## 2 Two-Row ESPAR Antenna
### Realized Antenna  
The fabricated antenna is presented in Figure 2. 1.55 mm thick FR4 substrate with metalized top layer has been used as a PCB for the switching circuitry and the ground plane of the antenna. The RF connector and switching circuits, as well as LED indicators have been located on the bottom layer as illustrated in Figure 2. The switching circuits employ NJG1681 MD7 SPDT switches providing a trade-off between high isolation, low insertion losses and power consumption in comparison to PIN diodes or varactors [28; 39; 40]. To provide proper performance and avoid eventual RF signal degradation, a decoupling capacitor and ESD protection coil have been placed in close proximity of the switch pins. An LED indicator has been located near each switching circuit to indicate the actual state of the switch (lights when the circuit is in open state). The steering is controlled by an external microcontroller connected to the board. The fabricated antenna has been measured and verified with the simulation model. The assumed three groups of similar beam configurations with different angle tilt in elevation have been simulated, measured and gathered in Figures 3 and 4, while the main antenna parameters for each configuration at the center frequency have been summarized in Table 1. The simulated results have been confirmed by the measurements and only small discrepancies in the backward radiation  
Figure 1: Two-row ESPAR antenna model.  
level can be observed. Measured gain for all characteristics is on a similar level around 8 dB. The input impedance matching results for all configurations are presented in Figure 5 which shows that the achieved \(|\)S11\(|\) values are close or below \(-10\) dB. The large difference of impedance matching between configurations is a trade-off to achieve the highest possible difference of maximal direction of the radiation pattern in elevation.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Configuration** & \(\theta_{max}\) & \(G_{max}\) & \(HPBW_{\theta}\) & \(HPBW_{\varphi}\) & \(SLL_{\theta}\) & \(SLL_{\varphi}\) & \(1\)S11\(|\) \\ \hline UP & \(46^{\circ}\) & 7.7 dB & \(45^{\circ}\) & \(88^{\circ}\) & \(10\) dB & \(14\) dB & \(-20.9\) dB \\ \hline MID & \(52^{\circ}\) & 7.8 dB & \(43^{\circ}\) & \(100^{\circ}\) & \(10\) dB & \(28\) dB & \(-10.5\) dB \\ \hline DOWN & \(56^{\circ}\) & 8.1 dB & \(46^{\circ}\) & \(93^{\circ}\) & \(12\) dB & \(25\) dB & \(-8.8\) dB \\ \hline \hline \end{tabular}
\end{table}
Table 1: Measured parameters of the realized two-row ESPAR antenna.  
Figure 2: Fabricated two-row ESPAR antenna.  
Figure 4: Measured 3D radiation patterns for each considered configuration with different inclination angles: \(\theta_{max\_up}\), \(\theta_{max\_mid}\), \(\theta_{max\_down}\) (from left to right).  
Figure 3: Simulated and measured antenna radiation patterns at 2.44 GHz in the elevation plane (for \(\varphi=90^{\circ}\)) and in the horizontal plane for three configurations (see text for explanations): (**a**) \(V_{\mathit{UID}}^{00}\) (maximum at \(\theta_{max\_up}=46^{\circ}\) ), (**b**) \(V_{\mathit{MID}}^{00}\) (maximum at \(\theta_{max\_mid}=52^{\circ}\) ), and (**c**) \(V_{\mathit{DONN}}^{00}\) (maximum at \(\theta_{max\_down}=56^{\circ}\)).