Untuned low insertion loss surface leaky wave filter

The letter presents a broadband low insertion loss surface leaky wave filter using reflective multistrip couplers on an optimum cut and orientation of lithium niobate. The insertion loss has been reduced to 3–4 dB without any inductors for phase-shift networks or tuning, and the out-of-band rejection is about 23 dB. The fractional bandwidth is up to 2–5%. The out-of-band rejection can be reduced to 40 dB, when the IDTs are apodised.