The present invention relates to a mobile radio communication apparatus and, more particularly, to a mobile radio communication apparatus having an improved antenna.
A mobile radio communication apparatus is extensively used today and implemented as an on-board telephone for vehicle use or a paging receiver by way of example. Generally, this kind of apparatus has a flat microstrip antenna which is short-circuited at one side thereof. Specifically, the microstrip antenna is mounted on the back or the top of the casing of the apparatus and extends in parallel to and at a predetermined spacing from the latter. The antenna has a flat rectangular conductive plate for radiation, a short-circuiting plate for short-circuiting the conductive plate and the casing which serves a grounding function, and a feed conductor. The resonance frequency of the antenna generally varies with the width of the conductive plate and that of the short-circuiting plate. By taking account of this characteristic, it has been customary to so select the individual widths as to set up a desired resonance frequency and to reduce the width of the conductive plate as far as possible. Assuming the application of the microstrip antenna to 900 MHz, for example, it has been impractical to reduce the width of the conductive plate to less than .lambda./8 wavelength, i.e. about 40 mm. However, even the antenna having such a small conductive plate occupies a substantial space at the back or on the top of the casing of the apparatus and is contradictory to the current trend toward to the miniaturization of a mobile radio communication apparatus. Another problem with this type of conventional antenna is that the antenna gain decreases when the antenna is held by hand or when the hand is brought close to the antenna. In addition, the manipulability achievable with such a conventional antenna is not satisfactory.