Girdhari Chaudhary

Dual-Band Bandpass Filter With Independently Tunable Center Frequencies and Bandwidths

This paper presents a novel approach to the design of tunable dual-band bandpass filter (BPF) with independently tunable passband center frequencies and bandwidths. The newly proposed dual-band filter principally comprises two dual-mode single band filters using common input/output lines. Each single BPF is realized using a varactor-loaded transmission-line dual-mode resonator. The proposed filter also offers switchable characteristics to select either of the passbands (either the first or the second passband only). To suppress the harmonics over a broad bandwidth, defected ground structures are used at input/output feeding lines without degrading the passbands characteristics. From the experimental results, it was found that the proposed filter exhibited the first passband center frequency tunable range from 1.48 to 1.8 GHz with a 3-dB fractional bandwidth (FBW) variation from 5.76% to 8.55% and the second passband center frequency tunable range from 2.40 to 2.88 GHz with the 3-dB FBW variation from 8.28% to 12.42%. The measured harmonic results of the proposed filters showed a rejection level of 19 dB, which is up to more than ten times of the highest center frequency of the first passband without degradation of the passbands.

Harmonic Suppressed Dual-Band Bandpass Filters With Tunable Passbands

This paper presents a novel approach to the design of tunable dual-band bandpass filter with broadband harmonic suppression characteristics. The proposed filter structure offers the possibility of two tunable passbands, as well as a fixed first passband and controllable second passband. The tunable passband frequency usually causes a shift of the harmonics, which need to be suppressed to improve out-of the passband characteristics. In order to suppress the harmonics over a broad bandwidth, defected ground structures are used at input and output feeding lines without degrading the passbands characteristics. Both theory and experiment are provided to validate the proposed filter. From the experimental results, it is found that the proposed filter exhibits a first passband center frequency tunable range of 34.14% from 0.85 to 1.2 GHz with the almost constant 3-dB fractional bandwidth (FBW) of 13% and second passband center frequency tunable range of 41.81% from 1.40 to 2.14 GHz with the 3-dB FBW of 11%. The measured results of the proposed filters show a rejection level of 20 dB up to more than ten times of second passband frequency can be obtained, thereby ensuring broad harmonics rejection characteristics without degradation of passbands. The measurement data have good agreement with the simulation.

Design of Dual-Band Bandpass Filter Using DGS With Controllable Second Passband

In this letter, the application of a variable characteristic impedance transmission line that can be used to design a dual-band bandpass filter (BPF) is presented. The proposed filter offers a fixed first passband and a controllable second passband. The tuning of the second passband is achieved by varying the characteristic impedance of the shunt open stub of stub loaded resonator (SLR) with the help of a defected ground structure (DGS) transmission line and varactor diodes. In order to validate the theoretical predictions and simulated results, a two stage dual-band BPF with three transmission zeros was implemented and experimentally verified.

Microstrip Line Negative Group Delay Filters for Microwave Circuits

This paper presents a novel approach to the design and implementation of a distributed transmission line negative group delay filter (NGDF) with a predefined negative group delay (NGD) time. The newly proposed filter is based on a simple frequency transformation from a low-pass filter to a bandstop filter. The NGD time can be purely controlled by the resistors inserted into the resonators. The performance degradation of the NGD time and signal attenuation (SA) of the proposed NGDF according to the temperature dependent resistance variation is also analyzed. From this analysis, it is shown that the NGD time and SA variations are less sensitive to the resistance variation compared to those of the conventional NGD circuit. For an experimental validation of the proposed NGDF, a two-stage distributed microstrip line NGDF is designed, simulated, and measured at an operating center frequency of 1.962 GHz. These results show a group delay time of -7.3 ns with an SA of 22.65 dB at the center frequency and have good agreement with the simulations. The cascaded response of two NGDFs operating at different center frequencies is also presented in order to obtain broader NGD bandwidth. NGDFs with good reflection characteristics at the operating frequencies are also designed and experimentally verified.

Design of Dual-Band Bandpass Filters with Controllable Bandwidths Using New Mapping Function

In this paper, a novel design method for a dual-band bandpass fllter (BPF) with arbitrary controllable bandwidths based on a simple frequency mapping function is proposed and its analytical design equations are also derived. The circuit conversion techniques are employed for implementation with distributed transmission line. To validate the proposed dual-band BPF with controllable bandwidths, a low temperature co-flred ceramic (LTCC) transmission line as well as microstrip lines are used, respectively. The two types of design for the dual-band BPF have the same and signiflcantly difierent fractional bandwidths (FBWs), respectively. The flrst type of dual- band BPF with same FBWs are implemented at 2.11{2.17 and 3.45{ 3.55GHz. The second type of dual-band BPF with difierent FBWs are implemented at 3.40{3.60 and 5.15{5.25GHz. The measured and theoretical results show good agreement, signiflcantly validating the proposed frequency mapping function methodology.

Low Signal-Attenuation Negative Group-Delay Network Topologies Using Coupled Lines

This paper presents the design and analysis of novel topologies of reflective-type negative-group-delay (NGD) networks with very small signal attenuation (SA). The proposed topologies are based on short-circuited coupled lines. Theoretical analysis shows that predefined group-delay (GD) time with very small SA can be obtained due to the high characteristic impedance of a coupled line and the small coupling coefficient. Due to the very low SA characteristics of the proposed networks, the burden of compensating general-purpose gain amplifiers can be reduced and provide stable operations while integrated to RF systems. This paper also analyses performance degradation of the GD time and SA of the proposed NGD networks according to the temperature-dependent resistance variation. For an experimental validation of the proposed topologies, distributed microstrip line NGD networks (type-I and type-II) are designed, simulated, and measured for a wideband code division multiple access (WCDMA) downlink frequency operating at a center frequency of 2.14 GHz. These results show a GD time of -7.27 ns with an SA of 7.43 dB for the type-I NGD network, and -6.3 and 9.23 dB for the type II- NGD network at the center frequency, and agree closely with the simulations. To enhance the NGD bandwidth, two NGD networks with slightly different center frequencies are connected in parallel, which provides wider bandwidth than the single stage case and shows practical applicability.

Distributed Transmission Line Negative Group Delay Circuit With Improved Signal Attenuation

In this letter, a novel design and implementation of a distributed negative group delay circuit (NGDC) with reduced signal attenuation is demonstrated. By inserting an additional transmission line Z2 into the conventional NGDC, the proposed NGDC provides further design parameters in order to obtain the required differential-phase group delay (GD) time and help to reduce the signal attenuation. As a result, the number of gain compensating amplifiers can be reduced, which can contribute to the efficiency enhancement as well as the stable operation when integrated into the RF system. Both theory and experiment are provided to validate the proposed structure. From the experiment, for the same GD time of -7.9 ns, the signal attenuation of the proposed circuit is 16.5 dB, an improvement signal attenuation of the conventional circuit of 19.2 dB.

Ultra-High Transforming Ratio Coupled Line Impedance Transformer With Bandpass Response

An impedance transformer (IT) with a ultra-high impedance transforming ratio (UHITR) is presented in this letter. The UHITR is obtained by controlling coupling coefficients of cascaded open-circuited coupled lines. Two transmission poles have appeared in the passband for an under-matched region. For the validation, the IT with impedance transforming ratio of 10 was designed at a center frequency (f0) of 2.6 GHz. From the experiment, insertion and return losses at f0 were determined as 0.55 dB and 21.47 dB, respectively. Within the operating band from 2.515 to 2.73 GHz, the insertion and return losses were better than 0.8 dB and 18 dB, respectively. The out-of-band suppression characteristics are higher than 20 dB from dc to 1.92 GHz and better than 18 dB from 3.28 to 7.2 GHz.

A DUAL-BAND RF ENERGY HARVESTING USING FREQUENCY LIMITED DUAL-BAND IMPEDANCE MATCHING

In this paper, a novel dual-band RF-harvesting RF-DC converter with a frequency limited impedance matching network (M/N) is proposed. The proposed RF-DC converter consists of a dual-band impedance matching network, a rectifler circuit with villard structure, a wideband harmonic suppression low-pass fllter (LPF), and a termination load. The proposed dual-band M/N can match two receiving band signals and suppress the out-of-band signals efiectively, so the back-scattered nonlinear frequency components from the nonlinear rectifying diodes to the antenna can be blocked. The fabricated circuit provides the maximum RF-DC conversion e-ciency of 73.76% and output voltage 7.09V at 881MHz and 69.05% with 6.86V at 2.4GHz with an individual input signal power of 22dBm. Moreover, the conversion e-ciency of 77.13% and output voltage of 7.25V are obtained when two RF waves with input dual-band signal power of 22dBm are fed simultaneously.

Transmission-Line Negative Group Delay Networks With Improved Signal Attenuation

This letter presents a novel design and implementation of a transmission-line negative group delay (NGD) network with improved signal attenuation (SA). Theoretical analysis shows that the NGD time can be controlled by characteristic impedance of the coupled line, coupling coefficients, and resistor, respectively. The low SA characteristic in the proposed structure is obtained due to high characteristic impedance of the coupled line. To validate the proposed structure, the transmission-line NGD networks are fabricated and measured at 2.14 GHz. From the experiment, the differential-phase group delay (GD) time and SA for a single stage are -6.16 ns and 8.65 dB over bandwidth of 15 MHz, respectively. For bandwidth enhancement, two-stage NGD networks with slightly different center frequencies are designed and fabricated, where GD of -7.48 ±0.84 ns and SA of 17.45 dB were obtained over a bandwidth of 28 MHz.