This thesis investigates advanced silicon micromachined passive component design solutions for high-performance millimetre and sub-millimetre-wave systems, representing the state-of-the-art in modern microwave and RF systems. The proposed designs are fabricated through deep reactive ion etching (DRIE). Silicon micromachining using DRIE offers the ability to fabricate small feature sizes, making it ideal for millimetre and submillimeter-wave systems applications, with low surface roughness and manufacturing tolerances in a scalable process. The proposed design solutions utilize waveguide-based technologies with the goal of advancing future generations of satellite communications, radar, remote sensing, and biomedical instrumentation. 

The core of this work is to propose design solutions to overcome manufacturing limitations, reduce transmission losses, introduce new design methods to enhance component performance, and simplify overall design complexity. 

The first part of the thesis introduces new platforms for transferring electromagnetic waves within silicon micromachined chips. Two structures are presented: a silicon-micromachined E-plane waveguide bend for flange-to-chip connection and a broadband on-chip rectangular waveguide 90º twist both for 220-325 GHz. The E-plane bend is crucial for transferring waves from outside the chip to the inside and eliminating reliance on external fixtures. The on-chip silicon micromachined twist enables interconnection of H-plane and E-plane waveguide subsystems, that increases fabrication flexibility. 

The second part discusses several novel filter design solutions operating at different frequency ranges from 90 to 300 GHz, each exhibiting state-of-the-art performance. An ultra-narrowband 4thorder filter with a wide spurious-free rejection band is developed for183 GHz. This filter utilizes high-Q-factor TM330 mode resonators and exhibits a measured Q-factor of 1000, surpassing any previously reported values in this frequency range. Additionally, a new negative coupling structure suitable for rectangular waveguide filters is proposed, offering compatibility with various fabrication methods, such as CNC milling and silicon micromachining. Using this negative coupling, a 4th-order quasi-elliptic bandpass filter with a centre frequency of 270 GHz and a fractional bandwidth of 2.2%is developed. Furthermore, a frequency variant coupling structure designed for rectangular cavities is proposed, enabling in-line filters with N+1 transmission zeroes, which can be easily manufactured and integrated with other subsystems. Using the proposed coupling structure, two filters are developed at 270 GHz: one 4th-order with 3transmission zeroes (TZs) and one 2nd-order with 3 TZs. Moreover, an integrated eighth-degree lowpass waveguide filter having a cut-off frequency of 280 GHz is presented. The lowpass filter is also fabricated using DRIE, with the aid of the twist proposed in section one. Furthermore, a compact band-pass filter with triplet response using one triangular singlet and two iris resonators is developed. Finally, a filtenna is introduced, combining a 4th-order filter with two slot antennas. The utilized filter employs 4 rectangular singlets introducing 4 transmission zeroes. The measured gain of the structure is 7 dBi, considering the use of on-chip E-plane bend transition to enable a direct connection to the flange.

Denna avhandling undersöker avancerade designlösningar för passiva komponenter tillverkade av mikromaskinerat kisel för högpresterande millimeter och sub-millimeter vågsystem, vilket representerar den senaste teknologin inom moderna mikrovågs och RF system. De föreslagna konstruktionerna tillverkas genom djup reaktiv jonetsning (DRIE). Kisermikromaskinering med DRIE erbjuder möjligheten att tillverka små detaljstorlekar, vilket gör den idealisk för tillämpningar inom millimeter och sub-millimeter vågsystem, med låg ytjämnhet och tillverkningstoleranser i en skalbar process. De föreslagna designlösningarna använder vågledarbaserade teknologier med målet att främja framtida generationer av satellitkommunikation, radar, fjärranalys och biomedicinsk instrumentering.

Kärnan i detta arbete är att föreslå designlösningar för att övervinna tillverkningsbegränsningar, minska transmissionsförluster, introducera nya designmetoder för att förbättra komponentprestanda och förenkla den övergripande designkomplexiteten.

Den första delen av avhandlingen introducerar nya plattformar för att överföra elektromagnetiska vågor inom kisermikromaskinerade chip. Två strukturer presenteras: en kisermikromaskinerad Eplan vågledarböjning för fläns-till-chip-anslutning och en bredbandig på-chip rektangulär vågledare 90º vridning, båda för 220-325 GHz. E-planböjningen är avgörande för att överföra vågor från utsidan av chipet till insidan och eliminera beroendet av externa fästanordningar. Den på-chip kisermikromaskinerade vridningen möjliggör sammankoppling av H-plan och E-plan vågledarsystem, vilket ökar tillverkningsflexibiliteten. 

Den andra delen diskuterar flera nya filterdesignlösningar som arbetar vid olika frekvensområden från 90 till 300 GHz, var och en med toppmoderna prestanda. Ett ultrasmalt 4:e ordningens filter med ett brett störningsfritt avvisningsband utvecklas för 183 GHz. Detta filter använder hög-Q-faktor TM330-lägesresonatorer och uppvisar en uppmätt Q-faktor på 1000, vilket överträffar alla tidigare rapporterade värden inom detta frekvensområde. Dessutom föreslås en ny negativ kopplingsstruktur lämplig för rektangulära vågledarfilter, som erbjuder kompatibilitet med olika tillverkningsmetoder, såsom CNC-fräsning och kisermikromaskinering. Med denna negative koppling utvecklas ett 4:e ordningens kvasi-elliptiskt bandpassfilter med en mittfrekvens på 270 GHz och en fraktionell bandbredd på 2,2%. Vidare förklaras en dispersiv kopplingsstruktur designad för rektangulära kaviteter, som möjliggör in-line filter med N+1 överföringsnollor, vilka enkelt kan tillverkas och integreras med andra delsystem. Med den föreslagna kopplingsstrukturen utvecklas två filter vid 270 GHz: ett 4:e ordningens med 3 överföringsnollor och ett 2:a ordningens med 3 TZ. Dessutom presenteras ett integrerat åttonde gradens lågpassvågledarfilter med en avskärningsfrekvens på 280 GHz. Lågpassfiltret tillverkas också med DRIE, med hjälp av den föreslagna vridningen i avsnitt ett. Slutligen introduceras en filtreringsantenn, som kombinerar ett 4:e ordningens filter med två slitsantenner. Det använda filtret utnyttjar 4 rektangulära singletter som introducerar 4 överföringsnollor. Den uppmätta förstärkningen av strukturen är 7 dBi, med tanke på användningen av på-chip E-plan böjövergång för att möjliggöra en direkt anslutning till flänsen.

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.

This paper introduces a silicon-micromachined lens antenna, fabricated for operation in the 500-750 GHz range, featuring an optimized Graded Index Fresnel Zone Planner Lens (FZPL) design. The antenna efficiently radiates a circularly polarized wavefront without the need for additional phase compensation components. Through fabrication, the antenna achieves a high gain of 36 dBi and maintains a -15 dB return loss across the entire waveguide band. Significantly, this all-dielectric lens antenna exhibits minimal loss, ensuring elevated efficiency in Terahertz (THz) communication applications. With its low profile and compact design, this antenna emerges as a promising solution for upcoming wideband THz communication applications. This work not only emphasizes the innovative design but also underscores the practical realization of high-performance antennas with a compact footprint, leveraging silicon micromachining in the THz frequency bands.

This paper introduces a silicon-micromachined lens antenna, fabricated for operation in the 500-750 GHz range, featuring an optimized Graded Index Fresnel Zone Planner Lens (FZPL) design. The antenna efficiently radiates a circularly polarized wavefront without the need for additional phase compensation components. Through fabrication, the antenna achieves a high gain of 36 dBi and maintains a -15 dB return loss across the entire waveguide band. Significantly, this all-dielectric lens antenna exhibits minimal loss, ensuring elevated efficiency in Terahertz (THz) communication applications. With its low profile and compact design, this antenna emerges as a promising solution for upcoming wideband THz communication applications. This work not only emphasizes the innovative design but also underscores the practical realization of high-performance antennas with a compact footprint, leveraging silicon micromachining in the THz frequency bands.

This paper introduces an innovative siliconmicromachined antenna operating in the 500-750 GHz range, based on an optimized elliptical Fresnel Zone Plate Lens (FZPL) design. The antenna radiates a circularly polarized wavefront without additional phase compensation components. With a gain of 25.7 dBi and a 15 dB return loss over the whole waveguide band, this low-profile, compact antenna presents a promising solution for upcoming wideband THz communication applications. This work highlights the potential of silicon micromachining in achieving high-performance antennas with a compact footprint in the THz bands.

This paper introduces an innovative silicon-micromachined, low-profile, high-gain antenna designed for wideband performance in the whole 500-750 GHz waveguide band. The novel antenna concept is based on an elliptical Fresnel Zone planner lens with optimized distribution of the zone dimensions. Furthermore, without requiring any extra phase compensating components, the design ensures circular polarization, which was measured to an axial ratio of better than 2.5 over the whole waveguide band (40% fractional bandwidth). The measured gain ranges from 24.3 to 25.7 dBi, and the return loss is better than 15 dB over the whole 250 GHz band. The 8.25mm×7.62mm large and only 526 μm thick antenna can be directly mounted onto a standard WM-380 waveguide flange. The measured radiation patterns for circular polarization, the gain, the axial ratio, and the return loss are excellently matching the simulated antenna performance. This work shows that all-dielectric antennas at THz frequencies easily outperform metal-based designs due to drastically reduced loss with only -0.85dB average radiation efficiency in the overall frequency band.

This article investigates the impact of antenna dispersion on wideband Terahertz (THz) imaging systems. It is demonstrated that the effective bandwidth is reduced from the nominal system bandwidth, and thus, the expected image resolution cannot be reached when the antenna system has inappropriate frequency dispersion characteristics. Besides a theoretical analysis and simulations, experiments were conducted using antennas with different dispersion characteristics in an ultra-wideband 500–750 GHz imaging setup to assess the impact on achievable resolution. When utilizing low dispersion dielectric-lens antennas, the system successfully detected multiple targets with a radius of 0.6 mm even when positioned at close distance (2 mm in cross-range and 3 mm in range). In contrast to that, when using higher dispersion horn antennas, the resolution of a dual-target scenario was reduced to 3 mm in cross-range and 4 mm in range. Furthermore, it is shown that the target position reconstruction accuracy, as well as the signal-to-clutter ratio (SCR), are also improved by 68% and 2.7 dB, respectively, when using low dispersion antennas in the same setup. This investigation, for the first time, highlights the importance of considering antenna dispersion for accurate image reconstruction, particularly for high-resolution wideband THz imaging systems.

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 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.

In this article, we report for the first time on a low-loss compact platform that enables the integration of H-and E-plane rectangular waveguide subsystems enabled by 90 ∘ polarization rotation of rectangular waveguide sections on a silicon-micromachined chip. The proposed platform offers unprecedented design flexibility for a 2.5D fabrication technology such as silicon micromachining, since orthogonal waveguide device sections with full design freedom in H-plane geometries can be cofabricated with sections with full design freedom in E-plane geometries, enabled by novel, integrated waveguide twists optimized for 2.5D fabrication. The platform is developed for use in broadband millimeter-and submillimeter-wave waveguide circuits and prototypes are implemented in the 220–325-GHz band. A prototype chip demonstrating the platform, implemented by bonding three stacked silicon chips, is fabricated. The measured results of the twist prototype exhibit a very low insertion loss of less than 0.2 dB and a return loss of 20 dB or better in most of the 220–325-GHz band. An integrated eighth-degree lowpass waveguide filter with axial ports having a cut-off frequency of 280 GHz is codesigned with the twist transition and fabricated on the platform to demonstrate its application. The filter shows 0.4-dB measured insertion loss and has a measured return loss in the passband of better than 14 dB.