JPS61171208A - Frequency converter - Google Patents

Abstract

PURPOSE:To improve the noise characteristic and to simplify the titled converter by connecting a radiator and a low noise amplifier with a coaxial line or a strip line and connecting a waveguide converter, a cut-off waveguide filter and a mixer in cascade to the post-stage of an output of the amplifier. CONSTITUTION:A helical antenna 12 comprising the coaxial or the strip line and the low noise amplifier 5 consisting of the coaxial or the strip line are connected in series by a coaxial or a strip line. Further, a reflection plate 13 is provided to the antenna 12. The waveguide converter 4 converting the line from the coaxial or strip line into a waveguide is provided at the post-stage of the output of the amplifier 5 and a mxier 7 is connected to the output side of the converter via a cut-off waveguide filter 3. A local oscillation signal of a local oscillator 8 and an input signal are mixed by the mixer 7 and a generated IF signal is extracted from an IF output terminal 11 via an IF amplifier 9. Thus, the noise characteristic is improved and the constitution is simplified.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention provides a coaxial amplifier/radiator for an amplifier/radiator that has low noise characteristics, high image signal suppression characteristics, and low local oscillation signal leakage characteristics. This relates to a frequency converter that is directly connected to a line.

<Summary of the Invention> The present invention uses a radiator (antenna) with a coaxial or strip line output end, connects the radiator (antenna) and an amplifier directly, and transmits an image and a station between the mixer and the mixer at the downstream stage of the amplifier. It consists of cascaded cut-off waveguide filters that block the passage of radiation.

<Background Art> In recent years, satellite broadcasting systems have appeared in many countries, and various satellite receiving devices have been developed. The main part of a satellite receiver is a frequency converter, and this converter is required to have low noise, high image suppression, low local leakage, etc.

The noise characteristics determine the receiving sensitivity of the converter, and also the image suppression characteristics.

Local leakage characteristics affect mutual interference with other communication lines. In other words, the incidence of external unnecessary signals and noise at the image frequency into the converter will result in deterioration of the reception demodulation SA, and the leakage of local oscillator signals from the converter to the outside will cause
Acts as an interference wave to other communication devices.

Although many efforts have been made to improve the characteristics of these converters, they must be realized easily and at low cost, especially when the purpose is for many individual uses, such as in a satellite broadcast receiving system.

Currently, as an effective means of forming converters for SHF band satellite broadcasting systems, low noise F
An ET (or transistor) is used, and in order to obtain a high image suppression effect and low local leakage characteristics, a filter using a cutoff waveguide that is easily manufactured and has good characteristics is used.

FIG. 2 shows the configuration of a typical frequency converter for satellite broadcast reception that is currently commonly used in the market.

In Figure 2, l is a circularly polarized wave linear polarized wave converter (circularly polarized wave is used in SHF band satellite broadcasting), 2 is a circular rectangular waveguide converter, and 3 is a cutoff for image frequency and local frequency. A cutoff waveguide filter (2 and 3 may be composed of cutoff circular waveguides), and 4 a waveguide converter for converting the waveguide into a coaxial or strip line.

5 is a FET (or transistor) low-noise amplifier usually composed of a strip line, 6 is a bandpass filter for preventing leakage of the image signal component of the mixer in the subsequent stage and the local signal, 7 is the mixer, and 8 is the local oscillator. (local oscillator), 9 is an IF signal amplifier, 10 is an input opening for the SHF signal, and 11 is an IF multiplied signal output terminal.

A circularly polarized to linearly polarized wave converter usually constructed of a circular waveguide.
A radiator (phone or antenna) is formed by the circular rectangular waveguide converter 2 and is quite long in terms of dimensions. The dimensions of the cut-off waveguide filter 3 vary depending on the degree of image suppression required, but for example, when a degree of suppression of 70 dB to 90 dB is required.
Its length J is approximately several α to 10 cm.

Currently, as the low noise amplifier 5, 2 to 4 stages of GaA
s@FET devices are used, but SHF (12GHz
) band, a noise figure of about 2.5 to 8.5 dB has been obtained. Here, the received signal is input from lO to D2,3°4
．． 5.6 to mixer 7. At 7, the signal and the local oscillation signal are mixed and outputted from the output terminal 11 through the generated IF multiplied signal 9.

<Problems to be Solved by the Invention> The drawbacks of the above-mentioned conventional system are that the circularly polarized wave linearly polarized wave converter 19 is composed of a circular waveguide; the circular rectangular waveguide converter 2. Since the cutoff waveguide filter 3 is entirely constructed in the form of a waveguide, its size and shape are very large and heavy.

Also, corresponding to the length, there is a loss in signal propagation. or,
Since the low-noise amplifier 5 is usually formed of a strip line, the waveguide converter 4 at the preceding stage is essential, and the conversion to the signal strip line involves a loss in the converter. These losses occurring before the low-noise amplifier 5 also result in deterioration of the substantial noise characteristics seen from the input aperture 10 of the radiator under equal constraints, resulting in a very undesirable effect.

The present invention was devised in order to improve the double size of the frequency converter and the deterioration of noise characteristics in the conventional system.゛〈Means for solving the problem〉 The present invention provides a satellite that uses an image composed of a normal radiator and a cut-off waveguide and a filter for preventing leakage of local oscillator signals to the outside in the front stage of a low-noise amplifier. A receiving frequency converter is directly connected to a helical antenna or stripline antenna based on a coaxial or stripline, and a low-noise amplifier composed of a stripline (or coaxial line), and a downstream stage of the amplifier is connected directly to the receiving frequency converter. A waveguide converter and a cutoff waveguide filter that blocks the passage of image and local signals are connected in cascade between the mixer and the mixer.

Effect〉 This configuration makes the radiator section compact and lightweight.
In addition, a waveguide converter and a cut-off waveguide filter are located after the low-noise amplifier to mask the loss and prevent it from affecting the noise characteristics.
The cutoff waveguide filter also serves as a bandpass filter before the mixer, further simplifying the circuit.

<Example> Figure 1 shows an example using the helical antenna of the present invention.
3 is a cutoff waveguide filter that cuts off the image frequency and the local frequency; 4 is a waveguide converter for converting from a coaxial or strip line to a waveguide; and 5 is usually composed of a strip line. FET (or transistor) low noise amplifier, 7 is mixer, 8 is local oscillator (local oscillator)
, 9 is an IF signal amplifier, summer 1 is an IF double signal output terminal, 1
2 is a helical antenna, and 13 is a reflector of the antenna.

The signal incident through the helical antenna 12 is transmitted to a low noise amplifier 5. Waveguide converter 4. It passes through a cutoff waveguide filter 3 and reaches a mixer 7. The mixer 7 mixes the local oscillator 8 signal and the input signal, and the resulting IF multiplied signal is amplified by the IF amplifier 9 and output from the IF output terminal II.

Figure 1 shows an example using a helical antenna, but the radiator (antenna) may be anything that has a coaxial or strip line output end, and other similar antennas such as patch antennas and strip antennas can be used. It is possible.

Here, when compared with the conventional method shown in FIG. 2, first, the helical antenna 12 (
(or a patch antenna or a strip antenna) can be configured to be extremely compact and lightweight compared to a waveguide radiator. Furthermore, these have good connectivity with the low-noise amplifier 5 composed of a strip line, and are directly connected to the low-noise amplifier 5 without requiring any conversion of the connection line. Therefore, unlike the conventional method, the distance from the antenna input end to the low noise amplifier (
(length) is unnecessary, and any loss for a perfect signal between them can be completely eliminated. This results in the overall 7° line sound characteristics including the radiator (the helical antenna 12 in the embodiment) being improved compared to the conventional system.

Next, the cutoff waveguide filter 3 and the waveguide converter 4, which were used before the low-noise amplifier 5 in FIG. 2, are arranged after the low-noise amplifier 5 in the present invention (FIG. 1). Ru. If the cutoff waveguide filter 3 and waveguide converter 4 are expected to have characteristics equivalent to those shown in FIG. 2, they need to be similar in size and length, and a corresponding loss occurs. However, since these losses are located after the low-noise amplifier 5, they are masked by the gain of the low-noise amplifier 5, and have little effect on the overall noise characteristics. This effect can be reduced as the gain of the low noise amplifier 5 increases.

Furthermore, in the conventional system shown in FIG. 2, between the low noise amplifier 5 and the mixer 7, a
A bandpass filter 6 is inserted in order to prevent image frequency components from leaking to the front stage of the local oscillator, but in the present invention (Fig. 1), the action of this filter 6 is that of a cut-off waveguide filter. 3 can be substituted, so it can be removed, which greatly simplifies the circuit and leads to lower costs.

Although 3 in FIG. 1 is a filter using a waveguide, basically any filter may be used as long as it has the same characteristics. However, at present, this method is the simplest and has a great advantage in that it has a significantly greater attenuation characteristic for unwanted waves than other filters.

FIG. 3 is a cross-sectional view of a main part showing another embodiment.
This shows the connection between a strip antenna (patch antenna and planar antenna are similar) and a low-noise amplifier using a rip line configuration.

In the figure, 5 is a low noise amplifier, 14 is a strip, a dielectric substrate forming a line, 15 is a ground plane, and I6 is a metal conductor antenna pattern forming an antenna. In this example as well, the configuration after the low-noise amplifier 5 is the same as that shown in FIG. 1, and the operation and effect of operation 2 are the same as in the previous example.

Note that the present invention can be applied not only to the reception of circularly polarized waves but also to the reception of linearly polarized signals by using a strip line type linear wave antenna.

<Effects of the Invention> As explained above, the present invention improves the noise characteristics of the conventional system and eliminates the bandpass filter used before the mixer, thereby simplifying and reducing the cost of the converter. In particular, an extremely effective frequency converter can be provided for application to satellite broadcast receivers and the like.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a block diagram of a typical conventional converter, and FIG. 3 is a sectional view of main parts showing another embodiment of the present invention. 3... Cutoff waveguide filter, 4... Coaxial waveguide converter, 5... Low noise amplifier, 7... Mixer, 8
...Local oscillator, 9...IF signal amplifier, 12...
・Helical antenna, 14... Dielectric substrate, 15...
・Earth surface. 16...Metal conductor antenna pattern. Agent Patent attorney Aihiko Fuku (and 2 others) 13
Not 144 a-j! Figure 1 of the example of the song, Figure 2 of the example of how to handle it.

Claims (1)

[Claims] 1. A radiator (antenna) having a coaxial or stripline output end, a low-noise amplifier composed of a coaxial or stripline, and a converter that converts the coaxial or stripline to a waveguide. , a cut-off waveguide filter made of a waveguide that passes the signal frequency and cuts off the image frequency and the local frequency, and a mixer, and the radiator and low-noise amplifier are connected by a coaxial line or a strip line. A frequency converter characterized in that the waveguide converter, the cutoff waveguide filter, and the mixer are connected in cascade after the output of the low-noise amplifier.