## 4 Proposed Right-Hand Sine Wave Smooth Edge Transmission Line-Based LWA
### Implementation and Results of the Proposed Right-Hand Sine Wave LWA  
This section describes the implementation of the proposed sine wave leaky wave antenna. The antenna properties obtained viz. antenna reflection-transmissions, radiation, leakage, and efficiency have been validated with the help of measurements. As explained previously, the smooth bend(s) in the unit element will result in the frequency scanning in the right-hand quadrant.  
Figure 15 shows the geometry of the proposed smooth-edge sine wave leaky wave antenna. The length of the antenna was 68.2 mm. The period of each unit cell was 6.0 mm. The proposed antenna was fabricated on a Rogers Duroid 5880 substrate using the standard fabrication technology. The dielectric constant and the thickness of the substrate were respectively 2.2 and 0.5 mm. The fabricated prototype of the proposed sine modulated leaky wave antenna is shown in Figure 16.  
Figure 17 depicts the simulated and measured S-parameters (S11 and S22) for the proposed antenna design. For simulating the design, the transient solver in CST Studio Suite has been used. It can be clearly seen from Figure 17 that the antenna achieved a broadband impedance matching across the Ku-band. The maximum return loss was around 30 dB. S21 had some discrepancies with the measured results due to some soldering or handling-induced errors. The antenna has been fabricated on an extremely thin substrate. Still, in both cases, the values were good enough to achieve an efficient antenna design. Moreover, the measurement results were much better than the simulated performance in this case. The S21 parameter varied from \(-7\) dB--15 dB across the whole frequency band.  
Figure 16: Prototype of the proposed sine wave leaky wave antenna.  
Figure 17: S-parameters of the proposed sine wave leaky wave antenna.  
Figure 18 shows the measured pattern of the proposed smooth edge sine wave leaky wave antenna. Figure 18 shows the power pattern at frequencies 15.0 GHz, 15.5 GHz, 16.0 GHz, 16.5 GHz, 17.0 GHz, 17.5 GHz, and 18.0 GHz. The antenna obviously exhibited a large scanning range of almost 50 degrees from 15 GHz-18 GHz. This type of right-hand scanning was observed as a result of the fast wave modes. Figure 19a,b shows the efficiency and 3-dB beamwidth graphs of the sine wave LWA as a function of frequency. The efficiency increased to 95 percent as the frequency increased from 15.0 GHz-18.0 GHz. However, the sidelobe levels at frequencies below 16 GHz were slightly higher as compared to those at other frequencies. At these frequencies (i.e., below 16 GHz), the S21 was slightly higher, but beyond this frequency, the efficiency continued to improve. In the desired operating frequency band (from 16-GHz onwards), the leakage radiation increased as the frequency went higher. Due to the frequency-dependent increase in leakage radiation along the transmission line, the gain also increased from lower frequencies to higher frequencies. At higher frequencies, the efficiency reached 90-95 percent, thus satisfying the criteria  
Figure 19: (**a**) Efficiency of the proposed sine wave leaky wave antenna and (**b**) 3-dB beamwidth variation with frequency.  
Figure 20: Measured radiation patterns at different frequencies of sine wave LWA.