JPS606121B2 - directional coupler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention generally relates to a directional coupler, and more particularly, the present invention relates to a directional coupler, and more particularly, to a 4-boat, 2-branch directional coupler that is more compact by providing a capacitive matching network in each boat of the directional coupler. Regarding the technology that constitutes the.

FIG. 1 shows a prior art coupling network constructed in a stripline, filed under application number 7664 by the applicant.
No. 31 is the same as that shown in US Application No. 31.

In a typical coupler, the physical line length 1 is inversely proportional to the operating frequency of the device. At high microwave frequencies, the line lengths are relatively short and the equipment is very small, so this poses no problem. However, at low microwave frequencies, the line length becomes long and the entire device becomes much larger than the device used at higher frequencies. Therefore, it is an object of the present invention to solve the problem of coupling using the secondary technique. The object of the present invention is to provide a directional coupler having a distributed constant circuit element that can be configured in a 4-type configuration than a conventional device, and in particular, to provide a compact directional coupler that operates at low microwave frequencies, that is, UHF frequency bands. That's true.

Another object of the invention is to provide a compact branch coupler which can be well integrated into striplines and which can be manufactured very easily and compactly.

In order to achieve the above objects and other objects of the present invention, 2.
Branch line directionality having pairs of two-boat networks, with the boats of each two-boat network connected to one of the respective boats of the other pair of two-boat networks, forming a basic four-boat combiner. A coupler is provided.

One port of the combiner is called the signal input port and the other two ports of the combiner are called the signal output ports. In fact, any port of the combiner can be used as an input port. In a preferred arrangement, each network takes the form of a portion of a transmission line, and the entire device is in a stripline configuration. According to the present invention, ``at a given operating frequency, the physical line length of the network is shorter than the physical line length used in known devices, resulting in a compact device. This introduces an inductive mismatch, which is compensated by a capacitive matching network connected to each port of the coupler.The equivalent admittance of the coupler is divided into a real part (conductance) and an imaginary part (susceptance). In addition, in known design techniques, the electrical length of the branch line is set to 8' or 9', and the device is perfectly matched.However, according to the design method of the present invention, at a given operating frequency, The physical line length can be shortened by selecting a small value for the length a.It is desirable to select the length a as 45o, for example.However, if selected in this way,
There is an inductive mismatch in the equivalent admittance, but this mismatch is compensated for by providing a capacitive matching network at each boat or relay section of the coupler, so that the overall susceptance is the same and the device is therefore at a:45o. be consistent. Conveniently, the capacitive matching network is placed in a central opening formed between the four strip transmission line sections that define the coupler. Another embodiment is to make the device larger so that the tolerance can be increased, a'
An inductive matching network is required, selected to be larger than 900, and coupled to each boat of the coupler. In a preferred configuration, the pair of two-boat networks form part of a transmission line, the transmission line extends in a circular shape, and the capacitive matching networks each form a substantial quadrant coupled to a boat of the coupler. and is disposed inside an area defined by a circular locus.

Other objects, features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings. FIG. 1 shows a typical conventional example of a branch line directional coupler.
It has four 2-boat networks interconnected to form 3 and 4.

In this example, the input strip I connected to the boat
An input signal is applied to A, and an output signal is applied to port 2 of the combiner.
output strips 2A and 3 respectively coupled to
It is supposed to be given by A. Boats 1, 4 and boats 2, 3 are connected by a two-boat network forming a transmission line N, while boats 1, 2 and boats 3, 4 are connected by a separate two-boat network (line) N' connected by. To design the general network of FIG. 1, the line lengths 1 of each network are typically of equal length and are inversely related to the operating frequency of the device.

The following equation shows the relationship between physical line length and operating frequency. Sagao...・'1' Here, 8=electrical length, 1=physical line length, ^=wavelength at operating frequency.

Normally, the electrical length is 9 at the frequency when the two branch cases are perfectly matched.

As is clear from Equation 01, in the design technique of the third standard, at lower microwave frequencies, that is, as the operating wavelength increases, the physical line length also increases. However, increasing the length of the line in this way requires relatively large equipment. For example, the relatively low frequency U
At 10Hz in the HF band, a coating as large as 645 (10 square inches) is required. US Patent No. 4127
No. 831 shows that a branch line directional coupler having two branches has the following relationship.

This is a well known theory for matched branch line directional couplers with two branches. lkil2=Y2-1 skin■ Here, S,2 is the amplitude of the signal transmitted from boat 1 to boat 2, S,3 is the amplitude of the signal transmitted from boat 1 to boat 3, and Y is the transmission line part. is the admittance level ratio between N and N'.

In the right angle hybrid embodiment of the invention shown in FIGS. 2 and 3, the admittance level ratio is zero. No. 412,783 by the inventor of the present invention
No. 1 describes that the equivalent admittance Yeq of an L4-boat two-branch coupler generally has the following relationship.

Yeq=Zodekocho Y, 20j (10Y)Y, . Here Y
、． and Y,2 are each the elements of the admittance matrix of the two-vote branch network N as shown in FIG. 1, and Y is the admittance' level ratio.

For a transmission line with a characteristic admittance Yo and an electrical length of 8 as shown in FIG. 1, the admittance matrix elements Y, . and Y,2 is Y, . =1 Yocot8, Y,
2=Yo/sin8. Therefore, the equivalent admittance Yeq is given by the following equation. Yeq = Sesame Sparrow 21
-i(10Y)Y.

■t8...'31 In a right-angle hybrid where Y is equal to 2, the formula {3'' is as follows. Yo Yeq=S Maeichi-j (10 no Pig) Yocot8...[4
'In a typical design, the electrical length is 8 scales/2 and the branch line admittance value is chosen to be 1 and perfectly matched.

As a result, line 1 is determined from equation {11' and has a fixed value once the operating frequency is selected. Equivalent admittances have only real parts equal to one. However, with the present invention, by providing each boat of the device with an appropriate matching network, it is possible to configure the device to operate with shorter electrical length branch lines, making the device very small. I can do it. This is particularly important in the UHF frequency band and at the lowest frequencies of the microwave spectrum, where typical devices are of very large size. In one example of the present invention, the electrical length 8 of the branch line is selected to be 450 degrees instead of the commonly selected 90 degrees.

This means that at the same operating frequency, the line length is halved and, as is clear from equation {1st), the junction (relay) area is reduced to 1/4. Looking at the equation {side, the real part of the equivalent admittance is equal to 2Yo. If the conductance is 1, the branch line admittance is Yo=1/2. Since 8 was chosen to be less than 90o, the imaginary term in equation (2) becomes the inductive susceptance -i(10<2>)/<2>.

This inductive mismatch can be easily compensated for by using capacitive networks at each junction of the device to bring the sum of the susceptances to zero, so that the device matches when 8=busy/4. 2 and 3 illustrate a preferred embodiment of a stripline structure according to the invention. The device has a multilayer structure, each layer being interconnected in a suitable manner.
The stripline device is primarily constructed on a printed circuit board 10 that is laminate to a conductor 12, the configuration of which is best shown in FIG. , 16 and an insulating sheet 18.A standard connector for grounding a suitable boat of a stripline device is shown in FIG.
and the two output boats are boats 22 and 23.
Boat 24 has a common termination that is coupled to connector 20. Preferably, the transmission line sections N and N' of the stripline shown in FIGS. 2 and 3 extend along a circular section.

In a quadrature hybrid coupler, the ratio of the admittances of networks N and N' is 2/2:10. This difference in admittance is shown in the figure by drawing the transmission line N narrower than the transmission line portion N'. For proper alignment, the present invention uses a capacitive plate 3.
1, 32, 33, and 34 are boats 21, 22, and 2, respectively.
3 and 24.

These capacitive flat plates are arranged in advance in a central spatial region 38 defined between transmission line sections N and N'. capacitive part 3
1-34 are insulated from each other and their adjacent regions as shown in FIG.

Furthermore, a central gateway portion 38 is provided passing through the substrate 10. The diameter of the closure 38 is controlled to allow adjustment of the surface area of the capacitive portion, thereby allowing tuning to the desired operating frequency. The capacitance of each of the capacitive plates shown in FIG. 2 is selected to balance the inductive mismatch, so that the susceptance of each portion of the stripline device is substantially zero. The capacitance and operating frequency are direct functions of the equivalent admittance as shown in equation {4), and the following relationship holds: C's = (10 no Pig) Yocot8...
{51 where C=capacitance of each capacitive part “Y
o=Admittance of branch line of transmission line section N, 0=4
It is 50.

In Equation '5}, since the values of variable 0 and Yo are known, the value of C when the predetermined operating frequency is exceeded can be calculated.

If you know the capacitance, the yield ratio of the substrate material, and the distance between the ground plate and the capacitive part, then the capacitive plate 3
Each region from 1 to 34 can be calculated. As mentioned above, substrate 1
The area of the capacitive plate can be further adjusted by controlling the dimensions of the closure 38 in the capacitive plate. In the embodiment of the present invention configured as shown in FIGS. 2 and 3, the center frequency at which the tosodo operates is approximately 50 Hz.

At this operating frequency, the magnitude in both directions is 635 skin (
2 inches). Prior art devices of this size operate only at frequencies of about 100 mM without the use of matching circuits. Although one embodiment of the present invention has been described above, it will be apparent to those skilled in the art that various other embodiments can be constructed.

For example, the capacitive plate shown in FIG. 2 can be replaced with a lumped capacitor while reducing dimensions. Furthermore, the device according to the invention can be of various shapes; for example, the device can be rectangular and the capacitive plate can also be rectangular. The reduction method described above does not have a significant effect on the relay swath width and can maintain approximately 10% of the reflection loss of 2B.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing a two-branch, four-boat branch line coupler based on the follow-up technology, and FIG. 2 is a front view showing a two-branch, four-boat directional coupler constructed according to the principles of the present invention.
FIG. 3 is a perspective view, partially in section, of the entire apparatus constructed according to the principles of the present invention. [Code explanation] “1, 2, 3, turtle...boat, 2A?
3A... Output strip "N, N... Transmission line, 12...
...Conductor 10...Printed circuit board, 14, 16...
・Ground plane, 18... Insulating thin plate, 21... Input boat, 22, 23... Output boat, 24... Boat, 20
... Connector, 36 ... Central space area, 31, 32, 3
3, 34...Capacitive part, 38...Central opening □ part. ('Ta' (Evening.2 line/Evening.3

Claims (1)

[Claims] 1. A directional coupler having four sections of signal transmission line interconnected to form four ports of the directional coupler, with a reactive matching element connected to each port of the directional coupler. , wherein the portion of the signal transmission line defines an open area inside thereof, and the reactive matching element is disposed within the open area, thereby reducing the overall area of the directional coupler. directional coupler.