Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Patent
1985-07-08
1987-09-08
LaRoche, Eugene R.
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
333212, 333251, H01P 120, H01P 1162
Patent
active
046927239
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention pertains to the field of filtering electromagnetic energy so that only a narrow band of frequencies is passed.
2. Background Art
U.S. Pat. No. 4,138,652 discloses a waveguide employing dielectric resonators, operating in an evanescent mode. The present invention differs from the device disclosed in the reference patent is that: (1) mode suppression rods 10 are located, not along the principal axes of the dielectric resonators 6, but midway between resonators 6; (2) the mode suppression rods 10 electrically connect opposing waveguide walls 2, 3, while the mode suppression rods in the patent are connected to just the lower waveguide wall; and (3) optional passive coupling means 40 are used, in which the waveguide 1 cross-section is smaller than in the sections 30 where the resonators 6 are situated. Advantages of the present invention include: (1) a simpler mechanical configuration, since no drilling of holes through the resonators 6 or mounting rings 7 is required; (2) suppression of the propagating spurious modes in the waveguide 1, not in the resonators 6; thus, the resonators 6 are less affected by the suppression rods 10; (3) higher Q factor of the resonators 6 (a severe degradation of Q factor would occur if a suppression rod were placed in the center of a dielectric resonator as in the reference patent and shorted to the top and bottom waveguide walls); (4) ability to use standardized waveguide housing; (5) more precise adjustment of coupling between active sections 30 via the passive coupling means 40; and (6) lower cost.
U.S. Pat. No. 4,124,830 discloses a waveguide filter operating in a propagating mode, not in an evanescent mode as in the present invention. The filter is a bandstop filter, not a bandpass filter as in the present invention.
U.S. Pat. No. 3,495,192 discloses a waveguide operating in a propagating mode, not in an evanescent mode as in the present invention. No suggestion of the dielectric resonators of the present invention is made.
Secondary references are: U.S. Pat. Nos. 4,251,787; 4,321,568; and 4,453,146.
DISCLOSURE OF INVENTION
The present invention is a very narrow-band bandpass filter comprising an electrically conductive hollow waveguide (1) having four elongated walls (2, 3, 4, 5). The waveguide (1) is "dimensioned below cutoff", where the "cutoff" frequency is the lowest frequency at which propagation can occur in the waveguide (1) in the absence of any internal structures such as the resonators (6). Thus, "dimensioned below cutoff" means that in the absence of dielectric resonators (6), the waveguide (1) is sufficiently small that propagation cannot take place at the chosen frequency. The presence of two or more dielectric resonators (6) within the waveguide (1) insures that propagation in an evanescent mode does occur within the waveguide (1).
Elongated electrically conductive mode suppression rods (10) connect opposing waveguide walls (2, 3) midway between each pair of adjacent dielectric resonators (6).
Preferred embodiments of the invention are illustrated infra, in which the dielectric resonators (6) are transversely oriented within the waveguide (1). The principal axis of each resonator (6) is substantially parallel to each mode suppression rod (10). In order to further shrink the physical size of the filter, which is very important for spacecraft and other applications, each pair of adjacent active sections (30) of the waveguide (1) (i.e., sections in which a resonator (6) is present) is separated by a passive coupling means (40) in which the waveguide (1) cross-section is smaller than in an active section (30). For example, inductive partitions (12) are used for the passive coupling means (40), providing some attenuation while enabling magnetic coupling between adjacent resonators (6).
The resonators (6) can be designed to provide thermal compensation. A dielectric perturbation means (9) can be generally aligned along the principal axis of each resonator (6) to effectuate fine increases in the resonant frequency.
REFERENCES:
patent: 3495192 (1970-02-01), Gerlack
patent: 4028652 (1977-06-01), Wakino et al.
patent: 4124830 (1978-11-01), Ren
patent: 4138652 (1979-02-01), Nishikawa et al.
patent: 4251787 (1981-02-01), Young et al.
patent: 4321568 (1982-03-01), Joyal et al.
patent: 4453146 (1984-06-01), Fiedziuszko
patent: 4477783 (1984-10-01), Atia
Fiedziuszko Slawomir J.
Ziegler Craig A.
Ford Aerospace & Communications Corporation
LaRoche Eugene R.
Lee Benny T.
Radlo Edward J.
Zerschling Keith L.
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