CN107732457B - Antenna unit and array antenna - Google Patents
Antenna unit and array antenna Download PDFInfo
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- CN107732457B CN107732457B CN201710916613.3A CN201710916613A CN107732457B CN 107732457 B CN107732457 B CN 107732457B CN 201710916613 A CN201710916613 A CN 201710916613A CN 107732457 B CN107732457 B CN 107732457B
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- 230000008878 coupling Effects 0.000 abstract description 38
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q1/00—Details of, or arrangements associated with, antennas
- H01Q1/52—Means for reducing coupling between antennas; Means for reducing coupling between an antenna and another structure
- H01Q1/521—Means for reducing coupling between antennas; Means for reducing coupling between an antenna and another structure reducing the coupling between adjacent antennas
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Abstract
The application discloses an antenna unit and an array antenna provided with the antenna unit, wherein an active loss resistance capable of actively consuming and absorbing radio frequency power in the antenna unit to reduce the Q value of the antenna unit is connected in the antenna unit. Preferably, the low-temperature device is in heat conduction connection with the active lossy resistor so as to cool the active lossy resistor. The method and the device can effectively reduce the coupling among the antenna units of the array antenna.
Description
Technical Field
The application belongs to the technical field of array antennas, and particularly relates to an antenna unit and an array antenna provided with the antenna unit, which are applicable to the fields of phased array antennas, phased array radars, magnetic resonance radio frequency array coils and the like.
Background
An antenna is a necessary energy conversion device for receiving and radiating electromagnetic waves in space, is an interface device between a circuit and the electromagnetic wave energy in space, and is widely applied in modern communication. In general, the task of transmitting and receiving electromagnetic waves can be accomplished by a single antenna. However, as the demand continues to develop, in many applications, multiple antennas must be used to arrange and finally connect together according to a certain rule to form an antenna array, see fig. 1, where each single antenna is an antenna unit. An array antenna may be defined as: one type of antenna combination is formed by arranging not less than two antenna elements regularly or randomly and by appropriately adjusting the power amplitude and phase of each element to obtain a predetermined characteristic. Five main parameters determining the characteristics of the array antenna are: i.e. the number of cells, the cell position, the radiation characteristics of the cells themselves, the amplitude weighting and the phase weighting of each cell.
In the initial research work of array antennas, it is often assumed that the antenna units are isolated and do not interfere with each other under ideal conditions, however, in a practical antenna array system, as shown in fig. 1, energy mutual coupling between the antenna units is an unavoidable phenomenon, especially when the distance between the units is relatively close, the mutual coupling between the units is strong, and electromagnetic coupling effect occurs between the units through interaction of electromagnetic fields radiated or received respectively, so that amplitude and phase of each unit are greatly changed, which affects amplitude-phase characteristics and reflection coefficients of each antenna unit, and finally overall performance of the antenna array, such as gain reduction in transmitting and signal-to-noise ratio reduction in receiving. Therefore, how to reduce the mutual coupling between the antenna array units has been a hot spot and a difficult problem in the field of antenna design. In view of the adverse effects of coupling, researchers have designed various methods and circuits for reducing coupling, such as electromagnetic bandgap, defected ground, shorting studs, etc., in hardware, and can design a series of decoupling networks with low or no consumption of high Q reactive elements. However, whatever the method, there are always limitations and advantages and disadvantages of this method, and there is no completely universal perfect decoupling method.
In the past, engineering researchers proposed decoupling schemes among antenna units in hardware, and the decoupling schemes are often based on analysis methods and results of electromagnetic fields radiated by the antenna units. The invention provides a new inter-unit decoupling method and an improvement scheme based on an analysis method of an antenna equivalent circuit.
The antenna structure can be equivalent to the composition of a resonant circuit and a matching circuit network in circuit. The principle of the antenna element may be equivalent to a circuit as shown in fig. 2, comprising a resonant tank and a matching network. Wherein X is 1 And X 2 Is an equivalent reactive element (inductance or capacitance); r is R Radiation Is the equivalent radiation resistance of the antenna, R Conductor Is the loss resistance of the antenna conductor itself; in addition, a matching network is needed to make X 2 Antenna impedance Z of port Antenna Conversion to transmission line matching (characteristic) impedance Z Match To satisfy noise matching of a pre-low noise amplifier at the time of reception or power transmission matching at the time of transmission.
It should be noted that R in FIG. 2 Radiation And R is Conductor Not the physical resistance applied to the antenna, but for more intuitive and simple reasons in the analysis of the circuit. Conventionally, in designing an antenna, R is used to improve efficiency at the time of transmission or signal-to-noise ratio at the time of reception as much as possible Radiation And R is Conductor In particular R Conductor To avoid and reduce the effects of (a) as much as possible, it is common to use good conductors of high conductivity. In addition X 1 Typically an inductance (hereinafter referred to as inductance L Antenna Representation), X 2 At the feed end of the antenna, typically a capacitor (hereinafter referred to as capacitor C P Representation). Also, each antenna requires the addition of an excitation source or termination, denoted termination impedance, typically a matched characteristic impedance (here represented by a relatively common characteristic impedance value of 50 ohms, so that fig. 2 can again be equivalently fig. 3.
The coupling between antenna elements is an unavoidable negative factor in the design of an array antenna, especially for multi-channel high density array antennas, the following analysis introduces the principle of coupling and the way of decoupling, based on fig. 3.
Fig. 4 shows a schematic diagram of two identical antenna elements and the coupling between them, with the model eliminating the common equivalent resistance, which is of little general use, for simplicity. Two antenna units are placed together, and mutual inductance phenomenon exists, and a mutual inductance coefficient is defined as K. Assuming that the current I1 in the left cell in fig. 3 is the normal operating current, I2 is the induced current caused by the mutual inductance phenomenon, i.e. the result of coupling (interference). Here, the coupling (interference) of the cell 1 to the cell 2 is defined as:
where I1 is the current required for the proper operation of the left cell and I2 is the disturbance current induced in the right cell due to the presence of I1.
According to the mutual inductance principle, the induced electromotive force on the right side unit resonant circuit is:
the size of epsilon 2 is related to the inductance of the two loops and the mutual inductance K, and the size of the interference current I2 is as follows:
where Z2 is the series impedance of the resonant tank of the unit 2, substituting (3) into (1) can result in the coupling (interference) of the unit 1 to the unit 2 as:
because the two units and the equivalent inductances L1 and L2 are fixed in size, C 21 The magnitude of (2) depends on the mutual inductance K and the impedance of the resonant tank of the right-hand cell. The manner and principle of decoupling is described in further detail below, based on relation (4):
1. the mutual inductance coefficient K is reduced: the common method is to optimize the radiation pattern of the units and the relative positions among the units, and in addition, the structures such as electromagnetic band gaps, defected ground, short-circuit columns and the like which are frequently reported can also effectively reduce the K value.
2. A decoupled circuit network is formed with non-dissipative or low-dissipative components such as capacitors or inductors in such a way that a further electromotive force is generated to cancel epsilon 2. As shown in fig. 5, a common capacitor C is added between the two antenna elements C Voltages equal to epsilon 2 and opposite to epsilon 2 can be generated at the end of the capacitor 2, so that the sum of the induced electromotive forces is 0. The inductive decoupling works similarly.
Principle and origin of the technical proposal of the invention
Based on the above relation (4) in the background art, the inventor found that there is a decoupling method, namely, increasing the loop impedance Z2 of the right antenna element in fig. 4, and analyzing the magnitude of Z2.
Fig. 6 is a diagram showing the impedance analysis of the resonant tank of the right antenna element in fig. 4, let L in fig. 6 for simplicity antenna Is L, R Radiation R is R Conductor And R, the impedance Z2 in the resonant tank is:
Z2＝jωL+R+Z Right (5)
here, an important concept of rf microwave circuit matching is applied: if there is a face in the radio frequency circuit whose 2-terminal impedance is conjugate matched, the impedance of either face is conjugate matched. The first face is set to the left of the output termination and it can be seen that the impedance across it is 50Ω, which is a conjugate match. The impedance should also be conjugate matched across the dashed line in fig. 6, since the impedance to the left of the dashed line is:
Z Left ＝R+jωL (6)
according to the conjugate matching principle, the impedance to the right of the dashed line should be:
Z Right ＝R-jωL (7)
substituting the relation (7) into (5) can obtain:
Z2＝2R (8)
substituting relation (8) into relation (4) gives a coupling (interference) C21 of cell 1 to cell 2 as:
it can be found from the relation (9) that by increasing the series resistance in the resonant loop of the right-side element, the resonant impedance of the loop can be increased, and the interference coupling of the left-side antenna element to the right-side antenna element in fig. 4 can be effectively reduced. Further analysis is performed assuming that the 2 cells are identical, the equivalent inductance L1 is equal to L2 and L. Then relation (9) can be further reduced to:
C 21 the absolute value is as follows:
wherein the Q value is the quality factor of the antenna element resonant circuit:
however, this method of reducing the coupling between the units by increasing the series resistance R of the resonant circuit of the antenna unit and reducing the Q value of the circuit has a very significant side effect, namely, reducing the transmission efficiency and the received signal-to-noise ratio of the antenna. It is also well known at the time of transmission that this sacrifice is sometimes worth in order to obtain better array antenna performance, because the power of the transmit power amplifier is large enough for some applications or the cost of the power amplifier is not very high.
But the signal-to-noise ratio at the time of reception is reduced-since the received signal-to-noise ratio is also often a very critical indicator-this approach to reducing the Q to reduce coupling is often not repairable. In order to solve the problem, the inventor further optimizes the scheme, and after the scheme is optimized, the coupling between units can be effectively reduced by increasing the series resistance of the loop, and adverse side effects of obviously reduced receiving signal-to-noise ratio can be eliminated.
In a specific electromagnetic environment, for an antenna unit of a fixed structure, the induced (received) signal in the resonant tank can be represented by an induced electromotive force (voltage) V S The representation remains unchanged. The noise source in the resonant circuit is a series resistor in the resonant circuit, each resistor can be equivalent to an ideal noise-free resistor connected in series with a noise voltage source, and the root mean square value of the noise voltage satisfies the following relation:
where K is the boltzmann constant, T is the absolute temperature (in K) corresponding to the resistance R, B is the receiver bandwidth, and R is the resistance value.
The above is a noise relation corresponding to a single resistor, if there are multiple resistors R1, R2..rn in the loop, the corresponding temperatures are T1, T2..tn, respectively, then the total noise satisfies the relation:
or it is:
since the thermal noise generated by each resistor is related to its temperature and resistance, the effect of the resistor on the coupling is independent of temperature and is related to the magnitude of the resistance. The actively increased resonant tank loss resistance can thus be placed in a low temperature environment, such as a liquid helium vessel, so that the decoupling effect of the resistance can be exploited without adding significant noise.
For example: assuming that an equivalent resistance R is already present in the resonant tank of the antenna unit 2, it is placed in a room temperature 17 ℃ (i.e. 290K), an additional resistance 3R is now added, and it is placed in liquid helium 4K through an ideal lossless wire (coaxial line). Coupling C before decoupling according to relation (4) and relation (8) 21 The method comprises the following steps:
and adding an additional resistor 3R to decouple the coupling C 21 The method comprises the following steps:
the coupling values before and after decoupling differ by 4 times, and the coupling value is converted into common dB to be expressed as about 12dB (note that the difference is not directly reflected in the coupling improvement value of instruments such as a network analyzer, the coupling value in the network analyzer also relates to the Q value of a resonant loop, more assumption is provided, and the coupling condition is greatly improved. Then, the noise change is evaluated, and the noise level before decoupling is as follows according to the noise sum relation (15):
and the decoupled noise level is:
the noise levels before and after decoupling differ only by 2%, that is to say the signal-to-noise ratios differ substantially. Of course, the assumption here is that the wire between the active resistor and the cryogenic vessel is an ideal wire (coaxial wire), so that in practical application, there is no possibility of the wire being consumed, so that in practical application, the signal to noise ratio may be worse, but there are other methods to reduce the noise increase caused by the wire loss, which will not be described in detail here.
Disclosure of Invention
The purpose of the present application is: in view of the problems in the background art, an antenna unit and an array antenna configured with the antenna unit are provided, so as to effectively reduce coupling between antenna units of the array antenna.
In order to achieve the above purpose, the technical scheme of the application is as follows:
an antenna unit has an active lossy resistor connected thereto for actively consuming and absorbing radio frequency power in the antenna unit to reduce the Q value of the antenna unit.
The antenna unit further comprises the following preferable schemes based on the technical scheme:
the low-temperature equipment is in heat conduction connection with the active lossy resistor so as to cool the active lossy resistor.
The cryogenic device is a cryogenic vessel, and the active lossy resistor is disposed in the cryogenic vessel.
The cryogenic container is provided with liquid nitrogen therein.
The number of the active lossy resistors is two, an on-off switch is arranged between each active lossy resistor and the antenna unit, and the low-temperature equipment is in heat conduction connection with only one active lossy resistor.
The active lossy resistor is connected in parallel with the reactive element of the resonant tank of the antenna element.
An array antenna comprises at least two antenna units, wherein at least one antenna unit adopts the structural form.
The array antenna further comprises the following preferable schemes based on the technical scheme:
all antenna units in the array antenna adopt the structural form.
The array antenna is a phased array antenna or a magnetic resonance radio frequency array coil.
The application also provides a phased array radar which is characterized by comprising the array antenna with the structure.
The application has the advantages that:
the active lossy resistor is additionally connected in the antenna units, so that coupling between the antenna units is effectively reduced. Preferably, the added active lossy resistor is thermally connected to the cryogenic device to cool the active lossy resistor to a lower temperature, thereby eliminating the adverse side effects of reduced received signal-to-noise ratio.
Drawings
Fig. 1 is a schematic diagram of a conventional array antenna, in which space electromagnetic coupling is indicated by hollow arrows, and in which antenna elements are indicated by thick, branched lines;
fig. 2 is a schematic circuit diagram of a conventional antenna element;
fig. 3 is a second schematic circuit diagram of a conventional antenna unit;
fig. 4 is a schematic diagram of coupling between two identical antenna elements in the prior art;
fig. 5 is a schematic diagram of the antenna unit of fig. 4 after a common capacitor is added between the two antenna units;
FIG. 6 is a graph of the impedance analysis of the resonant tank of the right antenna element of FIG. 4;
FIG. 7 is a schematic circuit diagram of an antenna unit according to an embodiment of the present disclosure;
FIG. 8 is a schematic circuit diagram of an antenna unit according to a second embodiment of the present disclosure;
fig. 9 is a schematic circuit diagram of an array antenna in the third embodiment of the present application, in which space electromagnetic coupling is indicated by hollow arrows, and in which the antenna elements are indicated by thick and branched solid lines.
Detailed Description
The present application is described in further detail below with reference to the accompanying drawings by way of specific embodiments. This application may be embodied in many different forms and is not limited to the implementations described in this example. The following detailed description is provided to facilitate a more thorough understanding of the present disclosure, in which words of upper, lower, left, right, etc., indicating orientations are used solely for the illustrated structure in the corresponding figures.
However, one skilled in the relevant art will recognize that the detailed description of one or more of the specific details may be omitted, or that other methods, components, or materials may be used. In some instances, some embodiments are not described or described in detail.
Furthermore, the features and aspects described herein may be combined in any suitable manner in one or more embodiments. It will be readily understood by those skilled in the art that the steps or order of operation of the methods associated with the embodiments provided herein may also be varied. Thus, any order in the figures and examples is for illustrative purposes only and does not imply that a certain order is required unless explicitly stated that a certain order is required.
The numbering of the components itself, e.g. "first", "second", etc., is used herein merely to distinguish between the described objects and does not have any sequential or technical meaning. The terms "coupled" and "connected," as used herein, are intended to encompass both direct and indirect coupling (coupling), unless otherwise indicated.
Embodiment one:
fig. 1 shows a specific embodiment of an antenna element of an array antenna of the kind of the present application, which, like a conventional antenna element, also comprises a resonant tank and a matching network connected to each other. Wherein X is 1 And X 2 Is an equivalent reactive element (inductance or capacitance); r is R Radiation Is the equivalent radiation resistance of the antenna, R Conductor Is the loss resistance of the antenna conductor itself. The matching network will X 2 Antenna impedance Z of port Antenna Conversion to transmission line matching (characteristic) impedance Z Match To satisfy noise matching of a pre-low noise amplifier at the time of reception or power transmission matching at the time of transmission.
Finger needsWhat is shown is R in FIG. 1 Radiation And R is Conductor Not the physical resistance applied to the antenna, but for more intuitive and simple reasons in the analysis of the circuit. In addition, X 1 Typically inductance, X 2 The feed end of the antenna is typically a capacitor.
The key improvement of this embodiment is: an active loss resistance R is additionally connected in the antenna unit Active The active loss resistance R Active The function of (2) is: actively consuming active loss resistance for absorbing radio frequency power in the antenna unit to reduce the Q value of the antenna unit.
The active loss resistor R Active In particular in the resonant tank of the antenna element.
As can be seen from the above description of the principle and the origin of the technical scheme of the invention, the active loss resistance R additionally arranged in the antenna unit Active The series resistance of the resonant tank of the antenna element is increased, thereby reducing the Q value of the tank to reduce the coupling between the antenna elements. Although this approach has very significant side effects: the transmitting efficiency and the receiving signal-to-noise ratio of the antenna are reduced. It is also well known at the time of transmission that this sacrifice is sometimes worth in order to obtain better array antenna performance, because the power of the transmit power amplifier is large enough for some applications or the cost of the power amplifier is not very high.
The term "active loss resistance" as used herein refers to a resistance device that is added to an antenna element only to reduce coupling between antenna elements, and is not an element that the antenna element itself originally has.
Embodiment two:
fig. 8 shows another embodiment of an array antenna element of the kind herein, which also comprises a resonant tank and a matching network connected to each other. Wherein X is 1 、X 2 And X 3 Is an equivalent reactive element (inductance or capacitance); r is R Radiation Is the equivalent radiation resistance of the antenna, R Conductor Is the loss resistance of the antenna conductor itself. Matching netX is a complex of 2 Antenna impedance Z of port Antenna Conversion to transmission line matching (characteristic) impedance Z Match To satisfy noise matching of a pre-low noise amplifier at the time of reception or power transmission matching at the time of transmission.
The key improvement of this embodiment is: an active lossy resistor R is also connected to the antenna element Active And the active loss resistance R Active Placed in a cryogenic vessel such that the active lossy resistor R Active Has a very low temperature.
From the previous analysis, we have known to add an active lossy resistance R in the antenna element Active Thereby effectively reducing the coupling between the antenna units. And will actively wear resistance R Active In a low-temperature environment, the adverse side effect of reduced receiving signal-to-noise ratio can be eliminated.
In general, we set liquid nitrogen in the above-mentioned low-temperature container to make it be an ultra-low-temperature container, and utilize ultra-low-temperature liquid nitrogen to absorb active lossy resistor R Active Thereby making the active loss resistance R Active With ultra-low temperature, so that the receiving signal-to-noise ratio of the coil cannot be increased due to the connection of the active loss resistance R Active But significantly reduced.
Of course, other low-temperature devices can be used to provide the active loss resistance R Active Cooling to make the active loss resistance R Active Has extremely low temperature.
In the present embodiment, the active loss resistor R Active Reactance element X connected in parallel with resonant circuit of antenna unit 3 Is provided. Of course, we can also use the active loss resistance R Active Parallel or series connected to other components and even to the matching network.
Embodiment III:
fig. 9 shows a specific embodiment of an array antenna of the type described in the present application, comprising a plurality of (n) antenna elements, each of which has an active lossy resistor connected thereto—R 1 、R 2 ……R n Thereby effectively reducing the coupling between the antenna units. At the same time, the active lossy resistors in each antenna element are also placed in a cryogenic vessel so that each active lossy resistor has a lower temperature. Increasing active lossy resistance R in antenna elements Active Therefore, the coupling between the antenna units is effectively reduced, and the adverse side effect of reduced receiving signal-to-noise ratio is eliminated.
Such an array antenna of the present embodiment may be a phased array antenna or a magnetic resonance radio frequency array coil (in which case each antenna element corresponds to a coil element of the array coil in fig. 9), which may be applied to a phased array radar.
Note 1: the resonant tank in the present application is a generalized resonant tank, and the matching network and the end load are also part of the resonant tank, and the specific definition refers to the description of fig. 6 and the background section.
And (2) injection: if the antenna is in a high-power emission state, after the active Q-reducing resistor placed in the low-temperature container absorbs power, the low-temperature liquid in the container may be volatilized greatly, at this time, 2 active Q-reducing resistors (i.e. the active lossy resistors described above) may be introduced, one of which is placed in the low-temperature container, and the other of which is placed in a normal-temperature environment, and each of which is connected to an on-off switch for switching the active Q-reducing resistor into or out of the antenna unit. Therefore, when high-power emission is carried out, the Q-reducing resistor in the low-temperature container is disconnected, and the Q-reducing resistor in the normal-temperature environment is connected. When the antenna is in a receiving state, the on-off states of the two resistors are reversed. Furthermore, if the values of the two Q-reduction resistors are not the same, a frequency compensation circuit and a matching compensation circuit can be introduced to meet the requirement that the antenna unit can still be in a good resonance and matching state when the different Q-reduction resistors work.
And (3) injection: the Q-reducing resistor may be in various forms, and may be a physical resistor or an equivalent resistor, so long as the Q-reducing resistor is actively added with loss to reduce the Q-value, and the mode for reducing the coupling between antenna units is within the scope of the patent.
The foregoing is a further detailed description of the present application in connection with the specific embodiments, and it is not intended that the practice of the present application be limited to such descriptions. It will be apparent to those skilled in the art to which the present application pertains that several simple deductions or substitutions may be made without departing from the spirit of the present application.
Claims (7)
1. An antenna unit is characterized in that an active loss resistance capable of actively consuming and absorbing radio frequency power in the antenna unit to reduce the Q value of the antenna unit is connected in the antenna unit;
the number of the active lossy resistors is two, and an on-off switch is arranged between each active lossy resistor and the antenna unit;
further comprising a cryogenic vessel provided with cryogenic liquid, only one of the two active lossy resistors being provided in the cryogenic vessel.
2. The antenna unit of claim 1, wherein the cryogenic liquid comprises liquid nitrogen.
3. An antenna unit according to claim 1, characterized in that the active lossy resistor is connected in parallel with the reactive element of the resonant tank of the antenna unit.
4. An array antenna comprising at least two antenna elements, wherein at least one of said antenna elements adopts the structure of an antenna element according to any one of claims 1-3.
5. An array antenna according to claim 4, wherein all antenna elements in the array antenna adopt the structure of the antenna element according to any one of claims 1-3.
6. The array antenna of claim 4, wherein the array antenna is a phased array antenna or a magnetic resonance radio frequency array coil.
7. A phased array radar comprising an array antenna as claimed in claim 4.
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| CN207743386U (en) * | 2017-09-30 | 2018-08-17 | 苏州美柯医疗科技有限公司 | Antenna element, array antenna and phased-array radar |
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|---|---|---|---|---|
| CN101884532A (en) * | 2009-05-15 | 2010-11-17 | 美时医疗技术(上海)有限公司 | Superconductive magnetic resonance imager as well as manufacturing method and application |
| CN103116147A (en) * | 2013-02-26 | 2013-05-22 | 江苏美时医疗技术有限公司 | Knee radiofrequency coil for magnetic resonance imaging system |
| CN106990372A (en) * | 2016-01-20 | 2017-07-28 | 中国石油化工股份有限公司 | A kind of magnetic nuclear resonance radio frequency antenna circuit and its impedance matching methods |
| CN106932743A (en) * | 2017-03-23 | 2017-07-07 | 苏州美柯医疗科技有限公司 | For the radio-frequency coil unit and radio-frequency coil of magnetic resonance imaging |
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