# A Novel SIW Leaky-Wave Antenna for Continuous Beam Scanning from Backward to Forward
###### Abstract  
A novel, periodic, leaky-wave array antenna using substrate-integrated waveguide (SIW) technology is proposed for continuous beam scanning applications. For this purpose, a periodic structure with the ability to radiate from backward to forward is proposed. The unit cell of this periodic structure includes a longitudinal slot and an H-plane discontinuity. The H-plane step discontinuity is suggested to suppress the open stopband (OSB) and enable continuous beam scanning from backward to forward through the broadside. The impedance matching technique is used to suppress the open stopband. In contrast to phased array antennas, this form of antenna is distinguished by its ability to scan without requiring a complex feeding network. These antennas are used for different factors such as scanning the beam, determining the direction of arrival, avoiding collisions, indoor communications, etc. A prototype of the proposed antenna was fabricated for experimental characterization. The overall physical dimensions of the fabricated antenna are 7.9 mm \(\times\) 128 mm. The results demonstrate that an adequate level of agreement between measurement and simulation is satisfactory. The results indicate that the suggested antenna can scan continuously in the frequency range of 14.5 to 22.5 GHz between \(-\)60 and +57.5 degrees through broadside with a maximum gain of 16 dBi and radiation efficiency of 71%. SIW; leaky-wave antenna; open stopband; impedance matching; frequency beam scanning Article  
A Novel SIW Leaky-Wave Antenna for Continuous Beam Scanning from Backward to Forward  
1180411180  
bulky and expensive, SIW LWAs are inexpensive, with low profiles, and simple to fabricate. The SIW LWA integrates easily with other planar circuits. The substrate's undesired radiation in the microstrip LWA is eliminated in SIW LWA [18]. Additionally, the SIW LWA has a substantially higher power handling capacity than the microstrip-line-based one. As a result, the SIW LWA is a lightweight and planar choice for applications requiring high power-handling capability. Due to the aforementioned benefits, SIW-based structures have become one of the most intriguing topics in the disciplines of LWA in recent years. SIW LWAs are classified into four types: uniform [16; 17], quasi-uniform [19; 20; 21], composite right/left-handed (CRLH) [22; 23], and periodic [24; 25]. The radiating element in the first type of SIW LWA is evenly dispersed along the path of wave propagation within the substrate [16; 17]. The quasi-uniform SIW LWA is a periodic structure with a spacing interval that is less than the wavelength [19; 20; 21]. These two classes of SIW LWA operate on the fundamental space harmonic, on which fast waves propagate inside the substrate. These structures can be used for beam scanning in the forward quadrant space while avoiding broadside radiation. The beam-scanning range is one of the most essential characteristics of LWAs. Beam scanning from backward to forward is necessary for many applications. Unlike the two previous kinds of SIW LWAs, the CRLH and periodic LWAs can enable backward-to-forward beam scanning [22; 23]. The open stopband (OSB) causes gain deterioration toward the broadside direction, which is one of the primary concerns with the CRLH and periodic LWAs [22; 23; 24]. Due to the fact that the reflected waves from each unit cell are in phase at the broadside frequency, electromagnetic energy cannot be transmitted from the antenna to the surrounding medium, resulting in the open stopband. In a CRLH LWA, the balanced transmission line must be employed to avoid the open stopband. One of the key disadvantages of the CRLH LWA is that its random behavior at the cutoff frequency is highly dispersed. Several strategies including impedance matching [26; 27; 28; 29; 30], reflection cancellation [31], and the use of an asymmetric structure [31; 32] are discussed for suppressing periodic LWAs with an open stopband.