Prof. T. L. Wu

Microwave Filter Design

Prof. Tzong-Lin Wu

Department of Electrical Engineering

National Taiwan University

Prof. T. L. Wu

Microwave Filter Design

Text book:J.-S. G. Hong and M. J. Lancaster, Microstrip filters for RF/microwave applications, John Wiley & Sons, Inc., 2001.

• References:1. G. Mattaei, L. Young, and E. M. T. Jones, Microwave filters, impedance

matching networks, and coupling structures, Artech House, Norwood, MA, 1980.

2. Richard J. Cameron, Chandra M. Kudsia, and Raafat R. Mansour, Microwave Filters for Communication Systems: Fundamentals, Design, and Applications, Wiley, 2007

3. Ian Hunter, Theory and Design of Microwave Filters, IEE, 20014. David. M. Pozar, Microwave Engineering, 3rd Edition, John Wiley &

Sons, Inc., 2004.

Prof. T. L. Wu

Contents

• 1: Microwave network analysis

• 2: Basic concept and theory of filters

• 3: Transmission lines and components

• 4: Lowpass and bandpass filters

• 5: Highpass and bandstop filters

• 6: Coupled resonator circuits

Prof. T. L. Wu

Prerequisites

• Prerequisites:

Electromagnetics, Microwave Engineering.

• Grading :

– Midterm Report: 40%

– Term Projects: 60%

Prof. T. L. Wu

Application of RF and Microwave Filter

RF front end of a cellular base station

Microwave and RF filters are widely used in the wireless communication systems in order to discriminate Between wanted and unwanted signal frequencies.

Cellular radio provides particularly stringent filter requirements both in the base stations and mobile handset.

Figure below is a block diagram of the RF front end of a cellular radio base station.

What is the specifications for the transmitter filters?

Prof. T. L. Wu

RF front end of a cellular base stationThe GSM system uses a time division multiple access technique (TDMA), so the base station is transmitting and receiving simultaneously.

The propagation effects require a system dynamic range in excess of 100dB.

The transmit power amplifier (30W) produces out-of-band intermodulation products and harmonics.

These must be filtered to prevent leakage into the receiver and to satisfy the out-of-band radiation.

Therefore the transmit filter must have a high level attenuation in the receive band. Furthermore, it should have low passband insertion loss to satisfy PA linearity and efficiency requirement.

Prof. T. L. Wu

Application of RF and Microwave Filter

Transmit Filter

How to implement?

Prof. T. L. Wu

Application of RF and Microwave Filter

The selectivity of a filter increases with the number of resonant sections.

The insertion loss in the passband is inversely proportional to the filter bandwidth and the resonator Q factor and is proportional to the number of resonators used.

The previous spec. requires at least eight resonators with unloaded Q factors of at least 5000.

The Q requirement dictates a certain physical size, resulting in typical size for commercial coaxial resonator filters of 15cm x 30cm x 5cm.

Considerable research is under way to achieve smaller filter with improved performance.

Prof. T. L. Wu

Application of RF and Microwave Filter

Typical GSM mobile handset RF front end

The handset is only handling one call at a given time in GSM does not transmit and receive Simultaneously.

Only a receive filter is required. The main purpose of the filter is to protect the LNA and mixer in the down-converter from being over-driven by extraneous signals.

Prof. T. L. Wu

Spec. for the Rx filter

The spec. of this filter is much less severe than for the base station filter, the miniaturization required Means that they are still an extremely challenging design problem.

Prof. T. L. Wu

Filter in WLAN SiP module

SiP Block Diagram and Circuit Layout

WM-G-MR-05 SMT Wireless LAN Module

Prof. T. L. Wu

Filter in WLAN SiP module

堆疊

65 µm

70 µm

75 µm

70 µm

65 µm

SiP Material εr: 4.1

�Stack up of the SiP module

Prof. T. L. Wu2011/2/17 13

SiP

PCB

< 60 dBuV/m

Prof. T. L. Wu

A commercial filter in WLAN

Prof. T. L. Wu

A commercial filter in WLAN