JP2637974B2 - Microwave band variable attenuator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave variable attenuator using a diode, and more particularly to a balanced variable attenuator capable of obtaining a wideband characteristic even at a high frequency and having a small size.

[Conventional technology]

Conventionally, a microwave band variable attenuator using a pin diode has been proposed, an example of which is shown in FIGS. 4 (a) and 4 (b). FIG. 4 (a) is a plan view and FIG. 4 (b)
Is a side sectional view. In these figures, reference numeral 11 denotes a strip line, which is formed on a dielectric substrate 15, and to which a pin diode 12 is connected in parallel. Also, 13
Is a through-hole bonding for grounding, and 14 is a bias line for applying a bias voltage to the pin diode 12. In addition, the above-mentioned through-hole bonding 13
May be configured by side bonding.

In this variable attenuator, since the resistance value of the pin diode 12 changes due to the flowing current, the pin diode 12 operates as a variable attenuator by controlling the voltage from the bias line 14 to control the resistance value of the pin diode.

As another example, as shown in FIG.
A balanced variable attenuator using a B branch line coupler has also been proposed. That is, pin diodes 22 and 23 are connected to the ladder-shaped 3 dB branch line coupler 21, and a bias line 24 is further connected.The voltage applied to the bias line 24 reduces the resistance of the pin diodes 22 and 23. By changing it, the signal from the input port is attenuated and operated as a variable attenuator.

[Problems to be solved by the invention]

Among the conventional variable attenuators described above, in the former configuration, the through-hole bonding 13 structure for grounding is:
In a low frequency band, it may be considered that the ground is completely grounded. Therefore, as shown in the equivalent circuit of FIG.
As a result, the inductive reactance 16 is connected in series to 17, and as a result, the frequency characteristic deteriorates as shown in FIG.
There is a problem that broadband characteristics cannot be obtained.

In the latter variable attenuator, the above-mentioned problems are less likely to occur, but there is a problem that the size of the circuit becomes large because a ladder-type 3 dB branch line coupler is used.

SUMMARY OF THE INVENTION An object of the present invention is to provide a microwave variable attenuator capable of improving frequency characteristics and achieving downsizing of a circuit.

[Means for solving the problem]

A microwave band variable attenuator according to the present invention includes a quarter-wavelength three-wire coplanar balun, an input terminal connected to an unbalanced end of the coplanar balun, and one end connected to the balanced end of the coplanar balun. A pair of strip lines having different line lengths of λ / 2, a pair of diodes connected to each other at the other ends of the strip lines, and one end connected to a connection end of these diodes, A bias line configured to apply a control voltage to each of the diodes, the signal being input to the input terminal is attenuated in accordance with the control voltage, and these are combined to produce the output. The output signal is obtained from the end.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. In FIG. 1 (a), reference numeral 1 denotes an unbalanced-balanced balun using a 線 wavelength three-wire coplanar balun. A coplanar balun is formed by forming a space region 6a indicated by a dotted line in the ground conductor 6 on the back surface so as to show a cross-sectional structure along the line AA. Strip lines 4a and 4b are connected to the balanced end of the coplanar balun 1, and these strip lines are
Here, the line length of the strip line 4b is set to the strip line 4a.
Is set longer than λ / 2.

Furthermore, a pin diode is connected to the strip lines 4a and 4b.
2, 3 are connected to face each other, and a DC bias line 5 is connected between these pin diodes 2, 3.

The operation of such a circuit as a variable attenuator will be described below.

The signal input from the input port is unbalanced-balanced converted by the coplanar balun 1 and divided into two signals having the same amplitude and opposite phases, and then applied to the pin diodes 2 and 3 through the strip lines 4a and 4b, respectively. Is done. At this time, since the strip line 4b is longer than the strip line 4a by λ / 2, the strip diodes 4 and 3 are applied to the pin diodes 2 and 3 with the same amplitude and the same phase. Also, since a bias voltage is applied to the pin diodes 2 and 3 via the bias line 5, the resistance value of the pin diodes changes in proportion to the voltage, the input RF signal is attenuated, and The three outputs are combined and extracted as an output signal. This equivalent circuit is shown in FIG.

Therefore, this variable attenuator operates in balanced mode,
Since the ground current does not flow, the characteristics do not deteriorate in a high frequency band due to through-hole bonding or side bonding for RF grounding, and have a wide band characteristic as shown in FIG. Further, since a coplanar balun is used, the size can be reduced compared to a balanced variable attenuator using a conventional ladder type 3 dB branch line coupler.

〔The invention's effect〕

As described above, according to the present invention, diodes are connected to quarter-wavelength three-wire coplanar baluns via strip lines having different wavelengths of λ / 2, and a control voltage is applied to each of these diodes to change a signal according to the control voltage. Since it is configured to attenuate and combine these to obtain an output signal, it operates in balanced mode, so that ground current does not flow, there is no deterioration in characteristics in the high frequency band, and no ladder type coupler is used Therefore, there is an effect that it can be made compact.

[Brief description of the drawings]

FIG. 1 is a view showing an embodiment of the present invention. FIG. 1 (a) is a plan view, FIG. 1 (b) is a sectional view taken along line AA of FIG. 1 (a), and FIG. 3, FIG. 3 is a diagram showing the frequency characteristic thereof, FIG. 4 is a diagram showing a conventional structure, FIG. 5 (a) is a plan view, FIG. 3 (b) is a side sectional view, and FIG. Is an equivalent circuit diagram of the configuration of FIG. 4, FIG. 6 is a frequency characteristic diagram thereof, and FIG.
The figure is a plan view of another conventional configuration. 1 ... coplanar balun, 2,3 ... pin diode, 4a,
4b: Strip line, 5: DC bias line, 6 ...
... outer conductor, 6a ... space area, 11 ... strip line, 12 ... pin diode, 13 ... through-hole bonding, 14 ... bias line, 15 ... dielectric substrate, 16 ...
... Inductive reactance, 17 ... Resistance, 21 ... Ladder type 3dB
Branch line coupler, 22, 23 ... Pin diode, 24
…… Bias line.

Claims (1)

(57) [Claims] A coplanar balun having a quarter-wavelength, an input terminal connected to an unbalanced end of the coplanar balun, and one end connected to the balanced end of the coplanar balun and having a line length of λ. A pair of different strip lines, a pair of diodes connected to each other at the other end of these strip lines, one end is connected to the connection end of these diodes, and the other end is configured as an output end And a bias line for applying a control voltage to each of the diodes, attenuating a signal input to the input terminal according to the control voltage, and combining them to obtain an output signal from the output terminal. A microwave variable attenuator characterized by having such a configuration.