UCLA

Metamaterials are artificial electromagnetic materials with novel effective medium properties that may not be available in nature. The concept of metamaterial structures has led to the design of many novel circuits exhibiting component enhancements. One type of metamaterial-based antenna structure that has been widely studied is the composite right/left-handed transmission line (CRLH-TL) leaky-wave antenna (LWA). This antenna structure has been shown to offer significant advantages over conventional LWAs. For example, a balanced CRLH-TL LWA is able to achieve continuous backfire-to-endfire frequency-dependent beam scanning with a true broadside beam, good impedance matching over an entire operating band, and simple feeding structure. Furthermore, if CRLH-TL LWAs are integrated into distributed amplifiers (DAs), which can be regarded as a microwave transversal filter with broadband amplification, the radiating power can be enhanced by the DA, and therefore DA-based CRLH-TL LWAs can realize high gain antennas while maintaining the aforementioned beam-scanning capability. Although the radiation power of the antennas can be increased by distributed amplification, power is dissipated in the termination. This issue can be resolved by introducing novel power recycling schemes to redirect the dissipated power and inject it into the antenna system again, thereby improving antenna efficiency significantly. The second part of this literature will be on negative group delay (NGD) circuits, another kind of artificial material engineered to exhibit negative group delays. Conventionally, in microwave regime, NGD circuits are based on bandstop structures using lumped elements such as

parallel RLC resonators that usually have a narrower bandwidth of NGD and lack a systematic design method. Toward this end, NGD circuits using transversal filter approach are proposed and have been shown to have a wide bandwidth of NGD with a comprehensive design method. By using these artificially engineered material based components, novel microwave imaging and communication systems as well as power amplifiers with enhanced efficiency can be realized. Lastly, novel resonator, oscillator and antenna based on substrate integrated waveguide (SIW) are introduced. Thanks to the waveguide-like cavity structure, high Q resonators can be achieved with a good tunability. In addition, by utilizing the fundamental mode of the cavity, we are able to build a planar dipole antenna that has vertical polarization.