THE UNIVERSITY OF MICHIGAN 7300-4-T Radant Analysis Studies Interim Report No. 4 1 June through 31 August 1966 C. T. Tai September 1966 Contract No. AF' 33(615)-281I Project 4161, Task 416103 Prepared for Air Force Avionics Laboratory, AVWE Research and Technology Division, AFSC Wright-Patterson Air Force Base, Ohio 45433

THE UNIVERSITY OF MICHIGAN 7300-4-T FORE WORD This report was prepared by The University of Michigan under contract No. AF 33(615)-2811, Task 416103, Project 4171. The work was administered under the direction of the Air Force Avionics Laboratory, Research and Technology Division, Air Force Systems Command: E.M. Turner, Technical Monitor; S. Pitts, Project Engineer. This report covers the work conducted from June through August, 1966. iii

I THE UNIVERSITY OF MICHIGAN 7300-4-T ABSTRACT In this fourth interim report, the planned experimental program is discussed, and preliminary results given for the effectiveness of the radant structure as a polarization transformer. The preliminary results indicate that there are critical frequencies at which the cross-polarized field slightly exceeds the like-polarized field, and approaches to within 3 db of the incident field. iv I,

THE UNIVERSITY OF MICHIGAN 7300-4-T I INTRODUCTION The main activity during this period involved the fabrication of the 196-element radant and the supporting structure, and preliminary transmission tests of the radant. An experimental program has been outlined, and will be presented here. The purpose of the program is to determine the transmission and cross-polarization effects of the radant, which consists of two 36-inch square panels of parallel dipoles oriented perpendicular to each other, and connected by transmission lines (Fig. 1). L I -r I -- — _ — I 1

THE UNIVERSITY OF MICHIGAN 7300-4-T [L~4 36" H _~36",- ] C[ HI I == i - I k | oDipoles located on| 1 outside surfaces of| 36" -panels. FIG. 1: ORIENTATION OF DIPOLE ARRAiYS /16(only 9 dipole pairs shown for clarity). Dipoles located on outside surfaces of panels. FIG. 1: ORIENTATION OF DIPOLE ARRAYS (only 9 dipole pairs shown for clarity). 2

THE UNIVERSITY OF MICHIGAN 7300-4-T II FABRICATION OF RADANT AND SUPPORTING STRUCTURE The design data for the radant was given in the third interim report. It consists of two panels of 196 dipoles each, imprinted on a 36-inch square, 1/16 inch fiberglass board, shown in Fig. 2. The two panels are oriented parallel to each other but in such a way that each (vertical) dipole on one is connected by a two-wire transmission line one inch long to a (horizontal) dipole on the other. The transmission lines are made of AWG-20 wire separated by 0. 06 inch, corresponding to an impedance of 160 ohms. Rather than twist the wires, it was decided to modify the feed region of the dipoles as shown in Fig. 3. For strength, the radant has been enclosed in a wooden frame (Fig. 4). This fits snugly into a vertical supporting rack, which is free to run forward and back along a track parallel to the line joining the transmitting and receiving antennas, as shown in Fig. 5. The track allows continuous adjustment of the spacing between radant and receiving antenna. The whole system is mounted on an antenna platform and can be rotated through the azimuth plane; that is, the angle p of Fig. 5 can be varied continuously. One of the difficulties encountered in the fabrication was the practical unfeasibility of attaining a two-wire transmission line having a characteristic impedance of 50 ohms, which is the measured impedance of an individual element at the design frequency of 3.0 GHz (see Interim Report No. 3). The final design uses transmission lines having an impedance of about 160 ohms. Thus there is an inherent mismatch at the terminals, corresponding to a power reflection coefficient of 0.28. Use of folded dipole elements has been suggested to effect a better match, and impedance data taken on an individual elemennt indicate an impedance near 140 ohms at 3.0 GHz. Future designs may incorporate these if the problem proves critical. a 3,, L

THE UNIVERSITY OF MICHIGAN 7300-4-T FIG. 2: ARRANGEMENT OF DIPOLE ELEMENTS OF FIBERGLASS PANEL. 4

THE UNIVERSITY OF MICHIGAN 7300-4-T I I I I I I I I I 0.0 o. o6',,/ I, I I I I I FIG. 3: RADANT DIPOLE ELEMENT 5

'TIE UNIV!ERS O TrY ( F M I C H-{ i G A N 7300-4-O T:..:.'.:ii.. A> PO x N, q4 z nC 0 i H zfl 64 Fl (3

THE UNIVERSITY OF MICHIGAN 7300-4-T z.y FIG. 5: SPHERICAL COORDINATE SYSTEM FOR RADANT STUDY 7

I THE UNIVERSITY OF MICHIGAN 7300-4-T III EXPERIMENTAL PROGRAM The frequency of the transmitting source is to be varied over the band 100-3000 MHz to determine the frequency bands at which the radant produces a large cross-polarized component. Initially the spacing between the radant and receiving horn is to be 15 inches. Data is to be taken with the transmitting antenna vertically polarized, and the receiving antenna both vertically and horizontally polarized. Sweep equipment is available between the frequencies of 1000 MHz and 4000 MHz and can be instrumental in determining critical frequencies. Pattern data is to be obtained at least every 100 MHz over the band. Once critical frequency bands are established, additional information will be sought: the effect of spacing variations between radant and receiving antenna, and the effect of rotation of the transmitting and/or the receiving antennas. If it is possible, other designs of radants will be considered, involving other spacings and elements. J 8

THE UNIVERSITY OF MICHIGAN 7300-4-T IV PRELIMINARY RESULTS Patterns taken at the design frequency of 3. OGHz are shown in Figs. 6 and 7, using Table I. Figure 6a shows that the cross-polarized component of the field with the radant removed is well down into the noise, so that the cross-polarized signals observed in Figs. 6b and 6c are indeed caused by the radant. The difference between the conditions of Fig. 6b and 6c is that the radant has been rotated by 90. The marked difference in the patterns indicates an appreciable effect due to the dielectric sheets. Comparison of the signals in Figs. 6b and 6c at nose-on incidence, or 00 with the nose-on levels of Fig. 7a indicates that the cross-polarized component is 17-20 db below the incident signal, much lower than had been anticipated in the discussion in Interim Report No. 3. (Note that the two patterns cannot be directly compared since they represent different pattern cuts of the receiving antenna.) Figures 7b and 7c have the same order of magnitude and pattern beamwidth (24 ) as the incident pattern of 7a, confirming that little energy has been transferred to the cross-polarized field. Sweep-frequency data was taken from 2. 2 GHz to 4.0 GHz and indicated that strong polarization transformation takes place at 3.63 GHz and to a lesser extent at 2.55 GHz, but not around 3.0 GHz. Patterns were then taken at 3.63 GHz, and are shown in Figs. 8a-8c. At nose-on incidence the cross-polarized component comes to within 3 db of the incident power, and slightly exceeds that of the like-polarized component. Patterns taken at close frequencies indicate a bandwidth of 0. 11 GHz, or about 3 percent. These results are very close to what had been anticipated, and indicate that a large part, about half, of the power incident on the radant is reradiated via the transmission lines. A possible explanation for the shift in frequency is that since the actual transmission lines are not well matched to the dipole elements, there are probably other frequencies at which the match is good. Impedance data on the individual elements 9 ~ I i, I

THE UNIVERSITY OF MICHIGAN 7300-4-T reported in Interim Report No. 3, suggests that this may be the case. The frequency band of that data was only from 2.2 GHz to 3.3 GHz, and so is not sufficient to verify this. Impedance data over a wider frequency range will be taken in the next period. TABLE I: CONFIGURATION DESIGNATION,__ __ Polarization of Transmitting I Antenna. V V H Polarization of Radant Dipoles Nearest Transmitter. Polarization of Radant Dipoles Nearest Receiver. Polarization of Receiving r1 -- Antenna. H 10

THE UNIVERSITY OF MICHIGAN 7300-4-T FIG. 6a: CROSS-POLARIZED INCIDENT PATTERN. Freq. 3.0 GHz. Radant Support to Antenna Spacing: 15 inches. Configuration Designation: V —H. Antenna to Antenna Spacing: 290 Ft. Pattern Description: E-Plane Cut. Transmitting Antenna: 6' Parabolic Dish, Splash Plate Feed. Receiving Antenna: Scientific Atlanta Type 2,6, 10 cm Gain Standard Horn. 11

THE UNIVERSITY OF MICHIGAN 7300-4-T FIG. 6b: CROSS-POLARIZED RADANT PATTERN. Freq. 3.0 GHz. Radant to Antenna Spacing: 15 inches. Configuration Designation: VVHH. Antenna to Antenna Spacing: 290 Ft. Pattern Description: E-Plane Cut. Transmitting Antenna: 6' Parabolic Dish,Splash Plate Feed. Receiving Antenna: Scientific-Atlanta Type 2.6, 10 cm Gain Standard Horn. 12

THE UNIVERSITY OF MICHIGAN 7300-4-T FIG. 6c: CROSS-POLARIZED RADANT PATTERN. Freq. 3.0GHz. Radant to Antenna Spacing: 15 inches. Configuration Designation: VHVH. Antenna to Antenna Spacing: 290 Ft. Pattern Description: E-Plane Cut. Transmitting Antenna: 6' Parabolic Dish, Splash Plate Feed. Receiving Antenna: Scientific Atlanta Type 2.6, 10 cm Gain Standard Horn. 13

THE UNIVERSITY OF MICHIGAN 7300-4-T FIG. 7a: LIKE-POLARIZED INCIDENT PATTERN. Freq. 3.0 GHz. Radant Support to Antenna Spacing: 15 inches. Configuration Designation: V —V. Antenna to Antenna Spacing: 290 Ft. Pattern Description: H-Plane Cut. Transmitting Antenna: 6' Parabolic Dish, Splash Plate Feed. Receiving Antenna: Scientific-Atlanta Type 2.6, 10 cm Gain Standard Horn. 14

THE UNIVERSITY OF MICHIGAN 7300-4-T FIG. 7b: LIKE-POLARIZED RADANT PATTERN Freq. 3.0 GHz. Radant to Antenna Spacing: 15 inches. Configuration Designation: VVHV. Antenna to Antenna Spacing: 290 Ft. Pattern Description: H-Plane Cut. Transmitting Antenna: 6' Parabolic Dish, Splash Plate Feed. Receiving Antenna: Scientific Atlanta Type 2.6, 10 cm Gain Standard Horn. 15

THE UNIVERSITY OF MICHIGAN 7300-4-T FIG. 7c: LIKE-POLARIZED RADANT PATTERN. Freq. 3.0 GHz. Radant to Antenna Spacing: 15 inches. Configuration Designation: VHVV. Antenna to Antenna Spacing: 290 Ft. Pattern Description: H-Plane Cut. Transmitting Antenna: 6' Parabolic Dish, Splash Plate Feed. Receiving Antenna: Scientific Atlanta Type 2.6, 10 cm Gain Standard Horn. 16

THE UNIVERSITY OF MICHIGAN 7300-4-T o n 0o = 180~ FIG. 8a: LIKE-POLARIZED INCIDENT PATTERN Freq. 3. 625 GHz. Radant to Antenna Spacing: 15 inches. Configuration Designation: V —V. Antenna to Antenna Spacing: 70 Ft. Pattern Description: H-Plane Cut. Transmitting Antenna: Narda Type 644 Horn. Receiving Antenna: Scientific- Atlanta Type 2.6, 10 cm Gain Standard Horn. 17

THE UNIVERSITY OF MICHIGAN 7300-4-T ___ = 0~ -- = 180~ FIG. 8b: LIKE- POLARIZE RADANT PATTERN Freq. 3.625 GHz. Radant to Antenna Spacing: 15 inches. Configuration Designation: VVHV. Antenna to Antenna Spacing: 70 Ft. Pattern Description: H-Plane Cut. Transmitting Antenna: Narda Type 644 Horn. Receiving Antenna: Scientific-Atlanta Type 2. 6, 10 cm Gain Standard Horn. 18

THE UNIVERSITY OF MICHIGAN 7300-4-T __- = 0 = 180~ FIG. 8c: CROSS-POLARIZED RADANT PATTERN. Freq. 3. 625GHz. Radant to Antenna Spacing: 15 inches. Configuration Designation: VVHH. Antenna to Antenna Spacing: 70 Ft. Pattern Description: E-Plane Cut. Transmitting Antenna: Narda Type 644 Horn. Receiving Antenna: Scientific-Atlanta Type 2. 6, 10cm Gain Standard Horn. 19

THE UNIVERSITY OF MICHIGAN 7300-4-T V FUTURE WORK During the next period, experimental work will proceed as outlined in Section III, covering frequency ranges above and below those reported here. The theoretical model developed in Interim Report No. 3 is presently being extended and applied to the scattering properties of a pair or dipoles joined by a transmission line. Calculations, not reported here, have yielded figures in approximate agreement with the observed behavior. The more refined model, which uses measured impedance data, is expected to determine the extent to which the two-dipole configuration is related to the radant panel and provide design criteria. Further impedance data will be taken on individual elements to supplement this effort. I I 20

THE UNIVERSITY OF MICHIGAN 7300-4-T VI ACKNOWLEDGMENTS The author is pleased to acknowledge the assistance of R. M. Kalafus, J. E. Ferris, W.E. Zimmerman, R.L. Wolford, and J.P. Bosel for their work on the experimental phases of this study.,,, I 21 I llvl I I,, -

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UNCLASSIFIED Security Classification II _ _ Q Ir-~ P I [g II iP~' 9-p I JseC I I _.~- _ DOCUMENT CONTROL DATA - R&D (Security claee*llctllon of title. body of abetrect ond Indexin# annotation must be entered when lhe overall moort ie cloeellled).. 1 1. ORI,^JTIN G ^C TIV t.yr (Corporate * thaS 3'.. REPORT SECURITY C LASSIPICATION The University of Michigan Radiation Laboratory UNCLASSIFIED Department of Electrical Engineering Ann Arbor, Michigan 48108 3. REPORT TITLE Radant Analysis Studies - Interim Report No. 4 4. DESCRIPTIVE NOTES (Typ of report and Inclfuelsv dtee.) Interim Technical Report 1 June through 31 August 1966 5. AUTHORQS) (Let naipe. frst namf, Inltiel) Tai, Chen-To 6. REPORT OATE' 7''. TOTAL NO. OFr ASE 7b. NO. or RrPS September 1966 21 8. CONTRA T OR GRANT NO. 94. OR IGNATOR' REPQRT NUMBIR(s) AF 33(615)-2811 7300-4-T h pROJECT NO. 4161 c. I b. OTHER RsPORT N'O(F (^/ny oth1er nnibers Mlat may be aoeideof Task 03 ^*o rportj d. 10. AVA IL ABILITY/I. ITATION NOTICKE Agencies of the Dept of Defense, their contractors or government agencies may obtain copies from DDC, Cameron Station, Alexandria, Va. 22314 11. SUPPIEMENTA"Y HOTES' IS.' rPONSORING MIAITARY ACTIVITY Air Force Avionics Laboratory, AVWE Research and Technology Div., AFSC Wright-Patterson AFB, Ohio 45433 13. ABSTRACT In this fourth interim report, the planned experimental program is discussed, and preliminary results given for the effectiveness of the radant structure as a polarization transformer. The preliminary results indicate that there are critical frequencies at which the cross-polarized field slightly exceeds the like-polarized field, and approaches to within 3 db of the incident field. DD I. JAN641473 UNCLASSIFIED Security Classification

UNCLASSIFIED I Security Classification e14. I LINK A LINK B LINK C KEY WORDS - 1l _______KEY WORDS _ROLE WT ROLE WT ROLE WT ANISOTROPIC PANEL RADANT STRUCTURE EXPERIMENTAL STUDY ANTENNAS SCATTERING ~~~~~~~i_ i..a INSTRUCTIONS 1. ORIGINATING ACTIVITY: Enter the name and address of the contractor, subcontractor, grantee, Department of Defense activity or other organization (corporate author) issuing the report. 2a. REPORT SECUUITY CLASSIFICATION: Enter the overall security classification of the report. Indicate whether "Restricted Data" is included. Marking is to be in accordance with appropriate security regulations. 2b. GROUP: Automatic downgrading is specified in DoD Directive 5200.10 and Armed Forces Industrial Manual. Enter the group number. Also, when applicable, show that optional markings have been used for Group 3 and Group 4 as authorized. 3. REPORT TITLE: Enter the complete report title in all capital letters. Titles in all cases should be unclassified. If a meaningful title cannot be selected without classific..tion, show title classification in all capitals in parenthesis immediately following the title. 4. DESCRIPTIVE NOTES: If appropriate, enter the type of report, e.g., interim, progress, summary, annual, or final. Give the inclusive dates when a specific reporting period is covered. 5. AUTHOR(S): Enter the name(s) of author(s) as shown on or in the report. Enter last name, first name, middle initial. If military, show rank and branch of service. The name of the principal author is an absolute minimum requirement. 6. REPORT DATE: Enter the date of the report as day, month, year; or month, yea.. ii more than one date appears on the report, use date of publication. 7a. TOTAL NUMBER OF PAGES: The total page count should follow normal pagination procedures, Le., enter the number of pages containing information 7b. NUMBER OF REFERENCES: Enter the total number of references cited in the report. 8a. CONTRACT OR GRANT NUMBER: If appropriate, enter the applicable number of the contract or grant under which the report was written. 8b, 8c, &s 8d. PROJECT NUMBER: Enter the appropriate military department identification, such as project number, subproject number, system numbers, task number, etc. 9a. ORIGINATOR'S REPORT NUMBER(S): Enter the official report number by which the document will be identified and controlled by the originating activity. This number must be unique to this report. 9b. OTHER REPORT NUIBER(S): If the report has been assigned any other repcrt numbers (either by the originator or by the sponsor), also enter this number(s). 10. AVAILABILITY/LIMITATION NOTICES: Enter any limitations on further dissemination of the report, other than those imposed by security classification, using standard statements such as: (1) "Qualified requesters may obtain copies of this report from DDC." (2) "Foreign announcement and dissemination of this report by DDC is not authorized " (3) "U. S. Government agencies may obtain copies of this report directly from DDC. Other qualified DDC users shall request through.t (4) "U. S. military agencies may obtain copies of this report directly from ]DC Other qualified users shall request through,, (5) "All distribution of this report is controlled. Qualified DDC users shall request through,, If the report has been furnished to the Office of Technical Services, Department of Commerce, for sale to the public, indicate this fact and enter the price, if known. 11. SUPPLEMENTARY NOTES: Use for additional explanatory notes. 12. SPONSORING MILITARY ACTIVITY: Enter the name of the departmental project office or laboratory sponsoring (paing for) the research and development. Include address. 13. ABSTRACT: Enter an abstract giving a brief and factual summary of the document indicative of the report, even though it may also appear elsewhere in the body of the technical report. If additional space is required, a continuation sheet shall be attached. It is highly desirable that the abstract of classified reports be unclassified. Each paragraph of the abstract shall end with an indication of the military security classification of the information in the paragraph, represented as (TS), (S), (C). or (U). There is no limitation on the length of the abstract. However, the suggested length is from 150 to 225 words. 14. KEY WORDS: Key words are technically meaningful terms or short phrases that characterize a report and may be used as index entries for cataloging the report. Key words must be selected so that no security classification is required. Identifiers, such as equipment model designation, trade name, military project code name, geographic location, may be used as key words but will be followed by an indication of technical context. The assignment of links, rules, and weights is optional. UNCLASSIFIED Security Classification

UNIVERSITY OF MICHIGAN 3 9015 03527 1959