The term microwaves may be used to describe electromagnetic (EM) waves with frequencies ranging from 300 MHz to 300 GHz, which correspond to wavelengths (in free space) from 1 m to 1 mm. The EM waves with frequencies above 30 GHz and up to 300 GHz are also called millimeter waves because their wavelengths are in the millimeter range (1–10 mm). Above the millimeter wave spectrum is the infrared, which comprises electromagnetic waves with wavelengths between 1 m (10–6 m) and 1 mm. Beyond the infrared spectrum is the visible optical spectrum, the ultraviolet spectrum, and x-rays. Below the microwave. | Microstrip Filters for RF Microwave Applications. Jia-Sheng Hong M. J. Lancaster Copyright 2001 John Wiley Sons Inc. ISBNs 0-471-38877-7 Hardback 0-471-22161-9 Electronic CHAPTER 1 Introduction The term microwaves may be used to describe electromagnetic EM waves with frequencies ranging from 300 MHz to 300 GHz which correspond to wavelengths in free space from 1 m to 1 mm. The EM waves with frequencies above 30 GHz and up to 300 GHz are also called millimeter waves because their wavelengths are in the millimeter range 1-10 mm . Above the millimeter wave spectrum is the infrared which comprises electromagnetic waves with wavelengths between 1 qm 10-6 m and 1 mm. Beyond the infrared spectrum is the visible optical spectrum the ultraviolet spectrum and x-rays. Below the microwave frequency spectrum is the radio frequency RF spectrum. The frequency boundary between RF and microwaves is somewhat arbitrary depending on the particular technologies developed for the exploitation of that specific frequency range. Therefore by extension the RF microwave applications can be referred to as communications radar navigation radio astronomy sensing medical instrumentation and others that explore the usage of frequency spectrums in the range of say 300 kHz up to 300 GHz Figure . For convenience some of these frequency spectrums are further divided into many frequency bands as indicated in Figure . Filters play important roles in many RF microwave applications. They are used to separate or combine different frequencies. The electromagnetic spectrum is limited and has to be shared filters are used to select or confine the RF microwave signals within assigned spectral limits. Emerging applications such as wireless communications continue to challenge RF microwave filters with ever more stringent requirements higher performance smaller size lighter weight and lower cost. Depending on the requirements and specifications RF microwave filters may be designed as lumped element or .
