GB2491379A - A low-loss microwave band-combining filter - Google Patents
A low-loss microwave band-combining filter Download PDFInfo
- Publication number
- GB2491379A GB2491379A GB1109201.2A GB201109201A GB2491379A GB 2491379 A GB2491379 A GB 2491379A GB 201109201 A GB201109201 A GB 201109201A GB 2491379 A GB2491379 A GB 2491379A
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- United Kingdom
- Prior art keywords
- filter
- band
- resonators
- band combining
- cascade
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- 230000007704 transition Effects 0.000 claims description 5
- 238000001914 filtration Methods 0.000 claims description 2
- 230000010363 phase shift Effects 0.000 claims description 2
- 230000001419 dependent effect Effects 0.000 description 14
- 230000005540 biological transmission Effects 0.000 description 8
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H7/00—Multiple-port networks comprising only passive electrical elements as network components
- H03H7/46—Networks for connecting several sources or loads, working on different frequencies or frequency bands, to a common load or source
- H03H7/461—Networks for connecting several sources or loads, working on different frequencies or frequency bands, to a common load or source particularly adapted for use in common antenna systems
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
- H01P1/00—Auxiliary devices
- H01P1/20—Frequency-selective devices, e.g. filters
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
- H01P1/00—Auxiliary devices
- H01P1/20—Frequency-selective devices, e.g. filters
- H01P1/213—Frequency-selective devices, e.g. filters combining or separating two or more different frequencies
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- Control Of Motors That Do Not Use Commutators (AREA)
Abstract
A band combining filter comprises a cascade of filter sections 2 and a phase shifter 9. Each filter section comprises 3dB hybrids 16,17 coupled by resonators, the resonators 26,27 in filter sections associated with a band edge being high-Q dielectric resonators and the resonators in the other filter sections being low-Q combline resonators. Although the band combiner has only two high-Q resonators it exhibits low loss across the entire passband. The predominant use of low-Q resonators provides cost, size and weight savings.
Description
A BAND COMBINING FILTER
The present invention relates to a band combining filter. More particularly, but not exclusively, the present invention relates to a band combining filter comprising a plurality of filter sections connected together in cascade along with a phase shifter, the filter sections including resonators and at least one of the filter sections being a high 0 filter section.
Band combining filters are known. Such band combining filters can include a plurality of resonators. In the case of a rapid transition from passband to stopband the resistive loss of the resonators causes a roll off of the insertion loss into the passband. In order to meet typical rejection requirements unloaded Os of greater than 20,000 are required resulting in the necessity, at microwave frequencies to use dielectric resonators for all of the cavities resulting in a physically large heavy and expensive filter.
The present invention seeks to overcome the problems of the prior art.
Accordingly, in a first aspect, the present invention provides a band combining filter for filtering a microwave signal, the band combining filter having at least one band edge at a band edge transition frequency, the filter comprising a plurality of filter sections, each filter section comprising first and second 3dB hybrid couplers, each 3dB hybrid coupler comprising first and second input ports and first and second output ports; a first resonator connected between the second input port of the first coupler and the first input port of the second coupler; and, a second resonator connected between the second output port of the first coupler and the first output port of the second coupler; each filter section comprising first and second input ports defined by the first input port of its first coupler and the second input port of its second coupler respectively; each filter section comprising first and second output ports defined by the first output port of its first coupler and second output port of its second coupler respectively; the filter sections being connected in cascade with the first and second outputs of one filter section being connected to the first and second inputs of the next filter section in the cascade; the band combining filter further comprising a coupled phase shifter in the cascade having first and second inputs adapted to receive microwave signals and provide them at output ports with a phase shift therebetween; characterised in that a subset of the filter sections are high Q filter sections with the 0 values of the resonators of those filter sections having values each of which are at least a factor of three higher than the 0 values of the resonators of the remaining filter sections.
The band combining filter according to the invention requires only two high 0 resonators per band edge and still has low loss across the entire passband.
The coupled phase shifter can be the last element of the cascade with the inputs of the phase shifter receiving the outputs from the final filter section of the cascade.
Alternatively, the coupled phase shifter can be arranged between filter sections in the cascade.
Preferably, the 0 values of the resonators in the subset are at least four times, more preferably five times, that of each of the remaining resonators.
Preferably, for each filter section the Q value of the first resonator in the filter section is equal to the 0 value of the second resonator in the same filter section.
Preferably, the number of high 0 filter sections is equal to the number of band edges.
The band combining filter according to the invention can have one band edge.
The band combining filter according to the invention can comprise two filter sections connected in cascade.
The band combining filter according to the invention can comprise at least three, preferably four, filter sections in cascade.
Preferably, the band combining filter further comprises an electrical signal generator.
The present invention will now be described by way of example only at not in any limitative sense with reference to the accompanying drawings in which Figure 1 shows a first embodiment of a band combining filter according to the invention; Figure 2 shows a second embodiment of a band combining filter according to the invention; Figure 3 shows a third embodiment of a band combining filter according to the invention; Figure 4 shows a fourth embodiment of a band combining filter according to the invention; Figure 5 shows a practical design of a band combining filter according to the invention; Figure 6 shows the performance of the filter of figure 5; Figure 7 shows a symmetrical four port structure; Figure 8 shows a 3dB hybrid with reactive admittances connected to two of the ports; and, Figures 9(a) to 9(c) show a sections which can be connected together in cascade to produce the filter of the invention.
Shown in figure 1 is a band combining filter 1 according to the invention. The filter 1 is a third order filter having a single band edge at a band edge transition frequency.
The band combining filter 1 comprises a plurality (in this case three) filter sections 2 connected in cascade. Each filter section 2 comprises first and second input pods 3,4 and first and second output pods 5,6. The first and second output pods 5,6 of one filter section 2 are connected to the first and second input pods 3,4 of the next filter section 2 in the cascade as shown. The first and second input pods 3,4 of the first filter section 2 comprise the input pods 7,8 of the filter 1.
The output pods 5,6 of the last filter section 2 are connected to a coupled phase shifter 9. The signals received at the input ports 10,11 of the coupled phase shifter 9 are presented at the output ports 12,13 of the coupled phase shifter 9 with a phase difference introduced therebetween. The output ports 12,13 of the coupled phase shifter 9 are the output ports 14,15 of the filter 1. The function of the coupled phase shifter 9 is explained in more detail below.
Each filter section 2 comprises first 16 and second 17 3dB hybrids. Each hybrid 16,17 has first and second input ports 18,19,20,21 and first and second output pods 22,23,24,25. The second input pod 19 of the first hybrid 16 is connected to the first input pod 20 of the second hybrid 17 by a first resonator 26. Similarly, the second output port 23 of the first hybrid 16 is connected to the first output pod 24 of the second hybrid 17 by a second resonator 27. In this embodiment within each filter section 2 the first and second resonators 26,27 have the same value.
One of the filter sections 2 is a high Q filter section. The Q values of the resonators 26,27 in this section are a factor of four higher than the Q values of the resonators 26,27 in the remaining filter sections 2.
Even though the band combining filter 1 according to the invention has only two high Q value resonators 26,27 the combining filter 1 shows low loss across the entire passband.
In this embodiment the 0 values of the resonators 26,27 of the high 0 filter section 2 are a factor of four higher than the 0 values of the resonators 26,27 of the remaining filter sections 2. More generally speaking, it is preferred that the 0 values of the resonators 26,27 of the high 0 filter sections 2 have values which are at least a factor of three, more preferably at least a factor of four, more preferably at least a factor of five larger than the Q values of the resonators 26,27 of the remaining filter sections 2.
The low 0 value resonators 26,27 are typically realised as combline resonators. High 0 resonators 26,27 are typically realised as ceramic resonators.
Shown in figure 2 is a second embodiment of a band combining filter I according to the invention. This embodiment is similar to that of figure 2 except the coupled phase shifter 9 is included between filter sections 2 in the cascade. In this embodiment the high 0 filter section 2 is the last filter section 2 in the cascade. More generally speaking, the coupled phase shifter 9 and the filter sections 2 can be arranged in any order in the cascade.
Shown in figure 3 is a further embodiment of a band combining filter I according to the invention. This filter I is a fourth order filter and as such has four filter sections 2.
The filter I has two band edges at band edge transition frequencies and accordingly has two high 0 filter sections 2. Generally speaking it is preferred that the number of high 0 filter sections 2 is equal to the number of band edges.
Shown in figure 4 is a further embodiment of a band combining filter 1 according to the invention. In this embodiment the filter I is a second degree filter having a single band edge. One of the two filter sections 2 is a high 0 filter section. The 0 values of the resonators 26,27 of this section 2 are a factor of 8 higher than the 0 values of the resonators 26,27 of the other filter section 2.
Shown in figure 5 is a practical design of a second degree band combining filter 1 according to the invention. The 0 values for the high 0 filter section are set at 25,000 whilst those for the low 0 filter section are set at 6000. Shown in figure 6 is the reflection and transmission performance of the filter as a function of frequency.
The operation of the band combining filter according to the invention is best described with reference to figure 7 and subsequent figures.
Consider a symmetrical four port structure 28 as shown in figure 7 defined by its even and odd mode reflection and transmission coefficients.
For a balanced structure Pe = Pa = 0 and ITeI2 = ITaI2 = 1 defining lYe Te -1+Ye 1-Yo T0 - Where Ye and 1a are obtained from a single two part filter one has -Te+To 1YY0 13 2 (1+Y)(1+Y) Which is the reflection coefficient of the equivalent two port filter and TeTo Y1'e 2 (1+Ye)(1+Yo) Which is the transmission coefficient of the equivalent 2 port filter. Hence, signals in the passband emerge at port 4 and signals in the stopband emerge at port 3. Since the structure is reciprocal then the device acts as a combiner with signals in the passband applied at port 4 and signals in the stopband applied at port 3 both emerge at port 1 which would normally be connected to an antenna.
Considering the specific example given for the filter, in this case one has to realise two all pass networks, the first being lYe Te1y Which becomes T -1-i-j(V+1) p-(il+1) e 1-j(iTh-1) p+(i/+1) * ________ = With p = 2 tan1(sI + 1) and, 1-Y0 1-j(s,1+1) p-('/-1) T0-1-1+j(+1) p+(-1) -. p-(sTh-1) = e p + (Vi -1) Each all pass section can be realised with two equal reactive admittances connected to two of the ports of a 3dB hybrid as shown in figure 8.
Hence, the resonant part of the even mode realisation is as shown in figure 9(a) and the odd mode is shown in figure 9(b) and the phase shifters required in the even and odd mode functions can be combined to form a single coupler shown in figure 9(c).
Hence, the whole band combining filter I is produced from the cascade of the sections shown in figures 9(a) to 9(c) which can be cascades in any order.
The impedance ration between Y1 and Y2 is (sh + 1)2 thus enabling the resonator Yi to be realised with a Q factor considerably less than the resonator Y2. In other words, with a band combining filter 1 having a structure according to the invention, provided the 0 values of the resonators 26,27 of one filter section 2 are sufficiently high then the loss of the filter 1 across the passband is determined by that of the high Q resonators 26,27 only.
For higher degree networks the synthesis process is similar in that the transfer functions of the even and odd mode networks can be factorised as unity degree all pass factors as Ne
T
eyj lki+Yer r=O and N0 lYoflflYor T0 - llkl+Yor where Ne and N0 are within one degree of each other and Yer, or are of unity degree, 1e0 and Y00 result in the frequency independent coupler 9. The overall realisation is the cascade of the independent filter sections 2 and the overall performance is independent of the order of the cascade.
Key for figure 5 Label Text P4 Z=50 Ohms (source/load impedance) (A power source/load) KflO Zref = Zhyl Ohms (Inverter Impedance) (A frequency dependent impedance Zf = 0 Ohm/Hz (rate of change of inverter) impedance) f0= 0 Hz (reference frequency) Line 13 Z=0.400274 Ohm (Line impedance) (A transmission line) L=38.1969mm (line length) R4 R=12741 Ohm (A resistor) B4 B = 0.0057 mho (A susceptance) Kf13 ZreFZhyl Ohms (A frequency dependent impedance Zf= 0 Ohm/Hz inverter) f0=0 Hz P2 Z= 50 Ohms (A power source/load) Kf12 Zref 50 Ohms (A frequency dependent impedance Zf= 0 Ohm/Hz inverter) f0= 0 Hz Kf 15 ZreF Zhy3 Ohms (A frequency dependent impedance Zf= 0 Ohms/Hz inverter) f0= 0 Hz Kf9 Zref= 50 Ohms (A frequency dependent impedance Zf= 0 Ohms/Hz inverter) f0= 0 Hz Kf16 ZrefZhyl Ohms (A frequency dependent impedance Zf= 0 Ohms/Hz inverter) f0= 0Hz Line 14 Z= 0.400274 Ohm (A transmission line) L= 38.1969mm R5 R= 12741 Ohm (A resistor) B5 B= 0.0057 mho (A susceptance) Line5 Z= 50 Ohm (A transmission line) L = 76.4 mm Kf5 Zref Zhy2 Ohm (A frequency dependent impedance Zf = 0 Ohm/Hz inverter) f0= 0 Hz Kfl I ZreF Zhyl (A frequency dependent impedance Z1= 0 Ohm/Hz inverter) f0= 0 Hz Line 11 Z= 0.400274 Ohm (A transmission line) L= 38.1969mm R2 R = 3000 Ohm (A resistor) B2 B=Omho (A susceptance) Kf3 Zref Zhy2 Ohm (A frequency dependent impedance Zf= 0 Ohm/Hz inverter) f0= o Hz Kf I Zref = 50 Ohm (A frequency dependent impedance Zf = 0 Ohm/Hz inverter) f0= 0 Hz Kf8 ZrefZhy4 Ohm (A frequency dependent impedance Zf = 0 Ohm inverter) f0= 0 Hz Kf2 Zref5O Ohm (A frequency dependent impedance Zf = 0 Ohm inverter) f0= 0 Hz Kf6 Zrei = Zhy2 Ohm (A frequency dependent impedance Zf = 0 Ohm inverter) f0= 0 Hz Line 12 Z = 0.400274 Ohm (A transmission line) L = 38.1969mm R3 R = 3000 Ohm (A resistor) B3 B=Omho (A susceptance) Kf4 Zref = Zhy2 Ohm (A frequency dependent impedance Zf = 0 Ohm inverter) f0= 0 Hz xl K = 0.32 (coupling value) (A coupled phase shifter) Phi = 90 degrees P1 Z = 50 Ohm (source/load impedance) (A power source/load) P3 Z = 50 Ohm (source/load impedance) (A power source/load) Zinl = 33S Ohm Zin2 = 97 Ohm Zinl Zhyl = Zin2 Zhy2 = (Zinl)2 Zhy3 = 100 (Zin2)2 Zhy4 = 100
Claims (12)
- CLAIMS1. A band combining filter for filtering a microwave signal, the band combining filter having at least one band edge at a band edge transition frequency, the filter comprising a plurality of filter sections, each filter section comprising first and second 3dB hybrid couplers, each 3dB hybrid coupler comprising first and second input ports and first and second output ports; a first resonator connected between the second input port of the first coupler and the first input port of the second coupler; and, a second resonator connected between the second output port of the first coupler and the first output port of the second coupler; each filter section comprising first and second input ports defined by the first input port of its first coupler and the second input port of its second coupier respectively; each filter section comprising first and second output ports defined by the first output port of its first coupler and second output port of its second coupler respectively; the filter sections being connected in cascade with the first and second outputs of one filter section being connected to the first and second inputs of the next filter section in the cascade; the band combining filter further comprising a coupled phase shifter in the cascade having first and second inputs adapted to receive microwave signals and provide them at output ports with a phase shift therebetween; characterised in that a subset of the filter sections are high Q filter sections with the Q values of the resonators of those filter sections having values each of which are at least a factor of three higher than the Q values of the resonators of the remaining filter sections.
- 2. A band combining filter as claimed in claim 1, wherein the coupled phase shifter is the last element of the cascade with the inputs of the phase shifter receiving the outputs from the final filter section of the cascade.
- 3. A band combining filter as claimed in claim 1, wherein the coupled phase shifter is arranged between filter sections in the cascade.
- 4. A band combining filter as claimed in any one of claims 1 to 3, wherein the 0 values of the resonators in the subset are at least four times, more preferably five times, that of each of the remaining resonators.
- 5. A band combining filter as claimed in any one of claims I to 4, wherein for each filter section the 0 value of the first resonator in the filter section is equal to the 0 value of the second resonator in the same filter section.
- 6. A band combining filter as claimed in any one of claims 1 to 5, wherein the number of high 0 filter sections is equal to the number of band edges.
- 7. A band combining filter as claimed in claim 6, having one band edge.
- 8. A band combining filter as claimed in claim 7, comprising two filter sections connected in cascade.
- 9. A band combining filter as claimed in any one of claims 1 to 7, comprising at least three, preferably four, filter sections in cascade.
- 10. A band combining filter as claimed in any of claims 1 to 9, further comprising an electrical signal generator.
- 11. A band combining filter substantially as hereinbefore described.
- 12. A band combining filter substantially as hereinbefore described with reference to the drawings.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1109201.2A GB2491379B (en) | 2011-06-01 | 2011-06-01 | A band combining filter |
| PCT/GB2012/051183 WO2012164264A1 (en) | 2011-06-01 | 2012-05-25 | A band combining filter |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1109201.2A GB2491379B (en) | 2011-06-01 | 2011-06-01 | A band combining filter |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB201109201D0 GB201109201D0 (en) | 2011-07-13 |
| GB2491379A true GB2491379A (en) | 2012-12-05 |
| GB2491379B GB2491379B (en) | 2017-10-11 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB1109201.2A Active GB2491379B (en) | 2011-06-01 | 2011-06-01 | A band combining filter |
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| Country | Link |
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| GB (1) | GB2491379B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2507668A (en) * | 2012-12-07 | 2014-05-07 | Radio Design Ltd | RF Selectivity using first and second set of 90 degree phase shift coupling means and at least one pair of resonating means |
| GB2516909A (en) * | 2013-08-06 | 2015-02-11 | Filtronic Wireless Ltd | A microwave filter and a microwave transceiver including such a microwave filter |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1442904A (en) * | 1964-08-07 | 1966-06-17 | Marconi Co Ltd | Device combining radio frequency signals |
| GB2444786A (en) * | 2006-12-15 | 2008-06-18 | Isotek Electronics Ltd | Band combining filter |
| GB2476868A (en) * | 2010-01-06 | 2011-07-13 | Isotek Electronics Ltd | A UHF filter using one high-Q resonator for each band edge |
-
2011
- 2011-06-01 GB GB1109201.2A patent/GB2491379B/en active Active
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1442904A (en) * | 1964-08-07 | 1966-06-17 | Marconi Co Ltd | Device combining radio frequency signals |
| GB2444786A (en) * | 2006-12-15 | 2008-06-18 | Isotek Electronics Ltd | Band combining filter |
| GB2476868A (en) * | 2010-01-06 | 2011-07-13 | Isotek Electronics Ltd | A UHF filter using one high-Q resonator for each band edge |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2507668A (en) * | 2012-12-07 | 2014-05-07 | Radio Design Ltd | RF Selectivity using first and second set of 90 degree phase shift coupling means and at least one pair of resonating means |
| GB2513724A (en) * | 2012-12-07 | 2014-11-05 | Radio Design Ltd | Apparatus for allowing radio frequency selectivity and method of use thereof |
| GB2507668B (en) * | 2012-12-07 | 2014-11-05 | Radio Design Ltd | Apparatus for allowing radio frequency selectivity and method of use thereof |
| GB2513724B (en) * | 2012-12-07 | 2015-04-29 | Radio Design Ltd | Apparatus for allowing radio frequency selectivity and method of use thereof |
| GB2516909A (en) * | 2013-08-06 | 2015-02-11 | Filtronic Wireless Ltd | A microwave filter and a microwave transceiver including such a microwave filter |
| GB2516909B (en) * | 2013-08-06 | 2020-10-28 | Filtronic Wireless Ltd | A microwave filter and a microwave transceiver including such a microwave filter |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2491379B (en) | 2017-10-11 |
| GB201109201D0 (en) | 2011-07-13 |
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