Eduardo A. Rojas-Nastrucci

A 2.45 GHz Phased Array Antenna Unit Cell Fabricated Using 3-D Multi-Layer Direct Digital Manufacturing

This paper reports on the design, fabrication and characterization of a 3-D printed RF front end for a 2.45 GHz phased array unit cell. The printed unit cell, which includes a circularly-polarized dipole antenna, a miniaturized capacitive-loaded open-loop resonator filter and a 4-bit phase shifter, is fabricated using a direct digital manufacturing (DDM) approach that integrates fused deposition of thermoplastic substrates with micro-dispensing for deposition of conductive traces. The individual components are combined in a passive phased array antenna unit cell comprised of seven stacked substrate layers with seven conductor layers. The measured return loss of the unit cell is > 12 dB across the 2.45 GHz ISM band and the measured gain is -11 dBi including all components. Experimental and simulation-based characterization is performed to investigate electrical properties of as-printed materials, in particular the inhomogeneity of printed thick-film conductors and substrate surface roughness. The results demonstrate the strong potential for fully-printed RF front ends for light weight, low cost, conformal and readily customized applications.

Meshed rectangular waveguide for high power, low loss and reduced weight applications

Additive manufacturing technologies are increasingly being demonstrated to be useful for microwave circuits, showing improved performance in multiple cases. In this work, a meshed rectangular waveguide structure is presented as an option for high power, low loss, but also reduced weight applications. A set of meshed Ku band waveguides was fabricated using binder jetting 3D printing technology showing that the weight can be reduced by 22% with an increase in loss of only 5%, from 0.019 dB/cm for the solid part to 0.020 dB/cm average across the band with the meshed design. Further weight reduction is possible if higher loss is allowed. To demonstrate the concept, a comparison is made between non-meshed and meshed waveguide 4 pole Chebyshev filters.

Simultaneous RF electrical conductivity and topography mapping of smooth and rough conductive traces using microwave microscopy to identify localized variations

This paper presents a near-field microwave microscope (NFMM) capable of simultaneous non-contact imaging of electrical conductivity (σ) and topography across the surface of microwave circuits without the need of a distance sensor. The microscope monitors the resonant frequency of a dielectric resonator-based microwave probe to acquire the surface topography, and the quality factor to determine the electrical conductivity. Conductivity and topography images of copper foil reveal an average conductivity of about 4e7 S/m and an arithmetic roughness of 0.2μm, respectively. Measured average roughness and conductivity of CB028 silver paste are 0.7e6 S/m and 1.1μm, respectively. The NFMM data reveal significant and correlated variation in surface features and conductivity across the surface of the printed CB028 films. The topography and conductivity images obtained demonstrate that the NFMM can be employed for localized characterization of smooth and rough conductive materials used in microwave devices.

3D tag with improved read range for UHF RFID applications using Additive Manufacturing

In this paper a 3D tag antenna geometry is proposed for UHF RFID systems. Two antennas were built over different dielectric materials with similar properties using both Direct Digital Manufacturing and traditional photolithography and copper etching. The impedance matching between the antenna arms and the passive RFID integrated circuit was accomplished with the H-slot matching technique with a simulated 10 dB return loss bandwidth that allows the tag to operate in the American and European ISM RFID bands of 902-928 MHz and 864-868 MHz, respectively. The antennas were compared to commercially available tags in size, weight and read distance, showing a read range improvement of 136% (for a threshold power of 30 dBm) with respect to the best tag tested. A reduction in length of 78 % with respect to a planar 2D model was also achieved. The radiation patterns were measured, showing an omni-directional beam pattern.

Ka-band characterization and RF design of Acrynolitrile Butadiene Styrene (ABS)

This paper presents high frequency characterization data of the commonly used 3D-printing material Acrynolitrile Butadiene Styrene (ABS). A cavity resonator was used to characterize the material around 30 GHz. The extrapolated data was used to design a microstrip patch antenna around 25 GHz. The antenna was fabricated using a combination of fused deposition modeling (FDM) and direct print additive manufacturing (DPAM). Good agreement was found between simulated and measured results. These are the first known results of ABS characterization and a digitally-manufactured antenna to be reported in this frequency range.

Propagation Characteristics and Modeling of Meshed Ground Coplanar Waveguide

Additive manufacturing (AM) is increasingly being used for the realization of microwave circuits. In this method of fabrication, conductive patterns can be printed directly without the need of a mask or subtractive techniques such as etching a metalized substrate surface. For most AM processes, the materials used for the conductive layer are the most expensive ones; hence, there is value in minimizing the conductor surface area used in a circuit. In this paper, the approach of meshed ground coplanar waveguide (MGCPW) is analyzed by simulating, fabricating, and measuring a broad set of MG geometry sizes. Furthermore, a physical-mathematical model is presented, which predicts the characteristic impedance and the capacitance per unit length of MGCPW with less than 5.4% error compared with simulated data. A set of filters is designed and fabricated in order to demonstrate the approach. The main parameter affected by meshing the ground plane is the attenuation constant of the waveguide. It is shown that 50% mesh density in the ground plane of an MGCPW line can be used with less than 25% increase in the loss. In contrast, the loss of finite ground coplanar waveguide can increase by as much as 108% when the ground size is reduced by the same factor (50%). Both 3-D printing (microdispensing) and traditional printed circuit board manufacturing are used in this paper, and most of the propagation characterization is performed at 4 GHz.

A multi-material 3D printing approach for conformai microwave antennas

In this paper a new approach for implementing conformal antennas using direct digital manufacturing is presented. The new approach is based on fused deposition printing of a 150 micron-thick thermoplastic layer on top of Kapton tape forming a smooth, thin and flexible substrate. The antenna metallization is then printed on the smooth face of the flexible substrate using micro-dispensing, and the substrate is subsequently adhered to a 3D form. This approach represents a simple and versatile method for building microwave components as 3D structures. A 6 GHz 3D dipole is presented as an example to validate the fabrication approach. An acrylonitrile butadiene styrene (ABS) substrate (relative permittivity of 2.7 and a loss tangent of 0.008) and Dupont CB028 silver paste are used to fabricate the dipole antenna.

Laser enhanced direct print additive manufacturing for mm-wave components and packaging

Direct print additive manufacturing (DPAM) is an additive manufacturing technique that combines fused deposition modeling with micro-dispensing. As a multimaterial 3D printing method it has proven to be effective for fabricating printed electronics that operate in the microwave frequency range. This paper discusses the addition of picosecond laser processing to the DPAM process, and the enhancements to high-frequency performance and design capability that are made possible. The use of laser-enhanced DPAM for 3D fabrication of transmission lines, passive components and packaging is discussed.

UHF RFID Tags for On-/Off-Metal Applications Fabricated Using Additive Manufacturing

Radio frequency identification (RFID) tag design is generally focused specifically on either off-metal or on-metal configurations. In this letter, passive 2-D and 3-D RFID tags are presented, which perform similarly in both configurations. The tags operate in the industrial, scientific, and medical (ISM) RFID UHF bands (864–868 MHz and 902–928 MHz). A matching loop consisting of two parallel stubs to ground is used for impedance matching to a passive integrated circuit, which has −18-dBm sensitivity. A planar 2-D tag with a footprint of 13126.5 mm2 is first introduced, showing a simulated gain of approximately 3 dBi and a measured read range of 10 m (for 31-dBm transmit power from the reader) in both on-metal and off-metal conditions. The tag is miniaturized into a 3-D geometry with a footprint of 2524.25 mm2 (520% reduction) and achieves the same broadside simulated on-metal gain. The antennas are fabricated using a 3-D printed acrylonitrile butadiene styrene. The conductive layer is realized by microdispensing silver paste (Dupont CB028). A meshed ground configuration is explored in order to accomplish a 50% conductive paste reduction without disrupting the performance. The proposed tags are compared to commercially available tags as well as previously published tags in terms of read range and size. The tags in this letter present an improvement in terms of read range, gain, and area with respect to previous designs covering the ISM RFID UHF bands. Moreover, the performance of these tags is maintained in on- and off-metal conditions, achieving comparable performance and a reduction in volume of 11 482% with respect to the best tag reported.

Metallic 3D printed Ka-band pyramidal horn using binder jetting

Metallic RF-Microwave components fabricated using additive manufacturing are continually being demonstrated as viable solutions in terms of cost and performance when compared to components fabricated by traditional methods such as machining. In this work, binder jetting is used to fabricate a Ka-Band pyramidal horn antenna, as a test structure to evaluate the performance of this metal 3D printing technology. The measured parameters (S11 and radiation pattern) have good agreement with the simulated ones. The measured return loss is >20 dB across the band. The simulated antenna gain is 8.43 dBi (at 26.5 GHz), and simulations show that the performance degradation due to the finite conductivity and surface roughness is less than 0.1 dBi.