In this study, two different voltage mode frequency agile filters employing voltage differencing trans-conductance amplifier (VDTA) are designed for encrypted communications. The agility of the designed frequency agile filters are supported by only switching transistors instead of feedback systems in the conventional designs. The proposed frequency agile filters are implemented by CMOS technology to benefit from easy and cheaper manufacturing of CMOS circuits. One of the designed frequency agile filter is realized by changing g(m) (trans-conductance) and the other is realized by varying capacitance. The MOS capacitor technique is used instead of conventional capacitors in the second frequency agile filter structure. The CMOS performance of designed frequency agile filter realized with VDTA is compared with the recently recommended frequency agile filter structure realized with Bi-CMOS technology. The performance parameters of the VDTA and agile filter structures are summarized and the suitability of the filters for different applications are given. The designed filter can be easily operated up to 1 GHz. In this study, HAVEQUICK operating UHF band between 225 and 400 MHz is selected as the essential application of the designed filters. Moreover, proposed structures are laid-out. To prove the performance of the designed frequency agile filters, post-layout simulations with Monte Carlo and corner analyses are performed as well. AMS 0.18 A mu m parameters are used for the CMOS realization of the designed frequency agile filter.