(a) (b) (c) (d)
Fig. 2. Surface current distributions for state 001 (a), state 100 (b), state 101 (c), and state 111 (d).
Antenna Configuration and Miniaturization Design:
Fig. 1 shows a miniaturized binary frequency-reconfigurable meander-line antenna. The main transmission line of the antenna is folded three times at different locations. Three meanders have uniform width.
As shown in Fig. 1, three PIN diode switches are introduced at the meander of the main transmission line, and short narrow strips extended from the meanders are used to place PIN diodes. By switching on the PIN diode switch, the relevant parts of the bending structure with different lengths are bypassed from the antenna structure. The current flows directly from the PIN switch without passing through the bypassed transmission line section, resulting in a shorter actual path length of the current. Consequently, the operating frequency of the antenna increases. On the contrary, the corresponding parts are connected to the antenna structure by turning off the switch. For example, when the PIN diode D1 is turned on, the BP1 section is bypassed, and the current passes directly through the switch D1without going through BP1. As a result, the actual path length of the current is shortened, and the frequency of the antenna is correspondingly increased. Different settings of the on/off status of D1, D2, and D3 result in changes in the effective length of the antenna, which can achieve 23 different operating frequencies and realize frequency reconfigurability.
As for the biasing circuit, C1, C2, C3, C4, and C5 achieve DC-blocking, dividing the antenna into multiple transmission line segments with different DC voltages. In1 and In2, as RC chokes, are connected to ground via holes and achieve DC grounding as one end of the PIN diodes D1, D2, and D3. The three control voltages, V1, V2, and V3 are respectively connected to the other end of D1, D2, and D3 via inductors In3, In4, and In5.