Embodiments of the present invention relate to the field of electrical filters. More specifically, embodiments relate to the field of microwave electrical filters.
Electrical filter structures are used in many applications. For example, electrical filter structures may be implemented as a low-pass filter, a bandpass filter, or a high-pass filter.
Normally, the filter is symmetrical, in that it is expressed as ST1=STN, ST2=STN−1, . . . and TL1=TLN−1, TL2=TLN−2, STk=STN+1−k TLk=TLN−k, k=1,2, . . . floor(N/2). These filters are particularly suitable for printed applications, for example, for use as microstrips or straplines. In the example of
As with many distributed RF/microwave filters, the DCSF has a periodic frequency response, with an infinite number of pass-bands centered at f0, 3 f0, . . . (2 h+1)*f0 (h=0,1,2, . . . ). In each pass-band the frequency response is symmetrical around its respective center.
First, the stubs (ST1, . . . STN) and the transmission lines (TL1, . . . TLN−1) of the filter depicted in
The filter design depicted in
Usually a design model simulation of a filter differs from the real response of the filter; with the difference at the low-pass side being especially large. As indicated in
Accordingly, embodiments of the present invention provide an electrical filter structure having a direct-coupled-stub filter (DCSF). The lengths of the transmission line portions can be arranged such that electrical lengths of the transmission line portions are shorter, by at least 10 percent, than a fourth of a wavelength of a signal having a frequency of a passband center frequency of the electrical filter structure. Moreover, lengths of the stubs can be selected so that the electrical lengths of the stubs are longer, by at least 2%, than a fourth of a wavelength of a signal having a frequency of a passband center frequency of the electrical filter structure. The filter structures of embodiments of the present invention can advantageously improve filter characteristics without changing the topological structure of the filter.
According to one embodiment, an electrical filter structure is disclosed. The electrical filter structure includes a microwave filter including a passband center frequency, a transmission line including a plurality of transmission line portions coupled to a plurality of junctions, a plurality of stubs coupled to the transmission line, a first port coupled to a first junction of the plurality of junctions, a first stub of the plurality of stubs is disposed at the first junction, a second port coupled to a last junction of the plurality of junctions, and a last stub of the plurality of stubs is disposed at the last junction.
According to some embodiments, the plurality of stubs include electrical lengths that are at least 2% longer than a quarter of a wavelength of a signal having a frequency of the passband center frequency of the microwave filter.
According to some embodiments, the microwave filter has a symmetrical structure.
According to some embodiments, the plurality of stubs includes N stubs having lengths, SST(s), with 1≤s≤N and N−1 transmission line portions having lengths, TLs, and the plurality of stubs are configured according to ST(k)=ST(N+1−k), [k≤floor(N/2)], where k is a positive integer.
According to some embodiments, the plurality of transmission line portions are configured according to the equation TL(k)=TL(N−k), [k≤floor(N/2)].
According to some embodiments, the microwave filter includes a Chebyshev filter characterized with a pass-band ripple of 0.1 dB in a tolerance of +/−5 percent.
According to some embodiments, the microwave filter includes a Chebyshev filter characterized with a pass-band ripple of 0.1 dB in a tolerance of +/−2 percent.
According to some embodiments, the microwave filter includes a band pass filter.
According to some embodiments, lengths of the transmission line portions are such that electrical lengths of the plurality of transmission line portions are shorter by between 15 to 50 percent of a fourth of a wavelength of a signal having a frequency of the passband center frequency of the electrical filter structure.
According to some embodiments, lengths of the plurality of stubs are such that their electrical lengths are 5 percent longer than a fourth of a wavelength of a signal having a frequency of the passband center frequency of the electrical filter structure.
According to some embodiments, lengths of the plurality of stubs are selected, and their electrical lengths are 2 percent longer than a fourth of a wavelength of a signal having a frequency of the passband center frequency of the electrical filter structure.
According to some embodiments, electrical lengths of the plurality of transmission line portions are at least 10 percent shorter than a quarter of a wavelength of a signal having the frequency of the passband center frequency of the microwave filter.
According to another embodiment, an electrical filter structure is disclosed, including a microwave filter including a passband center frequency, a transmission line including a plurality of transmission line portions coupled by a plurality of junctions, the plurality of transmission line portions include a length (TL), a plurality of stubs (N) coupled to the transmission line, a first port coupled to a first junction of the plurality of junctions, and a second port coupled to a last junction of the plurality of junctions. The plurality of stubs include a length (SST), and SST is determined according to the equation SST(k)=SST(N+1−k), where k is a positive integer.
According to some embodiments, the plurality of stubs include electrical lengths that are at least 2% longer than a quarter of a wavelength of a signal having a frequency of the passband center frequency of the microwave filter.
According to some embodiments, the microwave filter has a symmetrical structure.
According to some embodiments, the plurality of stubs includes N stubs having lengths, SST(s), with 1≤s≤N and N−1 transmission line portions having lengths, TLs, and the plurality of stubs are configured according to the equation ST(k)=ST(N+1−k), [k≤floor(N/2)], where k is a positive integer.
According to some embodiments, the plurality of transmission line portions are configured according to TL(k)=TL(N−k), [k≤floor(N/2)].
According to some embodiments, the microwave filter includes a Chebyshev filter characterized with a pass-band ripple of 0.1 dB in a tolerance of +/−5 percent.
According to some embodiments, the microwave filter includes a Chebyshev filter characterized with a pass-band ripple of 0.1 dB in a tolerance of +/−2 percent.
According to some embodiments, the microwave filter includes a band pass filter.
The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention:
Reference will now be made in detail to several embodiments. While the subject matter will be described in conjunction with the alternative embodiments, it will be understood that they are not intended to limit the claimed subject matter to these embodiments. On the contrary, the claimed subject matter is intended to cover alternative, modifications, and equivalents, which may be included within the spirit and scope of the claimed subject matter as defined by the appended claims.
Furthermore, in the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the claimed subject matter. However, it will be recognized by one skilled in the art that embodiments may be practiced without these specific details or with equivalents thereof. In other instances, well-known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects and features of the subject matter.
Portions of the detailed description that follows are presented and discussed in terms of a method. Although steps and sequencing thereof are disclosed in a figure herein describing the operations of this method, such steps and sequencing are exemplary. Embodiments are well suited to performing various other steps or variations of the steps recited in the flowchart of the figure herein, and in a sequence other than that depicted and described herein.
Some portions of the detailed description are presented in terms of procedures, steps, logic blocks, processing, and other symbolic representations of operations on data bits that can be performed on computer memory. These descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. A procedure, computer-executed step, logic block, process, etc., is here, and generally, conceived to be a self-consistent sequence of steps or instructions leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated in a computer system. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, parameters, or the like.
It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussions, it is appreciated that throughout, discussions utilizing terms such as “accessing,” “writing,” “including,” “storing,” “transmitting,” “associating,” “identifying,” “encoding,” “labeling,” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.
Some embodiments may be described in the general context of computer-executable instructions, such as program modules, executed by one or more computers or other devices. Generally, program modules include routines, algorithms, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Typically the functionality of the program modules may be combined or distributed as desired in various embodiments.
Embodiments of the present invention provide an electrical filter structure having a direct-coupled-stub filter (DCSF). The DCSF can be configured as depicted in in
Moreover, lengths of the stubs can be selected so that the electrical lengths of the stubs are longer, by at least 2%, than a fourth of a wavelength of a signal having a frequency of a passband center frequency of the electrical filter structure.
When the electrical filter structure includes N stubs having lengths SST(s), with 1≤s≤N and N−1 transmission line portions having lengths TLs, and the stubs are configured to fulfill a formula (1) within a tolerance of +/−5 percent or +/−2 percent, the transmission line portions are configured to fulfill a formula (2) within a tolerance of +/−5 percent or +/−2 percent:
SST(k)=SST(N+1−k) (1), [k≤floor(N/2)]
TL(k)=TL(N−k) (2), [k≤floor(N/2)]
k=a positive integer.
According to some embodiments, the criterion for simulating/designing DCSF is: DCSFs with N=9, pass-band 13 to 26 GHz; Chebyshev design with pass-band ripple of 0.1 dB (in-band return—loss˜16.4 dB); and Semi-ideal models for stubs and transmission lines (including loss).
As indicated in
According to
As indicated in
As a modification, the lengths of the transmission line portions can be selected so that electrical lengths of the transmission line portions are shorter, between 15 to 50 percent (preferably between 20 to 35 percent), than a fourth of a wavelength of a signal having a frequency of a passband center frequency of the electrical filter structure. In addition, the lengths of the stubs are selected such that electrical lengths of the stubs are longer, between 2 to 5 percent, than a fourth of a wavelength of a signal having a frequency of a passband center frequency of the electrical filter structure.
The structure of DCSF 650 as depicted in
Furthermore, lengths of the transmission line portions can be such that electrical lengths of the transmission line portions are shorter, by at least 10 percent, than a fourth of a wavelength of a signal having a frequency of a passband center frequency of the electrical filter structure. In this case, the lengths of the transmission line portions are such that electrical lengths of the transmission line portions are shorter by between 15 to 50 percent (preferably between 20 to 35 percent) of a fourth of a wavelength of a signal having a frequency of a passband center frequency of the electrical filter structure.
As a modification, according to some embodiments, the microwave filter has a symmetrical structure, and the electrical filter structure includes N short-circuited stubs having lengths, SST(s), with 1≤s<N, N open stubs having lengths, OSTs, and N−1 transmission line portions having lengths, TL. The short-circuited stubs are configured based on formula (1), the open stubs are configured based on formula (2), and the transmission lines are configured based on formula (3):
SST(k)=SST(N+1−k) (1), [k≤floor(N/2)]
OST(k)=OST(N+1+k) (2), [k≤floor(N/2)]
TL(k)=TL(N−k) (3), [k≤floor(N/2)]
k=a positive integer.
According to other embodiments, the microwave filter is a Chebyshev filter having a pass-band ripple of 0.1 dB in a tolerance of +/−5 percent or +/−2 percent. In addition, the microwave filter is a band pass filter. Furthermore, the open stub and the short-circuited stub of a pair have the same characteristic impedance. In addition, the electrical length of the open stub and short-circuited stub of the respective pairs is an eighth of a wavelength of a signal having a frequency of a passband center frequency of the electrical filter structure in tolerance of +/−2 to 5%.
Embodiments of the present invention are thus described. While the present invention has been described in particular embodiments, it should be appreciated that the present invention should not be construed as limited by such embodiments, but rather construed according to the following claims.
This application claims the benefit of and priority to international patent application PCT/EP2020/053351, with filing date Feb. 10, 2020, which is hereby incorporated by reference in its entirety.
Number | Date | Country | |
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Parent | PCT/EP2020/053351 | Feb 2020 | US |
Child | 17845825 | US |