Crossed-loop radiation synthesizer systems

Details Crossed-loop radiation synthesizer systems Crossed-loop radiation synthesizer systems

2002-04-02

2004-01-20

Phan, Tho (Department: 2821)

Communications: radio wave antennas

Antennas

High frequency type loops

C343S701000, C343S867000, C343S876000

Reexamination Certificate

active

06680710

ABSTRACT:

RELATED APPLICATIONS
(Not Applicable)
FEDERALLY SPONSORED RESEARCH
(Not Applicable)
BACKGROUND OF THE INVENTION
The present invention relates to radiating 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. No. 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, a complete implementation of which is provided in the '494 patent (see FIG.
12
). 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.
FIG. 2
shows a basic form of synthesizer radiating system. It uses a single switching circuit that is connected to the two input terminals of a standard loop antenna. Each switch may consist of several individual devices either connected in series or parallel in order to realize optimized performance at the desired radiation power level. At some frequencies of operation additional practical constraints may require consideration. As a first consideration, the device parameters may necessitate very low antenna input terminal impedance in order to realize acceptable performance. That impedance may not be compatible with a single-turn loop of appropriate size. As a second consideration, a single-turn loop may be subject to an electrical resonance when the antenna is moderately small. This resonance occurs when the distance around the loop perimeter approaches one-half wavelength at an operating frequency.
Pursuant to the '494 patent, a multi-segment loop configuration using distributed switching electronics provides a solution addressing these considerations. An embodiment in which the antenna has been broken into four loop segments and uses four switching circuits controlled by synchronous signals is described by way of example in this patent. The effective terminal impedance that is presented to each sub-circuit is equal to 1/N times the total loop impedance where N is the number of loop segments. Hence, the optimum low-impedance antenna impedance level may be achieved by dividing the loop into the appropriate number of segments. The electrical resonance of this approach occurs when each segment length approaches one-half wavelength. Therefore, the resonance is increased in frequency by a factor of N over the non-segmented approach. It is possible, using this approach, to obtain acceptable performance at any frequency by properly segmenting the loop.
FIG. 3
shows a synthesizer radiating system
30
, as described in the '494 patent, employing a multi-segment loop radiator

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