Wei Ren Ng

A 3-D Luneburg Lens Antenna Fabricated by Polymer Jetting Rapid Prototyping

In this work, we designed, built, and tested a low-gain 20 dBi Luneburg Lens antenna using a rapid prototyping machine as a proof of concept demonstrator. The required continuously varying relative permittivity profile was implemented by changing the size of plastic blocks centered on the junctions of a plastic rod space frame. A 12-cm ( 4λ0 at 10 GHz) diameter lens is designed to work at X-band. The effective permittivity of the unit cell is calculated by effective medium theory and simulated by full-wave finite-element simulations. The fabrication is implemented by a polymer jetting rapid prototyping method. In the measurement, the lens antenna is fed by an X-band waveguide. The measured gain of the antenna at X-band is from 17.3 to 20.3 dB. The measured half-power beam width is from 19° to 12.7° while the side lobes are about 25 dB below the main peak. Good agreement between simulation and experimental results is obtained.

Terahertz electromagnetic crystal waveguide fabricated by polymer jetting rapid prototyping

An all-dielectric THz waveguide has been designed, fabricated and characterized. The design is based on a hollow-core electromagnetic crystal waveguide, and the fabrication is implemented via polymer-jetting rapid prototyping. Measurements of the waveguide power loss factor show good agreement with simulation. As an initial example, a waveguide with propagation loss of 0.03 dB/mm at 105 GHz is demonstrated.

Terahertz Horn Antenna Based on Hollow-Core Electromagnetic Crystal (EMXT) Structure

An all-dielectric terahertz (THz) horn antenna based on hollow-core electromagnetic crystal structure is designed, fabricated and characterized. Simulation shows that the antenna works above 100 GHz, with better than 30 dB return loss and highly directional radiation pattern. Fabrication of the antenna is done using a THz polymer-jetting rapid prototyping technique. Characterization of the antenna is performed using a THz time-domain spectrometer. Measurement results of the far-field radiation patterns show good agreement with simulation results.

An X-band Luneburg Lens antenna fabricated by rapid prototyping technology

In this paper, a 3-D Luneburg Lens has been designed, fabricated and characterized. Refractive index control of the lens is based on the mixing ratio of air voids and a polymer. The 12 cm (4λ0 at 10 GHz) diameter lens is designed to work at X-band. The effective permittivity of the unit cell is estimated by effective medium theory and calculated by the finite-element simulation software Ansoft HFSS. Fabrication is implemented by a polymer jetting rapid prototyping method. In the measurement, the lens antenna is fed by an X-band waveguide. The half-power beam width of the antenna is 14 degrees and no obvious side lobe is found in the measurement above the noise floor.

Direction of arrival estimation using Luneburg lens

In this paper, a 3-D Luneburg Lens is employed for direction finding application. Using the special property of a Luneburg lens that every point on the surface of the Lens is the focal point of a plane wave incident from the opposite side, a number of detectors are mounted around the surface of the lens to estimate the direction of arrival (DOA) of a microwave signal. To demonstrate the proposed direction finding system, a Luneburg lens with five detectors mounted on its surface to receive the signal from −20° to 20° is measured at 5.6 GHz. The initial direction finding results using a correlation algorithm show that the estimated error is smaller than 2° within −15° to 15° incident angles.

Hollow-core electromagnetic band gap (EBG) waveguide fabricated by rapid prototyping for low-loss terahertz guiding

An all-dielectric THz waveguide has been designed, fabricated and characterized. The design is based on electromagnetic band gap (EBG) structures, and the fabrication is implemented with polymer-jetting rapid prototyping method. Measurement results show good consistency with design simulations. As an initial example, a waveguide with low propagation loss of 0.03 dB/mm at 105 GHz is demonstrated.

Broadband electronically beam scanning structure using Luneburg lens

A novel broadband electronically beam scanning structure based on Luneburg lens phased array is investigated in this paper. The radiation elements of the phased array are mounted on the surface of a Luneburg lens. Without amplitude and phase control of the elements, only discrete scanning angles are available. In this paper, beam scanning to arbitrary angle is demonstrated by fully controlling the amplitude and phase. Compare to conventional phased array beam scanning system, the proposed structure has no scan angle coverage limit and has a broadband working frequency. Also, due to the symmetry of Luneburg lens, no beam shape variation would occur during angle scanning. Moreover, this structure requires much less system complexity to achieve a highly directional beam and therefore the cost of this system could be much lower than conventional phased array.

Direct rapid-prototyping fabrication of computer-generated volume holograms in the millimeter-wave and terahertz regime.

Computer-generated volume holograms (CGVHs) are gradient refractive index (GRIN) devices that consist of a superposition of multiple periodic diffraction gratings. Fabrication of these components for the visible range is difficult due to the small length-scale requirements but is more tenable in the terahertz (THz), as the length scales become more practical (≥ 10-5 m). We successfully utilized polymer-based 3D additive rapid-prototyping technology to fabricate, to our knowledge, the worlds first 3D THz CGVH in approximately 50 minutes, using

All-dielectric low-loss terahertz waveguide fabricated by rapid prototyping

12 of consumables. This demonstration suggests that this technique could be extended to fabricate THz volumetric optics with arbitrary electromagnetic profiles.

Terahertz electromagnetic crystal (EMXT) based waveguide and horn antenna

An all-dielectric Terahertz waveguide is designed based on hollow-core photonic crystal fiber. Simulation shows a waveguide transmission loss as low as 0.019 dB/mm near 140 GHz with a working bandwidth of approximately 18 GHz. Several waveguides of identical cross-section and differing lengths have been fabricated using a polymer-jetting rapid prototyping technique. Measurement results from these samples will also be reported.