Synthesis of Rectangular Waveguide Filters With Smooth Profile Oriented to Direct Metal Additive Manufacturing

Abstract

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.

Design of an Additively-Manufactured Self-Supported All-Metal Coaxial-Line X-Band Bandpass Filter

“…The measured insertion loss (IL) is 0.722 dB at the filter central frequency, while a value equal to 0.066 dB is obtained in simulation when considering an electrical conductivity of 6.2•10 6 S/m, a value reported in similar fabrications with AlSi10Mg [17]. There exist two factors that contribute to the observed increase in the filter IL.…”

“…resulting in θ c = 45 • in our designed LPF. It should be remarked that (4) is valid only for ideal transmission line implementations (like our coaxial-line case) [17]. The next step is to choose a suitable outer conductor diameter D i .…”

“…Assuming a pure TEM single-mode operation, and considering the specifications described at the beginning of this section, the stepped-impedance commensurate-line distributed prototype (shown in Fig. 5) will exhibit a spuriousfree range of 2(f r − f c ) = 24 GHz, i.e., the first replica begins at 2f r − f c = 36 GHz, see [17]. However, even though the coaxial-line operates with a TEM mode, spurious effects can be observed when the outer conductor diameter is increased, since the spurious excitation of higher order modes is also enhanced.…”

Novel FR4‐based low loss reconfigurable filter with four operating modes using movable transmission lines

“…Bandpass filter plays an important role in wireless communication systems. There are many different technologies to implement bandpass filter, such as microstrip, [1][2][3] stripline, 4 substrate integrated waveguides (SIW), [5][6][7] metal rectangular waveguide, 8,9 substrate-integrated-suspended-line (SISL), [10][11][12] and so on. The reconfigurable technology in the bandpass filter is one of the key research contents.…”