2.6_Lehman-ATDS_Chamber Validation Test Plan.pdf

2685 Milscott Drive Suite 102 Decatur, GA 30033

404 292 0782 FAX 404 296 1 193 ITDS, TNC.

Fil( To: Ray Corlette From: CarlSirles

Fax: 540-653-7471 Pages: 13

Phone: 540-653-7472 Date: 06112198

Re: ChamberTest Plan fl Urgent E For Review I Please Gomment f] Please Reply I Please Recycle

Ray, Test Plan Attached for User Comment.

Carl

TEST PROCEDURE PLAN FOR CHAMBER VALIDATION

FOR

NAVAL SURFACE WARFARE CENTER

DAHLGREN DIVISION

PREPARED BY

ATDS INC

2685 MILSCOTT DR]VE

DECATUR GA. 30033

1. O GENERAL

This document. describes the test plan that will be used to verify the Naval Surface Warfare Center chamber performance over a frequency range of 100 MHz to 40 GHz-

This plan proposes to utilize the normal range instrumentation (augmented by the contractor as necessary) to perform the test. The standard range antennas will be used in their normal configuration to radiate into the chamber.

Standard gain horns or LPAs wil-l be used to receive at the test zone over the 100 MHz to 18 GHz - If no millimeter feeds are available as range equipment, the contractor will supply feeds for both transmit. and receive.

2.0 VERIFICATION TESTS

2.I Polarj-zation Verification - This test will verify that the chamber's axial ratio is less than 0.75 db from 100 MHz to 500 MHz and less than 0.5 db from 500 MHz through 18 GHz "

2.L.L Axial Ratio Test - These test wil-I be performed at 100 MHz, 500 MHz, 2 GHz, B GHz and 18 GHz. (Refer to figure 2.2-3)

The normal range antenna for each test frequency will be mounted in the chamber apex at its normal operating location. The receive SGH (or LPA) wilI be mounted on the test tower polarizalion positioner and aligned on bore-sight.

A polarization pattern will be recorded for transmitter antenna polarization settings of O, 30, 60,90, I20,150, and 180 degrees'

Note: Care musL be exercised to insure that both the transmitting and receiving feed horns are on axis for this test and that radiated power does not change with angular position. (such as variation in attenuation of rotary joints)

The peak amplitude of the plots wilI be compared for each transmitter polarization angle.

Verify that the variation in peak amplitude is within the specified limits.

2.2 Chamber Reffectivity Measurements - The reflectivity

measurement invol-ves probing the field in the quiet zone and eval-uating t.he data to determine the extraneous signal levels.

The model tower will be removed from the turntable for this test.

Ref er to f igures 2 .2-!, 2.2-2, 2.2-3 and 2 .2-4

The field probe device consists of a motorized platform and a feed support tower. The platform moves on a track that is attached to the range turntable. The feed tower supports the st.andard gain horn(scH) (or LPA) at a height approximately equal to the quiet zone center. The SGH feeds are mounted on the Lower so that they may be manually rotated 350 degrees in azimut.h.

The feed tower is at.tached to the moving platform which has a linear travel of eight feet. A synchro-mechanism, which interfaces with the instrumentation system, provides a position indication of the feed.

The l-inear travel is expressed in degrees such that the total l-inear distance traveled equals 360 degrees. (This allows standard antenna measurement instrumentaLion to be compatible with the probe position feedback)

The instrumentation confiquration for 100 MHz to 1B GHz is illustrated in figure 2.2--3 and figure 2.2-4 illustrates the configuration for 26.5 to 40 GHz.

The chamber area that is ilfuminated by the various look angles i-s illustrated in figure 2 "2-5.

For l-ateral probes, the range turntable will be positioned such that the probe travel is normal to the range axis. For longitudinal probes, it will rotate 90 degrees to allow the probe travel to be parallel to Lhe range axis.

The field probe track mechanism will be shadowed from the source by a temporary RAM fence located slightly in front of the track.

2.2.L Incident field assessment - The incident field assessment is made by field probing over a plane normal t.o the range axis. These measurements ident.ify extraneous signal energy reflected from areas in front and on the sides of the quiet zone.

The instrumentation is programmed to col}ect. relative amplitude power (in db) as a function of spat.ial position of the probe (expressed in degrees) . Extraneous signars are identified by evaluat.ing the ripple amplitude and frequency produced as the probe is moved.

In general, the amplitude of the extraneous signals. If source, the period of the direct.ion to the source.

the ripple determines the magnitude of the ripple is due Lo a predominate ripple can be used to determine the fncident field probes wi11 be performed look angles of +/ - 180 degrees in frequencies of 100 MHz, 500 MHz, 2 GHz, 40 GHz.

with "V" polartzation over 10 degree steps at the 8 GHz, 18 GHz, 26 GHz and

Note: The millimeter frequencies may vary slightly from 25 GHz and.

40 GHz depending on t.he millimeter sources and feeds that can be obtained for the measurement.

Probes wilr be made using H polarization at look angles of 0, +/-lo, +/- 20, and +/- 30 degrees at 2 GHz, g GHz and rg cHz to veriiy accept.able performance in both H and v polarizations.

2.2.2 Method of analysis - The probe made at zero degrees will establish the reference ampli_tude pr (X, e) as a function of look angle e - 0 and cross range position X, This prot is essentialry the pattern of the range transmitter feed.

Ideally the system gains should be set to have this trace represent the upper end of the l-inear dynamic range of the system.

Probes=will be made at look angles every 10 degrees over +/- 90 degrees. The largest rippre on the trace wirl be determined byinspection. Separate lines will be drawn connecting the largesl ripple positive peaks and connecting the largest ripple .regrti.re peaks. The ripple worst case peak-to-peak pex (x e) 1; deteimined(in DB) by t.he vertical separation of the two lines. Note the Xpositi-on for Pex

Figure 2.2.6 indicates the power ratio of reflected to direct(Pr/Pd) as a function of peak to peak ripple pex.

The average power Pa (X, e) of the trace at the worst case ripple Iocation is determined by reading a level halfway between t.he Lwo lines at X.

Determine the difference (pr-pa) between pr and pa at X. (this accounts for the probe antenna gain difference between e = 0 and 0 = measured look angle)

The extraneous revel is determined by the forlowing equation:

Extraneous leve1 = pr/pd + (pr-pa)

A measurement recording is to be mad.e at. each of the seven frequencies and each of t.he nineteen look angles for vpolarizat.ion.

The measurement is repeated for the select.ed frequencies of 2 GHz, B GHz and 18 Ghz and rook angles of 0, +/- 10, +/- 20 and +/- 30 degrees for H polarizat.ion.

2.2.3 Wide Angle Assessment - These measurements evaluate the extraneous signals reflected from the rear wa11 and chamber surfaces behind the quite zone.

The chamber Lurntable is rotated 90 degrees so that the field probe Lravel is on axis. The feed support is repositioned to orient t.he feed and tilt correctly.

The probing procedure for the rear hemisphere is similar to the incident field evaluation except the feeds are positioned to look at the rear of the chamber.

Measure the reference level Pr with a feed look angle e - 0 whil-e the probe moves longitudinally through the quiet zone. This trace is on bore-sight and should indicate the space loss variation from t.he f ront to the rear of t.he quiet zone.

Rotate the feed through angles of 90 through 270 tn 10 degree steps and record the levels

The extraneous signal l-evels are determined using the same technique as that used for incident field assessment.

3.0 TEST REPORT

The test report will include a block diagram and gleneral description of the tesl equipment and range geometry.

Each field probe data plot. will be labeled with frequency and look angle.

In addition, the calculated extraneous level for each plot wiIl be indicated and initialed by the test engineer.

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POST-AWARD CONFERENCE

N00178-98-C-3016

LEHMAN CHAMBERSIPAUL E. LEHMAN. INC.

9 APRIL 1998

ATTENDEES

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