JPH01236701A - Amplitude equalizer for very high frequency band - Google Patents

Abstract

PURPOSE:To obtain an amplitude equalizer which has the variable extent of equalization and can be used in several GHz by connecting parallel resonators with a transmission line having a length lambdaC/2 to constitute a pi type circuit. CONSTITUTION:A transmission line 11 of lambda/4, a resistance 13, a variable capacity element 15, a transmission line 12 of lambda/4, a resistance 14, and a variable capacity element 16 constitute parallel resonators. The other ends of elements 15 and 16 of this pair of parallel resonators are connected to an earth line 18, and the other ends of resistances 13 and 14 are connected to one end and the other of a transmission line 17 of lambda/2, and these connection points are used as input and output terminals to constitute the PI type circuit. The wavelength lambdais the wavelength lambdaC of the center frequency in the frequency band where the variable amplitude equalizer for very high frequency is applied. By this constitution, the operation in the several GHz band is possible and the capacity value is changed to obtain a right falling or left falling characteristic.

Description

[Detailed Description of the Invention] [Summary of the Invention] This invention relates to an ultra-high frequency band amplitude equalizer that is used in microwave communication equipment and corrects the frequency characteristics of the amplitude, and which can be used in several GHz bands and whose equalization amount is variable. The purpose is to provide an equalizer, and the wavelength of the center frequency of the applicable frequency band is λc, and λ
It is equipped with a pair of parallel resonators made by connecting in series a transmission line slightly longer than c/4, a resistor that makes out-of-band impedance resistive, and a variable capacitance element, and these parallel resonators are The configuration is such that a π-type circuit is formed by connecting with a transmission line of λc/2.

[Industrial application field]

The present invention relates to an ultra-high frequency band amplitude equalizer used in a microwave communication device to correct amplitude frequency characteristics.

Individual circuits such as amplifiers and mixers used in the ultra-high frequency section of microwave communication equipment are rarely designed or adjusted to have optimal characteristics for each transmission channel, and usually cover a large number of channels. The band has been expanded to allow for Such a wideband amplifier,
If you use a mixer or the like, you can use one with the same specifications for each channel.

However, even in wideband amplifiers, mixers, etc., the amplitude frequency characteristics are not flat over the entire band, but are curved, especially in the high frequency region. When looking at each channel), there are some that are downward to the right and downward to the left (a positive or negative first-order slope of the in-band amplitude deviation appears).

If strict flatness is required for the amplitude frequency characteristics within the band, an amplitude equalizer is required.The amount of equalization required varies depending on the channel, so a one-arrow width equalizer with variable equalization m is used. desired.

[Conventional technology]

An amplitude equalizer for a low frequency band, for example, an IF band of 70 to 140 MHz, is composed of an LC circuit as shown in FIG. 10(a). In the figure, DI is a varactor diode, and the capacitance value changes by changing the bias (the bias circuit is not shown). This is in series with capacitor C2,
And these are capacitor C+, inductance L
1, and this circuit ultimately constitutes an LC resonant circuit, with minimum impedance at the resonance point, capacitive and inductive impedance values to the left and right of the resonance point, and exhibits curved characteristics. This curved characteristic or its left side, right side down left side,
If you reverse the right-down characteristic to that of an amplifier, etc., you can cancel it out,
A flat amplitude frequency characteristic can be achieved.

The amplitude equalizer to be obtained by the present invention has a frequency range of IGHz to several GHz.
It is for a high frequency range such as a frequency band of Z and a channel width of 20 MHz, and does not pass a lumped constant type as shown in FIG. 10(a).

Amplifiers are connected in multiple stages to obtain a desired gain, but in this case it is necessary to ensure that the characteristic impedances on the output side and the input side are equal to prevent reflection from occurring. However, it is difficult to achieve matching at all frequencies, and therefore mismatching is likely to occur in frequencies other than the used frequency band. Therefore, as shown in Fig. 10(b), an isolator CIR is installed between the stages.
Alternatively, an attenuator ATT is inserted to prevent the reflected wave from the input side of the amplifier A2 from being returned to the output side of the amplifier A1. Note that Fl is a bandpass filter.

When the amplifier is composed of amplification elements such as transistors, spurious oscillations are likely to occur in the low frequency range due to the above reflection, since the transistor has a large amplification ability in the low frequency range. This oscillation can be prevented by inserting an isolator CIR or an attenuator ATT.

An isolator (circulator) CIH has no insertion loss, but an attenuator has an insertion loss, and the greater the insertion loss, the more effective it is in preventing oscillation.

To prevent low-frequency oscillation, it is best to lower the gain outside the band of use and at the same time make the impedance resistive to stabilize the circuit. By making the amplitude equalizer resistive outside the band of use and having a low gain, the amplitude equalizer can also function as the isolator or attenuator.

[Problem to be solved by the invention]

An object of the present invention is to provide an amplitude equalizer that can be used in several GHz bands and has a variable equalization amount.

This amplitude equalizer is also intended to have the ability to prevent low frequency oscillation.

[Failure to solve the problem]

FIG. 1 shows a diagram of the principle of the present invention. 11.12 is a transmission line of S/4, 13.14 is a resistor whose one end is connected to one end of the transmission line 11 and 12, and 15 and 16 are variable capacitance elements whose one end is connected to the other end of the same. i.e. 11 and 13
and 15.12, 14, and 16 constitute a parallel resonator.

The other ends of the variable capacitance elements 15 and 16 of these pair of parallel resonators are connected to the grounding line 18, and the other ends of the same resistance 13 and 14 are connected to one end and the other end of the λ/2 transmission line 17, These connection points become output terminals and constitute a π-shaped circuit.

The wavelength λ is the wavelength λc of the center frequency of the frequency band to which the ultra-high frequency variable amplitude equalizer of FIG. 1 is applied. Although the transmission lines 11 and 12 have a length of λ/4, it is not necessary to have a length of λc/4 strictly. Since the variable capacitance elements 15 and 16 are connected in series, the transmission line 11 and 12 are λ
It is appropriate to make it slightly longer than c/4.

A varactor diode or the like is suitable as the variable capacitance element, and the capacitance value of such a diode can be changed by voltage control.

[Effect]

The amplitude equalizer with the configuration shown in Figure 1 can operate in the several GHz band, and by changing the capacitance value, it is possible to obtain one-inch width frequency characteristics such as downward to the right or downward to the left, and it is possible to obtain frequency characteristics with a width of one arrow such as downward to the right or downward to the left. It has a low gain and has a low-frequency oscillation blocking function. Next, this will be explained in detail.

When trying to realize an equalizer for the microwave band or quasi-millimeter wave band above about IGHz, lumped constant type elements (capacitors, inductors) have problems with the accuracy of element values.
Problems with parasitic capacitance and inductance impair design efficiency, and circuit implementation is also difficult because it requires a combination of minute circuit components. Therefore, it is preferable to use a distributed constant type.

As shown in FIG. 3, when one end of the approximately λ/4 transmission line 25 is grounded with a variable capacitance element 26, a distributed constant resonator with a variable resonance frequency is obtained.

This transmission line 25 is obtained by forming a band-shaped conductor 11R25a on the surface of an insulating substrate 29 whose back surface is coated with a ground metal film 28, as shown in Figure b1.A transmission line 27 connecting between a person and an output end is formed in the same manner.

The characteristic impedance of these transmission lines is determined by the width W of the conductor film, the thickness t of the insulating substrate 29, and the dielectric constant ε, and is usually selected to be 50Ω or the like. In the several GH2 band, the width W is about several 1-. When one end of the transmission line 25a is connected to the transmission line 27 and the other end is connected to the back metal film 28 via the variable capacitance element 26, the result is shown in FIG. 3 (al).

When the other end of the transmission line 25 is directly grounded except for the variable capacitance element 26, the result is shown in FIG. 4(a), which is equivalent to FIG. 4(b). In other words, the transmission line 25 constitutes a parallel resonator, and the resonant frequency fr is fr=1/2πha1-. Since it is a parallel resonator, the impedance is such that the input frequency f is f=f
When r, oo (no insertion loss), when f>fr, C property, f
<fr When r, it is L property.

When the transmission line is terminated with impedance zR, Figure 4 (
It becomes (+). 25b is the transmission line, which has a length l and a characteristic invinidance Zo. This impedance Z is expressed as β=2π/λ, where β is a propagation constant. If impedance zR is a variable capacitance element and its capacitance is C, then the following equation is obtained. The condition for this circuit to resonate is that the denominator = O, so janβi! =-20+JJC. If the left side of the above equation is yl and the right side is y2, then y2
=-ZaωC (C is the speed of light, λf=C). These yl.

When y2 is plotted against frequency r, it becomes as shown in FIG. 6, and the resonance frequency is represented by the intersection of yl and y2. In this example, when the capacitance value C of the variable capacitance element is 5 pl'', approximately 2.
At 2GHz and 1pF, it is about 2.9GHz, and when C is 5
When changed in the range of ~1pF, the resonant frequency is 2.2~2
．． It varies in the range of 9 GHz.

As is clear from FIG. 6, the resonant frequency is higher than that in the case of direct grounding without a capacitor (approximately 1.87 GH2), and the smaller the capacitor, the higher the resonant frequency becomes. In this way, as shown in FIG. 5, by changing the capacitance 1c, the amplitude characteristics of the signal passing through this circuit are given a slope,
You can change that. In FIG. 5, curve A is the amplitude frequency characteristic when the resonant frequency is set to fC, and curve B is the amplitude frequency characteristic when the capacitance is reduced and the resonant frequency is set to fc'. Assuming that the band indicated by the dotted line is the frequency band (channel) to be used by this circuit, curve A is flat,
Curve B has a left-downward characteristic, and amplitude equalization of the right-downward amplifier can be performed. By using the portion to the right of fc of the curve A, a right-downward characteristic can be obtained, and amplitude equalization of the left-downward amplifier can be performed.

In this way, amplitude equalization can be performed by the parallel resonator shown in Fig. 3, but the circuit shown in Fig. 3 exhibits an impedance value of C-character or L-character at frequencies away from the center frequency fc, and Insertion causes impedance mismatch. Therefore, in order to function as a stabilizing circuit, a resistor is connected in series to the opposite side of the transmission line from the ground side, as shown in FIG. Furthermore, using a plurality of such parallel resonators in cascade rather than just one resonator increases the curvature of the composite amplitude frequency characteristic and is more effective in equalizing the amplitude. Therefore, as shown in Figure 1, two sets of parallel resonators (13 and 11) were installed.
, 15, 14, 12, and 16) are used, and these are connected by a transmission line 17 of λ/2 length to form a π-type circuit.

The transmission line 17 is designed to have high characteristic impedance. For example, if it is a 50Ω system, set it to 80Ω to cause impedance mismatch (impedance is inserted). 80Ω can be achieved by narrowing the width of the transmission line (strip line). A transmission line with a length l of λ/2 becomes a series resonator (equivalent to connecting an LC series circuit between output terminals) and exhibits bandpass characteristics. The resonant frequency fr is also fr=1/2π, and the wavelength λr of the resonant frequency is λr=2I! =c/fr. This also strengthens the curvature of the amplitude frequency characteristic shown in FIG.

〔Example〕

FIG. 2 shows an embodiment of the present invention. As throughout the design, like parts are numbered the same.

15.16 is a variable capacitance H composed of a paractor diode
The control voltage Vc and the filter (inductor 2 and capacitor 22) constitute a bias circuit for the diodes 15 and 16. By changing the control voltage VC,
The capacitance value of the varactor diode 15°16 changes. 19.
20 is a capacitor for DC blocking, and the control voltage Vc is
Prohibits input to the front and rear circuits through the output terminal. This circuit is a 50Ω system, and the transmission lines 11, 12, etc. are set as such, but the transmission line 17 is higher than 50Ω, for example, 80Ω. This means that for transmission line 11.12 the width is 'l am, for transmission line 17 the width is 0, 5*s
It can be obtained by

Figure 7 shows the reverse voltage VR (V
) and the capacitance Cv (pF).

As shown in the figure, the larger the reverse voltage vR becomes, the smaller the capacitance Mcv becomes.

When the capacitance Cv is changed by the reverse voltage vR as shown in Fig. 7,
FIG. 8 shows changes in the amplitude characteristics of the amplitude equalizer shown in FIG. 2. The resonance frequency when VR=11.7V is f'c
= 2.5 GHz, when VR = 15V, fc rises and has a downward left-hand characteristic, and when vR-9■, fc
c decreases, resulting in a downward-sloping characteristic.

Figure 9 shows the amplitude slope in dB by changing the reverse voltage ■R.
/100MHz change is shown. When VR=11.7V, the slope is 0. When VR becomes larger than that, the slope becomes positive (upward to the right), and when VR becomes smaller, the slope becomes negative (downward to the left).

The transmission line 17 with a length of λ/2 is fixed, but the parallel resonator 1
In principle, it is preferable to change the resonant frequency, for example, change the length, in accordance with changing the resonant frequencies of 3, 11, 15, 14, 12, and 16.

When the fixed transmission line 17 is used, the resonant frequency of the line 17 is set between the maximum and minimum values of the resonant frequencies of the parallel resonators.

(Effects of the Invention) As explained above, the amplitude equalizer of the present invention, which has a function of compensating for the first order one-term slope of the amplitude, can control the amplitude of broadband amplifiers and mixers with gentle wave characteristics by controlling the voltage. The deviation can be equalized over the channel band.

In addition, this amplitude equalizer has a bandpass characteristic that makes the impedance resistive outside the band and increases the amount of attenuation as the tune is detuned, so it can be used between multiple stages of circuits. This one-width equalizer has the advantage of operating as a stabilizing circuit.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing the principle of the present invention, Fig. 2 is a circuit diagram showing an embodiment of the invention, Fig. 3 is an explanatory diagram of a parallel resonator, Fig. 4 is an explanatory diagram of the principle of Fig. 3, Figure 5 is an explanatory diagram of changes in amplitude frequency characteristics, Figure 6 is an impedance characteristic diagram of a parallel resonator, Figure 7 is a voltage capacity characteristic diagram of a barrack diode, and Figure 8 is an amplitude characteristic diagram of an amplitude equalizer. , FIG. 9 is a primary slope versus control voltage characteristic diagram, and FIG. 10 is an explanatory diagram of a conventional example. In Figure 1, 11.12 is a λ3/4 transmission line, 13°14 is a resistor, 15.16 is a variable capacitance element, and 17 is a λc/2
The transmission line 18 is a ground conductor.

Claims (1)

[Claims] 1. Assuming that the wavelength of the center frequency of the applicable frequency band is λc, a transmission line (11, 12) slightly longer than λc/4 and a resistor (13, 14) that makes the impedance outside the band resistive are used.
) and a variable capacitance element (15, 16) are connected in series. An amplitude equalizer for an ultra-high frequency band, characterized in that it is connected by two transmission lines (17) to form a π-type circuit.