JPS6359606B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a mixer using a planar circuit such as a strip line or a microstrip line.
In particular, a microwave integrated circuit (MIC) integrated single circuit provides low noise characteristics over a wide range in the microwave band, and also provides a short-circuiting method for the diode loading point when the intermediate frequency signal frequency is high in the GHz band or near GHz. It concerns mixers.

In conventional mixers using MIC, a circuit like the one shown in Figure 1 was used to short-circuit the diode loading point at the intermediate frequency signal frequency. 1st
In the figure, a high frequency signal input from a terminal 1 propagates through a main line 2 and is applied to a mixer diode 3. On the other hand, the local oscillation signal input from the terminal 4 is coupled to the main line 2 at high frequency, passes through a local oscillation signal band-pass filter (local BPF) 5 that selectively passes only the local oscillation signal, and is sent to the mixer diode. 3 is applied. 6 is a low-pass filter that extracts an intermediate frequency signal that is the frequency component of the difference between the high frequency signal and the local oscillation signal, and at the same time short-circuits the terminal A of the mixer diode 3 for high frequency signals and local oscillation signals. The length provided for this purpose is 1/4 wavelength (λ/4) of the high frequency signal or local oscillation signal.
It consists of an open-ended stub and a series inductance. 7 is an intermediate frequency signal shorting circuit for shorting terminal B of mixer diode 3 to the intermediate frequency signal, which connects the 1/4 wavelength (λ/4) line with high characteristic impedance and the 1/4 wavelength line with low characteristic impedance. This is a low-pass filter consisting of an open-ended stub and a terminal short-circuited to ground. 8
is an intermediate frequency signal output terminal from which the intermediate frequency signal generated by the mixer diode 3 is taken out.

In the conventional intermediate frequency signal shorting circuit 7 using a low-pass filter whose terminal end is short-circuited to ground, there was no problem when the intermediate frequency signal frequency was relatively low, but as the intermediate frequency signal frequency became higher, Therefore, the impedance of the intermediate frequency signal short circuit 7 can no longer be ignored, and it is no longer considered a short circuit. At this time, the impedance of the intermediate frequency signal short circuit 7 exhibits the characteristics of an impedance circuit having a certain finite magnitude. Since this intermediate frequency signal shorting circuit 7 is connected in series with the mixer diode 3 when viewed from the output terminal 8, as the impedance of the intermediate frequency signal shorting circuit 7 increases, the coding bandwidth from the intermediate frequency signal side is limited. This ultimately limits the bandwidth of the mixer. At the same time, the main line 2 is connected to the terminal B of the mixer diode 3, so if the impedance of the intermediate frequency signal short circuit 7 increases, the intermediate frequency signal will change depending on the state of the circuit connected to the input terminal 1 side of the main line 2. The impedance seen from the signal output terminal 8 to the mixer diode 3 side is greatly affected, and there is a drawback that the performance of the mixer is degraded due to mismatching of the output impedance in the intermediate frequency signal.

In order to reduce the impedance of the intermediate frequency signal short circuit 7 in an attempt to alleviate this drawback, the dimensions of the intermediate frequency signal short circuit 7 may be shortened, or the width of the strip line constituting the intermediate frequency signal short circuit 7 may be increased. There are ways to lower the characteristic impedance, but if the dimensions are shortened or the line width is widened, the intermediate frequency signal short circuit 7 will greatly disturb the line impedance of the main line 2.
Another drawback is that it increases propagation loss.

One of the objects of the present invention is to eliminate the drawbacks of the above-mentioned conventional example, and to provide a main line in series with the main line that exhibits a passing characteristic for high frequency signals, but has an open impedance for intermediate frequency signals. An intermediate frequency signal blocking circuit is installed at a position 1/4 wavelength (λif/4) of the intermediate frequency signal from the mixer diode, and the intermediate frequency signal is used to block the mixer at high frequency using the main line.
By shorting the loading point of the diode, the loading point of the mixer diode is reliably shorted even when the intermediate frequency signal frequency is high.

FIG. 2 shows one embodiment of the present invention, and the same parts as in FIG. 1 are given the same numbers and will be explained. Terminal 1
The high frequency signal input from the main line 2 is applied to the mixer diode 3 after being propagated through the main line 2 . The local oscillation signal input from terminal 4 is coupled to the main line 2 at high frequency, and the local oscillation signal is selectively passed through.
It passes through BPF5 and is applied to mixer diode 3. Reference numeral 6 denotes a low-pass filter, which has a length provided to take out intermediate frequency signals and at the same time short-circuit terminal A of mixer diode 3 for high frequency signals and local oscillation signals. It consists of an open-ended stub with a quarter wavelength (λ/4) of the local oscillation signal and a series inductance. 8 is an intermediate frequency signal output terminal from which the intermediate frequency signal generated by the mixer diode 3 is taken out. 9 is an intermediate frequency signal blocking circuit that exhibits pass characteristics for high frequency signals but exhibits open impedance for intermediate frequency signals; located at a distance of

In the embodiment shown in FIG. 2, the intermediate frequency signal blocking circuit 9 has an open impedance with respect to the intermediate frequency signal, and the distance from the mixer diode 3 to the intermediate frequency signal blocking circuit 9 is equal to the length of 1/4 wavelength of the intermediate frequency signal. Therefore, the terminal B of the mixer diode 3 is short-circuited at high frequency by the intermediate frequency signal. Therefore, even if the intermediate frequency signal frequency is high, the diode loading point can be reliably shorted. Furthermore, the intermediate frequency signal blocking circuit 9
Since the diode is connected in series with the terminal 1, it is possible to eliminate the influence of the circuit connected to the terminal 1 side on the short-circuited state of the diode loading point B.

FIG. 3 shows another embodiment of the present invention, and the same parts as in FIG. 2 are given the same numbers and will be described. A high frequency signal input from terminal 1 propagates through main line 2 and is applied to mixer diode 3. The local oscillation signal input from the terminal 4 is coupled to the main line 2 at high frequency, and the local oscillation signal is selectively passed through the local oscillation BPF 5.
and is applied to the mixer diode 3.
Reference numeral 6 denotes a low-pass filter, which has a length provided to take out intermediate frequency signals and at the same time short-circuit terminal A of mixer diode 3 for high frequency signals and local oscillation signals. It consists of an open-ended stub with a quarter wavelength (λ/4) of the local oscillation signal and a series inductance. 8
is an intermediate frequency signal output terminal from which the intermediate frequency signal generated by the mixer diode 3 is taken out. 9 is an intermediate frequency signal blocking circuit that exhibits pass characteristics for high frequency signals but exhibits open impedance for intermediate frequency signals; It is provided in series with the main line 2 at a distance of . 10 is a low-pass filter whose terminal end is short-circuited to ground, and is connected in parallel to the main line 2 near the intermediate frequency signal blocking circuit 9, and the distance from the short-circuited end 11 of the low-pass filter 10 to the mixer diode 3 is is selected to be 1/2 wavelength (λif/2) of the intermediate frequency signal.

In the embodiment shown in FIG. 3, the distance from the mixer diode 3 to the ground shorting end 11 is 1/2 of the intermediate frequency signal
Since the intermediate frequency signal blocking circuit 9 exhibits an open impedance with respect to the intermediate frequency signal, the terminal B of the mixer diode 3 is short-circuited at high frequency by the intermediate frequency signal. Therefore, even if the intermediate frequency signal frequency is high, the diode loading point can be reliably shorted. Further, since the intermediate frequency signal blocking circuit 9 is provided in series with the main line 2, it is possible to eliminate the influence of the short circuit state of the diode loading point B from the circuit connected to the terminal 1 side. Moreover, since the low-pass filter 10 whose terminal end is short-circuited to ground also serves as a feedback circuit for the bias current flowing to the mixer diode 3, there is no need to form a separate feedback circuit for the bias current, and the mixer circuit The configuration is simplified.

FIG. 4 shows a specific method of constructing the intermediate frequency signal blocking circuit 9 in the embodiment of the present invention.
Figure 4a shows a 1/4 wavelength line-coupled interdigital DC blocking circuit, in which approximately 1/4 wavelength (λ/4) of the high frequency signal is transmitted from the open ends of two open-ended strip lines.
It has a simple configuration, small size, low insertion loss for high frequency signals, and exhibits bandpass filter characteristics over a wide band. However, the inter-gap capacitance due to the coupling gap of two open-ended strip lines that are distributed coupled is usually less than 0.1 P ^F when the high frequency signal frequency is 12 GHz, and even if the inter-gap capacitance is 0.1 P ^F , the intermediate frequency signal frequency At 1 GHz, the impedance shown by the inter-gap capacitance is approximately 1.6KΩ, which is almost the same as open impedance. Figure 4b shows a bandpass filter using a half-wavelength strip line resonator. By selecting the length of the half-wavelength strip line to be 1/2 wavelength (λ/2) of the high-frequency signal, high-frequency signals can be passed. However, since one end of the line is open to intermediate frequency signals, it operates as an intermediate frequency signal blocking circuit and exhibits open impedance.

In addition, in the past, two or four mixer diodes, which are relatively easy to obtain low noise characteristics over a wide band, are used as MIC mixers using planar circuits such as strip lines and microstrip lines.
Single-balanced mixers or double-balanced mixers were common.

Figure 5 is an example of a balanced mixer using MIC. The high frequency signal and local oscillation signal inputted from the high frequency signal input terminal 12 and the local oscillation signal input terminal 13 are power-divided by 3 dB by the 3 dB directional coupler 14 and sent to the mixer diode 1.
5 and 16. Then, an intermediate frequency signal, which is a frequency component of the difference between the high frequency signal and the local oscillation signal, is extracted from the intermediate frequency signal output terminal 18 via the low pass filter 17. Both 19 and 20 are intermediate frequency signal short circuits, and mixer diode 1
It is provided to short-circuit the diode loading points 5 and 16 at an intermediate frequency signal frequency, and is constituted by a low-pass filter whose terminal end is short-circuited to ground.

Although this balanced mixer can relatively easily obtain broadband characteristics, it has the drawback of requiring two mixer diodes, which increases the manufacturing cost of the mixer.

A single mixer, which requires only one mixer diode, is commonly used in waveguide circuits, and FIG. 6 is a block diagram thereof. To explain the operation of the mixer shown in Fig. 6, the high frequency signal input from the high frequency signal input terminal 21 is filtered through a band pass filter (BPF) that selectively passes only the high frequency signal.
22 and is applied to the mixer diode 23, while the local oscillation signal input from the local oscillation signal input terminal 24 is coupled to the main line 25 only at the local oscillation signal frequency, and selectively passes only the local oscillation signal. The intermediate frequency signal is passed through a band pass filter (BPF) 26 and applied to a mixer diode 23, and the intermediate frequency signal generated by the mixer diode 23 is outputted from an intermediate frequency signal output terminal 28 via a low pass filter (LPF) 27. taken out.

FIG. 7 shows the characteristics of BPF 22 and BPF 26 and important frequency components in the mixer. The high frequency signal frequency is _r , the local oscillation signal frequency is _l , and the intermediate frequency signal frequency is _if . In addition to the intermediate frequency signal, the mixer uses an image signal (having frequency components of 2 _l − _r and expressed by a frequency of _n ) and a sum signal ( _r
+ _l frequency component and _s frequency) also occurs, and the handling of this image signal and sum signal component is important, especially when dealing with image signals.
Suppression by the BPF 22 improves the performance of the mixer, so the BPF 22 is required to have characteristics that pass the high frequency signal _r and sufficiently suppress the image signal _n , as shown in the characteristic line 29. As shown by a characteristic line 30, a characteristic is required that allows the local oscillation signal _l to pass through and sufficiently suppresses the high frequency signal _r and image signal _n .

There are various problems that must be solved in order to realize the mixer with the configuration shown in Figure 6 using a planar circuit such as a strip line or a microstrip line, but this is mainly due to the low Q value of the planar circuit. . In order to realize a single mixer with a wide band, low noise, and high intermediate frequency signal frequency in the GHz band using MIC at a low cost, the following conditions must be satisfied.

(1) It must have a filter that has low insertion loss for high-frequency signals, high suppression of image signals, and satisfies these characteristics over a wide band.

(2) The bandpass filter for local oscillation signals has the characteristic of greatly suppressing high frequency signals and image signals.

(3) At the same time as suppressing the image signal, the image signal is reconverted back into an intermediate frequency signal to create a configuration with good noise characteristics.

(4) The propagation distance of the high-frequency signal from the high-frequency signal input terminal to the mixer diode should be as short as possible, and the configuration should have low propagation loss for the high-frequency signal.

(5) To realize an intermediate frequency signal short circuit in the GHz band that shorts the diode loading point of the mixer diode in the intermediate frequency signal.

(6) The mixer circuit configuration must be simple.

The present invention provides a low-cost MIC single mixer that satisfies the above conditions, has a simple configuration, low noise, and wideband characteristics.

FIG. 8 shows another embodiment of the present invention. The high frequency signal input from the high frequency signal input terminal 31 propagates through the main line 32 and is applied to the mixer diode 33. 34 is a filter that exhibits a pass characteristic for high-frequency signals but suppresses image signals, and is composed of three stages of open-ended stubs, and is located at a position where the impedance seen from terminal C of mixer diode 33 is short-circuited by the image signal. The distance between the filter 34 and the mixer diode 33 is
It is selected to be approximately 1/2 wavelength (λ _n /2) of the image signal. 35 is a low-pass filter that short-circuits the terminal D of the mixer diode 33 in terms of high frequency for high frequency signals, local oscillation signals, and image signals, and passes intermediate frequency signals. 36 is mixer
This is an intermediate frequency signal output terminal for taking out the intermediate frequency signal generated by the diode 33. Reference numeral 37 denotes an intermediate frequency signal matching circuit, which is configured such that the impedance viewed from the intermediate frequency signal output terminal 36 to the mixer diode 33 side satisfies matching conditions. In particular, the intermediate frequency signal matching circuit 37 includes a parallel inductance circuit 37';
7' also forms part of a feedback circuit for the bias current flowing through the mixer diode 33. 38 is an intermediate frequency signal blocking circuit that exhibits a pass characteristic for high frequency signals but exhibits an open impedance for intermediate frequency signals, in which two strip lines with open terminations pass from the open end to approximately 1/4 of the high frequency signal. It consists of a 1/4 wavelength line-coupled interdigital DC blocking circuit distributed over the length of the wavelength (λ _r /4), and outputs the intermediate frequency signal from the mixer diode 33.
It is located at a distance of 1/4 wavelength (λ _if /4). The local oscillation signal input from the local oscillation signal input terminal 39 is applied to the mixer diode 33 via the local oscillation BPF 40 configured with a half-wavelength strip line resonator. It is provided at a position where the impedance viewed from the coupling point E toward the filter 34 is open or close to open at the local oscillation signal frequency. 41 and 42 are high-frequency signal matching circuits, which are provided so that the impedance seen from the high-frequency signal input terminal 31 can be matched with the high-frequency signal.Here, the high-frequency signal matching circuit 41 is composed of an open-terminated stub, and is configured to match the high-frequency signal matching circuit 41 with the high-frequency signal input terminal 31. The circuit 42 is comprised of a low impedance line. 43 is a feedback circuit for the bias current flowing through the mixer diode 33, and is composed of a low-pass filter whose terminal end is short-circuited to ground.

In the embodiment shown in FIG. 8, a three-stage open-ended stub filter 34, which is simple in construction and small in size, is used as a filter that exhibits a pass characteristic for high-frequency signals and suppresses image signals. Since the impedance is placed at a position where the image signal is short-circuited, the high-frequency signal input from the high-frequency signal input terminal 31 is propagated to the mixer diode 33 with little propagation loss, and the image generated in the mixer diode 33 is Since the signal is efficiently converted back into an intermediate frequency signal, mixer characteristics with low conversion loss and high image suppression ratio can be obtained.

Further, for intermediate frequency signals, the intermediate frequency signal blocking circuit 38 exhibiting open impedance is provided at a position 1/4 wavelength of the intermediate frequency signal from the mixer diode 33.
The diode loading point C of No. 3 is short-circuited at high frequency by an intermediate frequency signal. Therefore, even if the intermediate frequency signal frequency is as high as the GHz band, the diode loading point C can be reliably short-circuited with the intermediate frequency signal. Further, since the intermediate frequency signal blocking circuit 38 is provided in series with the main line 32, it is possible to eliminate the influence of the short circuit state of the diode loading point C from the circuit connected to the high frequency signal input terminal 31 side.

Therefore, the matching band for intermediate frequency signals is rarely limited, and low-noise mixer characteristics can be obtained over a wide band in the GHz band and high intermediate frequency signal frequencies.

Further, the intermediate frequency signal generated by the mixer diode 33 is passed through the intermediate frequency signal matching circuit 3 including a low pass filter 35 and a parallel inductance circuit 37.
7 is sequentially passed through and taken out, and since a parallel inductance circuit 37' which also serves as a feedback circuit for the bias current flowing to the mixer diode 33 is used as the intermediate frequency signal matching circuit 37, a new feedback circuit for the bias current is added. No need to form
Furthermore, since the filter 34 has a simple configuration and small dimensions, the mixer circuit configuration can be made smaller and simpler. Furthermore, since only one mixer diode is used, the manufacturing cost of the mixer is reduced.

FIG. 9 shows the filter 34 in the embodiment of FIG.
This shows an example of a configuration method. Open-ended stubs 45 to 47 each having lengths l ₁ , l ₂ , and l ₃ are sequentially connected in parallel to the main line 44 with an interval l ₀ . l ₁ , l ₂ of the open-ended stubs 45 to 47,
l ₃ is selected to have a length around 1/4 wavelength (λ _n ) of the image signal so that the attenuation pole of the filter is near it within the band of the image signal, and at the same time, l ₂ < l ₁ and l ₂ <
Choose to satisfy the relationship l ₃ or the relationship l ₂ < l ₁ = l ₃ . Open end stub 45-4
For an interval l ₀ of 7, l ₁ < l ₀ < 2l ₂ and l ₃ < l ₀ < 2l ₂
This filter is determined in relation to l ₁ , _{l 2} , and _{l 3} in accordance with the characteristics required of the filter ₃₄ under the conditions _of It has been confirmed that it sometimes works effectively as a filter for single mixers. In particular, in places where the high frequency signal frequency _r and the image signal frequency _n are relatively close to each other, the interval l ₀ between the open-ended stubs 45 to 47 is longer than the 5/16 wavelength (λ _r ) of the high frequency signal. By selecting a wavelength shorter than 16 wavelengths (λ _r ), the effect of suppressing the image signal as a filter for a single mixer becomes greater.

As a specific example of the filter 34, for example, a dielectric substrate with a dielectric constant of 2.5 and a characteristic impedance of
A 50Ω open-ended stub is connected in parallel to the main line whose characteristic impedance is also 50Ω, l ₀ = 6.4 mm, l ₁
If we choose = l ₃ = 5.5 mm and l ₂ = 4.8 mm, then l ₂ < l ₁ = l ₃ < l ₀ <
The conditions of 2l ₂ are satisfied, and 11.7~
VSWR 1.6 or less, 8~ in the 13.0GHz frequency range
Filter characteristics with attenuation of 30 dB or more in the 10.5 GHz frequency range can be obtained. This is a high frequency signal frequency of 12GHz band, an intermediate frequency signal frequency of 1GHz band,
The image signal frequency is 9GHz band and the bandwidth is 1G.
It is effective as a filter for a single mixer around Hz, and both the stopband width and passband width are 1G.
It has a wide band of Hz or more. Moreover, since the filter shown in the embodiment of FIG. 9 has a simple structure and small dimensions, the insertion loss for high frequency signals is small.

In the embodiment described above, the local oscillation signal is applied to the mixer diode through the local oscillation BPF which is high frequency coupled to the main line between the intermediate frequency signal blocking circuit and the mixer diode. However, the method described in the embodiments does not necessarily have to be used. For example, by inputting a local oscillation signal from terminal 1 at the same time as the high-frequency signal, or by applying a local oscillation signal to the mixer diode via a local oscillation BPF that is high-frequency coupled to low-pass filter 6 or 35. Needless to say, it's a good thing.

As explained above, in the present invention, an intermediate frequency signal blocking circuit is provided on the main line, which exhibits a pass characteristic for high frequency signals, but exhibits an open impedance for intermediate frequency signals, and this intermediate frequency signal blocking circuit and a mixer are provided. - By selecting the distance to the diode to be 1/4 wavelength of the intermediate frequency signal, the loading point of the mixer diode is short-circuited at high frequency with the intermediate frequency signal. Therefore, even when the intermediate frequency signal frequency is high, the diode loading point can be reliably shorted. Furthermore, since the intermediate frequency signal blocking circuit is provided in series with the main line, it is possible to eliminate the influence of the short circuit state of the diode loading point from the circuit connected to the high frequency signal input terminal side. Therefore, the matching band for the intermediate frequency signal is less likely to be limited, and low-noise mixer characteristics can be obtained over a wide band at high intermediate frequency signal frequencies.
Moreover, since it is a single mixer, only one mixer diode is required, which has the effect of reducing the manufacturing cost of the mixer.

[Brief explanation of the drawing]

FIG. 1 is a pattern diagram of a conventional mixer circuit using MIC, FIG. 2 is a pattern diagram of a mixer circuit according to an embodiment of the present invention, and FIG. 3 is a pattern diagram of a mixer circuit according to another embodiment of the present invention. Figure 4a,
b is a pattern diagram of a specific configuration of the intermediate frequency signal blocking circuit in the embodiment of FIGS. 2 and 3;
1 shows a quarter-wavelength line-coupled interdigital DC blocking circuit, b shows a bandpass filter using a half-wavelength strip line resonator, FIG. 5 shows a pattern of a conventional balanced mixer using MIC, and FIG. A block diagram showing the configuration of a single mixer often used in wave tube circuits, Fig. 7 is a diagram showing the main frequency components of the mixer and the characteristics of the BPF shown in Fig. 6, and Fig. 8 is a diagram showing still another example of the present invention. Single according to example
FIG. 9 is a pattern diagram of a mixer circuit, and FIG. 9 is a pattern diagram of a filter with three stages of open-ended stubs used in the embodiment of FIG. 1...High frequency signal input terminal, 2...Main line, 3
...Mixer diode, 4...Local oscillation signal input terminal, 5...Local oscillation signal input terminal, 6...Low pass filter, 8...Intermediate frequency signal output terminal, 10...Intermediate frequency signal blocking circuit.

Claims (1)

[Claims] 1. In a single mixer using a microwave integrated circuit whose basic configuration is a strip line or a microstrip line, a high frequency signal input terminal is connected to one end of a mixer diode to transmit a high frequency signal to the mixer. Connected by the main line that transmits to the diode, applies a local oscillation signal to the mixer diode, and extracts an intermediate frequency signal that is the frequency component of the difference between the high frequency signal and the local oscillation signal at the other end of the mixer diode. A low-pass filter is connected, and an intermediate frequency signal blocking circuit is provided on the main line at a distance of 1/4 wavelength of the intermediate frequency signal from the mixer diode, and exhibits an open impedance to the intermediate frequency signal. A single mixer characterized by: 2. As an intermediate frequency signal blocking circuit, a 1/4 wavelength line coupling type interface in which two open-ended strip lines are distributed-coupled over a length of approximately 1/4 wavelength of the high-frequency signal from the open end of the open-terminated strip line is used. The single mixer according to claim 1, characterized in that it is constructed of a digital DC blocking circuit. 3. In a single mixer using a microwave integrated circuit whose basic configuration is a strip line or a microstrip line, a main line that connects a high frequency signal input terminal and one end of a mixer diode to transmit a high frequency signal to the mixer diode. A local oscillation signal is applied to the mixer diode, and a low-pass filter is connected to the other end of the mixer diode to extract an intermediate frequency signal that is a frequency component of the difference between the high frequency signal and the local oscillation signal. An intermediate frequency signal blocking circuit is provided on the main line at a distance of 1/4 wavelength of the intermediate frequency signal from the mixer diode, and exhibits an open impedance to the intermediate frequency signal. At a position where the impedance is short-circuited at the image signal frequency, a filter is provided, which is composed of multiple stages of open-ended stubs connected in parallel to the main line, and has a stop band at the image signal frequency and a pass band at the high frequency signal frequency. A single mixer characterized by: 4. The filters are connected in parallel to the main line at equal or approximately equal intervals l ₀ and have lengths l ₁ , l ₂ , and l _{3 ,} respectively, with open ends. 2 and a third stub,
Lengths of the first, second and third stubs l ₁ , l ₂ , l ₃
is chosen to be 1/4 wavelength or approximately 1/4 wavelength of the image signal so that the attenuation pole is within or near the image signal frequency band, and l ₂ < l ₁ < l ₀ < 2l ₂ and l ₀ , l ₁ , l _{2 ,} l so that the conditions l ₂ < l ₃ < l 0 < 2l 2 are satisfied, or the conditions _l 2 < l _{1 =} l ₃ < l ₀ < 2l ₂ are satisfied. 3. The single mixer according to claim ₃ , wherein the length of the mixer is 3. 5. A patent claim characterized in that the interval l ₀ between the first, second, and third stubs provided on the main line is selected to be longer than 5/16 wavelength and shorter than 7/16 wavelength of the high frequency signal. The single mixer according to item 4 in the range of . 6 As an intermediate frequency signal blocking circuit, a 1/4 wavelength line coupling type interface in which two open-terminated strip lines are distributed-coupled over a length of about 1/4 wavelength of the high-frequency signal from the open end of the open-terminated strip line is used. 4. The single mixer according to claim 3, wherein the single mixer is constructed of a digital DC blocking circuit. 7 In a single mixer using a microwave integrated circuit whose basic configuration is a strip line or a microstrip line, a main line that connects a high frequency signal input terminal and one end of a mixer diode to transmit a high frequency signal to the mixer diode. A local oscillation signal is applied to the mixer diode, and a low-pass filter is connected to the other end of the mixer diode to extract an intermediate frequency signal that is a frequency component of the difference between the high frequency signal and the local oscillation signal. An intermediate frequency signal blocking circuit is provided on the main line at a distance of 1/4 wavelength of the intermediate frequency signal from the mixer diode, and the intermediate frequency signal blocking circuit exhibits an open impedance to the intermediate frequency signal. In the vicinity of the circuit, a low-pass filter whose terminal end is short-circuited to ground is connected in parallel to the main line on the mixer diode side, and from the ground-short-circuited end of the low-pass filter whose terminal end is short-circuited to ground, the mixer diode is connected. A single mixer characterized in that the distance to the diode is selected to be 1/2 wavelength of the intermediate frequency signal.