1. A Multilayered Broadband Reflect-Array Manuel Romero

2. Outline Introduction and Project Goals Ideal Reflect-Array Cell Proposed Cell Experimental Results Conclusions

3. Introduction – Reflect-Arrays Reflect-arrays alter the scattered EM field to form a radiation maximum in a desired direction The reflection phase of the individual array elements is modified to form the desired scattered beam pattern A phase agility of 360 degrees per array element allows for a beam maximum at any angle Many applications in radar and communication systems.... Δφ2ΔφNΔφ d d Δφ 2Δφ NΔφ

4. Introduction – Microstrip Reflect-Arrays Microstrip reflect-arrays are low cost, low loss and low profile Potential substitutes for parabolic reflector antennas used in terrestrial and satellite communication systems. Previous work has focused on the patch antenna as the main array element Vary patch size, stub length and tilt angle to modify the reflection phase. The resonant nature results in poor phase agility and bandwidth

5. Project Goals To design a reflect-array at a center frequency of 10GHz Non-resonant structure unit cell  Linear reflection phase as function of frequency Fully printable structure  low cost  low profile  low loss Frequency Reflection Phase, Φ Typical Phase of Resonator Non-resonant Phase

6. Ideal Reflect-Array Cell Sample phase characteristic of each cell at f o  These samples create the phase gradient across the surface Large bandwidth if ΔΦ constant over frequency Linear phase profile desired  Matching helps achieve linear reflection phase cell at (N-1)Δx Position Reflection Phase 2Δx2Δx ΔxΔx (N-1)Δx NΔxNΔx Reflection Phase Frequency ΔΦ fofo cell at Δx cell at 2Δx cell at NΔx

7. Final Surface Unit Cell and Equivalent Circuit Center frequency of 10GHz Vary radii (r 1 and r 2 ) to obtain required phase Achieve high phase agility by increasing mismatch with free space Equivalent Circuit 2 βh, Z TL Input βh, Z TL TL βh, Z TL TL L2L2 L1L1 Dielectric (ε r =10) metal ground plane r1r1 r2r2 Input 2h d Chosen Structure d=5mm h h=1.9mm Three layers provide sufficient phase agility > 360° Use minimum mismatch for required phase agility

8. Measurements Measurements agree with theory High side lobes of -5dB due to phase errors in fabrication Achieved small error of ± 4° in maximum beam direction within 20% bandwidth around 10GHz

9. Conclusions Radiation beam direction controlled by reflection phase Linear phase gradient equivalent to slanted metal sheet  Not limited to linear phase gradient Designed unit cell at 10GHz cell with phase agility > 360° Phase agility - by increasing impedance mismatch with free space Smaller unit cell possible at the expense of phase agility  Thicker dielectric can offset the loss in phase agility for smaller cells Designed, built and tested a reflect-array at 10GHz with proposed cell Works for both TE and TM polarizations at various incidence angles Achieved small beam direction error over 20% bandwidth