Todays society is set on its course for multi gigabits-per-second wireless connectivity, internet of things, non-invasive medical diagnosis, intelligent mobility, and fully automated driving. This is a paradigm shift, one which requires constant advancements in the technologies present at the core of these applications. Furthermore, making these applications viable for massmarket requires regulating the cost and, depending upon the application, high reliability. Silicon-germanium (SiGe) heterojunction bipolar transistor (HBT) technology has proven itself as one of most valuable technology enabling systems operating at millimeter-wave (mm-wave) frequencies and beyond. Moving to higher frequencies results in increased absolute bandwidth, but based on past trends and future forecasts, there is a continuous demand on increased bandwidth which coarsely corresponds to higher information rate in communications or higher resolution in radars. This bandwidth requirements at the moment can not be simply met using conventional architectures and calls for intensive research. The work presented in this thesis is motivated by these factors and focusses on achieving very high fractional bandwidths in circuits operating at mm-wave and sub-millimeter wave frequencies. Although, some of the circuits presented here can be used in a wide variety of application scenarios, mostly are adapted for high resolution radar sensors. Two advanced 130 nm SiGe BiCMOS technolgies, one from Infineon Technogies and the other from IHP Microelectronics, have been used for this work. Starting with the design of broadband amplifiers, compact lumped circuit based amplifiers with a bandwidth extending from DC to 105 GHz are presented. These lumped circuit amplifiers are based on a novel topology of cascaded common-base, emitter-followers, and an output cascode stage which improves the performance on several aspects as compared to similar lumped architectures present in the existing literature. A thorough analysis based on analytical expressions of voltage transfer characteristics and input impedance is provided which aids in comprehending the circuit dynamics and in the design process. Special focus is given on stability issues of emitter follower chains which are prone to produce ringing. Another amplifier with a 3-dB fractional bandwidth of more than 50 % and a peak differential output power of 11 dBm is presented. It is the first Si-based amplifier which covers the entire D-band frequency range (110170 GHz). Based on four interstage-matched cascode amplifiers, it uses a T-type four-reactance matching network together with optimized HBT dimensions to construct a uniform gain profile. The efficacy of this technique is explained in terms of analytically calculated transimpedance gain profiles of the interconnected stages. By using these profiles and gain staggering broadband amplifiers can be designed also in other frequency bands. Measuring differential broadband circuits using single-ended equipment is a challenge. Therefore, during the course of this work broadband Marchand baluns operating in the D-band and in the J-band (220325 GHz) were designed based on a three-symmetric line modified topology which reduces the phase velocity difference between odd and even modes. Highly linear downconversion mixers with broadband conversion gain (CG) are essential for realizing high resolution radar sensors. In this work, a fundamental-wave and a novel subharmonic downconversion receivers are presented working in the D-band and J-band with a 3-dB CG bandwidth of 30 GHz and 73 GHz, respectively. An integral part of high performance radar sensors are high-power, low-noise signal sources based on either frequency multipliers or voltage controlled oscillators (VCOs). Design and analysis of these signal source working up to 300 GHz is a core part of this thesis. A fundamentalwave D-band signal source with a figure-of-merit of 185 dBc/Hz and an output power level of around 9 dBm around 160 GHz is presented. For signal sources operating in the J-band harmonic approaches must be utilized. By using a push-push topology the operating frequency can be doubled, however the resulting output power usually turns out to be much lower. In this work, a novel technique for improving the output power and efficiency of push-push based VCOs is proposed which in the presented case is able to enhance the output power of two 300 GHz VCOs by a factor of around 5 dB as compared to the conventional approaches. A complete theoretical analysis of the technique is provided by means of calculating the common-mode impedance of the VCOs. Towards the end of this work a frequency-modulated continuous-wave (FMCW) radar sensor in an embedded-wafer-level-ball-grid-array package working in the J-band is designed relying on many of the aforementioned techniques. At these frequencies antenna-on-chip, for most of the cases, is the only viable solution. The gain of the system can then be subsequently increased either by using a lens or a waveguide horn antenna thereby making the system bulky and increasing the form factor. In this work, for the first time an antenna-in-package working at more than 240 GHz is designed and implemented. The antenna shows a measured gain of more than 4 dBi and a 3-dB gain bandwidth of 24 GHz. The research carried out during this work demonstrates that the SiGe HBT technology shows a tremendous advantage in meeting not only the rising demands of current mm-wave systems but it also possesses an enormous capability for future THz applications. This however constantly requires adapting advanced and state-of-the-art circuit concepts and architectures so that the potential of this technology can be fully exploited.