Millimetre wave waveguide enclosed grid frequency multipliers and imaging

The utilisation of the THz spectrum ( 0.3-10 THz ) is hampered by fundamental difficulties in generating power at these frequencies. Applications within such diverse fields as radio astronomy, security imaging, life sciences, high data rate communications and production monitoring could benefit significantly from compact, high power THz signal sources operating at room temperature. This thesis reports on the design and fabrication aspects of varactor diode based waveguide enclosed grid frequency multipliers. The goal of this work has been to design, fabricate and characterise high power varactor grid frequency multipliers, enabling increased power handling capabilities and output power of future THz frequency multipliers. This approach is expected to offer excellent frequency and power scalability for THz signal sources.A tunable 240 - 290 GHz 72 element grid HBV frequency tripler is presented together with measurement data. With an output power of 35 mW at 247 GHz this is the highest frequency of operation reported to date for waveguide enclosed grid frequency multipliers. Furthermore, a 128 Schottky diode frequency doubler grid is presented, with a measured peak output power of 0.25 W at 183 GHz. With a peak conversion efficiency of 23 % it is the most efficient waveguide enclosed grid multiplier reported to date. A modelling approach using parallel sets of cascaded unit cells has been successfully developed as well as a full 3D simulation for grid frequency multipliers.Two application examples that could benefit from future high power THz sources are also presented. The first one is a 346 GHz imaging system using an imaging algorithm based on the Born approximation to produce images with a sub wavelength pixel size of 0.1 70.1 mm2. The second application example is a FMCW radar transceiver operating at 340 GHz, packaged into a compact modular system designed for array integration

Millimetre wave waveguide enclosed grid frequency multipliers and imaging

The utilisation of the THz spectrum ( 0.3-10 THz ) is hampered by fundamental difficulties in generating power at these frequencies. Applications within such diverse fields as radio astronomy, security imaging, life sciences, high data rate communications and production monitoring could benefit significantly from compact, high power THz signal sources operating at room temperature. This thesis reports on the design and fabrication aspects of varactor diode based waveguide enclosed grid frequency multipliers. The goal of this work has been to design, fabricate and characterise high power varactor grid frequency multipliers, enabling increased power handling capabilities and output power of future THz frequency multipliers. This approach is expected to offer excellent frequency and power scalability for THz signal sources.A tunable 240 - 290 GHz 72 element grid HBV frequency tripler is presented together with measurement data. With an output power of 35 mW at 247 GHz this is the highest frequency of operation reported to date for waveguide enclosed grid frequency multipliers. Furthermore, a 128 Schottky diode frequency doubler grid is presented, with a measured peak output power of 0.25 W at 183 GHz. With a peak conversion efficiency of 23 % it is the most efficient waveguide enclosed grid multiplier reported to date. A modelling approach using parallel sets of cascaded unit cells has been successfully developed as well as a full 3D simulation for grid frequency multipliers.Two application examples that could benefit from future high power THz sources are also presented. The first one is a 346 GHz imaging system using an imaging algorithm based on the Born approximation to produce images with a sub wavelength pixel size of 0.1 70.1 mm2. The second application example is a FMCW radar transceiver operating at 340 GHz, packaged into a compact modular system designed for array integration

HBV frequency multiplier 2D arrays and application

The utilisation of the THz spectrum ( 0.3-3 THz ) is hampered by technological difficulties to generate power at these frequencies. Applications within diverse fields such as radio astronomy, security imaging, life sciences, high data rate communications and production monitoring could benefit significantly from compact, high power THz signal sources operating at room temperature. This thesis reports on the design and fabrication aspects of varactor diode based 2D array frequency multipliers. Both free space operating and waveguide en- closed Heterostructure Barrier Varactors (HBVs) arrays are discussed in detail. The goal of this work has been to design, fabricate and characterise high power varactor 2D array frequency multipliers, enabling increased power handling capabilities and output power of future THz frequency multipliers. This approach is expected to offer excellent frequency and power scalability for THz signal sources.An altogether waveguide integrated 249 GHz HBV 2D array frequency tripler is presented together with measurement data. With an output power of 18 mW at 248 GHz and a conversion efficiency of 2 %, this is the highest frequency of operation and output power reported to date for waveguide enclosed 2D array frequency multipliers.A 346 GHz imaging system is also presented as an application example for powerful THz signal sources. The system uses an imaging algorithm based on the Born approximation and produces images with a voxel size of 0.1 7 0.1 mm2 (approximately 1/10 of the free space wavelength)

HBV frequency multiplier 2D arrays and application

The utilisation of the THz spectrum ( 0.3-3 THz ) is hampered by technological difficulties to generate power at these frequencies. Applications within diverse fields such as radio astronomy, security imaging, life sciences, high data rate communications and production monitoring could benefit significantly from compact, high power THz signal sources operating at room temperature. This thesis reports on the design and fabrication aspects of varactor diode based 2D array frequency multipliers. Both free space operating and waveguide en- closed Heterostructure Barrier Varactors (HBVs) arrays are discussed in detail. The goal of this work has been to design, fabricate and characterise high power varactor 2D array frequency multipliers, enabling increased power handling capabilities and output power of future THz frequency multipliers. This approach is expected to offer excellent frequency and power scalability for THz signal sources.An altogether waveguide integrated 249 GHz HBV 2D array frequency tripler is presented together with measurement data. With an output power of 18 mW at 248 GHz and a conversion efficiency of 2 %, this is the highest frequency of operation and output power reported to date for waveguide enclosed 2D array frequency multipliers.A 346 GHz imaging system is also presented as an application example for powerful THz signal sources. The system uses an imaging algorithm based on the Born approximation and produces images with a voxel size of 0.1 7 0.1 mm2 (approximately 1/10 of the free space wavelength)

Development of a waveguide integrated sub-millimetre wave spatially power combined HBV multiplier

The development of a sub-millimetre wave, spatially power combined, quasi optical HBV multiplier is presented. Emphasis is placed on key concepts of spatial power combining of frequency multipliers, as well as design challenges. The current state of the design as well as the final goal is further discussed

Development of a waveguide integrated sub-millimetre wave spatially power combined HBV multiplier

The development of a sub-millimetre wave, spatially power combined, quasi optical HBV multiplier is presented. Emphasis is placed on key concepts of spatial power combining of frequency multipliers, as well as design challenges. The current state of the design as well as the final goal is further discussed

Comparison of full 3D and unit cell models for waveguide-embedded frequency multiplier arrays

We present a full wave, large-signal analysis of a waveguide-embedded frequency multiplier array, solving the entire geometry using FEM EM modeling and including every nonlinear element in a Harmonic Balance simulation. The full 3D model employed provides the exact field distribution across the array, thus enabling us to account for substrate resonances, higher order mode excitation, instabilities, and diode yield. The model is compared with measurements on a 247 GHz fixed tuned 72-diode HBV tripler. In this example, higher order mode excitation was found due to the interaction between the filter and the diode array. This can only be observed using a full 3D model, which more accurately predicts the output power versus input power and frequency. Finally, the pros and cons of a full 3D model and a unit cell model for waveguide embedded multiplier arrays are discussed

A single-channel THz imaging system for biomedical applications

Due to technological advances, imaging in the THz-range of the electromagnetic spectrum is currently emerging as an interesting tool for security, safety, and biomedical applications. In this paper, a THz imaging system designed for biomedical analysis is described. The system consists of a pair of antennas operating in transmission mode at 335 GHz. The antennas can be moved independently of each other and a tomographic imaging algorithm is used to reconstruct the images

A THz imaging system for biomedical applications

Imaging using the THz-range of the electro-magnetic spectrum is currently emerging as an interesting tool for security, safety, and biomedical applications. In this paper, a THz imaging system designed for biomedical analysis is described. The system consists of a pair of antennas operating in transmission mode at 335 GHz. During measurements the antennas are moved parallel to the sample under investigation while data is collected

A Waveguide Embedded 250 GHz Frequency-Tripler 2D Array

This work reports on a 248 GHz HBV (Heterostructure Barrier Varactors)-varactor quasi-optical multiplier array with a maximum output power of 18 mW and a corresponding conversion efficiency of 2 %. The module utilizes a mechanically compact and simple shim system, combining the large array power handling capability with the convenience of waveguide interfaced circuits. At the same time this approach offers excellent power and frequency scalability. The multiplier is based on a 12 by 6 element, 72 in total, planar 2D HBV varactor array. The diodes are fabricated on a three barrier InGaAs/InAlAs material system on InP as carrier substrate. Easch diode consist of two 20um^2 serially connected mesas, yielding a total of six barrier per diode. The HBV diodes are coupled to a uniform dipole array through which the power is coupled in and out. One HBV diode and the corresponding dipole make up a square unit cell with a side of 211 um. The chip measures 2,54 x 1,27 mm^2, fitting inside a standard WR10 waveguide. The complete module consists of three parts, the 2D HBV array, a combined output filter and output matching slab and an input matching slab. A rhombic aperture frequency selective surface is used as the uutput bandpass filter and the quartz filter substrate also serves as a matching slab for the output tone. On the input a piece of InP substrate is used to match the incoming pump signal to the diodes. The components are mounted inside two WR-10 waveguide shims, providing an easy assembly and a modular system. The current version of the multiplier module produces 18 mW at 248 GHz but a significant increase in output power and efficiency is expected with a new output matching network and more pump power. Recent measurement results will be presented together with a detailed discussion regarding the design, pointing out advantages and challenges compared to more traditional approaches to frequency multiplier design in the frequency range. Future improvements and challenges will also be covered