Before the emergence of ultra-wideband (UWB) radios, widely used wireless communications were based on sinusoidal carriers, and impulse technologies were employed only in specific applications (e.g. radar). In 2002, the Federal Communication Commission (FCC) allowed unlicensed operation between 3.1–10.6 GHz for UWB communication, using a wideband signal format with a low EIRP level (−41.3dBm/MHz). UWB communication systems then emerged as an alternative to narrowband systems and significant effort in this area has been invested at the regulatory, commercial, and research levels.

IEEE Transactions on Microwave Theory and Techniques and Antennas and Propagation Announce a Joint Special Issue on Ultra-Wideband (UWB) Technology

A stub loaded resonator (SLR) is presented in this letter, which can achieve dual-band or tri-band differential-mode (DM) bandpass response with a high common-mode (CM) suppression. By changing the length of the center-loaded stub, the resonant frequency of the CM can be varied without affecting that of the DM. This helps in simplifying the design and tuning processes of the balanced filters. In order to validate its practicalbility, two balanced bandpass filters (BPFs) with two and three DM passbands and good CM suppression are designed. Good agreement between simulated and measured results is observed. To our best knowledge, the proposed balanced tri-band BPF is the first ever reported.

Compact Balanced Dual- and Tri-band Bandpass Filters Based on Stub Loaded Resonators

In this paper, two- and three-pole microstrip LC constant fractional bandwidth (CFBW) and constant absolute bandwidth (CABW) tunable bandpass filters are proposed. The equivalent-circuit models are presented to study the tunable mechanism. The filter can be reconfigured by changing the capacitance of the LC resonators. Based on electric coupling coefficient compensation, second- and third-order tunable equivalent-circuit models with CFBW/CABW are presented. For demonstration, a semiconductor varactor diode loaded microstrip LC resonator is adopted in our work to design the second- and third-order tunable filters. The S-parameters, group delays, and third-order intercept points for different center frequencies of the filters are presented. Each resonator requires only one varactor diode for both central frequency and resonator coupling coefficient control.

Electrical Tunable Microstrip LC Bandpass Filters With Constant Bandwidth

An original and simple approach to the design of fully reconfigurable multi-band microwave bandpass filters (BPFs) with an arbitrary number of passbands is reported in this paper. It exploits the use of an innovative quasi-BPF configuration made up of different sets of controllable mono-frequency resonators to separately shape each tunable passband. Thus, high-selectivity multi-band bandpass filtering transfer functions exhibiting independent control in terms of center frequency, bandwidth, and transmission zeros can be synthesized. Furthermore, as an unprecedented frequency-agility feature of the proposed reconfigurable multi-band BPF structure when compared to the state-of-the-art, its passbands can be merged together to form broader, and for certain realizations, higher order transmission bands. This allows even more degrees of reconfiguration to be achieved in the devised circuit, which can also operate as ultra-wideband BPF with flexible in-band notches or self-equalized flat-group-delay quasi-elliptic-type BPF. The theoretical foundations of the described reconfigurable multi-band BPF scheme, along with guidelines for its design and a triple-passband filter synthesis example based on the coupled-node formalism, are expounded. In addition, as an experimental proof-of-concept, two microstrip prototypes with high- $Q$ tuning implemented through mechanically variable capacitors are manufactured and tested. They are a wideband dual-band BPF and a quadruple-band BPF with narrow-bandwidth passbands.

Reconfigurable Multi-Band Microwave Filters

In this brief, a dual-mode dual-band filter based on half-mode substrate integrated waveguide (HMSIW) is presented. The proposed filter has the capability to tune the two pass-bands independently. The proposed filter consists of two HMSIW resonators coupled through a pair of ${E}$ -shaped coupling slots. Two resonating modes ( TE 101 and TE 102) are excited in each resonator. A varactor diode is used in the proposed filter for tuning purpose. The varactor diode is placed in the structure in such a way that both bands can be tuned independently. The lower passband can be tuned from 3.26 to 3.47 GHz with insertion loss of 0.2–2.9 dB. The higher passband can be tuned from 5.47 to 6.13 GHz with low insertion loss of 0.1–2.1 dB. The presented results show the flexibility of the filter to achieve desired responses and its suitability for integration with any tunable planar structure. A good agreement between the simulated and measured results is observed.

Dual-Band Half Mode Substrate Integrated Waveguide Filter With Independently Tunable Bands

This paper presents a two-pole dual-band tunable bandpass filter (BPF) with independently controllable dual passbands based on a novel tunable dual-mode resonator. This resonator principally comprises a λ/2 resonator and two varactor diodes. One varactor is placed at the center of the resonator to determine the dominant even-mode resonant frequency; the other is installed between two ends of the resonator to control the dominant odd-mode resonant frequency. These two distinct odd- and even-mode resonances can be independently generated, and they are used to realize the two separated passbands as desired. Detailed discussion is carried on to provide a set of closed-form design equations for determination of all of the elements involved in this tunable filter, inclusive of capacitively loaded quarter-wavelength or λ/2 resonators, external quality factor, and coupling coefficient. Finally, a prototype tunable dual-band filter is fabricated and measured. Measured and simulated results are found in good agreement with each other. The results show that the first passband can be tuned in a frequency range from 0.77 to 1.00 GHz with the 3-dB fractional-bandwidth of 20.3%-24.7%, whereas the second passband varies from 1.57 to 2.00 GHz with the 3-dB absolute-bandwidth of 120 ± 8 MHz.

Tunable Bandpass Filter With Independently Controllable Dual Passbands

In this letter, a novel quadruple-mode resonator bandpass filter (BPF) with tunable bandwidth is proposed. By using two types of microwave varactors to tune the resonant frequencies and transmission zeros (TZs), the high-side edge of the passband and low-side edge of the passband can be separately varied. Therefore, the bandwidth could be tunable with reasonable adjust of the values of varactors. Theoretical expressions have been derived for the resonant frequencies and the TZs. The measured results of the BPF show that the fractional bandwidth can be tuned from 22% to 34% at a fixed centre frequency 2.0 GHz with a return loss better than dB. The tested results show good agreement with simulated results.

Bandpass Filter With Tunable Bandwidth Using Quadruple-Mode Stub-Loaded Resonator

—In this paper, novel bandpass filter and tunable bandpass filter are designed based on half-mode substrate integrated waveguide (HMSIW) embedded with complementary resonators Various passband characteristics are observed, and lumped equivalent circuit analysis models are developed The configuration of the proposed bandpass filter is an open structure, and it is easy to load the active devices and build the bias/control networks on the signal plane The tunable bandpass filter is presented based on the proposed novel bandpass filter loaded with semiconductor varactor diodes, and it has good spurious suppression characteristics and excellent out of band rejection The prototype with overall size of 159 mm × 302 mm × 05 mm was designed and fabricated so as to validate the new structure The measured central frequency is 1538 GHz and 1718 GHz, and the insertion loss is 51 dB and 33 dB, at 0 V and 30 V, respectively

Half-Mode Substrate Integrated Waveguide (HMSIW) Filters and its Application to Tunable Filters

Novel bandstop filters based on the defected microstrip structure with complementary split-ring resonators (CSRRs)/half-CSRRs etched on the microstrip surface are presented in this paper. By changing the configurations of the CSRRs, varied stop-band and pass-band characteristics are observed, and half-CSRRs is proposed to build a novel bandstop filter. A detailed explanation for the generation and variations of the stop-band and pass-band has been given. Lumped equivalent circuit analysis model is developed as well. The proposed filters exhibit compact size due to the employment of sub-wavelength resonators, and the overall size of the prototype is 12.2 mm × 28.95 mm × 0.8 mm. The measured −20 dB bandwidth of S 21 is from 2.51 GHz to 3 GHz, and the S 21 exhibits a wide spurious free response up to 10 GHz.

Xiaoguo Huang

Papers

Electrical Tunable Microstrip LC Bandpass Filters With Constant Bandwidth

Tunable Bandpass Filter With Independently Controllable Dual Passbands

Bandpass Filter With Tunable Bandwidth Using Quadruple-Mode Stub-Loaded Resonator

Half-Mode Substrate Integrated Waveguide (HMSIW) Filters and its Application to Tunable Filters

Bandstop Filter based on Complementary Split Ring Resonators Defected Microstrip Structure