JPS6310801A - High frequency band-pass filter - Google Patents

Abstract

PURPOSE:To equivalently increase the sharpness Q of a filter by connecting an active element showing a negative resistance electrically to one or plural resonators in the resonance state so as to cancell the loss of the resonator. CONSTITUTION:With a resonator 21 at a first stege at the input side brought into the resonance state, an energy is supplied from an amplifier 5 showing a negative resistance. As a result, the loss in the resonator 21 is cancelled and the sharpness Q is increased equivalently. Since the increase in the sharpness Q is caused not only for the resonator 21 of the input side first stage combined with a positive feedback loop 6 but also for all resonators 22-24 coupled with the post stage of the resonator 21, the loss of all the resonators 21-24 is reduced. Although the power supply is required for the amplifier 5, the power supply to the amplifier 5 is less than the reduction in the power consumption of the filter 1 and then the power consumption for the entire transmitter combined with said filter 1 is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a distributed constant type high frequency band pass filter used mainly as a transmitting antenna filter.

<Prior Art> A transmitter is provided with an antenna filter in order to suppress unnecessary radiation.

FIG. 6 is a block diagram showing its configuration. As shown in the figure, an antenna filter 2° is connected to the output stage of a transmitter 1°, and an antenna 3° is connected to this antenna filter 2°. As the antenna filter 3°, a distributed constant type high frequency band pass filter using a dielectric coaxial resonator or a stripline resonator is used.

This high frequency band pass filter 3° usually includes a plurality of resonators 4°, . . . . In FIG. 3, each resonator 4° is a resonator with an electrical length of λ/2.

<Problems to be Solved by the Invention> By the way, distributed constant antenna filters have insertion loss, so for example, when a 5W high frequency signal is applied to an antenna filter with a 3dB insertion loss,
The antenna power is 2.5 W, and the difference between the input signal power and the antenna power of 2.5 W is consumed by the antenna filter. This is extremely inefficient when looking at the transmitter as a whole.

In particular, filters using stripline resonators have a low filter sharpness Q of the resonator (about several 10 to several 100 in the microwave region), resulting in a filter with a large insertion loss. When used as a filter, the overall efficiency of the transmitter becomes significantly lower.

To deal with this, it is possible to reduce the insertion loss by increasing the sharpness Q of the antenna filter, but in general, for filters using dielectric coaxial resonators or strip line resonators, the filter shape is The size and filter sharpness Q correspond to each other, and if an attempt is made to obtain a filter with a large sharpness Q, the shape will become large.

Therefore, in conventional high-frequency equipment such as transmitters, if you try to reduce power loss in the antenna filter, the overall shape becomes larger, and if you try to make the whole smaller,
There is a problem in that the power loss in the antenna filter increases, and this has been a bottleneck in downsizing high-frequency equipment.

The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to increase the sharpness Q of the filter and reduce the insertion loss X without increasing the size of the filter.

Means for Solving the Problems> By the way, the above-mentioned conventional problems are thought to be due to the fact that the antenna filter is a passive circuit.

Therefore, the present invention aims to achieve the above object based on this knowledge, and includes an active element that exhibits negative resistance when the resonator is in a resonant state, in one or more of the resonators. They were electrically coupled to form a high frequency band pass filter.

In the above configuration, when the resonator in which the active elements are combined is in a resonant state, energy is supplied from the active elements to the resonator, which cancels out the loss in the resonator and reduces the sharpness of the filter. The degree Q is equivalently increased.

<Example> Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 is a block diagram showing a circuit of a high frequency band pass filter according to the present invention. This high frequency band pass filter
is a four-stage filter with resonators 2. and 2. having an electrical length of λ/4. ．． 2. ．． 2. ．． 2. (hereinafter collectively referred to as 2). These resonators 2 have capacitances C, , C, , C3 coupled to each other at one end, and capacitances C to input terminal 3 in the first stage and to output terminal 4 in the final stage.
i, Co bonded. Further, the other end of each resonator 2 is open. Among these resonators 2, a positive feedback loop 6 including an amplifier 5 as an active element is formed at the open end of the first-stage resonator 21 at the input end. The positive feedback loop 6 is
It includes the amplifier 5 and the phase adjuster 7, both of which are connected to the resonators 2., . . . via gap capacitances C, C6. is connected to the open end of the

In the high frequency band pass filter 1 having the above configuration, when the first stage resonator 21 on the input side enters a resonant state, the amplifier 5 exhibits negative resistance, so that the amplifier 5 is connected to the resonator 2. energy is supplied to

As a result, the loss in the resonator 21 is canceled out, and the sharpness Q is equivalently increased.

Moreover, this improvement in sharpness Q is achieved not only in the first stage resonator 21 on the input side in which the positive feedback loop 6 is combined, but also in all the resonators 2. ~24
Since this occurs, the loss in all the resonators 21 to 24 is reduced.

Amplifier 5 requires power supply, but the amount of power supplied to amplifier 5 is small compared to the reduction in power consumption in filter 1. Therefore, when looking at the entire transmitter combined with filter 1, , power consumption is reduced.

As shown in this embodiment, when the amplifier 5 is combined with the input-side first-stage resonator 2 closest to the transmitter, the second-stage and subsequent resonators 2
．． 24 acts as a noise removal filter, the influence of noise from the amplifier 5 is not externally exposed.

The resonator 2 constituting the filter may be a dielectric coaxial resonator or a stripline resonator, and the number of stages of the resonator 2 may be single or plural.

FIG. 2 shows an example in which the present invention is implemented in a four-stage combline type stripline resonator. This stripline bandpass filter 11 includes a dielectric substrate 81. Four stages of stripline resonators 21 (211, 212, 213, 214) are provided on one main surface of the dielectric substrate 81.
) is formed. Each stripline resonator 21 is a resonator having an electrical length of λ/4, and one end is short-circuited to the ground electrode 91 and the other end is open. A ground electrode (not shown) is formed on the entire other main surface of the dielectric substrate 81, and is continuous with the ground electrode 91 on the front side through one end surface of the dielectric substrate 81. Among the strip line resonators 21, the first and third input stage resonators 21. ．． An amplifier 51.5 is connected to the open end of 213, respectively.
1 and phase adjustment strip lines 71, 71. ...
are coupled through the gap capacitance, and a positive feedback loop 61.
61 is formed. In addition, when there are multiple stages of stripline resonators 21 in this way, the stages of the stripline resonators 21 in which the positive feedback loop 61 is provided are not particularly limited to the stages shown in the figures.

FIG. 3 shows an example in which the present invention is implemented in a one-stage λ/2 stripline resonator. In this stripline bandpass filter 12, one λ/2 stripline resonator 22, an input stripline 152, and an output stripline 1 are provided on one main surface of the dielectric substrate 82.
62 is formed.

An input strip line 152 and an output strip line 162 are capacitively coupled to one end of the strip line resonator 22 . An amplifier 5 is connected to the open end of the resonator 22.
2 and phase adjustment strip lines 72, 72 are coupled via a gap capacitance to form a positive feedback loop 62.

FIG. 4 shows the present invention in one stage of λ/4 strip line: t
An example of implementation on I2@ vessel is shown. In this stripline bandpass filter 13, one end of the stripline resonator 23 is short-circuited to the ground electrode 93 on the dielectric substrate 83, and the other end is open. An input strip line 153 and an output strip line 154 are capacitively coupled to this open end. An amplifier 53 and a phase adjustment strip line 73, 73 are coupled to the open end of this strip line resonator 23 via a gap capacitance, forming a positive feedback loop 63.

In each of the above embodiments, the positive feedback loop of the amplifier is combined with the resonator by capacitive coupling, but the same effect as described above can be obtained even if the positive feedback loop is combined with the resonator by inductive coupling.

FIG. 5 shows an example in which an amplifier is inductively coupled to a one-stage λ/4 stripline resonator. The stripline bandpass filter 14 in this example has a λ/
It has four stripline resonators 24. An input strip line 154 and an output strip line 164 are capacitively coupled to the open end of the strip line resonator 24. The amplifier 54 and phase adjustment strip lines 74 and 74 are inductively coupled to the short-circuited end of the strip line resonator 24, forming a positive feedback loop 64.

In each of the above embodiments, only the case where the band-pass filter of the present invention is used as a transmitting antenna filter has been described, but the band-pass filter of the present invention can also be used as a receiving filter.

<Effects of the Invention> As described above, according to the present invention, when the resonator combined with active elements is in a resonant state, energy is supplied from the active elements to the resonator. losses are canceled out.

As a result, the sharpness Q of the filter can be equivalently increased, and when connected as an antenna filter to the output stage of a transmitter, the power consumption of the transmitter can be significantly reduced.

In this case, the space required for providing the active element is relatively small, and the conventional space for the filter can be used, so the filter does not become large. Therefore, power consumption can be reduced without increasing the size of the entire filter.

[Brief explanation of drawings]

1 to 5 relate to the present invention, and FIG. 1 is a circuit diagram;
FIG. 2 is a plan view of the first embodiment, FIG. 3 is a plan view of the second embodiment, FIG. 4 is a plan view of the third embodiment, and FIG. 5 is a plan view of the fourth embodiment. FIG. 6 is a block diagram of a conventional example. 1.11, 12, 13.14...Band pass filter,
2.21.22゜23.24...Stripline resonator, 5.51,52,53.54...Amplifier (active element), 6.61,62,63.64...Positive feedback loop .

Claims (1)

[Claims] (1) In a high-frequency band-pass filter that allows a high-frequency signal in a predetermined frequency band to pass through a single or multiple resonators, when one or more of the resonators is in a resonant state. A high frequency band pass filter characterized in that an active element exhibiting negative resistance is electrically coupled to the filter.