Date of Award
Doctor of Philosophy (PhD)
Electrical Engineering and Computer Science
Tapan K. Sarkar
The objective of this dissertation is to illustrate that computational electromagnetics can be used to improve the accuracy and efficiency of antenna pattern measurements.
This can be accomplished in many different ways, such as moving a single probe over the measurement plane to generate accurate planar near field to far field transformation methodology over the classical Fourier based modal expansion methods. Also, one can use an array of probes instead of moving a single probe over the measurement plane to eliminate the inaccuracy of a mechanical movement of the probe antenna over a large planar surface and make the measurement methodology more accurate and efficient. Another unique feature of this methodology is that as long as the sizes of the measurement planes are chosen to be approximately equal to or larger than the size of the actual source plane of the antenna under test, one is guaranteed to obtain the accurate results.
In addition, other two approaches are proposed which under some conditions to further increase the efficiency of the whole processes of the methodology. For example, for a linearly polarized antenna, performance is often described in terms of its principal E-plane and H-plane patterns. If that is the goal, then one can use a planar dipole probe array to measure the near field over a sector and then use that to obtain the far field pattern along principal planes with engineering accuracy and so precision mechanical measurement gadgets will not be required and thus minimizing the cost and speeding up the measurement process. Another scenario is that the near field data contain complex numbers, and it’s very difficult to measure the complex data, especially for high frequency applications, say at M, V and W-bands. One can still obtain acceptable far field results by using the amplitude only data of the near field measurements, which significantly reduced the workload of the measurements, hence increased the efficiency.
The whole methodology is accomplished by solving for the equivalent magnetic current over a plane near the original source antenna under test and then employing the Method of Moments approach to solve for the equivalent magnetic currents on this fictitious surface. The two components of the equivalent currents can be solved independently from the two components of the measured electric fields. The resultant method of moments matrix equation can be solved very efficiently and accurately by using the iterative conjugate gradient method enhanced through the incorporation of the Fast Fourier Transform techniques. In all these approaches, there is no need to incorporate probe correction unlike in the existing approaches, no need to satisfy the Nyquist sampling criteria and a super resolution can be achieved in the solution of the equivalent magnetic current to predict the operation of the antenna. Also, the presence of evanescent fields does not make this methodology unstable unlike the Fourier based techniques.
Sample numerical results are presented to illustrate the potential of a novel planar near field to far field transformation for the planar near field measurement technique.
Chen, Heng, "Use of Computational Electromagnetics to Enhance the Accuracy and Efficiency of Antenna Pattern Measurements" (2019). Dissertations - ALL. 1008.