GB1358980A - Microwave filters - Google Patents

Abstract

1358980 Microwave filters FERRANTI Ltd 15 June 1971 [17 March 1970] 12681/70 Heading H1W A narrow-band microwave filter comprises a number of electrically non-commensurate resonators separated by coupling sections of lengths not necessarily equal to an odd number of quarter wavelengths, the element values of the filter being in accordance with formulae comprising realizations of either inverse Chebychev or Elliptic junction approximations. Such filters may be of odd or even order and may provide symmetrical or asymmetrical characterestics. An outline of the theory of such filters is given in the Specification and the method of determining the dimensions of the resonators and coupling sections of the described embodiments is explained. In the fifth-order digital line filter shown in Fig. 4(a), the bar resonators 7-11 approximate to a half-wavelength and are short-circuited at either end. They may have different lengths and/or different cross-sections and/or different dielectric properties. The broken lines indicate the positions of tuning screws for the resonators and coupling sections. In a filter using resonators approximating to a quarter wave, the bars are open-circuited at one end. The even degree (fourth degree) waveguide filter of Fig. 7(a), comprises four stubs of different cross-sections arranged symmetrically about an impedance discontinuity 37 and coupled to the broad side of a rectangular waveguide 32. The positions of tuning screws are indicated by broken lines. An odd-numbered degree waveguide filter would have two impedance discontinuities.