Physically/Electrically Enhanced Microwave & Millimeter Wave Front-ends with Modern Manufacturing Technologies

The growing demand toward designing miniaturized microwave and millimeter wave (mm-wave) front-ends with enhanced electrical performance (e.g., low losses, wideband functionality, high selectivity, etc.) is becoming of utmost importance. In addition, enabling functionalities such as selection/rejection of specific frequency channels (i.e., filtering), power division, and amplification is essential for any wireless system. This dissertation proposes new design methodologies for various front-ends using different manufacturing technologies. The proposed designs are verified by full-wave EM simulations and experimental results of passive front-ends at microwave and millimeter wave frequencies. The aim is to enhance their electrical and physical characteristics without degrading their intended performance. The developed designs are essential to the upcoming wireless technologies such as fifth generation (5G) mobile communication and satellite systems.The first proposed component is a substrate integrated waveguide (SIW) bandpass filter (BPF). The design procedure starts by varying the width between the metallic walls of via-holes according to a truncated Fourier series to achieve a desired passband/stopband performance. The theory of rectangular waveguide is used to establish the optimization framework and obtain the series coefficients under predefined physical constraints. Two types of end-terminations are studied, namely, with and without SIW-to-microstrip transitions. The proposed design methodology is systematic and results in single-layered structures. For verification purposes, several Ku-band BPFs with different fractional bandwidths (FBWs) are designed, simulated, and measured. Simulated and measured results are in close proximity with passband matching and transmission losses better than -15 dB and -2.5 dB, respectively. The proposed methodology allows for designing BPFs with predefined wideband or narrowband functionality by modifying the underlying physical constraints and optimization parameters.The second proposed component is a highly-selective SIW filtering Wilkinson power divider (WPD). The design procedure is accomplished by replacing the uniform transmission lines in each arm of the conventional divider with width-varied arms governed by a truncated Fourier series. Even-mode analysis is adopted to obtain the Fourier-varying transmission lines with predefined bandwidth; whereas three isolation resistors are optimized in the odd-mode analysis to achieve proper isolation and output ports matching over the frequency range of interest. The half-mode (HM) SIW structure is used to cut the PD size by 50%. For verification purposes, a 2-way equal-split filtering WPD is designed and simulated. The obtained results show that the input and output ports matching as well as the isolation between the output ports are below -13 dB; whereas the transmission parameters are around -6 dB across the operating band. Such results adjoined with compact size show that the proposed PD will be a competitive candidate for microwave and millimeter wave application.Next, an impedance-varying multi-way microstrip WPD with bandwidth redefinition characteristics is proposed. The microstrip WPD finds many applications due to its convenient electrical performance, which is characterized by high isolation between its output ports and perfect matching at all ports. However, such performance is realized only at a very small fraction of bandwidth. Hence, the proposed impedance-varying WPD aims to broaden the bandwidth without increasing the circuitry size or fabrication complexity. Quarter-wave matching uniform transmission lines in the conventional design are replaced with non-uniform transmission lines (NTLs) governed by a truncated Fourier series. Compactness is achieved by incorporating only one quarter-wave wideband NTL transformer, with a length computed at the center frequency, in each arm. For verification purposes, 3- and 4-way WPDs are designed and simulated. In addition, a wideband 3-way WPD operating over 4-10 GHz band is fabricated and measured. Results show input and output ports matching and isolation below -15 dB, and transmission parameters in the range of [-4.9,-6.2] dB across the operating band of the 3-way and WPD.The last proposed component is a miniaturized coplanar waveguide (CPW) matching transformers implemented on flexible substrates. The signal trace and the adjacent ground planes in the conventional CPW structure are width-modulated along the propagation path of the electromagnetic wave while maintaining a constant ground-trace separation. Validation is carried out by designing and simulating single-, multi-, and wide-band transformers operating at 1.0 GH, 0.9, 3.6, 5.4 GHz, and 1-3 GHz, respectively. Full-wave simulation results verify the proposed design procedure which show input port matching values below -23 dB for single- and multi-frequency transformers, whereas they are below -15 dB for the wideband one. In addition, insertion losses are better than -0.25 dB for all designed transformers.The proposed designs are targeting the less congested higher frequency bands, specifically, super high frequency (SHF) band. Moving toward higher frequencies enables higher data rates, supports more connected wireless devices, and leads to more miniaturized front-ends.