JPH08335841A - 90-degree hybrid and variable phase shifter - Google Patents

Abstract

PURPOSE: To provide a 90-degree hybrid/variable phase shifter which consists of only a concentrated constant element in a compact structure and with high integration density. CONSTITUTION: Four terminals 1, 2, 3 and 4 are grounded via the ground capacitors C1 , and the 1st and 2nd terminals 1 and 2 and the 3rd and 4th terminals 3 and 4 are connected together respectively via the coupling capacitors C2 . Then the terminals 1 and 3 and the terminals 2 and 4 are connected together respectively via the inductors L. The capacitor C1 is larger than the capacitor C2 by about √2-1) times. Then the terminals 1 and 2 are used as the input/output terminals, and the capacitors C1 of both terminals 3 and 4 use the variable capacity elements having the capacitance equal to each other. In such a constitution, a variable phase shifter is obtained.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a beam forming circuit used in a microwave phased array antenna,
The present invention relates to a microwave integrated circuit which requires compact integration of large-scale distribution / synthesis / phase shift / attenuation functions.

[0002]

2. Description of the Related Art A 90-degree hybrid is widely used for processing microwave signals, that is, for combining, distributing, phase shifting, and attenuating. As a circuit configuration of the 90-degree hybrid, a combination of distributed constant lines such as branch lines is general and most widely used. Also, in order to make the circuit compact, an example of a circuit in which a lumped constant element is combined instead of the distributed constant line has been announced. (For example, literature; (1) RK Gupta et al: "Qu
asi-runped-element 3-and
4-port networks for MIC
and MMIC applications "IEE
E MTT-S 1984 Internationala
l Microwave Symposium Dig
est, pp. 409-411. , (2) Shigematsu and others:
"Reflective analog phase shifter that shares the parallel capacitance of the hybrid circuit and the capacitance for determining the phase shift amount with the capacitance of the varactor diode" Proceedings of the 1992 Autumn Meeting of the Institute of Electronics, Information and Communication Engineers
-405)

2 and 3 are examples disclosed in the above-mentioned documents 1 and 2. In these examples, four inductors and four capacitors are used.

[0004]

In the structure in which the distributed constant lines are combined, the circuit size is on the order of the wavelength of microwaves. Therefore, it is not suitable when high-density integration is required. In addition, four inductors are required in a configuration in which lumped constant elements are combined. MMIC
In (monolithic microwave integrated circuit), since the inductor element has a larger occupied area on the chip than the capacitor element, using four of them has a limit in integration density. In particular, in a beam forming circuit for a large-scale phased array antenna that uses many phase shift circuits, there is a drawback that the circuit area is considerably large and it is difficult to integrate it into a one-chip MMIC.

The present invention overcomes the above-mentioned drawbacks and is composed of only lumped constant elements, which makes it possible to achieve smaller size and higher integration density.
It is an object to provide a 0 degree hybrid variable phase shift circuit.

[0006]

A feature of the present invention for achieving the above object is that it has four terminals, each of which is grounded by a grounding capacitor and has a first terminal and a second terminal.
The terminals are connected by a coupling capacitor, the third terminal and the fourth terminal are connected by another coupling capacitor, the first terminal and the third terminal are connected by an inductor, and the second terminal and the fourth terminal are connected by another inductor. The capacitances of the ground capacitors connected to the terminals are substantially equal to each other, the capacitances of the first and second inter-terminal coupling capacitors are approximately equal to the third and fourth inter-terminal coupling capacitances, and The inductance is approximately equal to the coupling inductance between the second and fourth terminals, and the capacitance of the ground capacitor is approximately (√2-
1) In a 90 degree hybrid equal to double.

A variable phase shifter is obtained by implementing the first terminal and the second terminal as input / output terminals and realizing the ground capacitors of the third terminal and the fourth terminal by variable capacitance elements having substantially equal capacitances.

According to the present invention, the number of inductors can be reduced to half that of the conventional one, and the circuit size can be reduced by using only lumped constant elements and devising a method of combining inductors and capacitors. Is different from the conventional technology.

[0009]

EXAMPLE An example of the 90-degree hybrid of the present invention is shown in FIG. Four ground capacitors C whose four terminals have the same value
It is grounded at ₁ and is respectively coupled by two coupling capacitors C ₂ and two inductors L. These values are

(Equation 3) To satisfy the relationship. This circuit has a symmetrical and vertically symmetrical circuit configuration. Since it has a double symmetric structure, any of the four terminals may be used as the input terminal. A terminal 2 capacitively coupled to the input terminal 1 is an isolation terminal, a terminal 3 inductively coupled to the input terminal is a quadrature phase output terminal, and a diagonal terminal 4 of the input terminal is an in-phase output terminal.

The operating principle will be described below. The symbols are defined as follows. f = frequency of microwave signal ω = 2πf Z ₀ = source and load impedance Y ₀ = 1 / Z ₀ C ₁ = ground capacitance (all four equal values) C ₂ = coupling capacitance (two equal values) L = Coupling inductance (two equal values) a ₁ = Input signal of terminal 1 b ₁ = Output signal of terminal 1 a ₂ = Input signal of terminal 2 b ₂ = Output signal of terminal 2 a ₃ = Input signal of terminal 3 b ₃ = output signal of terminal 3 a ₄ = input signal of terminal 4 b ₄ = output signal of terminal 4 S _ij = scattering parameter from terminal j to terminal i (i, j =
1, 2, 3, 4)

From the definition of the scattering parameter, b ₁ = S ₁₁ * a ₁ + S ₂₁ * a ₂ + S ₃₁ * a ₃ + S ₄₁ * a ₄ (1) Here, the symmetry of the circuit is used to simplify the following calculation. To do. First, assuming that all of terminals 1 to 4 are excited by an in-phase input signal having an amplitude of 1, if a ₁ = a ₂ = a ₃ = a ₄ = 1 then b ₁ = S ₁₁ + S ₂₁ + S ₃₁ + S from equation (1) ₄₁ . At this time, since magnetic walls are formed on the vertical and horizontal symmetrical planes shown in FIG. 4, b ₁ is equal to the reflection coefficient Γ _a of the equivalent circuit diagram 5 (a). That is, S ₁₁ + S ₂₁ + S ₃₁ + S ₄₁ = Γ _a (2). Next, assuming that terminals 1 to 4 are excited by a left-right antisymmetrical input signal, and a ₁ = −a ₂ = a ₃ = −a ₄ = 1 then b ₁ = S ₁₁ −S ₂₁ from equation (1). + is an S ₃₁ -S _41. At this time, an electric wall is formed on the longitudinally symmetrical surface and a magnetic wall is formed on the laterally symmetrical surface, so that b ₁ is equal to the reflection coefficient Γ _b in the equivalent circuit diagram 5 (b). That is, S ₁₁ −S ₂₁ + S ₃₁ −S ₄₁ = Γ _b (3). Similarly, if put as _{a 1 = a 2 = -a 3} = -a 4 = 1 from terminal 1 4 As was excited by an input signal of the upper and lower anti-symmetric, b from equation _{(1) 1 = S 11 +} S 21 - it is the S ₃₁ -S _41. At this time, since a magnetic wall is formed on the longitudinally symmetric surface and an electric wall is formed on the laterally symmetric surface, b ₁ is equal to the reflection coefficient Γ _c in the equivalent circuit diagram 5 (c). That is, S ₁₁ + S ₂₁ −S ₃₁ −S ₄₁ = Γ _c (4). Finally, assuming that terminals 1 to 4 are excited by input signals which are vertically and horizontally antisymmetrical, if a ₁ = -a ₂ = -a ₃ = a ₄ = 1 then b ₁ = S ₁₁ -S from equation (1). ₂₁ −S ₃₁ + S ₄₁ . At this time, since electric walls are formed on both the vertical and horizontal symmetrical planes, b ₁ is equal to the reflection coefficient Γ _d in the equivalent circuit diagram 5 (d). That is, S ₁₁ −S ₂₁ + S ₃₁ −S ₄₁ = Γ _d (5).

The equivalent circuits (a) (b) (c) shown in FIG.
Since (d) is a simple circuit, these reflection coefficients can be easily obtained. Using the relationship of equation (0),

[Equation 4] Becomes These are the simultaneous equations (2) (3) (4) (5)
Substituting into S ₁₁ , S ₂₁ , S ₃₁ , S ₄₁ ,

(Equation 5) Is obtained. That is, the input signal from the terminal 1 is not reflected to the terminal 1 (impedance matching). 2) No output to terminal 2 (isolation is obtained). 3) 3 dB is coupled to the terminal 3 with a phase difference of 90 degrees. 4) 3 dB coupling to the terminal 4 in phase. It was shown that. In this way, this circuit
It functions as a 90 degree hybrid with respect to the frequency of the microwave signal satisfying the above and the source / load impedance.

However, in the formula (0), C ₁ = (√2-1)
C ₂ is a necessary condition,

(Equation 6) Does not necessarily limit the scope of the present invention. Because, for any value of C ₂ and L, the above 2
This is because there are ω and Z ₀ that satisfy the formula and function as a 90-degree hybrid with respect to the frequency and the signal source / load impedance.

Next, an embodiment of a variable phase shifter constructed by modifying a part of the circuit of the 90-degree hybrid of the present invention is shown in FIGS. It is generally known that when two terminals of the four terminals of a 90-degree hybrid are replaced with two equal variable reactance elements, it operates as a variable phase shifter (Reference 2). Regarding the 90-degree hybrid of the present invention, as shown in FIG. 6, for example, if the grounding capacitor of the third and fourth terminals is replaced with a variable reactance element (for example, a varactor diode), a variable phase shift using the first and second terminals as input / output terminals. It works as a container. FIG. 7 shows a variable phase shifter having a wide variable range, which is implemented by cascade-connecting these in multiple stages. In this case, since the grounded capacitor of the first and second terminals can be shared between the stages, the case of three stages in addition to the case of one stage will be described as an example.

[0015]

According to the present invention, the number of inductors can be reduced to two in a lumped constant 90 degree hybrid. Therefore, the present invention is very effective in reducing the chip area in an MMIC in which the area of the inductor element dominates the area of the circuit. In particular, it is extremely effective in the case of integrating a circuit network, such as a multi-element phased array, which has a large-scale signal distribution / synthesis / phase shifting function into one chip.

[Brief description of drawings]

FIG. 1 illustrates a 90 degree hybrid of the present invention.

FIG. 2 shows a conventional 90 degree hybrid.

FIG. 3 shows a conventional 90 degree hybrid.

FIG. 4 is an explanation of the operating principle (terminal number and symmetry plane).

FIG. 5 is an explanation of the operating principle (equivalent circuit in the case of symmetrical excitation).

FIG. 6 shows an embodiment of a variable phase shifter configured by partially modifying the 90-degree hybrid of the present invention.

FIG. 7 shows an embodiment of a variable phase shifter in which the variable phase shifter of the present invention is connected in three stages and a part thereof is modified.

Claims (4)

[Claims] 1. A terminal comprising four terminals, each of which is grounded by a grounding capacitor, a first terminal and a second terminal being connected by a coupling capacitor, and a third terminal and a fourth terminal being another coupling. Connected by a capacitor, the first terminal and the third terminal are connected by an inductor, the second terminal and the fourth terminal are connected by another inductor, and the capacitances of the ground capacitors connected to the respective terminals are substantially equal to each other. 1 The capacitance of the second inter-terminal coupling capacitor is the third
The coupling capacitance between the fourth terminals is substantially equal to the inductance of the first and third coupling terminals between the terminals.
The 90-degree hybrid, wherein the coupling capacitance between the fourth terminals is approximately equal to the capacitance of the ground capacitor is approximately equal to (√2-1) times the capacitance of the coupling capacitor. 2. When the signal angular frequency is ω and the signal source and load impedance are Z ₀ , the coupling capacitance C _{2 of} the coupling capacitor and the coupling inductance L of the inductor are expressed by a relational expression: The 90 degree hybrid according to claim 1, characterized in that: 3. The terminal comprises four terminals, each of the four terminals being grounded by a grounding capacitor, the first terminal and the second terminal being connected by a coupling capacitor, and the third terminal and the fourth terminal being another coupling. Connected by a capacitor, the first terminal and the third terminal are connected by an inductor, the second terminal and the fourth terminal are connected by another inductor, and the capacitances of the ground capacitors connected to the respective terminals are substantially equal to each other. 1 The capacitance of the second inter-terminal coupling capacitor is the third
The coupling capacitance between the fourth terminals is substantially equal to the inductance of the first and third coupling terminals between the terminals.
The capacitance of the ground capacitor is approximately equal to (√2-1) times the capacitance of the coupling capacitor, the first terminal and the second terminal are the input / output terminals, and the third terminal is the third terminal. A variable phase shifter characterized in that the ground capacitors of the terminal and the fourth terminal are realized by variable capacitance elements having substantially the same capacitance. 4. When the signal angular frequency is ω and the signal source and load impedance are Z ₀ , the coupling capacitance C _{2 of} the coupling capacitor and the coupling inductance L of the inductor are expressed by a relational expression: The variable phase shifter according to claim 3, wherein