**2.1 Antenna front end**

Antenna front ends (AFE) are employed to condition the received signal coming from the antenna port to make it usable for the following sub-systems, an example of which is described in Section 3.

The main functions of an AFE circuit are: low-noise amplification, protection against strong interference, signal routing when multiple I/O ports are present, and partitioning into sub-bands if needed. **Figure 1** depicts a simplified schematic.

The first, leftmost, section of the AFE contains the protection and signal routing function. The protection against strong interfering signals is accomplished using a limiting circuit commonly realized through a shunt diode. The limiter has to be the first circuit in order to protect the following components from strong interference signals that might damage sensitive circuitry. Next, there is a signal routing section

**21**

**Figure 2.**

*0.5–18 GHz.*

*UWB Circuits and Sub-Systems for Aerospace, Defence and Security Applications*

and its role and properties are described in Section 2.1.1.

(commercial off-the-shelf) available components.

(switch), which is necessary when multiple inputs are present. Switching circuits

Once the signal has been routed, and strong interference has been eliminated then the signal is fed to a frequency diplexer (if necessary) and subsequently to a low-noise amplifying (LNA) stage. The frequency diplexer is inserted when the following stages operate at sub-bands that are less than the total RF input band-width (BW). In **Figure 1**, the bands are indicated as low-band (LB) and high-band (LB). The single sub-bands can cover a decade BW, so that the overall BW of the module is more than a decade. Finally, the LNA is the key-component of AFE circuit

**Figure 2** reports the AFE circuit's noise figure and gain in the two LB and NB sub-bands. This is a typical performance that can be accomplished by using COTS

The gain (dashed lines) are plotted on the left axis while the NF (solid line) on the right. Some observations in the following: first, the effect of the input diplexer is quite evident around 2.5 GHz were the two gains cross. This is a side-effect of applying the RF at one input and then di-plexing into two sub-bands. The relatively high NF in LB and HB is mainly due to all the passive and protection circuits before the LNAs-Reasonably, all there passive structure will account for 4/5 dB losses. Additionally summing the NF of the LNA will lead to 5 dB in LB and typical 8/10 dB in HB. The gain ripple, more evident in the HB sub-band is due to the electrically long interconnects at microwave frequencies. Superior performance in terms of NF

Low-noise amplifiers are an omnipresent component in any microwave receiving system. The LNA's role is to increase the power of the input signal, usually very low especially in long-distance communications, without adding an excessive noise contribution that would make the signal unmanageable by the following stages. The LNA's key characteristics are its gain (G) and noise figure (NF). Secondary, but still

important parameters are linearity, power consumption and port matching.

*Antenna front end (AFE) typical RF performance: gain (dashed) and NF (solid). Operating BW is* 

can be obtained by designing by oneself the critical circuits (i.e. LNA).

*DOI: http://dx.doi.org/10.5772/intechopen.87095*

are described in Section 2.1.2.

*2.1.1 Low-noise amplifiers (LNA)*

**Figure 1.** *Antenna front end (AFE) schematic diagram.*

### *UWB Circuits and Sub-Systems for Aerospace, Defence and Security Applications DOI: http://dx.doi.org/10.5772/intechopen.87095*

(switch), which is necessary when multiple inputs are present. Switching circuits are described in Section 2.1.2.

Once the signal has been routed, and strong interference has been eliminated then the signal is fed to a frequency diplexer (if necessary) and subsequently to a low-noise amplifying (LNA) stage. The frequency diplexer is inserted when the following stages operate at sub-bands that are less than the total RF input band-width (BW). In **Figure 1**, the bands are indicated as low-band (LB) and high-band (LB).

The single sub-bands can cover a decade BW, so that the overall BW of the module is more than a decade. Finally, the LNA is the key-component of AFE circuit and its role and properties are described in Section 2.1.1.

**Figure 2** reports the AFE circuit's noise figure and gain in the two LB and NB sub-bands. This is a typical performance that can be accomplished by using COTS (commercial off-the-shelf) available components.

The gain (dashed lines) are plotted on the left axis while the NF (solid line) on the right. Some observations in the following: first, the effect of the input diplexer is quite evident around 2.5 GHz were the two gains cross. This is a side-effect of applying the RF at one input and then di-plexing into two sub-bands. The relatively high NF in LB and HB is mainly due to all the passive and protection circuits before the LNAs-Reasonably, all there passive structure will account for 4/5 dB losses. Additionally summing the NF of the LNA will lead to 5 dB in LB and typical 8/10 dB in HB. The gain ripple, more evident in the HB sub-band is due to the electrically long interconnects at microwave frequencies. Superior performance in terms of NF can be obtained by designing by oneself the critical circuits (i.e. LNA).
