plane are traced initially for comparative

d

rNCuV

u

0amX

FlangeNo,

Horn E,at flangeangle (2f3)

Horn E.at flangeangle (2$)

Horn E3at flangeangle (213)

30' 450 60' 45" 600 90" 30" 45' 60.

1 11.64 15.93 110 16.15 16.18 6.57 12.38 12.69 11.712 10.53 12.81 10.81 18.29 17.21 10.88 12.28 15.69 11.50

3 11.10 10.55 10.81 18.40 15,01 7.23 13.70 13.68 10.764 7.00 15.12 6.49 11.47 15.36 934 11,69 14.97 8.82

5 10.76 15.80 12.97 19.62 15,56 8.53 11.93 14.47 10.16

6 11.69 15.25 13.73 19.22 13.46 9.91 13 52 13.84 11.87

L

NXd

8 0.570

rv

d 0"C t 1 ! 1 tEI. . 0 6 8 11 14 19

NO, ot` corrugations (n )

Fig. 5 -- Dependence of normalized P„ for the number of

corrugations (n) (Horn Er: Curves A, U. Care for 2f3 - 30,45 and

60", respectively.)

C 0.5

O-L30

1 1 iI

45 60

Flange angle (2 P )

l ig.6 v i iii", of norm lined P„ with flange angle (?fp(Curves A. B, C, 1) and E are for corrugation numbers 0, 6, S. I t

and 14. respectively.)

z Bearing angle 18 )Fig. 7---Typical radiation patterns [(a) Natural H-

plane pattern , (b) shaped 11-plane pattern and (c)natural E- plane pattern.]

%1011AVAh rt uL S1'MMt IRK RAJ,IArION PATTE'R'S f ROM SECIORAL HOR,V FEEDS

;utalysis. The flange is now kept at the '01, and W,positions' and radiation patterns in both planes areagain plotted. Fig. 7 shows these typical radiationpatterns. Fig. 7 shows that at '0' position (on A-axis)the beam is highly sharpened and beam width isreduced. Considerable improvement in the gain is alsorioted. The gain is calculated from the radiationpatterns.

It can he shown that by choosing the proper valuesof 211, Z and n the axially symmetric radiation patternsfrom a E-plane sectoral horn can be achieved. In Fig. 7,the normal gain is 17.25 dB and HPBW in H- and E-planes is 74.37 and 21.79-, respectively, But when the

flange is kept at the '0' position the gain is found to be24.97 dB and HPBW in H-plane is found to be 22.26°.Thus ' we could make almost identical radiationpatterns in both F,- and H-planes with the adjustment

of the flange parameters. From the observations it isfound that corrugated flanges are more effective thanplane flanges to sharpen the 11-plane radiation patternof E-plane sectoral horns. It is found that the flange ismore effective when the corrugation width is of the

order of A/2.

4 ConclusionIt has been established that conducting corrugated

metallic flanges satisfying certain optimum conditionsare very effective in modifying the H-plane radiationpatterns of E-plane sectoral horns. By proper selectionof the flange angle, the number of corrugations and thedistance of the flange from the aperture, it is possible toobtain symmetrical E- and H-plane patterns.Compared to the fixed system of sectoral horns with

corrugated sides, the present system offers greatconvenience in adjusting antenna characteristics bytrimming the flange parameters. These axially

symmetric patterns may find application forilluminating axially symmetric antennas like para-boloids and polarization measurements in radioastronomy.

AcknowledgementThe authors gratefully acknowledge the financial

assistance accorded by Council of Scientific andIndustrial Research. New Delhi and SERC,Department of Science and Technology, Governmentof India. The authors wish to thank Prof. KSathianandan, Head of the Department of Physics,University of Cochin, for providing all facilities forthis work.

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(1966) 605.3 Rumsey V H, IEEE Trans Antennas & Propag (USA), 14 (1966)

656.4 Minnett H C& Mac A Thomas B, IEEE Trans Antennas & Fropag

(USA), 14 ( 1966) 654.S Roos Calde Cott, Mentor C A & Leon Peters , IEEE Trans

Antennas & Propag (USA), 21 ( 1973) 562.6 Narasimhnn M S & Rao V V, IEEE Trans Antennas & Propag

(USA), 21 (1972) 320.7 K.oshy V K, Nair K G & Srivastava G P, I Inst Telecommun Frig

(India), 14 (1968) 519.8 Zacharish E J, Vasudcvaa K & Nair K G, IEEE Trans Antennas &

PropaR (USA), 27 (1979) 708.9 Nair K G & Srivastava G P, ! Inst Telccanintun Eng (India), 13

(1967) 76.