Qingduan Meng

A 12-Pole Narrowband Highly Selective High-Temperature Superconducting Filter for the Application in the Third-Generation Wireless Communications

An ultra-selective high-temperature superconducting bandpass filter was designed and fabricated to satisfy the demands of the third-generation wireless communications. This filter was designed to have 12-pole quasi-elliptic response with 4.68-MHz bandwidth in the third-generation communications band (a fractional bandwidth of 0.0023). Full-wave simulations were conducted by using Sonnet software. A novel, compact, and low radiation resonator with a high-quality (Q) factor value was developed to reduce the parasitical coupling. In order to satisfy the demand of high band-edge steepness, three pairs of transmission zeros at finite frequencies were introduced in the cascaded quadruplet coupling structure. The filter was fabricated on a 2-in-diameter 0.43-mm-thick sapphire wafer with double-sided YBCO films. The measurements showed that the passband center frequency (f0) of the filter is 2.038 GHz at 67 K with a midband insertion loss of 0.67 dB and the return loss better than 15 dB. The measured response of the filter also exhibited ultra-high band-edge steepness of 140-220 dB/MHz. Better than 60 dB of out-of-band rejections for frequencies very close to the band edge (|f-f0|>2.7 MHz), better than 90 dB at frequencies 7.5 MHz away from the center frequency and up to 100 dB of wideband rejections were achieved

A 24-pole high Tc superconducting filter for mobile communication applications

This paper presents a highly selective 24-pole Chebyshev HTS bandpass filter. The filter was designed at 1748 MHz centre frequency with 75 MHz bandwidth, which was suitable for the GSM base station. The filter was fabricated using double-sided YBCO films on a 3 in diameter, 0.43 mm thick sapphire substrate. The simulation of the filter performance was carried out using Sonnet software. A novel resonator structure was proposed. The resonator exhibited a very high Q value of about 30 000 at 77 K. The filter showed an excellent selectivity. At the band edge of the filter, the slope was about 17 dB MHz(-1). Out of the band, the rejection level is better than -90 dB.

A HTS Bandpass Filter for a Meteorological Radar System and Its Field Tests

This paper presents recent progress of a high temperature superconducting (HTS) filter designed for a meteorological radar system (wind profiler) and its field tests results. The filter was designed to exhibit a ten-pole quasi-elliptic response with a fractional bandwidth of 0.35% in L band. It was fabricated using double-sided YBCO films on a 50-mm-diameter, 0.5-mm-thick MgO substrate. A HTS subsystem was assembled by connecting the filter with a cryogenic low noise amplifier (LNA), fixing them on a cryocooler and enclosing in a cryopackage. With the HTS subsystem substituting the corresponding conventional part (the conventional subsystem) of the wind profiler, two stages of experiments including field test were carried out. The first stage experimental results showed that while employing the HTS subsystem the sensitivity of the wind profiler improves 3.7 dB and the anti-interference ability improves 48.4 dB. The second stage experiment-field test results showed the improvement visually through the wind charts and wind profiles obtained in the field trial.

Influence of oxygen pressure on the structural and dielectric properties of laser-ablated Ba0.5Sr0.5TiO3 thin films epitaxially grown on (001) MgO for microwave phase shifters

Highly oriented Ba0.5Sr0.5TiO3 (BST) thin films were grown on MgO (001) single-crystal substrates by pulsed-laser deposition at 800 degrees C in oxygen pressure ranging from 1.2 x 10(-3) to 40 Pa. A strong correlation was observed between the growth process, structure and dielectric properties for the BST films. The dielectric properties in the low frequency range 10k-1MHz were measured in the interdigital capacitor configuration. The tetragonal distortion (ratio of in-plane and surface normal lattice parameters, D = a/c), surface morphology and dielectric response of the films are strongly dependent on the oxygen deposition pressure. With increase in oxygen pressure, the in-plane strain for the BST films changes from compressive to tensile. The BST film grown at 25 Pa exhibits the best overall dielectric properties. This corresponds to the film with a slight in-plane tensile strain (D = 1.0012). It is believed that a reasonable tensile strain, which increases the ionic displacement and thus promotes the in-plane polarization in the field direction, could enhance the tunability and dielectric constant. Based on the BST film grown at 25 Pa, distributed phase shifters were successfully fabricated with promising performance. The phase shifter shows a relatively low insertion loss of about 3.5 dB at zero bias and 10 GHz, a good return loss better than -15 dB for all phase states from dc to 16 GHz and a differential phase shift of about 43 degrees with 120V dc bias at 10 GHz.

An impedance matched phase shifter using BaSrTiO/sub 3/ thin film

We present a distributed phase shifter with an equal ripple return loss at its operation frequency range. The phase shifter is based on a periodic structure and consists of a coplanar waveguide (CPW) line periodically loaded with voltage-variable barium strontium titanate (BST) interdigitated capacitors. Measurements show that its return loss is better than -15dB at frequencies from direct current to 16GHz, and at 9.4GHz, its phase shift is 41/spl deg/ under 120-V applied bias voltage.

A highly selective HTS bandpass filter on sapphire substrate

This paper presents a highly selective 24‐pole Chebyshev HTS bandpass filter. The filter was designed at 1748 MHz center frequency with 75 MHz bandwidth, which was suitable for the GSM base station. The filter was fabricated using double‐sided YBCO films on a 3 inch diameter, 0.43‐mm thick sapphire substrate. A novel resonator structure was proposed. The filter showed an excellent selectivity. At the band edge of the filter, the slope was about 17dB/MHz. Out of band the rejection level is better than −90 dB.

Study of temperature and field dependence of ferroelectric thin films at microwave frequencies

Ferroelectric thin films (e.g. Ba0.5Sr0.5TiO3) require systematic studies of their dielectric properties at microwave frequencies. We propose a new method employing comparisons between the measured and the simulated microwave responses of a coplanar waveguide (CPW) bandstop filter, which is made of the thin film to be studied. The temperature and field dependence of the dielectric constant and loss tangent of the ferroelectric thin film are then deduced from the systematic comparison studies. Attention is also paid to the effect of the temperature dependent conductivity of the conducting layer of the filter, which has a noticeable effect on both the resonant frequency and the Q value of the filter. For an accurate determination of the dielectric constant and loss tangent of the ferroelectric thin film, such effect should be carefully analyzed and eliminated.

A high performance HTS filter for the third generation mobile communications

Design and fabrication of an ultra selective 12‐pole HTS band‐pass filter with three pairs of transmission zeroes at finite frequencies is presented. This filter was designed to have quasi‐elliptic response with 5 MHz bandwidth in the 3G communication band (a fractional bandwidth of 0.0025). The filter was fabricated on a 2 inch‐diameter 0.43 mm‐thick sapphire wafer with double‐sided YBCO films. The measured results showed that the pass‐band center frequency of the filter is 2.038 GHz at 68 K with a pass‐band insertion loss of −0.67 dB and a return loss better than −15 dB. The measured filter also exhibited ultra high skirt slop of 200–300 dB/MHz and excellent out of band rejections (better than 60 dB for | f‐f0 | > 2.7 MHz and better than 90 dB for | f‐f0 | > 7.5 MHz, where f0 is the pass‐band center frequency).