JPS6118367B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a broadband solid-state sweep signal generator in the microwave band and millimeter wave band using impact diodes.

Impact diodes make effective use of the avalanche effect and transit time effect to oscillate in the microwave and millimeter wave bands.For example, they have a stepped P ⁺ NN ⁺ structure as shown in Figure 1. is doing. An example of a rectangular waveguide oscillator using this impact diode is shown in FIG. FIG. 2 is a cross-sectional view, where A is a diode, B is a gold lead, C is a quartz post, and D is a diode heat sink. E is a metal post for supplying DC bias, and constitutes a millimeter wave circuit. Furthermore, F is a rectangular waveguide whose height is lowered to lower the characteristic impedance to match the negative resistance of the diode, and G is the height of the standard waveguide with the height of F being lowered. This is a tapered waveguide for matching the waveguide. Behind the diode is an H variable shorting plate. A bias current is supplied to impact diode A through E and B, and negative resistance is generated depending on the travel time of electrons traveling through the depletion layer of the diode, causing oscillation.

Figure 3 shows an example of oscillation characteristics when a diode with a drop voltage of 11.2 V is applied to an oscillator using an R-500 (IEC standard) waveguide as a rectangular waveguide. a is the characteristic of the oscillation frequency with respect to the bias current, and by varying the bias current, jumps in the oscillation frequency occur at various locations. b is the oscillation characteristic when the bias current is fixed and the variable short circuit plate behind the diode is varied. 42GHz ~ by changing the distance between the diode and the variable shorting plate
It can be seen that the oscillation frequency changes continuously over 49.5GHz (in the figure, the distance between the diode and the shorting plate is 0.4λg, normalized by the tube wavelength [λg)]. That is, this oscillation characteristic is a mechanically tuned oscillation characteristic in which the oscillation frequency is swept by moving the variable short circuit plate. Recently, a current-controlled impact sweep signal generator has been proposed as a simpler method of sweeping the oscillation frequency using such an impact diode by changing the bias current of the diode.

However, the current controlled impact sweep signal generator having the above-described configuration has the following problems.

(1) In other words, a jump occurs in the oscillation frequency and the sweep frequency range is narrow.

(2) Also, parasitic oscillations other than the main oscillation waves are likely to occur.

(3) Oscillation often stops.

For example, in a conventional current-controlled impact sweep signal generator, when the bias current is gradually increased, the oscillation frequency jumps from point P to point P' as shown in FIG. Another drawback was that the oscillation stopped as shown at point Q in FIG.

The present invention provides a new relationship between the breakdown voltage of the diode and the oscillation frequency, and The present invention aims to provide a current-controlled impact sweep signal generator that can vary the oscillation frequency over a wide range with a single diode by applying new usage conditions to the transmission line into which the oscillation element is inserted. This will be explained in detail below using the drawings.

First, in order to investigate the cause of the above-mentioned problem, detailed experiments and studies were conducted, and the following new matters were discovered.

(A) Oscillation frequency band and diode breakdown voltage V _B
(There is a reverse current in the diode at room temperature below 25℃.
There is a range of appropriate voltage relationships (when only 1mA flows) that differs from conventional impact oscillators.

(B) The attenuation of the higher-order configuration of the transmission line into which the oscillation element is inserted and the dispersion characteristics of the basic configuration (a phenomenon in which the ratio of the channel wavelength to the free space wavelength becomes 1 or more) are the same as those described in (1), (2), There is a deep correlation with the phenomenon (3).

That is, as described above, an impact diode generates negative resistance depending on the travel time of the carrier traveling through the depletion layer, and exhibits this negative resistance over a relatively wide frequency range. However, since the magnitude of the negative resistance and the magnitude of the imaginary term of the diode impedance change depending on the frequency to be oscillated, various oscillation states occur, and the oscillation frequency suitable for current-controlled oscillators varies. There is a relationship between and diode constant. The size of the depletion layer formed in the diode is determined by the breakdown voltage of the impact diode, so find a suitable one for a current-tuned oscillator between the breakdown voltage of the diode and the frequency to be oscillated. be. Also, if a higher-order state occurs in the transmission line where the diode is inserted,
The impedance on the transmission line side as seen from the diode varies depending on the amount of generation. When a higher-order state occurs rapidly, the impedance on the transmission line side changes rapidly, and the impact diode shifts to a point where the oscillation conditions are more stable. (for example, the above-mentioned mechanically tuned oscillation mode). Similarly, when the ratio of the tube wavelength in the transmission line to the free-air tube wavelength increases, the impedance on the transmission line side changes rapidly, making it impossible to maintain the current-tuned oscillation mode.

As a result of conducting more extensive experiments, the following facts were revealed.

Condition (A) The attenuation of higher-order structures is 23 dB or more per free space wavelength at the upper limit of the applicable frequency. In addition, the ratio of the fundamental wavelength to the free space wavelength in the tube at the lower limit frequency of the applicable frequency must be 10 or less.

Condition (B) Center frequency of the applied frequency ₀ (GHz) and the above V
_B There is a relationship between (V) and Equation (1) below.

2.73≦log ₁₀ f ₀ +0.865log ₁₀ V _B ≦2.85 …(1) Therefore, if the above two conditions are satisfied, the above (1),
Phenomena (2) and (3) can be suppressed.

Figure 6 shows an example of an experiment conducted to find condition (A). The hatched area in the figure is the range of condition (A), and the circles and circles are measured (experimental) data. When the attenuation of the higher-order state becomes 23 dB or less per free space wavelength, the impedance of the transmission line as seen from the diode changes rapidly, and the oscillation state jumps to another oscillation state at the point marked with an ○ in the figure. In addition, the symbol ● is a plot of the oscillation opening point of the current-controlled type, and the oscillation of the current-controlled type starts at the point where the ratio of the tube wavelength to the free space wavelength is 10 or less. In this way, the types of waveguides in the range of 20GHz to 90GHz are R-220, R-320, R-
Condition (A) was determined from the results of using various waveguides of 500, R-620, and R-740. Also, the fourth
Figure 5 does not satisfy this condition (A), so P
It can be seen that the oscillation frequency jumps and the oscillation stops at the point and Q point.

Figure 7 is an example of an experiment conducted to find condition (B). The hatched area in the figure is the range of condition (B). Stable current-controlled oscillation is obtained within the hatch region at breakdown voltages of 9.8V to 38V. Also,
An example of the characteristics of the part that protrudes upward from the hatch area is the amount of bias current supplied to the diode, which is close to thermal breakdown of the diode, and an example of the characteristics of the part that protrudes downward from the hatch area indicates that the amount of bias current supplied to the diode is large. Condition (B) is a range in which the oscillation output is small and sufficient oscillation output cannot be obtained as a sweep oscillator, and the range of condition (B) is optimal for obtaining a current-controlled sweep oscillator. Note that since this condition (B) was determined from experimental results, each constant term in the above equation (1) is not a strict value, and a slight deviation is allowed if measurement errors are taken into consideration.

FIG. 8 shows an example of characteristics when the present invention is applied to an R-620 rectangular waveguide, and stable oscillation was obtained over a wide range of 51 GHz to 75 GHz with respect to changes in diode bias current. Figure 9 shows R-
This shows an example of the characteristics when the present invention is applied to a 500 rectangular waveguide.
Stable oscillation was obtained over a wide range of 36GHz to 55GHz. Therefore, the sweep bands shown in FIGS. 8 and 9 are dramatically improved compared to the sweep bands of the conventional current-controlled impact sweep signal generators shown in FIGS. 4 and 5. Recognize.

In addition, in the solid-state sweep signal generator according to the present invention, by providing a variable shorting plate in the oscillator and setting its loss and position to appropriate values, the frequency characteristics of the output can be flattened, and the output can be flattened. There is no need to provide any other circuit for this purpose. Furthermore, in such a current-controlled oscillator, even if the variable shorting plate behind the diode is moved, the oscillation frequency is hardly affected.

The flattening of the output by the variable shorting plate will be explained below.

FIG. 10 is an equivalent circuit viewed from the diode to the transmission line side. R _L is the load, R _S is the equivalent loss resistance of the variable shorting plate (the contact resistance of the shorting plate, the equivalent series resistance caused by electromagnetic wave leakage from the air gap, etc.),
is the distance of the variable shorting plate.

Now, if power p is applied from the oscillator cavity side to the load side and a voltage V is generated across R _L , then the power P _L consumed by R _L is expressed as follows.

P _L =V ₂ /R _L Also, the impedance Z _S when looking to the right from Q-Q' in Fig. 10 is Z _S =Z _O R _S +jZ _O tanβ ₁ /Z _O +jR _S t
anβ ₁ Z _O : Characteristic impedance of the waveguide β : Phase constant, the real part of Z _S is R _e {Z _S }, the imaginary part is I _n {Z
_S }, the power P _S consumed by the variable shorting plate is P _S = _Re {Z _S }・V ² /{ _Re {Z _S }} ² +{
I _n {Z _S }} ² . On the other hand, the power ratio A consumed by the load _{R L} with respect to the power P output from the _oscillator cavity, which is the sum of P _L and P _S , is expressed as follows.

A=10log ₁₀ P _L /P=10log ₁₀ {R _e {Z _S }} ² + {I _n {Z _S }} ² /R _e {Z _S }・R _L + {R _e {Z _S }
} ² + {I _n {Z _S }} ² (dB) In Figure 11, the load is set as the distance of the variable shorting plate as a parameter, and the loss (R _S ) of the variable shorting plate is expressed as V・S・
The above formula was calculated when W・R・=6, and if the distance is selected appropriately, the power consumed by the load (R _L ) can be reduced as the frequency increases. It shows. In a bias current tuned impact oscillator, the frequency is varied by changing the input power of the diode, so as the oscillation frequency becomes higher, that is, as the input power of the diode increases, the oscillation output increases. This increase in oscillation output is calculated by appropriately adjusting the position and loss of the variable shorting plate to generate the loss R _S of the shorting plate.
If the power is consumed by the load R L , the power consumed by the load R _L can be kept constant.

Figure 12 shows an example of the characteristics when the variable shorting plate described above is applied to an R-620 rectangular waveguide, and the output fluctuation in the 10 GHz band is ±1 dB.
It is as below. There has been no known current-controlled impact sweep signal generator that satisfies these two conditions.

As explained above, the present invention eliminates the conventional drawbacks by configuring a sweep signal generator under the above two conditions, and also makes it possible to obtain a sweep signal generator with a wide sweep frequency width and good performance. Applications include not only sweep signal generators but also wide applications as oscillation sources for microwave and millimeter wave measuring instruments such as loss measuring instruments and standing wave measuring instruments.

[Brief explanation of the drawing]

Fig. 1 shows an example of an impact diode, Fig. 2 shows an example of the structure of a waveguide type impact oscillator, Fig. 3 shows an example of mechanically tuned oscillation characteristics, Figs. FIG. 5 is a diagram showing an example of the characteristics of a conventional current-controlled impact sweep signal generator; FIGS. 6 and 7 are diagrams showing an example of the operating range of the present invention and experimental data obtained therefrom; FIG. FIG. 9 is a diagram showing an example of the characteristics of the current-controlled impact sweep signal generator according to the present invention, FIG. 10 is a diagram showing an equivalent circuit on the transmission line side of the oscillator, and FIG. FIG. 12 is a diagram showing an example of characteristics when the oscillation output is flattened by a variable short circuit plate in the current control type impact sweep signal generator according to the present invention.

Claims (1)

[Claims] 1. In a current-controlled impact sweep signal generator, the attenuation of the high-order form of the transmission line into which the oscillation element is inserted is 23 dB or more per free space wavelength at the upper limit of the applicable frequency, and the lower limit of the applicable frequency. The sweep signal is generated using conditions in which the ratio of the basic wavelength of the basic wavelength to the free space wavelength is 10 or less, and the loss and position of the variable short circuit plate in the oscillator are selected to oscillate. A current-controlled impact sweep signal generator characterized by flattened output frequency characteristics.