**5. UWB antennas for radar applications**

In many types of radars such as GPR, through-wall imaging radars, or even breast imaging systems, UWB signals are required. For high-gain and high-power radars, end-fire UWB antennas are preferred because they perform with unidirectional, high gain which is necessary for enhanced radar range. Linearly tapered antennas (LTA) like Vivaldi antennas [26, 27] are widely used, and the more complex double exponentially tapered slot antennas (DETSA) can also be used. **Figure 9** presents a high-gain DETSA antenna fabricated on flexible liquid crystal polymer (LCP) substrate [28]. The implemented gain varies between 7 and 12 dBi. The use of flexible substrate such as LCP allows the adoption of the longitudinal antenna along a non-planar surface as can be seen in **Figure 9b**. End-fire DETSA has been shown to redirect the maximum gain direction along the tangent of the ending point; therefore, it can be used to implement high-gain directive radar front ends where two or even four DETSA antennas can be combined to form a confocal high-gain

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*Antennas for UWB Applications*

**Figure 9.**

**Figure 10.**

*DOI: http://dx.doi.org/10.5772/intechopen.86985*

*(a) Planar DETSA, (b) conformal DETSA, (c) DETSA antennas confocal array.*

array as can be seen in **Figure 9c**. For GPR or through-wall imaging radars, a directive confocal array is placed about the ground target or on the wall. These radars are mono-static, and the same antenna system operates both as the transmitter and the receiver. It is desired to have high penetration capability which means that high-gain antennas and high-gain amplifiers are used to detect reflected signals propagating through high-loss media. End-fire high-gain antennas such as the Vivaldi antennas and their variations are usually used for these applications. In (**Figure 10**) it can be seen that good agreement is achieved between simulated and measured S11 and

In several occasions UWB antennas need to be integrated or mounted on nonplanar surfaces, and consequently the use of conformal UWB antennas has been investigated by several researchers. In [22, 29] three distinct UWB antennas are used in order to test their matching and radiation characteristics when the antennas are

there is no difference between planar and folded DETSA return loss.

**6. Conformal UWB antennas**

*Simulated and measured S11 for planar and folded DETSA [22].*

**Figure 9.**

*UWB Technology - Circuits and Systems*

indicative signature of a retransmitted signal can be seen in **Figure 8**. The chipless UWB RFID schematic that is presented in **Figure 8** consists of a pair of UWB monopoles which are connected with a common feeding line. The feeding line is loaded with eight resonators forming an 8-bit word. Each resonator which has a slightly different size causes a frequency notch at a different frequency, and at the same time, it causes a phase discontinuity. With the use of a UWB interrogator, a wideband signal is sent, and the tag receives the signal, and it retransmits it back to the reader. The combination of resonators causes a unique electromagnetic signature, which identifies the tag. There is a variety of resonators that can be used, such as slits, CLLs, or slot ring resonators (SRRs). Batteryless, chipless, and entirely passive UWB RFIDs can be inkjet-printed on paper substrates and be massively and rapidly produced for disposable RFID tags, such as the baggage paper-based tags which are used to identify the checked-in luggage. A pair of microstrip-fed UWB monopole antennas

In many types of radars such as GPR, through-wall imaging radars, or even breast imaging systems, UWB signals are required. For high-gain and high-power radars, end-fire UWB antennas are preferred because they perform with unidirectional, high gain which is necessary for enhanced radar range. Linearly tapered antennas (LTA) like Vivaldi antennas [26, 27] are widely used, and the more complex double exponentially tapered slot antennas (DETSA) can also be used. **Figure 9** presents a high-gain DETSA antenna fabricated on flexible liquid crystal polymer (LCP) substrate [28]. The implemented gain varies between 7 and 12 dBi. The use of flexible substrate such as LCP allows the adoption of the longitudinal antenna along a non-planar surface as can be seen in **Figure 9b**. End-fire DETSA has been shown to redirect the maximum gain direction along the tangent of the ending point; therefore, it can be used to implement high-gain directive radar front ends where two or even four DETSA antennas can be combined to form a confocal high-gain

is well-suited for the implementation of chipless UWB RFIDs.

**5. UWB antennas for radar applications**

*Operation principle and schematic of chipless UWB RFIDs.*

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**Figure 8.**

*(a) Planar DETSA, (b) conformal DETSA, (c) DETSA antennas confocal array.*

**Figure 10.** *Simulated and measured S11 for planar and folded DETSA [22].*

array as can be seen in **Figure 9c**. For GPR or through-wall imaging radars, a directive confocal array is placed about the ground target or on the wall. These radars are mono-static, and the same antenna system operates both as the transmitter and the receiver. It is desired to have high penetration capability which means that high-gain antennas and high-gain amplifiers are used to detect reflected signals propagating through high-loss media. End-fire high-gain antennas such as the Vivaldi antennas and their variations are usually used for these applications. In (**Figure 10**) it can be seen that good agreement is achieved between simulated and measured S11 and there is no difference between planar and folded DETSA return loss.
