An electromagnetic wave transmission structure (10, 10A, 10B, 10C, 10D, 10E, 10F, 10G, 20, 30), comprising: a substrate (100, SUB); at least one transmission line (120, 120A, 121, 122, 123, 124) disposed on the substrate (100, SUB), wherein each of the at least one transmission line (120, 120A, 121, 122, 123, 124) comprises: a first extending portion (120P1) extended in a first direction; and a plurality of second extending portions (120P2, 120P2-A) respectively extended from two opposite edges (e1, e2) of the first extending portion (120P1), wherein an extending direction of the second extending portions is parallel to a second direction, the second extending portions (120P2, 120P2-A) are arranged at a pitch P along the first direction, any two adjacent ones of the second extending portions (120P2, 120P2-A) arranged along the first direction have a spacing S, and each of the second extending portions (120P2, 120P2-A) has a length L along the second direction; a plurality of antennas (140, 140A, 140B, 140D) disposed on the substrate (100, SUB) and adjacent to the at least one transmission line (120, 120A, 121, 122, 123, 124); and a plurality of tunable dielectric units (160, 160A, 160B, 160C, 160D, 161, 162, 163) overlapped at a plurality of portions of the at least one transmission line (120, 120A, 121, 122, 123, 124) located between the antennas (140, 140A, 140B, 140D), wherein each of the tunable dielectric units (160, 160A, 160B, 160C, 160D, 161, 162, 163) has a first electrode layer (EL1, EL1-A, EL1-B) and a controllable dielectric layer overlapped with each other, the controllable dielectric layer is disposed between the first electrode layer (EL1, EL1-A, EL1-B) and the at least one transmission line (120, 120A, 121, 122, 123, 124), and the pitch P, the spacing S, and the length L satisfy the following relationship: S P 2 = ck sspp ω ε r 2 − 1 cot 2 2 L ε r ω c, wherein k sspp is a wavenumber of an electromagnetic wave signal transmitted via the at least one transmission line (120, 120A, 121, 122, 123, 124), ε r is an effective dielectric constant of the controllable dielectric layer, ω is an angular frequency of the electromagnetic wave signal transmitted via the at least one transmission line (120, 120A, 121, 122, 123, 124), and c is a speed of light. a substrate (100, SUB); at least one transmission line (120, 120A, 121, 122, 123, 124) disposed on the substrate (100, SUB), wherein each of the at least one transmission line (120, 120A, 121, 122, 123, 124) comprises: a first extending portion (120P1) extended in a first direction; and a plurality of second extending portions (120P2, 120P2-A) respectively extended from two opposite edges (e1, e2) of the first extending portion (120P1), wherein an extending direction of the second extending portions is parallel to a second direction, the second extending portions (120P2, 120P2-A) are arranged at a pitch P along the first direction, any two adjacent ones of the second extending portions (120P2, 120P2-A) arranged along the first direction have a spacing S, and each of the second extending portions (120P2, 120P2-A) has a length L along the second direction; a first extending portion (120P1) extended in a first direction; and a plurality of second extending portions (120P2, 120P2-A) respectively extended from two opposite edges (e1, e2) of the first extending portion (120P1), wherein an extending direction of the second extending portions is parallel to a second direction, the second extending portions (120P2, 120P2-A) are arranged at a pitch P along the first direction, any two adjacent ones of the second extending portions (120P2, 120P2-A) arranged along the first direction have a spacing S, and each of the second extending portions (120P2, 120P2-A) has a length L along the second direction; a plurality of antennas (140, 140A, 140B, 140D) disposed on the substrate (100, SUB) and adjacent to the at least one transmission line (120, 120A, 121, 122, 123, 124); and a plurality of tunable dielectric units (160, 160A, 160B, 160C, 160D, 161, 162, 163) overlapped at a plurality of portions of the at least one transmission line (120, 120A, 121, 122, 123, 124) located between the antennas (140, 140A, 140B, 140D), wherein each of the tunable dielectric units (160, 160A, 160B, 160C, 160D, 161, 162, 163) has a first electrode layer (EL1, EL1-A, EL1-B) and a controllable dielectric layer overlapped with each other, the controllable dielectric layer is disposed between the first electrode layer (EL1, EL1-A, EL1-B) and the at least one transmission line (120, 120A, 121, 122, 123, 124), and the pitch P, the spacing S, and the length L satisfy the following relationship: S P 2 = ck sspp ω ε r 2 − 1 cot 2 2 L ε r ω c, wherein k sspp is a wavenumber of an electromagnetic wave signal transmitted via the at least one transmission line (120, 120A, 121, 122, 123, 124), ε r is an effective dielectric constant of the controllable dielectric layer, ω is an angular frequency of the electromagnetic wave signal transmitted via the at least one transmission line (120, 120A, 121, 122, 123, 124), and c is a speed of light.