  Breaking reciprocity in the microwave frequency range will have important
implications for modern electronic systems. Since it usually involves bulky
biasing magnets or complex spatial-temporal modulations, exploring a
lightweight, all-passive approach becomes intriguing. Starting from a circuit
model, we theoretically demonstrate the nonreciprocal behaviour on a
transmission line building block creating a strong field asymmetry with a
switchable matching stub to enable two distinct working states. After
translating to an electromagnetic model, this concept is first proved by
simulation and then experimentally verified on a microstrip-line-based
diode-integrated metasurface showing nonreciprocal transmission. This printed
circuit board design is expected to find various applications in
electromagnetic protecting layers, communication systems, microwave isolators
and circulators.
