THE CESSNA AIRCRAFT COMPANY ELECTROMAGNETIC EFFECTS GROUP P.O. BOX 7704 WICHITA, KANSAS GPS ANTENNA IPL TEST MEASUREMENT ENGINEERING EVALUATION

Transcription

1 THE CESSNA AIRCRAFT COMPANY ELECTROMAGNETIC EFFECTS GROUP P.O. BOX 7704 WICHITA, KANSAS GPS ANTENNA IPL TEST MEASUREMENT ENGINEERING EVALUATION Cessna s Mission Statement: To provide Cessna Aircraft Company and it s customers, a cost effective, world class engineering test and analysis capability, which ensures the safe and reliable operation of our aircraft and associated systems against all forms of electromagnetic effects

2 Cessna Aircraft Company Page SUBJECT The purpose of this testing was to evaluate the path loss between a piece of aircraft equipment mounted in the instrument panel and a GPS antenna mounted in its natural state (i.e. on top of the fuselage). This document describes the evaluation testing performed on the GPS Antenna IPL Test Measurement setup. This testing was accomplished using guidance from the document titled Path Loss Test Method from Panel Mount to GPS Antenna, which was created from the latest SC-135 committee meeting. Testing was performed in the Cessna W-12 hanger facility and the Cessna W-2 hanger facility on August 13, 2009, August 24, 2009 and September 30, Data graphs, pictures, and test log scans are provided in the pages that follow.

3 Cessna Aircraft Company Page TESTING SUMMARY Three separate tests were conducted, using a Cessna Citation XLS aircraft, Cessna Citation X aircraft, and Cessna Citation CJ3 aircraft with all systems installed. In all cases, a multi-function display, MFD, was removed and the antenna placed within the empty volume. The CX contains five display units, the XLS contains four display units, and the CJ3 contains three display units across the front and center of the instrument panel. The center display was removed from the CX and CJ3. The number two pilots MFD was removed from the XLS, which is closest to the center of the instrument panel, for this testing. The following table lists the testing configurations: Transmit Antenna Polarity Horizontal Horizontal Vertical Vertical Table 1: IPL Test Configurations IPL Test Configurations Receive Transmit Antenna Antenna Location Location Recessed in Top of Fuselage Instrument Panel Flush with Top of Fuselage Instrument Panel Recessed in Top of Fuselage Instrument Panel Flush with Top of Fuselage Instrument Panel Receive Equipment Location Outside Outside Outside Outside The test equipment used for the testing consisted of an Agilent N5242A network analyzer, a DC power supply, associated coax and adapters, and a custom transmit antenna of two different frequencies. The on aircraft GPS antenna functioned as the receive antenna. The following table lists the GPS antennas and their applicable aircraft:

4 Cessna Aircraft Company Page 3 Table 2: GPS Receive Antennas GPS Receive Antennas Aircraft GPS Antenna Pre-Amplifier Gain XLS Prototype Comant CI dB CX Prototype Sensor Systems S No built-in pre-amplifier CJ3 Prototype Sensor Systems S dB Due to the fact that the antenna on the CX is a passive antenna (e.g. does not contain a pre-amp) an Agilent 83006A pre-amplifier was used in order to boost the RF signal out of the noise floor. This amplifier has a gain of 25.5dB. This pre-amplifier is powered by an external power supply, independent of the RF signal path. The GPS receive antennas on the XLS and CJ3 aircraft are active antennas with an internal pre-amp located within the antenna itself and were powered at 12 volts using the DC power supply. A biased tee adapter fitting was used to prevent damage to the network analyzer and power the receive antennas at the same time. A block diagram of the two setups and a picture of the biased tee are contained in figures 1, 2, and 3. The pre-amplifier gain for these two antennas is contained in table 2.

5 Cessna Aircraft Company Page 4 Figure 1: Test Setup Block Diagram for XLS & CJ3 Figure 2: Test Setup Block Diagram for CX

6 Cessna Aircraft Company Page 5 Figure 3: Bias Tee Setup The transmit antenna was a monopole attached to a six inch circular ground plane. There were two monopoles constructed corresponding to the frequency/wavelength under test. Two GPS frequency bands were tested, L1 at MHz and L5 at MHz. The transmit antennas are shown in figure 4.

7 Cessna Aircraft Company Page 6 Figure 4: GPS Transmit Antennas The recessed transmit location in table 1 above was approximately six inches behind the vertical plane of the instrument panel in the cavity used to house the pilots MFD (on the XLS, center display on CX and CJ3). The flush transmit location in table 1 above was even with the vertical plane of the instrument panel. The outside location of the receive equipment was on the left side of the fuselage approximately three to four feet from the aircraft. Two coax bulkhead connectors mounted in the forward pressure bulkhead were used to pass the RF signal into the aircraft and to receive the RF signal from the GPS antenna on the XLS. The CJ3 featured the transmit side passing through a coax bulkhead connector mounted in the forward pressure bulkhead, with the receive side passing through a similar connector at the rear pressure bulkhead in the aft baggage compartment. The CX testing coaxes were routed through the pilots #1 window, which opens to the inside. The nose baggage doors and the cabin door were closed for the test. Testing for the L1 band was conducted from MHz to MHz. Using the network analyzer at 0dBm, a sweep was taken across this frequency range. The data

8 Cessna Aircraft Company Page 7 collected across the band was then converted to watts, averaged, and then converted back to db. Prior to the testing, all of the coax assemblies used for the test were swept prior to testing, with the exception of the coax that travels from the GPS receive antenna to its associated bulkhead connector/gps receiver on all three aircraft. This coax was unable to be removed and its associated loss was not removed from the measurement. However, this extra loss only reasonably accounts for a maximum of db of total loss. The swept coax assemblies were subtracted out of the final measurement. Table 3 details the transmit antenna orientation and the applicable data signal in db. Transmit Antenna Polarity Table 3: Total Path Loss L1 Band MHz Antenna CX Aircraft Receive Transmit Antenna Equipment Orientation Location Path Loss w/pre-amplifier Correction (db) Horizontal Recessed Outside Horizontal Flush Outside Vertical Recessed Outside Vertical Flush Outside Transmit Antenna Polarity L1 Band MHz Antenna XLS Aircraft Receive Transmit Antenna Equipment Orientation Location Path Loss w/pre-amplifier Correction (db) Horizontal Recessed Outside Horizontal Flush Outside Vertical Recessed Outside Vertical Flush Outside Transmit Antenna Polarity L1 Band MHz Antenna CJ3 Aircraft Receive Transmit Antenna Equipment Orientation Location Path Loss w/pre-amplifier Correction (db) Horizontal Recessed Outside Horizontal Flush Outside Vertical Recessed Outside Vertical Flush Outside

9 Cessna Aircraft Company Page 8 No receive antenna in the L5 frequency band is available on any of the Citation product line. Data was collected for the L5 frequency band, using the L1 GPS receive antennas, but this data was basically just noise and of no meaningful value. Therefore, no data for the L5 frequency band is included in this report. 3.0 CONCLUSIONS The data collected shows an increase in path loss as the size of the aircraft is increased, which is to be expected. Another interesting note, is that the CX and XLS aircraft both contain electrically heated (AC) windshields, where as the CJ3 does not. Therefore, it can be reasonably assumed that the electrically heated windshield also contributed to some of the additional losses.

10 Cessna Aircraft Company Page A-1 APPENDIX A PICTURES

11 Cessna Aircraft Company Page A-2 INDEX Figure A - 1: Vertical Polarity Recessed Location... A-3 Figure A - 2: Vertical Polarity Flush Location... A-3 Figure A - 3: Horizontal Polarity Recessed Location... A-4 Figure A - 4: Horizontal Polarity Flush Location... A-4

12 Cessna Aircraft Company Page A-3 Figure A - 1: Vertical Polarity Recessed Location Figure A - 2: Vertical Polarity Flush Location

13 Cessna Aircraft Company Page A-4 Figure A - 3: Horizontal Polarity Recessed Location Figure A - 4: Horizontal Polarity Flush Location

14 Cessna Aircraft Company Page B-1 APPENDIX B TEST LOG SCANS

15 Cessna Aircraft Company Page B-2 INDEX Figure B - 1: Page 1... B-3 Figure B - 2: Page 2... B-4 Figure B - 3: Page 3... B-5 Figure B - 4: Page 4... B-6 Figure B - 5: Page 5... B-7 Figure B - 6: Page 6... B-8 Figure B - 7: Page 7... B-9 Figure B - 8: Page 8... B-10

16 Cessna Aircraft Company Page B-3 Figure B - 1: Page 1

17 Cessna Aircraft Company Page B-4 Figure B - 2: Page 2

18 Cessna Aircraft Company Page B-5 Figure B - 3: Page 3

19 Cessna Aircraft Company Page B-6 Figure B - 4: Page 4

20 Cessna Aircraft Company Page B-7 Figure B - 5: Page 5

21 Cessna Aircraft Company Page B-8 Figure B - 6: Page 6

22 Cessna Aircraft Company Page B-9 Figure B - 7: Page 7

23 Cessna Aircraft Company Page B-10 Figure B - 8: Page 8