**3.1 Introduction**

Filter bank modules are an important module in direction finding, radar, seeker, and communication systems. The electrical performance of the filter bank determines if the system will meet the system-required dynamic range and signal-tonoise ratio (SNR) specifications. Moreover, in several cases the filter bank performance limits the system dynamic range. This section describes the design and development of an integrated, low-cost, 18 to 40 GHz wideband compact filter bank module. Design and fabrication considerations are presented.

that the spacing between the filter carriers and the switch carriers should be less than 0.03 mm to get S11 and S22 better than 9.5 dB and flatness better than 1 dB.

The filters were designed by employing AWR and ADS software. **Figure 16** presents single filter response requirements. **Table 8** and **Figure 17** show the SFB expected frequency response. **Table 9** presents the advantages of the integrated design over the discrete design. For example, the weight of a discrete SFB is 1 kg and the weight of an integrated SFB is 50 g. The volume of the discrete SFB is twice the volume of the integrated SFB. The filter contains nine side-coupled microstrip lines printed on a 5-mil alumina substrate. ADS and AWR software were applied to optimize the filter dimensions and structure to meet the system requirements. **Figures 18**–**20** show the computed results of the filters. The sensitivity of the design to substrate tolerances such as height and dielectric constant has been optimized by using RF analysis software, see (**Figure 21**). We fabricated the filter configuration

**Figure 22** presents computed *S*<sup>11</sup> and *S*<sup>21</sup> parameters for the SFB using ADS software. **Figure 23** presents the expanded S12 computed results of the filter bank. **Figure 24** presents the SFB board drawing. **Figure 25** is a photo of the SFB. **Figure 26** presents the S21 SFB results of the first unit measured during the production process. A comparison of the SFB computed and measured results proves

that there is a good agreement between computed and measured results.

**Parameter Requirements** Frequency range 18–40.1 GHz Number of channels 3

Rejection 40 dB min @ F0 8GHz

Flatness 1.2 dB max. For 4 GHz

Power Supply voltages 5 V DC. Heat dissipation – 1 W max

Switching time 100 nsec Input Power 25 dBm max VSWR 2.5:1 max Control 2 LVTTL lines

Dimension 5 x 2 x 1 cm

8 GHz

50 dB min @ F0 11GHz

12–14.5 dB 10.5–13.5 dB 9–12 dB

**3.3 Wideband switch filter Bank specifications**

*Ultra-Wideband MM Wave System and RF Modules DOI: http://dx.doi.org/10.5772/intechopen.97853*

**3.4 Wideband filter design**

Channel Passband

I.L CH-1 CH-2 CH-3

**Table 7.**

**37**

*Wideband SFB specifications.*

**Table 7** lists the specifications of the wideband SFB.

that was less sensitive to production tolerances (**Figure 24**).

The wideband SFB consists of three wideband side-coupled microstrip filters. The SFB MIMIC switches operate in the 18 to 40 GHz frequency range and are used to select the required filter. The insertion loss of each filter section is less than 11.5 dB 1.5 dB. The passband bandwidth of each filter is around 8 GHz. The received signal is rejected by 40 dB at 7GHz from the center frequency. The received signal is rejected by 60 dB at 11GHz from the center frequency. The SFB volume is 2 x 5 x 1 cm.

#### **3.2 Description of the filter bank**

**Figure 15** presents the block diagram of the compact SFB unit. The SFB The module consists of three side-coupled microstrip filters. Each side-coupled filter consists of nine sections. The filters are printed on a 5-mil alumina substrate. One to two dB attenuators connect the filters input and output ports to wideband MMIC SPDT switches. The attenuators are used to adjust each channel's losses to the average required level. The module losses are adjusted to be higher in the low frequencies and lower in the high frequencies. The adjustment of the attenuation level improves the filters flatness over a wideband, 18–40GHz frequency range. The filters are assembled to the surface of the package metal box. The SFB switches are assembled on a CoVar carrier. In the development process of the SFB unit, we found

**Figure 15.** *Block diagram of the compact filter bank module.*

that the spacing between the filter carriers and the switch carriers should be less than 0.03 mm to get S11 and S22 better than 9.5 dB and flatness better than 1 dB.
