This paper presents a dual-band bandpass filter with independent switchability of each passband. By taking advantage of harmonic ratio of asymmetric stepped-impedance resonators, 2.4- and 5.2-GHz resonators are designed. The second resonance of 2.4-GHz resonators is designed to be suppressed by a transmission zero created by extended feed lines. To achieve a wide upper stopband, 5.2-GHz resonators are designed with a scheme that the second peak of these resonators would not appear at a frequency lower than a third peak of 2.4-GHz resonators. Several design graphs for deciding both geometric parameters and transmission zeros are plotted by using the information obtained from electromagnetic simulations. While extracting coupling coefficients between resonators, an external quality factor at 50-Ω port is fixed to determine the precise transmission zeros. Two kinds of feed lines, such as a hook type and a spiral type, are developed, and spiral-type feed lines are chosen for realizing switchable filters. By controlling p-i-n diodes, four states of switchable dual bands are clearly presented in simulations and experiments.

Independently Controllable Dual-Band Bandpass Filters Using Asymmetric Stepped-Impedance Resonators

New compact quad-channel diplexer (1.5/2 GHz and 2.4/3.5 GHz) using the coupled stepped impedance resonators (SIRs) is proposed. The quad-channel diplexer is composed of two pairs of coupled SIRs with impedance ratio $({\rm K} > 1)$ and the source-load coupling lines. By tuning the impedance ratio and length ratio $(\alpha)$ of SIRs, the resonant modes can be easily determined so as to implement a two-order bandpass filter with very close dual-passbands. The source-load coupling lines are designed to correspond to the quarter-wavelength at the center frequency of first passband for each output port. The proposed quad-channel diplexer is showing a simple configuration, an effective design method and a small circuit size.

Design of New Quad-Channel Diplexer With Compact Circuit Size

A new concept of tuning transmission zeros (TZs) in 4-pole tunable bandpass filters is demonstrated. In this work, the tuning elements that were conventionally used for bandwidth control are also utilized for adjusting the TZs at the same time. As a result, the selectivity of the tunable filter can be controlled without increasing the filter order and complexity. A 4-pole stripline filter is used to demonstrate this concept. The filter can be continuously tuned from 1.25 to 2.1 GHz and two TZs are employed to improve the stopband suppression to $> {\hbox{60 dB}}$ at 200 MHz from the passband. These TZs can also be moved from the upper stopband to the lower stopband without any auxiliary tuning elements to significantly change the stopband suppression. The high rejection filter is useful in wireless systems and cognitive radios with large interferers.

Tunable 1.25–2.1-GHz 4-Pole Bandpass Filter With Intrinsic Transmission Zero Tuning

This paper presents a novel method for designing single- and dual-band filtering switches based on coupling control. First, the ON- and OFF-state coupling matrices are analyzed to achieve bandpass responses and high isolation, respectively. Then, they are used to guide the low temperature cofired ceramic circuit realization. The ON- and OFF-states are enabled by controlling the PIN diodes in the filter feeding structures. In the ON-state, the circuit is equivalent to a bandpass filter without signals passing through the PIN diodes, which avoids additional loss introduced by the PIN diodes. For the OFF-state isolation, it is realized by controlling the coupling of the filtering circuit, which is different from that of conventional switches by turning off transistors or diodes to obtain isolation. Thus, isolation is considerably enhanced. For demonstration, a single-band filtering switch is implemented with a compact size of 0.050 λg × 0.048 λg × 0.023 λg . Furthermore, a dual-band one of the same dimension is realized with controllable passband frequencies and bandwidths in the ON-state as well as high isolation in OFF-state. The presented filtering switches feature compact size, low ON-state insertion loss, high OFF-state isolation, and high reliability, which are suitable for industrial applications.

Single- and Dual-Band LTCC Filtering Switch With High Isolation Based on Coupling Control

A switchable microstrip bandpass filter (BPF) with reconfigurable on-state frequency responses is proposed. The filter consists of a two-pole BPF and two switchable delay lines. The proposed filter features not only switch ability with an on-off ratio of 41.2 dB but also two on-state frequency responses: Chebyshev response and quasi-elliptic-function response. Experiment was carried out to validate the design concept, and the simulation agrees well with the measurement.

Switchable Microstrip Bandpass Filters With Reconfigurable On-State Frequency Responses

In this paper, new designs of a bandpass diplexer and switchplexer are presented. Based on the proposed design method, they can be implemented by the direct connection of two parallel-coupled bandpass filters. As a result, the circuit size and mismatch losses can be reduced compared with conventional designs. In addition, based on the proposed filter prototypes, multiple functional blocks in the RF front end can be integrated into a single component. As an example, a balun-integrated bandpass switchplexer that effectively integrates all the functional blocks between the antenna and the TX/RX amplifiers in a single-band RF transceiver is demonstrated. In this way, not only can the level of integration of the RF front end be further improved, but the circuit size and power losses can also be reduced.

New Designs of Bandpass Diplexer and Switchplexer Based on Parallel-Coupled Bandpass Filters

In this letter, a compact electronically switchable parallel-coupled microstrip bandpass filter (BPF) based on quarter- wavelength resonators and p-i-n diode switch is proposed. The proposed filter occupies only half the circuit size of the conventional parallel-coupled filter. In addition, the type and length of each coupled-line section is suitably chosen such that the inherent transmission zeros associated with the coupled-lines can be used to reject the spurious passbands effectively. By adding only one p-i-n diode along with a simple bias control circuitry, the proposed filter becomes electronically switchable with no current consumption when the filter is turned off. Specifically, a switchable fourth-order microstrip BPF with a center frequency f0 of 2 GHz, passband insertion loss less than 3 dB, and wide stopband up to 7.7 f0 in the ON state is demonstrated. The isolation of the filter is better than 30 dB from dc up to 7.7 f0 in the OFF state.

Compact Electronically Switchable Parallel-Coupled Microstrip Bandpass Filter With Wide Stopband

In this work, compact microstrip diplexer designs based on two parallel-coupled bandpass filters are presented. By the proper adjustment of line lengths of the coupled-line sections, the phase of the input reflection coefficient for parallel-coupled bandpass filter can be adjusted to the desired value so as to minimize the interaction between the two bandpass filters. The diplexer may then be easily realized by the direct connection of two bandpass filters in parallel with no further fine-tuning required. This leads to a simpler design procedure as well as more compact circuit size. In addtion, good stopband rejection can be obtained. Specifically, two microstrip diplexer design examples with passband center frequencies (F 01 , F 02 ) = (2GHz, 2.8GHz) and (2GHz, 2.32GHz) are presented to validate the effectiveness of proposed design method.

Compact parallel-coupled microstrip diplexers with good stopband rejection

In this work, an electronically switchable cross-coupled microstrip bandpass filter using p-i-n diodes is proposed. The basic filter structure is based on the cascade of λ/8 parallel and anti-parallel coupled-line sections. Therefore, it occupies only about half the circuit size of conventional parallel-coupled filters. The magnetic cross-coupling is also introduced to achieve two transmission zeros in the lower and upper stopbands. In addition, by employing the four-line anti-parallel coupled microstrip structure, two more transmission zeros in the upper stopband are obtained. Two p-i-n diodes along with a common bias control circuitry are then introduced to allow the bandpass filter to be switched on and off. For design purpose, suitable equivalent-circuit for the filter is also introduced. Specifically, a switchable 4th-order microstrip bandpass filter with a center frequency of 1.5 GHz, passband insertion loss less than 2 dB, 3-dB bandwidth of 19.5%, and four transmission zeros is demonstrated. The ON-OFF isolation is better than 20 dB from dc up to 4.3 GHz.

Po-Ying Chang

Papers

New Designs of Bandpass Diplexer and Switchplexer Based on Parallel-Coupled Bandpass Filters

Compact Electronically Switchable Parallel-Coupled Microstrip Bandpass Filter With Wide Stopband

Compact parallel-coupled microstrip diplexers with good stopband rejection

Electronically switchable microstrip bandpass filter with good selectivity