A miniaturized self-matched negative group delay (NGD) microwave circuit without the need for external matching networks is proposed. The NGD circuit is based on a modified parallel-type RLC resonator, in which lumped elements (capacitors and inductors) are implemented by microstrip gaps and high-impedance and short-circuited microstrip lines. To verify the design concept, an NGD circuit with the size of 0.21λg×0.29λg is designed and fabricated. From the measurement results, the NGD time of -5.9 ns at the center frequency of 1.532 GHz is obtained with insertion loss of less than 12.5 dB, return losses of more than 25 dB and the NGD bandwidth of 45 MHz.
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