David Benito

In this article, a novel design method for rectangular waveguide filters intended for fabrication using direct metal additive manufacturing (AM) is proposed. The synthesized filters will feature a smooth profile that allows us to fabricate them orienting the filter propagation axis in the vertical building direction, achieving an optimum configuration for direct metal AM fabrication. The novel design method is valid for any all-pole transfer function, which is initially implemented with a commensurate-line distributed unit element prototype. The impulse response of that initial prototype is then properly interpolated to obtain the target response for a smooth-profiled filter with similar length and profile excursion. Finally, the target impulse response just generated is implemented in the rectangular waveguide technology employing a novel inverse scattering synthesis technique that relies on the coupled-mode theory to model the electromagnetic behavior of the waveguide filter. The novel inverse scattering synthesis technique is general and also valid for the case of filters with very high rejection levels, which is of great relevance in rectangular waveguide technology. A Ku-band low-pass filter with stringent satellite specifications is designed using the proposed method, fabricated by means of a direct metal AM technique, and measured with a vector network analyzer. A very good agreement is achieved between the simulated and measured results, fulfilling the required specifications and demonstrating the feasibility and performance of the novel design method.

A rectangular waveguide bandpass filter for $Q$ -band with simple fabrication is proposed in this letter. The design is based on the use of the first passband replica of commensurate-line stepped-impedance structures and achieves the suppression of their inherent low-pass response. In order to do it, the filter is implemented by rectangular waveguide sections with different widths and heights that can be analytically calculated. The technique is validated by a ninth-order Chebyshev filter with passband between 40 and 43 GHz and fabrication yield equal to 84% for a manufacturing error of $\pm 20~\mu \text{m}$ . The measured results of the prototype fabricated with computer numerical control (CNC) milling are in good agreement with the simulated ones.

From our first proposals of periodic Photonic Bandgap (PBG) structures in microstrip to the complex Inverse Scattering synthesis methods that we use nowadays and that give rise to synthesized structures with smooth profiles in microwave planar or waveguide technology, the UPNA Microwave Components Group (MCG-UPNA) has made significant contributions to the microwave theory (partially related to previous optical developments) and has also made several proposals of applications that will be reviewed in this paper from an historical perspective. Our group is a multidisciplinary group, focused also on the industry needs.

In this paper, we propose and demonstrate a new technique for the design of arbitrary-order differentiators, intended for ultra-wideband (UWB) applications in microwave coupled-line technology. The technique employs an exact analytical series solution for the synthesis problem derived by the authors from the coupled-mode theory. This solution allows for the synthesis of microwave devices with arbitrary frequency responses, only limited by the principles of causality, passivity, and stability. The method has been successfully applied in the past to the design of two-port waveguide and transmission-line components operating in a reflection-type configuration. Here, the synthesis technique is extended to coupled-line structures, where the input port is matched at all frequencies and the reflected signal is redirected to the coupled port, enabling an effective transmission-type operation for the device. First-, second-, third-, and fourth-order UWB differentiators have been successfully designed, fabricated, and measured, validating the general design technique proposed.

In this letter, a new method for the design of high-power low-pass harmonic filters in rectangular waveguide technology is proposed. Based on a 2-D arrangement of bandstop elements of sinusoidal profile, a filter with a wide spurious-free frequency response (up to the third harmonic) for the fundamental TE₁₀ mode, as well as higher-order TE_n0-mode suppression, is achieved. Compared to the classical waffle-iron solution, the novel proposal has a highly increased power-handling capability for the same frequency specifications.

A signal processing algorithm is used to reconstruct the phase response of fiber Bragg gratings from easy-to-obtain module data. The algorithm is applied to optical spectrum analyzer measurements, avoiding the use of costly and complex equipment for the direct measurement of the complete frequency response. Reconstructed results, both in transmission and reflection, are then validated by comparison with three of the most common experimental techniques (interferometric, modulation phase shift, and single-sideband modulation).