In-band Return Loss Research Articles

QUASI-ELLIPTIC WIDEBAND BANDPASS FILTERS USING STUBS LOADED ANTI-PARALLEL COUPLED-LINE

This paper presents a new type of wideband bandpass fllter (BPF) with quasi-elliptic frequency response by using proposed stubs loaded anti-parallel coupled-line. With difierent loads, the proposed stubs loaded anti-parallel coupled-line has difierent numbers of transmission zeros (TZs). These TZs are symmetrical along the designing frequency f0. By using a quarter-wavelength parallel coupled-line to connect two proposed stubs loaded anti-parallel coupled-line, three wideband BPFs centered at f0 = 1:575GHz with quasi-elliptic frequency response are successfully designed. Good agreements between the simulations and measurements can be observed. The measured results also exhibits that the fabricated BPFs have the merits of low in-band insertion loss, good in-band return loss, sharp passband selectivity and high out-of-band rejection.

Miniature on-chip bandpass power divider with equal-ripple response and wide upper stopband

In this study, a miniature bandpass power divider based on capacitive-loaded multicoupled line is proposed, which features equal-ripple insertion loss, return loss and isolation responses. Owing to the employment of capacitive-loaded transmission line resonators, it can achieve very compact size and wide upper stopband. The proposed bandpass power divider can be designed according to the conventional filter synthesis techniques, and is suitable for on-chip implementation. Specifically, a bandpass power divider with a centre frequency f0 of 5.5 GHz, 18.2% fractional bandwidth, and third-order equal-ripple response is designed and implemented using the commercial GaAs pseudomorphic high electron mobility transistor (pHEMT) process. The circuit size without pads is 0.87 mm×0.95 mm, and the electrical size is only 0.057 λg×0.062 λg at f0. The in-band insertion loss is less than 6 dB with a minimum insertion loss of 5.12 dB. The in-band return loss is better than 10 dB, and the isolation is better than 15 dB. In addition, a wide 30-dB upper stopband up to 57 GHz is achieved.

Compact Second-Order LTCC Substrate Integrated waveguide Filter with Two Transmission Zeros

A compact second-order substrate integrated waveguide (SIW) filter using low-temperature co-fired ceramic (LTCC) technology with two transmission zeros for high-selectivity application is presented. The proposed filter is composed of a Modified Doublet (MD) and input/output (I/O) SIW. The MD comprises two resonators that are not coupled to each other, whereas the two resonators are placed below and above the I/O SIW, respectively. The input and output SIW are directly coupled in order to generate up to two finite transmission zeros. The filter not only has good selectivity owing to the controllable transmission zeros by tuning the coupling manner and strength between the I/O SIWand two resonators, but also has a small size by profit from LTCC structure. A demonstration filter having a center frequency of 10 GHz and a 3 dB fractional bandwidth of 2.5% is designed and fabricated to validate the proposed structure. The measured results exhibit high selectivity, minimum passband insertion loss of 2.09 dB, and in-band return loss greater than 14 dB, agree well with simulated ones. Furthermore, based on the vertically multilayer structure using LTCC technology, the overall size of the filter is only 18 × 10 × 1.2mm3.

Miniaturized Metamaterial Narrow Bandpass Filters Using CRLH Transmission Line CL-Loaded Approach

In this paper metmaterial narrow band bandpass filter is designed and tested. The filter designed has the following properties, resonant frequency at 900MHz for mobile communications, bandwidth equal to 80MHz, insertion loss lower than -1.3dB, with in-band return loss lower than -16dB, and a wide stopband. The total filter size is about 2cm×2.4cm which is very compact compared to other metamaterial and conventional microstrip filters. This metmaterial narrow bandpass filter is designed based on composite right left handed (CRLH) Transmission line CL-loaded approach. The design steps, simulated and experimental results of the designed filter are presented

Hilbert-shaped complementary ring resonator and application to enhanced-performance low pass filter with high selectivity

In this article, a novel single negative metamaterial (MTM) transmission line (TL) consisting of a Hilbert-shaped complementary ring resonator (H-CRR) on the ground plane is initially presented and studied in depth. Then based on the proposed MTM TL, a novel six-section Hi-Lo microstrip low-pass filter (LPF) with a cut-off frequency 2.5 GHz is developed, fabricated, and measured. Measurement results indicate that: by integrating H-CRR, the selectivity has been significantly improved which is 77.3 dB/GHz due to the single negative permittivity; by etching a crown square on low-impedance section, the bandwidth characterized by 20 dB return loss was obviously enhanced by 26.2% and the maximal sidelobe level of in-band return loss was reduced from 22 to 24.6 dB. What' more, the developed LPF achieved a 36.3% size reduction with respect to its conventional counterpart. The design concept, which was confirmed by the measurement data, is of practical value and can be popularized in other microwave devices where high selectivity is requested. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.

Compact ultra-wideband filter using coupled-line and short-ended stub

A compact ultra-wideband filter is presented. The filter consists of a section of coupled microstrip-line and a short-ended stub. It has a simple structure and small size (4.7×6.2 mm2), but exhibits good performance. The filter has been investigated numerically using the simulator IE3D, and samples were fabricated and measured. Measured results show that the filter has a fractional bandwidth of 103.2% (from 3.05 to 9.55 GHz) and minimal insertion loss of −0.4 dB. The measured in-band return loss is better than −15.0 dB.

Sectorial-Beam Dielectric Resonator Antenna for WiMAX With Bent Ground Plane

A dielectric resonator (DR) antenna with a well is proposed, of which the beamwidth is increased to more than 120deg by bending the ground plane. This DR antenna has its 10 dB return-loss band in 3.4-3.8 GHz, thus can be used as a sectorial antenna in WiMAX (3.4-3.7 GHz) base station.

Compact (<0.5 mm 2 ) K-band metamaterial bandpass filter in MCM-D technology

A bandpass filter based on complementary split ring resonators (CSRRs) and implemented in MCM-D technology is presented for the first time. It is a thin-film microstrip structure with CSRRs etched in the ground plane and interdigital capacitors in the signal strip. In addition, the structure includes grounded stubs. The combination of CSRRs and such stubs is useful to generate a transmission zero above the left-hand passband of the filter, and thus improve frequency selectivity. The filter, consisting of two CSRR cells, has a central frequency of fo=19 GHz and a fractional bandwidth of FWB=18%. Inband return losses (RL=−15 dB) are satisfactory, while insertion losses (IL=−7.4 dB) are affected by the very small size of the resonant elements. Filter size is as small as 918×450 µm, i.e. 0.094 λg×0.045λg, where λg is the guided wavelength at fo. The implementation of these metamaterial-based structures in MCM-D technology opens new directions for the synthesis of ultra-small filters operating at millimetre wavelengths.

Multiple solutions for the synthesis of microwave filters with predistorted transfer functions

This paper examines the problem of multiple solutions for the synthesis of predistorted transfer functions of microwave narrow-band bandpass filters. The losses in narrow-band bandpass filters affect the flatness of the in-band transfer function and the selectivity sharpness. The predistortion is a synthesis technique used to recover acceptable flatness and selectivity of the transfer function knowing the level of losses. Applying this technique, multiple solutions are available, leading to different circuit realizations and, as a consequence, to different electrical behaviors in presence of losses. In particular, the return loss level in the passband depends deeply on the selected solution. The return loss is generally not a problem in case of IMUX filters but it has generally to be considered in other applications. Simple rules are given in this article in order to select the more appropriate solution in the late case. The theoretical demonstration is illustrated by an example of a 5 pole filter with a predistorted transfer function. The multiple solutions are determined and the effects of losses in term of minimum in-band return loss level are compared for each solution. An experimental model is then used to validate these theoretical results. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007.

A wideband meander‐line probe‐fed patch antenna

AbstractIn this paper, the characteristics of a bent meander‐line probe fed patch antenna are investigated. The air‐filled patches are designed at a height of about 9% of the wavelength and the bent meander‐line probe fed antenna is able to achieve an impedance bandwidth of about 31% for a VSWR of less than 2. The four basswoods, which support the microstrip patch, are noticed experimentally to have little effect on the overall performance. The in‐band return loss of the proposed antenna is found experimentally to be better than the recently proposed L‐shaped probe patch antenna. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 401–403, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10930