Kenneth S.K. Yeo

The design of microstrip six-pole quasi-elliptic filter with linear phase response using extracted-pole technique

The development of microstrip filters has been in great demand due to the rapid growth of wireless communication systems in this decade. Quasi-elliptic response filters are very popular in communication systems because of their high selectivity, which is introduced by a pair of transmission zeros. A number of ways of implementing the quasi-elliptic response filter on microstrip have been studied over the last two decades, i.e., the cascaded quadruplet filter, canonical filter, and extracted-pole filter. However, there is very little information in the literature giving the design details for microstrip extracted-pole filters. In this paper, design equations of the extracted-pole filter for microstrip are reviewed. A new class of microstrip filter is also presented here. This class of filter will have a quasi-elliptic function response and at the same time linear phase in the passband. The linear phase of the filter is introduced by an in-phase cross coupling, while the transmission zero is realized using an extracted-pole technique. Experimental results, together with a theoretical comparison between the group delay of this design, and the conventional quasi-elliptic six-pole filter are also presented.

A novel tap input coupling structure for a narrow bandpass filter using TM/sub 010/ mode of a microstrip circular-disk resonator

This paper discusses a new method to couple into the TM/sub 010/ mode of a microstrip circular-disk resonator. This method can achieve reasonably strong input coupling, which is useful for narrow-band filters with fractional bandwidths of approximately 0.5% and above. A comparison between this newly proposed input coupling structure and the conventional gap input coupling structure will be addressed. A decision threshold for using either the tap input or the conventional gap-coupled input is also explained. Experimental results of a filter fabricated using this novel input coupling structure is also presented.

Cost effective ferroelectric thick film phase shifter based on screen-printing technology

A cost effective phase shifter technology based on ferroelectric thick film fabricated by screen-printing technology is described in this paper. As the demonstration device, a reflection-type phase shifter is designed and fabricated. At 2.2GHz to 2.6GHz band, the reflection-type phase shifter offers an average differential phase shift about 48/spl deg/ with a mean insertion loss of -2.4dB. The biasing DC voltage to achieve this performance is about 100V. This is the first report on screen-printed ferroelectric thick film phase shifter which offers promising device performance.

A NOVEL MICROSTRIP DUAL-BAND BANDPASS FILTER USING DUAL-MODE SQUARE PATCH RESONATORS

Dual-mode square patch resonator is well known in the design of a single band quasi-elliptic bandpass filter response. Here, the dual-mode square patch resonator is employed to achieve a dualband bandpass filter. A 6 pole dual-band bandpass filter response with 3 poles at each passband will be presented. The dual-band filter also exhibits a transmission zero between the two passbands. A detailed discussion on the design procedure together with the simulation and experimental results will be presented.

High frequency thick film BST ferroelectric phase shifter

This paper discusses the performance of a thick-film ferroelectric phase shifter at high frequency. The phase shifter is fabricated from Barium Strontium Titanate (BST) thick-films on alumina substrates using a screen-printing method, and the electrodes are patterned using direct gravure-printing. We have achieved down to 40 μm gaps between electrodes using this method. Comparison between the theoretical response and experiment results will be presented. The extracted dielectric constants of the BST material using this phase shifter is also be presented here.

Microstrip Dual-Band Bandpass Filter Using U-Shaped Resonators

Coupled resonators are widely used in the design of filters with dual-passband responses. In this paper, we present a dual-band bandpass filter using only couplings between adjacent resonators without cross-couplings. The dual-band bandpass filter with centre frequencies of 1747MHz and 1879MHz respectively is designed and fabricated using microstrip U-shaped resonators. Using the coupled resonator pair as a dual-band cluster, a miniaturised structure is achieved as compared to the conventional topology. The measured responses agree closely with the simulations.

8 pole high temperature superconductor microstrip dual band bandpass filter design

Dual-band filters are normally used for filtering two frequency bands that are not too close together. However, this paper presents a HTS dual-band bandpass filter that can be used to achieve isolation between two frequency bands that are only a few tens of MHz apart. Transmission zeros are placed in between the two frequency bands using electromagnetic coupling between non-adjacent resonators which result in high isolation between the two bands. The simulation and experimental results of a High Temperature Superconductor dual-band bandpass filter with very narrow bandwidth will be presented here.

High temperature superconducting ferrite phase shifter with new latching structure

Superconductor ferrite phase shifters are attractive for phased array radar systems. The huge reduction in size and losses mean that smaller systems are possible. This paper reports a new latching structure for a superconducting ferrite phase shifter which is compact in size and has low losses. The total size of the phase shifter is 6.0 cm/spl times/3.0 cm/spl times/2.5 cm including housing. It should be pointed out that two phase shifters can be accommodated in this size. The minimum insertion loss of the designed phase shifter was measured at 0.8 dB. The phase shifter is fabricated using a Yttrium Barium Copper Oxide (YBCO) microstrip meander-line on a one centimetre square low loss sapphire substrate. We press contacted a magnetized ferrite substrate, with a silver ground plane, onto the fabricated YBCO meander-line to obtain non-reciprocal phase shifting. To magnetize the ferrite substrate without causing magnetic field penetration into the high temperature superconductor (HTS), we propose a new latching structure comprising a single ferrite layer with magnetizing coils. This new structure will confine the magnetic field within the ferrite substrate by providing a closed magnetic path. This is achieved by making a large hole at center of the ferrite substrate.

Quasi-Elliptic Microstrip Bandstop Filter Using Tap Coupled Open-Loop Resonators

In this paper, we will present a quasi-elliptic bandstop filter using asynchronously tuned resonators. To demonstrate this technique, a novel broadband microstrip bandstop filter is also proposed using distributed resonators. To achieve wide bandwidth using distributed resonators, strong couplings are required. This is achieved using tap coupled to avoid very narrow gaps which are costly to manufacture. The filter exhibits a factional bandwidth of approximately 35%. A simple practical transformation technique for transforming Chebyshev bandstop filter to asynchronously tuned quasi-elliptic bandstop filter will be presented.

New model for the effective permeability of ferrite microstrip

This work is to develop a new model for the effective permeability of ferrite microstrips which is based on Wheelers (1977) microstrip impedance model. The newly developed model for the effective permeability will have some improvements over the well-known model developed by Pucel and Masse (1972). In this model, the transition error (or the discontinuity) from a narrow to wide ferrite microstrip has been removed. Unlike Pucel and Masses model, where one equation is derived for the narrow ferrite microstrip and another for the wide ferrite microstrip, this model only uses a single equation to predict the effective permeability of the ferrite microstrip for the entire range of width.