**6. Stacked mono-pulse Ku-band patch antenna**

A mono-pulse double-layer circular patch antenna was designed at Ku band, 15 GHz. The mono-pulse antenna consists of four circular patch antennas and a feed network as presented in **Figure 23**. The circular resonator and the branch coupler were printed on a substrate with a relative dielectric constant of 2.45 and with a thickness of 0.8 mm. The diameter of the circular microstrip resonator is 0.42 cm. The circular radiator was printed on a substrate with a relative dielectric constant of 2.25 and with a thickness of 0.8 mm. The diameter of the circular patch is 0.45 cm. The comparator consists of three 3 dB, 180° rat-race couplers that are connected to four circular patches via the antenna feed lines, as presented in **Figures 23** and **24**. The strip-line 3 dB, 180° rat-race couplers are printed on a substrate with a relative dielectric constant of 2.2 and thickness of 0.8 mm. The comparator structure and ports are shown in P **Figures 23** and **24**. The comparator output ports are: a sum port , difference port **Δ**, an azimuth difference port **Δ**Az, and an elevation difference port **Δ**El. The antenna bandwidth is 11% for VSWR better than 2:1. The antenna beam width is around 36°. The computed and measured antenna gain is around 10.5 dBi. The maximum comparator losses are 0.75 dB.

**Figure 23.** *A microstrip stacked mono-pulse antenna.*

feeding network than Type A array. In the Type C array, a 10-cm coaxial line was used to replace the same length of microstrip line in the Type A array. Comparison of measured results of the arrays, given in **Table 4**, shows that the gain of the

*Comparison of electrical performance of 256 stacked patch microstrip antenna arrays.*

**Parameter Type A Type B Type C** Number of radiators 256 256 256 Beamwidth (°) 4.2 4.2 4.2 Computed gain(dBi) 32 32 32 Microstrip line loss(dB) 3.1 3.1 1.5 Radiation loss T-J. (dB) 0.72 0.72 0.72 Radiation loss bends(dB) 0.13 1.17 0.13 Radiation loss steps(dB) 0.12 — 0.12 Mismatch Loss (dB) 0.5 0.5 0.5 Expected Gain(dBi) 27.43 26.5 29.03 Measured Gain(dBi) 27.5 26.5 29.5 Efficiency (%) 34.9 28.2 51

*Advanced Radio Frequency Antennas for Modern Communication and Medical Systems*

**Figure 22.**

**Table 4.**

**36**

*Radiation pattern of the microstrip stacked patch.*

**7.2 Stacked microstrip antenna with SRR**

*DOI: http://dx.doi.org/10.5772/intechopen.93492*

*Wideband Wearable Antennas for 5G, IoT, and Medical Applications*

**Figure 25.**

**Figure 26.**

**39**

*A microstrip stacked patch antenna.*

*Computed S11 of the microstrip stacked patch.*

Stacked microstrip patches antennas with and without SRR has been designed, see Refs. [1–5]. The antennas was designed on the same substrate. The antennas are stacked double-layer antennas. The first layer consists of a FR4 substrate with a dielectric constant of 4.2 and 1.6 mm thickness. The second layer consists of a dielectric substrate with a dielectric constant of 2.3 and 1.6 mm thickness. The antenna has been analyzed and optimized by using full wave electromagnetic software. The dimensions of the microstrip stacked patch antenna are 33 20 3.2 mm as presented in **Figure 25**. The antenna bandwidth is around 6% for VSWR better than 3:1. The antenna beam width is around 74°. The stacked antenna directivity and gain are around 7 dBi. The computed S11 parameters are presented in

**Figure 26**. Radiation pattern of the microstrip stacked patch is shown in **Figure 27**. The stacked patch antenna with SRR is presented in **Figure 28**. This antenna has the same structure as the stacked antenna shown in **Figure 25**. The spacing between the SRR rings is 0.25 mm and the ring width is 0.2 mm. Four rows of seven SRRs are placed on the radiating patch. The measured S11 parameters of the antenna with SRR are presented in **Figure 29**. The antenna bandwidth is around 13% for VSWR better than 2.5:1. By adding an air space of 4 mm between the antenna layers, the VSWR was improved to 2:1. The antenna gain is around 9–10 dBi. The antenna's

**Figure 24.** *Rat-race coupler.*

#### **6.1 Rat-race coupler**

A rat-race coupler is shown in **Figure 24**. The rat-race circumference is 1.5 wavelengths. The distance from A to **Δ** port is 3λ\4. The distance from A to P port is λ\4.

For an equal-split rat-race coupler, the impedance of the entire ring is fixed at 1.41 Z0, or 70.7 Ω for Z0 = 50 Ω. For an input signal V, the outputs at ports 2 and 4 are equal in magnitude, but 180 degrees out of phase.
