JP2008508788A - Apparatus and method for split feed coupled ring resonator versus elliptic function filter - Google Patents

Abstract

  The filter includes a coupled resonator pair disposed between the split feed lines on the same plane as the split feed line. The filter has two pairs of resonators. The coupled branch lines of the split feed lines are substantially parallel to each other. The resonator is coupled to the split feed line at the coupled branch line. Each pair of resonators is also coupled to each other. This structural form effectively forms an elliptic function response bandpass filter with high proximity frequency rejection capability. The filters can be cascaded to provide improved frequency rejection. Furthermore, this structural form can be created at a relatively low cost using standard lithographic techniques.

Description

  The present invention relates to filters, and more particularly to coupled ring resonator-to-band filters.

  In general, a filter in an electrical circuit “passes” a selected signal while simultaneously blocking other signals. One type of filter is a bandpass filter. A typical bandpass filter is an electrical element or circuit that passes signals in a specific frequency range but blocks signals at other frequencies.

  Bandpass filters are often used in the electrical circuitry of devices such as radios, televisions, cordless or mobile phones, wireless communication systems, radars, sensors and certain types of manufacturing measurement / instrumentation systems. These devices transmit and receive signals using electromagnetic waves.

  The primary function of the bandpass filter at the transmitter is to limit the bandwidth of the output spectrum. At the receiver, the bandpass filter causes the receiver to receive a selected range of frequencies and removes signals of unwanted frequencies. The bandpass filter also optimizes the signal-to-noise (sensitivity) of the receiver. A well-designed bandpass filter that has the optimal bandwidth for the communication mode and speed used, in both transmission and reception applications, maximizes the number of signals that can be transmitted to the system. Minimize interference or contention.

  One example of the use of filters in electronics is microwave communication, i.e. wireless communication using signals in the microwave region of the electromagnetic spectrum. Conventional filter configurations intended for operation at high frequencies include end-coupled filters, surface acoustic wave (SAW) filters, dielectric resonator filters, and waveguide filters. Another type of conventional filter used for microwave communications has two square loop resonators, which are arranged on both sides of the core material, with the loop centers offset from each other. It is a filter. This type of filter can be realized, for example, in two layers of a printed wiring board. In operation, the square loop resonators cross-couple with each other, thus each affecting the electrical response of the other, creating a signal useful for microwave communications. The response of this filter is controlled by changing the amount of offset at the relative position of the resonator.

  The configuration and operation of conventional filters have problems arising from various difficulties. For example, in the conventional signal filtering technique, generally, sufficient filtering is not performed when the unnecessary frequency is close to the selected pass frequency. For this reason, it is often difficult to block unnecessary signals. In such situations, filters are commonly used to band limit thermal noise and to remove image frequencies and other nearby spurious signals. The requirements for high frequency band filters generally include a small structural form, a narrow and strict passband, high proximity frequency rejection and low total manufacturing / tuning adjustment costs. In the conventional end-coupled filter, surface acoustic wave (SAW) filter, dielectric resonator filter, and waveguide filter described above, the resonator structure is relatively expensive, bulky, and difficult to tune. It still remains desirable to have a method and apparatus for a bandpass filter that is sensitive to pass the desired frequency and at the same time rejects nearby unwanted frequencies.

  Embodiments of the present invention significantly overcome the above disadvantages by providing a technique for filtering using a novel filtering structure having a coupled ring resonator structure configuration. Such a structure is well suited for bandpass filtering because it provides a high close frequency rejection elliptic response. Such a structure provides a small, narrowband filter. Furthermore, this configuration is advantageous in that it can be implemented using standard lithography techniques that are relatively inexpensive.

  More particularly, embodiments of the present invention provide a method and apparatus that uses a pair of ring resonators disposed orthogonal to a feed line in a filter circuit. The feed line is split for coupling with two resonator pairs. The resonators of each resonator pair are coupled to each other and to the feed line. In order to tune the filter circuit to pass a selected frequency, the resonator placement and resonator coupling length relative to another resonator is used. The resonator arrangement and the resonator width for the feed line are also used to tune the filter circuit. In one embodiment, this structural form effectively forms an elliptic function response bandpass filter with high near frequency rejection capability. Furthermore, such structural forms of embodiments of the present invention can be created at a relatively low cost by standard lithographic techniques, such as those used in printed wiring board manufacturing or thin film manufacturing.

  One such embodiment of the filter includes a first feeder line having a first trunk line connected to a first coupled branch line and a second coupled branch line, and a third coupled branch line and a first coupled line. A second feed line having a second trunk line connected to the four coupled branch lines, the first coupled branch line being substantially parallel to the third coupled branch line and the second coupled line The branch line is substantially parallel to the fourth coupled branch line. The present embodiment further includes four ring resonators arranged on the same plane as the first and second feed lines, and the four ring resonators are connected to the feed line to form a first resonance circuit. Two of the ring resonators are disposed between the first coupled branch line and the third coupled branch line, and another two of the ring resonators are coupled to the second coupled branch line. It arrange | positions between 4th coupling branch lines. A resonant circuit of this configuration provides a well-defined passband that allows signals of selected frequencies to pass but blocks nearby frequencies.

  In another embodiment of the invention, each ring resonator is substantially quarter wavelength (λ / 4) in length on each side and substantially centered at a selected frequency. Give the passband. Therefore, the center of the pass band of the filter can be set at a specific frequency by expanding or reducing the resonator length in proportion to the wavelength.

  In another embodiment of the invention, each ring resonator is a square ring resonator. Square ring resonators couple more effectively to feed lines and to each other than circular ring resonators. In another embodiment of the invention, the length of each side of the square ring resonator is substantially a quarter wavelength (λ / 4) of the selected center frequency. Further, a portion of each coupled branch line adjacent to the side of each square ring resonator forms a coupling point, and each coupling point is a quarter wavelength coupler. Thereby, the balanced resonance over the whole resonance circuit is obtained.

  In another embodiment of the present invention, the feed line, the coupled branch line, and the ring resonator are conductive signal layer structures on a substrate. In such embodiments of the invention, the bandpass filter formed using the disclosed inventive features is part of the circuit.

  In another embodiment of the present invention, the bandpass filter further includes a fifth ring resonator between the first coupled branch line and the third coupled branch line, and the second coupled branch line and the fourth coupled line. A sixth ring resonator is provided between the coupled branch lines. The additional resonator of the bandpass filter improves the passband boundary limitation.

  In another embodiment of the invention, the ring resonators are arranged relative to each other such that each ring resonator affects the resonance of an adjacent resonator, thus defining the passband of the bandpass filter. The band filter is effectively tuned by the mutual arrangement of the ring resonators.

  In an embodiment of the invention, the bandpass filter is configured to operate in a relatively low radio frequency region of the electromagnetic spectrum. In this way, the size of the bandpass filter structure can be varied from a relatively low radio frequency range according to the frequency chosen.

  In another embodiment of the present invention, a first resonant circuit having a ring resonator as described above and a second resonant circuit having a ring resonator as described above are connected in series. This is also called “cascading” of filters. A series connected filter provides a steeper passband than a single filter alone.

  The method embodiment of the present invention includes a step of providing a first feed line and a second feed line, a step of providing a pair of ring resonators arranged orthogonal to the feed line, and a pair of rings of the feed line. A filtering method is included, including the step of providing a coupling branch line connected to each feed line so as to be coupled to the resonator to form a first resonance circuit.

  In another embodiment of the present invention, the method further includes affecting at least two ring resonators, each ring resonator affecting an adjacent resonator, such that the passband of the bandpass filter is defined, Placing relative to each other so as to be tuned.

  In another embodiment of the present invention, the method further configures the first feed line, the second feed line, at least two pairs of ring resonators and the coupled branch line to operate at a relatively low radio frequency. Process.

  In another embodiment of the present invention, the method further includes combining a first feed line, a second feed line, at least two pairs of ring resonators and coupled branch lines on the same side of the substrate using printed wiring board technology. Forming the upper structure. In another embodiment of the present invention, the method further forms the first feed line, the second feed line, the ring resonator and the coupled branch line as a structure on the same surface of the substrate using thin film technology. The process of carrying out is included. In this way, the bandpass filter can be constructed using standard manufacturing techniques that are relatively inexpensive, thus making the bandpass filter relatively inexpensive and easy to implement.

  The above and other objects, features and advantages of the present invention will become apparent from the following description of specific embodiments of the invention, as illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout the various views. It will be.

  Wireless communication requires a filter structure that provides a filter that is small, narrow band, and provides high proximity signal rejection. Embodiments of the present invention provide mechanisms and techniques for coupled ring resonator structure configurations that provide such filters. Furthermore, embodiments of the present invention are advantageous in that they can be implemented using relatively low cost standard lithography techniques, such as those used in printed wiring board manufacturing or semiconductor manufacturing. Embodiments of the present invention have two pairs of ring resonators. In one configuration, the ring resonators are arranged side by side and orthogonal to the input and output lines. In one configuration, the resonator is a square ring resonator. The side length of each ring resonator is tuned to substantially λ / 4 of the circuit operating frequency. The input and output lines are split for coupling with all ring resonators in the configuration. Each ring resonator is arranged with respect to the split feed line in such a manner that the ring and the feed line substantially form a λ / 4 coupler. The elliptic function response achieved by one embodiment of the filter structure form of the present invention allows 10% narrower bandwidth and higher rejection than an equivalent Chebyshev filter.

  1-6 are presented to provide the reader with an understanding of the filter and filter signal response, particularly for filters used in high frequency applications. For example, in wireless communication, a radio signal and a carrier wave are inputs to a signal mixer, and the respective frequencies can be changed. In performing this conversion, spurious signals are randomly generated by the circuit or environment or a combination thereof. In many cases, the spurious signal is very close to the desired signal. FIG. 1 is a graph 100 of frequency versus signal in a conventional filter circuit, which shows the desired signal and the spurious signal. In the graph, the horizontal axis is the frequency measured in hertz, and the vertical axis is the amplitude. The selected pass frequency 105 is the signal having the maximum signal amplitude. There is a spurious signal 110 in proximity to the desired signal 105 on either side of the desired frequency. The conventional filter cannot pass a desired signal, but cannot obtain a bandpass filter that passes only a sandwiched band that cuts off a spurious signal, particularly a close spurious signal. However, in the embodiment of the present invention, signals in one band are allowed to pass, but other frequencies can be blocked even if they are close to the pass frequency.

  In particular, modern microwave systems require high performance, narrowband bandpass filters with low insertion loss and high sensitivity with linear phase or flat group velocity in the passband. These criteria are generally met by a conventional filter having an elliptic function response. In general, cross coupling between resonators that are not adjacent to each other is required to realize elliptic function response filter characteristics.

  FIG. 2 is a top view of elements on a substrate of a conventional five-resonator-end coupled bandpass filter that provides a Chebyshev filter response. In one configuration of these elements, the element is a printed signal layer element on a printed wiring board. In another configuration of these elements, the elements are made on a substrate using thin film technology.

  The conventional band-pass filter of FIG. 2 is composed of a plurality of half-wave resonators that are cascaded in an end-coupled manner. This conventional band-pass filter 150 has a first feed line 155-1 and a second feed line 155-2. Each feeder line 155 has a quarter-wave transformer 160 connected to a quarter-wave coupler 165. A 5-cascade half-wave resonator or waveguide 170-1, 170-2, 170-3, 170-4, 170-5 between the first feed line 155-1 and the second feed line 155-2. There is a 5-node resonator with (collectively 170). The length of each half-wave resonator 170 is ½ wavelength of the selected center frequency. Each half-wave resonator 170 has a ground point at the substantial center point of the strip. Each half-wave resonator 170 is further open at both ends of the half-wave resonator 170. In FIG. 2, grounding and opening are shown for half-wave resonator 170-1.

  In the conventional filter of FIG. 2, the half-wave resonators 170 are end-coupled to each other and to the feed line quarter-wave coupler 165. That is, the quarter-wave coupler 165-1 of the first feed line 155-1 is end-coupled to the adjacent half-wave resonator 170-1, and the second quarter-wave coupler 165-2 is adjacent. End-coupled to half-wave resonator 170-5. The middle three resonators 170-2, 170-3, and 170-4 are end-coupled to the resonators 170-1 and 170-5 at both ends. The midpoint of each half-wave resonator, that is, the ground point, is a reference point. There is a quarter wave of vibration from the reference point to the end of the half-wave resonator. The resonator 170 resonates only in a specific frequency band. If each resonator 170 is slightly offset, a wider pass frequency band is formed. The resonators 170 interact with each other. If the gap between the resonators 170 is large, the interaction between the resonators is weakened. If the gap between the resonators 170 is small, each resonator overlaps an adjacent resonator.

  A conventional solution to increase the steepness of the filter has been to cascade several resonators as in the bandpass filter shown in FIG. In practice, when many conventional resonators are combined in a circuit, the desired output is not always obtained. As the steepness of the filter is increased by adding the resonator, the insertion loss and the feedback loss are deteriorated, and the manufacturability of the filter is also deteriorated.

  FIG. 3A shows a basic series resonator representation 200 for the resonator 170 of FIG. Resonator representation 200 for half-wave resonator 170 has an inductance component 205 and a capacitance component 210.

FIG. 3B shows a graph of amplitude versus frequency of the passband response of half-wave resonator 170 for a conventional filter. When a capacitor is combined with an inductor, a circuit having very steep frequency characteristics can be created. A circuit having capacitance and inductance is represented by Equation 1:

As shown, the resonance frequency is inversely proportional to the square root of the product of capacitance and inductance.

Due to the conflicting behavior of the inductor and capacitor, the theoretical impedance of the parallel inductor / capacitor (LC) resonant circuit becomes infinite at the resonant frequency F _resonance , resulting in theoretically the same as the peak 215 shown in FIG. 3B. A peak occurs in the circuit response at the resonance frequency. In practice, the steepness of the response peak is limited due to losses in the inductor and capacitor.

FIG. 4 is a graph 250 of output power versus frequency for the passband response of a hypothetical conventional bandpass filter. FIG. 4 is included here to illustrate the expected signal response of a conventional bandpass filter and to illustrate the elements of the filtered signal response having the type of response produced by the filter shown in FIG. FIG. 4 shows a passband between the frequency f ₁ 255 and the frequency f ₂ 260, approximately centered on the resonance frequency f ₀ 265. The cut-off frequencies, f ₁ 255 and f ₂ 260 are frequencies at which the output signal power drops to ½ of the output signal level at f ₀ 265. The value of the difference between the frequencies, namely _(f 1 -f ₂₎ defines the filter bandwidth. The frequency range between the frequency f ₁ 255 and the frequency f ₂ 260 is the filter passband. FIG. 4 is included to illustrate aspects of the desired bandpass filter response curve. The rising edge and falling edge of the curve are called skirts 270. Ideally, the tail 270 of the bandpass filter response curve is steep, the bandwidth response 275 is flat, and the shoulder 280 whose tail meets the top of the curve is not rounded. The graph of FIG. 4 is a typical response obtained when using a prior art bandpass filter. The passband response for filtering adjacent spurious frequencies needs improvement in all aspects of the response curve.

FIG. 5A shows a partial circuit diagram of the bandpass filter of FIG. 2, with parts representation, and is presented here to model the combined stripline bandpass filter of FIG. The feed line 155 in FIG. 2 is represented by a V _input 155-1 ′ lead and a V _output 155-2 ′ lead. Each resonator 170 of FIG. 2 is represented here by a resonator conceptual diagram 170 ′. Each circuit component is affected by adjacent components to give the response shown in FIG. 5B.

  FIG. 5B shows a graph of output signal amplitude versus frequency for a bandpass filter circuit of the type shown in FIG. 5A. The response curve (indicated by the dashed line) is the result of the combined response of each individual resonator in the circuit (indicated by the solid line). As mentioned above, the prior art solution to increase the steepness of the filter was to introduce many resonators, as in the bandpass filter shown in FIG. 2 and represented in FIG. 5A. Note that the circuit response shown in FIG. 5B is similar to the circuit response shown in FIG. However, as described above, as the steepness of the filter is increased by adding the resonator, the electrical characteristics of the filter deteriorate.

FIG. 6 is a graph showing an example of a passband response by simulation of the filter of the prior art of FIG. The graph of FIG. 6 is an amplitude vs. frequency graph where the amplitude is normalized and given in decibels. Curve S ₂₁ 300 is an example of a passband response by simulation of the prior art bandpass filter 150 of FIG. As can be seen, the tails 305-1 and 305-2 of the curve 300 are not so steep, so it can be seen that the proximity frequency blocking capability by the bandpass filter 150 of FIG. 2 may not be optimal. The minimum bandwidth of the structural form of the bandpass filter of FIG. 2 is approximately 10% of the center frequency. Passband pinching implies widening of the gap between half-wave resonators, which makes the passband “shape” of this structural form very sensitive to surrounding circuitry and the environment. In order to enhance the near frequency rejection of the end-coupled filter as shown in FIG. 2, an additional half-wave resonator can be further added to the configuration to increase the steepness of the filter tail. However, the addition of additional poles degrades filter performance and manufacturability (ie reproducibility).

  The present invention employs a ring resonator that is arranged orthogonally between feed lines, that is, without overlapping. Such a configuration provides a strictly defined passband with a steep tail that improves the ability to block adjacent spurious signals compared to the previously disclosed filters.

FIG. 7 is a top view of elements on a substrate of a coupled ring bandpass filter in accordance with the principles of the present invention. The coupled ring band filter is configured by a plurality of rings that are arranged orthogonally between the feed lines and coupled to the feed lines. Coupling herein refers to electromagnetic coupling and no physical connection is required. A typical operating range for the filter is the high frequency range of the electromagnetic spectrum. This range includes a relatively low radio frequency range (RF), generally defined as frequencies below 3 × 10 ⁹ Hz, and microwaves generally defined as frequencies in the range of 3 × 10 ⁹ Hz to 3 × 10 ¹⁰ Hz. Included are millimeter wave ranges defined as ranges and frequencies generally in the range of 3 × 10 ¹⁰ Hz to 3 × 10 ¹¹ Hz.

  In one configuration, the element shown in FIG. 7 is implemented as a microstrip circuit. In the microstrip, the element is part of the signal surface layer on the top surface of the core material, and the core material has a ground plane on the back surface of the core material. The ground plane of the microstrip is generally a metal coating layer. In the second configuration, the element shown in FIG. 7 is realized as a strip line, for example, where the element is part of a signal layer embedded in a multilayer printed wiring board. On the outside of the core material, ie the outside of the structure, there is a metal coating layer that serves as a ground plane. In the third configuration, the element shown in FIG. 7 is realized as a coplanar waveguide in which ground is located on the same plane as the element. These configurations can be created using standard lithographic techniques, such as printed wiring board technology or thin film technology.

  The coupling ring band filter 400 of FIG. 7 includes a first feed line 405-1 and a second feed line 405-2. In operation, one feed line is an input and the other feed line is an output, but the circuit is symmetrical, so the input and output are shown in the same terms for the sake of brevity. The center of the feeder lines 405-1 and 405-2 is substantially on an intermediate line that defines a bisector of the surface of the circuit 400. Each feed line 405 is divided and has a main line 410, and the main line 410 is connected substantially vertically to a cross member having two coupled branch lines 420 extending on both sides of the main line 410. Each trunk line 410 has a quarter-wave transformer 415 at a connection point 407 to the coupled branch line 420. The transformer in this application is an impedance transformer, which is a quarter wave element that matches the impedance of one line with the different impedance of the other line. The coupled branch line 420-1 of the first feeder line 405-1 is substantially parallel to the coupled branch line 420-2 of the second feeder line 405-2. The input coupled branch line forms a first straight edge and the output coupled branch line forms a second straight edge. Each coupled branch line 420 includes a quarter wavelength transformer 425 and a quarter wavelength coupler 430, and the transformer 425 is between each pair of couplers 430 on each coupled branch line 420.

  There are a plurality of ring resonators 435 on the same plane as the feed line between the first feed line 405-1 and the second feed line 405-2. The resonator 435 is arranged such that two of the resonators 435 are on one side of the intermediate line 409 and two of the resonators 435 are arranged on the other side of the intermediate line 409. The ring resonators 435 have straight regions to provide better coupling with the feed line 405 and with each other, so that each ring resonator 435 is generally square. That is, each resonator 435 has a square shape. The length of each side of each ring resonator 435 is substantially a quarter wavelength (λ / 4). The selected frequency is a resonant frequency that is substantially centered in the passband of the filter 400. The selected frequency is basically the frequency that is to be passed by the bandpass filter 400. Each ring resonator 435 has a theoretical open end and a theoretical ground. Further, each ring resonator 435 is coupled to the first coupler 430-1 on the first feed line 405-1, and the second coupler 430-2 on the second feed line 405-2. Also join. The ring resonator 435 is end-coupled to each other and is also end-coupled to the feed line quarter wavelength coupler 430.

  The ring resonator 435 resonates only in a specific frequency band. Ring resonators 435 interact in pairs. Each pair of ring resonators 435 interacts with an adjacent resonator to affect the resonant frequency of the other resonator. Thus, each ring resonator 435 is slightly out of tune and provides a composite pass frequency band. If the gap 437 between the ring resonators 435 is large, the interaction between the resonators 435 is weakened. If the gap 437 between the ring resonators 435 is small, each resonator greatly overlaps the adjacent resonator. In this way, a resonator arrangement is used to tune the bandpass filter. Other factors in filter tuning include the overall length of the resonator and the placement of the resonator relative to the feed line. Although less effective than the other factors disclosed above, the width of the resonator line can be used to tune the filter.

  Although only two pairs of ring resonators are shown here, another embodiment of the present invention is a triple resonator having six resonators combined with three ring resonators on each side of the feed trunk line. Can be formed. Yet another embodiment has eight ring resonators combined with four ring resonators on each side of the feed trunk line to form four pairs of ring resonators. The same applies hereinafter. The scope of the present invention is not limited to two pairs of ring resonators. Yet another embodiment of the invention has a resonator with an open ring. Specifically, the ring will have a gap on one side of the resonator, typically the side that is not coupled to an adjacent resonator or feedline. The sides of the ring resonator with the air gap are “open” sides, but remain substantially λ / 4 length, as are the other three sides of the resonator.

FIG. 8 is a graph illustrating the passband response from simulation of the coupled ring resonator filter of FIG. 7 when operating according to the principles of the present invention. The graph of FIG. 8 is a graph of amplitude versus frequency, and the amplitude is normalized and given in decibels. An S ₂₁ curve 450 is an example of a pass band response obtained by simulation of the band filter 150 of FIG. The passband response shown in FIG. 8 is different from the above-described prior art bandpass filter response. As can be seen, the proximity skirt 455 of the curve 450 is steeper compared to the prior art curve shown in FIG. Accordingly, it can be seen that the band-pass filter 400 of FIG. 7 improves the filtering capability of the near frequency and is superior to the band-pass filter of the prior art. If the filter tail is steep, the passband is strictly defined. In this case, the slope of the line through the cutoff frequency (as defined above in connection with FIG. 4) is approximately vertical. The side lobe 460 of the graph is part of the filter rejection band. The side lobe 460 of the graph is the ripple portion in the rejection band commonly found in elliptic response filters. As can be seen in a cascaded filter, the passband can be further improved.

The simulated passband response shown in FIG. 8 was verified by testing the actual circuit. FIG. 9 is a graph of an example of a passband response from a test of a coupled ring resonator of the type shown in FIG. The graph of FIG. 9 is amplitude versus frequency, and the amplitude is normalized and given in decibels. The frequency axis shown in the graph of FIG. 9 is in the range of 23.85 GHz to 33.85 GHz. Curve S ₂₁ 500 has a maximum amplitude at 28.85 GHz, which is 2.5 dB below the reference amplitude of 0 dB. The first skirt 505-1 between 27.15 GHz and 28.07 GHz and the second skirt 505-2 between 29.90 GHz and 30.60 GHz of the curve skirt 505 are according to the simulation shown in FIG. It is steep as predicted by the passband response. The shape of the passband and skirt 500 has characteristic elliptic function response ripples in both the passband 510 and the rejection band 515-2.

  FIG. 10 is a top view of two coupled ring resonators in a cascade configuration. The coupled ring resonator disclosed above can be cascaded to improve the passband response. In FIG. 10, the coupled ring resonator filter 400 of FIG. 7 having the input feed line 402-1 and the output feed line 405-2 is replaced with the second coupled ring resonator filter 402, and the output feed line 405 of the first filter 400. -2 is connected in series by connecting it to the input feed line 406-1 of the second filter 402. The resulting passband response is shown in FIG. In another embodiment of the invention, three or more coupled ring resonator filters can be cascaded to enhance rejection outside the passband.

FIG. 11 is a graph illustrating an example of a passband response by simulation for the cascaded coupled ring resonator filters 400, 402 of FIG. 10 when operating according to the principles of the present invention. The graph of FIG. 11 is a graph of amplitude versus frequency, and the amplitude is normalized and given in decibels. Curve S ₂₁ 550 is an example of a passband response by simulation of cascaded bandpass filters 400 and 402 of FIG. The passband response shown in FIG. 11 is different from the response of the prior art bandpass filter 150 described above. As can be seen, the tail 555 of the curve 550 is steep, and the removal of the near spurious signal 560 is improved over the single coupled ring filter 400 shown in FIG. Thus, it can be seen that the cascaded bandpass filters 400, 402 of FIG. 10 will improve the near-frequency filtering removal capability and will be superior to the prior art bandpass filter 150.

  FIG. 12 is a flowchart of the assembly and operation of the filter 400 shown in FIG. In step 600, a first feed line 405-1 and a second feed line 405-2 for signal transmission are provided. Further, a plurality of ring resonators 435 for resonance in the filter circuit 400 are provided. A plurality of coupled branch lines 420 are also provided. The coupled branch line 420 is actually connected to the feed line 405 and is signal-coupled to the resonator 435. Each feeder line 405 has two coupled branch lines 420. The ring resonator 435 is disposed between the coupled branch lines 420 so as to form a resonance circuit 400 that can perform signal filtering.

  In step 605, the second resonance circuit 402 is provided in series with the first resonance circuit 400 established in step 600. The second resonance circuit 402 has third and fourth feed lines, and the third feed line is connected to the second feed line and receives an output signal of the first resonance circuit. The filtered output of the two circuits connected in series is available on the fourth feed line.

  In step 610, a signal is applied to the first feed line. A first resonant circuit and then a second resonant circuit filters the signal. In step 615, the filtered signal is received at the fourth feed line.

  FIG. 13 shows a transmitter system with a filter according to the principles of the present invention, and FIG. 14 shows a receiver system with a filter according to the principles of the present invention. Transmitter systems and receiver systems can be used in any frequency dependent application including, for example, radio, television, radar, cordless phones and cellular mobile phones, satellite communication systems and some types of test, measurement and instrumentation systems. Could also be used.

  FIG. 13 is a block diagram of a transmitter system 650 that includes a filter in accordance with the principles of the present invention. The transmitter 650 has a signal source 655 connected to a filter 660 connected to an output device 665. Filter 660 is constructed and operates in accordance with the principles of the invention disclosed above. Signal source 655 provides a signal to filter 660. Filter 660 filters the signal and provides the filtered signal to output device 665.

  FIG. 14 is a block diagram of a receiver system 700 comprising a filter in accordance with the principles of the present invention. The receiver 700 has a signal receiving device 705 connected to a filter 710 connected to a filtered input receiver. The signal receiving device 705 receives a signal to be filtered. The signal receiving device 705 sends the signal to the filter 710. Filter 710 filters the signal and sends the filtered signal to filtered input receiver 715.

  In summary, the coupled ring resonator filter 400 provides a strict elliptic function cutoff at frequencies close to both ends of the passband. The use of the above-described structure of the present invention results in a filter that is relatively small, narrowband, and provides high close-in frequency rejection. The structure of the coupling ring resonator 400 enables practical implementation of a filter having a narrow band (bandwidth narrower than 10%) and a relatively high Q. The structure of the present invention is also advantageous in that it can be implemented using a relatively low cost standard lithography process, such as thin film technology or printed circuit board technology.

  Although the coupling ring resonator filters 400, 402 disclosed above have been described for use in a high frequency environment, the structure of the present invention may be used in other frequency ranges. Filters 400 and 402 can be effectively resized for operation at lower frequencies. The spacing between the resonators 435 and the spacing between the resonator and the feedline coupler 420 can also be varied to achieve different passband characteristics.

  In yet another embodiment of the invention, the ring resonator could be a circular ring instead of a square. In this embodiment, the coupled branch line may be straight or follow the contour of the ring resonator. In another embodiment, the feeder main line has a split, and both ends of the split are actually connected to one end of the split instead of the mutual connection on the feed line, and the split is then fed to the feeder trunk line. Connected to the coupling connection.

  Of course, the above-described embodiments are merely illustrative of the principles of the present invention. Various and other modifications and changes may be made by those skilled in the art that embody the principles of the invention and that fall within the spirit and scope of the invention.

4 is a graph of amplitude versus frequency in a prior art filter circuit. FIG. 6 is a top view of an element on a substrate of a prior art five resonator-end coupled bandpass filter. 1 is a conceptual diagram of a simple prior art resonator. 3B is a graph of the electrical performance of the prior art resonator of FIG. 3A. FIG. 6 is a graph of passband response output signal power versus frequency for a hypothetical prior art bandpass filter. FIG. 3 is a partial circuit diagram of parts display of the prior art bandpass filter of FIG. 5B is a graph of amplitude versus frequency of a representative passband response of the prior art bandpass filter of FIG. 5A. FIG. 3 is a graph showing an example of a passband response by simulation of the resonator of the related art of FIG. 2. FIG. 3 is a top view of an element on a substrate of a coupled ring resonator filter in accordance with the principles of the present invention. FIG. 8 is a graph showing an example of a passband response by simulation of the coupled ring resonator filter of FIG. 7. FIG. 8 is a graph of an example tested passband of a coupling ring resonator of the type shown in FIG. FIG. 8 is a top view of two coupled resonators of FIG. 7 arranged in cascade. FIG. 11 is a graph illustrating an example of a passband response by simulation for the cascaded coupled ring resonator filter of FIG. 10. 8 is a flowchart of assembly and operation of the filter of FIG. It is a transmitter provided with the filter of FIG. It is a receiver provided with the filter of FIG.

Explanation of symbols

400 coupling ring band filter 405 feed line 409 intermediate line 410 trunk line 415, 425 1/4 wavelength transformer 420 coupling branch line 430 1/4 wavelength coupler 435 ring resonator

Claims (29)

In the filter,
A first feeder line having a first trunk line connected to the first coupled branch line and the second coupled branch line;
A second trunk line connected to a third coupled branch line and a fourth coupled branch line, wherein the first coupled branch line is substantially parallel to the third coupled branch line; A second feed branch line, which is substantially parallel to the fourth join branch line, and a second feed line arranged on the same plane as the first feed line and the second feed line; Two ring resonators, two of the ring resonators and the first coupled branch line such that the four ring resonators are coupled to the feed line to form a first resonant circuit. Forming a first pair disposed between the third coupled branch lines, and another two of the ring resonators between the second coupled branch line and the fourth coupled branch line; Four ring resonators forming a second pair to be arranged;
A filter comprising:   The length of each side of each of the ring resonators is substantially a quarter wavelength of the selected center wavelength, and the center of the passband of the filter is substantially at the selected center frequency. The filter according to claim 1.   The filter of claim 1, wherein the at least one ring resonator is a square ring resonator.   The length of each side of the square ring is substantially ¼ wavelength of the selected center frequency, and the center of the passband of the filter is substantially at the selected center frequency. The filter according to claim 3.   A part of each said coupling branch line adjacent to one side of each said square resonator forms a coupling point, and each said coupling point is a 1/4 wavelength coupler substantially. Item 5. The filter according to item 4.   The filter according to claim 1, wherein the feed line and the ring resonator are conductive signal layer structures on a substrate.   A fifth ring resonator between the first coupled branch line and the third coupled branch line; and a sixth ring resonator between the second coupled branch line and the fourth coupled branch line. The filter according to claim 1, further comprising:   The ring resonators are arranged with respect to each other such that each of the ring resonators affects resonance in adjacent resonators, thus defining the passband of the filter and tuning the filter. The filter according to claim 1.   The filter of claim 1, wherein the filter is configured to operate in a relatively low radio frequency region of the electromagnetic spectrum.   The filter of claim 1, wherein the filter is configured to operate in the microwave region of the electromagnetic spectrum.   The filter of claim 1, wherein the filter is configured to operate in a millimeter wave region of an electromagnetic spectrum. A second resonance circuit is further provided in series with the first resonance circuit, and the second resonance circuit includes:
A third feeder line having a third trunk line connected to the fifth coupled branch line and the sixth coupled branch line;
A fourth trunk line connected to a seventh coupled branch line and an eighth coupled branch line, wherein the fifth coupled branch line is substantially parallel to the seventh coupled branch line; The sixth coupling branch line is substantially parallel to the eighth coupling branch line, the fourth feeding line, and the third feeding line and the fourth feeding line orthogonal to the same plane. A second set of four ring resonators arranged in the second set, wherein the second set of four ring resonators are coupled to the third feed line and the fourth feed line to provide a second Two of the second set of ring resonators are disposed between the fifth coupled branch line and the seventh coupled branch line to form a resonant circuit, and the second set of ring resonators. A second set of four ring co-axes, in which another two of the resonators are arranged between the sixth coupled branch line and the eighth coupled branch line. Vibrator,
The filter according to claim 1, comprising:   The filter according to claim 1, wherein the filter is a bandpass filter. In the filtering method,
Providing a first feed line and a second feed line;
Providing four ring resonators configured as two pairs of two ring resonators disposed on the same plane substantially orthogonal to the feed line; and the first feed line A first pair of coupled branch lines and a second pair of coupled branch lines connected to the second feeder line, and the first pair of coupled branch lines substantially correspond to the second pair of coupled branch lines. And providing the feed line coupled to the four ring resonators to form a first resonant circuit;
A method comprising the steps of:   The method further comprises the step of configuring the first feed line, the second feed line, the four ring resonators, and the coupled branch line to operate at a relatively low radio frequency. 14. The method according to 14.   15. The method of claim 14, further comprising: configuring the first feed line, the second feed line, the four ring resonators, and the coupled branch line to operate at a microwave frequency. The method described.   15. The method of claim 14, further comprising: configuring the first feed line, the second feed line, the four ring resonators, and the coupled branch line so as to operate at a millimeter wave frequency. The method described.   The method of claim 14, wherein providing the four ring resonators further comprises providing a substantially square ring resonator.   The step of providing four ring resonators further comprises the step of providing square ring resonators, wherein the length of each side of each of the square rings is substantially 1/4 wavelength of the selected center frequency. 19. The method of claim 18, wherein a filter passband center is substantially at the selected center frequency.   Providing a second resonant circuit in series with the first resonant circuit such that the first resonant circuit and the second resonant circuit form a bandpass filter having a well-defined passband. The method of claim 14, further comprising:   The method further includes the step of forming the first feed line, the second feed line, the four ring resonators, and the coupling branch line as a structure on the same surface of the board using a printed circuit board technology. 15. The method of claim 14, wherein:   The method further includes the step of forming the first feed line, the second feed line, the four ring resonators, and the coupling branch line as a structure on the same surface of the substrate using thin film technology. 15. A method according to claim 14, characterized in that Applying a first signal to the first feed line; and receiving a second signal from the second feed line that is a filtered signal filtered by the resonator;
The method of claim 14, further comprising: In the filter,
An input configured to receive an input signal,
An output configured to provide an output signal,
An intermediate line between the input and the output defining a plane bisector, and a set of resonators symmetrically disposed between the input and the output, wherein at least two resonators are bisected The set of resonators disposed substantially in the plane on one side of a line and at least two other resonators disposed substantially in the plane on the other side of the bisector. A set of resonators that provide a signal coupling between the input and the output, wherein the output signal is based on the input signal;
A filter comprising: The input is
An input feed line having a first end and a second end configured to receive the input signal, and a set of input coupling branch lines, each of the input coupling branch lines being connected to the input feed line A set of input coupling branch lines extending from the second end of the input feed line in a substantially vertical manner;
And the output of the filter is
An output feed line having a first end and a second end configured to provide the output signal, and a set of output coupling branch lines, each output coupling branch line being the output feed line A set of output coupling branches extending from the second end of the output feed line in a manner substantially perpendicular to
Have
The input coupling branch lines are substantially parallel to the output coupling branch lines, and an even number of resonators are arranged in a row between the set of input coupling branch lines and the set of output coupling branch lines. 25. The filter according to claim 24, wherein:   The set of input coupled branch lines defines a first linear edge, the set of output coupled branch lines defines a second linear edge, and each of the resonators includes the first linear edge. 26. The filter of claim 25, having a substantially square shape adjacent to any of the second straight edges. In the transmitter,
A source circuit configured to provide an input signal,
An output circuit configured to send an output signal; and an input coupled to the signal source circuit; an output coupled to the output circuit; and a set of resonators, wherein an intermediate line between the input and the output A plane bisector is defined, at least two resonators are disposed substantially in the plane on one side of the bisector, and at least two other resonators are on the other side of the bisector A filter disposed substantially in the plane on the side of the filter, the set of resonators providing a signal coupling between the input and the output, the output signal being based on the input signal;
A transmitter comprising: In the receiver,
An input circuit configured to receive an input signal;
A rendering circuit configured to provide an output signal; an input coupled to the input circuit; an output coupled to the rendering circuit; and a set of resonators, wherein an intermediate line between the input and the output is planar And at least two resonators are disposed substantially in the plane on one side of the bisector, and at least two other resonators are on the other side of the bisector. A filter disposed substantially in the plane on the side, wherein the set of resonators provides a signal coupling between the input and the output, the output signal being based on the input signal,
A receiver comprising: In a method for filtering a signal,
Capturing an input signal;
Applying the input signal to an input of the filtering structure to generate an output signal on an output of the filtering structure, the filtering structure having a set of resonators, intermediate between the input and the output The line defines a planar bisector, at least two resonators are disposed substantially in the plane on one side of the bisector, and at least two other resonators are the bisector. Arranged in the plane substantially on the other side of the first and the set of resonators to provide a signal coupling between the input and the output, the output signal being based on the input signal, as well as,
Transmitting the output signal from the output;
A method comprising the steps of:

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