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An experimental investigation has been made of the characteristics of single- and multi-iris rectangular structures of various dimensions in a thin diaphragm which is placed transversely across a rectangular, standard S-band waveguide. The irises (or windows) are parallel to the "aa" dimension of the waveguide, and varied in position along the "b" dimension of the waveguide. Measured values of resonant frequency, bandpass and Q, and the correlation between single- and double-iris structures are presented as a function of the position of the iris in the diaphragm. Data are also presented for other parameters of interest, such as the impedance. It is shown that the Q of a single iris of fixed dimensions in the center of a thin diaphragm can be appreciably increased by moving it closer to the wide waveguide wall. In addition, a low-Q multi-iris structure can be realized in which the Q of each iris is comparatively high.