On Common Misconceptions

In my first book. Frequency Selective Surfaces, Theory and Design [1], I introduced at the end of each chapter a section called Common Misconceptions. It was intended to eradicate some of the many myths and misunderstandings that seem so prevalent out there. It was also intended to form the basis for further discussion in class. It soon became very popular. In fact, I became aware that these sections were often read with great glee before the text preceding them. This was manifested in well-meaning comments like Well, it is fine that you tell us what will and will not work. But you must also teU us why. It slowly dawned on me that a new misconception had arrived You just had to read the sections about common misconceptions and you would be up to speed and not make a fool out of yourself. 

Furthermore, it was often implied that the design examples were the results of either a parametric study or an optimization process or were based on many years of experience.  

While I will admit to some parametric observations where no specific theoretical background could be estabUshed right away, we are basically using an analytic approach that not only leads to a clear understanding of the problems but also establishes whether solutions exist and what they are. 

I think it was Edison that once stated, There is no substitute for hard work.  

This title will undoubtedly raise a few eyebrows. As stated in many respectable textbooks, surface waves do not radiate—period. What is not always emphasized is the fact that the theory for surface waves in general is based on a two-dimensional model like for example an infinitely long dielectric coated wire. And as discussed in this chapter infinite array theory may reveal many fundamental properties about arrays in general but there are phenomena that occur only when the array is finite. The fact is that surfaces waves are associated with element currents. They will radiate on a finite structure in the same manner an antenna radiates, namely by adding the fields from each column in an end-fire array. Numerous examples of this kind of radiation pattern will be shown in Chapter 4. They are typically characterized by having a mainbeam in the direction of the X axis that is lower than the sidelobe level. The reason for this abnormality is simply that the phase delay from column to column exceeds that of the Hansen-Woodyard condition by a considerable amount [29]. They also have a much lower radiation resistance. 

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