High efficiency planar microwave antennas assembled using millimetre thick micromachine polymer structures

Communication systems at microwave and millimetre wave regimes require compact broadband high gain antenna devices for a variety of applications, ranging from simple telemetry antennas to sophisticated radar systems. High performance can usually be achieved by fabricating the antenna device onto a substrate with low dielectric constant or recently through micromachining techniques. This thesis presents the design, fabrication, assembly and characterisation of microstrip and CPW fed micromachined aperture coupled single and stacked patch antenna devices. It was found that the micromachining approach can be employed to achieve a low dielectric constant region under the patch which results in suppression of surface waves and hence increasing radiation efficiency and bandwidth. A micromachining method that employs photolithography and metal deposition techniques was developed to produce high efficiency antenna devices. The method is compatible with integration of CMOS chips and filters onto a common substrate. Micromachined polymer rims (SU8 photoresist) was used to create millimetre thick air gaps between the patch and the substrate. The effect of the substrate materials and the dimensions of the SU8 polymer rims on the performance of the antenna devices were studied by numerical simulation using Ansoft HFSS electromagnetic field simulation package. The antenna structures were fabricated in layers and assembled by bonding the micromachined polymer spacers together. Low cost materials like SU8, polyimide and liquid crystal polymer films were used for fabrication and assembly of the antenna devices. A perfect patch antenna device is introduced by replacing the substrate of a conventional patch antenna device with air in order to compare with the micromachined antenna devices. The best antenna parameters for a perfect patch antenna device with air as a substrate medium are ~20% for bandwidth and 9.75 dBi for antenna gain with a radiation efficiency of 99.8%. In comparison, the best antenna gain for the simple micromachined patch antenna device was determined to be ~8.6 dBi. The bandwidth was ~20 % for a microstrip fed device with a single patch; it was ~40 % for stacked patch devices. The best bandwidth and gain of 6.58 GHz (50.5%) and 11.2 dBi were obtained for a micromachined sub-array antenna device. The simulation results show that the efficiency of the antenna devices is above 95 %. Finally, a novel high gain planar antenna using a frequency selective surface (FSS) was studied for operation at ~60 GHz frequency. The simulation results show that the novel antenna device has a substantial directivity of around 25 dBi that is required for the emerging WLAN communications at the 60 GHz frequency band

Polymer-Based Low-Cost Micromachining of Gap Waveguide Components

The millimeter-wave (mmWave) and sub-millimeter-wave (sub-mmWave) frequency bands have gained significant attention over the past few years due to the growth of commercial wireless applications. As the operating frequency approaches these higher frequencies, the dimensions of the waveguide-based components continue to decrease. The decreasing feature size of those waveguide components makes the traditional machine-based (computer numerical control, CNC) fabrication method increasingly challenging in terms of time and cost, especially above 100 GHz. Additionally, this method is a serial process and cost will not scale with volume production. Micromachining has the potential of addressing the manufacturing issues of mmWave components. However, the existing microfabrication techniques either suffer from technological immaturity, are time-consuming, or lack sufficient cost-efficiency. A straightforward, fast, and low-cost fabrication method that can offer batch fabrication of waveguide components operating at mmWave and sub-mmWave frequency range is desirable to address the needs for hardware on the growing market of mmWave and sub-mmWave wireless systems.Conventional metal waveguides have very strict fabrication requirements in terms of mechanical assembly and integration of RF electronics. In comparison, gap waveguide technology not only offers competitive loss performance but also provides several benefits in terms of assembly and integration of active components. A gap waveguide is a planar waveguide technology which does not suffer from the dielectric loss in planar waveguides and which does not require any electrical connections between the metal walls, in contrast to hollow waveguides. This thesis aims to realize gap waveguide components operating at mmWave and sub-mmWave frequency range, in a low-cost and time-efficient way by developing new polymer-based fabrication methods.A template-based injection molding process has been designed to realize a high gain antenna operating at D band (110 -170 GHz). We can confirm that injection molding of OSTEMER is a straightforward and fast device fabrication method. In the proposed method, the time-consuming and complicated parts need to be fabricated only once and can later be reused.A dry film photoresist-based method is also presented in this thesis to fabricate waveguide components operating between 220 - 320 GHz. Dry film photoresist offers rapid fabrication of waveguide components without using sophisticated tools. The measurement results presented in the thesis indicate that this dry film-based method is a promising method for fabricating waveguide components operating in mmWave and sub- mmWave frequency ranges

Additively Manufactured RF Components, Packaging, Modules, and Flexible Modular Phased Arrays Enabling Widespread Massively Scalable mmWave/5G Applications

The 5G era is here and with it comes many challenges, particularily facing the high frequency mmWave adoption. This is because of the cost to implement such dense networks is much greater due to the high propagation losses of signals that range from 26 GHz to 40 GHz. Therefore there needs to be a way to utilize a method of fabrication that can change with the various environments that 5G will be deployed in, be it dense urban areas or suburban sprawl. In this research, the focus is on making these RF components utilized for 5G at low cost and modular with a focus on additive manufacturing. Since additive manufacturing is a rapid prototyping technique, the technology can be quickly adjusted and altered to meet certain specifications with negligible overhead. Several areas of research will be explored. Firstly, various RF passive components such as additively manufactured antennas and couplers with a combination hybrid inkjet and 3D printing will be discussed. Passive components are critical for evaluating the process of additive manufacturing for high frequency operation. Secondly, various structures will be evaluated specifically for packaging mmWave ICs, including interconnects, smart packaging and encapsulants for use in single or multichip modules. Thirdly, various antenna fabrication techniques will be explored which enables fully integrated ICs with antennas, called System on Antenna (SoA) which utilizes both inkjet and 3D printing to combine antennas and ICs into modules. These modules, can then be built into arrays in a modular fashion, allowing for large or smaller arrays to be assembled on the fly. Finally, a method of calibrating the arrays is introduced, utilizing inkjet printed sensors. This allows the sensor to actively detect bends and deformations in the array and restore optimal antenna array performance. Built for flexible phased arrays, the sensor is designed for implementation for ubiquitous use, meaning that its can be placed on any surface, which enables widespread use of 5G technologies.Ph.D

Polymer-Based Micromachining for Scalable and Cost-Effective Fabrication of Gap Waveguide Devices Beyond 100 GHz

The terahertz (THz) frequency bands have gained attention over the past few years due to the growing number of applications in fields like communication, healthcare, imaging, and spectroscopy. Above 100 GHz transmission line losses become dominating, and waveguides are typically used for transmission. As the operating frequency approaches higher frequencies, the dimensions of the waveguide-based components continue to decrease. This makes the traditional machine-based (computer numerical control, CNC) fabrication method increasingly challenging in terms of time, cost, and volume production. Micromachining has the potential of addressing the manufacturing issues of THz waveguide components. However, the current microfabrication techniques either suffer from technological immaturity, are time-consuming, or lack sufficient cost-efficiency. A straightforward, fast, and low-cost fabrication method that can offer batch fabrication of waveguide components operating at THz frequency range is needed to address the requirements.A gap waveguide is a planar waveguide technology which does not suffer from the dielectric loss of planar waveguides, and which does not require any electrical connections between the metal walls. It therefore offers competitive loss performance together with providing several benefits in terms of assembly and integration of active components. This thesis demonstrates the realization of gap waveguide components operating above 100 GHz, in a low-cost and time-efficient way employing the development of new polymer-based fabrication methods.A template-based injection molding process has been designed to realize a high gain antenna operating at D band (110 - 170 GHz). The injection molding of OSTEMER is an uncomplicated and fast device fabrication method. In the proposed method, the time-consuming and complicated parts need to be fabricated only once and can later be reused.A dry film photoresist-based method is also presented for the fabrication of waveguide components operating above 100 GHz. Dry film photoresist offers rapid fabrication of waveguide components without using complex and advanced machinery. For the integration of active circuits and passive waveguides section a straightforward solution has been demonstrated. By utilizing dry film photoresist, a periodic metal pin array has been fabricated and incorporated in a waveguide to microstrip transition that can be an effective and low-cost way of integrating MMIC of arbitrary size to waveguide blocks

Microsystem technology for microwave applications at frequencies above 100 GHz

The rapid development of wireless technology today shows an increasing need for<br /><br />electromagnetic components operating at even higher frequencies. Higher frequencies offer wider bandwidth, higher spatial resolution and are needed for technologies such as automotive car radars, wireless media communication and body scanners.<br /><br />The biggest issues with developing high frequency components are the small dimensions needed. With the small dimensions, issues with connectivity and resolution of the structures have become difficult to handle at frequencies above 100 GHz. The most common fabrication method used is micro-milling in brass, however this is limited in its resolution and micro-milling is not a mass production method, thus making it expensive.<br /><br />This thesis aims to realize electromagnetic components at high frequencies, more specific above 100 GHz, with the help of microsystem technology. The thesis covers a background and history of the field, a discussion of the technologies used, and presents the fabricated devices, made with microsystem technology.<br /><br />In this thesis, gap waveguides ranging from 100-325 GHz, gap adapters, and transitions fabricated with microsystem technology have been explored. Three different materials: silicon, SU8, and carbon nanotubes, have been tested as base materials together with a gold surface, for a gap waveguide component. The silicon-based structure performed overall the best, while the SU8 process was less costly, the carbon nanotube based structure was determined to be the lossiest of these realizations. The knowledge obtained from these fundamental structures were used to fabricate and measure a ridge gap antenna prototype. A gap adapter was used to connect to the antenna, to reduce leakage without using damaging screws. The antenna, was fabricated in silicon for 100 GHz. A new transition, based on the knowledge of previous transitions was used to connect the waveguide flange to the feed of the antenna. The ridge gap antenna has a 15.5% bandwidth and a gain of 10.3 dBi matching perfectly the simulated design.<br /><br />The presented work in this thesis shows how microsystem technology can realize mass producible microwave components operating above 100 GHz

The Design, Fabrication and Characterization of Integrated Photoconductive Antennas for On-Chip Terahertz Wave Radiation and Detection

Terahertz (THz) wave (between 0.1 and 10 THz) is attracting a lot of attention due to its unique properties that are favorable to various applications. These include non-ionizing radiation, better resolution than a microwave, unique spectral absorption, and an ability to propagate through many types of materials. It has been intensively researched in sensing and imaging technology for a wide range of applications in areas such as biology, pharmaceutical, food and drug control, medical science, and security screening. Driven by mostly scientific research interests, the majority of THz systems are more focused on system performance rather than system size, integration, and cost. Many THz applications aforementioned would be benefit from the compact integration of THz devices and other types of functional devices. This dissertation research focuses on developing a THz source based on heterogeneous thin film device integration. The demonstration shows a cost-effective integration approach and a feasibility to develop a THz integrated system that utilizes separately optimized LTG-GaAs based THz devices with other types of Si-based devices. The key aspect of the integration lies in the thin-film format of LTG-GaAs based THz devices, which allows their seamless integration on a final integration substrate and subsequent fabrication processes on the top of the THz devices. Using this approach, THz devices can be integrated on any host substrate (including organic and inorganic substrates), which gives a design freedom to enhance THz integrated system performances. Based on post-integration approach, the demonstrated method does not require significant modification of a host substrate technology. This allows THz functional devices to be integrated on various integration platforms including microfluidics, optics, and digital electronics. Intimate integration of THz devices with other functional devices will benefit a broad range of applications, which has limitations due to the current bulky THz systems

LIGA mold insert fabrication using SU-8 photoresist

The LIGA process potentially enables economic mass-production of devices with high aspect ratio geometry. Central to the LIGA process is the fabrication of high quality LIGA molds. But in the traditional LIGA mold insert fabrication process, the x-ray photoresist poly-methyl-methacrylate (PMMA) is not highly sensitive to x-rays and a thick piece of PMMA sheet (\u3e1mm) needs too much time to get exposed (bottom dose: 3500J/cm3), which results in excessive cost/ fabrication difficulty of the mold insert. Thus, in this thesis a negative photoresist SU-8 was tested as an x-ray photoresist in the LIGA fabrication process. SU-8 is much more sensitive (bottom dose: 20 J/cm3) than PMMA to x-rays, and the exposure time for SU-8 is decreased by a factor of a few hundred compared to PMMA, which is the primary motivation of this thesis. From the preparation of SU-8 samples to the removal of exposed SU-8 embedded in the electroplated nickel mold insert, the whole procedure for LIGA mold insert fabrication using SU-8 photoresist was successfully developed in this thesis. Compared with several other removal methods, ashing in nitrogen was selected as the method to remove the SU-8 embedded in the electroplated nickel mold insert because it is effective and inexpensive. Next the Scanning Electron Microscope (SEM) photos were taken to analyze the removal of the SU-8. Since the SU-8 removal was involved a high temperature (600„aC) step, the mechanical properties of the mold insert were degraded. Therefore, the strength and microhardness were tested to quantify the degradation. It was found that the microhardness was reduced about 46.8% and the modulus of rupture was reduced about 38%. For most applications, the degradation of strength and hardness is still acceptable