5.1 Modified CMRC LPF using novel fractal patches

A modified compact microstrip resonance cell (CMRC) low-pass filter (LPF) using novel fractal patches was proposed in [54], see Figure 28. The fractal patches produce additional transmission zeros to the stop-band, while the open-ended stubs cause an extension in the stopband achieving a compact ultrawide and deep stopband filter with good selectivity and low insertion loss in the passband. The results show 10 dB bandwidth from 3.3 to 67 GHz with 181.5% relative stopband bandwidth. The 3-dB cutoff frequency is 2.85 GHz and less than 1.5 dB insertion loss in the passband and 0.55 GHz transaction from 3 to 20 dB and 20 dB suppression from 3.5 to 67 GHz, so that the filter can be expected to suppress the unwanted harmonics and prevent inter-modulation with the new systems with high frequency operating bands. The filter has been designed on a Rogers 5880 substrate with a relative dielectric constant of 2.2, substrate thickness of 0.508 mm, and 0.0009 loss tangent. Figure 28 shows the proposed filter design, and it consists of two traditional triangle taper resonance cells in one side of the transverse connecting narrow width transmission line which has almost the same performance of the complete CMRC structure, while two different sizes circular fractal patches are present on the other half. Each fractal consists of main circular patch and additional small circular patches at edges. The two fractals act as a dual behavior resonator to have additional transmission zeros in the stopband. Each fractal is resonating at certain frequency in addition with enhancing the low suppression bands of the entire stop-band. Also, four open ended stubs are used to extend the

Figure 28. The design of proposed low-pass filter [53].

Photos for the fabricated filter with open stub are shown in Figure 25. Figure 26 (a) shows the measured and simulated results of the proposed filter with open stub at D1, D2 ON state, and D3 OFF with frequency range from 1 to 20 GHz. It should be noted that the out of band rejection is good, and the measured 3 dB passband of the proposed filter is between 3.6 and 10.6 GHz. Figure 24(b) shows the measured and simulated results of the proposed filter with open stub at D1, D2 OFF state and D3 ON, and the dual bands with 3 dB passbands extend from 3.8 to 5 GHz and from

The simulated and measured S11 and S21 with O.C stub. (a) D1, D2 ON, and D3 OFF, (b) D1, D2 OFF and

In general, the filtenna consists of a filter and antenna that are combined in one structure. The proposed filtenna operates at three bands of frequency (2.4, 5.5, and 28 GHz) to cover the 4G/5G communication system. It consists of three parts, namely, Franklin strip monopole antenna to cover 4G, WLAN, and WiMAX and a rectangular patch antenna to cover 5G band. The third part consists of a modified CMRC low-pass filter that exists between the two antenna parts to isolate the Franklin antenna from the rectangular patch antenna at 5G band. It also allows feeding the Franklin antenna at low frequency bands. The total size of the filtenna is <sup>45</sup> <sup>40</sup> 0.508 mm<sup>3</sup> and fabricated on Teflon dielectric substrate (Roger 5880). The proposed filtenna has wide impedance bandwidth (15.8, 23.5, and 11.3%) and high gain (1.95, 3.76, 7.35 dBi) [53]. The proposed multiband filtenna is shown in

9.5 to 10.8 GHz [50].

Figure 25.

Figure 26.

D3 ON [50].

A photo for the fabricated filter of Figure 10.

UWB Technology - Circuits and Systems

5. UWB filtenna

Figure 27.

120

stopband by adding new transmission zeros without increasing the circuit size. The main dimensions are given in Table 6, all dimensions in millimeter.
