This work presents a filtenna concept based on cascaded singlet filters, which inherits independent controllability of attenuation poles from the filter design and has high stopband performance. Two fourth-order filters with a center frequency of 270 GHz, a 14 GHz bandwidth, and in-band return losses of 15 dB and 18 dB, respectively, are manufactured and measured to verify the proposed concept. The filtennas with a single-slot and a double-slot configuration are fabricated by the silicon deep reactive ion etching technology and have the size of 3.65x2.6 mm2. Detailed explanations of the synthesis procedure, which was validated through EM simulation, and measurement results are provided. The measured single-slot and double-slot filtennas exhibit broadside radiation gains of approximately 4.5 dBi and 6.5 dBi at 270 GHz, respectively. Moreover, the challenges and details of silicon micromachining in fabricating the two filtering antennas are discussed.

A new transition from coplanar waveguide probe to micromachined rectangular waveguide for on-wafer device characterization is presented in this article. The transition is fabricated in the same double H-plane split silicon micromachined waveguide technology as the devices under test, requiring no additional post-processing or assembly steps. We outline the design and fabrication process of the transition for the frequency band of 220–330 GHz. A coplanar waveguide structure acts as the probing interface, with an E-field probe protruding in the waveguide cavity exciting the fundamental waveguide mode. Guard structures around the E-field probe increase the aspect ratio during deep reactive ion etching and secure its geometry. A full equivalent circuit model is provided by analyzing its working principle. RF characterization of fabricated devices is performed for both single-ended and back-to-back configurations. Measured S-parameters of the single-ended transition are obtained by applying a two-tiered calibration and are analyzed using the equivalent circuit model. The insertion loss of the single-ended transition lies between 0.3 dB and 1.5 dB over the whole band, with the return loss in excess of 8 dB. In addition to previously reported characterization of a range of devices under test the viability of the transition for on-wafer device calibration is demonstrated by characterizing a straight waveguide line, achieving an insertion loss per unit length of 0.02–0.08 dB/mm in the frequency band of 220–330 GHz.

This paper explores the impact of etch holes on sub-terahertz (THz) waveguide transmission performance and presents a silicon micromachined WR-03 waveguide with etch holes. The influence of etch-hole size and grid size is investigated through simulations. The waveguide prototype is realized through deep reactive ion etching (DRIE) and low-temperature thermal-compression bonding. Measurements reveal a low transmission loss (average 0.04 dB/mm) for the etched waveguide, with negligible influence on transmission loss observed for etch hole sizes below a specific threshold, which agrees with the simulations. The findings guide the design and optimization of micromachined THz waveguide components with etch holes applied in some specific situations.

This article presents a novel design of a full-band E -plane waveguide bend for direct flange-to-chip connection. The proposed E -plane bend concept is validated with a reduced-height bend prototype designed for standard WR-3.4 waveguide flange-to-chip connection, fabricated by silicon micromachining, and characterized by de-embedding the S -parameters with a custom-made offset-short calibration kit. The measured insertion and return losses are 0.08–0.3 dB and better than 14.7 dB, respectively, for the whole waveguide band of 220–320 GHz, and better than 0.15 and 20 dB, respectively, for more than 80% of the waveguide band. The measured results are in excellent agreement with the simulation data. Besides, a two-port waveguide structure with WR-3.4 interfaces is fabricated and measured to confirm the functionality of the designed E -plane bend. Furthermore, sensitivity analysis shows the robustness of the proposed geometry against fabrication tolerances.

In this paper, we introduce a novel negative coupling structure that is suitable for fabrication using milling and micromachining technologies. The proposed negative coupling structure is designed in three sections: a central bow-shaped iris is sandwiched between two sections that manipulate electromagnetic fields, causing a 180-degree phase rotation. To validate this concept, we have developed a silicon micromachined fourth-degree quasi-elliptic bandpass filter with a center frequency of 270 GHz and a fractional bandwidth of 2.2\%. The measured results of the filter display two transmission zeros in the stopband thus demonstrating the correct performance of the negative coupling structure.

In this paper, a lattice-based model of balanced filters is proposed. The symmetric lattice model is derived directly from the transversal circuit model of coupled-resonators filters through a series of equivalent transformations. Expressions for S-parameters of general symmetric lattice network are derived, as well as equations for S-parameters of balanced bandpass and bandstop filters utilizing the lattice model; the dualism of their transmission and reflection coefficients is demonstrated. Two numerical examples of modelling balanced bandpass and bandstop filters are presented.

In this paper, we present a fifth-order sub-THz direct-coupled E-plane waveguide bandpass filter fabricated through micromachining. The all-pole filter operates at the center frequency of 400 GHz with fractional bandwidth of 5% and occupies an area of only 1 mm2. The filter can be directly inserted between two standard WR-2.2 waveguide flanges due to axially arranged interfaces. The compactness and axial interfaces are simultaneously achieved by bending of the E-plane filter. The structure is realized using an E-plane split design where waveguides are etched in the handle layer of a silicon-on-insulator (SOI) wafer and couplings are realized through E-plane septa fabricated in the SOI device layer. External couplings are facilitated by means of slots in the device layer. The proposed design is highly resistant to the underetching effect, as E-plane septa are not influenced by the underetching, thus enabling accurate coupling control. The measured return loss is better than 20 dB in the most of the passband, with the worst-case return loss of 11 dB, and the insertion loss of only 1.1 dB is measured. A very good agreement between measured and simulated data is obtained.

In this article, we present an ultra-narrowband silicon-micromachined bandpass filter with a wide and high-rejection stopband. The proposed filter uses high- Q factor TM330 mode resonators. To avoid near-passband spurious resonances typically associated with higher order modes, a novel method of arranging the positions of the coupling slots is carried out. A fourth-order filter with a center frequency of 183 GHz and a fractional bandwidth (FBW) of 0.5% has been fabricated by silicon micromachining for the first time. The prototype employs out-of-plane transitions on the input and output ports, which results in axial ports enabling a direct characterization with the device simply mounted between the two standard waveguide test ports. The unloaded Q factor extracted from the measurements is 1000, which is unparalleled by any previously reported narrowband filter in any technology in this frequency range. A spurious free response with a high stopband rejection in the entire waveguide band is obtained. The measured worst-case insertion loss and return loss (RL) in the passband are 4.5 and 9 dB, respectively.

This letter presents a novel broadband diplexer design that is capable of achieving highly stringent rejection characteristics through the use of singlets whose interconnecting irises are formulated as resonant slot irises. The combination of these two resonant-cavity types allows for a unique filtering solution with increased filter order, wide available bandwidth, low geometric complexity, and simple milling requirements, which can be suitably applied to millimeter-wave and submillimeter-wave applications. A prototype is fabricated for operation in the -band (75–110 GHz) in order to cover a 10% fractional bandwidth in each passband. Measurement of the prototype denotes highly accurate results and exemplifies the use of all resonator and coupling elements in order to support ten poles and four transmission zeros in an elegant diplexer solution.

In this paper, a lattice-based model of balanced filters is proposed. The symmetric lattice model is derived directly from the transversal circuit model of coupled-resonators filters through a series of equivalent transformations. Expressions for S-parameters of general symmetric lattice network are derived, as well as equations for S-parameters of balanced bandpass and bandstop filters utilizing the lattice model; the dualism of their transmission and reflection coefficients is demonstrated. Two numerical examples of modelling balanced bandpass and bandstop filters are presented.