Communications: radio wave antennas – Antennas – High frequency type loops
Reexamination Certificate
2002-04-01
2003-09-02
Phan, Tho (Department: 2821)
Communications: radio wave antennas
Antennas
High frequency type loops
C343S701000, C343S742000, C343S876000, C331S016000, C333S103000
Reexamination Certificate
active
06614403
ABSTRACT:
RELATED APPLICATIONS
(Not Applicable)
FEDERALLY SPONSORED RESEARCH
(Not Applicable)
BACKGROUND OF THE INVENTION
The present invention relates to radio type systems and, more particularly, to improved radiation synthesizer systems enabling efficient use of small high-Q antennas by active control of energy transfer back and forth between an antenna reactance and a storage reactance.
The theory and implementation of Synthesizer Radiating Systems and Methods are described in U.S. Pat. No. 5,402,133 of that title as issued to the present inventor on Mar. 28, 1995. Further aspects are described in U.S. Pat. 6,229,494, titled Radiation Synthesizer Systems and Methods, as issued to the present inventor on May 8, 2001. These patents (“the '133 patent” and “the '494 patent”) are hereby incorporated by reference.
A basic radiation synthesizer circuit, as described in the '133 patent, which combines transfer circuits in both directions using two switches is shown in
FIG. 1
a
. This circuit functions as an active loop antenna where the loop antenna L is the high Q inductive load and a capacitor C is used as the storage reactor. The
FIG. 1
a
circuit uses two RF type switching transistors, shown as switches RC and DC, for rate and direction control, respectively. Because the devices are operated in a switch mode, efficient operation is obtained since, in theory, no instantaneous power is ever dissipated by such devices. A slower switching device, shown as power control switch PC, can be used to add energy to the circuit from the power supply as energy is radiated. The voltage and current sensor terminals VS and CS, respectively, are used to monitor and calculate the total amount of stored energy at any instant in time, while a feedback control circuit is used to maintain the total energy at a preset value through use of the power control switch PC.
In the
FIG. 1
a
circuit, when the direction control switch is open, energy can be transferred from current through the inductor L to voltage across the capacitor C, as illustrated by the L to C energy transfer diagram of
FIG. 1
b
. With the rate control switch closed, current flows from ground, through diode D
1
and L, and back to ground through the rate control switch RC. In the absence of circuit losses, the current would continue to flow indefinitely. When the rate control switch RC is opened, the inductor current, which must remain continuous, flows through diode D
2
and charges up the capacitor C. The rate at which C charges up is determined by the switch open duty cycle of the switch RC. The capacitor will charge up at the maximum rate when the switch is continuously open. The charging time constant is directly proportional to the switch open duty cycle of the rate control switch RC.
When the direction control switch DC of
FIG. 1
a
is closed, energy can be transferred from voltage across the capacitor to current through the inductor, as shown in the C to L energy transfer diagram of
FIG. 1
c
. Diode D
1
is always back biased and is, therefore, out of the circuit. When the rate control switch RC is closed, the capacitor C will discharge through L, gradually building up the current through L. If the rate control switch is opened, the capacitor will maintain its voltage while the inductor current flows in a loop through diode D
2
. In this C to L direction transfer mode, the rate is controlled by the switch closure duty cycle of switch RC. The maximum rate of energy transfer occurs when the switch RC is continuously closed. Its operation is the inverse of that in the other direction transfer mode (L to C).
It should be noted that, in either direction, charge or discharge is exponential. Therefore, the rate of voltage or current rise is not constant for a given rate control duty cycle. In order to maintain a constant rate of charging (ramp in voltage or current), it is necessary to appropriately modulate the duty cycle as charging progresses. Duty cycle determinations and other aspects of operation and control of radiation synthesizer systems are discussed at length in the '133 patent (in which
FIGS. 1
a
,
1
b
and
1
c
referred to above appear as FIGS. 8
a
, 8
b
and 8
c
).
In theory, since the power which is not radiated is transferred back and forth rather than being dissipated, lossless operation is possible. However, as recognized in the '133 patent losses are relevant in high frequency switching operations, particularly as a result of the practical presence of ON resistance of switch devices and inherent capacitance associated with switch control terminals. While such device properties are associated with very small losses of stored energy each time a switch is closed, aggregate losses can become significant as high switching frequencies are employed. In addition, if small loop antennas are to be employed, for example, antenna impedance may be higher than basic switching circuit impedance levels, necessitating use of impedance matching circuits which may have less than optimum operating characteristics.
The basic radiation synthesizer circuit discussed above can be reduced to the simplified ideal model shown in FIG.
2
. This model replaces the diodes in the basic circuit by ideal switches, and provides push-pull operation (current can flow in either direction through the loop antenna). The push-pull, or bipolar circuit, is more efficient than the single-ended circuit by a factor of
2
(3 dB). The
FIG. 2
system includes four power switch devices comprising a switching circuit pursuant to the invention. The
FIG. 2
system includes loop antenna
12
, storage capacitor
14
and power switch devices
21
,
22
,
23
and
24
, which will also be referred to as switch devices S
1
, S
2
, S
3
and S
4
, respectively. Three possible states exist: linear charging of inductor current, linear discharging, and constant current. It is possible to synthesize any waveform using this circuit, with waveform fidelity dependent on sampling speed.
A more complete block diagram of a radiation synthesizer system is shown in FIG.
3
. Since each pair of switch devices (i.e., S
1
/S
2
and S
3
/S
4
) is always switched in a coordinated manner, and each pair is antiphase, a common control circuit C is used for each pair. Each control circuit C implements sequential switching by delaying the appropriate short circuit transition until after an open circuit transition has been made. This process occurs for each change of state in input driver logic signals provided at the input to control circuit C. Operational and other aspects of the circuits of
FIGS. 2 and 3
are described in greater detail in the '494 patent (in which
FIGS. 2 and 3
referred to above appear as FIGS. 2 and 12, respectively).
In addition to applications for signal transmit purposes, it is desirable to apply radiation synthesizer systems to receive applications.
Objects of the invention are, therefore, to provide new and improved radiation synthesizer systems, particularly such as enable one or more of the following advantages and capabilities:
efficient signal reception;
broadband operation;
signal reception using electrically small antennas;
efficient low frequency, small antenna systems;
systems providing signal receive and transmit;
simplified direct synthesis receivers (e.g., no IF processing or detection); and
receivers enabling monolithic circuit construction (e.g., while minimizing number of receiver components).
SUMMARY OF THE INVENTION
In accordance with the invention, a radiation synthesizer system, to receive incident signals, includes an antenna element having a first reactive characteristic and a storage element having a second reactive characteristic. At least one switch module is coupled between the antenna element and the storage element and includes switch devices arranged for controlled activation to transfer energy back and forth between the storage element and the antenna element. An output device is coupled to the storage element to enable use of output signals derived, via activation of the switch devices, from signals incide
Bae Systems Information and Electronic Systems Integration Inc.
Phan Tho
Robinson Kenneth P.
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