ilar to the dipole PCA. This bow-tie shaped antenna as shown in Figure 12.4 is the first introduced standard design as Laser Source Illumination Anode electrode Cathode electrode Substrate Terahertz waves FIGURE 12.3 Structure of dipole PCA. 5G Wireless Communication System in Healthcare Informatics THz radiation 30 um ATHZ <3 mm Femtosecond laser <500fs pulse A - 800nm or 1550nm <100fs Width FIGURE 12.4 Bow-tie photoconductive antenna. FIGURE 12.5 Bow-tie photoconductive antenna array. a photoconductive emitter and acts as an appropriate reference case. The DC bias voltage is applied across the arms of the bow-tie antenna. As mentioned for the dipole PCA, the transient photocurrent is generated in the bowtie PCA by the acceleration of carriers, resulting in the terahertz emission. With motivation from the design (see Figure 12.4) in [Khiabani, Huang, Shen, & Boyes (2013)], many innovative designs are proposed to overcome the drawbacks of the general PCA performance. This bow- tie element is integrated with an artificial magnetic conductor (AMC) or a silicon lens to reinforce its directivity. The bow-tie antenna array can also be designed as shown in Figure 12.5 by connecting the DC bias and ground lines in series to their respective electrodes. One capacitance can be employed parallel to the DC source to nullify the fluctuations in DC source. The bow-tie shaped antenna consists of aluminium, titanium, silver, gold, metal films in some micrometer thicknesses over a substrate Terahertz Antenna in Future Healthcare Informatics material such as LT-GaAs, SI-GaAs, and the like. Each electrode of the bowtie looks like a trapezoid in which the width of the small arm and large arm can be increased SO that the resonant frequency can be varied. To tune the antenna at an operating fre- quency, the width of the antenna should be properly selected. The radiation efficiency is far improved while using the silicon lens based bowtie PCA. 12.7.3 INTERDIGITATED PCA To emit the terahertz field with large spectral bandwidth and with