Carlos A. Leal-Sevillano

Silicon Micromachined Canonical

In this letter, several bandpass filters operating in the WR-1.5 band (500 to 750 GHz) are presented. The deep reactive ion etching (DRIE) silicon micromachining process is used for the fabrication of the filters. Two canonical filter topologies based on E- and H-plane are implemented. The work presented here has two specific objectives: a) to get important fabrication process parameters, such as tolerances, vertical angles, surface roughness, and repeatability and b) to validate the proper working of the waveguide filters in the terahertz band. These filters do not have any tuning element. Experimental results show better than 10 dB return loss and approximately 1 and 2.5 dB insertion loss (for 6% fractional bandwidth) for the E- and H-plane topology, respectively. The obtained results are in agreement with fabrication tolerances of 2 μm and vertical angles deviations up to 3°.

{\hbox{E}}

The design and experimental validation of a pseudo-elliptical response filter at W-Band is presented. A micromachining technique based on the thick SU-8 photo-resist is used to construct the filter. The optimized structure is specially well-suited for the implementation of filters with transmission zeros by means of micromachining techniques, since the extracted poles are implemented by simple stubs without irises. Furthermore, a novel topology based on the use of only three SU-8 layers is presented. This new topology, which includes a novel optimized input/output routing, can be potentially used for the design of high-performance devices with a fast and low-cost production. A fourth-order filter with two transmission zeros has been fabricated (bandwidth 5%), presenting 1.2 dB of insertion loss. This level of loss is equivalent to the actual state-of-art for micromachined filters at W-band, in spite of the reduced height and the split block in the H-plane used in the presented design.

-Plane and

The design, method of fabrication and experimental validation of a pseudo-elliptical four-poles asymmetric response filter at 100 GHz with 10% of fractional bandwidth is presented. The designed filter is part of an image radar system and must fulfill stringent specifications. The proposed topology and method of fabrication improves the out of band rejection above the pass band in comparison with other classical structures, while keeping a low insertion loss level. A two-fold geometry for implementing a transmission zero is proposed, avoiding the excitation of the first higher order mode and easing the manufacturing without any tuning element. A low-cost milling process is used for the fabrication of the device. The final design fulfills the desired specifications and presents 0.6 dB of insertion loss level at 100 GHz. The excellent agreement between simulations and measurements at this frequency band in both, return loss and insertion loss, is pointed out.

{\hbox{H}}

In this paper, an orthomode transducer (OMT) for dual-band operation and optimized for stacked micromachined layers implementation is presented. The proposed design avoids the use of septums, irises, pins, or small features and minimizes the number of equal-thickness micromachined layers required. In this way, the micromachining fabrication is simplified, making the proposed design a very attractive candidate for high frequency applications and for low-cost batch production. A W-band dual-band design (one different polarization in each frequency band) with more than 10% fractional bandwidth for each band and 30% separation between bands is presented. In addition, proper routing and layered bends are designed for an optimum standard interfacing with the same orientation of the input/output ports. Two OMTs in a back-to-back configuration are fabricated using a thick SU-8 photo-resist micromachining process. A total of six stacked SU-8 layers, all of them with the same thickness of 635 μm, are used. The experimental results are coherent with the tolerance and misalignment of the process, validating the proposed novel OMT design.

-Plane Bandpass Filters at the Terahertz Band

In this paper, we present the modeling and experimental validation of an efficient, compact, and high-isolation waveguide duplexer operating at 225 GHz. While duplexers based on ferrite circulators are key components of many monostatic radar systems, at W-band frequencies and above the performance of waveguide circulators rapidly deteriorates. The design presented here uses a ferrite-free duplexing concept based on transmitting and receiving in orthogonal circular polarizations. The circular polarization is efficiently generated in waveguide using a septum orthomode transducer polarizer, leading to a compact device with a single horn antenna. The complete duplexer is designed using efficient numerical algorithms, resulting in a fabricated device with a measured 10% fractional bandwidth, a return loss better than 20 dB, isolation of 30 dB, and insertion loss below 1 dB.

A Pseudo-Elliptical Response Filter at W-Band Fabricated With Thick SU-8 Photo-Resist Technology

This paper presents the application of the low cost additive manufacturing technique named fused filament fabrication (FFF) to implement waveguide devices. In addition to the reduced price, it also has the added benefit of rapid prototyping, allowing the designer to modify the geometry swiftly. Otherwise this kind of manufacture opens the way to experiment with shapes until now unachievable by traditional subtractive techniques. In order to demonstrate its feasibility, the experimental results of three filters with low-pass, high-pass, and band-pass responses respectively, designed in Ku band with usual specifications in satellite communication systems have been designed, printed, metallized and measured. In the conclusion, the advantages and limitations are highlighted, with special attention dedicated to the metallization process, since it is the bottleneck of the process.

Low-Loss Elliptical Response Filter at 100 GHz

In this paper, we report the development of a wideband compact orthomode transducer (OMT) for the 180-270 GHz band. The OMT design is based on the classical high performance Bøifot waveguide junction and implemented in split-block using high precision CNC milling. The obtained results validate the high performance operation in a 40% fractional bandwidth and constitute a remarkable achievement at this high frequency band.

A Micromachined Dual-Band Orthomode Transducer

A general and rigorous formulation is proposed for the analysis of hollow metallic waveguides from the gigahertz to the terahertz band. The analysis is based on a hybrid mode formulation and the Drude model for the dielectric permittivity of metallic conductors. The obtained results for the circular waveguide are compared with the classical microwave approach (surface impedance approximation or Leontovich condition). The validity range of the surface impedance approximation in both the propagation constant and the electromagnetic field pattern is studied. As a consequence, a direct relation between the error in the propagation constant and the electromagnetic field configuration is shown. Moreover, this formulation shows the evolution in the field pattern: from TE/TM modes at microwaves to the so-called Surface Plasmon Polariton at terahertz frequencies.

A 225 GHz Circular Polarization Waveguide Duplexer Based on a Septum Orthomode Transducer Polarizer

This is the accepted version of the following article: K. S. Reichel, N. Sakoda, R. Mendis, D. M. Mittleman, Evanescent wave coupling in terahertz waveguide arrays, Optics Express, 2013, 21, 14, 17249, which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1029/2011RS004838/full

Design of microwave waveguide devices for space and ground application implemented by additive manufacturing

In this paper it is shown that the traditional shunt admittance represented by a rational function yields an accurate wideband equivalent circuit for multi-aperture waveguide irises. The electromagnetic analysis of the structures reveals two different types of resonant phenomena. The first type of resonance is associated with the cutoff frequency of the TE10 mode. The second type or antiresonace corresponds to short-circuit TEM modes. These antiresonances are generated when the asymmetry of the iris allows the excitation of electric fields with opposite phases at contiguous apertures. The proposed equivalent circuit is a shunt admittance represented by a rational function. This rational function is analytically obtained from the singular points (resonances and antiresonances) identified in the full-wave analysis. It is straightforward to obtain the circuit elements from the rational function by following the classical one-port synthesis leading to Fosters or Cauerss canonical realizations. One advantage of the proposed equivalent circuit is that it represents the electromagnetic behavior of complicated structures with a minimum number of circuit elements or degrees of freedom. Several examples, with different number of apertures and symmetry, are presented to illustrate the proposed general equivalent circuit. Finally, the proposed procedure is extended to the case of arbitrary shaped irises, such as those used in frequency-selective surfaces.