1 Antenna design and optimisation Test-bed of mechanical tilt CSEM

2 Document Properties

3 Reminder: antenna specification Frequency range and BW: down link GHz, up link GHz -> 13% BW Half power beam width (HPBW): 5° (best result 2°) Gain:30 dBi Polarisation: circular polarisation (CP) Size: 25255 cm Scan angle and speed: 180° semi-sphere by mechanical steering system 0.4°/s for train running at 500 Km/h Scan angle precision 0.8° for 5° HPBW 0.32° for 2° HPBW

4 Array factor (1) Angle  referred to far field observation point Normalized Array Factor (AF) of a 8-element linear array with spacing d = 2   = 90°  = -90°  = 0° x y z array dxdx dydy Nearest grating lobes at  30°

5 Array factor (2) Non-uniformly spaced array reduces side lobes when d /2 Non-uniform power distribution reduces side lobes but not grating lobes d n = (n/2 +  n )d

6 Single element design (1) Technology giving large bandwidth SSFIP – Strip Slot Foam Inverted Patch antenna Substrate Inverted patch Foam Slot Strip Substrate BW achieved with one patch was as large as 14% and can be improved to 33% with stacked patches. Gain for single element is about 8 dBi. (Reference: J.-F. Zürcher, F. E. Gardiol, “Broadband Patch Antennas”,Artech House,1995)

7 Single element design (2) ADS simulation results SSFIP with fundamental mode: patch size  /2 Z in = 100  Substrates: -RT/Duroid 5870 (for strip and slot layers)  r = 2.33, tan = , h = mm -Foam Rohacell (spacer)  r = 1.07, tan = 0.001, h = 1 mm -Kapton (for patch layer)  r = 3.2, tan = 0.005, h = 0.1 mm

8 Single element design (3) Key results (not optimised) f 0 = 29 GHz BW > 27.6% Gain = 5.2 dBi HPBW = 66°

9 Single element optimisation (1) SSFIP with high-order mode: patch size  3/2 Z in = 50  Modelling by Ansoft Designer

10 Single element optimisation (2) Key results f 0 = 28.5 GHz BW = 10.9% Gain = -5.7 dBi (broadside) HPBW : - Conclusion Not a good solution

11 HPBW  =0° = 40° HPBW  =90° = 90° f 0 = 29.9 GHz Single element optimisation (3) SSFIP with gap-coupled patches: patch size  /2 Asymmetrical radiation pattern

12 Single element optimisation (4) SSFIP with gap-coupled patches: patch size  /2 f 1 = GHz BW = 30.7%

13 Single element optimisation (5) Key results f 1 = GHz BW =30.7% Gain = 9.8 dBi HPBW =0° = 40°, HPBW =90° = 50 ° Conclusion Probably a good solution but need more refinement to improve the gain

14 Radiation of the array + = There should be a way to do better… Element radiation: EM simulationAF: theoretical computation

15 Principle Array of structures which appears to be predominantly inductive to one polarization and predominantly capacitive to the orthogonal polarization. (Ref. L. Young, L. A. Robinson and C. A. Hacking, “Meander-line Polarizer”, IEEE Trans. on Antenna and Propagation, pp , May, 1973) Meander-line polarizer (1) Kapton & meander line Rohacell Layer 1 Layer 2 Layer 3 Layer 4 Advantages High polarization purity compact size at Ka band Low complexity low cost

16 Meander-line polarizer (2) Layer 1 & 4Layer 2 & 3 Zoom

17 Antenna test-bed description Fixed transmitter Antenna Signal generator Mobile platform Pan-tilt unit Antenna & support RF detector Low frequency amplifier PC with DAQ card running tracking algorithm

18 Antenna test-bed signal acquisition In order to see a significant power change, a filtered white noise perturbation is injected, amplitude 5° on the pan and tilt angles. Transmitter attenuation

19 Tracking algorithm description To find an RF signal, the pan-tilt mechanism will follows a spiral trajectory Maximum found using the algorithm To determine the algorithm performances, a trajectory perturbation is added on the pan and tilt angle commands.

20 Pan-Tilt mechanism requirements Pan-Tilt mechanism specifications Payload 1.8 kg Max speed 300°/sec Resolution 0.05° Tilt range 111° Pan range 360° Market survey performed to identify available mechanisms: High-speed pan-tilt unit identified

21 Pan-Tilt mechanism Commercial off-the-shell motor units Algorithm to be developed to provide the tracking error Mechanical mount for antenna support Preliminary tests with horn antenna Final configuration with flat antenna Material needed for the test-bed RF detector and amplifier PC with acquisition card