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 dual-mode dual-bandpass filter for the U-NII bands is proposed and demonstrated. Its effective size reduction is achieved by using a multilayer configuration. The first and the third layers incorporate microstrip dual-mode bandpass filters with operating center-frequencies of f1 =5.2 GHz and f2 =5.8 GHz, respectively. The second layer is used as a common ground plane for both filters, which also serves as a decoupling interface. Capacitive coupling transition is used to connect both filters to I/O coplanar waveguide (CPW) ports. Single and dual-band passband filter prototypes are designed, fabricated, and measured in this work, thus validating the design principle. Designed topologies of single passband filters with center frequencies of 5.2 and 5.8 GHz exhibit an out-of-band rejection better than 40 dB with a 3 dB bandwidth of 5.8% and 6%, respectively. The proposed multilayer dual-passband response with center frequencies of 5.2 and 5.8 GHz provide band-to-band isolation better than 30 dB. Measured insertion losses are lower than 2.76 dB, with 3 dB bandwidth lower than 5%.

Multilayer Dual-Mode Dual-Bandpass Filter

The latest wireless products demand ever-greater functionality, higher performance, and lower cost in smaller and lighter formats. This demand has been satisfied to date by major advances in integrated circuits and high-density packaging technologies, even though the RF sections have been continuing to demand high-performance and miniaturized passive components such as matching and filtering circuitries. Continuing reductions in the size of discrete surface-mounted components are having diminishing returns because of the incompatibility of printed circuit board (PCB) technology as well as the high cost of assembly for those tiny discrete components. Therefore, new technological approaches are required to address the integration of passives. One of the important means today for integrating passives, particularly for RF functions, is low temperature cofired ceramics (LTCCs). Besides the use of this technology for highly integrated RF front-end modules [1]‐[4], there has also been a great deal of interest in realizing compact LTCC-embedded or isolated components, ranging from traditional baluns [5], couplers [6], and filters [7]‐[10] to more sophisticated diplexers [11] and balanced filters [12]‐[13], for different wireless communication technologies such as mobile phones, Bluetooth, and/or wireless LAN (WLAN) equipped terminals. This article specifically focuses on the design and implementation details for lumped or semi-lumped LTCC bandpass filters. A variety of LTCC chip-type filters with different characteristics are widely available commercially. They are often specified by the center frequency, fractional bandwidth, insertion loss, and stopband attenuation. Some examples are given in Table 1. These filters are usually second-order or third-order and have their responses optimized for specific applications by taking advantage of flexible filtering characteristics of LTCC LC filters. In general, their design process starts with a schematic circuit usually obtained by computer-aided design techniques from which a physical layout realization is generated through electromagnetic (EM) simulation tools. Nevertheless, the conventional analytical design methods can always be used as a starting point in the design process. The general design procedure for an LTCC filter can be summarized as • derive a schematic circuit including parasitic elements • optimize the circuit to meet required specifications • generate a physical layout based on the circuit • tune the layout to meet required specifications • fabricate prototypes to verify the performance. Each of these steps has its own design aspects and should be addressed carefully. Generally, layout tuning is the most time-consuming step as it involves full-wave EM simulations. Therefore, having a good layout design to minimize the number of simulations is of primary concern. As miniaturized LTCC filters are usually second-order or third-order, their layouts should not be too complicated. Indeed, there are some well-known standard layout strategies that are commonly used in practice. In the following section, we will discuss some important issues for the whole design process.

https://www.ee.cuhk.edu.hk/~klwu/pdf/microwave_magazine_oct_08.pdf

Low-Temperature Cofired Ceramic LC Filters for RF Applications

Over the past few years, a great amount of effort has been spent on LTCC filters or related research [21]?[28]. Some of these components have more advanced functionalities, such as a combination of filter and balun, or a complete front-end module with balun, filter, and matching network. At the same time, advanced methodologies have also been developed to design these components [29]. All the enjoyment of miniaturized RF components or modules is due to the promising three-dimensional design flexibility of LTCC technology. It is expected that a variety of functionally complex components will be continuously available on the market such that the cost and size of the overall wireless terminal can be further reduced. Various aspects of designing miniaturized LTCC LC filters have been briefly discussed here. Conventional coupled LC resonators are commonly used in LTCC filters for RF applications because of their compact size advantage. The shunted parallel resonator in this type of filter can be realized directly as a lumped-element or distributed quarter- wavelength stripline with or without loaded capacitors. Filters with distributed resonators in general have better passband insertion loss performance. Moreover, there are many ways to improve the rejection performance in an LTCC filter design; for example, by modifying the resonators or admittance inverters so as to introduce transmission zeros at the stopband. It was demonstrated, through a design example, that by making use of the flexibility of LTCC technology, a compact LC bandpass filter can be realized for various RF applications.

Low-temperature cofired ceramic LC filters for RF applications [Applications Notes]

A tunable dual-band bandpass microstrip filter is proposed and presented. It is composed of two pairs of quarter-wavelength transmission line resonators and two bandstop structures made of open stubs. Each operation bandpass frequency, denoted by f
 1
 and f
 2
, is generated by a pair of coupled resonators. The first coupled resonator is fed via a tap-coupled structure, while the second is fed through a coupling structure. The tunability of each bandpass and harmonic suppression is achieved by modifying the electrical length of the resonators and the electrical length of the open stubs by using varactor-diode capacitors. Finally, a 2.5 and 4.25 GHz dual band bandpass filter is designed, fabricated and measured as one example and a tunability of 22.2% and 19.6%, respectively, is obtained for the first and second bands. These excellent experimental results validate the proposed structure and design technique for dual-band bandpass filters.

Varactor-tuned quarter-wavelength dual-bandpass filter

This study proposes a second-order bandpass filter of serial configuration. The filter schema incorporates a grounding capacitor, connecting the two conventional parallel LC resonators with the ground, to provide two finite transmission zeros. The impedance matrix and graphical solutions describe proposed filter's operation principle. To demonstrate the proposed filter schema, two bandpass filters, with center frequencies of 2.44 and 4.8 GHz, were designed and implemented using low-temperature co-fired ceramic multilayer technology. The measured results were found to agree well with the simulation results. The 2.44-GHz fabricated bandpass filter was found to possess low in-band insertion loss and high out-band suppression, making it suitable in wireless local area networks, Bluetooth, and RF home links.

https://ir.nctu.edu.tw:443/bitstream/11536/13509/1/000230356600018.pdf

Bandpass filter of serial configuration with two finite transmission zeros using LTCC technology

A dual-bandpass filter that utilizes a serial configuration of the inductive coupled-line (ICL) filter and the capacitive coupled-line (CCL) filter is investigated in this study. Numerical analysis is presented for the difference between the ICL and CCL filters. The dual-bandpass filter has a similar behavior to the individual single-band filter around the corresponding passband. An extra transmission zero can be generated between the two passbands of the dual-bandpass filter in that the ICL and CCL filters exhibit an out-of-phase response. Four architectures of dual-bandpass filters are proposed for the 2.4/5-GHz systems. Two of them are demonstrated by the low-temperature co-fired ceramic multilayer technology. Measurements results agree quite well with the simulation ones

https://ir.nctu.edu.tw:443/bitstream/11536/12179/1/000238318700004.pdf

Dual-bandpass filters with serial configuration using LTCC technology

This study proposes a compact 5-GHz front-end module with embedded antenna on a low-temperature co-fired ceramic substrate, which is to be used for the IEEE 802.11a wireless local area network applications. The module comprises an embedded inverted-F antenna, a bandpass filter, and a low-pass filter. Both the proposed filters possess transmission zeros at out band for suppressing unwanted signals. A double-pole double-throw bare die transmitting/receiving switch is mounted on the surface of the substrate. The interconnection between the bare die switch and the buried circuits is established by bond wires. The effect of the bond wire is considered by incorporating its equivalent inductance into the design of the filters. The overall size of the antenna front-end module is only 6.2 mm times 5.4 mm times 0.98 mm with most of the space (near two-thirds of the volume) reserved for the antenna so as to have a better radiation performance. Also, to avoid the potential close proximity coupling among the buried circuits and the antenna, numerous metal vias connecting the top and bottom grounds in the module are designed for shielding. Since the radiation of a small antenna is influenced by the nearby circuit ground due to induced ground current, the developed antenna front-end module is tested on two FR4 printed circuit boards (PCBs) with different sizes (i.e., 55 mm times 20 mm and 80 mm times 46 mm). It is demonstrated that the antenna module performs well on these two grounded PCBs. The achieved 10-dB return-loss bandwidths are near 900 MHz for the transmitting and receiving paths. The measured radiation patterns are quite omnidirectional with peak gains (including the losses of circuit components) at approximately 0 dBi for the transmitting path and -1.7 dBi for the receiving path.

https://ir.nctu.edu.tw:443/bitstream/11536/8167/1/000261009100011.pdf

Development of a Compact Low-Temperature Co-Fired Ceramic Antenna Front-End Module

A second-order bandpass filter having an improved frequency response is disclosed, in which a grounding capacitor is connected electrically to a two-port network as a feedback path so as to provide two finite transmission zeros. With the two transmission zeros, signals of second harmonic frequency and GSM signals may be blocked out from the pass band of the filter and thus filtered out. As such, the filter may be utilized in wireless local area network (WLAN) application. Further, since no extremely small value component is used within the filter, the frequency response may not be influenced by a manufacturing process of the filter. In addition, the thus formed filter has a relatively smaller volume.

Second order bandpass filter

Two second-order bandpass filter are connected serially to obtain a dual bandpass filter. One is inductive and the other is capacitive. One has a low passband and the other has a high passband. Between them, a finite transmission zero is formed to suppress noise. The present invention achieves a passband as wide as 1 gigahertz so that it can be applied to a wireless local network, communication equipments and electronic devices.

https://ir.nctu.edu.tw:443/bitstream/11536/105629/1/20070257746.pdf

Chun-Fu Chang

Papers

Bandpass filter of serial configuration with two finite transmission zeros using LTCC technology

Dual-bandpass filters with serial configuration using LTCC technology

Development of a Compact Low-Temperature Co-Fired Ceramic Antenna Front-End Module

Second order bandpass filter

Dual bandpass filter having serial configuration of coupled-line filters