WO1994015410A1

WO1994015410A1 - Interconnection of components

Info

Publication number: WO1994015410A1
Application number: PCT/SE1993/001103
Authority: WO
Inventors: Krister Ripstrand
Original assignee: Telefonaktiebolaget Lm Ericsson
Priority date: 1992-12-23
Filing date: 1993-12-22
Publication date: 1994-07-07
Also published as: JPH07504307A; SE9203903L; NO308720B1; AU5825894A; SE9203903D0; SG49042A1; FI943855A; CN1093212A; SE500713C2; NO943081L; EP0679299A1; CN1035463C; NO943081D0; FI943855A0

Abstract

The present invention relates to a device and a method respectively for interconnection of or communication between components or elements preferably intended for radio communication of which at least one is selective and reflective, a tunable phasor being arranged between 0 and 180° corresponding to a full turn in a Smith-chartTM.

Description

Interconnection of components

TECHNICAL FIELD:

The present invention relates to an arrangement fo interconnection of components or elements according to th first part of claim 1.

Within for example radio communication at interconnectin of or connection between different elements or component of which at least one is selective and reflex generatin problems arises due to reflection interaction betwee components if there is no wideband isolation between them, which for different reasons often is the case. Examples o elements or components may e.g. be antennas, pre-selecto filters and a number of others.

In e.g. VHF-communications systems (30-90 MHz) transmitte and receiver respectively may be arranged very close t each other. This means that e.g. the transmitter must hav a high selectivity, i.e. damp the power on othe freguencies which are not used which is problematica although freguency planning is applied. With this hig selectivity which is reguired by a transmitter as well a a receiver follows a high current consumption which in man cases is negative e.g. if the transmitter/receiver i portable. It is furthermore desirable, to the larges extent possible, to be able to use the same components. I this case may e.g. extra filters be used preceding th receiver frontend as well as preceding the transmitter. Th transmitter output comprises the output of an activ component which is impedance-matched over the whol frequency range, therefore no problems arise. Whe arranging a filter before the receiver frontend a proble arises since the receiver frontend comprises a filter wit bandpass-selectivity wherethrough the impedance is not the same across the whole band which is a requirement on an external passive filter to function as a bandpass filter with to the receiver added selectivity. What has been described in the foregoing is however merely an example which is intended to illustrate one of the areas which can be of interest.

STATE OF THE ART:

A known interconnected system is a so called "front-end"- radio receiver, usually a bandpass pre-selector filter preceded by antenna. Since this antenna is adapted for wideband signals this means that variations in impedance are very large. If it is a so called "short whip"-antenna of 30-88 MHz the standing wave ratio, VSWR, may reach 1:6 whereas when it is question about an antenna which is mounted on a vehicle the VSWR may be up to 1:4. The phase of the VSWR fluctuates depending on cable length and tuned frequency which strongly affects and degrades the selectivity of the system.

In another known system it has been tried to increase the selectivity of a system by arranging an external

"reflective" filter between the antenna and the receiver pre-selector. The intention is then to add the selectivity of each bandpass filter respectively. This may however instead lead to a total selectivity which is smaller than the selectivity of the individual bandpass filters. One of the explanations thereto is that the bandpass range merely constitutes a small part of the whole freguency range over which it is desired to control the bandpass filters. The degradation of the total system selectivity upon interconnection of two elements resides in the uncontrolled phase of the reflection coefficients of the input and output signals respectively. With selective elements it is the object to obtain reflection of power in the stopband and matching in the passband. Depending on the VSWR of t both elements at the point of interconnection and the phase a non desired matching in the stopband may resu which degrades and in the worst case even destroys t selectivity. A known solution to this problem is to ove dimension the external filter, or that margins a introduced in relation to prevailing system requirements that the degraded selectivity therethrough is compensat so that the system requirements in spite of all may be me This method is however generally current consuming a furthermore requires expensive, passive components.

According to an alternative embodiment buffers a interconnected between the receiver frontend and t external filter. These buffers may e.g. comprise amplifie or isolators to obtain a good isolation. The intention to keep the nominal impedance of the frequency range whi at least corresponds to the nominal freguency range (e. 30-90 MHz) . If however an amplifier is connected to t receiver frontend for isolation of the impedance variati of the antenna, this requires a high current consumpti which also involves costs. This also influences t frequency of faults occurrence of the system in a negati way. The connection of passive isolators is hard to car out among others depending on size at lower nominal syst frequencies whereas passive isolators as well as amplifie also require transmitter/receiver re-coupling in order maintain the performance of the system. Conseguently, al this solution based on arranging buffers consume curre and furthermore will among others maintenance reguiremen on a further component or an element be introduced. F e.g. a narrowband radio the cablelength between an extern filter and the receiver can be specified. With e.g. wideband radio a controllable cable length is require i.e. a phase shifter. In US-A-4 799 066 and US-A-4 965 6 arrangements are described for minimizing the loss betwe the welldefined, as far as the impedance is concerned i and output respectively at a received/transmitted frequen and a less well defined antenna. Therethrough is howeve not maximum selectivity obtained but the optimization i carried out for minimum passband loss. In e.g. EP-A-0 40 176 and US-A-4 232 399 examples of phase shifters ar shown.

SUMMARY OF THE INVENTION:

An object with the present invention is to provide a arrangement for interconnection of components e.g. in radi communication which are selective and reflective to obtai a high system selectivity without having to over-dimensio its component/components to comply with given syste requirements or to obtain an acceptable selectivity. It i further an object with the present invention to provide a arrangement wherein the phase can be controlled, where n buffers, e.g. in the form of amplifiers or passiv isolators between the components as well as also n transmitters/receiver selectors are required. It is thus a object with the invention to enable the interconnection o components without this leading to any loss in syste selectivity. It is furthermore an object of the inventio to be able to interconnect selective components without th total selectivity being lower than the selectivities o each component respectively or particularly that the tota selectivity even exceeds the sum of the individua selectivities. An object of the invention is to reduce o eliminate the loss in passband selectivity whe interconnecting selective and (narrowband) reflectiv components.

An arrangement through which these as well as other object are achieved is given by the characteristics of th characterizing part of claim 1. A method through which th above mentioned objects are achieved as given by claim 22.

Preferred embodiments are given by the characteristics o the subclaims. BRIEF DESCRIPTION OF THE DRAWINGS:

The invention will in the following be further describe under reference to the appended drawings in an explanator and by no means limiting way wherein

Fig. 1 illustrates interconnection of two "reflective elements, antenna and pre-selector filte respectively, Fig. 2 illustrates interconnection of antenna-externa filter-pre-selector filter, Fig. 3 schematically illustrates an example o interconnection of a wideband antenna with

VSWR-ratio of 3,5:1 and a pre-selector with 5 phase resolution,

Fig. 4 statistically illustrates the embodiment o

Fig. 3, Fig. 5 schematically illustrates interconnection o antenna-external filter-pre-selector with no iso lation and with 5° phase resolution.

Fig. 6 is a statistic illustration of the embodiment o

Fig. 5 in comparison to a perfect isolation.

DETAILED DESCRIPTION OF THE INVENTION:

Interconnection of two elements of the reflective kind, a antenna and a pre-selector filter or a bandpass filter i illustrated in Fig. 1. Between the two reflective element 1, 3 a phasor 2 is arranged. The phasor 2 is tunabl between 0 and 180° which corresponds to a full turn in

Smith-chart™, wherefrom a Smith-chart phase and amplitud for different reflection parameters can be plotted and rea and wherefrom further the corresponding complex conjugate impedance is obtained. With a correct tuning of the phaso 2 no degradation in selectivity occurs when interconnectin the two elements or components 1, 3. A correct tuning ma instead give rise to an increase or improvement of th total selectivity of the system which may be 6 dB. The pre selector filter is connected to a receiver 6 whic corresponds to an extra pole in the filter.

In Fig. 2 an embodiment is illustrated wherein a pre selector filter or a bandpass filter 3 of a radio input i preceded by an outer or an external bandpass filter 5. Fo interconnection of the different elements a phasor (phas tuner) 4 is interconnected between the pre-selector filte

3 and the external bandpass, BP, filter 5. It is then als possible to arrange a first phasor 2 ' before the externa bandpass filter 5, i.e. between the external filter 5 an the antenna 1. It is now significant how the phasor 2; 2'

4 is tuned or controlled, i.e. which phase positions i shall take for different, in this particular case receiving frequencies. '

According to one embodiment the phasor 2; 2 ' , 4 may b controlled or tuned with application of the so called dead count-method. With this method initially a number of value of the reflection parameters of the elements or component to be measured and the phase values of the tune frequencies are to be calculated and stored in a look-u table. Then one phase value is valid for one frequency fo a given cable length. Consequently a value for the phaso for the tuned frequency can be found in the table. Thi method is simple to apply but it does not take into accoun the aging of components e t c. It is furthermore necessary as stated above, that a cable of a well defined length i arranged between the external filter and the radio.

An alternate way for tuning or controlling of the phasor i to find the phase value which gives the best performanc for the system adaptively, via tuned freguencies with th use of SNR (Signal to Noise Ratio) or BER (Bit Erro Rate) . With the assistance of these methods, the solutio will also be independent of the length of the cable whic thus may take different sizes. With adaptive matching th bit errors are detected in the receiver whereafter th phasor is matched for minimum bit error. The tuning of th phase shifter merely insignificantly affects the passban damping and therethrough the desired signal.

It is also possible to in a number of other ways arrang the phasor either in a continuous or discrete mode with lo through losses, preferably less than 1 dB. Following wha has been said in the foregoing it is not possible to avoi passband mismatch. This is however possible through a adaptive eguivalent transformer ratio for adaption of th passband VSWR. This is however of minor importance i comparison to the loss of selectivity in the stopband.

In Fig. 3 are illustrated the effects of non phase matchin with a pre-selector filter or a bandpass filter which i preceded by an antenna with a VSWR-ratio of 3,5:1. Th figure shall also illustrate (not all shown) 36 curve corresponding to an antenna impedance with a phas resolution of 5°, i.e. one curve corresponds to eac setting of the phasor. It is of course possible to us another phase resolution which will be given by th application and chosen in an appropriate manner. I.e. th phase resolution is system-related and will be so chose that the best system performance is achieved. It may, a stated above be continuous, e.g. be voltage controlled o have discrete steps, wherein 5° merely is given as a example. It can be coarser as well as finer. In th embodiment is illustrated a frequency of between 47,5 MH to 52,5 MHz and region I corresponds to the passband regio whereas the regions denoted II illustrate stopband regions

The 36 curves, 36,5° x 5 = 180° corresponds to a full tur in the Smith-chart™. The curve illustrated ^• correspond to the passband filter at a nominal load and sourc impedance and in the figure is illustrated the loss whic an incorrect phase shifter tuning would give rise to i decibel, corresponding to b, whereas the gain selectivit by using the phasor is denoted a. The antenna is in thi case a wideband antenna. From the figure it is clear tha the different phases have a little effect on the passban loss compared to the variations in selectivity.

Fig. 4 statistically illustrates the result of Fig. 3 wherein curve c (denoted ^• in Fig. 3) corresponds to nominal filter for nominal load, curve d corresponds to minimum selectivity, curve e to average selectivity for all phase positions and finally curve f (dashed) corresponds to maximum received selectivity which is obtained through a correct tuning of the phasor.

In Fig. 5 (relative frequency deviation) is illustrated a interconnection essentially corresponding to Fig. 2 above with an external bandpass filter preceding a pre-selector filter or a bandpass filter. Between them phase shifters with a 5° resolution are arranged. The curve denoted ^• corresponds to the external bandpass filter whereas the curve illustrated by rings (0) corresponds to the pre¬ selector filter. The group of curves corresponds to phase shifter interconnection with a resolution of 5°. In the embodiment shown herein the components (external bandpass filter and pre-selector filter) are interconnected without any isolation arranged between them.

In Fig. 6 is compared the statistics of the embodiment illustrated in Fig. 5 with no isolation between the components and an embodiment with isolation, particularly perfect isolation, between the components, i.e. pre¬ selector filter and external bandpass filter. In the embodiment shown herein curve g corresponds to minimu selectivity, a full line corresponds to average selectivity, curve i illustrates the embodiment with a perfect isolator arranged between the components whereas curve j corresponds to a maximum resulting selectivity corresponding to perfect phasor tuning wherein A corresponds to selectivity gain through the use of a phasor which is perfectly tuned in relation to a perfect isolator arranged between the components. Depending on the frequency band being used, or within a frequency band, the filter may be active as well as passive, this having no effect This also applies to the phasors, i.e. they may within frequency band be either active or passive.

The invention shall of course not be limited to the sho embodiments but may be freely varied within the scope o the claims. The invention relates to interconnection of al elements as well as components which are selective an reflective. Furthermore, a number of components may b interconnected wherein phasor may be arranged between on or more of the components. Tuning or controlling of th phasor may further be carried out in a number of differen ways of which merely a limited number are mentioned here wherein those may be selected depending on the application A particular embodiment wherein the invention may b applied relates to wideband high selective receivers whic are connected to "bad" antennas, i.e. they have bad voltag standing wave ratios (VSWR) over the frequency range, e.g due to lack of space. Furthermore, a number of differen embodiments are of course possible wherein the presen invention can be applied.

Claims

CLAIMS :

1. Arrangement for interconnection of at least two components (1, 3; 1, 5; 3; 5) preferably intended for radio communication, the components or elements to be inter- connected being selective and reflective, c h a r a c ¬ t e r i z e d in that between the at least two components (1, 3; 1, 5; 3; 5) is arranged a tunable phasor (2; 2 ; 4) which is tunable between 0-180°, corresponding to a full turn in a Smith-chart™.

2. Arrangement according to claim 1, c h a r a c t e r i z e d in that the tuning is adaptiv or automatic.

3. Arrangement according to claim 1, c h a r a c t e r i z e d in that the phasor (2; 2'; 4) is tuned for a given cable length between the components using the so called dead-count-method.

4. Arrangement according to claim 1, c h a r a c t e r i z e d in that the phasor (2; 2' ; 4) is tuned with use of the so called SNR-(Signal to Noise Ratio)-method.

5. Arrangement according to claim 1, c h a r a c t e r i z e d in that the phasor (2; 2' ; 4) is tuned with use of the so called BER (Bit Error Rate)- method.

6. Arrangement according to claim 1, c h a r a c t e r i z e d in that at least one of the elements or components which are to be interconnected comprises a wideband designed antenna.

7. Arrangement according to claim 1, c h a r a c t e r i z e d in that at least one of th components comprises a filter (3; 3', 5).

8. Arrangement according to claim 7, c h a r a c t e r i z e d in that the filter comprises pre-selector filter (3, 3').

9. Arrangement according to claim 7, c h a r a c t e r i z e d in that two components (3', 5) comprise filters.

10. Arrangement according to claim 9, c h a r a c t e r i z e d in that the filters comprise bandpass filter (5) and a pre-selector filter (3) wherei the bandpass filter (5) preferably precedes the pre selector filter (3) .

11. Arrangement according to claim 1, c h a r a c t e r i z e d in that at least two of th components which are to be interconnected comprise a filte and a transmitter.

12. Arrangement according to claim 1, c h a r a c t e r i z e d in that for interconnection o three components, preferably an antenna (1) , a bandpas filter (5) and a pre-selector filter (3'), it comprises first (2') and a second (4) phasor.

13. Arrangement according to any one of claims 1-12, c h a r a c t e r i z e d in that at least one phasor i passive.

14. Arrangement according to any one of claims 1-12, c h a r a c t e r i z e d in that at least one phasor i active.

15. Arrangement according to any one of claims 1-12 c h a r a c t e r i z e d in that at least one filter i passive.

16. Arrangement according to any one of claims 1-12, c h a r a c t e r i z e d in that at least one filter i active.

17. Arrangement according to any one of claims 1-12, c h a r a c t e r i z e d in that the phase resolution o the phasor is adapted to and depending on the system.

18. Arrangement according to any one of claims 1-12, c h a r a c t e r i z e d in that the phase tuning i discrete.

19. Arrangement according to any one of claims 1-12, c h a r a c t e r i z e d in that the phasor has a phas resolution of 5°.

20. Arrangement according to any one of claims 1-12, c h a r a c t e r i z e d in that the phase tuning i continuous.

21. Arrangement according to any one of claims 1-12, c h a r a c t e r i z e d in that at least one phasor i active or passive, at least one filter is active o passive, and in that the phase tuning is discrete o continuous.

22. Method for interconnecting elements or component which are selective and reflective wherein a tunable phaso is arranged between the components which are to b interconnected, said phasor being tunable between 0-180°, corresponding to a full turn in a Smith-chart™.