Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
1999-03-12
2001-05-15
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S202000, C333S034000, C333S210000
Reexamination Certificate
active
06232853
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention is directed to the field of electronic filters. More particularly, the present invention provides a compact waveguide filter exhibiting high-pass, band-pass and low-pass response from a single filter structure, which is capable of handling high-powered microwave signals in the GHz frequency range.
2. Description of the Related Art
Waveguide filters are known in this art. There are two primary types of filters for use in the microwave frequency range (i.e. from about 2-15 GHz), symmetrically corrugated filters and iris filters. However, both of these types of filters suffer from many disadvantages.
An example of a symmetrically corrugated filter is shown in U.S. Pat. No. 3,597,710 to Levy (“the ′720 patent). FIG. 1 of the ′720 patent shows a standard E-plane corrugated structure having a uniform waveguide channel with a plurality of symmetrical corrugations. But as noted in the ′720 patent, these types of corrugated filters are typically low-pass only. Such a filter typically cannot provide a band-pass response.
The ′720 patent purports to have advantages over the standard corrugated structure by forming a plurality of capacitive irises. Instead of forming a uniform waveguide channel, the ′720 patent provides a series of iris structures (FIGS. 2 and 6), which have different heights. Although the irises and the corrugations are of different height, for any one iris or corrugation, the structure is symmetrical. Another example of an iris filter (known as an H-plane iris filter) is shown in U.S. Pat. No. 2,585,563 to Lewis, et al. These types of iris filters suffer from many disadvantages, however. First, they typically provide band-pass response only, i.e., they are incapable of providing a combination response, such as low-pass and band-pass. Secondly, the iris filter is typically a large structure, as the irises are generally separated along the waveguide channel by a half of a wavelength (&lgr;g/2). Since the number of irises typically correlates to the order of the filter, this results in a very large filter when the order of the filter is high, such as 5th order or greater.
Other types of filters include resonant iris filters (as shown in U.S. Pat. Nos. 1,788,538 to Norton and 1,849,659 to Bennett) and evanescent-mode ridged filters (as shown in U.S. Pat. No. 4,646,039 to Saad). The resonant iris filter utilizes a plurality of resonant diaphragms as resonating elements that are separated by a quarter of a wavelength (&lgr;g/4). The evanescent-mode ridged filter is based on a wavelength structure with a ridged cross section. However, a common problem with both of these types of filters is that they typically cannot handle high-powered signals.
Therefore, there remains a general need in this field for a compact waveguide filter that provides a combination response and is capable of handling high-powered signals in the GHz range.
SUMMARY OF THE INVENTION
A waveguide filter is provided having a plurality of asymmetrical corrugated resonators. The filter may also include an input section and an output section including a low-pass filter unit and a transformer unit. The low-pass filter unit includes a plurality of symmetrically corrugated slots, and the transformer unit includes at least one stepped transformer section for matching the filter to an external waveguide line. Each of the asymmetrically corrugated resonators may include a pair of opposed slots of different depth, a long slot and a short slot. The resonators provide at least one reflection zero and two transmission zeros to the frequency response of the filter, thus providing high-pass, band-pass and low-pass filter properties in a single filter structure.
According to one aspect of the invention, a waveguide filter is provided that includes an input section, an output section and a band-pass filter unit coupled between the input and output sections. The input section includes a transformer unit and a low-pass filter unit, wherein the transformer unit includes at least one stepped transformer section for matching the input section of the waveguide filter to an external waveguide line, and the low-pass filter unit includes a plurality of symmetrically corrugated slots. The output section also includes a low-pass filter unit and a transformer unit, wherein the low pass-filter unit includes a plurality of symmetrically corrugated slots, and the transformer unit includes at least one stepped transformer section for matching the output section of the waveguide filter to an external waveguide line. And the band-pass filter unit includes a plurality of asymmetrically corrugated resonators, each resonator having a long slot and a short slot.
Another aspect of the invention provides a waveguide filter having an input section and an output section coupled to external waveguide lines, and a band-pass filter unit coupled between the input section and the output section, the band-pass filter having N asymmetrically corrugated resonators, wherein each resonator provides one reflection zero and two transmission zeros to the frequency response of the waveguide filter.
Still another aspect of the invention provides a filter having a plurality of asymmetrically corrugated resonators having two opposed slots of different depth, a long slot and a short slot.
It should be noted that these are just some of the many aspects of the present invention. Other aspects not specified will become apparent upon reading the detailed description set forth below.
The present invention overcomes the disadvantages of presently known filters and also provides many advantages, such as: (1) compact size; (2) high-powered capability; (3) combination frequency response; (4) sharp roll-off on both sides of the pass band; (5) wide and deep rejection response; (6) optional addition of extra low-pass rejection; (7) optional transformer units; and (8) exhibits narrower spurious pass band corresponding to high-order modes than conventional filters.
These are just a few of the many advantages of the present invention, which is described in more detail below in terms of the preferred embodiments. As will be appreciated, the invention is capable of other and different embodiments, and its several details are capable of modifications in various respects, all without departing from the spirit of the invention. Accordingly, the drawings and description of the preferred embodiments set forth below are to be regarded as illustrative in nature and not restrictive.
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COM DEV Limited
Glenn Kimberly E
Jones Day Reavis & Pogue
Lee Benny
LandOfFree
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