JPS6224963Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a microwave filter that outputs a double wave of a fundamental wave, such as a microwave mixer or a frequency multiplier circuit.

Conventionally, this type of microwave filter has the configuration shown in FIGS. 1a and 1b.

The structure shown in Fig. 1a has the disadvantage that the pass band becomes extremely narrow, while the structure shown in Fig. 1b requires a large number of filter stages in order to obtain good characteristics. The drawback was that it became complicated.

An object of the present invention is to eliminate these drawbacks and provide a microwave filter that has a simple structure and provides good pass and block characteristics.

The present invention consists of a directional coupler with an output phase difference of substantially 90 degrees and a power distribution ratio of 1/2, a matched resistive load connected between the input and output terminals of this directional coupler and ground, and It consists of a transmission line connected in parallel with a resistive load, and the transmission line is open to microwave frequencies that are odd multiples of 1/4 of the wavelength at the input and output ends of the directional coupler, and is even multiples of the wavelength. The microwave filter has an electrical length that causes a short circuit at the microwave frequency.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 2 is a configuration diagram of an embodiment of the present invention. That is, a directional coupler 1 with an output phase difference of 90° and a power distribution ratio of 1/2, a transmission line 6 of a predetermined length and a resistive load 7 are connected in parallel between the terminals 3 and 4 of this directional coupler 1 and the ground. It consists of: With this configuration, among the microwave signals incident on the input terminal 2, signals of a frequency such that the electrical length of the transmission line 6 is an integral multiple of 1/2 of the wavelength can be detected by short-circuiting the impedance of the transmission line 6 at the terminals 3 and 4. becomes. Therefore, the signal is totally reflected at terminals 3 and 4 and appears at output terminal 5. Furthermore, for a signal at a frequency where the electrical length of the transmission line 6 is an odd multiple of 1/4 of the wavelength, the impedance of the transmission line 6 at the terminals 3 and 4 becomes open, so this signal is absorbed by the resistive load 7 and output. It does not appear on terminal 5. At this time, by setting the center frequency of the directional coupler 1 to the passband frequency, loss in the passband can be reduced. As such a directional coupler 1, for example, the one described in Japanese Utility Model Application No. 53-63087 can be applied.

FIG. 3 shows a characteristic diagram of an example in which the embodiment of the present invention is constructed using microstrip lines. This filter has a directional coupler with a length of λ/4 (2.35 mm) at 12 GHz on an alumina ceramic substrate (dielectric constant 10.1), and a directional coupler with a length of λ/2 (4.7 mm) on both ends of this directional coupler. The microstrip line constitutes a very small filter. In this case, the passband frequency is 12GHz and the stopband frequency is
6GHz, good VSWR in the stopband and passband, and a wide passband width. Furthermore, the filter in this embodiment can be made compact by being constructed with microstrip lines, and can be applied particularly as a filter in a microwave integrated circuit over a wide frequency range.

[Brief explanation of the drawing]

Figures 1a and b are configuration diagrams of conventional filters;
The figure is a configuration diagram of an embodiment of the present invention, and FIG. 3 is an electrical characteristic diagram of the embodiment of the present invention. In the figure, 1... Directional coupler with output phase difference of 90° and power distribution ratio 1/2, 2... Input terminal, 3, 4... Output terminal of directional coupler 1, 5... Output terminal, 6... ...Transmission line, 7...Resistive load.

Claims (1)

[Scope of utility model registration request] The output phase difference is essentially 90 degrees and the power distribution ratio is 1/
2, a matching resistive load connected between the input/output end of the directional coupler and ground, and a transmission line connected in parallel with the resistive load, and the transmission line is connected to the It is characterized by having an electrical length at the input/output end of the directional coupler that is open to microwave frequencies that are odd multiples of 1/4 of the wavelength and short-circuited to microwave frequencies that are even multiples of the wavelength. microwave filter.