LTCC transmit array antennas for the D band

Transmit arrays are two-dimensional surface antennas that shape and direct incident waves through locally defined phase steps. Operating in the D band (110–170 GHz) requires extremely small structural dimensions and precise positional alignment, placing the highest demands on manufacturing. Low Temperature Cofired Ceramics (LTCC) technology offers a robust, dimensionally stable, non-dispersive, and monolithic platform that enables high-precision implementation with via-free transmitter array architectures with three metal layers. Two orthogonal polarization gratings on the top and bottom sides and a central embedded rotator layer with subwavelength unit cells (resolution below the wavelength) were printed onto the LTCC tapes. The LTCC components are also characterized by very low thickness variation and minimal misalignment between layers, which minimizes frequency shifts and pattern distortions. Controlled shrinkage and tightly tolerated conductor geometries ensure the dimensional accuracy of the rotary structures and congruent superposition with the polarization gratings across the entire aperture. Quality assurance and analytics, such as X-ray analyses, confirm the precise layer fit, in particular the congruent superimposition of the polarization gratings on the rotator structures across the entire aperture. The rotator layouts show dimensionally stable contours without warping or compression artifacts after lamination and sintering at 850 °C.

The transmit arrays achieve approximately 18 % bandwidth over the frequency range of 140–167.5 GHz, an insertion loss better than ~1 dB, a cross polarization of < −20 dB, and good matching (reflection < −8 dB). Measurements in the absorber room show peak gains of up to 34.5 dBi at θ=0° alignment, maximum aperture efficiency of up to 56 %, low side lobe levels (≤ –19 dB), and stable dual-beam steering at ± 30° with low pointing error deviation. These results demonstrate the suitability of LTCC technology for subwavelength unit cells and broadband beamforming in the D band.

• Manufacture of LTCC transmit arrays according to customer layout specifications, including design review prior to manufacture
• Development and qualification of process-compatible screens (including high-resolution “trampoline” screens) and determination of printing parameters for reproducible fine structures
• Complete service from stacking, laminating, sintering, laser processing, and sawing with documented quality assurance
• Prototype, pilot, and small series production; consulting on costs and scaling
• Provision of material and microstrip line substrates for simulation verification; integration of external RF measurement partners on request

• Multipanel manufacturing (LTCC 4“ x 4” or 6“ x 6”, unsintered)
• LTCC type A6M-E with ɛ_r=5.8 and tan δ=0.001 at 20 GHz
• 6 single layers (LTCC: 127 µm and 256 µm, unsintered)
• High-resolution screen printing with up to 50 µm print resolution
• ± 5 µm layer alignment with semi-automatic stackers

This work was carried out in close collaboration with CEA-LETI (France), who were responsible for developing the component layout and measurements.

This measure is co-financed with tax revenue based on the budget approved by the Saxon State Parliament. The ULTCC solutions are being developed by the ULTCC6G_EPac M.ERA.NET consortium with support from the Saxon State Ministry of Science and the Arts (SMWK). Project number: 100574063