The implementation of a low-profile wide-angle moderate-gain mechanical beam-scanning antenna in the satellite Ka-band, required:
- The development of an in-plane transmit-array translation concept for beam scanning;
- Definition of an appropriate planar transmit-array and its design principles
- Finding a way to lower F/D without sacrificing significantly the scanning performance
- Finding the appropriate dual-band phase delay cell configuration, along with an efficient cell-populating strategy for the transmit-array
- Developing a viable simulation strategy compatible with the large size and complexity of the electromagnetic numerical model
- Developing a viable antenna fabrication, compatible with modest accuracy requirements to lower the production cost
- Demonstrating all the concept feasibility with fabricated prototypes and measurements in the Ka-band.
The proposed solution requires modest operation volume, it is light-weight. Very low-power motors are enough to drive the two movements required for steering. The electric performance is comparable bulkier structures based on reflectors. At the same time, the developed solution allows very low production costs for mass-market deployment.
Circular polarization, dual-band operation at 20 and 30 GHz, and elevation scanning range of [15º - 50º] with simultaneous mechanical 360º azimuth scanning. Elevation scan is obtained by in-plane translation of the lens in front of the primary feed and the 360° azimuth scan is obtained by the lens rotation.
The antenna is composed of four elements:
- The primary feed - a CP patch antenna with near 7 dBi gain;
- An intermediate small planar lens to enhance the patch gain and move the phase centre to a lower plane to produce a virtual focus at reduced F/D;
- A passive dual-band planar transmit-array, compatible with circular polarization.
- A light support tructure capable of in-plane translation of the transmit-array in front of the feed with simultaneous in-plane rotation in azimuth. Alternatively, the feed can translate linearly below the transmit-array while the whole structure rotates in azimuth. The latter reduces considerably the operation volume, which becomes a cylinder with diameter equal to the transmit-array diagonal and height F.
Four different lens designs were developed and tested during this project. A full-size 40 dBi lens was evaluated numerically. Due to practical manufacturing limitations in our lab facilities, the experimental prototypes are restricted to lower gains. The first fabricated prototype was a single band 30 dBi lens fed by a horn antenna or by small feed lens placed in front of a planar patch. Additionally, two dual band 30 dBi gain lens with two different phase corrections were also prototyped.
- Development of a single band transmit-array, with moderate gain (30 dBi) scanning beams, obtained by in-plane translation.
- Design of a feeding system to reduce the overall antenna height using a small lens in front of a primary source
- Prototyping and testing of the proposed single band antenna composed
- Devising of a set of phase-delay dual band unit cells to operate at the Ka-band
- Design of two dual band transmit-array with moderate gains
- Development of the designated bifocal lens design, suitable for a high gain antenna (40 dBi);
- Fabrication and experimental evaluation of the final lens prototype – a dual band transmit array with moderate gain (30 dBi)
The project is completed. The main achievement of the project was the demonstration by simulation and experiment of the feasibility of a fully mechanical beam steering antenna for satellite-on-the-move terminals in the Ka-band, based on a reasonably thin dual-band planar metamaterial lens with in-plane translations above the primary feed.
A couple of other achievements concurred for the above main result:
- Design guidelines for designing dual-band transmit-arrays
- Bifocal lens design for high gain transmit-arrays
- Concept of virtual focus to reduce antenna height
- Faster simulation methods for large transmit-arrays
- Universal method for design of dual-band cells
- Novel dual-band cell with high transmission