Communications: directive radio wave systems and devices (e.g. – Clutter elimination – Mti
Reexamination Certificate
2001-11-29
2003-02-25
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Clutter elimination
Mti
C342S194000, C342S102000
Reexamination Certificate
active
06525686
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a receiving/transmitting apparatus for radiating a predetermined signal and receiving a signal arriving as a response to the radiated signal and a radar equipment in which the receiving/transmitting apparatus is installed.
2. Description of the Related Art
In recent years, a technique for realizing sophisticated signal processing at a high speed and at a low price has been established and such signal processing has been widely applied to various electronic apparatuses and systems.
This signal processing technique has been increasingly applied to, for example, radio application equipments and navigation aids such as radar equipments, among the above-mentioned electronic apparatuses, as an indispensable element technique for achieving high performance and reliability under desirable environment conditions or for heightening added values as well as for realizing adaptability to severe demands for price reduction, downsizing, lightening, energy saving, and others.
FIG. 8
is a diagram showing a first structure example of a receiving/transmitting part of a radar equipment to which the signal processing technique is applied.
In
FIG. 8
, one output of a COHO oscillator
51
is connected to an input of a mixer
52
, and to a local-frequency input of the mixer
52
, one output of an STALO oscillator
53
is connected. An output of the mixer
52
is connected to a first aperture of a circulator
56
via a pulse modulator (SW)
54
and a power amplifier
55
which are connected in cascade. To a second aperture of the circulator
56
, a feeding point of an antenna
57
is connected, and a third aperture of the circulator
56
is connected to an input of the mixer
58
. To a local-frequency input of the mixer
58
, the other output of the STALO oscillator
53
is connected. An output of the mixer
58
is connected to an input of a quadrature demodulator
59
. To a carrier input of the quadrature demodulator
59
, the other output of the COHO oscillator
51
is connected and an output of the quadrature demodulator
59
is connected to an input of a not-shown signal processing part.
In the radar equipment as structured above (hereinafter referred to as a ‘first conventional example’), the COHO oscillator
51
constantly generates a reference signal with a predetermined frequency fc. The STALO oscillator
53
also generates a local-frequency signal with a predetermined frequency fs constantly.
The mixer
52
generates a transmitting signal with a frequency ft (=fc+fs) equal to the sum of the frequencies of the reference signal and the local-frequency signal. The pulse modulator
54
performs on-off keying of the transmitting signal at a predetermined duty factor to generate a transmission wave and radiates the transmission wave via the power amplifier
55
, the circulator
56
, and the antenna
57
.
A reflected wave reaching the antenna
57
from a target in response to the transmission wave is fed to the mixer
58
via the circulator
56
.
The mixer
58
converts the reflected wave to an intermediate frequency signal with a frequency equal to a difference fr (=ft−fs=fc) between a frequency of the reflected wave and the frequency of the local-frequency signal which is generated by the STALO oscillator
53
.
The quadrature demodulator
59
quadrature-demodulates the intermediate frequency signal according to the reference signal which is given by the COHO oscillator
51
to generate demodulation signals I, Q which are in quadrature.
The aforesaid signal processing part performs predetermined signal processing for the demodulation signals I, Q to realize, for example, improvement in SN ratio, MTI, and others.
Incidentally, in the process of the signal processing, as long as the COHO oscillator
51
and the STALO oscillator
53
constantly generate the aforesaid reference signal and the local-frequency signal respectively with desirable precision, phases of components of the reflected wave, which arrives from the target located in a fixed relative distance, relative to a phase of the reference signal do not vary (hereinafter, to satisfy this condition is simply referred to as ‘coherency’), and therefore, the improvement in the SN ratio and so on based on integrating processing and the like is achieved with high reliability.
FIG. 9
is a diagram showing a second structure example of a receiving/transmitting part of a radar equipment to which the signal processing technique is applied.
The radar equipment shown in
FIG. 9
is characterized in that:
a variable frequency oscillator
61
is provided to substitute for the COHO oscillator
51
;
a coupler
62
is provided to substitute for the mixer
52
;
neither the pulse modulator
54
nor the STALO oscillator
53
is provided; and
the power amplifier
55
has a control terminal to which a later-described control signal is given together with a control input of the variable frequency oscillator
61
.
Note that the same numerals and symbols are used to designate elements having the same functions as those of the elements shown in FIG.
8
and explanations thereof are omitted here.
In the radar equipment as structured above (hereinafter referred to as a ‘second conventional example’), the variable frequency oscillator
61
alternately generates two signals having the same frequencies as those of the aforesaid transmitting signal and the local-frequency signal respectively (hereinafter referred to as a ‘transmission wave signal’ and a ‘receiving local-frequency signal’ respectively) according to logical values of a binary control signal which gives the aforesaid duty factor.
Note that periods during which the transmission wave signal and the receiving local-frequency signal are generated by the variable frequency oscillator
61
are hereinafter referred to as ‘transmitting time’ and ‘receiving time’ respectively for simplification.
The coupler
62
processes the following based on a difference between the frequency of the transmission wave signal and the frequency of the receiving local-frequency signal which are thus generated by the variable frequency oscillator
61
.
to send the transmission wave signal to the power amplifier
55
but prevent its feeding to the mixer
58
to send the receiving local-frequency signal to the mixer
58
but prevent its feeding to the power amplifier
55
The power amplifier
55
amplifies the transmission wave signal to be fed via the coupler
62
within the transmitting time which is given as the logical value of the aforesaid control signal and radiates the transmission wave signal as a transmission wave via the circulator
56
and the antenna
57
.
The mixer
58
generates an intermediate frequency signal with a frequency equal to a difference between the frequency of the reflected wave, which reaches the antenna
57
during the above receiving time and is fed thereto via the circulator
56
, and the frequency of the receiving local-frequency signal, which is fed thereto via the coupler
62
during the receiving time, and feeds the intermediate frequency signal to the quadrature demodulator
59
.
In other words, the variable frequency oscillator
61
is commonly used for generating the receiving local-frequency signal during the receiving time and generating the transmission wave signal during the transmitting time while securing isolation between a transmitting part and a receiving part.
Therefore, in the second conventional example, where neither the pulse modulator
54
nor the STALO oscillator
53
shown in
FIG. 8
is provided, the hardware structure is simplified compared with that in the first conventional example.
Incidentally, the same processing as in the first conventional example is performed by the quadrature demodulator
59
and the signal processing part which is provided on a subsequent stage of the quadrature demodulator
59
and therefore, explanations thereof are omitted here.
Note that the reference signal and the local-frequency signal are constantly generated in the above-describ
Haruta Tomohiro
Miyoshi Akito
Fujitsu Limited
Katten Muchin Zavis & Rosenman
Sotomayor John B.
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