Abstract-In this paper antenna measurements in the presence of multipath waves are discussed. Methods are proposed to diagnose the degradation sources of a compact range measurement system operating at a frequency much lower than the designed frequency range. A range-gating technique is employed to improve the capability of the compact range measurement system. With this technique, the field responses over a bandwidth for each rotation angle are coherently measured, and the fast Fourier transform is applied to obtain the range profile. A suitable window function is applied to extract the desired path and eliminate all other undesired paths. The antenna pattern is plotted according to the filtered response of the desired path. We have expressed the receiving voltage of a testing antenna in terms of its gain pattern and input impedance of the testing antenna operating in multipath environment. If the bandwidth of the testing antenna is very narrow and the mismatch problem is very serious over the required bandwidth, an algorithm is proposed to compensate the mismatch effect so that the obtained radiation pattern and the antenna gain are more accurate. Numerical and experimental results have verified the effectiveness of our method.
An effective quadrature mirror fdter (QMF) proposed by Vaidyanathan has been used to solve 2D scattering problems. QMF has been popular for some time in digital signal processing, under the names of multirate sampling, wavelets, etc. In this work, the impulse response coefficients of QMF were used to construct the wavelet transform matrix. Using the matrix to transform the impedance matrices of 2D scatterers produces highly sparse moment matrices that can be solved efficiently. Such a presentation provides better sparsity than the celebrated and widely used Daubechies wavelets. These QMF coefficients are dependent on the filter parameters such as transition bandwidth and filter length. It was found that the sharper the transition bandwidth, the greater the reduction in nonzero elements of the impedance matrix. It also can be applied in the wavelet packet algorithm to further sparsify the impedance matrix. Numerical examples are given to demonstrate the effectiveness and validity of our finding.
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