Microwave mixing circuit and down-converter

Details Microwave mixing circuit and down-converter Microwave mixing circuit and down-converter

1998-09-24

2001-01-23

Kuntz, Curtis A. (Department: 2743)

Telecommunications

Receiver or analog modulated signal frequency converter

Frequency modifying or conversion

C455S318000, C455S333000

Reexamination Certificate

active

06178319

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a microwave mixing circuit and a down-converter incorporating the same for receiving satellite broadcasting and communication via broadcasting satellites and communication satellites.
BACKGROUND OF THE INVENTION
There are increasing occasions for ordinary households to directly receive a plurality of satellite broadcastings in recent years, as satellite broadcastings have come to a stage of being wide spread and communication satellite broadcastings in digital signal have since started using commercial communication satellites. With this trend, there is an increasing demand for reduction in both size and cost of antennas for receiving the broadcastings. In case of the communication satellite broadcastings, receiving antennas often incorporate therein a low-noise down-converter having a polarization selecting function since they are multi-channel broadcastings by utilizing electromagnetic waves of different polarizations (e.g. horizontally polarized waves and vertically polarized waves) of same frequency for a reason of efficient use of the frequencies.
A microwave mixing circuitry and an intermediate frequency amplifier having polarization selecting function of the prior art are described hereinafter by referring to FIG.
5
.
Both horizontally and vertically polarized microwave signals (e.g. signals in a frequency band of 12 GHz) input to microwave signal input terminals
101
and
102
are converted into intermediate frequency signals of 1 GHz in Schottky barrier diodes (hereinafter referred to as “SBD”)
148
and
149
for frequency conversion connected to microwave strip transmission lines (hereinafter referred to as “MSL”)
106
and
107
by being mixed respectively with local oscillation signals (e.g. signals of 11.2 GHz) supplied from a local oscillator
103
via band-pass filters (hereinafter referred to as “BPF”)
104
and
105
.
Here, a frequency conversion loss in the SBD's
148
and
149
increases in case that an output of the local oscillation signal supplied by the local oscillator
103
is small. The SBD's
148
and
149
are provided with bias currents in the forward direction in order to prevent an increase of the frequency conversion loss. These bias currents are supplied from bias terminals
110
and
111
through connections with anodes of the SBD's
148
and
149
.
The intermediate frequency signals that have passed through lowpass filters (hereinafter referred to as “LPF”)
112
and
113
, which allow the intermediate frequency signals to pass through, further pass through PIN diodes
138
and
139
after having amplified by intermediate frequency amplifiers
134
,
135
,
136
and
137
.
Current supply terminals of the intermediate frequency amplifiers
134
and
135
and an anode of the PIN diode
138
are connected with a collector of a transistor
142
through an input signal selection control terminal (hereinafter referred to as “polarization selection control terminal”)
146
for selecting between input signals of horizontally polarized waves and vertically polarized waves.
Likewise, current supply terminals of the intermediate frequency amplifiers
136
and
137
and an anode of the PIN diode
139
are connected with an emitter of a transistor
143
through a polarization selection control terminal
147
.
The microwave mixing circuitry is supplied with a polarization selection signal (e.g. a D.C. voltage of either 11 V or 15 V) from the outside through an intermediate frequency signal output terminal
145
.
A comparator
144
outputs a D.C. signal of different values in response to the polarization selection signal.
In the event the polarization selection signal is 11 V, the transistor
142
turns on and the transistor
143
turns off simultaneously. As a consequence, an electrical potential of the polarization selection control terminal
146
increases whereas that of the control terminal
147
decreases.
On the other hand, in the event the polarization selection signal is 15 V, the transistor
143
turns on and the transistor
142
turns off simultaneously. Hence, the electrical potential of the control terminal
147
increases whereas that of the control terminal
146
decreases.
In case the polarization selection signal is 11 V, the intermediate frequency amplifiers
134
and
135
and the PIN diode
138
turns on and the intermediate frequency amplifiers
136
and
137
and the PIN diode
139
turns off, so that intermediate frequency amplifiers
140
and
141
are supplied with an intermediate frequency signal corresponding to the horizontally polarized microwave signal input through the microwave signal input terminal
101
, and the signal is output from the intermediate frequency signal output terminal
145
after being amplified to a desired magnitude.
In the same way, if the polarization selection signal is 15 V, the intermediate frequency amplifiers
134
and
135
and the PIN diode
138
turns off and the intermediate frequency amplifiers
136
and
137
and the PIN diode
139
turns on, so that intermediate frequency amplifiers
140
and
141
are supplied with an intermediate frequency signal corresponding to the vertically polarized microwave signal input through the microwave signal input terminal
102
, and the signal is output from the intermediate frequency signal output terminal
145
after being amplified to a desired magnitude.
With this structure of the prior art, however, it is quite difficult to reduce the size as is also inimical to the cost reduction because it requires the intermediate frequency amplifiers
134
,
135
,
136
and
137
and the PIN diodes
138
and
139
responsive to the microwave signal input terminals
101
and
102
to which two different polarized waves are input.
SUMMARY OF THE INVENTION
A microwave mixing circuitry having a plurality of microwave signal input terminals, a local oscillator for outputting a local oscillation signal for the purpose of generating an intermediate frequency signal from microwave signal input by microwave signal input terminals, a plurality of field effect transistors (“FET”) for converting frequency, of which gates are input with the microwave signal input from microwave signal input terminals, and of which drains are input with an output of local oscillator, a plurality of gate voltage control circuitries for controlling gate voltages of FET's thereby causing one of FET's to perform nonlinear operation while turning off the another of FET's at the same time, and an intermediate frequency signal output terminal for outputting the intermediate frequency signal produced by the nonlinear operation of one of the FET's.
The microwave mixing circuitry of the present invention is able to select one microwave signal among a plurality of different signals and convert it into intermediate frequency signal by controlling the gate voltages of the FET's for converting frequency with the gate voltage control circuitries.


REFERENCES:
patent: 4509198 (1985-04-01), Nagatomi
patent: 5584064 (1996-12-01), Nakamura
patent: 0 523 770 A1 (1992-06-01), None
patent: 0 759 656 A1 (1997-02-01), None
patent: 05022248 (1993-01-01), None
patent: 5-167352 (1993-07-01), None
patent: 7-211969 (1995-08-01), None
patent: 8-45741 (1996-02-01), None
patent: 9-121177 (1997-05-01), None

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