Harmonic-suppression Using Adaptive Surface Meshing and Genetic Algorithms

A novel design strategy for microstrip harmonic-suppression antennas is presented. The computational method is based on an integral equation solver using adaptive surface meshing driven by a genetic algorithm. Two examples are illustrated, all involving design of coaxially-fed air-dielectric patch antennas implanted with shorting and folded walls. The characteristics of the antennas in terms of the impedance responses and far fleld radiation patterns are discussed theoretically and experimentally. The performances of all of the GA-optimised antennas were shown to be excellent and the presented examples show the capability of the proposed method in antenna design using GA. 1. REVIEW AND SUMMARY OF THE METHOD Harmonic suppression antennas (HSAs) are used to suppress power radiation at harmonic frequen- cies from active integrated antennas. An antenna that presents a good impedance match at the fundamental design frequency (fo) and maximised re∞ection at harmonic frequencies is said to be a harmonic suppression antenna. In addition, the input impedance of any HSA design has to have minimised resistance at the harmonic frequencies and hence will be largely reactive (1,2). Several techniques have been proposed to control such harmonics, such as shorting pins, slots or photonic bandgap structures (3,4). In (5), the modifled rectangular patch antenna with a series of shorting pins added to the patch centre line was applied to shape the radiated second harmonic from the active amplifying-type antenna, in order to increase the transmitter e-ciency. Unfortunately, the proposed design does not provide the termination for the third harmonic. A circular sector patch antenna with 120 - cut out was investigated and proved to provide additional harmonic termina- tion for the third harmonic, also claiming a further enhancement in the transmitter e-ciency (2). Further, an H-shaped patch antenna was designed and applied in oscillator-type active integrated antennas for the purpose of eliminating the unwanted harmonic radiation (6,7). The present work presents a clear motivation to develop a coherent design strategy for microstrip HSA in active inte- grated applications. The technical work, adopts a computational technique using adaptive surface meshing driven by a genetic algorithm. The beneflt of applying GA methods is that they provide fast, accurate and reliable solutions for antenna structures. A genetic algorithm driver (8{10), written in Fortran, was adopted in this work in conjunction with the authors' Fortran source code (11), which was used to evaluate the randomly-generated antenna samples. Several antenna designs, derived using GA in previous work by the authors (12{14), have shown that the GA method to be an e-cient optimiser tool that can be used to search and flnd rapid solutions for complex antenna design geometries. An adaptive meshing program was also written in Fortran by the present authors and added as a subroutine to the GA driver, with the primary objective of simulating air-dielectric planar microstrip patch antenna designs: this used a surface patch model in cooperation with a GA. In addition to microstrip patch designs, the program can support the design of any 3D antenna geometry structure, including moderate amounts of dielectric materials. The present work is an extended version of preliminary work reported in (15). The design of coaxially-fed air-dielectric microstrip harmonic-rejecting patch antennas for 2.4GHz was investigated, enforcing suppression of the flrst two harmonic frequencies, using a genetic algorithm. The designs included patch antennas with shorted and folded walls.