GB2444786A - Band combining filter - Google Patents

Band combining filter Download PDF

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Publication number
GB2444786A
GB2444786A GB0625062A GB0625062A GB2444786A GB 2444786 A GB2444786 A GB 2444786A GB 0625062 A GB0625062 A GB 0625062A GB 0625062 A GB0625062 A GB 0625062A GB 2444786 A GB2444786 A GB 2444786A
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GB
United Kingdom
Prior art keywords
filter
directional
filters
band
band combining
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
GB0625062A
Other versions
GB2444786B (en
GB0625062D0 (en
Inventor
John David Rhodes
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Filtronic Wireless Ltd
Original Assignee
Isotek Electronics Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Isotek Electronics Ltd filed Critical Isotek Electronics Ltd
Priority to GB0625062A priority Critical patent/GB2444786B/en
Publication of GB0625062D0 publication Critical patent/GB0625062D0/en
Publication of GB2444786A publication Critical patent/GB2444786A/en
Application granted granted Critical
Publication of GB2444786B publication Critical patent/GB2444786B/en
Withdrawn - After Issue legal-status Critical Current
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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
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS OR SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING; SPEECH OR AUDIO CODING OR DECODING
    • G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
    • 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
    • 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
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03J—TUNING RESONANT CIRCUITS; SELECTING RESONANT CIRCUITS
    • H03J3/00—Continuous tuning
    • H03J3/02—Details
    • H03J3/06—Arrangements for obtaining constant bandwidth or gain throughout tuning range or ranges
    • H03J3/08—Arrangements for obtaining constant bandwidth or gain throughout tuning range or ranges by varying a second parameter simultaneously with the tuning, e.g. coupling bandpass filter
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/66—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission for reducing bandwidth of signals; for improving efficiency of transmission

Abstract

A band combining filter comprising a plurality of cascaded directional filters, each directional filter having at least two inputs and at least two outputs, the nth directional filter being arranged such that the output signals from the first and second outputs are related to the input signals to the first and second inputs characterized in that the directional filters are connected in a cascade with the first and second inputs of the nth directional filter being connected to the first and second outputs of the (n-1)th directional filter respectively in the cascade.

Description

A band combining filter The present invention relates to a band
combining filter and a signal transmitter including such a filter. More particularly, but not exclusively, the present invention relates to a band combining filter comprising a plurality of directional filters connected together in a cascade.
There is an increasing demand to combine different types of communications systems on to a common antenna by subdividing a communication band by frequency allocation. There are several known techniques by which this may be accomplished however the need for a high power and high linearity makes known systems complex and expensive.
The band combining filter according to the invention seeks to overcome this problem.
Accordingly, in a first aspect the present invention provides a band combining filter comprising a plurality of cascaded directional filters, each directional filter having at least two inputs and at least two outputs, the nth directional filter being arranged such that the output signals 0 and 02 from the first and second outputs are related to the input signals 1, 12 to the first and second inputs by the relation (o1(R1 T2yJI 2)tJnI It3I' with R and I being reflection and transmission functions respectively.
characterised in that the directional filters are connected in a cascade with the first and second inputs of the nth directional filter being connected to the first and second outputs of the (n-I)th directional filter respectively in the cascade.
The use of cascaded directional filters provides a compact band combining filter * providing complex filtering characteristics with a relatively simple filter structure.
Preferably the directional fitters are symmetric and reciprocal filters with R=R2=R **1* , and T1T2T.
*: *.: Preferably, at least one of the directional filters comprises a first signal splitter having a first input port connected to the first input and a first output port connected to the first output; a second signal splitter having a second input port connected to the second input and a second output port connected to the second output; each of the first and second signal splitters having first and second connection ports; the two first connection ports being connected together by a first filter; the two second connection ports being connected together by a second filter.
The first and second signal splitters can be 3dB hybrids.
The first and second filters can be identical.
Alternatively, the first and second filters can be different to each other.
Preferably, the first and second filters of at least one directional filter are at least one of a low pass filter, high pass filter, band stop filter or band pass filters.
Preferably, the first and second filters of at least one directional filter are frequency independent.
The band combining filter can comprise first and second directional filters only.
The first and second filters of the first directional filter can be at least one of a low pass filter, a high pass filter, a band stop filter or band pass filter and the first and second filters of the second directional filter can be frequency independent.
Preferably, the low pass filter is a ladder filter,-preferably of even order.
In a further aspect of the invention there is provided a signal transmitter comprising a band combining filter comprising a plurality of cascaded directional filters, each directional filter having at least two inputs and at least two outputs, the nth directional filter being arranged such that the output signals O and Oi from the first and second outputs are related to the input signals 1, 12 to the first and second inputs by the relation * (O, (RAI 72Y'1 o2Ji R2JtI3 *.*. * *
with R and T being reflection and transmission functions respectively, ** S characterised in that *SSSs * . the directional filters are connected in a cascade with the first and second I. * inputs of the nth directional filter being connected to the first and second * outputs of the (n-I)th directional filter respectively in the cascade; a first signal source in electrical communication with the first input of the first directional filter in the cascade; a second signal source in electrical communication with the second input of the first directional filter in the cascade; and an antenna connected to an output of the last directional filter in the cascade.
The present invention will now be described by way of example only, and not in any limitative sense, with reference to the accompanying drawings in which Figure 1 shows a directional filter; Figure 2 shows the directional filter of Figure 1 in schematic form; Figure 3 shows two directional filters connected in a cascade; Figure 4 shows in schematic form N directional filters connected in a cascade; Figures 5 to 7 show the isolation, amplitude and delay plots of a band combining filter according to the invention.
In its simplest form the directional filter is a 4-port device consisting of two identical filters and a pair of 3dB hybrids as shown in Fig. 1.
If the scattering matrix of one of the reciprocal filters is:-cs1=[:li:] and a signal is applied at port (1), then none of the power is reflected at port 1; port 2 is totally isolated and the transfer characteristics to ports 3 and 4 are:-T4 =jS,, * ** . 2 T3 =JS2, *... If the filters are assumed to be lossless then 2 2 .: T T =1 * S. 3 3
S ________________________________
*5*SSS * , Multipath Directional Filters S..
To simplify the analysis, it will be assumed that the filters are symmetrical, although .: this is not a necessary requirement. A single directional filter is then defined in Fig 2, and for a lossless network:-. 2 3
T i-R =1 4
I I
Cascading two directional filters is shown in Fig 3.
The outputs are:-P1=R1Q,T, 5 and P2=P1R2 Q1T2 6 Q2 = P1T2 + Q1R2 For a lossless network then 2 2 7 P +Q =1 2 2 For the general case containing a directional filters if an additional device is added one has the situation shown in Fig 4, where = PR+ + QT1 - = + QR+1 8 and for the lossless case. 2 2
P +Q =1 9 ni-I n+I Thus, the recurrence formula for generating the overall network performance is, P+ PrR1+i + QrTr*i 10 Q+ = P1T+1 + * for r = I -n, with the initial conditions, Is.' *055 P1 = R1. Q = . --...--. * e.. I. S * S. * I.
S
*SS b SI * S 5. * I
SSSS S. * * S. * SI
* )esign example for a cascade of two directional filters For the case of two directional filters in cascade one has the network equations given in equation 6. Let the first network consist of two Iowpass ladder networks of even degree where one may write, D2(p) I and
R
I D2(p) 13 Where N and D are known terms in network theory.
For a lossless network D2(p)D2(-p) = 1 N2 2) 14 Let the second network be frequency independent defined as:-1 3
-_______
-I
S R, -
which can be realised as a single proximity coupler with s' relatively small.
Hence, P (2) + i I i I 2 / sJ1+eD2Lp) tl+e D2p * S. .1 Ii\
-_____________
-and S. S * S S
* S. j f 2.
* -_ --17 IS....
* JI e2D,(p) p..
::::; Hence, the overall group delay is the same as the ladder filter and - 2 ____________ 2 (1+e21l+N(_w2)j 1Q212 = [Nfw2)+e (1 E l N(- )J If N(_ 2)= _e(cos[2ncos' ]_i) 19 then i 12 = Ii + - cosE2ncos ]r 2 (l+s2j+c3(cos[2ncosiw)_l) 20 and 2 E2 cos2[2ncosla,] = 2 1 (l+e-ji+ (cos[2ncos-w}_lj which for s' small is approximately equiripple in the passband -I = w = +1 The maximum value of [2]2 in the passband is 1 2 and in the stopband Q2 for large 0)' approaches 2 1 e If this level is chosen as approximately 15dB, then for n=2 we have the isolation, amplitude and delay plots as a function of frequency shown in Figs 5, 6 and 7, for signal inputs at ports 1 and 2 with a common output at port 3 where the device has been scaled to 900MHz with a 4.4MHz bandwidth. Network 2 is a 15dB directional coupler and the ladder networks in network I are defined by: IR1f3 = eos1_nco 22 l+e2[cos[2ncos w]_l * S. * S S *5** S...
This may be factorised in the normal way and synthesised as a 2n th degree ladder * structure. * . .
The ba combining filter of the invention shows a high degree of uniformity in amplitude and phase across a wide range of frequency making it suitable for signal combining applications. *SS*
. : Cascaded directional filters can provide a compact band combining filter which can * provide complex filtering characteristics with relatively simple filter structures. A 4th degree example operating at 900MHz has been given which is suitable for combining a UMTS channel with an existing GSM system. Furthermore, due to its simplicity, it may readily be reconfigured by tuning the resonant frequencies of the resonators.
Whilst only an example comprising a fourth degree filter and two directional filters has been provided other examples are possible comprising higher order filters or larger numbers of directional filter stages. All show the advantages according to the invention.
Similarly, alternative to low pass ladder networks for the first and second filters of the directional filters may be alternative low pass filter types, high pass filters, band slop filters and band pass filters. * S. * S * S... 5.. * . * . S * S.
S * S S.. * . *SSS S. * * S S * .5 1aims

Claims (14)

  1. I. A band combining filter comprising a plurality of cascaded
    directional filters, each directional filter having at least two inputs and at least two outputs, the nth directional filter being arranged such that the output signals 0, and 02 from the first and second outputs are related to the input signals l, i = to the first and second inputs by the relation (o1(R, Tfl2'(Jj 102) (7,I R,,1AI with R. and T being reflection and transmission functions respectively, characterised in that the directional filters are connected in a cascade with the first and second inputs of the nth directional filter being connected to the first and second outputs of the (n-l)th directional filter respectively in the cascade.
  2. 2. A band combining filter as claimed in claim 1, wherein the directional filters are symmetric and reciprocal filters with R,=R2=R and T1=T=T.
  3. 3. A band combining filter as claimed in either of claims I or 2, wherein at least one of the directional filters comprises a first signal splitter having a first input port connected to the first input and a first output port connected to the first output; a second signal splitter having a second input port connected to the second input and a second output port connected to the second output; each of the first and second signal splitters having first and second connection ports; the two first connection ports being connected together by a first filter; : *". the two second connection ports being connected together by a second filter. *.S.
  4. 4. A band combining filter as claimed in claim 3, wherein the first and second signal splitters are 3dB hybrids.
    *
  5. 5. A band combining filter as claimed in either of claims 3 or 4, wherein the first and second filters are identical.
    *
  6. 6. A band combining filter as claimed in either of claims 3 or 4, wherein the first and * second filters are different to each other. I. * * * * * **
    *
  7. 7. A band combining filter as claimed in any one of claims 3 to 6, wherein the first and second filters of at least one directional filter are at Least one of a low pass filter, high pass filter, band stop filter or band pass filter.
  8. 8. A band combining filter as claimed in any one of claims 3 to 7, wherein the first and second filters of at least one directional filter are frequency independent.
  9. 9. A band combining filter as claimed in any one of claims 1 to 8, comprising first and second directional filters only.
  10. 10. A band combining filter as claimed in claim 9, wherein the first and second filters of the first directional filter are at least one of a low pass filter, a high pass filter, a band stop filter or band pass filter and the first and second filters of the second directional filter are frequency independent.
  11. 11. A band combining filter as claimed in claim 10, wherein the low pass filter is a ladder filter of even order.
  12. 12. A signal transmitter comprising a band combining filter as claimed in any one of claims 1 to 11; a first signal source in electrical communication with the first input of the first directional filter in the cascade; a second signal source in electrical communication with the second input of the first directional filter in the cascade; and an antenna connected to an output of the last directional filter in the cascade.
  13. 13. A band combining filter substantially as hereinbefore described.
  14. 14. A signal transmitter substantially as hereinbefore described. * I. *. S S... S... * S *5., 5* * * S S * S. *
    * SS S S S * S 55. * I **S. 5 * SI * S.
GB0625062A 2006-12-15 2006-12-15 A band combining filter Withdrawn - After Issue GB2444786B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB0625062A GB2444786B (en) 2006-12-15 2006-12-15 A band combining filter

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Application Number Priority Date Filing Date Title
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GB0625062D0 GB0625062D0 (en) 2007-01-24
GB2444786A true GB2444786A (en) 2008-06-18
GB2444786B GB2444786B (en) 2011-10-05

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2491379A (en) * 2011-06-01 2012-12-05 Filtronic Wireless Ltd A low-loss microwave band-combining filter
WO2013068728A1 (en) * 2011-11-07 2013-05-16 Radio Design Limited Combining apparatus for use in signal transmitting and/ or receiving apparatus
US8686808B2 (en) 2011-06-01 2014-04-01 Filtronic Wireless Ltd Band combining filter

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002047195A1 (en) * 2000-12-05 2002-06-13 Telefonaktiebolaget Lm Ericsson (Publ) A method and apparatus for tuning a combiner filter
US20050143973A1 (en) * 1999-11-26 2005-06-30 Matsushita Electric Industrial Co., Ltd. Digital signal sub-band separating/combining apparatus achieving band-separation and band-combining filtering processing with reduced amount of group delay

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1442904A (en) * 1964-08-07 1966-06-17 Marconi Co Ltd Device combining radio frequency signals

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20050143973A1 (en) * 1999-11-26 2005-06-30 Matsushita Electric Industrial Co., Ltd. Digital signal sub-band separating/combining apparatus achieving band-separation and band-combining filtering processing with reduced amount of group delay
WO2002047195A1 (en) * 2000-12-05 2002-06-13 Telefonaktiebolaget Lm Ericsson (Publ) A method and apparatus for tuning a combiner filter

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2491379A (en) * 2011-06-01 2012-12-05 Filtronic Wireless Ltd A low-loss microwave band-combining filter
US8686808B2 (en) 2011-06-01 2014-04-01 Filtronic Wireless Ltd Band combining filter
GB2491379B (en) * 2011-06-01 2017-10-11 Filtronic Wireless Ltd A band combining filter
WO2013068728A1 (en) * 2011-11-07 2013-05-16 Radio Design Limited Combining apparatus for use in signal transmitting and/ or receiving apparatus

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Publication number Publication date
GB2444786B (en) 2011-10-05
GB0625062D0 (en) 2007-01-24

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WAP Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1)
Q107 Correction of irregularities (according pat. rules 2007)

Free format text: THIS APPLICATION WAS ANNOUNCED AS TERMINATED (AFTER PUBLICATION) IN PDJ NUMBER 6259 DATED 6 MAY 2009. THE APPLICATION WAS TERMINATED IN ERROR AND HAS BEEN REINSTATED UNDER THE PROVISIONS OF RULE 107