Two miniaturized tunable filters with two zeros to result in sharp skirts were developed at 1.4-2.0 GHz on epsivr=6.15 substrate. The filters were built using single and back-to-back varactor diodes and compared for linearity characteristics. The single-diode filter has a 1-dB bandwidth of 5plusmn0.5% and an insertion loss of 2.5-1.8 dB. The back-to-back diode filter has a 1-dB bandwidth of 4.9 plusmn0.5% and an insertion loss of 2.9-1.25 dB (resonator Q of 56-125). The back-to-back diode filter was designed for improved linearity characteristics using two uniformly doped varactor diode and biased with a high impedance circuit. A detailed Volterra series analysis is done on the back-to-back diode including the effect of the bias network and diode mismatches. The measured IIP3 for the back-to-back diode tunable filter is 22-41 dBm depending on the bias voltage and is 13-15 dB better than the single-diode design. The power handling capabilities of both designs is explored using large-signal S 21 measurements. To our knowledge, these planar tunable filters represent state-of-the-art insertion loss and linearity characteristics performance with varactor diodes as the tuning elements.

A Two-Pole Two-Zero Tunable Filter With Improved Linearity

A new methodology for the synthesis of tunable patch filters is presented. The methodology helps the designer to perform a theoretical analysis of the filter through a coupling matrix that includes the effect of the tuning elements used to tune the filter. This general methodology accounts for any tuning parameter desired and was applied to the design of a tunable dual-mode patch filter with independent control of center frequency and bandwidth (BW). The bandpass filter uses a single triangular resonator with two etched slots that split the fundamental degenerate modes and form the filter passband. Varactor diodes assembled across the slots are used to vary the frequency of each degenerate fundamental mode independently, which is feasible due to the nature of the coupling scheme of the filter. The varactor diode model used in simulations, their assembling, the dc bias configuration, and measured results are presented. The theory results are compared to the simulations and to measurements showing a very good agreement and validating the proposed methodology. The fabricated filter presents an elliptic response with 20% of center frequency tuning range around 3.2 GHz and a fractional BW variation from 4% to 12% with low insertion loss and high power handling with a 1-dB compression point higher than .

Synthesis Methodology Applied to a Tunable Patch Filter With Independent Frequency and Bandwidth Control

With advances in telecommunications, an increasing number of services rely on high data rate spectrum access. These critical services include banking, telemedicine, and exchange of technical information. As a result, spectrum resources are in ever-greater demand and the radio spectrum has become overly crowded. For efficient usage of spectrum, smart or cognitive radios are sought after. However, current wireless phones can only select a few specific bands. In this paper, we discuss the advantages of reconfigurable radios in not only increasing the efficiency of spectrum usage but also in potentially reducing the cost of wireless handsets and the barriers for new wireless service providers to enter the market. We review available technologies that make the implementation of reconfigurable radios possible and discuss technical challenges that need to be overcome before multistandard reconfigurable radios are put into practice. We also evaluate the ability of reconfigurable radios in reducing entry costs for new competitors in wireless service.

Reconfigurable Radios: A Possible Solution to Reduce Entry Costs in Wireless Phones

This paper reports on tunable 2- and 3-pole bandpass filters with a wide frequency tuning range (tuning ratio >3) and a constant bandwidth using switchable varactor-tuned resonators. The wide center frequency tuning range is obtained using p-i-n diodes to switch in and out quarter-wavelength ( $\lambda $ /4) or half-wavelength ( $\lambda $ /2) resonators for low-band or high-band modes, without increasing the tuning capacitance range of the varactors. A combination of electric and magnetic coupling is utilized to realize a near constant absolute bandwidth across the tuning range. A switchable feed line with a fixed matching capacitance is used to realize the external coupling. Two filters are designed and fabricated on a Duroid substrate with $\varepsilon _{r} = 2.2$ and $h =0.787$ mm. For the 2-pole filter, the center frequency is tuned from 550 to 1900 MHz while maintaining a 3-dB bandwidth of 92 ± 6 MHz, insertion loss of 3.2~4.4 dB, and return loss of better than 15 dB. For the 3-pole filter, the center frequency is tuned from 540 to 1800 MHz while maintaining a 3-dB bandwidth of 89 ± 4 MHz, insertion loss of 4~5.4 dB, and return loss of better than 12 dB. For both filter types, the third-order intercept point and 1-dB compression point ( $P_{\mathrm {1~dB}})$ are 11 and 7 dBm, respectively. The rejection level at 200-MHz offset frequency from the passband center frequency is better than 25 and 41 dB for 2- and 3-pole filters, respectively, across the entire tuning range. To the best of our knowledge, this planar bandpass filter exhibits the widest tuning range with a near-constant bandwidth.

Continuously Tunable 0.55–1.9-GHz Bandpass Filter With a Constant Bandwidth Using Switchable Varactor-Tuned Resonators

There has been recent progress on CMOS non-magnetic circulators based on switch-based spatio-temporal conductivity modulation, but these initial demonstrations remain limited in transmitter power handling, linearity, and ability to combat antenna variations. This paper describes a non-magnetic circulator in 180nm SOI CMOS that uses no external components, and employs various linearity enhancement techniques such as device stacking, optimal switch biasing, and localized ESD design to achieve >1W TX-ANT PldB and >+50dBm TX-ANT IIP3 at 1GHz. A new loss-free and inductor-free antenna balancing approach enables high isolation for as high as 1.85 ANT VSWR and beyond. The circulator also exhibits low insertion losses of 2.1dB/2.9dB in the TX-ANT and ANT-RX paths, and ANT-RX NF of 3.1dB. These results represent a 10–100×enhancement in linearity/power handling over prior CMOS non-reciprocal circulators, and are shown to lower the power consumption of a communication link when compared with state-of-the-art electrical balance duplexers in scenarios where dynamic range is limited by P1dB, NF.

Fully-Integrated Non-Magnetic 180nm SOI Circulator with > 1W P1dB, >+50dBm IIP3 and High Isolation Across 1.85 VSWR

The design of a new class of band-select filters is proposed. For operation between the load and source impedances of Z 0 Ω, the filter is composed of a carrier line of the same impedance that is loaded by capacitors and inductors. The choice of active inductors and capacitors enables the band-select filtering. The frequency response characteristics for each band are independent of the rest of the bands, and therefore the proposed topology is suitable for multi-band designs with many degrees of freedom. Two different examples of this topology are presented.

Design of band-select filters with arbitrary characteristics using overlapped loaded line topologies

This paper introduces hybrid structures with unit cells that are a combination of lattice and ladder topologies. These unit cells dramatically increase the quality factor, miniaturization, and maximum frequency of synthetic transmission lines. Also, it is shown that lattice topologies in general are less vulnerable to the effect of parasitics, such as self resonance of loading capacitors or mutual inductance between different cells. The underlying theory is studied, and simple formulas are given for predicting the behavior of these lines. A few examples are presented that, based on full-wave simulations, show the large gain in minia- turization, quality factor, or bandwidth compared to the simple ladder or lattice structures. Measured results for a fabricated synthetic line are presented that show a miniaturization factor of for and a very small dispersive behavior from dc to 2.5 GHz.

Miniaturized Transmission Lines Based on Hybrid

A semi-analytical method for finding the elastic modes propagating along the edge of an anisotropic semi-infinite plate is presented. Solutions are constructed as linear combinations of a finite number of the corresponding infinite plate modes with the constraint that they decay in the direction perpendicular to the edge and collectively satisfy the free boundary condition over the edge surface. Such modes that are confined to the edge can be used to approximate solutions of acoustic ridge waveguides whose supporting structures are sufficiently far away from the free edge. The semi-infinite plate or ridge is allowed to be oriented arbitrarily in the anisotropic crystal. Modifications to the theory to find symmetric and antisymmetric solutions for special crystal orientations are also presented. Accuracy of the solutions can be improved by including more plate modes in the series. Numerical techniques to find modal dispersion relations and orientation dependent modal behavior, are discussed. Results for ridges etched in single crystal Silicon are found to be in good agreement with Finite Element simulations. It is found that variations in modal phase velocity with respect to crystal orientation are not significant, suggesting that anisotropy may not be a critical issue while designing ridge waveguides in Silicon.

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Masoud Koochakzadeh

Papers

Design of band-select filters with arbitrary characteristics using overlapped loaded line topologies

Miniaturized Transmission Lines Based on Hybrid

Elastic Modes of an Anisotropic Ridge Waveguide