EP2044649A2 - A microwave circuit with improved quadrature balance. - Google Patents

A microwave circuit with improved quadrature balance.

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Publication number
EP2044649A2
EP2044649A2 EP07825898A EP07825898A EP2044649A2 EP 2044649 A2 EP2044649 A2 EP 2044649A2 EP 07825898 A EP07825898 A EP 07825898A EP 07825898 A EP07825898 A EP 07825898A EP 2044649 A2 EP2044649 A2 EP 2044649A2
Authority
EP
European Patent Office
Prior art keywords
circuit
impedance
phase difference
quadrature
input port
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.)
Withdrawn
Application number
EP07825898A
Other languages
German (de)
French (fr)
Other versions
EP2044649A4 (en
Inventor
Karl Martin Gjertsen
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.)
Ceragon Networks AS
Original Assignee
Nera Networks AS
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 Nera Networks AS filed Critical Nera Networks AS
Publication of EP2044649A2 publication Critical patent/EP2044649A2/en
Publication of EP2044649A4 publication Critical patent/EP2044649A4/en
Withdrawn legal-status Critical Current

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Classifications

    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01PWAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P5/00Coupling devices of the waveguide type
    • H01P5/12Coupling devices having more than two ports
    • H01P5/16Conjugate devices, i.e. devices having at least one port decoupled from one other port
    • H01P5/19Conjugate devices, i.e. devices having at least one port decoupled from one other port of the junction type
    • H01P5/22Hybrid ring junctions
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01PWAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P5/00Coupling devices of the waveguide type
    • H01P5/12Coupling devices having more than two ports
    • H01P5/16Conjugate devices, i.e. devices having at least one port decoupled from one other port
    • H01P5/19Conjugate devices, i.e. devices having at least one port decoupled from one other port of the junction type
    • H01P5/22Hybrid ring junctions
    • H01P5/22790° branch line couplers

Definitions

  • a microwave circuit with improved quadrature balance is provided.
  • the present invention discloses a microwave circuit in which there is a so called quadrature circuit which has first and second inputs, and first and second outputs.
  • the quadrature circuit is designed so that when a signal is input to its first input port, there will be a certain desired phase difference and amplitude between the signals at the output ports, and the second input port of the quadrature circuit will at the same time be connected to a specified impedance.
  • quadrature balance refers to the fact that two channels are often used, the so called I- and Q-channels, between which there must be a phase difference of exactly 90 degrees, and which must also have equal amplitudes.
  • the balance which it is sought to obtain and maintain is thus the phase difference and the equal amplitudes. Even slight deviations from this balance can cause rather grave errors in a system which uses the two signals.
  • a microwave circuit comprising a quadrature circuit with a first and a second input, and a first and a second output.
  • the quadrature circuit is designed to give a certain desired phase difference and a desired amplitude ratio between the output signals of said output ports when a first input signal is applied to the first input port, and the second input port of the quadrature circuit is connected to specified impedance.
  • said impedance is chosen so that the desired phase difference between the output signals is obtained and maintained, and also so that the desired ratio between the amplitudes of the output signals is obtained and maintained.
  • the impedance which is connected to the second input port is used to connect the second input port to ground.
  • other connections are also possible.
  • the impedance is of course chosen so that the quadrature balance is maintained as near to perfect as possible, but the phase difference is at least obtained and maintained at the desired value with a variation of +/- 1 degree, and the ratio between the output amplitudes obtains and maintains a value in the range of [-0.25,0.25] dB.
  • the impedance connected to the second input port is optimized depending on the loads at the output ports of the quadrature circuit.
  • the impedance is tuneable.
  • the invention also discloses a method for choosing the impedance so that the desired phase difference between the output signals is obtained and maintained, so that the equality between the amplitudes of the output signals is obtained and maintained.
  • the desired phase difference is ninety degrees, and the desired amplitude ratio is equality between the amplitudes, but the invention can be used for other phase differences and amplitude ratios as well.
  • Fig 1 shows an example of a larger circuit in which the invention can be applied
  • Fig 2 shows a circuit according to the invention
  • Fig 3 shows the quadrature circuit
  • Fig 4 shows a rough flowchart of a method of the invention
  • Fig 5 shows a circuit according to the invention, including terminations on the output ports
  • Fig 1 shows an example of an application 100 in which a circuit of the invention can be used.
  • the application 100 is an MMIC-modulator, which in this case comprises four quadrature circuits, one of which has been given the reference number 110.
  • the quadrature circuit 110 comprises two input ports, shows as 1 and 2, and also two output ports, shown as 3 and 4.
  • the invention can be applied to all of the quadrature circuits shown in the MMIC-modulator of fig 1 , but will be described in more detail with reference to the quadrature circuit 110, which is shown separately in fig 2.
  • fig 2 shows only the quadrature circuit 110, with the first and second input ports 1 and 2, and the first and second output ports 3 and 4.
  • one of the input ports 2 of the quadrature circuit 110 is connected to an impedance shown as 220.
  • the input port 2 is shown here as connected to ground via the impedance 220, which is a common application of the impedance 220.
  • the invention will in the following be described throughout with the impedance 220 connecting the second input 2 port to ground, but those skilled in the field will realize that other applications are equally possible, such as applications with quadrature circuits used in phase shifter networks.
  • the impedance which connects to the input port 2 of the quadrature circuit may be connected to a matching network, which will have as one of its tasks to achieve an impedance which gives the desired quadrature properties.
  • the quadrature circuit 300 shown in fig 3 can basically be seen as a lossless four-port with a high degree of symmetry. All reflection coefficients of the quadrature circuit are in the following assumed to be equal.
  • the full S-matrix of the quadrature circuit 300 can be written as shown in equation (1 ) below, with the indexed matrix elements having been replaced by unique letters, for clarity in the continued description.
  • Requiring unitahty for the matrix implies the four equations 2-5 shown below, in which ⁇ is used to denote the phase rotation (also sometimes referred to as "phase shift") for signals propagating from input port 1 to output port 3, (or from input port 2 to output port 4, due to the symmetry of the circuit) r is used to denote the amplitude of the mismatch reflection on all the ports, and k is used to distinguish the four theoretical solutions, which differ in the phase of the mismatch reflections.
  • phase rotation ⁇ depends on where the ports of the quadrature circuit are located. If a transmission line is included at each port of the quadrature circuit, the phase rotation will change.
  • the output signals at the four ports 1 -4 will be referred to, consecutively, as a, b, c and d, which leads to the following:
  • This expression can be used for obtaining the phase and amplitude ratio between signals d/c at output ports 4 and 3 respectively, when the quadrature circuits 110 and 300 of figs 2 and 3 respectively are excited by an input signal at port 1.
  • M and N can be precisely determined, we find that it will almost always be possible to define a value for U that in theory will provide perfect quadrature balance, and in practice will give at least very much improved results as compared to present solutions. Naturally, M and N can also be known a priori from the design process or from a manufacturer's data sheets.
  • the refection coefficients of the quadrature circuit 110 should be established.
  • the reflection coefficients at all four ports 1 , 2, 3, 4, of the quadrature circuit will be equal, but if this is not the case, all coefficients should be established. This can be done by, for example, measurements, simulations, or possibly from a manufacturer's data sheet.
  • Equation (9) The integer k used in equation (9) is then selected to best suit the set of S- parameters found for the quadrature circuit.
  • the reflection coefficients M and N of the output loads should be found from available sources.
  • the quadrature circuit 110 is then attached to the phase corrected loads M and N, as shown in block 430 of fig 4, and U, the termination load is connected to the port 2 of the quadrature circuit 110.
  • This operative bandwidth can be established at any interval over a wide frequency band by tuning the termination impedance to the desired frequency interval. In the case illustrated in fig 6, this can be obtained over the whole frequency range 5-7 GHz
  • the termination impedance can be tuned by means of, for example, a semiconductor circuit, suitably but not necessarily a FET (Field Effect Transistor) with variable input current at one of its inputs, or as an alternative, it can be a diode with variable bias voltage.
  • a semiconductor circuit suitably but not necessarily a FET (Field Effect Transistor) with variable input current at one of its inputs, or as an alternative, it can be a diode with variable bias voltage.
  • the invention can be used to obtain and maintain phase differences and amplitude ratios between the output signals in a range about the optimum quadrature value. This is achieved by finding a correct value of the termination of the quadrature circuit.
  • circuit of the invention has been described with the aid of an example in which the invention is applied in a modulator.
  • Other applications in which the invention can be applied include:
  • Quadrature modulators in which it is desired to use the quadrature circuits both to achieve the desired quadrature properties and to suppress a carrier wave signal.
  • Phase shifters in which the quadrature circuit is used both to define signal components with orthogonal phase, and to amplitude modulate the signal components with reflections which vary over a dynamic range, starting from 0 and extending up to maxima with a high reflection.

Abstract

The invention discloses a microwave circuit (500) comprising a quadrature circuit (300) with first (1 ) and second (2) inputs, and first (3) and second outputs (4), the quadrature circuit (300) being designed to give a desired phase difference and amplitude ratio between the output signals of said output ports (3, 4) when a first input signal is applied to the first input port (1 ). The second input port (2) of the quadrature circuit (300) is connected to impedance (120, 220), and said impedance (120, 220) is chosen so that said desired phase difference between the output signals (3, 4) is obtained and maintained, and also so that said amplitude ratio between the amplitudes of the output signals is obtained and maintained. Suitably, the phase difference is ninety degrees and the amplitude ratio is equality of the amplitudes

Description

TITLE
A microwave circuit with improved quadrature balance.
TECHNICAL FIELD The present invention discloses a microwave circuit in which there is a so called quadrature circuit which has first and second inputs, and first and second outputs.
The quadrature circuit is designed so that when a signal is input to its first input port, there will be a certain desired phase difference and amplitude between the signals at the output ports, and the second input port of the quadrature circuit will at the same time be connected to a specified impedance.
BACKGROUND
Obtaining and maintaining quadrature balance is a well known problem within, for example, the field of communications technology. The term "quadrature balance" refers to the fact that two channels are often used, the so called I- and Q-channels, between which there must be a phase difference of exactly 90 degrees, and which must also have equal amplitudes.
The balance which it is sought to obtain and maintain is thus the phase difference and the equal amplitudes. Even slight deviations from this balance can cause rather grave errors in a system which uses the two signals.
One particular area of technology in which there have been difficulties with obtaining and maintaining the quadrature balance is MMIC-technology (Monolithic Microwave Integrated Circuits). SUMMARY
There is thus a need for a microwave circuit in which quadrature balance can be obtained, and be maintained once it has been obtained. In particular, the circuit should be suitable for MMIC-applications.
This need is addressed by the present invention in that it discloses a microwave circuit comprising a quadrature circuit with a first and a second input, and a first and a second output.
The quadrature circuit is designed to give a certain desired phase difference and a desired amplitude ratio between the output signals of said output ports when a first input signal is applied to the first input port, and the second input port of the quadrature circuit is connected to specified impedance.
In the microwave circuit of the invention, said impedance is chosen so that the desired phase difference between the output signals is obtained and maintained, and also so that the desired ratio between the amplitudes of the output signals is obtained and maintained.
In a preferred embodiment of the invention, the impedance which is connected to the second input port is used to connect the second input port to ground. However, other connections are also possible.
The impedance is of course chosen so that the quadrature balance is maintained as near to perfect as possible, but the phase difference is at least obtained and maintained at the desired value with a variation of +/- 1 degree, and the ratio between the output amplitudes obtains and maintains a value in the range of [-0.25,0.25] dB.
Also, suitably, the impedance connected to the second input port is optimized depending on the loads at the output ports of the quadrature circuit. In a particular embodiment, the impedance is tuneable.
The invention also discloses a method for choosing the impedance so that the desired phase difference between the output signals is obtained and maintained, so that the equality between the amplitudes of the output signals is obtained and maintained.
Suitably, the desired phase difference is ninety degrees, and the desired amplitude ratio is equality between the amplitudes, but the invention can be used for other phase differences and amplitude ratios as well.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in more detail in the following, with reference to the accompanying drawings, in which Fig 1 shows an example of a larger circuit in which the invention can be applied, and
Fig 2 shows a circuit according to the invention, and
Fig 3 shows the quadrature circuit, and
Fig 4 shows a rough flowchart of a method of the invention, and Fig 5 shows a circuit according to the invention, including terminations on the output ports
Fig 6 shows results obtained by means of the invention.
DETAILED DESCRIPTION Fig 1 shows an example of an application 100 in which a circuit of the invention can be used. The application 100 is an MMIC-modulator, which in this case comprises four quadrature circuits, one of which has been given the reference number 110.
The quadrature circuit 110 comprises two input ports, shows as 1 and 2, and also two output ports, shown as 3 and 4. The invention can be applied to all of the quadrature circuits shown in the MMIC-modulator of fig 1 , but will be described in more detail with reference to the quadrature circuit 110, which is shown separately in fig 2.
Thus, fig 2 shows only the quadrature circuit 110, with the first and second input ports 1 and 2, and the first and second output ports 3 and 4. As previously shown in fig 1 , one of the input ports 2 of the quadrature circuit 110 is connected to an impedance shown as 220. The input port 2 is shown here as connected to ground via the impedance 220, which is a common application of the impedance 220. Hence, the invention will in the following be described throughout with the impedance 220 connecting the second input 2 port to ground, but those skilled in the field will realize that other applications are equally possible, such as applications with quadrature circuits used in phase shifter networks. In such applications, the impedance which connects to the input port 2 of the quadrature circuit may be connected to a matching network, which will have as one of its tasks to achieve an impedance which gives the desired quadrature properties.
In previously known applications with quadrature circuits, such as those shown in figs 1 and 2, this connection has usually been made with a standard impedance of 50 Ω, with little or no thought as to the implications of the impedance 220 on the quadrature balance between the output signals.
With reference to the schematic quadrature circuit shown in fig 3, we will in the following show an expression that describes the amplitude and phase balance in a quadrature circuit. This will, in turn, be used to show our inventive method for using the specified impedance to optimize the quadrature balance between the signals at the output ports 3 and 4 of the circuit 300 in fig 3.
The quadrature circuit 300 shown in fig 3 can basically be seen as a lossless four-port with a high degree of symmetry. All reflection coefficients of the quadrature circuit are in the following assumed to be equal. Using the well known and established S-parameter notation, we thus have Si3=S24 and Si4=S23, using the reference numerals 1 and 2 of fig 3 for the two input ports and reference numerals 3 and 4 for the two output ports of fig 3. The quadrature property for the desired phase difference of ninety degrees and equal amplitudes between the output signals can be described by Si4=jSi3, where j = V^T .
The full S-matrix of the quadrature circuit 300 can be written as shown in equation (1 ) below, with the indexed matrix elements having been replaced by unique letters, for clarity in the continued description.
Requiring unitahty for the matrix implies the four equations 2-5 shown below, in which τ is used to denote the phase rotation (also sometimes referred to as "phase shift") for signals propagating from input port 1 to output port 3, (or from input port 2 to output port 4, due to the symmetry of the circuit) r is used to denote the amplitude of the mismatch reflection on all the ports, and k is used to distinguish the four theoretical solutions, which differ in the phase of the mismatch reflections.
(3)
We note that solutions to equations 2-5 above require k& {0,1,2,3} , while the mismatch reflection amplitude r is defined by re [θ,l] .
The phase rotation τ depends on where the ports of the quadrature circuit are located. If a transmission line is included at each port of the quadrature circuit, the phase rotation will change.
To simplify in the following description, we will assume that the ports are set such that τ = 0.
Using the notations of fig 3, we will now analyse a situation where port 1 is excited with a driving signal from a source with reflection coefficient r, port 2 is associated with the reflection coefficient U, while ports 3 and 4 are terminated with reflections M and N, respectively.
The output signals at the four ports 1 -4 will be referred to, consecutively, as a, b, c and d, which leads to the following:
The outgoing signal vector in the column vector to the left in equation (6) below equals the sum of the propagated excitation and the propagated reflections from all ports. (6)
We are mainly interested in the ratio d/c, in other words the ratio between the signals at the output ports 3 and 4, which is expressed analytically in equation (7) below:
d_ I2UMQ + IUT-2IURMT + TMI + T2UQM + Q-QMR-QUR + QUR2M-Q3UM C UIQ-2UIQNR+UI2NT + T-NTR+QNI-URT + UR2NT-UT3N + UTNQ2
Inserting the S-matrix elements, using equations (1) - (5) above, gives us the following expression:
This expression can be used for obtaining the phase and amplitude ratio between signals d/c at output ports 4 and 3 respectively, when the quadrature circuits 110 and 300 of figs 2 and 3 respectively are excited by an input signal at port 1.
The signal balance (d/c) shown above depends on the matches around the quadrature circuit. It will be realized that if r=0 and U=O, i.e. the quadrature circuit and the load at the "terminated port" are perfect, the ratio d/c will be
J=V-T, and we would thus have a perfect signal balance regardless of the mismatches M and N.
However, perfect quadrature circuits are nonexistent, as are perfect loads, but the inventors of the present invention have realized that the load or impedance connected to the second input port of the quadrature circuit, i.e. port 2 in figs 1-3, can be successfully tuned to obtain and maintain the desired quadrature balance, as it hitherto has served no other purpose than termination.
The degree of freedom given by this realization is of high value - we can choose the termination U at the second input port 2 of the quadrature circuit so as to provide the best possible quadrature balance. Requiring, as shown above, f = V-T gives a well-defined value for U, being:
If M and N can be precisely determined, we find that it will almost always be possible to define a value for U that in theory will provide perfect quadrature balance, and in practice will give at least very much improved results as compared to present solutions. Naturally, M and N can also be known a priori from the design process or from a manufacturer's data sheets.
When determining the termination U, we need to avoid the possibility of a zero in the denominator of equation (9). It is also of interest to obtain an impedance U which has a low absolute value, since this will result in robustness for the quadrature balance (phase and amplitude) against variations in, for example, input frequency.
A low absolute value of U is thus beneficial, and will be obtained if the denominator in equation (9) above has a large absolute value, which shows us that robustness in quadrature balance assumes a certain phase relation between the quadrature circuit mismatch and the two terminations M and N. In most applications, M and N will be close or equal to each other in phase and amplitude, and for robust terminations, the relation ZN = z[i - sin(kγ)- cos(kγ)] will be a first target for connecting M and N in favourable phase. The symbol in front of the letter N is here used to signify the phase angle.
In the following, we will, with reference to the rough flowchart 400 shown in fig 4, describe how the method of the invention can be used to achieve a circuit 500 (fig 5) in which a desired phase difference between the output signals 3, 4, is obtained and maintained, and in which circuit equality between the amplitudes of the output signals 3, 4, is also obtained and maintained.
It should be pointed out that the sequence of steps described in the following is not fixed, the order used below and in the flowchart of fig 4 is merely used to illustrate the method of the invention.
As indicated in block 410 of fig 4, the refection coefficients of the quadrature circuit 110 should be established. Usually, the reflection coefficients at all four ports 1 , 2, 3, 4, of the quadrature circuit will be equal, but if this is not the case, all coefficients should be established. This can be done by, for example, measurements, simulations, or possibly from a manufacturer's data sheet.
The integer k used in equation (9) is then selected to best suit the set of S- parameters found for the quadrature circuit. The reflection coefficients M and N of the output loads should be found from available sources.
The values of the reflection coefficients M and N and the value of the parameter k for the quadrature circuit are then used in equation (9) above in order to determine the necessary phase shift to obtain as large a value as possible of the denominator in equation (9). It should be taken into account that equation 9 assumes that the ports of the quadrature circuit are located such that the quadrature circuit parameter τ=0.
The phrase "as large as possible" is used in this context to signify that the difference between the phase of M+N and the phase of the reflection coefficient of the quadrature circuit 110 should be larger than or equal to ninety degrees.
The quadrature circuit 110 is then attached to the phase corrected loads M and N, as shown in block 430 of fig 4, and U, the termination load is connected to the port 2 of the quadrature circuit 110.
In fig 6, a diagram is shown of the results which can be obtained by means of the invention. In this diagram, we see that at a centre frequency of 5.6 GHZ, the phase balance (left hand vertical axis) is maintained within ± 1 degree and the amplitude balance (right hand vertical axis) is maintained within ±
0.25 dB, when the loads at the output ports are varied between 20 and 200 Ω in real impedance, and between -50 and 50 Ω in imaginary impedance. The desired phase ratio and amplitude balance can be maintained within these limits over an operative bandwidth of at least 100 MHz.
This operative bandwidth can be established at any interval over a wide frequency band by tuning the termination impedance to the desired frequency interval. In the case illustrated in fig 6, this can be obtained over the whole frequency range 5-7 GHz
The termination impedance can be tuned by means of, for example, a semiconductor circuit, suitably but not necessarily a FET (Field Effect Transistor) with variable input current at one of its inputs, or as an alternative, it can be a diode with variable bias voltage. As indicated in the text, the invention can be used to obtain and maintain phase differences and amplitude ratios between the output signals in a range about the optimum quadrature value. This is achieved by finding a correct value of the termination of the quadrature circuit.
The invention is not limited to the examples of embodiments shown and described above, but can be freely varied within the scope of the appended claims.
For example, the circuit of the invention has been described with the aid of an example in which the invention is applied in a modulator. Other applications in which the invention can be applied include:
• Balanced structures in which one signal path uses a quadrautre circuit in order to split the signal into two parallel paths in which the same operations are carried out (for example amplification), followiong which the signals are connected to each other again. In such applications, the invention will offer very good adaption to the surrounding connections.
• Quadrature modulators, in which it is desired to use the quadrature circuits both to achieve the desired quadrature properties and to suppress a carrier wave signal.
• Phase shifters, in which the quadrature circuit is used both to define signal components with orthogonal phase, and to amplitude modulate the signal components with reflections which vary over a dynamic range, starting from 0 and extending up to maxima with a high reflection.

Claims

1. A microwave circuit (500) comprising a quadrature circuit (300) with a first (1 ) and a second (2) input, and a first (3) and a second output (4), the quadrature circuit (300) being designed to give a certain desired phase difference and amplitude ratio between the output signals of said output ports (3, 4) when a first input signal is applied to the first input port (1 ), with the second input port (2) of the quadrature circuit (300) being connected to an impedance (120, 220), the microwave circuit (500) being characterized in that said impedance (120, 220) is chosen so that said desired phase difference between the output signals (3, 4) is obtained and maintained, and also so that said amplitude ratio between the amplitudes of the output signals is obtained and maintained.
2. The microwave circuit (500) of claim (1 ), in which the impedance (120, 220) which is connected to the second input port (2) is used to connect the second input port (2) to ground.
3. The microwave circuit (500) of claim 1 or 2, in which the phase difference is obtained and maintained at the desired value with a variation of +/- 1 degree, and the ratio between the output amplitudes obtains and maintains a value in the range of [-0.25,0.25] dB.
4. The microwave circuit (500) of any of claims 1 -3, in which the impedance (120, 220) connected to the second input port (2) is optimized depending on the loads at the output ports (3, 4).
5. The microwave circuit (500) of any of claims 1 -4 in which said impedance (120, 220) is tuneable.
6. The microwave circuit (500) of claim 5, in which the desired phase difference and amplitude ratio are maintained over an operative bandwidth of at least 100 MHz, said operative bandwidth being tuneable by means of the impedance (120, 220) over a relative bandwidth of 10%.
7. The microwave circuit (500) of claim 6, in which the impedance (120, 220) is tuneable by means of being a semiconductor circuit.
8. The microwave circuit (500) of claim 7, in which the semiconductor circuit is a FET with variable input current at one of its inputs, or a diode with variable bias voltage.
9. The microwave circuit (500) of any of claims 1 -8, in which said phase difference and amplitude ratio can be maintained over a relative bandwidth of 10%.
10. The microwave circuit (500) of any of the previous claims, in which the desired phase difference is ninety degrees and the amplitude ratio is equality between the amplitudes.
11. The microwave circuit (500) of any of claims 1 -10, in which both of the input ports (1 ) and (2) are terminated with the same impedance, so that if a signal is introduced at the second input port (2), the output signals at the first (3) and second (4) output ports obtain the same amplitude relation as for signals introduced at the first input port (1 ), while obtaining the opposite phase relation.
12. A method for obtaining and maintaining a desired phase difference and amplitude ratio between the output signals of a first (3) and a second (4) output of a quadrature circuit (300) which has a first (1 ) and a second (2) input and a first (3) and a second (4) output, the quadrature circuit (300) being part of a microwave circuit (500), the quadrature circuit (300) being designed to give a certain desired phase difference and amplitude ratio between the output signals of said output ports (3, 4) when a first input signal is applied to the first input port (1 ), the method comprising connecting the second input port (2) of the quadrature circuit (300) to an impedance (120, 220), the method being characterized in that said impedance (120, 220) is chosen so that the desired phase difference between the output signals (3, 4) is obtained and maintained, and also so that said ratio between the amplitudes of the output signals is obtained and maintained.
13. The method of claim 12, according to which the impedance (120, 220) which is connected to the second input port (2) is used to connect the second input port (2) to ground.
14. The method of claim 12 or 13, by means of which the phase difference is obtained and maintained at the desired value with a variation of +/- 1 degree, and the ratio between the output amplitudes is obtained and maintained within the range [-0.25,0.25] dB.
15. The method of any of claims 12-14, by means of which the impedance (120, 220) connected to the second input port (2) is optimized depending on the loads at the output ports (3, 4).
16. The method of any of claims 12-14, according to which said impedance (120, 220) is tuneable.
17. The method of claim 15, according to which the desired phase difference and amplitude ratio are maintained over an operative bandwidth of at least
100 MHz, said operative bandwidth being tuneable by means of the impedance (120, 220) over a relative bandwidth of 10%.
18. The method of claim 16, according to which the impedance (120, 220) is a semiconductor circuit such as a FET with variable input current at one of its inputs, or a diode with variable bias voltage.
19. The method of any of claims 12-17, according to which said phase difference and amplitude ratio can be maintained over a relative bandwidth of 10%.
20. The method of any of claims 12-18, according to which the desired phase difference is ninety degrees and the amplitude ratio is equality between the amplitudes.
EP07825898A 2006-07-07 2007-07-05 A microwave circuit with improved quadrature balance. Withdrawn EP2044649A4 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE0601491A SE532094C2 (en) 2006-07-07 2006-07-07 A microwave circuit with improved quadrature balance
PCT/IB2007/052643 WO2008007317A2 (en) 2006-07-07 2007-07-05 A microwave circuit with improved quadrature balance.

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EP2044649A2 true EP2044649A2 (en) 2009-04-08
EP2044649A4 EP2044649A4 (en) 2011-10-26

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SE532094C2 (en) 2009-10-20
WO2008007317A3 (en) 2008-04-24
WO2008007317A2 (en) 2008-01-17
SE0601491L (en) 2008-01-08

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