The design of mixed-technology quasi-reflectionless planar bandpass filters (BPFs), bandstop filters (BSFs), and multi-band filters is reported. The proposed quasi-reflectionless filter architectures comprise a main filtering section that determines the power transmission response (bandpass, bandstop, or multi-band type) of the overall circuit network and auxiliary sections that absorb the reflected radio-frequency (RF) signal energy. By loading the input and output ports of the main filtering section with auxiliary filtering sections that exhibit a complementary transfer function with regard to the main one, a symmetric quasi-reflectionless behavior can be obtained at both accesses of the overall filter. The operating principles of the proposed filter concept are shown through synthesized first-order BPF and BSF designs. Selectivity-increase techniques are also described. They are based on: (i) cascading in-series multiple first-order stages and (ii) increasing the order of the filtering sections. Moreover, the RF design of quasi-reflectionless multi-band BPFs and BSFs is discussed. A hybrid integration scheme in which microstrip-type and lumped-elements are effectively combined within the filter volume is investigated for size miniaturization purposes. For experimental validation purposes, two quasi-reflectionless BPF prototypes (one- and two-stage architectures) centered at 2 GHz and a second-order BSF prototype centered at 1 GHz were designed, manufactured, andmore »
High-Order Input-Reflectionless Bandpass/Bandstop Filters and Multiplexers
A coupling-matrix approach for the theoretical design of a type of input-reflectionless RF/microwave bandpass filters (BPFs) and bandstop filters (BSFs) is presented. They are based on diplexer architectures with arbitrary-order bandpass and bandstop filtering channels that feature complementary transfer functions. The transmission behavior of these reflectionless filters is defined by the channel that is not loaded at its output, whereas the input-signal energy that is not transmitted by this branch is completely dissipated by the loading resistor of the other channel. Analytical formulas for the coupling coefficients for the first-to-fourth-order filter designs are provided and validated through several synthesis examples. This theoretical design methodology, along with an optimization step, is also exploited to design input-quasi-reflectionless quasielliptic- type BPFs with a transmission-zero-(TZ)-generation cell in their bandpass filtering channel. In addition, the application of the proposed input-reflectionless BPF and BSF networks to input-quasi-reflectionless multiplexer design is approached. It is shown that a single resistively terminated multi-band BSF branch can absorb the input-signal energy not transmitted by the multiplexer channels in their common stopband regions to achieve quasi-reflectionless characteristics at its input. Moreover, experimental microstrip prototypes consisting of 2-GHz third-order BPF and BSF circuits, a 2-GHz sharp-rejection thirdorder BPF with two close-to-passband TZs, and a second-order diplexer device with channels centered at 1.75 and 2.1 GHz are developed and measured.
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- IEEE Transactions on Microwave Theory and Techniques
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- National Science Foundation
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A class of out-of-phase 3-dB bandpass-filtering couplers with input-reflectionless capabilities is presented. To obtain the bandpass-filter (BPF) functionality, identical BPF sections are respectively co-integrated in the coupler signal paths from the input to the direct and coupled ports. Furthermore, a resistivelyterminated bandstop-filter (BSF) section with complementary transfer function with regard to the one of the BPF section is loaded at the coupler input access. In this manner, the RF inputsignal energy that is not transmitted to the direct and coupled terminals is dissipated by the loading resistor of the BSF section. Hence, the input-reflectionless behavior is realized. Optimizationbased first-to-third-order design examples are shown. Moreover, for practical-validation purposes of this RF tri-functional device, a 2-GHz second-order microstrip prototype is built and tested.
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