This article presents a novel subterahertz (sub-THz) crossover waveguide switch concept operating in the 220–260-GHz frequency band. The crossover switching circuit is implemented by two hybrid couplers and two single-pole-single-throw (SPST) switching mechanisms, utilizing microelectromechanically reconfigurable switching surfaces. The silicon-micromachined crossover switch prototype is very compact, with a total footprint of 5.6 × 5 × 1.2 mm, including four standard WR-3.4 waveguide ports and the waveguide routing to these ports. The measured insertion loss (IL) is 0.9–1.4 dB in the crossover state and 0.8–1.3 dB in the straight state from 220 to 260 GHz, and the isolation (ISO) is better than 29.3 and 29 dB, respectively, for these states. The measured return loss (RL) is better than 14 dB in the crossover state and better than 13.6 dB in the straight state. Besides, the measured input-to-input ISO is better than 13.7 and 34 dB in the crossover and straight states, respectively. The measurement results are in excellent agreement with the simulation data. Moreover, the signal paths are fully symmetric for all input-to-output signal paths, making the crossover switching circuit suitable for redundancy applications.

This article presents a highly integrated novel silicon micromachined single-pole-single-throw waveguide switch based on two microelectromechanically reconfigurable switching surfaces (MEMS-RSs), which allows optimizing the switching performance by tuning the interference between the two such MEMS-RSs utilizing integrated electrostatic comb-drive actuators. The switch prototype is implemented with axially aligned standard WR-3.4 waveguide ports with a total footprint of 3 mm×3.5 mm×1.2 mm. The measured blocking ( off ) state insertion loss (isolation) and return loss, measured between two standard WR-3.4 waveguide flanges, are 28.5–32.5 dB and better than 0.7 dB, and the propagating ( on ) state insertion and return losses are 0.7–1.2 dB and better than 17 dB in the 220–290 GHz frequency band, respectively. The measured results were in excellent agreement with the simulation data, implying 27.5% fractional bandwidth, which is very close to a full waveguide band performance. For further investigations, two variants of the switching circuit with only a single MEMS-RS and without any MEMS-RSs have also been fabricated. The single MEMS-RS switch achieved the off -state isolation, on -state insertion loss, and return loss of only 11.5–12.5 dB, 0.8–1.3 dB, and better than 12 dB from 220 to 274 GHz, respectively, which clearly indicates the drastic performance improvement of the interference-based double MEMS-RS switch design. Moreover, measurement of the waveguide-only reference structure showed that the waveguide section alone attributed to 0.2–0.5 dB of the measured on -state insertion loss of the double MEMS-RS switch, and the rest is due to the introduction of the MEMS-RSs inside the waveguides.

 This paper investigates the performance of a frequency-sweeping steering notch beam implemented with a simple two-element antenna array operating within the frequency range of 238 to 248 GHz. We assess the performance of this minimalistic scanning notch beam antenna array for three single-target measurement scenarios, comparing the effectiveness of different algorithms, including IFFT, FISTA, and MUSIC. The results demonstrate that the MUSIC algorithm achieves a range resolution of 13.5 mm, surpassing that of both FISTA and IFFT algorithms. Additionally, the steering notch exhibits superior angular resolution, with a resolution better than 9◦ compared to MUSIC and FISTA. This study explores the potential capabilities of this minimalistic radar and optimized signal processing techniques to reduce hardware complexity in radar systems and address evolving demands for cost-effective radar applications. 

This article experimentally demonstrates a frequency-sweeping notch-beam sub-THz radar frontend based on a two-line array antenna featuring computational imaging. Operating within 237.5 GHz and 250 GHz with 12.5 GHz bandwidth, the radar utilizes a 12 λc delay line to achieve frequency-sweeping capabilities. This configuration allows dynamic notch-beam scanning across angular ranges from − 26.5 ∘ to 28 ∘ . The radar frontend is highly compact with a total size of 20 mm× 14.3 mm× 1.2 mm, including the beam-steering network, a magic-tee for creating the 180 ∘ phase shift required for creating the notch-beam, and the antenna array, and is implemented by silicon micromachining. The radar was evaluated with single and dual-target scenarios utilizing and benchmarking different computational imaging algorithms, i.e., matched filter (MF), fast iterative shrinkage-thresholding algorithm (FISTA), and multiple signal classification (MUSIC). It was found that the MUSIC algorithm outperforms MF and FISTA in range and angular resolution in single-target scenes, achieving a range resolution of 7.8 mm and an angular resolution of 15.7 ∘ , with detection errors of less than 6.6 mm and 3.5 ∘ , respectively. Although the MUSIC algorithm maintains reliable range resolution in dual-target scenarios, it performs poorly in providing angular information.

This article experimentally demonstrates a frequency-sweeping notch-beam sub-THz radar frontend based on a two-line array antenna featuring computational imaging. Operating within 237.5 GHz and 250 GHz with 12.5 GHz bandwidth, the radar utilizes a 12 λc delay line to achieve frequency-sweeping capabilities. This configuration allows dynamic notch-beam scanning across angular ranges from − 26.5 ∘ to 28 ∘ . The radar frontend is highly compact with a total size of 20 mm× 14.3 mm× 1.2 mm, including the beam-steering network, a magic-tee for creating the 180 ∘ phase shift required for creating the notch-beam, and the antenna array, and is implemented by silicon micromachining. The radar was evaluated with single and dual-target scenarios utilizing and benchmarking different computational imaging algorithms, i.e., matched filter (MF), fast iterative shrinkage-thresholding algorithm (FISTA), and multiple signal classification (MUSIC). It was found that the MUSIC algorithm outperforms MF and FISTA in range and angular resolution in single-target scenes, achieving a range resolution of 7.8 mm and an angular resolution of 15.7 ∘ , with detection errors of less than 6.6 mm and 3.5 ∘ , respectively. Although the MUSIC algorithm maintains reliable range resolution in dual-target scenarios, it performs poorly in providing angular information.

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 presents the design, fabrication, and characterization of a novel crossover switch implemented by silicon micromachining. The switch consists of two single-polesingle-throw switches, two hybrid couplers, and four E-plane transitions to standard WR-3.4 waveguide, with a total footprint of 5.6mm×5mm×1.2mm. The switching is performed based on short-circuiting the electric field of the dominant mode of the rectangular waveguide by two sets of microelectromechanically reconfigurable switching surfaces (MEMS-RSs) controlled by electrostatic actuators. It has two input ports and two output ports, which are completely symmetric regarding input-output signal paths, making the designed switch well-suited for adding redundancy to RF systems. The measured isolation and insertion loss of better than 29.3 and between 0.9-1.4 dB and better than 29 and between 0.8-1.3 dB are achieved in the crossover (propagating) and straight (reflecting) states, respectively, with the return loss of better than 14 and 13.6 dB, for these states in the 220-260 GHz frequency band. Moreover, the measured results are in excellent agreement with the simulated data.

This article presents an unbalanced-fed silicon micromachined dual-port dual-line antenna array. The radiation pattern of the antenna array can be steered in the E -plane by sweeping the frequency and can be switched between a broad and a notched beam by exciting the ports with in-phase or out-of-phase signals. The antenna is designed for and implemented by silicon micromachining. Each single-line subarray consists of #8 antenna apertures in which the field amplitude is tapered in the H-plane, and the phase imbalance of unbalanced power dividers is minimized by integrated delay sections in the feed network. The measured return loss of the antenna is better than 10 dB from 220 to 295 GHz for both input ports (29.1% fractional bandwidth). The antenna prototype is designed for 40° of beam steering in the E -plane (scanning speed of 4°/GHz) by sweeping the frequency from 238 to 248 GHz. The measured sidelobe level of the broad beam in the H-plane is better than 18.5 dB, and the measured depth of the notched beam is better than 22.5 dB in the entire scanning range. In addition to the dual-port dual-line antenna array, a single-line 1 × 8 antenna array is also implemented for reference measurement purposes. The measured return loss of the single-line antenna array is better than 10 dB from 220 to 314 GHz (35.2% fractional bandwidth), and its measured sidelobe level is between 18 and 21.3 dB in the H-plane from 220 to 280 GHz. Besides, the simulation data and the measurement results are in excellent agreement.

Sub-terahertz (Sub-THz) and THz spectrums are being used increasinglydue to the short wavelength and wide available bandwidthat these ranges. These spectrums hold significant importance in scientificand commercial applications such as detection, ranging, imaging,security screening, car radars for passenger monitoring and autonomousdriving, telecommunication, sensing, spectroscopy, and deep space exploration.However, implementing components and circuits in thesespectrums has many challenges due to high fabrication tolerance requirements.Therefore, there is a need to surpass conventional fabricationtechniques like computer-numerical-control (CNC) milling to fullyexploit the vast potential of these spectrums.

Silicon micromachined waveguides, realized by deep-reactive-ionetching(DRIE) of silicon-on-insulator (SOI) wafers and sidewall metallization,have been used to implement different components in this thesis.Silicon micromachining offers several advantages compared to otherfabrication techniques, such as micrometer range accuracy, smaller andlighter devices, nanometer range surface roughness leading to low insertionloss, integrability of active and passive components on a single chip,low cost, and volume manufacturability. This thesis presents severalnovel sub-THz components and systems that are composed of multipleelements, all designed to be implemented by silicon micromachining.

The thesis is structured as follows. After a short introduction, thefirst part of the thesis provides a detailed overview of the fabricationtechnology and presents a step-by-step fabrication process flow thatincludes various processes. This section also covers the challenges andlimitations of silicon micromachining and the strategies for addressingthem.

The second part of the thesis focuses on designing and characterizingdifferent silicon micromachined passive waveguide components, such asa full-band E-plane waveguide transition from reduced-height in-planewaveguides embedded inside the silicon substrate to standard out-ofplanewaveguide sizes, a rectangular waveguide-based magic-T, and adual-port dual-line 2 × 8 antenna array with frequency beam steering.The characterization procedure for every component is presented thoroughly,and the measured results are discussed shortly, as the resultsare already published in detail in the appended publications (Papers I,II, and III).

The third part of the thesis elaborates on MEMS-based waveguideswitches (Papers IV and V). This part explains the design and characterizationof a novel single-pole-single-throw (SPST) switch operatingin the 220-290 GHz frequency range with excellent insertion loss and isolation performance. The SPST switch is then integrated into a morecomplex signal chain and combined with hybrid couplers to create anovel crossover switching circuit. The designed crossover switch operatesin the 220-260 GHz frequency range with excellent insertion loss,return loss, and isolation, making it well-suited for receiver calibrationapplications. Additionally, the designed crossover switch is fullysymmetric regarding input-output signal paths, making it suitable forapplications with redundancy requirements.

Finally, the last part of the thesis presents a complex reconfigurablecar radar frontend circuit (Papers VI and VII). Several componentsare integrated into this signal chain with a compact footprint of only20mm × 14mm × 1.2mm. The designed radar frontend features frequencybeam steering and beam shape switching between a broad anda notched radiation pattern. It operates in the 220-260 GHz frequencyrange with a beam steering range of 238-248 GHz. The features of thedesigned radar frontend make it well-suited for target detection, ranging,and imaging applications.

Sub-terahertz (Sub-THz) och THz-spektrum anv¨ands alltmer p˚agrund av dess korta v˚agl¨angden och breda tillg¨angliga bandbredden viddessa intervall. Dessa spektrum har stor betydelse i vetenskapliga ochkommersiella till¨ampningar som detektering, avst˚andsm¨atning, bildbehandling,s¨akerhetskontroll, bilradar f¨or passagerar¨overvakning och autonomk¨orning, telekommunikation, avk¨anning, spektroskopi och utforskningav rymden. Att implementera komponenter och kretsar i dessaspektrum har dock m˚anga utmaningar p˚a grund av h¨oga tillverkningstoleranskrav.D¨arf¨or finns det ett behov av att ¨overtr¨affa konventionellatillverkningstekniker som dator numerisk styrning (CNC) fr¨asning f¨oratt fullt ut utnyttja den stora potentialen hos dessa spektrum.

Mikromaskinbearbetade v˚agledare av kisel, realiserade genom djupreaktivjonetsning (DRIE) av kisel-p˚a-isolator (SOI) wafers och sidov¨aggsmetallisering, har anv¨ants f¨or att implementera olika komponenter i dennaavhandling. Kiselmikrobearbetning erbjuder flera f¨ordelar j¨amf¨ortmed andra tillverkningstekniker, s˚asom mikrometeromr˚adesnoggrannhet,mindre och l¨attare enheter, nanometers omr˚ade av ytj¨amnhet som ledertill l˚ag ins¨attningsf¨orlust, integrerbarhet av aktiva och passiva komponenterp˚a ett enda chip, l˚ag kostnad och volymtillverkning. Denna avhandlingpresenterar flera nya sub-THz-komponenter och system som¨ar sammansatta av flera element, alla designade f¨or att implementerasmed kiselmikrobearbetning.

Uppsatsen ¨ar uppbyggd enligt f¨oljande. Efter en kort introduktionger den f¨orsta delen av uppsatsen en detaljerad ¨oversikt av tillverkningsteknikenoch presenterar ett steg-f¨or-steg tillverkningsprocessfl¨ode sominkluderar olika processer. Det h¨ar avsnittet t¨acker ocks˚a utmaningarnaoch begr¨ansningarna f¨or mikrobearbetning av kisel och strategierna f¨oratt hantera dem.

Den andra delen av avhandlingen fokuserar p˚a att designa och karakteriseraolika kiselmikrobearbetade passiva v˚agledarkomponenter, s˚asomen fullbands E-plane-v˚agledar¨overg˚ang fr˚an reducerad h¨ojd in-planev˚agledare inb¨addade i kiselsubstratet till standard out-of-plane v˚agledarestorlekar, en rektangul¨ar v˚agledarbaserad magic-T och en 2 × 8 dubbelportsantennupps¨attning med tv˚a linjer med frekvensstr˚alestyrning.Karakteriseringsproceduren f¨or varje komponent presenteras grundligtoch de uppm¨atta resultaten diskuteras inom kort, eftersom resultatenredan publiceras i detalj i de bifogade publikationerna (Paper I, II ochIII).

Den tredje delen av avhandlingen utvecklar MEMS-baserade v˚agledaromkopplare(Paper IV och V). Den h¨ar delen f¨orklarar designen och karakteriseringenav en ny enkelpolig enkelkastsswitch (SPST) som arbetar i frekvensomr˚adet 220-290 GHz med utm¨arkt ins¨attningsf¨orlust ochisoleringsprestanda. SPST-omkopplaren integreras sedan i en mer komplexsignalkedja och kombineras med hybridkopplare f¨or att skapa en nycrossover omkopplingskrets. Den designade crossover-switchen fungerari frekvensomr˚adet 220-260 GHz med utm¨arkta ins¨attningsf¨orluster, returf¨orluster och isolering, vilket g¨or den v¨al l¨ampad f¨or mottagarkalibreringsapplikationer.Dessutom ¨ar den designade crossover-omkopplarenhelt symmetrisk vad g¨aller in- och utg˚angssignalv¨agar, vilket g¨or denl¨amplig f¨or applikationer med redundanskrav.

Slutligen presenterar den sista delen av avhandlingen en komplexrekonfigurerbar frontendkrets f¨or bilradar (Paper VI och VII). Flerakomponenter ¨ar integrerade i denna signalkedja med ett kompakt fotavtryckp˚a endast 20mm × 14mm × 1.2mm. Den designade radarfrontenhar frekvensstr˚alestyrning och str˚alform som v¨axlar mellan ett brettoch ett sk˚arat str˚alningsm¨onster. Den fungerar i frekvensomr˚adet 220-260 GHz med ett str˚alstyrningsomr˚ade p˚a 238-248 GHz. Funktionernahos den designade radarfronten g¨or den v¨al l¨ampad f¨or m˚aldetektering,avst˚andsavst˚and och avbildningstill¨ampningar.

In this paper, an H-band radar system is built, and measurement of in-cabin object detection and passenger monitoring is demonstrated to better understand the in-cabin propagation environment at sub-THz frequencies.