A NOVEL OSCILLATING RECTENNA FOR WIRELESS MICROWAVE POWER TRANSMISSION



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Introduction

The rectenna is a rectifying antenna operating in a receiving mode for reception of
microwave power and subsequent conversion to dc by a diode rectifier. However if an
IMPATT diode is used to rectify microwave power, the same diode can also operate in
the avalanche region to generate and radiate RF power in the same circuit. Thus, the
circuit can convert RF to dc and vice versa but not concurrently. The polarity of the dc
voltage determines the operating mode. The dc current flow is in the same direction for
either mode of operation.


Rectenna Element Design

a photograph of the rectenna element used in this experiment. Two
aluminum strips form the dipole and balanced transmission line. An added aluminum
piece, located at the diode, is shown for heat sinking and securing the element to a
support that suspends the element above a reflecting plane. As seen in Figure 2, the
rectenna consists of a half wave dipole antenna, a two section input low pass filter, a
GaAs IMPATT diode, and an output 30 pF capacitor for shorting RF power and tuning
the diode. A 165 Q dc resistive load is also connected in parallel at the output to
complete the dc circuit and achieve a conversion efficiency of greater than 85°/0. More
details on the rectenna design are given by Brown in [7] and [8].



Conclusion

A microwave circuit that can either rectify or oscillate has been demonstrated. As a
rectifier, the rectenna element had been previously tested with greater than 85°/0 RF to dc
conversion efficiency. In this work, the same circuit has been shown to generate RF
power at 3.3 GHz. Although the oscillating circuit has a low dc to RF conversion
efficiency, circuit optimization is needed to improve its performance without altering the
RF to dc efficiency.