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In this article, the first W-band laser-enhanced direct print additive manufacturing (LE-DPAM) monolithic microwave integrated circuit (MMIC) chip-carrier assembly is demonstrated. Acrylonitrile butadiene styrene (ABS) is 3-D printed using fused deposition modeling to form substrate layers, and DuPont CB028 conductive paste is microdispensed to form transmission lines and on-chip interconnects. These processes are combined with picosecond-pulsed laser micromachining using two wavelengths in the infrared (IR) (1064 nm) and ultraviolet (UV) (355 nm) regions to create features as small as 5 μm for printed layers with a high 6:1 aspect ratio and to improve the effective conductivity of the printed traces. The laser machining process is also adopted to fabricate vertical interconnections (vias) over multilayer substrates while also suppressing higher order modes. Four different dc-to-110-GHz transmission-line configurations have been investigated, including a coplanar waveguide (CPW), a grounded CPW (GCPW), a novel multilayer CPW-microstrip transition, and a GCPW-microstrip transition with attenuation 10 dB. This process is extended to embed a W-band MMIC low-noise amplifier (LNA) die inside a laser-machined cavity with a carrier-chip gap less than 5 μm. Also, RF/dc interconnects were microdispensed to connect the transmission lines on the substrate and MMIC die. Chip-to-board transition loss as low as 0.03 dB per interconnect with return loss >7.5 dB was achieved with performance that is comparable to that of the probed MMIC die. The MMIC chip-carrier assembly provides a low-cost, versatile yet simple on-demand laser-enhanced additive manufacturing process to package a wideband MMIC die using a single automated LE-DPAM platform.

This article presents a comprehensive study of the design and performance of a multilayer dielectric rod waveguide (MDRW) with a rectangular cross section. The design is comprised of a high permittivity core encased by a low permittivity cladding. A mathematical model is proposed to predict the fundamental mode cutoff frequency in terms of the core dimensions and the core and cladding permittivity. The model is useful for design purposes and it offers an excellent match to full-wave electromagnetic (EM) simulation results. The MDRW performance is measured for the extended Ku -band (10–18 GHz) considering straight and bent waveguides with different radius of curvatures. The particular multilayer configuration shows a 16.7% and 24% extension of the 1 dB low-band cutoff frequency for a $10\times10$ mm2 and $20\times20$ mm2 cladding area, respectively, when compared to a single layer dielectric rod waveguide (DRW) design of the same core dimensions. MDRW bends also exhibit a significant reduction of the 1 dB low-band cutoff frequency from 20% to 40% when compared to single-layer designs, for the different radius of curvature bends.

The performance of additively manufactured microwave passive elements and interconnects continues to improve as better materials, and process techniques are developed. In this paper, laser-enhanced direct print additive manufacturing (LE-DPAM) is used to fabricate capacitors and inductors for coplanar waveguide (CPW) circuits. Acrylonitrile butadiene styrene is used as the dielectric that is printed using fused deposition modeling, and DuPont CB028 conductive paste is deposited using microdispensing. These two techniques are combined with picosecond-pulsed laser machining to achieve $\simeq 12$ - $\mu \text{m}$ slots on printed conductors, producing aspect ratios greater than 2:1. The same laser is used to fabricate vertical interconnections that allow for the fabrication of multilayer inductors. Inductances in the range of 0.4–3 nH are achieved, with a maximum quality factor of 21, selfresonance frequencies up to 88 GHz, and an inductance per unit of area of 5.3 nH/mm2. Interdigital capacitors in the range of 0.05–0.5 pF are fabricated, having a maximum quality factor of 1000, a capacitance per unit area of 1 pF/mm2, and selfresonances up to 120 GHz. All the components are made on the center line of a CPW that is 836- $\mu \text{m}$ wide. The results show that LE-DPAM enables the fabrication of compact passive circuits that can be easily interconnected with MMIC dies, which at the same time can be manufactured as part of a larger component. This enables the fabrication of structural electronics that are functional into the millimeter-wave frequency range. Bounds on the inductances and capacitances per unit area are related to material and geometry limitations.

To address the challenging needs of small size, wide bandwidth, and low-frequency applicability, a novel phase shifter implementation is introduced that utilizes tunable active differential inductors within all-pass networks. The inductor tuning is used to achieve phase shifts up to 180°. A switchable active balanced-to-unbalanced transition (balun) circuit is included in front of the all-pass network to complement its phase shift capability by another 180°. In addition, the all-pass network is followed by a variable-gain amplifier to correct for gain variations among the phase shifting states and act as an output buffer. Although active inductors have previously been used in the design of various components, to the best of our knowledge this is the first time that they have been used in an all-pass phase shifter. The approach is demonstrated with an on-chip design and implementation exhibiting wideband performance for S- and L-band applications by utilizing the 0.5- $\mu \text{m}$ TriQuint pHEMT GaAs monolithic microwave integrated circuits (MMIC) process. Specifically, the presented phase shifter $1 \times 3.95~ \text {mm}^{2}$ die area and operates within the 1.5–3-GHz band (i.e., 2:1 bandwidth) with 10-dB gain, less than 1.5-dB root-mean-square (rms) gain error and less than 9° rms phase error. Comparison with the state-of-the-art MMIC phase shifters operating in S- and L-bands demonstrates that the presented phase shifter exhibits a remarkable bandwidth performance from a very compact footprint with low-power consumption. Consequently, it presents an alternative for the implementation of wideband phase shifters where all-passive implementations will consume expensive die real estate.

Microdispensing of thick-film conductive paste has been demonstrated as a viable approach for manufacturing microwave planar transmission lines. However, the performance and upper frequency range of these lines is limited by the cross-sectional shape and electrical conductivity of the printed paste, as well as the achievable minimum feature size which is typically around $100~\mu \text{m}$ . In this paper, a picosecond Nd:YAG laser is used to machine slots in a 20–25- $\mu \text{m}$ -thick layer of silver paste (Dupont CB028) that is microdispensed on a Rogers RT5870 substrate, producing coplanar waveguide (CPW) transmission lines with 16– $20~\mu \text{m}$ -wide slots. It is shown that the laser solidifies an about 2- $\mu \text{m}$ -wide region of the edges of the slots, thus significantly increasing the effective conductivity of the film and improving the attenuation constant of the lines. The extracted attenuation constant at 20 GHz for laser machined CB028 is 0.74 dB/cm. CPW resonators and filters show that the effective conductivity is in the range from 10 to 30 MS/m, which represents a $100\times $ improvement when compared to the values obtained with the exclusive use of microdispensing. This paper demonstrates that a hybrid approach of additive manufacturing and laser machining enables the fabrication of higher frequency circuits (up to at least 40 GHz) with improved performance.

The performance of additive manufactured (AM) RF circuits and antennas is continuously improving, and in some cases these AM components are comparable to state-of-the-art circuits made with traditional manufacturing techniques. Medium to high-power waveguides made with AM methods such as copper-plated plastics, selective laser melting (SLM), and copper additive manufacturing (3-D CAM) have shown good performance up to terahertz frequencies. In this paper, binder jetting (BJ) metal printing is characterized using electron beam microscopy [scanning electron microscopy (SEM)] and energy dispersive spectroscopy. The RF performance of the 3-D-printed circuits is benchmarked with Ka-band cavity resonators, waveguide sections, and a filter. An unloaded resonator $Q$ of 616 is achieved, and the average attenuation of the WR-28 waveguide section is 4.3 dB/m. The BJ technology is tested with a meshed parabolic reflector antenna, where the illuminating horn, waveguide feed, and a filter are printed in a single piece. The antenna shows a peak gain of 24.56 dBi at 35 GHz.

A new kind of high permittivity (high- $k$ ) and low-loss composite material for fused deposition modeling (FDM) technology based on a cyclo-olefin polymer (COP) thermoplastic matrix embedded with sintered ceramic fillers was developed and characterized up to $ku$ -band. FDM printed samples made of 30 vol.% COP-MgCaTiO2 composites, with filler particles sintered at 1200 °C, show a relative permittivity ( $\varepsilon _{r}$ ) of 4.82 and a loss tangent (tan $\delta$ ) below 0.0018. Meanwhile, 3-D-printed samples composed of 25 vol.% COP-Ba0.55Sr0.45 TiO3 with particles sintered at 1340 °C exhibit a $\varepsilon _{r}$ of 4.92 and a tan $\delta$ lower than 0.0114. Also, 30 vol.% COP-TiO2 specimens with filler particles sintered at 1200 °C exhibit a $\varepsilon _{r}$ of 4.78 and a low tan $\delta$ lower than 0.0012, whereas acrylonitrile butadiene styrene-Ba0.55Sr0.45TiO3 specimens with a 6% volume fraction loading of microparticle fillers sintered at 1340 °C have demonstrated a $\varepsilon _{r}$ of 3.98 and a tan $\delta$ less than 0.0086. Edge-fed microstrip patch antennas operating at 17 GHz were fabricated by a direct digital manufacturing (DDM) approach that combines FDM of electromagnetic composites and microdispensing for deposition of conductive traces and compared with reference designs implemented using commercial microwave laminates regarding antenna size and performance. Evidently, the newly developed ceramic-thermoplastic composites are well suited for microwave device applications up to $Ku$ -band and can be adapted to 3-D printing technologies.

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.

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.

A compact 3-D dual-channel transceiver for passive wireless sensor node design is described herein. The transceiver contains two harmonic repeaters, one to be connected to a sensor and one to provide a reference signal for remote channel calibration and node identification (ID). Each repeater consists of a diode-based frequency doubler and conjugate-matched receive and transmit meandered monopole antennas. The sensing repeater operates by receiving a 2.4-GHz signal and reradiating a modulated 4.8-GHz return signal. The reference and sensing repeaters are optimized for RF input power level ranges from $-{\hbox{30}}$ to $-{\hbox{20 dBm}}$ with zero dc power. The diagonal of the transceiver measures 0.25 $\lambda $ at the fundamental frequency of 2.4 GHz and its measured conversion gain (CG) is $-{\hbox {12.4 dB}}$ with a 2% 3-dB CG bandwidth at $-{\hbox{20-dBm}}$ input power. With this performance, the communication range using an interrogator with a 2-W effective isotropic radiated power is $> {\hbox{40 m}}$ in a free-space environment. To the best of the authors' knowledge, the presented transceiver is the first completely passive design with built-in passive remote channel calibration and ID capability. The performance and size of the proposed design compare well with previously published passive single-channel harmonic repeaters.

A high-efficiency 3-D harmonic repeater for narrow band, wireless sensing applications is described herein. This repeater consists of a diode doubler and conjugate-matched 3-D receive and transmit antennas. The antennas are designed on the surface of a cube in part to provide a convenient volume for packaging the sensor electronics. The device operates by receiving a 2.4-GHz signal and re-radiating a 4.8-GHz signal and has been optimized for an RF input power level between - 30 and -20 dBm with zero dc power. The design enables the return signal to be readily modulated with very low ( ; 50 m in a free space environment. To the best of the authors' knowledge, the presented harmonic repeater has the best overall performance among previously published designs, in terms of conversion gain, communication range, and occupied electrical volume. A new approach for remote calibration of passive sensors using orthogonal polarization of the interrogation signal is also proposed in this paper.

Magneto-dielectric polymer nanocomposites are investigated as a new class of functional materials well suited for RF and microwave device applications. Magnetite (Fe3O4) nanoparticles are homogeneously dispersed in a polymer matrix, which exhibits low losses at microwave frequencies. The monodispersion of the magnetic nanoparticles, with sub-10-nm diameters and tight size distribution, enhances the microwave properties of the engineered composite material by increasing the relative permeability and relative permittivity. Moreover, complex permeability and permittivity of the nanocomposite material can be tuned by an externally applied dc magnetic field with a strength that is achievable with commercial permanent magnets. Multilayered microstrip test fixtures and preexisting measurement techniques were conjointly implemented to extract the microwave properties of the nanocomposite material in the frequency range between 1-6 GHz. The measured data revealed tunability of 5.5% in the permittivity, 37% in the permeability, and more than 100× reduction in the loss tangent at specific frequencies under externally applied magnetic fields.

In this study, a coupled-line coupler was evaluated for its potential to shape sub-nanosecond ultra-wideband (UWB) pulses. The coupler was shown to exhibit a natural tendency to differentiate sub-nanosecond pulses, owing to its bandpass nature. Next, a Schottky detector diode was applied to confirm that the small parasitic reactance in the coupler gives rise to the differentiation behavior. The unconventional application of a coupler and Schottky diode towards signal differentiation culminated in the development of a novel UWB generator that simultaneously produces: a square waveform that has a 20%-80% rise time of 850 ps, a Gaussian waveform that has a pulse duration of 100 ps, and a monocycle waveform that has a 80 ps rise time between its peaks. These waveforms were obtained by taking advantage of the dc isolation of the coupled line structure and using step recovery diodes to compress the edges of a 14 MHz sinusoidal source. The resulting multiport circuit for simultaneous shaping of sub-nanosecond pulses (MCS3P) showed good agreement between measured and simulated results.

A true-time-delay multibit microelectromechanical systems (MEMS) phase-shifter topology based on impedance-matched slow-wave coplanar-waveguide sections on a 500-mum-thick quartz substrate is presented. A semilumped model for the unit cell is derived and its equivalent-circuit parameters are extracted from measurement and electromagnetic simulation data. This unit cell model can be cascaded to accurately predict N-section phase-shifter performance. Experimental data for a 4.6-mm-long 4-bit device shows a maximum phase error of 5.5deg and S11 less than -21 dB from 1 to 50 GHz with worst case S21 less than -1.2 dB. In a second design, the slow-wave phase shifter was additionally loaded with MEMS capacitors to result in a phase shift of 257deg/dB at 50 GHz, while keeping S11 below -19 dB (with S21

This paper presents a 10-GHz cross-coupled bandpass filter integrated onto low-resistivity silicon. The filter is fabricated on a quartz substrate and then mounted onto the silicon using benzocyclobutene and inverted microstrip interconnects. The approach enables the integration of low-loss distributed microwave components onto CMOS-grade Si substrates while occupying a small effective footprint on the silicon. Experimental and theoretical results are given for 10-GHz filters integrated onto a 10-/spl Omega//spl middot/cm silicon substrate.

In this paper, a substrate-dependent lumped-element model for ceramic multilayer capacitors is presented. The height and dielectric constant of a substrate have a significant impact on the frequency response of a chip capacitor, and these effects cannot be treated independently from the capacitor model. Rather, the equivalent-circuit parameters in the model must be made to vary in accordance with changes in the substrate. The model presented in this paper is suitable for microstrip-mounted components, and has been applied up to 10 GHz for values from 0.5 pF to 0.47 /spl mu/F, and for FR-4 substrates ranging in height from 5 to 62 mil. The modeling and extraction procedure is demonstrated for 0805- and 1206-style capacitors.

This paper describes a systematic study of coplanar waveguide discontinuities that are requisite components of high-frequency distribution networks. The specific geometries addressed are air bridges, right-angle bends, tee junctions, and Wilkinson dividers. Relative to typical monolithic-microwave integrated-circuit designs, the components studied herein are electrically large in order to minimize signal attenuation. The large size leads to pronounced parasitic effects, and the emphasis of this study was to optimize the electrical performance using simple compensation techniques. The optimization methods are developed using full-wave simulation and equivalent-circuit modeling, and are verified experimentally up to 60 GHz. Part II of this paper describes the implementation and packaging of the components to realize a three-dimensional W-band distribution network.

This paper describes a new technique for the design of edge-coupled coplanar waveguide (CPW) bandpass filters at microwave and millimeter-wave frequencies. The topology consists of coupled-slot pairs that are symmetric about the center of the CPW line. By applying duality and symmetry, a design methodology is developed that follows the well-known coupled-strip approach. In order to provide filter design guidelines, a spectral domain integral equation analysis was used to characterize coupled slots on silicon with a range of geometrical parameters, through which a series of design curves were generated. Experimental results are given for 10-GHz filters printed on high-resistivity silicon, with bandwidths from 5% to 20%. It is shown how the manner of connecting filter sections can influence the frequency response.

This paper describes the implementation and packaging of the components, described in Part I of this paper, to realize a three-dimensional W-band distribution network.

In this paper, the finite-difference time-domain (FDTD) method is used to calculate the propagation characteristics of cylindrical transmission lines. An efficient two-dimensional FDTD algorithm is developed by projecting the three-dimensional FDTD cell in the cylindrical coordinates onto the r-/spl phi/ plane. An effective absorbing boundary condition is employed to truncate the mesh at its outer radial boundary. Numerical results are derived for different cylindrical transmission lines and compared to data available in the literature. Specifically, the newly proposed cylindrical coplanar waveguide is studied both theoretically and experimentally.

This paper describes micromachined, membrane-supported low-pass and bandpass filters which are suitable for microwave and millimeter-wave (MM-wave) application. The designs are realized in coplanar-waveguide (CPW) form using short- and open-end series stubs with integrated metal-insulator-metal (MIM) capacitors, and are compact in lateral and longitudinal dimensions. A computationally efficient analysis has been developed for the design and characterization of the filters. The technique is based on a quasi-static coupled-line (CL) treatment of the series stubs, and uses normal mode impedance parameters, which are calculated with the spectral-domain approach (SDA). Due to the broad TEM-bandwidth of the membrane-supported transmission lines, the method can accurately predict filter responses well into the rejection band. To demonstrate the above claims, the measured and simulated S-parameters of a 0.3 mm /spl times/2.2 mm low-pass filter with a cutoff frequency at 17 GHz, and a second passband at 115 GHz, are presented. The new approach is also used in the design of bandpass filters which exhibit 1.5-2-dB insertion loss and bandwidths around 10%.

This paper describes recent results which pertain to the integration and reliability testing of micromachined, membrane-supported transmission line circuits. These circuits employ a 1.4-/spl mu/m-thick dielectric membrane to support thin-film conducting lines above an air substrate. With regard to integration, the development of a Ka-band solid state power amplifier (SSPA) is presented. The design includes a membrane-supported Wilkinson power divider/combiner with 0.2 dB loss, along with a commercially available monolithic microwave/millimeter wave integrated circuit (MMIC) amplifier stage. Also reported are tests which investigated the survivability of membrane lines under space qualification conditions. No failures occurred as a result of thermal cycling and vibration testing at levels which reached 39.6 grms.

A new noncontacting waveguide backshort has recently been developed for millimeter- and submillimeter-wave frequencies. The design consists of a metal bar with rectangular holes cut into it, which is covered with a dielectric layer to form a snug fit with the broadwalls of a waveguide. It is mechanically rugged and can be readily fabricated for frequencies from 1-1000 GHz. This paper presents a technique for the theoretical characterization of the backshort, using an approach that combines the mode-matching method and a set of coupled space-domain integral equations. The convergence characteristics of the analysis are included, along with a set of general design guidelines. >

Several millimeter-wave passive components have been fabricated using the microshield transmission line geometry, and their performance is presented herein. Microshield is a quasi-planar, half-shielded design which uses a thin dielectric membrane (1.5 /spl mu/m) to support the conducting lines. This approach provides a nearly homogeneous, air-filled environment and thus allows extremely broad-band TEM operation. This paper examines the conductor loss and effective dielectric constant of microshield lines and presents results on transitions to conventional coplanar waveguide, right-angle bends, different stub configurations, and lowpass and bandpass filters. Experimental data is provided along with numerical results derived from an integral equation method. The microshield line is shown to be very suitable for high performance millimeter and submillimeter-wave applications. >

Coplanar striplines and waveguides capable of supporting ultra-high-frequency pulses over many millimeters of propagation length have been fabricated on low-permittivity substrates, including a durable 1.4-/spl mu/m-thick membrane. These transmission lines were characterized using broadband pulses from a novel in situ optoelectronic test-signal generator together with an electro-optic probe tip and an optically-based sampling technique. Pulse-propagation characteristics for the coplanar lines on the low-permittivity substrates have been compared in both the time and frequency domains with the transmission behavior of lines on GaAs substrates. A semi-empirical model has also been used to simulate the experimental results with good agreement, helping to indicate the origin of the distortion mechanisms involved. In addition, for the coplanar waveguide structures, waveforms corresponding to the even and odd modes have been individually resolved in the time domain for lines fabricated on the GaAs and membrane substrates. >