Transmission lines are the basic building blocks of any RF and microwave circuits. The width of a microstripline increases as the characteristic impedance is lowered for a given substrate. Wide microstriplines suffer from spurious and higher order modes at higher frequencies and may not behave as transmission lines. This means the lower limitation for a realisable microstripline is about 10 ohm. In this project microstriplines with characteristic impedances of 7 ohm and 25 ohm at a frequency of 2 GHz were designed and realised using the artificial transmission lines (ATL) concept. Detailed theoretical analysis and circuit and EM simulations were used for the design and implementation of the ATLs. Taconic TLY-5 substrate was used for the PCB fabrication. The substrate thickness was 0.787 mm and the dielectric constant was 2.2. The measured results were de-embedded and compared with the simulation results. The detailed procedure of modelling and de-embedding of an SMA connector is also given. The 25 ohm ATL was realised using microstriplines only, where as microstriplines and chip capacitors were used in realising the 7 ohm ATL. The measured characteristic impedance of the 25 ohm ATL was 24.4 ohm and the measured electrical length of the 25 ohm ATL was 180 degrees at 2.1 GHz. To realise a 25 ohm ATL with 90 degrees electrical length, the half-wavelength 25 ohm ATL geometry was cut into half and one of the half geometries was EM simulated. The EM simulated electrical length of the 25 ohm ATL was 90 degrees at 1.9 GHz. The measured characteristic impedance of the 7 ohm ATL was 5.9 ohm and the measured electrical length of the 7 ohm ATL was 90 degrees at 1.8 GHz. The main advantage of an ATL is size reduction. A 25 ohm meandered microstrip line (substrate thickness = 0.787 mm, dielectric constant = 2.2) with 180 degrees electrical length at 2 GHz has a size of 34 mm x 15 mm. The 25 ohm ATL with 180 degrees electrical length at 2.1 GHz was realised in a size of 22 mm x 19 mm. The design of the 25 Ω ATL resulted in 18 percent reduction in area compared to the meander line. A 7 ohm conventional microstripline (substrate thickness = 0.787 mm, dielectric constant = 2.2) with 90 degrees electrical length at 1.8 GHz has a size of about 28 mm x 27 mm. The 7 ohm ATL with 90 degrees electrical length at 1.8 GHz was realised in a size of 7 mm x 8.4 mm which is only 8 percent of the conventional 7 ohm microstripline area. In general, a spacing of 3h where h is the substrate thickness is required between the adjacent microstriplines. In this project detailed investigations were done to see if the spacing can be reduced without any detrimental coupling affects and a spacing of 0.6 mm was used. This reduction in spacing has resulted in reduced size of the ATL. For an asymmetrical power splitter based on the Wilkinson topology, the power splitter output power split ratio depends on the square of the characteristic impedances of the quarter-wavelength arms. In this project an asymmetrical power splitter was designed and realised using a 7 ohm ATL and a 25 ohm ATL as the quarter-wavelength arms. The desired centre frequency of the power splitter was 2 GHz and the measured centre frequency was 1.6 GHz. At the centre frequency the phase difference between the output ports of the power splitter will be zero. The simulated power split ratio was 10.1 dB and the measured power split ratio was 13 dB. The power split ratio calculated using the measured characteristic impedances of the ATLs (24.4 ohm and 5.9 ohm) will be 12.4 dB which is very close to the measured power split ratio.

1 x N optical power splitters using hybrid sol-gel glasses based on buried waveguide structure on silicon substrate were fabricated. The advantage over conventional ridge structures is the fact that Y branch of the splitters can be easily obtained with the buried structure using standard photo lithography processes. Now we can successfully make the width of Y branch of less of 1um. Proximity printing was used to define the waveguide trench on sol-gel films. Then burying the sol-gel glass into the trench to define waveguide core. Finally the waveguide was packaged for measurement after coating a sol-gel top cladding layer onto the guiding layer. The propagation losses of this waveguide device are 0.69 dB/cm and 0.70 dB/cm for TE and TM polarized lights. The coupling losses are 1.57 dB and 1.89 dB for TE and TM lights with a index contrast of 0.66 %. The insertion loss and the branching loss of the 1¡Ñ2 splitter are 5.7 dB and 0.3 dB¡Arespectively.

A rigorous power coupling model for three-core optical waveguides is proposed based on a full-wave vector boundary element method (VBEM). In addition to the influence of the state of the polarization (SOP) of the input light on the coupling behavior of the three-core optical waveguides can be simulated, the polarization dependent loss (PDL) of the three-core optical waveguides can also be investigated by combining the Mueller matrix method into the power coupling model. In this dissertation, the power coupling model is applied to investigate two kinds of power splitters. The first power splitters are constructed of step-index single mode fibers called triangular 3 3 fused tapered couplers. The influence of the SOP of the input light on the coupling behavior of the triangular 3 3 fused tapered couplers and the effect of fabricating parameters of the coupler, fusion degree, and heated length on the PDL of the coupler are investigated in this dissertation. The second kind of power splitters are constructed of photonic crystal fibers (PCFs). And, several fundamental coupling properties of three-core photonic crystal fibers (PCFs) with equilateral triangular cores are investigated numerically included coupling length, bandwidth, and polarization dependent loss (PDL). It is found the three-core PCFs are good candidate to be realized as an ultra-compact power splitter. And, for three-core PCFs that chose a proper coupling point can raise the yield and performance stability of the power splitter. In addition to the coupling behavior of the power splitters, two-dimensional photonic crystals (PCs) are also studied in this dissertation based on finite-difference time-domain (FDTD) method. The phase interference phenomenon due to the multiple plane-wave signals as initial conditions of the FDTD method for computing band structure of two-dimensional PCs is studied in this dissertation. It is found some normal modes supposed to exist could be lost if the phase interference is nearly out of phase at eigenfrequency. To overcome this problem, we proposed a new solving procedure based on FDTD algorithm which can avoid mode loss phenomenon and obtain complete normal modes over interested frequency range.

In this work, an innovative approach for effective modeling of substrate integrated waveguide (SIW) devices is firstly proposed. Next, a novel substrate integrated waveguide power splitter is proposed to feed antenna array elements in series. This feed network inherently provides uniform output power to eight quadrupole antennas. More importantly, it led to a compact configuration since the feed network can be integrated inside the elements without increasing the overall array size. Its design procedure is also presented. Then, a series feed network was used to feed a novel compact omnidirectional antenna array. Targeting the 5G 26 GHz mm-wave frequency band, simulated results showed that the proposed array exhibits a broad impedance bandwidth of 4.15 GHz and a high gain of 13.6 dBi, which agree well with measured results. Its attractive features indicate that the proposed antenna array is well suitable for millimeter-wave wireless communication systems.