JPS6041489B2 - Variable AM-PM converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a compensation variable AM-PM converter for reducing deterioration of transmission characteristics due to amplitude modulation-phase modulation (AM-PM) conversion phenomenon occurring in a microwave repeater.

A microwave repeater basically consists of a receiver and a transmitter, but if the input signal to the repeater or the signal inside the repeater contains an amplitude modulation (AM) component, In the transmitter, this AM component is phase modulated (P
In microwave communication that uses frequency modulation (FM), which causes FM (hereinafter referred to as AM-PM conversion), the above-mentioned PM component generated in the middle of the line becomes noise and changes the characteristics of the communication line. deteriorate.

For this reason, in the past, an amplitude limiter was installed in the repeater and the AM
In an effort to prevent the occurrence of PM, they suppressed the amount of PM generated. However, such a system has the disadvantage that it cannot deal with PM once generated in the middle of the line, and that the amplitude limiter itself causes some AM-PM conversion. The purpose of the present invention is not to provide a system that prevents the generation of PM in a relay device as much as possible, as in the case of using the above-mentioned amplitude limiter, but to convert the PM signal once generated by AM-PM conversion into an opposite-phase PM signal by the same amount. To provide a variable AM-PM converter that compensates for PM components generated in a relay device, etc. by performing PM in advance by the same amount in an opposite phase to a device that causes harmful NM-PM conversion. be.

According to the present invention, there is provided a hybrid transformer having an input terminal and an output terminal, a phase shift circuit having a phase shift amount 1 whose one end is connected to the hybrid transformer, and the phase shift amount ? a circuit connected to the other end of the phase shift circuit of No. 1 and capable of short-circuiting or opening the termination condition at this end; a phase shift circuit having one end connected to the hybrid transformer and having a phase shift amount different from the CI by 450; A variable AM-PM converter is obtained, which includes an impedance element whose impedance changes non-linearly with respect to the input signal power, which is connected to one end of the phase shift circuit and has an amount different from ◇1 to 45o.
According to the variable AM-PM converter of this invention, AM-
Since the positive/negative and absolute value of the PM conversion coefficient can be freely changed, AM generated in microwave communication lines can be
-PM conversion can be compensated arbitrarily, and the disadvantage of the method of suppressing the occurrence of AM-PM conversion using the amplitude limiter described above can be completely overcome. Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing the principle of the invention.

The signal applied to the signal input terminal 1 is divided into two by the hybrid transformer 3, one of which passes through a phase shift circuit 4 with a phase shift amount of 01, and a switch (which can shorten or open the termination condition of this phase shift circuit 4). or equivalent circuit) 7. Since the switch 7 short-circuits or opens the termination condition, the signal is totally reflected and returns to the hybrid transformer 3 through the phase shift circuit 4 having the phase shift amount JI. The other of the signals applied to the signal input terminal 1, which is divided into two by the hybrid transformer 3, passes through a phase shift circuit 5 with a phase shift amount ◇2, and then passes through a nonlinear circuit whose impedance changes nonlinearly with respect to the input signal. It reaches the linear impedance element 7 and is reflected, passes through the phase shift circuit 5 with a phase shift amount ◇2 again, and returns to the hybrid transformer 3. The two signals reflected by the hybrid transformer 3 are each split into two again by the hybrid transformer 3, appear at terminals 1 and 2, and are combined. The reflected wave reaching the signal input terminal 1 is absorbed by the signal source impedance element, and the reflected wave reaching the signal output terminal 2 is used as an output. Referring to Fig. 2, for the sake of simplicity, this shows the relationship between each reflected wave component appearing at the signal output terminal 2 in the form of a vector in the case where the nonlinear impedance element is a resistance element. .

In Figure 2, the voltage of the reflected wave at the switch 6 that appears at the signal output terminal 2 when the switch 6 in Figure 1 is open is V6, and the voltage when the switch 6 is short-circuited is V8'. The voltage of the reflected wave appearing at the nonlinear impedance element 7 is assumed to be V7.

At the signal output terminal 2, V6 and V7 or V6' and V7 are combined to become V2 or V7. Further, in FIG. 2, "small" indicates the phase difference between V7 and V2, and "gu'" indicates the phase difference between V7 and V2'. The reflection coefficient at switch 6 is 11 or -1
Therefore, V6 or V6'' is proportional to the input. Since the impedance of the non-linear impedance element 7 changes depending on the level of the incident signal, let the impedance be ZR, and let the characteristic impedance of the branch of the hybrid transformer 3 be Zo, the reflection coefficient yR is the voltage ratio of the incident wave and the reflected wave. As is well known, yR; wheat fever
Represented by '1'.

Since ZR changes depending on the input signal level, yR also changes. That is, V7 also changes non-linearly with respect to the input.
here,.

:-? '=Nen・Waka=C' is ``yR ■'', so if R changes depending on the input signal level, the above ?' changes, causing so-called AM-PM conversion.Therefore, the If the coefficient of change in impedance of the linear impedance element can be changed, it is possible to change the coefficient of phase change with respect to the input signal level, that is, the AM-PM conversion coefficient.

The fact that straddle=-◇' indicates that the sign of the AM-PM conversion coefficient can be easily changed by opening or shorting the switch 6 in FIG. As can be seen from equations {1) and '2}, the method of controlling the sign of other conversion coefficients is to use the nonlinearity in the area where ZR>Zo, R>0, and ZR<Z. When using the nonlinearity in the region, the method uses the fact that yR<0.
In this case, AM-
It is possible to control whether the PM conversion coefficient is positive or negative. Third
Referring to the figures, the parts of this figure correspond to those in Figure 1 using reference numerals: 11 is 1, 12 is 2, 13 is 3, and 14 is 4.
, 15 corresponds to 5, 16 corresponds to 6, L 17 corresponds to 7, respectively.

Further, reference numeral 19 is a DC bias voltage input terminal.
Reference numeral 13 is a hybrid transformer composed of a broadband transformer, 14 is a phase shift circuit using a coaxial cable, and 15 is an all-frequency pass type phase shift circuit.The difference in the amount of phase shift between the phase shift circuits 14 and 15 is: The constant is set to be approximately 45 degrees at the frequency used (7 MHz in this example). Reference number 16 is a switch, reference number 17 is a nonlinear impedance using a diode, and X,
, X2 are diodes, R, , R2 are resistors, L, , L2 are high frequency blocking coils, and C, , C2, C3 are high frequency bypass capacitors. When a negative voltage is applied to the DC bias voltage input terminal 19, the resistors R,
, R2, and as the bias voltage increases, the impedance of the diode decreases.

That is, by changing the bias voltage, the above
The reflection coefficient yR defined by equation 1' can be controlled. Therefore, by controlling the bias voltage of the DC bias voltage input terminal 19, the AM-PM conversion coefficient can be easily controlled. Referring to Figure 4, this is the third
3 shows a characteristic curve of bias voltage versus AM-PM conversion coefficient measured at 70 MHZ in the circuit of the example shown in the figure. A characteristic curve 41 shows the characteristics when the switch 16 is short-circuited, and a characteristic curve 42 shows the characteristics when the switch 16 is opened.As is clear from FIG. 4, the AM-PM conversion coefficient can be changed by changing the bias voltage. This shows that the polarity can be reversed by opening or shorting the switch 16. As is clear from the above description, according to the present invention, it is possible to obtain a variable AM-PM converter that can be easily controlled using AM-PM conversion coefficients, and to reduce the AM-P
It can be applied as a compensator for characteristic deterioration of microwave communication lines due to M conversion phenomenon.

[Brief explanation of drawings]

Fig. 1 is a block diagram for explaining the principle of the present invention, Fig. 2 is a vector diagram for explaining the principle of the present invention, and Fig. 3 is a block diagram for explaining the principle of the present invention.
The figure is a circuit diagram of an embodiment of the present invention, and FIG. 4 is a diagram showing the characteristics actually measured with the circuit of FIG. 3. Evening 1, Evening 2, O and 3

Claims (1)

[Claims] 1. A hybrid transformer 3 having an input terminal 1 (FIG. 1, the same applies hereinafter) and an output terminal 2, a phase shift circuit 4 with a phase shift amount φ1 whose one end is connected to the hybrid transformer 3, and a phase shift circuit 4 with a phase shift amount φ1 connected to the hybrid transformer 3 at one end. A circuit 6 connected to the other end of the phase shift circuit 4 and capable of short-circuiting or opening the termination condition at the other end, and a phase shift circuit 5 having one end connected to the hybrid transformer 3 and having a phase shift amount that is approximately 45° different from the φ1. and an impedance element whose impedance changes non-linearly with respect to input signal power, which is connected to the other end of the phase shift circuit in which the phase shift amount differs from the φ1 by approximately 45 degrees.