Abstract
This paper presents novel designs of frequency reconfigurable
distributed non-reciprocal bandpass filter and diplexer based on
spatio-temporally modulated microstrip λg/2 resonators. The modulation
is achieved by loading both ends of the λg/2 transmission line
resonators with time-modulated capacitors. To provide an inherent
biasing isolation between the RF and the modulation signals, the
modulation voltage source is connected at the center of the resonator,
where there is a natural voltage null. A single inductor is used to
further enhance such biasing isolation. The wideband nature of this
isolation scheme enables the tuning of the devices over a wide frequency
range. With more than 30-dB RF to modulation isolation, the proposed
resonator structure also enables low insertion loss by eliminating RF
signal leakage to the modulation ports. Two examples of a 3-pole
bandpass filter and a diplexer are demonstrated with good agreement
between the measurement and the simulation. The fabricated filter shows
a minimal insertion loss of 3.9 dB, a 20-dB isolation bandwidth of 42
MHz at 1.0 GHz, and frequency tuning range of 885-1031 MHz. The measured
diplexer has two non-reciprocal bandpass channels at 829 MHz and 997
MHz, respectively. The two channels can be independently reconfigured
without affecting each other.