Monolithic Multiband Coaxial Resonator-Based Bandpass Filter Using Stereolithography Apparatus (SLA) Manufacturing

Abstract

This article reports on a new class of additive manufacturing (AM) and monolithically integrated multiband coaxial bandpass filters (BPFs). They are based on N in-series cascaded multiresonant sections that each of them consists of K resonators and K − 1 admittance inverters. In this manner, a transfer function containing K Nth-order passbands in between K − 1 stopbands can be realized. A monolithic stereolithography apparatus (SLA)-based integration concept is proposed for these BPFs for the first time. For proof-of-concept validation purposes, multiple multiband BPF prototypes at the S-and C-bands were designed, manufactured, and tested. They include: 1) a dual-band second-order BPF with passbands centered at 3.7 and 4.2 GHz, fractional bandwidths (FBWs) of 8.1% and 4.2%, and effective quality factors ( Q eff ) above 1000 for both of its passbands; 2) a dual-band third-order BPF with passbands centered at 3.7 and 4.0 GHz, FBWs of 4.9% and 3.3%, and Q eff above 1300; and 3) a triband second-order BPF with passbands centered at 3.5, 3.7, and 4.2 GHz, FBWs of 4.6%, 2.7%, and 5.5%, and Q eff above 1100, successfully validating the proposed monolithic multiband coaxial BPF concept.

Vertically Integrated Coaxial Resonator-Based Multiband Bandpass Filters Using SLA 3-D Printing

“…The interresonator coupling between the in-line resonators 1 and 3 (m a1 in Fig. 2) is provided by the coupling iris [10]. For each pair of vertically stacked resonators (e.g., 1 and 2), the interresonator coupling m 1 is materialized by partially removing their shared ground plane and its magnitude is controlled by the size of the coupling window d i [15].…”

“…By altering m 1 and m 2 , the separation between the passbands can be controlled, where increasing their magnitude leads to lager separation. Compared to a multiband CRD topology where all shunt resonators are placed on the same side of the in-line resonators [9], [10], the proposed CRD allows for independent tuning of the passbands and stopbands and facilitates asymmetrical transfer functions with different BWs.…”

“…Most of the existing coaxial multiband BPFs are based on multimode or steppedimpedance resonators [5], [6], [7], [8] that are hard to be extended to more than two bands. Multiband configurations where a narrow set of frequencies are notched out from a wide passband have been shown in [9] and [10]. Although they exhibit a greater number of passbands (>2), they require large number of resonators that result in increased volume and high manufacturing cost.…”

“…Although it is fairly straightforward to manufacture monolithic waveguides [11], [12], most of the 3-D coaxial filters have been materialized as split blocks due to their geometrical complexity [13], [14]. A monolithic integration approach using SLA was demonstrated in [10] for in-line multiband BPFs. In [15], vertically integrated coaxial BPFs were presented with significantly reduced size; however, they were only shown for single-band topologies.…”

“…Expanding upon [10] and [15], this letter explores the potential to realize highly miniaturized vertically integrated multiband filters using coaxial-resonator-based configurations alongside a novel compact monolithic integration scheme for single SLA printing. The proposed multiband concept exhibits the following unique characteristics: 1) compact size and minimized (8× improvement) axial ratio (AR) enabled by vertical integration of subwavelength coaxial resonators; 2) combined use of inline and vertical couplings within the 3-D volume of the filter; 3) transfer functions with independently controlled passbands and stopbands; and 4) monolithic integration facilitated by SLA manufacturing.…”