In this paper, a new parallel-coupled-line microstrip band pass filter (BPF) improving the harmonic suppression performance of the second harmonic signal (2 , twice the passband frequency) is described. It is found that the desired passband performance is improved and the harmonic passband signal is diminished by enforcing the consecutive patterns in coupled-line and increasing the number of grooves to the optimum values. The recalculation of design parameters such as space-gap between lines, line widths and lengths is not required due to the simple modification of the conventional filter by inserting periodic patterns. To evaluate the validity of this novel technique, order-3 Butterworth BPF centered at 2.5 GHz with a 10% fractional bandwidth (FBW) and order-5 Chebyshev BPF centered at 10 GHz with a 15% FBW were used. When five and three square grooves are used, over 30-dB suppression at second harmonic signal is achieved in simulation and experiment. Finally, the comparison between the characteristics of filters with square and semicircular periodic grooves has been carried out by using the simulated results.

An electrically controllable terahertz (THz) square-loop metamaterial based on tungsten (W)-doped vanadium dioxide (VO2) films was designed and evaluated. The structure acts as both the bandpass filter and micro-heater. The various W concentrated VO2 films used to integrate with the metamaterial were successfully grown through the sol-gel method. The transition temperature decreased by ∼14 K/at% and the resistance–temperature hysteresis curves broadened with higher doping concentrations. By utilizing the designed device, the transmitted THz wave can be tuned precisely, and the modulation depth can reach up to 0.72 in the 0.3–0.7 THz passband with a bias voltage below 2 V.

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In this paper, a new parallel-coupled-line microstrip BPF(Bandpass Filter) improving the suppression performance of 2 nd harmonic signals is described. Using the consecutive patterns in coupled-line, the desired passband performance is improved and harmonic passband signal is diminished. Recalculation of design parameters(space-gap between lines, line widths and lengths) of conventional filters is not required. Because, after using the conventional design methodology for parallel-coupled-line BPF, new filters can be easily realized by inserting periodic patterns in coupledline. To evaluate the validity of this novel technique, order-3 Butterworth BPF centered at 2.5 GHz with a 10% FBW(Fractional Bandwidth) and order-5 Chebyshev BPF centered at 10 GHz with a 15% FBW were used. When five and three square grooves are used, over 30 dB suppression at 2 nd harmonic is achieved in simulation and experiment.

A low-loss fully embedded bandpass filter (BPF) is proposed using low-temperature co-fired ceramic (LTCC) technology with enhanced stopband characteristics for the broadband multimedia wireless system (BMWS) applications. The measured insertion loss was as small as 1.7 dB at a center frequency of 41.8 GHz, and the return loss was 10.2 dB including the loss associated with two stripline-to-CPW transitions. This six-layer BPF showed 3-dB bandwidth of 8.4 % at a center frequency of 41.8 GHz and suppressed the local oscillator (LO) signal to 20 dB at a local oscillator frequency of 38.8GHz.