JPH0770928B2 - Frequency converter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a frequency converter, and in particular, it is used in a frequency range from a microwave band to a millimeter wave band using a planar circuit such as a strip line or a microstrip line. It relates to a frequency converter.

(Prior Art) FIG. 5 shows the configuration of a conventional frequency converter using a planar circuit. This converter comprises an input signal frequency bandpass filter 34 using a distributed constant line on a dielectric substrate, a local oscillation frequency bandpass filter 35, an intermediate frequency bandpass filter 37 and a mixer diode 36. Diode 36 is located between filters 34 and 35 and is positioned to match the impedance of diode 36 to the input signal and local oscillation.

Generally, the input signal is matched by adjusting the length L _{1 of the} line between the filter 35 and the diode 36 on the local oscillation side,
The local oscillation is matched by the filter 34 and the diode 36 on the input signal side.
Adjust the length L _{2 of the} line between and. As a result, the lengths L ₁ and L ₂ are uniquely determined. Meanwhile to the noise figure to minimize the mixer circuit, the impedance processing for image frequency (image frequency f _m, the local oscillation frequency f _P, the input signal frequency is _{f S f m = 2f P -f} S) Is required. The impedance for the image frequency f _m seen from both ends of the diode (hereinafter referred to as the image impedance) is determined by the lengths L ₁ and L _2, but the length is determined by the matching conditions of the input signal and the local oscillation as described above.
Since L ₁ and L ₂ are determined, the image impedance is not always selected to be an appropriate value and the noise figure deteriorates.

On the contrary, if the lengths L ₁ and L ₂ are adjusted so that the image impedance has an appropriate value, the matching condition for the input signal and the local oscillation is impaired, which is also accompanied by the deterioration of the noise figure.

(Problems to be Solved by the Invention) As described above, in the conventional frequency converter, the image impedance processing for reducing the noise figure of the frequency converter and the impedance matching of the input signal and the local oscillation are matched. However, even if they are matched, they have a drawback that they are very troublesome.

Therefore, an object of the present invention is to provide a frequency converter for a planar circuit in the microwave band to the millimeter wave band, which can eliminate the above-mentioned drawbacks with a relatively simple structure.

(Means for Solving the Problems) In order to achieve this object, the frequency converter of the present invention is a frequency converter using a planar circuit, in which a dielectric resonance is provided close to a transmission line to which a frequency conversion diode is connected. An input signal frequency band pass filter by a filter and a local oscillation frequency band pass filter by a dielectric resonator are arranged, and the input signal and the local oscillation respectively input through the two filters are transmitted. The electromagnetic field coupling to the line is applied to the diode, both frequency difference signals are taken out from the diode, and the image impedance seen from the diode is determined by the length of the transmission line. Is.

(Example) The present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows an embodiment of the frequency converter configuration of the present invention. In FIG. 1, this converter comprises an input signal input microstrip line 2 and a local oscillation input microstrip line 3 on a dielectric substrate 1, and one or a plurality of dielectric resonators between them. An input signal frequency band pass filter 4 and a local oscillation frequency band pass filter 5 according to 11, 12 and 13 are arranged. A coupling microstrip line 6 is arranged between the filters 4 and 5. One end of the mixer diode 7 is connected to one end of the coupling microstrip line 6, and an intermediate frequency component is taken from the intermediate frequency output terminal 8 via the intermediate frequency bandpass filter 14 connected to the other end of the diode 7. I will put it out.

The operation of the frequency converter of this embodiment will be described in detail below.

First, the length of the microstrip line 6 is selected so as to obtain the required image impedance. For example, λ / 4 for the image frequency (λ is the wavelength of the image frequency)
In the case of a long open-ended line, the impedance is zero. Dielectric resonators 12 and 13 that resonate with the input signal and local oscillation are placed on the left and right sides of this line, respectively, but since both resonators have high Q and are completely detuned with respect to the image frequency, both resonances occur. The image impedance is determined only by the length of the line without being affected by the container.

Next, the matching between the input signal and the diode is performed by adjusting the coupling position between the dielectric resonator 12 used in the input signal frequency band pass filter 4 and the line 6. In this case, since the resonance frequency is different from that of the dielectric resonator 13 used for the local oscillation frequency bandpass filter 5 on the opposite side of the line 6, signals can be matched independently without being affected by this.

Further, the local oscillation and the matching can be independently performed without being influenced by the position of the resonator 12 only by adjusting the coupling position of the resonator 13 and the line 6 for the same reason.

Next, the above will be described using an equivalent circuit. FIG. 2 (a) shows FIG. 1 by an equivalent circuit in the input signal, local oscillation and image frequency band.

Dielectric resonators 23 and 24 that resonate with the input signal and local oscillation
Is detuned with respect to the image frequency, and the Q of the dielectric resonator is high. Therefore, as shown in FIG. 2 (b), the diode 26 has a strip line of length L ₄ for the image frequency. Only 25 are considered to be connected, and the impedance seen from both ends of the diode is pure reactance. If the line L ₄ is selected to be λ / 4 with respect to the image frequency, the impedance will be zero.

For the input signal frequency, the dielectric resonator 23 that resonates with this signal is coupled to the line 25, and the dielectric resonator 24 that resonates with the local oscillation frequency is in a detuning state, so the equivalent circuit is shown in FIG. ), The input signal power is injected into the diode 26 without being affected by the resonator 24. For the same reason, the local oscillation frequency power is injected into the diode 26 without being affected by the resonator 23.

When the distributed constant lines are used for the resonators 23 and 24, the Q of the resonator is lower than that of the dielectric resonator, and the resistance loss of the resonator is comparable to that of the lines. Part of the power is absorbed by this, resulting in deterioration of noise characteristics.

The converter having the above structure was prototyped on an alumina substrate having a thickness of 0.38 mm, and an experiment was carried out by enclosing it in a case where the cutoff was sufficient in the input signal band. The unloaded Q of the used dielectric resonator (relative permittivity: about 31, diameter: 2.8 mm) in the 22 GHz band is about 30.
It was about 00. The characteristics of the input signal frequency band pass filter are shown in FIG. 3. The insertion loss is 0.4 dB or less, and the attenuation in the image frequency band (19.8 to 20.3 GHz) is 45 dB or more.

Also, the conversion loss 28 and the total noise figure 27 of the prototype converter were
Is shown in FIG. An IF amplifier with a gain of 40 dB and a noise figure of 1.2 dB or less was used for the measurement. Conversion loss 28 is 5.6 to 6.5 dB and total noise figure is 6.5 to 7.6 dB for input signals of 22.5 to 23.0 GHz
Met. The image suppression ratio was 56 dB or more.

(Effects of the Invention) As described above, the frequency converter according to the present invention has a degree of freedom to independently perform the processing of the image impedance and the matching with the input signal circuit and the local oscillation circuit. It has become possible to provide a microwave and millimeter-wave frequency converter which can obtain an excellent frequency converter and which is highly practical and easy to adjust.

[Brief description of drawings]

FIG. 1 shows a configuration of an embodiment of a frequency converter according to the present invention, FIG. 2 (a) shows an equivalent circuit of the configuration shown in FIG. 1, and (b), (c) and (d) of FIG. An equivalent circuit for the image frequency, the input signal frequency and the local oscillation frequency is shown, FIG. 3 shows the characteristics of the input signal frequency band pass filter used in the apparatus of the present invention, and FIG. 4 is a prototype of the present invention. The characteristics of the conversion loss and total noise figure of the converter are shown, and FIG. 5 shows the configuration of the conventional example. 1 …… Dielectric substrate 2 …… Input microstrip line for input signal 3 …… Input microstrip line for local oscillation 4,23,24 …… Input signal frequency band pass filter 5,24,35 …… Local oscillation frequency Bandpass filter 6 …… Coupling microstrip line 7,26,36 …… Mixer diode 8,33 …… Middle frequency output terminal 9,21,31 …… Input signal input terminal 10,22,32 …… Local Oscillation input terminal 11,12,13 …… Dielectric resonator 14,37 …… Intermediate frequency band pass filter 15 …… DC return circuit for diode 16,38 …… Ground conductor 25 …… Microstrip line 27 …… Overall noise figure, 28 …… Conversion loss 29 …… IF amplifier noise figure

Claims (1)

[Claims] 1. A frequency converter using a planar circuit,
The input signal frequency band pass filter by the dielectric resonator and the local oscillation frequency band pass filter by the dielectric resonator are arranged close to the transmission line to which the frequency conversion diode is connected, and the two filter The input signal and the local oscillation respectively input via the electromagnetic field coupling to the transmission line and applied to the diode, and both frequency difference signals are taken out from the diode, and the image impedance seen from the diode is A frequency converter characterized by being determined by the length of a transmission line.