JPH0583147A - Low noise amplifier - Google Patents

Abstract

PURPOSE:To obtain the low noise amplifier of small size not attended with an increase in a transmission loss whose connection to a pre-stage isolator without use of a connector and to absorb an undesired signal at the outside of a band of a resonance frequency of a filter with respect to the configuration of the low noise amplifier(LNA) used for a microwave band receiver. CONSTITUTION:A filter 1 and a LNA2 are contained in a same case 3 and the LNA2 is connected directly to a coupling line 12 of an output section of the filter 1. Then a tip open stub whose total electric length is equal to nearly 3lambdag/4 equivalent to a resonance frequency of the filter 1 is provided to a coupling line 12 of the output section of the filter 1 and a resistor whose electric length is equal to nearly lambdag/4 equivalent to the resonance frequency of the filter 1 is provided to a position apart from the electric length equal to nearly lambdag/2 equivalent to the resonance frequency of the filter 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of a low noise amplifier used in the front stage of a microwave band receiver.

[0002]

2. Description of the Related Art Conventional low noise amplifiers
ier, hereafter referred to as LNA) was a so-called modular structure that was individually housed in a case and tested and adjusted as a single unit. In the receiver, it is input to the LNA after passing through the filter that passes only the signal in the required frequency band of the received signal, but the filter is susceptible to external loads (transmission bandwidth deviation, transmission loss fluctuation, (For example, impedance variation), after the filter, as in the configuration of the conventional example shown in FIG.
In front of the LNA, there was inserted a so-called isolator that absorbs the reflected wave and passes only the signal wave in the traveling direction to maintain a constant impedance. This isolator also helped to make the LNA less susceptible to the effects of changes in external impedance (noise figure fluctuations, amplification gain fluctuations, etc.).

[0003]

However, the conventional low noise amplifier LNA shown in FIG. 3 has a large size because it is connected as a separate module with the isolator in the preceding stage by means of a connector. However, there were problems such as increased transmission loss. An object of the present invention is to realize a low noise amplifier which is compact in shape and does not cause an increase in transmission loss, as in the conventional example, because the connection with the isolator in the preceding stage does not depend on the connector.

[0004]

Considering the configuration of the low noise amplifier of the present invention for achieving this object, in general, a low noise amplifier LNA has a load impedance when its input side impedance is 50Ω. For example, the circuit is configured and adjusted in a balanced type so that is optimal, but normally the impedance seen from the input side of the LNA is
The characteristic impedance is largely deviated from 50Ω.
The filter is generally adjusted so that its characteristics can be obtained when its input and output terminals are connected with a characteristic impedance of 50Ω. Therefore, if the filter and LNA are connected without the isolator, not only the input impedance of the LNA affects the filter and the transmission loss increases due to impedance mismatch, but the impedance seen from the input side of the filter is The impedance does not become 50 Ω. Therefore, in the past, an isolator was necessary at all. However, since the transmission loss of the isolator itself is large and cannot be ignored, it is indispensable to eliminate the isolator to reduce the transmission loss in the present invention, and this also contributes to downsizing and cost reduction of the LNA. Paying attention to this, the input impedance of the LNA deviates from the characteristic impedance of 50Ω, but the filter is directly connected to the LNA. Then, considering adjusting the filter and LNA together to obtain their respective characteristics,
It is configured as in the principle diagram of. That is, first, as a claim 1 for the purpose of downsizing and cost reduction, the filter (1) and the LNA
(2) and (2) are housed in the same case (3), and a low noise amplifier is constructed so that the LNA (2) is directly connected to the coupling line (12) of the output part of the filter (1). Next, as a claim 2 for the purpose of absorbing an unnecessary signal outside the band of the resonance frequency λg of the filter (1), in the low noise amplifier of the claim 1, for coupling the output part of the filter (1) The total electrical length of the line (12) is about the resonance frequency λg of the filter (1).
Open-ended stub (13) equal to 3/4 (3λg / 4) and the stub
The electrical length from the open end of (13) is equal to about 1/4 (λg / 4) of the resonance frequency λg of the filter, and the electrical length from the short-circuited end of the other end is about 1 of the resonance frequency λg of the filter. The resistor 14 is provided at a position equal to / 2 (λg / 2).
Next, as a claim 3 for the purpose of making it possible to confirm the characteristics of the filter (1) and the LNA (2), in the low noise amplifier of claim 1, the entire electrical length of the low noise amplifier is A detachable monitor terminal (15) is provided at the open end of the open-end stub (13) equal to about 3/4 of the resonance wavelength.

[0005]

In the claim 1 of the present invention, the filter (1) and the LNA are
Since (2) and (2) are housed in the same case (3) and the LNA (2) is directly connected to the coupling line (12) at the output of the filter (1), the overall size and cost can be reduced. The purpose is achieved. And in claim 2, in the low noise amplifier of claim 1,
The total electrical length of the output line of the filter (1) from the coupled line (12) is about 3/4 (3) of the resonance frequency λg of the filter (1).
open-ended stub (13) equal to λg / 4) and its electrical length from the open end of the stub (13) to the resonance frequency λg of the filter.
Of the resistor (14) at a position equal to about 1/4 (λg / 4) of the filter and its electrical length from the short-circuited end of the other end to about 1/2 (λg / 2) of the resonance frequency λg of the filter. Therefore, the purpose of absorbing unnecessary signals outside the band of the resonance frequency λg of the filter (1) is achieved. According to a third aspect of the present invention, in the low noise amplifier of the first aspect, a detachable monitor terminal is provided at the open end of the open-end stub (13) whose total electrical length is equal to about 3λg / 4 of the resonance wavelength of the filter. Since it has (15), the filter (1)
And the purpose of being able to identify the characteristics of LNA (2) is achieved.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The principle diagram of FIG. 1 is also a diagram showing the configuration of a low noise amplifier according to an embodiment of the present invention, in which a filter 1 and an LNA 2 are housed in the same case 3. A dielectric resonator is used for the filter 1, and its input and output are coupled by each coupling pattern provided on the coupling substrates 11 and 12. The coupling substrates 11 and 12 are dielectric substrates on which stripline patterns are formed. The LNA 2 has a module completed in advance fixed to the housing case 3 with screws, and is connected to the coupling board 12 on the input side and the transmission board on the output side. A screw for adjusting the coupling of the filter 1 is provided on the side surface of the storage case 3, and a screw for adjusting the frequency is provided on the lid. Fix the lid to storage case 3 with screws and adjust the frequency adjustment screw. Adjust the passband width so that the impedance seen from the input side becomes the characteristic impedance of 50Ω, and while watching the output waveform. 2 (a) shows a coupling pattern provided on the coupling substrate 12, a λg / 2 stub with an open end having an electrical length of λg / 2 with respect to the resonance frequency λg of the filter, and a terminating resistor 14 connected to it. It is shown that the terminating resistor is arranged so as to be coupled to the dielectric resonator with an electrical length of λg / 4. This improves the out-of-band impedance (LNA 2
Therefore, the disturbance of the amplitude characteristic outside the band of LNA2 and unnecessary oscillation can be suppressed and reduced. Figure 2 (b) shows a stub with an open tip of 3λg / 4 electrical length from the point of coupling with the dielectric resonator.
13 and a monitor terminal 15 at the open end of the filter
It is designed to monitor each performance of 1 and LNA 2, and after roughly adjusting beforehand with this monitor terminal 15,
By removing this monitor terminal 15 and leaving the stub tip open, it is shown that the adjustment of each performance of the filter 1 and LNA 2 can be facilitated. Further, the cut in the casing 3 for housing a filter 1 and the LNA 2 in the low-noise amplifier, elements 1 _1, 1 ₂ which constitutes the filter 1, the width of the relative input and output direction of signals case 3 the passage of signals Since it is placed in the cut-off waveguide of the size to turn off, the storage case
Unwanted wave leakage from 3 is prevented. Also, between the lid of LNA2 and the lid of storage case 3 in the low noise amplifier,
Since the electrical short-circuit portion 4 made of a conductor is provided, the size of the storage case 3 can be reduced and unnecessary resonance can be suppressed.

[0007]

As described above, according to the present invention, the conventional isolator is removed and the filter and the LNA are directly connected and housed in the same case. Low noise can be realized. Further, by adding a resistor for absorbing unnecessary waves outside the band to the coupling substrate, it is possible to effectively suppress the disturbance of the amplitude characteristic and the oscillation of the low noise amplifier outside the band. Also, by utilizing the coupled line of 3λg / 4 electric length, it becomes possible to monitor each performance of the filter and LNA, and the effect of facilitating the adjustment can be obtained.

[Brief description of drawings]

FIG. 1 is a principle diagram showing a basic configuration of a low noise amplifier of the present invention.

FIG. 2 shows a filter of a low noise amplifier according to an embodiment of the present invention.
Pattern diagram of substrate for coupling with LNA

FIG. 3 is a diagram showing a configuration of a conventional low noise amplifier.

[Explanation of symbols]

1 is a filter, 2 is an LNA, 3 is a storage case, 4 is an electrical short circuit part by a conductor, 11 and 12 are coupling substrates, and 13 is 3λg /
4 Electrical length open stub, 14 is a resistor, and 15 is a monitor terminal.

Claims (3)

[Claims] 1. A case (3) accommodating a filter (1) on the input side and a low noise amplifier (2) on the output side, the case, the filter and the low noise amplifier are mutually connected to a line board ( 1
A low noise amplifier, characterized in that the coupling of the entire case can be adjusted by adjusting a coupling adjusting screw (14) provided on the case (3). 2. In the line substrate (12) of the low noise amplifier, the entire electrical length of the output from the coupling line (12) of the filter (1) is about 3 times the resonance frequency (λg) of the filter. /
An open-end stub (13) equal to 4 (3λg / 4) and the stub
The electrical length from the open end of (13) is equal to about 1/4 (λg / 4) of the resonance frequency of the filter, and the electrical length from the short-circuit end at the other end is about 1/2 of the resonance frequency of the filter. The low noise amplifier according to claim 1, further comprising a resistor (14) at a position equal to (λg / 2). 3. In the line substrate (12) of the low noise amplifier, the entire electrical length of the line substrate (12) is the resonance wavelength (λ) of the filter.
2. A low noise amplifier according to claim 1, further comprising a detachable monitor terminal (15) at the open end of the open-end stub (13) which is equal to about 3/4 of g).