Antenna patterns of the simulated system steering from 0 to +90 degrees in 3-degree increments are shown in Figure 4. Each set of patterns for a given target steering angle in the overlaid chart has a unique phase and amplitude profile for the radiating elements. Since the lens is symmetrical, similar performance is expected from 0 to -90 degrees. The drop in directivity from boresight to 90 degrees is approximately 2 dBi, while flat panel phased arrays, alone, typically drop around 3 dBi from boresight to 60 degrees.
Figure 4 Simulated antenna patterns for 30 beam steering states between 0 and +90 degrees, overlaid and shown at 37, 38.5 and 40 GHz for each state.
Manufacturing is accomplished relatively easily with a digital manufacturing process like 3D-printing. With a varying density lattice that has small enough features relative to the operating wavelength, the component behaves like one graded dielectric constant structure as designed in simulation. There is little change in manufacturing complexity with alterations in design, and many different iterations can be made and tested quickly. In combination with Rogers Corporation’s new RadixTM 3D-printable dielectric materials, designers can take advantage of the most scalable, high-resolution process to realize these components. A rendering of the lens design as a printable part is shown in Figure 5.
Figure 5 Rendering of the simulated phased array GRIN lens as a 3D printable component in nTopology software.
To verify that the complete flexibility of GRIN and 3D printing is required, simulations are done on an approximated version of the design, where the dielectric constant values are approximated into three “buckets” used within the overall structure versus an optimized design with a more graded transition. The designs and resulting antenna patterns are shown in Figures 6 and 7 respectively. The near continuous gradient is likely needed to maximize performance, and a process like 3D printing is one of the few processes that can produce it.
Figure 6 Optimized phased array lens design (green outline) versus an approximated design (orange outline).
Figure 7 Simulated antenna pattern of a target beam peak at +90 degrees for the optimized (green) and approximated design (orange).
TAKING A CLOSER LOOK
To see how the high steering angles are achieved, a closer look at the antenna element amplitude and phase profile is needed. In addition to large phase shifting between adjacent elements, a significant amplitude tapering is implemented. Specifically, for the 90-degree steering case, the elements on the same side as the formed beam are not illuminated while the center and opposite elements are illuminated with a slight amplitude taper. A hybrid of switching and phase shifting helps achieve the steering performance in its current embodiment due to refraction within the lens mandated by the dielectric gradient. Notice that the effective aperture for this 90 degree beam is equal to the height of the lens. An illustration of these points can be seen in Figure 8. One drawback of the proposed solution is a reduced effective isotropic radiated power by using only a given portion of the flat array patches.
Figure 8 Antenna port layout (a) with relative element amplitudes to achieve 90-degree steering (b) and an illustration of the refraction effect within the dielectric lens (c).
FUTURE POSSIBILITIES
With new dielectric 3D printing manufacturing technology, exotic GRIN parts that enhance the figure-of-merits of any antenna system can be realized. The combination of this technology with new computational tools allows designers the flexibility to no longer be constrained to classical lens designs from literature, like the Luneburg Lens. In fact, many variations and alterations of the simulated system shown here could be designed and produced for different performance goals.
While traditional lens antenna designs often have their merits compared with phased array systems, as seen from this design, there are opportunities to use lenses synergistically with phased array antennas to enhance certain requirements such as gain over angle performance.
ACKNOWLEDGMENTS
We thank Ben Wilmhoff and team at BluFlux for radiation pattern measurements and Stephen O’Connor at Rogers Corporation for material formulation. We also thank Shawn Williams, Karl Sprentall and Bob Daigle at Rogers Corporation for valuable discussions and feedback.
References
- B. Sadhu and L. Rexberg, 2019, Phased Arrays for 5G Millimeter-Wave Communications, G. Hueber and A. M. Niknejad (Eds.), Millimeter-Wave Circuits for 5G and Radar, pp. 243- 272, Cambridge University Press.
- B. Nevius and P. Freud, “Enabling Scalable + Affordable SATCOM Solutions,” SatMagazine, September 2020.
- M. Ascione, G. Bernardi, A. Buonanno, M. D'Urso, M. Felaco, M. G. Labate, G. Prisco and P. Vinetti, “Simultaneous Beams in Large Phased Radar Arrays,” IEEE International Symposium on Phased Array Systems and Technology, October 2013.
- “Phased Array Antennas,” Microwaves101, Web: www.microwaves101.com/encyclopedias/phased-array-antennas.
