Optimization of noise performance for various topologies of planar microwave active filters using noise wave techniques

Dual-Band Tunable Recursive Active Filter

“…It should be noticed that half-power combiners increment the noise of the filter more than 3 dB with respect to the isolated gain block. The noise figure can be improved by using asymmetric combiners [2]. Finally, the main results are summarized in Table I.…”

“…Plp2lL/HA (2) where ai/ 2 are the transmission parameters of the lower branches of the combiners. On the other hand, the noise factor of the filter Ff can be obtained as [6] i )+ i'*^i) OLXOL^A (3) where FA is the noise factor of the amplifier.…”

“…This topology presents several advantages, such as simple design and high gain. Additionally, it can be easily implemented in both discrete [1] and monolithic (MMIC) [2] technologies.…”

Multiple Order Dual-Band Active Ring Filters With Composite Right/Left-Handed Cells

“…One of the main drawbacks of the proposed ring topology is that the power balance of the coupled lines is very asymmetric (α i β i ), and therefore this filtering structure will be very noisy in comparison with filters that make use of other type of combiners (e.g., 3-dB hybrids). If there were strong requirements in terms of noise, the corresponding figure could be improved by choosing a better power balance in the combiners (α i and β i ) [28]. However, there are strong limitations when working with microstrip coupled lines since, in practice, it is very difficult to increase the coupling factor above a certain limit.…”

“…4. Based on the noise wave analysis developed in [28], the noise factor F a for the scheme shown in Fig. 4(a) can be obtained as…”