## 2 Concept of Periodically-Distributed Bends Along a Microstrip Transmission Line  
Leaky wave antennas normally radiate from the slots and edges of the structures. These slots and edges will lead to radiation of energy in some particular directions according to the designs. Transmission lines periodically loaded with bends with different sharpness tend to radiate differently due to various perturbations. Conventional transmission lines on the other hand can only propagate waves in one direction and cannot radiate on their own unless they have some perturbations or modulations. The whole idea is to turn these conventional transmission lines into periodically-loaded transmission lines to achieve leaky wave radiation. In the proposed antenna, a homogeneous transmission line with multiple periodically-loaded sharply-discontinuous sections is employed for the excitation of leaky waves on the broadside with the help of its intrinsic negative permittivity and permeability. The idea of this antenna was originally inspired by the observations from our previous work, which did not support the left-hand features: (1) the observation that CRLH behavior was found in sharp bends of a modified transmission line; (2) right-hand quadrant scanning was found to be possible with a smooth edge sine wave modulated transmission line; and (3) the generated CRLH behavior can be modified to facilitate backward and forward scanning. Along the body of the antenna, leakage of superimposed electromagnetic waves fed by a single input port boosts the overall antenna gain even though the proposed antenna has a low profile in the direction of radiation. The proposed LWAs supports the propagation of a traveling wave, which continuously radiates through the sharp discontinuities along the body of the antenna so as to generate a highly-focused beam of radiation. The overall topology of the proposed antenna eliminates the need for conventional signal feeds with added phase shifters or complicated signal feeding lines, which are not only high profile, but also technically complicated. As a whole, low profile leaky wave antennas for Ku-band applications, frequency scanning applications, as well as sensor networks have been implemented. An efficient transmission line modulated with bends of different sharpness has been realized and analyzed using model analysis. Furthermore, CRLH behavior has been observed in a transmission line modulated with sharp bends, which features backward and forward scanning (see Figure 1). On the other hand, right-hand quadrant scanning has been observed in a transmission line periodically loaded with a smooth edge sine wave pattern (see Figure 1). Efficient, high gain, and broadband characteristics have been achieved by simply introducing bends in the transmission line without introducing any stubs or components or any other SIW structures, which are comparatively more typical and costly. It has further been proposed that transmission lines periodically loaded with sharp bends or smooth bends have completely different impacts on radiation and frequency scanning. In our model analysis, a unit cell with sharp bends provides frequency scanning in both directions, i.e., forward and backward quadrants along with a dual-frequency operation. Furthermore, another unit cell with a smooth corner has been proposed for changing the radiation direction and scanning in the forward quadrant. The main point is that different kinds of frequency scanning features have been observed when the transmission line was periodically loaded with sharp or smooth bends at a particular angle. The angle at which each unit cell of the transmission line has been bent further decides the direction of propagation of the wave and hence the direction of radiation from the bends. After rigorous optimization, it has been observed that high gain and better radiation properties have been obtained at  
Figure 1: Principle of the proposed designs: (**a**) sharp edge (**b**) smooth edge. a bending angle of 56 degrees for the proposed designs.