Millimeter-wave Waveguide Research Articles

Dry Film Photoresist-Based Microfabrication: A New Method to Fabricate Millimeter-Wave Waveguide Components.

This paper presents a novel fabrication method based on dry film photoresists to realize waveguides and waveguide-based passive components operating at the millimeter-wave frequency (30–300 GHz). We demonstrate that the proposed fabrication method has a high potential as an alternative to other microfabrication technologies, such as silicon-based and SU8-based micromachining for realizing millimeter-wave waveguide components. Along with the nearly identical transfer of geometrical structures, the dry film photoresist offers other advantages such as fewer processing steps, lower production cost, and shorter prototyping time over the conventional micromachining technologies. To demonstrate the feasibility of the fabrication process, we use SUEX dry film to fabricate a ridge gap waveguide resonator. The resonator is designed to exhibit two resonances at 234.6 and 284 GHz. The measured attenuation at 234 GHz is 0.032 dB/mm and at 283 GHz is 0.033 dB/mm for the fabricated prototype. A comparative study among different existing technologies indicates that the reported method can give a better unloaded Q-value than other conventional processes. The measured unloaded Q-values are in good agreement with the simulated unloaded Q-values. The signal attenuation indicates that SUEX dry film photoresists can be used to fabricate passive devices operating at millimeter-wave frequencies. Moreover, this new fabrication method can offer fast and low-cost prototyping.

Design of Broadband W-Band Waveguide Package and Application to Low Noise Amplifier Module

In this paper, the broadband millimeter-wave waveguide package, which can cover the entire W-band (75–110 GHz) is presented and applied to build a low noise amplifier module. For this purpose, a broadband waveguide-to-microstrip transition was designed using an extended E-plane probe in a low-loss and thin dielectric substrate. The end of the probe substrate was firmly fixed on to the waveguide wall in order to minimize the performance degradation caused by the probable bending of the substrate. In addition, we predicted and analyzed in-band resonances by the simulations that are caused by the empty spaces in the waveguide package to accommodate integrated circuits (ICs) and external bias circuits. These resonances are removed by designing an asymmetrical bias space structure with a radiation boundary at an external bias connection plane. The bond-wires, which are used to connect the ICs with the transition, can generate impedance mismatches and limit the bandwidth performance of the waveguide package. Their effect is carefully compensated for by designing the broadband two-section matching circuits in the transition substrate. Finally, the broadband waveguide package is designed using a commercial three-dimensional electromagnetic structure simulator and applied to build a W-band low noise amplifier module. The measurement of the back-to-back connected waveguide-to-microstrip transition including the empty spaces for the ICs and bias circuits showed the insertion loss less than 3.5 dB and return loss higher than 13.3 dB across the entire W-band without any in-band resonances. The measured insertion loss includes the losses of 8.7 mm-long microstrip line and 41.8 mm-long waveguide section. The designed waveguide package was utilized to build the low noise amplifier module that had a measured gain greater than 14.9 dB from 75 GHz to 105 GHz (>12.9 dB at the entire W-band) and noise figure less than 4.4 dB from 93.5 GHz to 94.5 GHz.

Additive Manufacturing of Complex Millimeter-Wave Waveguides Structures Using Digital Light Processing

Additive manufacturing technology has enabled the manufacturing of complex structures, especially those with intricate internal features. This paper proposes a method for building complex-structured millimeter-wave waveguides using a strategy that combines digital light processing 3-D printing technology, a curved corner design, an off-axis print angle of 45°, and a robust postmetallization process. To demonstrate the capability of this combined-strategy method, a traditional magic tee prototype and an adapted inherently matched magic tee prototype are fabricated for use in the W-band. The measured performance of the fabricated inherently matched magic tee demonstrates return loss better than 13.5 dB, isolation coefficients higher than 15.7 dB, insertion losses smaller than 1.3 dB, and a magnitude imbalance of less than 1.3 dB across 80-105 GHz. The 3-D printed magic tee has a comparable performance to a W-band CNC-machined magic tee but weighs 77.5% less than the metallic one.

Uniform-Field Over-Mode Waveguide for Spatial Power-Combining Applications

A new and effective millimeter-wave waveguide packaging technique suitable for 1-D spatial power-combining applications is presented. The transition structure using narrow corporate channels preserves the uniform field distribution when expanding the ${E}$ -plane width of a standard waveguide to several wavelengths. A Q-band test module, containing back-to-back transitions for an increased width from 2.84 to 52 mm, shows an average insertion loss of 0.34 dB in the 40–50-GHz range. The radiation patterns from an open-end module, cut in half from the original test module, confirm uniform field distribution across the over-mode guide aperture.

Monolithically 3-D Printed Hemispherical Resonator Waveguide Filters With Improved Out-of-Band Rejections

This paper provides a comprehensive presentation for the RF design and implementation of novel millimeter-wave waveguide bandpass filters (BPFs) that are composed of compact hemispherical resonators. The proposed hemispherical resonator features a high unload quality factor and a volume 50% smaller than a spherical one and more significantly is much less degenerate than the latter due to its structural asymmetry. With proper geometrical configurations, the hemispherical resonator BPF can perform significantly improved out-of-band rejections compared with the spherical resonator BPFs of the same orders. The second- and fourth-order waveguide-fed BPFs are designed at $X$ and $Ka$ band s with flexible inter-resonator coupling geometries. The proof-of-concept $Ka$ -band filters are monolithically prototyped with a high-temperature-resistant ceramic-filled photosensitive resin by using a fast and low-cost stereolithography (SLA)-based additive manufacturing technique. A proprietary electroless nickel/copper/silver plating process is reported for surface metallization of the utilized commercially available resin. The $Ka$ -band filters demonstrate in the passbands small insertion losses (0.43–1 dB), good return losses (mostly >10–17 dB), and small frequency shifts (0.01%–0.47%), which validates excellent fabrication accuracy and reliability of the SLA printing and the metal plating. Characterization and quantification of surface morphology for SLA-printed samples are performed by employing contact profilometry and scanning electron microscopy.

Novel compact millimeter‐wave gap waveguide filter with double‐sided selectivity

AbstractNovel compact gap waveguide (GW) filter with negative coupling structure is proposed. GW is an attractive technology to design accurate millimeter‐wave components without electrical connection. It takes advantages of high Q‐factor, low loss, capability of integration with MMICs and multilayer implementation. GW features with stacked and negative coupling topology are effectively employed here to bring a high performance interconnect, miniaturized and cost‐effective filter. A fourth‐order Ka‐band filter with two prescribed symmetric transmission zeros is designed and fabricated based on the groove GW platform. The simulation and measurement results verify the validity of the method and exhibit high double‐sided selectivity.

A Millimeter-Wave Gyroelectric Waveguide Isolator

In this paper, a new type of millimeter-wave waveguide isolator is demonstrated. After developing an analytical model for a rectangular waveguide loaded with stratified media, all the modes propagating through the structure are found. Isolators are then designed by utilizing the frequency ranges where high nonreciprocal attenuation is identified. Here, an isolator is designed to work within the Ka-band by loading a WR-28 waveguide with a transversely magnetized indium antimonide (InSb) slab cooled to 77 K. Measured performance shows more than 20-dB isolation with 1-dB insertion loss, which agrees with theoretical predictions. Moreover, the effects of changing the magnetic bias ( $B_{0}$ ) and adding dielectric layers above the InSb slab were analyzed theoretically and verified through measurement. Results prove the possibility of achieving high isolation using a weaker magnetic bias by topping the gyroelectric slab with dielectric layers. Nonreciprocal behavior was also demonstrated using an isolator working at 105 GHz, where simulated results show more than 33-dB isolation with 1.16-dB insertion loss. The results presented in this paper could pave the way toward the realization of nonreciprocal components working in the submillimeter-wave and terahertz frequency ranges, where the performance of the classical ferrite device deteriorates.

Short waveguide load for millimetre‐wave applications

A compact millimetre-wave waveguide load with wedge-shaped dielectric inserts is considered. Its reflectivity is studied numerically and experimentally. Chosen absorber shape and sizes provide good matching over a wide-frequency range 37.5–53.57 GHz. Simulations are carried out for two options of waveguide sizes.

Waveguide Slot Array Antenna with a Hybrid-Phase Feed for Grating Lobe Reduction

The design of a 112-element millimeter-wave waveguide slot array antenna to reduce the grating lobe level is presented. A hybrid-phase feeding technique combining a cophase feed and an alternating-phase feed is applied to facilitate the suppression of grating lobes. In addition, a stepped feed waveguide and offset coupling slots aligned in a line are employed to realize a tapered aperture distribution. As a result, grating lobe suppression of 8.1 dB was achieved on the diagonal planes compared to a conventional alternating-phase-fed waveguide slot array antenna. A prototype of the proposed antenna was fabricated and measured. The measured results show that the proposed antenna exhibits a −15 dB reflection bandwidth of 3.4%and an average realized gain of 26.72 dBi within the measured frequency range. Good agreement between the simulated and measured radiation patterns is also observed.

A Configurable Coupling Structure for Broadband Millimeter-Wave Split-Block Networks

In order to realize series-fed millimeter-wave hollow waveguide array antennas, small slots or holes can be used to couple a defined amount of power from the main feed line to the radiating elements. Due to the small size of these structures, they are challenging to manufacture. Moreover, if the size of the required slots or holes are smaller than the available drill, they are not realizable at all. This paper describes a coupling structure, which uses laser-cutting to realize a small slot, while all the other parts of the waveguide circuit can be milled in split-block technology. A deployment in harsh environments such as fusion experiments is feasible, as the whole structure can be built from metal. By design, it is possible to configure the coupling slots, and thus, adjust or modify the tapering of the array antenna. A theoretical model of the proposed structure is given and measurements of $W$ -band prototypes are presented. The manufactured slots achieve coupling factors ranging from ${-{\hbox{24.2 dB}}}$ to ${-{\hbox{9.4 dB}}}$ . Measurements prove the applicability of the proposed design in broadband feed networks as the coupling values are nearly frequency independent with a deviation from the mean coupling ranging from $\pm {\hbox{0.6 dB}}$ to $\pm {\hbox{0.9 dB}}$ in the whole $W$ -band. The maximum phase variability between the evaluated slots is $\pm {\hbox{10}}^{\circ }$ .

Broadband Millimeter-Wave In-Phase and Out-of-Phase Waveguide Dividers with High Isolation

In this paper, two novel broadband in-phase and out-of-phase waveguide power dividers with high isolation are presented. Based on the substrate-integrated waveguide (SIW) divider and SIW-to-waveguide transition circuit, two kinds of E-plane waveguide dividers have been implemented. Due to the features of in-phase and out-of-phase performances, the proposed waveguide dividers can provide much more flexibilities than that of conventional E-plane waveguide T-junction. A broadband phase and amplitude performances are achieved across the whole Ka-band owing to the wideband characteristic of the SIW divider and transition circuits. To minimize the size and loss of the divider, a compact and low-loss SIW-to-waveguide transition circuit has been developed using the antisymmetric tapered probes. Two prototypes of the Ka-band waveguide dividers, including the in-phase and out-of-phase types, have been fabricated and measured. Measured results show that the isolation, input return loss, output return loss, amplitude imbalance, and phase imbalance of the in-phase divider are better than 15.5, 13.1, 10.8, 0.4 dB, and 3.50, while those of the out-of-phase divider are better than 15.0, 13.4, 10.4, 0.5 dB, and 3.60, respectively, over the frequency range from 26.5 to 40 GHz. The measured results agree well with the simulated ones. Considering their wide bandwidth, high isolation, good port matching performance, and compact configuration, the two types of waveguide dividers can be good candidates for broadband applications in millimeter-wave waveguide systems.

Design of millimetre wave diplexers with relaxed fabrication tolerances

A novel millimetre wave waveguide diplexer topology that can be fabricated using relaxed fabrication tolerances is presented. This is achieved by using a highpass filter/hybrid coupler topology in addition to a low order capacitive iris bandpass filter. By targeting the most sensitive centre resonators in the bandpass filter and increasing their length to full wavelength, the sensitivity to fabrication errors associated with changes to the resonator length can be reduced without the introduction of spurious responses close to the passband. The main benefit of this topology is that only one bandpass filter is required to realise the final diplexing response. This is advantageous when tolerance is considered as it is found that resonating structures associated with bandpass filters contribute to tolerance effects. In addition to this, the authors find that the choice of iris discontinuity used to realise the impedance inverters in the bandpass filter can help to relax fabrication tolerances. By subjecting the proposed circuit to a tolerance analysis, simulated results suggest that the circuit can be fabricated with relaxed fabrication tolerances. These discussions are verified with the fabrication of a Ka-band waveguide diplexer, where the measured and simulated scattering parameters are in very good agreement.

A millimeter-wave gain equalizer using E-plane microstrip-line probe and waveguide resonator

This paper presents a millimeter-wave wideband gain equalizer-based metallic waveguide, which is implemented by E-plane microstrip-line probe, metallic waveguide resonator, waveguide coupling groove, and millimeter-wave absorber. The proposed gain equalizer has advantages of high Q-factor and high power-handling capacity. In order to validate the new proposed topology, an ultra-wideband millimeter-wave gain equalizer, operating from 26.8 to 40 GHz, is designed and fabricated using rectangular waveguide. The R320 standard waveguide is used as main transmission line for convenient measurement. The fabricated gain equalizer exhibits excellent performances: the input return loss and the output return loss are all less than −14 dB in whole operating frequency band, and the maximum equalization value is about 11 dB.

Design of Millimeter-wave Rectangular Waveguide to HMSIW Transition Based on Trapezoidal-shaped Probe

In this letter, a compact rectangular waveguide-to-half mode substrate integrated waveguide (HMSIW) transition is presented. It uses a trapezoidal-shaped probe to couple the energy from rectangular waveguide to HMSIW. A back-to-back test module at Ka-band is fabricated and measured. It provides a return loss better than 15 dB and an insertion loss of 0.85 to 1.3 dB within a frequency range from 25 to 40 GHz. The circuit size of the proposed transition is reduced by approximately 81.8% as compared with the waveguide-to-HMSIW transition using antipodal fin-line. Additionally, no intermediate transition is needed for this transition, which simplify the design of transition circuit. The measurement results agree well with simulation results, which validate the feasibility of the transition. Also, a tolerance analysis is performed via the simulation to verify the reliability of this transition design.

Modeling and Performance of Microwave and Millimeter-Wave Layered Waveguide Filters

This paper presents the novel designs, analysis, and performance of 4-pole and 8-pole microwave and millimeter-wave (MMW) waveguide filters for operation at X and Y frequency bands. The waveguide filters have been designed and analyzed based on the mode matching and coupled resonators design techniques employing layered technology. Thorough waveguide filters working at X-band and Y-band have been designed, analyzed, fabricated, and tested along with the analysis of the output characteristics. Accurate designs of RF waveguides along with their filters based on the E-plane filter concept have been carried out with the ability of fitting into layered technology in high frequency production techniques. The filters demonstrate the appropriateness in order to develop high-performance well-established designs for systems that are intended for the multi-layer microwave, millimeter- and sub-millimeter-waves devices and systems; with the potential employment in radar, satellite, and radio astronomy applications. DOI: http://dx.doi.org/10.11591/telkomnika.v11i7.2411 Full Text: PDF

Optimization of a corrugated millimeter-wave waveguide and a miter bend by FDTD simulation

We estimate the transmission efficiency of the electromagnetic wave through the system composed of waveguide and miter bend by Finite-Difference Time-Domain (FDTD) simulation. As the fisrt approach of this estimation, we choose the case that the input wave is TE11 mode. In this case, the efficiency is estimated as 99.65 % for the system without grooves and 76.48 % for the system with grooves (which is called as "corrugate"). Comparing the distributions of the input electric field with that of the output electric field, the effect of the grooves is found as follows: Because the TE11 mode has an anisotropy, its shape is changed by the miter bend. This property appears in the corrugated system more strongly than the non-corrugated system.

Parameter Analysis of Millimeter-Wave Waveguide Switch Based on a MEMS-Reconfigurable Surface

This paper presents a novel concept of a millimeter-wave waveguide switch based on a microelectromechanical (MEMS)-reconfigurable surface with insertion loss and isolation very similar to high performance but bulky rotary waveguide switches, despite its thickness of only 30 μm. A set of up to 1470 micromachined cantilevers arranged in vertical columns are actuated laterally by on-chip integrated MEMS comb-drive actuators, to switch between the transmissive state and the blocking state. In the blocking state, the surface is reconfigured so that the wave propagation is blocked by the cantilever columns short-circuiting the electrical field lines of the TE 10 mode. A design study has been carried out identifying the performance impact of different design parameters. The RF measurements (60-70 GHz) of fabricated, fully functional prototype chips show that the devices have an isolation between 30 and 40 dB in the off state and an insertion loss between 0.4 and 1.1 dB in the on state, of which the waveguide-assembly setup alone contributes 0.3 dB. A device-level yield analysis was carried out, both by simulations and by creating artificial defects in the fabricated devices, revealing that a cantilever yield of 95% is sufficient for close-to-best performance. The actuation voltage of the active-opening/active-closing actuators is 40-44 V, depending on design, with high reproducibility of better than (σ = 0.0605 V). Lifetime measurements of the all-metal, monocrystalline-silicon core devices were carried out for 14 h, after which 4.3 million cycles were achieved without any indication of degradation. Furthermore, a MEMS-switchable waveguide iris based on the reconfigurable surface is presented.

Study of Contact Resistance for Curled-Up Beams in Waveguide Switch

In this letter, we are proposing a new technique to determine the contact resistance of the curled up beams in RF MEMS waveguide switches. Unlike the previous studies on the contact resistance of RF MEMS switches, here the contact resistance is measured at the “OFF” state of the switch with no dc voltage applied. The presented concept has been analyzed theoretically and verified by simulations and experimental data, illustrating less than 10% error. This study provides a measure for estimating the contact resistance of the emerging RF and millimeter-wave MEMS waveguide switches and paves the way for commercialization of such devices.

Simple e-beam air-bridge technology for mm-wave applications

► A new and simple air-bridge fabrication technology. ► Simple resist selection gives fewer and simpler fabrication processes. ► No special e-beam dose or process calibration required. ► The process latitude of UVIII resist and polyamide is exploited. ► Excellent experimental demonstration for mm-wave application. We describe a new air-bridge fabrication technology using electron beam lithography. This novel technique greatly simplifies the lithographic process, eliminating the requirement for complex writing control procedures used in established electron-beam lithography based processes. The new technique is demonstrated using single-dose per layer electron beam lithography and is applied to the fabrication of microwave and millimeter-wave waveguide structures.

60-GHz Millimeter-Wave Life Detection System (MLDS) for Noncontact Human Vital-Signal Monitoring

A first reported experimental study of a 60 GHz millimeter-wave life detection system (MLDS) for noncontact human vital-signal monitoring is presented. This detection system is constructed by using V-band millimeter-wave waveguide components. A clutter canceller is implemented in the system with an adjustable attenuator and phase shifter. It performs clutter cancellation for the transmitting power leakage from the circulator and background reflection to enhance the detecting sensitivity of weak vital signals. The noncontact vital signal measurements have been conducted on a human subject in four different physical orientations from distances of 1 and 2 m. The time-domain and spectrum waveforms of the measured breathing and heartbeat are presented. This prototype system will be useful for the development of the 60-GHz CMOS MLDS detector chip design.