Nonreciprocal Leaky-Wave Antenna Based on Coupled Microstrip Lines on a Non-Uniformly Biased Ferrite Substrate

Previous work demonstrated that nonreciprocal slow waves can be guided on a pair of coupled transmission lines printed on a magnetic substrate. This was done by designing the unit-cell geometry to exhibit spectral asymmetry near the band edge ($K = pi$) frequency in its dispersion (K-ω) diagram. In this effort, the same concept is adapted to attain nonreciprocal radiation by operating the coupled lines in the fast wave region (|β| <; k₀) of the K-ω diagram. To validate the nonreciprocal radiation, an 8-unit-cell leaky-wave antenna (LWA) was constructed and tested in presence of a non-uniform external magnetic field. Specifically, 5 dB contrast was observed between the measured transmit and receive gain in the E-plane. Importantly, good agreement was observed between measurements and simulations once non-uniformities in the magnetic field were taken into account. We note that the external magnetic field can be changed to achieve beam scanning. This is unlike traditional LWAs that achieve beamscanning via frequency control.