GB903889A - Improvements in microwave filter - Google Patents

Abstract

903,889. Waveguide transmission arrangements. GENERAL ELECTRIC CO. March 29, 1960 [March 31, 1959], No. 11030/60. Class 40 (8). A filter designed to eliminate unwanted harmonics from a band of frequencies comprises a waveguide capable of transmitting the fundamental band coupled at a number of spaced points with transmission means or an array of transmission means which are capable of transmitting only the harmonics and which are provided with energy absorbers. As shown in Fig. 2, each waveguide 23 in the array 22 is coupled at one end to the waveguide 20. The waveguides 23 are dimensioned to have cut-off frequencies above the frequency band transmitted by the guide 20 and are provided with dissipative terminations 27 whereby the harmonic content of the transmitted energy is eliminated. The array comprises two rows of such waveguides and is constructed from a series of plates separated by square-section posts 25 and dividing strips 26. In an alternative construction, Fig. 5, pairs of waveguides 36 arranged side-byside alternate with single waveguides symmetrically positioned with respect to the alternating pairs. This arrangement ensures coupling to both the H 10 and H 20 modes of the harmonic frequencies. Improved coupling of the harmonic frequencies may be obtained by forming the waveguide 20 with a double cosine taper 21. In a modified arrangement, the dissipative waveguides 46, 57, 62, Fig. 8, are arranged parallel and contiguous to the main guide and the coupling comprises rows of holes 54 or of slots 58, 63. The dissipative elements consist of strips 50 of resistive ceramic material arranged on the inside of the broad faces of the guides opposite the coupling apertures. Blocks of dissipative material extending over the whole cross-section of the guide may be used (Fig. 9, not shown). In the alternative constructions of Figs. 10 and 12, the dissipative guides 76 form ridges within the transmission guide 75. The coupling is provided by regularly-spaced slots 81 or by spaced pairs of slots 79. The dissipative elements are either in the form of continuous strips 82 on one face of the guide or of spaced plates 80 located in the median plane of the guides. The transmission and dissipative guides may be circular and coaxial, the smaller, dissipative guide being coupled to the surrounding transmission guide by spaced apertures (Figs. 13-16, not shown).