This section presents the structural details of the proposeddual-port antenna design with dimensional information andtopology.We explain the design approaches to achieve a goodisolation between two radiators and the frequency tuningscheme. Different from the previous studies on the dual-portantennas [12], [13], [17] where two PIFAs are merged or asingle element PIFA plate with two feeding ports are used, wecombine two different types of antenna topologies to form adual-port antenna, which is the key to achieve a good port-toportisolation.Fig. 1 shows a mock-up antenna to evaluate the characteristicsof the dual-port MIMO antenna. The size of thePCB board is 60 100 1 mm3, and it is printed on thetop of an FR4 substrate. The overall antenna PCB circuitheight is 1.3mm, considering the SP4T RF switch componentsize (3mm 3mm 0.6mm) on the front side directionand voltage component size (2.1mm 2.1mm 0.7mm)on the rear side direction. The antenna patterns are located at the bottom of the front side of the PCB, and an SP4T RFswitch is mounted near the ground short pin of the antenna forimpedance switching. To keep a smaller volume, the CCSLand the signal port 2 are folded by 90 degrees perpendicularlyto the PCB board. The overall dimensions of the antenna are27.5 8 mm2 for PIFA part and 10 17.3 mm2 for CCSLpart. These dimensions are compact enough to t in mobilehandsets. To facilitate measurements, 50ohm-shielded semirigidcables with SMA connectors are connected to both signalfeed ports of the dual-port antenna as shown in Fig. 1 (a).DC bias circuitries and a Li-ion battery as a power supplyof SP4T are mounted on the back side of the PCB board asshown in Fig. 1 (b).As shown in Fig. 2. a PIFA is used to realize signal port 1and the ground. The primary signal port (port 1) is branchedfrom the radiator just as a normal PIFA. A coupling slotplaced in parallel to the PIFA is used to enhance the operatingbandwidth by creating the second resonance at 3.5 GHz.An inverted L-shaped branched out from the ground short of the PIFA is the secondary radiator and the coupled signal feedport 2 comprise the CCSL in Fig. 2.The output port of the SP4T RF switch is connected tothe ground short and the four input ports are connected tothe four different lumped components. The impedance tuningof the antenna can be done by switching the connectedload impedances. Table 1 shows the four different frequencytuning states of the dual-port antenna and associated lumpedcomponent values.