JPH01141409A - Filter - Google Patents

Abstract

PURPOSE:To obtain a filter to be miniaturized and simplified at low cost by executing two functions of a filter for removing a third higher harmonic and a pi/2 phase device by means of one circuit. CONSTITUTION:The circuit is composed of two L elements and an opening line with a length(l) and a characteristic impedance W, and an inductance L of the L elements and the length(l) and characteristic impedance W of the opening line are obtained from equations I and II. Here, a Z0 is the characteristic impedance of the line. Thus, the filter for removing a third higher harmonic having a pi/2 phase can be composed. A filter 24 for removing the third higher harmonic having the pi/2 phase is arranged between a band elimination filter 22 for an f1 and a band elimination filter 23 for an f2 to follow a band-pass filter 21 for an f0. Thus, the number of parts can be reduced, and an attainment to cause the title filter to be miniaturized at low cost can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a filter etc. that prevents spurious radiation contained in one transmitted signal in a radio device or the like.

(Prior art) Generally, when transmitting a signal from a radio, if the target frequency is fo, some radio waves emitted from the transmitter through the antenna include radio waves that cause interference (radio waves other than fe). These unnecessary radio waves are called spurious emissions.

In order to prevent or reduce this spurious radiation, a bandpass filter is usually inserted between the transmitter and the antenna.

Ideally, this band-pass filter should only pass fo, and as a band-pass filter of this type,
Typically, a coaxial resonator with 174 wavelengths was used.

However, this bandpass filter consisting of a 174-wavelength coaxial resonant base was not able to ideally pass only f and remove everything else. This will be explained below.

This 174-wavelength coaxial resonator generates even harmonics (2f,
, 4f, ) can be obtained, but it is difficult to remove odd harmonics (3f@). Furthermore, spurious waves other than harmonics f1. The amount of attenuation was also insufficient for f. The attenuation characteristics of the bandpass filter consisting of this 174-wavelength coaxial resonator are shown by the solid line in FIG. 3, where fl.

Desired attenuation amounts at f2.2f, 3f, 4f are shown at points a, b, c, d, and e in FIG. 3, respectively.

As shown in Fig. 3, a bandpass filter consisting of a 174-wavelength coaxial resonator has the second harmonic, 2f, and the fourth harmonic.
The desired amount of attenuation can be satisfied for the harmonic 4f, but the attenuation cannot satisfy the desired value for fi, f, which is a spurious wave other than the harmonic, and 3f, which is the third harmonic. . Therefore, conventionally, f,,f,,3
In order to compensate for insufficient attenuation in f, band elimination filters were added for each frequency.

A block diagram of this conventional example is shown in FIG.

Conventionally, f, a band pass filter (B P F) 4
1 and band elimination filter for f1 (BEF
)42. A total of four filters are used, including three BEFs: band elimination filters 44 and 3f for f, and band elimination filter 45 for It was configured by arranging a phase circuit 43. This π/2 phase circuit required connecting BEFs other than harmonics. In this way, by inserting a band elimination filter for each frequency, the amount of attenuation shown by the dotted line in FIG. 3 was obtained, and the desired amount of attenuation was satisfied.

(Problems to be Solved by the Invention) Conventional bandpass filters use a combination of a plurality of filters and use a large number of parts, and there has been a desire for the filter as a whole to be smaller and cheaper.

In view of the above, the present invention achieves miniaturization and cost reduction of a filter.

(Means for Solving the Problems) The present invention uses a circuit that achieves the two functions of a third harmonic removal filter and a π/2 phase shifter in one circuit.

(Operation) To explain the present invention, first, the π/2 phase circuit is
Generally, a 1/4 wavelength coaxial line is used, and a circuit diagram of this line is shown in FIG. Since this 1/4 wavelength coaxial line has a long line length, one possible way to shorten this is to use the circuit shown in FIG. 6. As a result of our study to add a function as a third harmonic removal filter to the circuit shown in FIG. 6, we were able to achieve this with the circuit shown in FIG.

The circuit shown in FIG. 1 is composed of two L elements and an open line having a length Ω and a characteristic impedance W. The inductance L of the element, the length Ω of the open line, and the characteristic impedance W are determined by the following equations.

First, in order to shorten the line length in FIG. 5, the inductance L and capacitance C in FIG. 6 are given by the following equations.

c=-(1) ωZ6 1l L=-(2) ω Z,=R(R is input/output impedance, Z is,
(Characteristic impedance of the line) Next, based on the correspondence between Fig. 6 and Fig. 1.

W λ Furthermore, in order to have the attenuation characteristics as shown in Fig. 7, (λ is the wavelength of f), and from equations (3) and (4), we have f=f, Substituting equation (1) in , we get:

An L element with an inductance L given by the above formula,
Length 2. From an open line with characteristic impedance W, π/2
A third harmonic removal filter having a phase could be constructed.

(Example) As an example of the present invention, f o =100 MHz,
A filter was constructed for Zo = 50Ω. In this example, from equations (2), (6), and (4), L = 0
．． 0796 μH W = 28.9 Ω Q = 50 am, and according to this value, π/
A third harmonic removal filter having two phases was constructed.

This circuit was formed by filling ceramics with a dielectric constant of 5r=25. Therefore, when calculated using equation (4), Ω is 250 mm (in vacuum), but due to the effect of Er, it becomes 50 mm.
It has been shortened to m. As shown in the block diagram shown in FIG. 2, the third harmonic removal filter 24 having the π/2 phase is connected to
It is placed between the i band elimination filter 22 and the f2 band elimination filter 23. The filter according to this embodiment of the present invention had an attenuation amount equivalent to that of the conventional filter (shown in FIG. 4). In other words,
The present invention can reduce the number of parts while maintaining attenuation characteristics equivalent to those of conventional filters, thereby achieving miniaturization and cost reduction.

(Effects of the Invention) In the present invention, the π/2 phase circuit itself has the function of a third harmonic removal filter, and the entire filter can be made smaller, simpler, and less expensive. It is extremely useful for industry.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a third harmonic removal filter having a π/2 phase according to an embodiment of the present invention, and FIG.
FIG. 3 is a block diagram of an embodiment according to the present invention, and FIG.
FIG. 4 is a block diagram of a conventional filter, and FIGS. 5 and 6 are attenuation characteristic diagrams of the filter.
FIG. 7 is a circuit diagram of a phase circuit, and FIG. 7 is an attenuation characteristic diagram of a third harmonic removal filter. Book-1

Claims (1)

[Claims] A filter characterized by using a circuit that achieves two functions of a third harmonic removal filter and a π/2 phase shifter in one circuit.