Physically and Electrically Large Antennas for Antenna Pattern Measurements and Radar Cross Section Measurements in the Upper VHF and UHF bands

Transcription

1 Physically and Electrically Large Antennas for Antenna Pattern Measurements and Radar Cross Section Measurements in the Upper VHF and UHF bands Vince Rodriguez, PhD Product Manager, Antennas ETS-Lindgren, 1301 Arrow Point Dr. Cedar Park, TX 78613

2 Outline Introduction and Background The new horn The Open Boundary Quad-ridged Horn. History Lower frequency: Problems with scaling Totally open The Super Open boundary Quad-ridged Horn Computed performance

3 Outline II The 100MHz to 1GHz Horn, some measured data The 400MHz to 10GHz Horn, comparison of the OBQH and the SuperOBQH The 60MHz to 1GHz Horn. Absorber effects on an SuperOBQH Conclusion

4 4 To download and follow up

5 BACKGROUND INFORMATION

6 Introduction Over the last 7 years of attending AMTA Symposia became aware of the need for a dual polarized antenna for antenna measurement at low frequencies At those frequencies tapered chamber are the preferred range. Log periodic array antennas not suitable for tapered chambers Decided to improve available 400MHz to 6GHz antenna using lessons from S-Ku band horn presented at AMTA 2005 in Newport

7 For more Background V. Rodriguez An Open-Boundary Quad-ridged Guide Horn Antenna for Use as a source in Antenna Pattern Measurement Anechoic Chambers IEEE Antennas and Propagation Magazine, Vol. 48, No. 2, April 2006 V. Rodriguez Recent Improvements to Dual Ridge Horn Antennas: The 200MHz to 2GHz and 18GHz to 40GHz Models 2009 IEEE International Symposium on EMC. Austin, TX Aug V. Rodriguez Improvements to Broadband Dual Ridge Waveguide Horn Antennas 2009 IEEE International Symposium on Antennas and Propagation and USNC/URSI National Radio Science Meeting. Charleston SC June V. Rodriguez, A new broadband Double Ridge guide Horn with improved Radiation Pattern for Electromagnetic Compatibility Testing,16th international Zurich symposium on Electromagnetic compatibility, Zurich, Switzerland, February 2005.

8 Introduction Existing design has been used successfully in Tapered chambers as a feed. Has a range of 400Mhz to 6GHz Goal was to improve this design using the tricks learned in developing the S-Ku band horn* *V. Rodriguez An Open-Boundary Quad-ridged Guide Horn Antenna for Use as a source in Antenna Pattern Measurement Anechoic Chambers IEEE Antennas and Propagation Magazine, Vol. 48, No. 2, April 2006 A Diagonal Dual Polarized Horn Antenna, US Patent number 6,489,931

9 New Horn: Design of the UHF to S band antenna One goal was to get good shielding for the cavity so when the antenna is mounted to the shield of the chamber it does not compromise the shielding effectiveness of the enclosure. A cylindrical cavity makes it easier to machine a single block of aluminum for the cavity. A cylindrical cavity was modeled The ridge profile is based on the same as in the previous design, but the curve was modified to have a larger aperture that will allow for better radiation at lower frequencies

10 New Horn: Design of the UHF to S band antenna The measured pattern for the DDPH at 3GHz. As it can be seen it exhibits a notch in the center of the main beam. This is caused by reflections from the Lexan (polycarbonate) sides. These effects were described in: 1. V. Rodriguez-Pereyra New Broadband EMC double-ridge guide horn antenna RF Design. May 2004, pp The new antenna at the same frequency showing a well formed beam.

11 New Horn: Design of the UHF to S band antenna The model from CST MW studio was send to Solidworks for mechanical design. Once the mechanical design was finalized it was time to build a prototype and to start measuring the performance of the horn.

12 The antenna was characterized per the IEEE/ANSI C63.5 method where the antennas are calibrated over a ground plane and one of the them scanned from 1 to 4m to isolate the effects of the ground plane, that accounts for some of the difference between polarizations Measured Performance

13 The measured VSWR show how close both inputs are even when they are not exactly at the same location as feeds would intersect. Only at high frequencies is the difference apparent Measured Performance

14 The antenna exhibits a good isolation between the two ports when the S21 is measured between them. Measured Performance

15 Measured Performance

16 Measured Performance

17 the S to Ku band Horn (courtesy of Imbriale et al.) (courtesy of Imbriale et al.) The antenna will be used in a cryogenically cooled cell to reduce the thermal noise. Low noise amplifiers located right at the feed of the antenna.

18 Use of the 300MHz to 6GHz and the 2 to 18GHz designs

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20 The Design is Scalable 300MHz-6GHz 700MHz-10GHz 2GHz-18GHz

21 THE 100MHZ TO 1GHZ HORN THE INTRODUCTION OF THE SUPER OPEN BOUNDARY QUADRIDGE HORN CONCEPT

22 The problems with scalability Simply scaling the design may work electrically as the next slides show But mechanically is a nightmare Very heavy 5.5ft 5.ft 5.5ft Very expensive to machine

23 The weight issue can be solve by hollowing the ridge which does not appear to affect the performance Scaled Model

24 The VSWR barely changes as the ridges are hollowed. The gap between the ridges is critical and reducing it improves the performance Performance of scaled horn

25 The cavity problem The scaled cavity is massive. At 18 inches across and a total 40 inches including the mounting flange it is extremely expensive to manufacture and it also makes the antenna extremely heavy 18 40

26 Totally open or Eliminate the cavity Study the possibility of an octagonal cavity Which had been used in other horns including dual ridge units covering 200MHz to 800MHz

27 Totally Open No change in VSWR when the cavity is changed. Decided to go ahead and totally eliminate the cavity. The Open Boundary Quadridge Horn goes to its most extreme evolution with a totally open horn.

28 Totally open or Eliminate the cavity

29 RF Performance: input parameters 3.5:1 1.9:1

30 RF Performance: gain As with all the Open Boundary horns this one shows a very flat gain behavior for most of its range. The lack of feed cavity has not affected its performance.

31 RF Performance: HPBW

32 Computed patterns

33 Computed patterns

34 Pattern 100 MHz

35 Pattern 200 MHz

36 Pattern 300 MHz

37 Pattern 400 MHz

38 Pattern 500 MHz

39 Pattern 600 MHz

40 Pattern 700 MHz

41 Pattern 800 MHz

42 Pattern 900 MHz

43 Pattern 1000 MHz

44 Mechanical Specifications Height: inches (1.88m) Width: inches (1.88m) Depth: inches (1.74m) Approximate Weight: 152 Lbs (69kg) Two (2) N-type Connectors Aluminum construction with dielectric supports

45 The Horn itself

46 VSWR Measured results (VSWR) Better than the predicted results Frequency (MHz)

47 Gain (near Field) (db) Measured results (Near Field Gain) 2m test distance) The Purpose of this measurement is to check the difference between the ports Frequency (MHz)

48 X-port isolation (db) Measured results (Cross Port Isolation) Frequency (MHz)

49 HIGHER FREQUENCIES SUPER OPEN BOUNDARY QUADRIDGE HORN ANTENNAS

50 Upper Frequency Unit 700MHz to 10GHz OBQH Equal size S-OBQH 400MHz to 10GHz Eliminating the cavity reduces lowest usable frequency

51 comparison OBQH 36.07cm 36.07cm 36.58cm 5.1kg 700MHz to 10GHz S-OBQH 36.07cm 36.07cm 36.58cm 3.4kg 400MHz to 10GHz

52 Performance

53 MHZ TO 1GHZ SUPER OPEN BOUNDARY QUAD RIDGE HORN FOR RCS MEASURMENT

54 Low frequency RCS Pulses are used so LPDA not suitable To reduce ringing very good return loss is required, less than 2:1(-10dB return loss) for the range of interest Super Open Boundary Quadridge Horn concept is used to solve the problem.

55 Lower Frequency Unit 60MHz to 1GHz SOBQH Size 3.65m x3.65m x 3.35m 500kg Compare with the 700MHz to 10GHz OBQH 36cm by 36cm by 36.5cm 5kg 3.65m 12ft 3.35m 11ft

56 Factory Test:Transmission measurement

57 Factory VSWR measurement

58 X-port coupling

59 Installed in a chamber

60 Measured data on site during installation and tuning The horn is reassembled in-situ Horizontal port VSWR before and after improvement Vertical port VSWR Before and after improvement Freq S11 h s11 V 66MHz MHz MHz GHz

61 SUPER OPEN BOUNDARY QUADRIDGE HORNS NESTED IN ABSORBER FIELDS

62 Absorber effects This antenna is designed to be used either in open area test sites or in chambers In chambers it must operate in close proximity to the absorber Model of slightly customized model for lower VSWR

63 Absorber effects on boresight gain Using absorber complex permittivity values (assuming constant across range)

64 Absorber effects on VSWR Using absorber complex permittivity values (assuming constant across range)

65 Conclusions The Open Boundary Quadridge horn concept is extended to lower frequencies While electrical scaling is a simple approach mechanically it can be a nightmare A totally open horn is introduced where not only the flare of the horn is open but the feed cavity is also left open The concept is easier to scale mechanically to lower frequencies

66 Conclusions The antenna performance is very similar regardless of the type of use Free space Shield mounted Shield mounted with absorber Additionally the absorber permittivity changes make little difference.

67 Follow-up Information Vince Rodriguez, PhD / vince.rodriguez@ets-lindgren.com