Radiation-efficient unidirectional printed slot antennas and arrays using phase cancellation techniques

In this thesis, novel approaches have been developed to design printed slot antennas with unidirectional radiation patterns and high radiation efficiency. First, a unified approach is developed for computing the radiation efficiencies from arbitrarily shaped slot type antennas on dielectric substrates backed by a ground plane. In this approach, different classifications of the surface-wave modes in the literature are linked together in a unified manner. The developed theory is then applied for investigating the surface-wave/parallel-plate mode characteristics of printed slot antennas and arrays. It has been found that high radiation efficiency can be achieved by using twin slots with proper dimensions and spacing through phase cancellation. Subsequently, microstrip corporate-fed slot arrays printed on electrically thin substrates with a back-reflector and CPW series-fed slot arrays printed on electrically thick substrates are designed for suppressing the parallel-plate and surface-wave modes, respectively. To eliminate both the parallel-plate and surface-wave modes and simultaneously achieve smaller element size, a novel twin arc-slot element has been developed. Unwanted lateral-wave phenomena have been linked to operation close to the cutoff frequency of a surface-wave mode. These effects have been rigorously explained using the modified saddle-point method. A compact element with simultaneous surface-wave, parallel-plate mode and lateral-wave reduction has been successfully designed and tested. Such a compact antenna element can be used for phased array applications.