RU2479918C2 - Microwave mixer - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: mixer has a dielectric substrate, on one side of which there are two microstrip lines which are inputs of high-frequency signal paths and a heterodyne. On the other side of the electric substrate, there are slotted path lines in a metal coating, which lie coaxially with respect to each other and orthogonally with respect to the corresponding microstrip line. One end of the slotted lines is shorted and the other is the input of a conversion circuit which is made on one chip. The slotted line of each path, parallel to its input into the circuit, on the side of each conductor, includes short-circuited sections of slotted lines having a length which is equal to 1/4 of the heterodyne wavelength - in the heterodyne path, and 1/4 of the signal wavelength - in the signal path, which enables to achieve a high degree of decoupling between inputs of the high-frequency signal and the heterodyne. On the side of the dielectric substrate which is not metal coated, there are capacitance pads which are movable along the slotted lines on the section between its feed point and the circuit.

EFFECT: high decoupling between inputs of the high-frequency signal and the heterodyne.

4 cl, 5 dwg

Description

FIELD OF THE INVENTION

The invention relates to radio engineering, and more particularly to devices for converting microwave (microwave) oscillations into intermediate frequency signals, and can be used in transceiver and measuring equipment.

State of the art

The most widespread are mixers made using semiconductor diodes as converting active elements. Thus, a microwave microwave mixer is known, which contains a dielectric substrate on which two segments of slotted transmission lines are located, which are inputs of RF and local oscillator signals coming from coaxial cables, matching transformers in the form of smooth transitions from a slotted transmission line to a planar two-wire line, and a ring diode bridge , to the diagonals of which the second ends of planar two-wire lines are connected (see patent for invention SU 1169175, IPC H04B 1/26, publ. 07.23.1985). The intermediate frequency signal is removed from both diagonals of the annular bridge through an intermediate frequency filter. The symmetry of the transformers and diodes used in the circuit provides mutual isolation of the signal inputs, the local oscillator and the mixer output. The use of microstrip manufacturing technology provides small dimensions of the device.

A disadvantage of the known mixer is the high level of conversion by-products, which is due to the use of diodes characterized by load inconsistency in a wide frequency range and the presence of the inverse conversion.

Known ring frequency converter, made on bipolar transistors of different types of conductivity, connected according to the scheme of the ring bridge (see patent for invention SU No. 1587616, IPC H03D 7/12, publ. 08.23.1990). At the input and output of the annular bridge there are differential transformers made on inductors. A disadvantage of the known Converter is the inability to implement on the microwave.

As the closest analogue to the claimed technical solution, a double balanced microwave mixer for field effect transistors was selected (see patent for US invention 4603435, IPC H04B 1/26, publ. 29.07.86 g). The mixer device includes a dielectric substrate, on one side of which there are microstrip conductors, which are inputs of a high-frequency signal and a local oscillator, connected with a directional Lange coupler, four field-effect transistors connected in a two-balanced circuit, and an output path with an intermediate frequency power amplifier. The use of field-effect transistors, which have greater linearity compared to diodes, can significantly reduce the level of conversion by-products.

The main disadvantage of this mixer is the insufficient isolation between the signal and local oscillator inputs, which is due to the use of a directional Lange coupler as an decoupling device. Insufficient isolation between the signal lines leads to an increase in conversion losses and to an increased effect of the local oscillator signal on the LNA output stage, which is the source of the information signal.

Another disadvantage is the high requirements for observing the symmetry and equality of the balanced arms of the circuit and, as a result, the high requirements for the accuracy of the topology drawing and the need for semiconductor elements with identical characteristics, which is possible only in a batch of simultaneously manufactured products. The use of separate transistors, obviously having among themselves a spread of high-frequency characteristics, complicates the implementation of matching circuits.

Disclosure of invention

The task of the invention is to eliminate the above-mentioned disadvantages and to develop a microwave mixer device based on field-effect transistors having a high degree of isolation between the signal and local oscillator inputs and the simplicity of technological implementation.

The problem is solved due to the fact that in a mixer containing a dielectric substrate, on one side of which are two microstrip lines, which are inputs of the RF and local oscillator signal paths, the conversion circuit performed on four field-effect transistors and the intermediate frequency path, according to the claimed invention, are field transistors are turned on in a ring circuit with the possibility of operating in controlled resistance mode, the circuit being implemented on a single chip, each of the RF and hetero signal paths the dyne contains a slit line made in metallization on the opposite side of the dielectric substrate, orthogonally to the corresponding microstrip line, the slit lines of the paths are aligned, one end of the slit lines is shorted and forms a quarter-wave loop transition with a microstrip line, and the other is the input of the conversion circuit, while the slit line of each path parallel to the entrance, from the side of each of its conductor introduced short-circuited segments of the slit lines, made with a length equal to second ¼ wave length LO - a LO path and a ¼ wave length of the RF signal - in the signal path.

One positive technical result of the claimed invention is to increase the isolation between the inputs of the high frequency signal and the local oscillator.

Another positive result of the claimed invention was the reduction of requirements for the accuracy of the topological drawing, which allowed to simplify the manufacturing process of the device.

As in the prototype, field-effect transistors are used as active converting elements in the conversion (frequency mixing) circuit, which are characterized by high linearity and, as a result, by a low level of conversion by-products.

In the inventive device field-effect transistors are included in a ring circuit and operate in a controlled resistance mode. The use of a ring connection circuit of field-effect transistors, in contrast to the two-balanced circuit of the prototype, can significantly reduce the requirements for the symmetry of the input arms of the circuit, and therefore, to the accuracy of the topological pattern and the identity of the parameters of the used transistors. Even with asymmetric excitation of the bridge arms, the ring circuit allows one to obtain at the output the best suppression of the side channels of the transformation with respect to the balanced circuit.

The input RF signal is fed to one diagonal of the annular bridge, the local oscillator signal to the midpoints of the bridge diagonals. The intermediate frequency is removed from the second diagonal of the annular bridge through a matching resistance transformer.

Another difference from the prototype, in which individual transistors are used, obviously having a spread of high-frequency characteristics among themselves, is the implementation of a conversion circuit, i.e. the actual mixer circuit, on a single chip in the form of a single integrated circuit. This made it possible to achieve the maximum possible coincidence of the parameters of field-effect transistors and to practically eliminate the influence of variations in their parameters on the electrical characteristics of the mixer.

However, the implementation of the circuit on a single chip led to the need for the location of the input signal paths and the local oscillator on the same line, which made it possible for the paths to mutually bypass along the ground surface of the board. To exclude the specified probability and to ensure high mutual isolation of the RF and local oscillator signal inputs, the claimed original mixer topology allowed.

Each of the signal paths of the RF and local oscillator in the inventive mixer includes a microstrip line, which is the input of the corresponding signal, and a slot line orthogonally located thereto, made in metallization on the opposite side of the substrate. A quarter-wave loop junction is formed between the microstrip and slot lines, which makes it possible to propagate microwave signals from the microstrip line to the slot and performs the functions of a balancing transformer. The slotted lines of the paths are coaxial, which ensures the supply of RF and local oscillator signals to the inputs of the conversion chip.

To prevent mutual shunting of the slotted lines by the “earthen” surface of the board and to prevent the signals supplied to the circuit from passing through the opposite slotted line in each path, two short-circuited pieces of slotted lines having a length equal to a quarter of the wavelength of the corresponding signal are introduced, i.e. ¼ the local oscillator wavelength in the local oscillator path and 1/4 of the HF signal wavelength in the signal path. Short-circuited slot segments are located symmetrically relative to the main slot line of the path and are connected in parallel to the input of this slot line in the microcircuit, i.e. form two parallel shoulders.

The short-circuited quarter-wave length of the slit line is equivalent to a parallel resonant circuit. At the input of such a circuit, a high input resistance is formed, which tends to infinity, which prevents further signal propagation and contributes to the fact that all the signal power is applied to the relatively low-impedance input of the mixer microcircuit. Thus, on the side of each conductor of the slit line, i.e. on the metal surfaces of the board, located on the sides relative to the slit line, in the signal path and in the local oscillator path, high-resistance sections are organized, which provides high isolation of the RF and local oscillator signal inputs. This isolation of inputs allows reducing signal power loss and reducing the level of conversion by-products, thereby increasing the useful output of the device, as well as eliminating the influence of the local oscillator signal at the output of a low-noise amplifier when using the mixer in various transceiver devices.

To match the RF and local oscillator signals, the slotted path lines from the transition point from the microstrip line to the slotted line (otherwise, from the excitation point of the microstrip slot line) to the input of the microcircuit are performed with a length equal to выполня of the length of the corresponding signal. In fact, a quarter-wave matching transformer is formed at the inputs of the microcircuit in each path. The wave resistance of each slot line, which determines its width, is calculated by known methods for each specific case of execution.

To compensate for inaccuracies in the implementation of slot lines and the scatter of the parameters of the used microcircuits, corrective capacitive platforms made in the form of metal rectangles are introduced into the mixer circuit. Each pad is moved along the corresponding slot line from the opposite, non-metallized side of the dielectric substrate (board) in the area between the point of excitation of the slot line and the microcircuit. Moving capacitive platforms provide a change in the parameters of the slot lines, their wave impedance, which allows you to correct the inaccuracies in the manufacture of slot lines when setting up the device and to compensate for the parasitic input reactance of the chip.

The presence of such capacitive platforms can reduce the requirements for the accuracy of the design of the mixer topology and ensure that the device is configured for each microcircuit used, which, as you know, have a range of parameters.

Short-circuited segments of the slotted lines can be made either rectilinear or curved (see example below), which may be due to specific design parameters of the slotted lines or considerations of a more compact arrangement of the elements of the device.

Brief Description of the Drawings

Figure 1 presents a diagram of the inventive mixer;

figure 2 is a topological drawing of the proposed device;

figure 3 is a section aa from figure 2;

figure 4 shows the device of the inventive mixer assembly, a view of the metallized side of the dielectric substrate;

figure 5 is the same, view of the non-metallic side of the dielectric substrate.

The implementation of the invention

The inventive microwave range mixer relates to ring balanced mixers. The mixer includes (see Fig. 1) a conversion circuit 1, made according to a ring circuit on field-effect transistors operating in the controlled resistance mode, an RF (high frequency) signal path, consisting of a microstrip line (MPL) 2 and a slit line orthogonal to it (ЩЛ) 3, and the local oscillator path, consisting of a microstrip line (MPL) 4 and a slot line (ЩЛ) 5 orthogonally located to it.

MPL 2 and 4 end with a quarter-wave open loop, and slot lines 3 and 5 with a short-circuited quarter-wave loop. Transitions from a microstrip line to a slot line perform the functions of balancing transformers located at the input of the RF and local oscillator signal paths. The open ends of the slit lines 3 and 5 provide signals to the conversion circuit 1, the RF signal being fed to one diagonal of the ring bridge, the local oscillator signal to the midpoints of the diagonals, and the intermediate frequency output signal is taken from the second diagonal of the bridge of circuit 1 through a resistance transformer 6.

Mixer circuit 1 is made on a single chip in the form of a single microcircuit with the findings of RF (RF signal) and LO (LO signal) and IF (intermediate frequency signal). Similar microcircuits are currently produced by various industrial enterprises. In the specific case of the invention, in the manufacture of the prototype was used commercially available scheme PE4140, however, this does not limit the possibility of using other schemes.

Figure 2-5 shows the topology of the inventive mixer. All elements of the mixer are placed on a dielectric substrate 7, on the non-metallized side 8 of which microstrip conductors 2 and 4 and a resistance transformer 6 are located (see Fig. 2, 3, 5), and on the second, metallized side 9 (see Fig. 2 -4) the coaxial slotted lines 3 and 5 of the RF and local oscillator signal paths and the short-circuited sections of the slotted lines 10, 11, 12 and 13 are made. The length of the short-circuited slotted sections 10 and 11 in the signal path is λ _sig / 4. The length of the short-circuited slotted segments 12 and 13 in the local oscillator path is λ _get / 4. The open ends of the short-circuited quarter-wave segments are connected to the outputs of the slotted transmission lines 3 and 5 of the signal and the local oscillator, respectively.

The mixer operates as follows.

The RF input signal is supplied in antiphase via MPL 2, excites the slot line 3 and is fed to the inputs of RF microcircuit 1 through it. The local oscillator signal in antiphase goes to the MPL 4, excites the slot line 5 and is fed to the inputs of LO microcircuit 1. The result of the conversion is the intermediate frequency signal is also removed in antiphase from the output IF of the microcircuit 1 using a concentrated balancing transformer 6. This ensures the optimal addition of IF currents of the form F _IF = F _RF ± F _LO and the maximum suppression of other combination posing.

The segments of the slit lines 10 and 11 provide high resistance at the output of the SchL 3 of the signal path, the segments of the slit lines 12 and 13 provide high resistance at the output of the SchL 5 of the local oscillator path, because wave resistance at the open end of a quarter-wave short-circuited loop tends to infinity. This prevents mutual shunting of the transmission lines and contributes to the fact that all the power of the RF and local oscillator signals is applied to the corresponding inputs of the mixer chip 1.

Above the slotted lines 3 and 5 of the signal and local oscillator paths on the side 8 of the substrate 7, capacitive platforms 14 and 15 are located, the location of which can be changed during the device setup.

When moving capacitive pads 14 and 15, the wave resistance of the slotted lines changes, which allows you to compensate for the input reactivity of the mixer chip and the inaccuracy of making the pattern of the slotted lines. After adjustment, the position of the pads is fixed.

To match the 50-ohm paths of the input signal and the local oscillator signal with the 200-ohm inputs of the RF and LO microcircuits, matching resistance transformers are used, made in the form of quarter-wave sections of the slot lines 3 and 5 from the point (16, 17) of the excitation of the corresponding alkali to the corresponding input to the microcircuit .

Claims (4)

1. Microwave mixer containing a dielectric substrate, on one side of which are two microstrip lines that are inputs of the RF and local oscillator signal paths, a conversion circuit made on four field-effect transistors, and an intermediate frequency path, characterized in that the field-effect transistors are connected in a ring circuit with the possibility of operating in controlled resistance mode, the aforementioned circuit being implemented on a single chip, each of the RF and local oscillator signal paths contains a slot line made in metallis on the opposite side of the dielectric substrate orthogonally to the corresponding microstrip line, the slotted lines of the paths are aligned, one end of the slotted lines is shorted and forms a quarter-wave loop transition with a microstrip line, and the other is the input of the conversion circuit, with the slotted line of each path parallel to the input , on the side of each of its conductors, short-circuited segments of slot lines are introduced, made with a length equal to ¼ the wavelength of the local oscillator in the path of the local oscillator, and ¼ length HF signal waves in the signal path. 2. The mixer according to claim 1, characterized in that it is equipped with capacitive platforms made in the form of rectangular metal plates moved along slotted lines from the nonmetallized side of the dielectric substrate, in the area between the slotted line excitation point and the microcircuit. 3. The mixer according to claim 1, characterized in that the length of the slit line of the signal path from the point of its excitation by the microstrip line to the input of the microcircuit is equal to ¼ of the signal wave. 4. The mixer according to claim 1, characterized in that the length of the slot line of the local oscillator path from the point of its excitation by the microstrip line to the entrance to the microcircuit is equal to ¼ of the local oscillator wave.

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