JPS61146006A - Microwave power amplifier - Google Patents

Abstract

PURPOSE:To execute easily an adjustment without being influenced by an out- band characteristic of an isolator, etc., by providing a transmission line stub whose tip is opened, on at least one of an input matching circuit and an output matching circuit by making it adjacent to a transistor. CONSTITUTION:A transmission line stub 21 and 41 which become a 1/4 wavelength against a frequency of two times of a center frequency of an amplification band, and whose tip is opened are provided on the side being adjacent to a GaAs MOSFET3 of an input matching circuit 2 and an output matching circuit 4, and constituted so as to have a roughly constant impedance, irrespective of an out-band characteristic of an isolator 1 and 5 against the second higher harmonic. Even if a resonance to the second higher harmonic is generated in the isolators 1, 5, no ripple is generated in a frequency characteristic of a fundamental wave.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a microwave power amplifier using transistors.

[Conventional technology]

In recent years, advances in semiconductor technology have made it possible to conveniently use transistors for power amplification in microwaves, and they are used for a variety of purposes. For amplifiers where third-order cross-modulation distortion is a problem when multiple carrier waves are commonly amplified, it is desirable to use class iA amplifiers with low distortion transistors for linear operation, but there are restrictions on power consumption. In a microwave power amplifier installed on a satellite, etc., a monogallium arsenide barrier gate field effect transistor (hereinafter abbreviated as GaAa MES FET) is sometimes used in class AB operation in consideration of power efficiency. In this case, due to the operating conditions and the characteristics of the GaAs MES FET, high-order distortion of the third order or higher is not likely to occur, but a considerable amount of second-order distortion components will occur.

[Problems to be solved by the invention]

The second-order distortion bottom is the sum or twice the frequency of the amplified signal, and its frequency is greatly different from that of the fundamental wave to be amplified. Therefore, it can be easily removed by a filter, etc., but the amplification band For example, if non-reciprocal circuit elements such as isolators and circulators are connected to the input/output circuit, the characteristics of these circuit elements This resonance characteristic is often not guaranteed at frequencies outside the band, and often exhibits sharp resonance characteristics at specific frequencies outside the band.Such resonance characteristics occur at the frequency of the second harmonic of the amplified signal, I! If it exists in the band, the second harmonic generated by the amplification element will be strongly reflected by that frequency, for example, and will return to the amplification element and be converted back into the fundamental wave.
A rapid ripple-like change occurs in the characteristics of the amplification band.

In the case of this nib, conventional methods include replacing the isolator, shifting the resonant frequency by adjusting the matching circuit, and
? However, there is a problem in that unforeseen extra man-hours are required for adjustment, even if measures such as reducing the amount of water are taken individually.

The object of the invention is to eliminate this conventional problem and provide a microwave power amplifier that is not affected by out-of-band characteristics of an isolator and does not require extra man-hours for adjustment.

[Elaborate means of solving problems]

The microwave power amplifier of the present invention is a microwave power amplifier configured with an input matching circuit, a transistor, and an output matching circuit. The transmission line stub having an open end is provided adjacent to the transistor in at least one of the input matching circuit and the output matching circuit.

[Example J Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit configuration diagram of an embodiment of the invention, in which an input isolator 11 a manual matching circuit 2. Source grounded GaAs
MB2 FET3. It is composed of an output matching circuit 4 and an output isolator 5. 81, the input matching circuit 2 and the output matching circuit 3 are made of GaAs MES FE.
On the T3 K adjacent side Kd, transmission line stubs 21 and 41 with open ends are provided which have a quarter wavelength for a frequency twice the center frequency of the amplification band, and an isolator 1 is provided for the second harmonic. 15, which has an approximately constant impedance regardless of the out-of-band characteristics of 5 and 5. Each impedance transformation element 22.42 and parallel matching element 23.43 of the input and output matching circuits 2 and 4 handle the input/output load including the capacitive impedance exhibited by the transmission line stub 21°41 with respect to the frequency aIIc of the amplification band. It was selected as a measure to achieve consistency with the above. In the conventional circuit, if there is resonance for the second harmonic in the isolator 1.5 in the configuration shown in Fig. 1 without the transmission line stub 21.41, ripples will occur in the frequency characteristics of the fundamental wave as described above. However, if the configuration shown in the MB1 diagram is used, the wc2 high harmonic load seen from the transistor is almost constant and there is no sudden change due to resonance, so ripples may occur in the frequency characteristics of the fundamental wave. There is no effect, therefore, no extra adjustment is required.

In the above embodiment, isolators are connected to both the input and output, and transmission line stubs are provided to both the input and output matching circuits, but when the impedance for the second harmonic of either one is guaranteed, Similar effects can be obtained by providing transmission line stubs only on one side. In addition, in the above embodiment, the resonance for the second harmonic is explained as occurring in the isolator section, but when resonance occurs in a location other than the non-reciprocal circuit element such as the isolator (in terms of dimensions, it is considered that the resonance occurs in the matching circuit). The technical idea of the present invention can also be applied to cases in which this phenomenon occurs in F-fields used for shielding, and similar effects can be obtained. Furthermore, although the transistor in the embodiment shown in FIG. 1 is a source-grounded GaAs MESFET, silicon bipolar transistors may also be used in the low frequency microwave band, and the technical idea of the present invention can be similarly applied. Needless to say.

〔Effect of the invention〕

As described in detail above, the microwave power amplifier of the present invention has the effect of facilitating adjustment without being affected by the out-of-band characteristics of isolators or the like connected to the input/output.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram of an embodiment of the present invention, in which reference numbers 1 and 5 are isolators, 2 is an input matching circuit, and 3 is a gallium oxide semiconductor barrier gate field effect transistor (GaAs ME8 FET). 4 is an output matching circuit.

Claims (2)

[Claims] (1) In a microwave power amplifier configured with an input matching circuit, a transistor, and an output matching circuit, an open-ended transmission line has a quarter wavelength for a frequency twice the center frequency of the amplification band. A microwave power amplifier characterized in that a stub is provided adjacent to the transistor in at least one of the input matching circuit and the output matching circuit. (2) The transistor is a source-grounded gallium arsenide Schottky barrier gate field effect transistor used in class AB operation, and is connected to the input side of the input matching circuit provided with the transmission line stub or the output side of the output matching circuit. 2. The microwave power amplifier according to claim 1, further comprising a non-reciprocal circuit element connected thereto.